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A stratigraphical framework for the Upper Cretaceous Chalk of England and Scotland with statements on the Chalk of Northern Ireland and the UK Offshore Sector

By P M Hopson

Bibliographical reference: Hopson, P M. 2005. A stratigraphical framework for the Upper Cretaceous Chalk of England and Scotland, with statements on the Chalk of Northern Ireland and the UK Offshore Sector. British Geological Survey Research Report RR/05/01 102pp.

British Geological Survey Research Report RR/05/01

The National Grid and other Ordnance Survey data are used with the permission of the Controller of Her Majesty’s Stationery Office. Licence No: 100017897/2005.

Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail ipr@bgs.ac.uk. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract.

Maps and diagrams in this book use topography based on Ordnance Survey mapping.

Keywords: Geology, Statigraphy, Upper Cretaceous, Chalk

(Front cover) Chalk cliff and the Pinnacles stacks south of Handfast Point, north-east of Swanage, Dorset.

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Foreword

The Stratigraphy Committee of the British Geological Survey (BGS) is undertaking a review of stratigraphical classification for all parts of Great Britain. Several Stratigraphical Framework Committees (SFC) have been established to review problematical issues for various parts of the stratigraphical column. Each SFC has the following terms of reference:

to review the lithostratigraphical nomenclature of designated stratigraphical intervals for a given region, identifying problems in classification and correlation
to propose a lithostratigraphical framework down to formation level
to organise a peer review of the scheme
to present the results in a document suitable for publication
to ensure that full definitions of the lithostratigraphical scheme are held in the web-accessible BGS Stratigraphical Lexicon for the areas of responsibility covered by the SFC

This report is the published product of a study by the British Geological Survey Stratigraphical Framework Committee (BGSSFC) for the Upper Cretaceous of Great Britain. The report provides a summary of the lithostratigraphical schemes for the five Upper Cretaceous provinces in England (Southern, Transitional and Northern), Scotland and Northern Ireland.

BGS Stratigraphical Framework reports are published in collaboration with the Stratigraphy Commission of the Geological Society through the BGS Internet www.bgs.ac.uk where they are available as free downloads. Reports are peer reviewed via the Stratigraphy Commission.

Acknowledgements

This document is the statement on the stratigraphical terminology of the Chalk Group presented to the BGS Stratigraphical Framework Committee and Stratigraphy Commission of the Geological Society. It contains a review of the nomenclature currently used in BGS publications and maps and sets out the terms to be utilised within current and future BGS publications. This statement draws heavily on the work of BGS staff as well as contributions from the academic community and the deliberations of a meeting on Chalk Lithostratigraphy convened at the BGS in Keyworth by the Stratigraphy Commission of the Geological Society. In this context special mention should be made of Professor Peter Rawson, Professor Andy Gale, Professor Rory Mortimore, Dr Don Aldiss, Dr Roger Bristow, Dr A R Farrant, Mr Peter Hopson, Mr Mike Sumbler, Dr Ian Wilkinson, Mr Chris Wood, Mr Mark Woods, and, of course, all of the members of staff of the BGS who have special responsibility for the characterisation of the Chalk. The reviewers for the Geological Society are given thanks for their perceptive comments and corrections to the draft of this document.

Summary

It was agreed that the Chalk Group should be divided into a Grey Chalk Subgroup and a White Chalk Subgroup on a national basis for England. The base of the Grey Chalk Subgroup being everywhere placed at an erosional contact that marks the base of the Upper Cretaceous; and the base of the White Chalk Subgroup being everywhere placed at the base of the Plenus Marls Member. In addition the meeting agreed that there were sufficient lithological and faunal differences to sustain a lithostratigraphical nomenclature at formational level (and below) for a ‘Northern Province’ and a ‘Southern Province’. A ‘Transitional Province’ covers part of the Chilterns and much of East Anglia and here diagnostic lithologies and faunas characteristic of the Northern and Southern provinces interdigitate. It was the recommendation of the meeting that the appropriate nomenclature from either the Northern or Southern provinces be applied in the Transitional Province although it is generally the case, based on historic records, that the ‘southern’ terms can be applied widely. The lack of modern surveying and the opportunity to assess the chalk at outcrop over much of the East Anglia region has meant that the highest preserved chalks on the UK mainland (representing the upper Campanian to lower Maastrichtian stages), for which various schemes have been proposed, have not been studied in terms of their mappability and the informal terms Norwich Chalk and Trimmingham Chalk are adopted herein as an interim measure.

This framework accorded with the best practise of the BGS surveying activities throughout the Chalk Group of England, with the proviso that, in the Southern Province, the terms ‘Lower, Middle and Upper Chalk formations’ were abandoned; that the ‘members’ being utilised as mapping units (after Bristow et al. 1997) should be redesignated as formations; and that the Holywell Nodular Chalk Formation, newly created as a consequence, should include the Plenus Marls Member as its basal unit. A Plenus Marl Member is also defined for the Northern Province at the base of the Welton Chalk Formation to provide continuity between the provinces. In the case of the Hunstanton Formation the consensus in the meeting was that it was a formation, but not part of the newly defined Chalk Group, and as defined it is older than the major hiatus at the base of the Cenomanian (a definition is included for completeness).

A summary of that unified scheme, its relationship to earlier schemes and definitions of each term are given herein. Beyond formational level, members of historical value or local significance, some of which are traceable over unexposed countryside and therefore deemed to be ‘mappable’, are also defined. Reference is also given to the principal lithostratigraphical schemes of earlier authors and correspondence of their terms to this new scheme given where it can be determined. It is strongly recommended that in future local variations in lithology that are deemed sufficiently mappable and provide additional data on the structure and distribution of the Chalk be formally designated as members within the formational schemes erected here. It would not be necessary for any given formation to be divided entirely into members.

The schemes for Scotland and Northern Ireland are discussed in the light of the most recent publications and it is suggested that they be referred to as the Scottish Chalk Province and the Ulster Cretaceous Province. It is confirmed herein that formal schemes be adopted for both areas with the following provisos. In the case of Scotland formations are defined within an Inner Hebrides Group. Whilst in the case of Northern Ireland the Hibernian Greensand and Ulster White Limestone formations are upgraded to group level with two subgroups to divide the Ulster White Limestone and numerous formations created by upgrading the presently defined members within both groups. In both provinces lithological variation is rapid within and between basins and sub-basins that are heavily influenced by extensional tectonics associated with the opening of the Atlantic Ocean. By adopting the formation as the basic unit, new research will be able to define local variations at member level.

Stratigraphies for the UK offshore sector are well documented elsewhere and only a summary is included here to demonstrate the correspondence between the onshore and offshore schemes.

Chapter 1 Introduction

This document is the formal statement on the stratigraphy of the Chalk Group as adopted by the British Geological Survey and ratified by the BGS Stratigraphical Framework Committee and the Stratigraphy Commission of the Geological Society. It contains a review of the nomenclature currently used in BGS publications and maps and makes proposals for a new scheme. This review draws heavily on the work of BGS staff as well as contributions from the academic community and the deliberations of a meeting on Chalk Lithostratigraphy convened at the BGS in Keyworth by the Stratigraphy Commission of the Geological Society.

The document is mainly concerned with the successions outcropping in the southern and eastern part of England from Devon to Kent, in East Anglia, and in Lincolnshire and Yorkshire. Within the English outcrop Northern and Southern provinces are well established in the literature (strictly these should be referred to, for example, as the Northern Chalk Province etc., although most of the literature omits the chalk descriptor), separated by an informal Transitional Province that includes the Chilterns and East Anglia (Figure 1). The concept of a Transitional Province is less meaningful in the light of the proposed lithostratigraphical terminology for the Northern and Southern provinces, whose defined terms should be used wherever possible across the transition. However these provinces are a useful concept and should not be abandoned as they are defined principally on the basis of their faunal content (the biostratigraphical Boreal Realm [northern] and Tethyan Realm [southern] respectively). Other less easily defined factors such as the influence of the Anglo-Brabant Massif on sedimentological processes, physical properties of the chalk and the interdigitation of diagnostic lithologies and faunas characteristic of the Northern and Southern provinces are also a feature of the transition. Whilst the Tethyan Realm is richly fossiliferous and has an agreed international standard biostratigraphy based on planktonic foraminifera its relationship to the Boreal Realm is only tenuously correlated at many levels and further justifies the separation of the Northern and Southern provinces. Indeed the general absence of planktonic forms has led to a benthonic foraminiferal scheme being developed for the UK (Figure 2).

The limited outcrops in Scotland (Scottish Chalk Province) are also discussed and a proposal to formalise the nomenclature within the Inner Hebrides Group and based on the most modern literature is included.

For Northern Ireland (Ulster Cretaceous Province), there is a well-established lithostratigraphy but it is proposed herein to raise the status of the units defined by one level thus creating the Hibernian Greensand Group and the Ulster White Limestone Group with various subgroups and formations. These two groups are effectively the mapping units since there are only limited outcrops of the Cretaceous succession at the margin of the overlying Palaeogene basalts. In both provinces lithological variation is rapid within and between basins and sub-basins as a consequence of the heavy influence of extensional tectonics associated with the opening of the Atlantic Ocean. By adopting formation as the basic unit new research will be able to define local variations at member level without the need to demonstrate lateral continuity and mappability.

A brief statement of the terminologies used within the UK Offshore Sector is given in Section 6 and summarised in Figure 11.

1.1 History of research

The following text relies heavily on the following documents, but has been modified, to remove ambiguity and bias; a personal communication between Prof. Andy Gale and Peter Allen prior to the Chalk Lithostratigraphy meeting at Keyworth (Gale, 1999, pers. comm.); a review of the Chalk Group for Yorkshire and Lincolnshire prepared as a BGS Technical Report (Sumbler, 1999); the paper by Bristow et al. (1997); reviews of the Chalk of the South and North Downs (Aldiss, 2002) and (Hopson, 1999) respectively; and the most recently published Geological Conservation Review book by Mortimore et al. (2001).

The earliest lithostratigraphical divisions of the Chalk were provided W Phillips (1818, 1821) for Kent, by Mantell (1822) for Sussex, and by Woodward (1833) for Norfolk (Figure 3, Columns 1, 2 and 3^‡1 respectively). These schemes were based primarily on the clay content of the chalk and the relative abundance (or absence) of flints. These early classifications had a degree of agreement although the boundaries between units chosen by the authors differed.

These authors recognised a ‘marly’ lower unit termed the Grey Chalk, Grey Chalk Marl or Chalk Marl but always overlain by the Lower Chalk distinguished by its hardness and absence of flint. This lower ‘marly’ unit corresponds approximately with the subsequently devised ‘traditional scheme’ term of Chalk Marl (see below and (Figure 2, Column 1)) with or without the lower part of the Grey Chalk included (also part of the ‘traditional scheme’ nomenclature but not to be confused with the ‘Grey Chalk’ of W Phillips, 1818). Each of these schemes introduced an ‘Upper Chalk’ which was characterised by numerous flints. W Phillips and Woodward separated a unit at the base of the Upper Chalk as their Chalk with few flints or Medial Chalk. Similar schemes were utilised by Bogg (1816) for Lincolnshire and by J Phillips (1829) for Yorkshire.

It is interesting to note that the Lower–Middle Chalk boundary at the base of the Melbourn Rock, considered to be so distinctive nowadays, did not appear in these schemes. The use of a ‘Lower Chalk’ (incorporating the Chalk Marl/Grey Chalk) without flints and an ‘Upper Chalk’ with flints continued for much of the remainder of the 19th century (e.g. Whitaker, 1865b; Dowker, 1870)((Figure 3), Column 4 and (Figure 5a), Column 2); (e.g. Whitaker, Bristow and Hughes, 1872) ((Figure 3), Column 5 and (Figure 5a), Column 3).

Sharpe (1853) was the first author to revise this system by placing the Chloritic Marl and the Chalk Marl within the Lower Chalk, and establishing a Middle Chalk characterised by a sparse fauna. In 1880, Jukes-Browne described the Melbourn Rock in Cambridgeshire, and Penning and Jukes-Browne (1881) used this feature-forming and easily traceable unit to divide their Lower from a new Middle Chalk unit. They also determined that a higher hard rock band, the Chalk Rock, containing a characteristic fauna and preservation style, formed a similar feature separating the Middle from the Upper Chalk ((Figure 2), Column 1). An integrated bio- and lithostratigraphical scheme (the ‘traditional scheme’ herein) was developed in memoirs of the Geological Survey and presented in the seminal works of Jukes-Browne and Hill (1903, 1904) ((Figure 3), Column 6, (Figure 5a), Column 6, (Figure 5b), Column 4 and (Figure 6), Column 4) (The 1904 volume also contains a comprehensive bibliography of published works on the Chalk in the period 1628 to 1903). It is these two volumes that formed the basis of the Geological Survey’s mapping of the Chalk of southern England until the 1990s and are the basis for the Geological Society’s correlation of the ‘Southern Province’ Chalk (Rawson et al., 1978). Certain aspects of the ‘traditional scheme’ were, however, difficult to apply in mapping terms to the Chalk of Lincolnshire and Yorkshire and the Middle–Upper Chalk boundary, in particular, was a matter of some conjecture.

Rowe (1900 to 1908), working from a biostratigraphical premise, did not recognise the separate Middle and Upper Chalk divisions as they were based on what he saw as an ephemeral and diachronous lithological feature (the Chalk Rock). Instead he used the term ‘White Chalk’ to include both Middle and Upper Chalk of the ‘traditional scheme’. This concept of the term ‘White Chalk’ was accepted by Mortimore (1983, 1986) ((Figure 3), Column 8, (Figure 2), Column 3 and (Figure 5a), Column 9), if on somewhat different criteria, and he formally introduced the lithostratigraphical term of the ‘Sussex White Chalk Formation’.

Bristow et al. (1997) ((Figure 3), Column 10, (Figure 2), Column 5, (Figure 5a), Column 10) reintroduced a threefold terminology with Lower, Middle and Upper Chalk classed as formations, each redefined to include slightly different strata than before and designed to provide a basis for mapping and a connection to the ‘traditional scheme’. These formations were further divided into newly defined members.

The threefold division was justified by using the base of the Lewes Chalk Member of Mortimore (1983) that could be widely mapped in southern England as the base of the Upper Chalk. Although it was recognised as a diachronous boundary marked by the onset of distinct nodularity, it corresponded approximately with the old Middle–Upper Chalk boundary. Gale and Hancock (1999), in correspondence, argued that this was an arbitrary division and Middle and Upper Chalks defined thus lacked lithological integrity. Their arguments were strongly refuted (Bristow et al., 1999) in correspondence in the same volume.

The first attempt last century to separate the litho- and biostratigraphy of the Chalk was by Wood and Smith (1978) who erected a new fourfold lithostratigraphical scheme for Yorkshire and Lincolnshire ((Figure 3), Column 7 and (Figure 6), Column 5). They established the Ferriby, Welton, Burnham and Flamborough Chalk formations. The Ferriby Formation is dominantly white chalk with marly partings overlying the Red Chalk. A thin but distinctive Black Band at the base of the overlying Welton Chalk Formation which commences with a marly unit (the Plenus Marls ‘Member’ of Witham, 1991 and others) is overlain by massive to thickly bedded chalks with flint nodules. The succeeding Burnham Chalk Formation comprises thinly bedded chalks with tabular and semi-tabular flints overlain by the essentially flint-free and softer chalks of the Flamborough Chalk Formation. This paper is particularly important in that it established the distinctive and separate lithological succession of the Chalk in Yorkshire and Lincolnshire for the first time. Lott and Knox (1994) (Figure 11, Column 4) working in the North Sea introduced the term Rowe Chalk Formation to cover the very highest Chalk concealed beneath Quaternary deposits in the Hornsea area and immediately offshore. Sumbler (1999) described these beds, based on geophysical logs from boreholes, as 70 m or so of flint-bearing chalks characterised by the inferred presence of Belemnitella mucronata (a species commonly reworked into the overlying Quaternary deposits) and also indicated that still younger beds were present offshore.

Formal lithostratigraphical schemes followed for the chalk successions of the Southern Province with proposals by Mortimore (1986) ((Figure 5a), Column 9) for the South Downs, by Robinson (1986) ((Figure 5a), Column 8) for the North Downs and by Jarvis and Woodroof (1984) ((Figure 5b), Column 7], for the marginal facies in south east Devon. The amalgamation of the Middle and Upper Chalk into ‘White Chalk’ as proposed by Rowe (1900 to 1908), was accepted by Mortimore (1983, 1986), who formally named the lithostratigraphical unit Sussex White Chalk Formation. This he divided into six members (and each into a number of ‘beds’), which overlay a Lower Chalk Formation (undivided other than in terms of the ‘traditional’ named subdivisions). This division of the Sussex White Chalk Formation was based on the presence or absence of flints and marls, and the incidence of hard chalks or nodularity. In the North Downs, Robinson (1986) divided the Chalk Group into five lithostratigraphical formations, based on diverse criteria including the presence or absence of rhythmicity, flint, and clay content. Three formations formed the traditional Lower Chalk interval and two the remainder of the Chalk. With the exception of the thin ‘Plenus Marl Formation’ he divided each formation into members but left a large part of the ‘East Wear Bay Chalk Formation’ undivided. Developing the work of Mortimore, and consolidating the field-based observations by a large body of surveyors in the British Geological Survey during the 1990s, Bristow, et al. (1997) ((Figure 3), Column 10, (Figure 2), Column 5 and (Figure 5a), Column 10) formally proposed a scheme for the lithostratigraphical mapping of the Chalk of the Southern Province.

In November of 1999 a meeting held at the BGS in Keyworth, co-sponsored by the BGS and the Stratigraphy Commission of the Geological Society, brought together experts on the Chalk to standardise the nomenclature on BGS maps and to act as a framework for the new Cretaceous correlation publication of the Geological Society. Agreement was reached, with some reservations, on a framework to guide future workers in Chalk research and the application of this should standardise terminology. It was agreed that the Chalk Group should be divided into a Grey Chalk Subgroup and a White Chalk Subgroup on a national basis. The base of the Grey Chalk Subgroup being everywhere placed at an erosional contact that marks the base of the Upper Cretaceous; and the base of the White Chalk Subgroup being everywhere placed at the base of the Plenus Marls Member. In addition the meeting agreed that there were sufficient lithological and faunal differences to sustain a lithostratigraphical nomenclature at formational level (and below) for a Northern Province and a Southern Province (see (Table 1)).

This accorded with the best practise of the BGS surveying activities at the time, with the proviso that the ‘Lower, Middle and Upper Chalk Formations’ were abandoned; that the ‘members’ being utilised as mapping units (after Bristow et al., 1997) in the Southern Province should be redesignated as formations; and that the Holywell Nodular Chalk Formation, newly created as a consequence, should include the Plenus Marls Member as its basal unit. A summary of that unified scheme, and its relationship to earlier schemes, is shown in (Figure 3), Column 11, (Figure 2), Column 6 and (Figure 5a), Column 11. Beyond formational level, members of local significance, some of which may prove to be traceable over unexposed countryside and therefore deemed to be ‘mappable’, can be erected without the need for any given formation to be divided entirely into members. It is strongly recommended herein that local variations in lithology that are deemed sufficiently mappable and provide additional data on the structure and distribution of the Chalk be formally designated as members within the formational scheme erected here.

To aid the understanding of the changes in terminology used in BGS publications over time, and the relationship between those terms and the unified scheme, a comprehensive Lexicon of informal/formal and current/redundant terms will be developed by the BGS. It follows that as BGS maps come up for revision, whether in paper or digital format, the new terminology will be adopted.

(Table 1) The agreed lithological framework from the Chalk Lithostratigraphy meeting held at BGS, Keyworth, on the 3–4 November 1999 (after Rawson, Allen and Gale, 2001).

1.2 Review of present practice and usage in the BGS

At present many BGS publications base their interpretation of the Chalk of England on the ‘traditional scheme’ ((Figure 2), Column 1) and, within the most recent output, on the various stages of the development of the new lithostratigraphical schemes.

As maps come up for revision the traditional scheme is being replaced by the most appropriate Southern or Northern Province nomenclature (see Sections 2 and 3 respectively). Thus, for some years the scheme exemplified within Wood and Smith (1978) ((Figure 3), Column 7 and (Figure 6), Column 5) and later workers in Lincolnshire and Yorkshire has been used instead of the traditional scheme of Jukes-Browne and Hill (1903, 1904) ((Figure 3), Column 6 and (Figure 5a), Column 6). South of The Wash through East Anglia and into southern England (with the exception of the most north-westerly outcrops that have used elements of the Northern Province terminology) the traditional scheme held sway until well into the 1990s. That traditional nomenclature is being comprehensively replaced by the scheme developed on the Wincanton (297), Shaftsbury (313) ((Figure 2), Column 4) and Chichester (317/332) 1:50 000 scale sheets and later formalised in the paper by Bristow et al., (1997) ((Figure 3), Column 10, (Figure 2), Column 5 and (Figure 5a), Column 10). The most recent maps such as Winchester (299) in the Southern Province use nomenclature recommended in Rawson et al., (2001) ((Figure 3), Column 11, (Figure 2), Column 6 and (Figure 5a), Column 11) which is a development of the earlier Bristow et al., (1997) paper.

It follows that there are a large number of lexicon entries, which require full descriptions so that both the traditional scheme and the various iterations of the new terminology can be adequately understood. It is recommended that henceforth the new approved scheme be used for all England and Wales BGS maps and publications. There should be no need to vary terminology within the new framework, but it is envisaged that entirely new terms will only be required at member level (for which full lexicon entries will be required) as investigations proceed. In other circumstances the new group and formation terminology should be adhered to even if this means that amalgamations of strata (e.g. Lewes Nodular Chalk and Seaford Chalk formations, undifferentiated) are mapped to accommodate either the available field data or the type of map (e.g. full survey, revision, desk study). As time progresses the traditional scheme entries will become redundant in terms of the new maps and reports published.

In Scotland the extremely condensed succession preserved beneath ‘Tertiary’ basalts, has been assigned, by the Survey, to a simple informal nomenclature: Morvern Greensand, Loch Aline Glass Sand and Silicified Limestone that has more in common with the Upper Cretaceous of Northern Ireland than England. Braley (1990) and Lowden et al., (1992) ((Figure 7), Column 6) introduced a number of formations within an ‘Inner Hebrides Group’ to encompass all of the Cretaceous (implying an Albian age for the lowest beds) rocks of north-west Scotland. Emeleus (1997) in the Rum memoir followed this nomenclature. The recently published Geological Conservation Review volume (Mortimore et al., 2001) ((Figure 7), Column 7) completely revised the terminology for the Scottish outcrops (formalising many existing terms but with the proviso that the dating of the sequence proposed by Braley was uncertain). As yet this scheme has not been tested by mapping. A digest of the terminology is added to the discussions in Section 4 (see (Figure 8)).

The scheme for Northern Ireland has been well established following the work of Fletcher (1977) ((Figure 9), Column 6) with the two principal units being designated as the Hibernian Greensands Formation and overlying it, the Ulster White Limestone Formation. Each are divided into members. A brief outline of the Northern Ireland Upper Cretaceous succession is given below (Section 5). It is the recommendation of this report that it is now time to upgrade the framework for Northern Ireland by raising the status of the presently defined formations to group and the present members to formation. Thus permitting other workers the greater latitude for the naming of stratal units at member and bed levels in detailed investigations.

A note on offshore nomenclature developed in response to hydrocarbon investigations since the early 1960s is included at the end of this report and in (Figure 11).

Appendices 1 and 2 give an appraisal of the terms used on BGS onshore geological maps available at the 1:50 000 and 1:63 360 scales. Appendix 3 gives the Lexicon style definitions for the redundant terminology used in older BGS publications and a listing of lithostratigraphical terms used in key papers from which the current terminology has been derived. Where possible cross-reference is made to redundant terms commonly used in the literature.

Chapter 2 Southern Province Chalk nomenclature

The palaeogeographical and structural features affecting the Chalk of the Southern Provinces are shown in (Figure 4). The Chalk Group has been in use informally for a number of years. Its first formal use was by Rhys (1974) ((Figure 11), Column 1) to cover the Chalk in the North Sea and by Wood and Smith (1978) ((Figure 3), Colulmn 7 and (Figure 6), Column 5) to cover the whole of the Chalk succession in the Northern Province but this also included the Red Chalk (now excluded from the definition as the Hunstanton Formation). Rawson et al., (1978) used the term Chalk Formation to cover the whole of the Chalk (Cenomanian to Maastrichtian). Robinson (1986) ((Figure 3), Column 9, (Figure 2), Column 2 and (Figure 5a), Column 8) in the North Downs and Mortimore (1986) ((Figure 3), Column 8, (Figure 2), Column 3 and (Figure 5a), Column 9), by implication, in the South Downs, used the term Chalk Group to cover the succession from the basal unconformity to the youngest known chalk beneath the Palaeogene unconformity in those areas. Bristow et al. (1997) ((Figure 3), Column 10, (Figure 2), Colulmn 5 and (Figure 5a), Column 10) used Chalk Group to include Lower, Middle and Upper Chalk formations. Rawson et al., (2001) ((Figure 3), Column 11, (Figure 2), Column 6 and (Figure 5a), Column 11) formalised the terminology, agreed at the November 1999 meeting, using Chalk Group to cover a lower Grey Chalk Subgroup and a higher White Chalk Subgroup. These divided further into formations.

It should be emphasised that the use of the Southern Province terms throughout the Transitional Province must be tested as these areas come up for revision. It is known with some certainty that Southern Province formations can be readily applied throughout the Chilterns and northwards into Cambridgeshire within the scarp facing west over the River Ouse/Wash Basin. The continuity of these formations beneath the thick Quaternary superficial deposits to the east and north needs to be tested. Geophysical borehole records and the interpretations of Murray (1986) show that there is a continuity of widespread identifiable marl seams in Essex, southern Suffolk and further north which confirm a framework of events that are correlated to marker beds in the Southern Province. Of course these geophysical results show inflections interpreted as marls and do not give comprehensive information on the nature of the intervening chalk lithologies. These lithologies need to be characterised to be certain of the use of Southern Province terms but it is envisaged that the formational framework may still be applied widely beneath East Anglia; and that variations in chalk successions may be better attributed to locally named units. It is suggested that such units as are identified be designated as members principally because their ‘mappability’ beneath the Quaternary cover may merely reflect an inappropriate borehole spread unrelated to their true extent.

A digest of the development of terminology in the Southern Province (and for the south-east Devon and Norfolk sequences) is given in (Figure 5a) (Figure 5b) and (Figure 5c).

The Grey Chalk Subgroup is defined as the succession from the basal Cenomanian unconformity up to the base of the Plenus Marl Member of the succeeding White Chalk Subgroup. It comprises two formations, a lower West Melbury Marly Chalk Formation and an upper Zig Zag Chalk Formation with the boundary between placed at the base of the Cast Bed. Historically this succession has been included within the Lower Chalk which itself has been further subdivided. A short review of the development of the terminology for this subgroup is given below.

In the earlier part of the 19^th century, the terms Grey Chalk, Chalk Marl or even the combination of Grey Chalk Marl were applied generally to the lowest part of what is now called the Grey Chalk Subgroup. The ‘Grey Chalk’ of W Phillips (1818) ((Figure 5a), Column 1) is approximately coincident with the lower three-quarters of the Grey Chalk Subgroup as presently understood. The presence of Chloritic Marl at the base of the chalk succession was recognised by Forbes and Ibbetson in 1844 (see Jukes-Browne and Hill, 1903).

In 1877, Price used a classification of the Lower Chalk at Folkestone that separated marly (more clayey) Chalk Marl from an overlying more carbonate-rich Grey Chalk (not to be confused with the ‘Grey Chalk’ of W Phillips). This scheme was used in his classification of the Lower Chalk by Jukes-Browne and Hill (1903) [Geological Survey memoir on the ‘Lower and Middle Chalk of England’]. They retained selected traditional lithological names from the 19^th century, including Chloritic Marl, Chalk Marl, Totternhoe Stone and Grey Chalk, and introduced two faunal zones in the Lower Chalk; a lower Schloenbachia varians Zone (equivalent to the Chloritic Marl and Chalk Marl) overlain by the Holaster subglobosus Zone (Grey Chalk and Belemnite Marl [Plenus Marls Member in present usage]). They noted that the lithological divisions could not be recognised everywhere; for example, the succession equivalent to the Chalk Marl of south-east England comprises hard white and grey chalk containing little clay in north Norfolk, Lincolnshire and Yorkshire (see following section). Furthermore, they did not recognise the Totternhoe Stone (or equivalent) south of the Thames, making separation of the Chalk Marl and Grey Chalk very difficult south and west of Berkshire. They circumvented problems posed by these lateral variations in lithology by describing only the corresponding biostratigraphical divisions in areas where the Chalk Marl and Grey Chalk could not be separated lithologically. However, where possible, Survey memoirs referred to lithological units and a fourfold division at ‘member’ level was widely recognised in England, south of north-west Norfolk: Glauconitic (Chloritic in early texts) Marl, the Chalk Marl, the Grey Chalk and the Plenus Marls.

An upwards decrease in clay content (of 10 to 20%) from the Chalk Marl to the Grey Chalk occurs gradationally over a considerable (but laterally variable) thickness of the succession and the boundary can be difficult to recognise especially in incomplete inland exposures. In the Boulonnais of northern France, this difficulty has been overcome by the creation of a separate formation for the transitional unit. In Berkshire and farther northwards, a major erosive event cutting into the Chalk Marl is found everywhere, and a condensed transgressive lag deposit (Totternhoe Stone), forming the lower part of the Grey Chalk, rests nonsequentially on various levels of the Chalk Marl. This event is equivalent to the transitional unit between the Chalk Marl and Grey Chalk, and marks the boundary between them. In the southern outcrop this event is represented by the Cast Bed (Price, 1877). It is used, together with the Totternhoe Stone farther north, to define the base of the newly formed Zig Zag Chalk Formation, thereby removing one of the long running arguments in Chalk correlation.

Robinson (1986) ((Figure 5a), Column 8) introduced an entirely new lithostratigraphy for the North Downs by dividing the strata previously described as Lower Chalk into three formations. The lowest East Wear Bay Formation (equivalent to the Chalk Marl and lower part of the Grey Chalk) is characterised by its rhythmicity; the middle Abbot’s Cliff Formation comprised massive slightly marly chalks, with the Plenus Marl Formation found at the top. He split the Abbot’s Cliff Formation into two members, the Hay Cliff (equivalent to Jukes-Browne Bed VII) and the Capel-le-Ferne Member. Robinson makes no mention of the Cast Bed but it is evident from Kennedy (1969) and more succinctly in Gale (1989) that it occurs in Kent and would adequately divide the East Wear Bay Formation.

Bristow et al., (1995) ((Figure 2), Column 4) created a new lithostratigraphy for the Lower Chalk in the Shaftesbury area of Dorset, and subsequently applied it, with modifications, across southern England (Bristow et al., 1997) ((Figure 5a), Column 10). Originally they included the Glauconitic Marl (known locally as the Melbury Sandstone) in the Upper Greensand, and split the Lower Chalk into two members; the West Melbury Marly Chalk and the Zig-Zag Chalk members. Subsequently the Glauconitic Marl/Melbury Sandstone was considered to be the basal bed of the West Melbury Marly Chalk Member because it was demonstrably of Cenomanian age and rested on a significant erosion surface. The boundary between the West Melbury and Zig Zag members, thus defined, was marked by a topographical slope change. This topographic feature coincides with the top of the thin Tenuis Limestone, where the full succession (rarely) exists, but is better defined by the base of the overlying Cast Bed (a lateral equivalent of the Totternhoe Stone). This boundary is some distance below the traditional Chalk Marl–Grey Chalk boundary as supported by Gale and Hancock (1999) but does represent a marked upward decrease in clay content. The Cast Bed is equivalent to bed C1 of Gale (1995).

In the most westerly outcrops of the Chalk Group in Devon (Jarvis and Woodroof, 1984) ((Figure 5b), Column 7) the lithology of the Grey Chalk Subgroup changes and the new nomenclature at formation level is difficult to apply. The term Beer Head Limestone Formation (which is equivalent to the Grey Chalk Subgroup) will be used on the Sidmouth (326, 340) and westernmost Bridport (327) geological sheet areas to cover the succession below the Holywell Nodular Chalk Formation.

The White Chalk Subgroup in the Southern Province is defined as the succession from the base of the Plenus Marls Member of the Holywell Nodular Chalk Formation up to the youngest chalk beneath the unconformity at the base of the overlying Palaeogene or Quaternary deposits onshore south of the Wash (but see definition in the Northern Province). It comprises seven formations: The Holywell Nodular Chalk, the New Pit Chalk, the Lewes Nodular Chalk, the Seaford Chalk, the Newhaven Chalk, the Culver Chalk and the Portsdown Chalk. Historically this succession has been included within the Middle and Upper chalks. A short review of the development of the terminology for this subgroup is given below.

The first attempt to characterise any chalk units, which we might nowadays consider ‘members’, was by Whitaker (1865a) who described the Broadstairs Chalk and Margate Chalk as discrete lithological units with type localities. The ensuing decade saw a succession of papers naming chalk units after localities in Kent (Dowker, 1870) ((Figure 5a), Column 2); (Whitaker et al., 1872) ((Figure 5a), Column 3) and Surrey (Evans, 1870) ((Figure 5a), Column 4). Evans named units have not been employed subsequently, but those of Whitaker and Dowker were used by Robinson (1986) ((Figure 5a), Column 8) and Gale et al., (1987) and taken to have member status in a modern sense.

A monograph by Barrois (1876) ((Figure 5a), Column 5) also pioneered the zonal stratigraphy of Hébert in Great Britain, and every time he used the term Chalk with a prefixed locality (i.e. Portsdown Chalk, Brighton Chalk, etc) he showed clearly which zone it belonged to. However, the units cannot be considered to be lithostratigraphical. The pattern of stratigraphical usage for the succeeding 100 years was set by Hill (1886) ((Figure 5a), Column 6), who used the terms Lower, Middle and Upper Chalk, which were subdivided into Hébert's assemblage zones and retained other informal named lithological units.

Following the work of Rowe (1899 to1908) (see discussion in Gale and Cleevley, 1989) assemblage zones were used exclusively to subdivide chalk successions until the 1980s. However, lithological features and named beds were used continually as an aid to mapping, as with the case of the Middle-Upper Chalk boundary in the North Downs, and the feature-forming Chalk Rock and Melbourn Rock.

In addition to the work of the Survey, the first authors to introduce a lithostratigraphical scheme for the Chalk were Peake and Hancock (1961) ((Figure 5c), Column 2) who placed Late Campanian to Maastrichtian chalks of north-east Norfolk within a series of informal members named after localities near Norwich and on the coast (e.g. Eaton, Weybourne and Beeston Chalks). Johansen and Surlyk (1990) ((Figure 5c), Column 5) gave these units formal member status.

Jarvis and Woodroof (1984) ((Figure 5b), Column 7) provided a lithostratigraphical subdivision of the Middle Chalk of Devon, which they placed within the Seaton Formation. They created two new members (Connet's Hole Chalk and Beer Roads Chalk). Bromley and Gale (1982) described the lithostratigraphy of the hardground complex called the Chalk Rock, which they took to be a formation.

Mortimore (1983, 1986) ((Figure 5a), Column 9) published a new lithostratigraphy based on the South Downs for what he called the Sussex White Chalk Formation within which he created six new members with distinctive lithologies each with stratotypes in Sussex, Hampshire and the Isle of Wight (Ranscombe, Lewes, Seaford, Newhaven, Culver, and Portsdown). Each of these units was demonstrated in field meetings of the Geologists’ Association in 1977 and 1980.

This precedent and guiding ethos was used by Robinson (1986) ((Figure 5a), Column 8) to create a separate lithostratigraphy for the North Downs. He in effect treated the Chalk as a group, and divided the White Chalk into two formations (Dover and Ramsgate) approximately equivalent to the Middle and Upper Chalk. These formations were divided into six members, three of which were taken from earlier researches (St Margaret's, Broadstairs and Margate members).

Mortimore (1987) suggested a correlation between his 1986 South Downs scheme and Robinson’s (1986) North Downs scheme, successfully applying his Sussex terminology to the Kent and Surrey succession. In reply, Robinson (1987) claimed that the succession in the North Downs differed from that in Sussex and required a different nomenclature. This has substantially not proved to be the case.

Gale et al., (1987) attempted to construct a compromise between the Mortimore and Robinson schemes, based on first usage priority of names, and incorporating some prezonal names employed by Robinson (1986) and many of the new ones of Mortimore (1986). This classification differed from the 1986 papers in one important respect — the concept of the term member. For both Robinson and Mortimore, members were recognisable along the entire outcrop, defined precisely by marker beds, and essentially synchronous. However in the Gale et al., (1987) scheme, some lithologically distinct members were recognised locally over a few square kilometres (e.g. Downend Member, Whitecliff Ledge Member) whilst others were recognised over hundreds (e.g. Chalk Rock Member). Gale et al., (1987) also introduced the term Studland Chalk for the unit of flinty, marl-free chalk that overlies the Portsdown Member of Mortimore but it has not proved mappable. The term Portsdown Chalk Formation is utilised herein to cover the highest outcropping chalk in Southern England. Mortimore (1988) provided a detailed criticism of the Gale et al., (1987) scheme. Subsequently, Rawson (1992) suggested a correlation between the schemes of Robinson (1986) and Mortimore (1986).

Mortimore and Pomerol (1987) extended the scheme developed in the South Downs (Mortimore 1986) to the Paris Basin, and traced the members and many marker beds across the Channel, through Normandy and Picardy to the Valley of the Yonne. It should be noted that other schemes of classification exist for the Chalk of the Pas de Calais (Robaszynski and Amedro, 1986) and Normandy coast (Juignet and Breton 1994) but that most recently the French state survey has shown an interest in applying the lithological framework defined herein across the Chalk of north-east France.

Gale (1996) provided a detailed account of the lithostratigraphy of the Turonian chalks of southern England, and introduced one new member, the Ballard Head Chalk, a replacement name for the Melbourn Rock of the south coast, sensu Mortimore (1986).

Following the introduction of the first detailed truly lithostratigraphical schemes for the Chalk of the Southern Province in 1986 the British Geological Survey (BGS) began to question the appropriateness of the traditional scheme. Thus, mapping of the western South Downs, east Hampshire and Wiltshire–Dorset areas by the BGS in the 1990s established a close correlation between units mappable across these areas with the scheme devised by Mortimore. A unified lithostratigraphy for the mapping of the Chalk was published (Bristow et al., 1997) ((Figure 5a), Column 10) following a BGS meeting at Wallingford on the 9 June 1994. This scheme has been further modified by agreement at the Chalk Lithostratigraphy meeting held at BGS Keyworth in November 1999, resulting in the short letter published in the Geoscientist (Rawson et al., 2001) ((Figure 5a), Column 11) and demonstrated more fully on the Geological Society’s Web Site. The principal elements of that new stratigraphy are presented in (Figure 2) and are described below (see (Figure 5a), Column 10 and 5a, Column 11).

The following definitions cover the New Chalk Stratigraphy as promulgated in Rawson, Allen and Gale 2001 following the joint stratigraphical framework meeting held at BGS Keyworth in November 1999. As such they should be taken as the standard nomenclature in all future BGS publications in the Southern (including where possible the Transitional) Province of England. The lithostratigraphical units used on 1:50 000 geological maps and in descriptive memoirs for the Southern and Transitional provinces are set out in (Table 2).

2.1 Chalk Group

Name: The term Chalk Group was introduced by Wood and Smith (1978) to cover all of the chalk in the Northern Province (as such it included the Hunstanton Formation). It had previously been used offshore by Rhys (1974) and by Robinson (1986) to cover the entirely Upper Cretaceous chalks in Kent. Bristow, Mortimore and Wood (1997) used the term to cover the chalks of the Southern Province as part of their new chalk nomenclature and this usage was agreed and published by Rawson, Allen and Gale (2001) following the stratigraphic meeting held at the BGS in 1999.

Type section: With the exception of well sections in the North Sea there is no single expanded and entire succession known for the whole group. The most complete onshore exposure is in the near vertically inclined cliff sections on the Isle of Wight where, under favourable conditions, the greater part of the known Southern Province sequence can be seen.

The sea cliffs of Sussex and Kent afford many of the individual formation stratotype sections for the Southern Province, whilst the sea cliffs and extensive inland exposures in Yorkshire and Lincolnshire provide the stratotypes for the constituent Northern Province formations.

Primary reference section

See notes above.

Formal subdivisions: The group is formally divided into two subgroups, the Grey Chalk and White Chalk subgroups, and numerous formations throughout England with schemes developed for the Northern and Southern provinces. Well-known units used to divide the succession further are given member status. These units are defined herein.

Lithology: Chalk, with or without flint and discrete marl, sponge, calcarenite, phosphatic, hardground and fossil-rich beds.

Definition of upper boundary: Unconformable beneath the Palaeogene or Quaternary basal unconformity onshore in the UK. Conformable beneath Danian age Maureen Formation in parts of the North Sea. Elsewhere unconformable.

Definition of lower boundary: Generally unconformable (at a burrowed surface) on the underlying Lower Cretaceous strata (Upper Greensand and Gault formations in the Southern Province and on the Hunstanton Formation in the Northern Province). Oversteps onto older strata in limited basin marginal situations.

Thickness: The thickness of the whole group is variable depending on the degree of post-Cretaceous erosion and the relative development of its constituent formations. Onshore the thickest development is within the Hampshire/Sussex area of the Southern Province, where up to about 560 m of strata are preserved; the most chronostratigraphically complete succession is in Norfolk but it is thought to be only some 400 m thick there; within the Northern Province up to 530 m are preserved but the thickest succession is within the North Sea area where about 1000 to 1300 m are preserved.

Distribution: The group is known throughout the onshore outcrops in England and offshore in the Southern, Central and Northern North Sea areas.

Previous names: Known simply as the Chalk, or the Chalk Formation since the earliest writings it is perhaps the most readily identifiable geological unit and rock type in the world. The word chalk is derived from the Saxon cealc or German kalk and has been in use since the Middle Ages with Martin Lister (1684) frequently being credited with the first publication of the name. The use of the term Chalk Group was formally proposed by Wood and Smith (1978) in their classification of the ‘Northern Province’; it was introduced to cover the Chalk of the North Sea by Rhys (1974) and is used by Robinson (1986) specifically to describe the whole of the Chalk of the North Downs. Group is implied by the use of the term formation to describe its constituent parts by Mortimore (1986). The Correlation of Cretaceous Rocks of the British Isles (Rawson et al., 1978) uses the term Chalk Formation and utilises the traditional terms Lower, Middle and Upper Chalk without recourse to a formal status suffix. Bristow, Mortimore and Wood (1997) used the term Chalk Group to encompass their Lower, Middle and Upper Chalk formations. It is equivalent to the Inner Hebrides Group in Scotland (see Section 4), the Hibernian Greensand and Ulster White Limestone groups taken together in Northern Ireland (see Section 5) and the Shetland Group in the Northern North Sea.

Parent: None

Age and biostratigraphy: Upper Cretaceous, Cenomanian to Maastrichtian.

References: Rawson, Allen and Gale, 2001; Wood and Smith, 1978; Rhys, 1974.

2.1.1 Grey Chalk Subgroup

Name: First proposed in Rawson, Allen and Gale (2001) as part of the agreed standard for the Chalk Group of England.

Type section: None defined for the whole subgroup. Full succession visible under favourable conditions in the Isle of Wight and on the Kent coast around Folkestone in the Southern Province where the constituent formations have their type sections. Can be considered as defined by reference to the type sections of the Ferriby Chalk Formation in the Northern Province.

Primary reference section: The coastal section between Copt Point, Folkestone [TR 242 365] and Hay Cliff [TR 301 394] including Abbots Cliff path [TR 268 385] in the Southern Province as discussed in Robinson (1986).

Speeton Cliffs [TA 162 752] to [TA 192 744] (Wright, 1968; Mitchell, 1995a) in the Northern Province.

Formal subdivisions: Divided in the Southern Province into the West Melbury Marly Chalk Formation and the Zig Zag Chalk Formation as defined herein. Is coextensive with the Ferriby Chalk Formation of the Northern Province.

Lithology: Clayey (‘marly’) chalk without flint. The lower part comprises limestone/marl ‘couplets’ equivalent to the West Melbury Marly Chalk Formation in the Southern Province. Upper part distinctly less ‘marly’ with notable calcarenite beds and is equivalent to the Zig Zag Chalk Formation of the Southern Province. The Ferriby Formation of the Northern Province is the lateral equivalent of the Grey Chalk Subgroup and comprises grey, soft, marly, flint-free chalk, typically weathering buff in exposures; locally includes pinkish bands; some harder, gritty, shell-debris-rich beds, and thin discrete marl seams.

Definition of upper boundary: Conformable at the highest bedding plane beneath the lowest bed of the Plenus Marls Member of the Holywell Nodular Chalk Formation in the Southern Province and the Welton Chalk Formation in the Northern Province. (Note that the Plenus Marls Member is now considered as part of the overlying subgroup thus providing a consistent datum throughout the Chalk Group of England and the North Sea).

Definition of lower boundary: Unconformable, set at the burrowed erosion surface marking the base of the Cenomanian. In the Southern Province this marks the distinct change from chalk-free to chalk-rich sediment. In the Northern Province the boundary is at an erosion surface between the Ferriby and Hunstanton formations.

Thickness: Variable, generally between 45 and 90 m in Southern Province. Is equivalent to the 30 m or so of the Ferriby Chalk Formation of the Northern Province.

Distribution: The subgroup is known throughout the onshore outcrops in England and offshore in the Southern, Central and Northern North Sea areas. In the Northern Province the term Ferriby Chalk Formation is analogous.

Previous names: Equivalent in part to the Lower Chalk (with the exception of the Plenus Marls Member) of the traditional scheme in the Southern and Northern provinces; to the Ferriby Chalk Formation of Woods and Smith (1978), and most of the Lower Chalk Formation of Bristow, Mortimore and Wood (1997). Equivalent to the Hydra or Swarte formations, respectively in the Central and Northern, North Sea Basins.

Parent: Chalk Group.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Mantelliceras mantelli to Calycoceras guerangeri zones.

References: Subgroup first defined herein, with the term only published in Rawson, Allen and Gale (2001).

2.1.1.1 West Melbury Marly Chalk Formation

Name: First proposed in Rawson, Allen and Gale (2001) as part of the agreed standard for the Chalk Group of England. This term is essentially the same as the member defined in Bristow et al., (1997) ((Figure 5a), Column 10).

Type section: Disused Melbury Quarry [ST 8753 2015] south of Shaftsbury as in Bristow, Mortimore and Wood (1997), but better defined and seen at the reference sections below.

Primary reference section: The three most significant reference sections are to be found in the cliff sections of the Kent and Sussex coasts and on the Isle of Wight. Copt Point [TR 242 365] to Hay Cliff [TR 301 394] (including Abbots Cliff and path [TR 268 385]), Folkestone to Dover, Kent; Southerham Grey Pit, Sussex [TQ 427 090]; Compton Bay, Isle of Wight [SZ 350 855]; Chinor [SU 754 994] in Oxfordshire.

Formal subdivision: Includes the equivalents of the Melbury Sandstone Member, Glauconitic Marl Member and the Cambridge Greensand Member at the base.

Lithology: Buff, grey and off-white, soft, marly chalk and hard grey limestone arranged in couplets.

Definition of upper boundary: Conformable in ‘full’ sequences at the erosional base of the overlying Cast Bed ‘Member’ (Bed C1 of Gale, 1995) of the Zig Zag Chalk Formation in the Southern Province and by the base of the Totternhoe Stone Member, its lateral equivalent, in the Transitional Province north of the Thames. This mid-Cenomanian erosional break marks the change from well-defined limestone marl couplets below to chalks with marls above and also the boundary between the ‘B’ and ‘C’ Chalk Marl couplets of Gale (1995). In full sequences the ‘Tenuis Limestone’ is the bed immediately beneath the mid-Cenomanian break.

Definition of lower boundary: Unconformable. Base marked by an erosion surface, frequently bored, at the base of the Glauconitic Marl Member (Southern Province), Melbury Sandstone Member (western Southern Province) or Cambridge Greensand Member (Transitional Province).

Thickness: In general between 15 and 25 m of these beds are preserved but they are absent over the Mid Dorset Swell (Drummond, 1970; Kennedy, 1970; Bristow et al., 1995) and thin over other syndepositional structural highs.

Distribution: Throughout the Southern Province and the Transitional Province of England. Is known to be absent or attenuated over structural highs. Most notably the Mid Dorset Swell.

Previous names: In part equivalent to the Chalk Marl of the traditional scheme. Formerly known as the West Melbury Marly Chalk Member as first proposed (Bristow, Mortimore and Wood, 1997) and upgraded to formation status in Rawson, Allen and Gale (2001). Equivalent to the lower part of the East Wear Bay Chalk Formation of Robinson (1986).

Parent: Grey Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Mantelliceras mantelli to Cunningtoniceras inerme zones.

References: Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore and Wood 1997.

Glauconitic Marl Member

Name: Traditionally termed the Glauconitic Marl for example in Jukes-Browne and Hill (1903). By implication a member in Robinson (1986), and in Survey memoirs in Sussex e.g. Young and Lake (1988) and as defined herein.

Type section: East Wear Bay [TR 261 383], Kent.

Primary reference section: Isle of Wight: coastal section, Compton Bay.

Formal subdivision: None

Lithology: Calcareous glauconitic sand and glauconitic sandy silty chalk with phosphatic nodules.

Definition of upper boundary: Upward cessation of sand and/or abundant glauconitic grains (and phosphatic pebbles)(can occur as a rapid transition over 10 cm or less) into grey, sparsely glauconitic chalky marl or marly chalk, comprising the rest of the West Melbury Marly Chalk Formation.

Definition of lower boundary: Base of glauconite-rich sand or clay resting disconformably, at a strongly burrowed surface, on pale grey siltstones of the Upper Greensand (or grey mudstones of the Gault), which contain only a trace of glauconite at most. (Note: bioturbation may carry glauconitic sediment down into underlying formation).

Thickness: Between 2 and 4 m throughout much of Southern Province but may be only a few tenths of a metre elsewhere over synsedimentary structural highs. Up to 5 m in Kent and at Eastbourne, East Sussex.

Distribution: Known throughout much of the Southern Province in Kent, Surrey, Sussex, Hampshire and Berkshire.

Previous names: Chloritic Marl in older publications due to the misidentification of the glauconite. Laterally equivalent to the Cambridge Greensand of the Transitional Province; and the Melbury Sandstone Member in the western outcrops. Over the Mid Dorset Swell and other synsedimentary highs in the western area Kennedy (1970) uses the term ‘Basement Bed’ to describe the diachronous phosphatic and glauconite-rich basal unit of the Chalk whose age ranges up to the Upper Cenomanian.

Parent: West Melbury Marly Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Mantelliceras mantelli Zone, Neostlingoceras carcitanense Subzone. (Note: over synsedimentary highs such as the Mid Dorset Swell the age range may well included zones up to Acanthoceras rhotomagense).

References: Jukes-Browne and Hill, 1903; Kennedy, 1969; Robinson, 1986; Young and Lake, 1988; Lake, Young, Wood and Mortimore, 1987.

Melbury Sandstone Member

Name: Defined in Bristow (1989) where it was considered to be the highest unit within the Upper Greensand Formation and formerly known as the Cenomanian Sands, Passage Beds or Warminster Greensand. Regarded in recent BGS publications and herein as the lateral equivalent of the Glauconitic Marl Member.

Type section: Old quarry (now backfilled), 700 m at 276 degrees from Melbury Abbas church. Section recorded by Jukes-Browne and Hill (1900, 1903).

Primary reference section: See above

Formal subdivision: None

Lithology: Richly fossiliferous, glauconitic, fine-grained sand and weakly cemented sandstone.

Definition of upper boundary: The incoming of marl is taken as the basal bed of the overlying remainder of the West Melbury Marly Chalk Formation. This can frequently be a minor erosion surface.

Definition of lower boundary: Above the highest bed of chert of the Boyne Hollow Chert.

Thickness: Between 0 and 6 m (1.22 m at type locality).

Distribution: Known for Dorset and Wiltshire.

Previous names: Cenomanian Sands, Passage Beds, Warminster Greensand. Laterally equivalent to the Glauconitic Marl Member and the Cambridge Greensand Member. Formerly considered to be the highest member of the Upper Greensand Formation.

Parent: West Melbury Marly Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Mantelliceras mantelli Zone, Neostlingoceras carcitanense Subzone.

References: Bristow, 1989; Drummond, 1970; Kennedy, 1970; Jukes-Browne and Hill, 1900, 1903; White, 1923.

Bookham Conglomerate Bed

Name: The Bookham Conglomerate is defined in Bristow et al., (1995) where it was considered to pass laterally into the basal part of the Melbury Sandstone Member (which itself was considered therein to be the highest unit within the Upper Greensand Formation at that time).

Type section: Bookham Farm [ST 7065 0414]

Primary reference section: See above

Formal subdivision: None

Lithology: Clasts of very glauconitic shelly sandstone, up to cobble size, commonly with a phosphatic rind, together with phosphatised shells (bivalves and ammonites) in a matrix of sandy glauconitic chalk. The derived fauna is latest Albian; the indigenous fauna is early Cenomanian.

Definition of upper boundary: At the disconformable contact with phosphatic pebble bed at the base of the Zig Zag Chalk Formation or the West Melbury Marly Chalk Formation (at the base of the Chalk Basement Bed of Kennedy, 1970).

Definition of lower boundary: Unconformable, locally strongly erosive boundary with underlying Shaftesbury Sandstone Member.

Thickness: Up to 1 m.

Distribution: Known from Dorset and Wiltshire over the Mid Dorset Swell.

Previous names: Passage Beds. Formerly considered to be the highest bed of the Upper Greensand Formation.

Parent: West Melbury Marly Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, lower and upper Cenomanian. Up to Acanthoceras rhotomagense zone.

References: Bristow et al., 1995; Drummond, 1970; Kennedy, 1970; Jukes-Browne and Hill, 1900, 1903; White, 1923; Smart, 1955.

Cambridge Greensand Member

Name: Known by a number of different names (see below) and given member status in Hancock (1972). Called the Cambridge Greensand on the Hitchin Sheet and formally regarded as a member equivalent to the Glauconitic Marl Member herein.

Type section: Established in brick pits as exposures become available. Currently Arlesey Brickpit. Active clay pit to west of mainline railway, west of Arlesey. Disused parts of pit used for landfill. Varies according to working.

Primary reference section: Arlesey Brickpit [TL 1879 3476] and Borehole (TL13SE/45) [TL 1887 3463].

Formal subdivision: None

Lithology: Glauconitic marl. Thin but distinctive condensed basement bed of pale greenish grey marl rich in phosphatic nodules (so called ‘coprolites’) at base. Much dark green glauconite as sand-sized grains, disseminated or concentrated in pods and layers giving a sandy texture and hence name ‘greensand’. Rare erratic pebbles at base (Hawkes, 1943).

Definition of upper boundary: Rapid upward transition to ‘Chalk Marl’ or Lower Chalk lacking distinctive glauconite grains and nodule concentrations.

Definition of lower boundary: Disconformity. Sharp contact; commonly burrowed on underlying grey Gault Clay; glauconitic burrow infill to 0.3 below junction.

Thickness: Typically 0.1–1.0 m thick. Locally thicker developments infilling hollows on top of Gault. About 0.5–0.7 m at Arlesey Brickpit [TL 188 347] (Hopson, 1992).

Distribution: Known from the north Hertfordshire and Cambridgeshire area within the Transitional Province.

Previous names: Cambridge Bed, Chloritic Marl, Coprolite Bed, Glauconitic Marl, Nodule Bed, Phosphate Bed. Laterally equivalent to the Glauconitic Marl and Melbury Sandstone members.

Parent: West Melbury Marly Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Mantelliceras mantelli Zone, Neostlingoceras carcitanense Subzone.

References: Hancock, 1972; Edmonds and Dinham, 1965; Fitton, 1836; Hart, 1973; Hawkes, 1943; Hopson, 1992; Jukes-Browne, 1875; Rawson et al., 1978; Seeley, 1866.

2.1.1.2 Zig Zag Chalk Formation

Name: First proposed in Rawson, Allen and Gale (2001) as part of the agreed standard for the Chalk Group of England. This term replaces that defined by Bristow et al. (1997) ((Figure 5a), Column 10) and specifically excludes the Plenus Marls Member.

Type section: Bristow, Mortimore and Wood (1997) did not give a type section for the whole of the formation in Dorset but named it from the lower boundary reference section at the foot of Zig Zag Hill [ST 891 207] near Shaftsbury in Dorset. They referred to the sections in Kent and Sussex that can be considered as primary reference sections.

Primary reference section: The three most significant reference sections are to be found in the cliff sections of the Kent and Sussex coasts and on the Isle of Wight. Copt Point [TR 242 365] to Hay Cliff [TR 301 394] (including Abbots Cliff and path [TR 268 385]), Folkestone To Dover, Kent; the Southerham Grey Pit and the adjacent Southerham Machine Bottom Pit, Sussex [TQ 427 090]; Compton Bay, Isle of Wight [SZ 350 855]; Chinor [SU 754 994] in Oxfordshire.

Formal subdivision: Includes the Totternhoe Stone Member and the laterally equivalent but informally named Cast Bed at its base.

Lithology: Mostly firm, pale grey to off-white blocky chalk with a lower part characterised by rhythmic alternations of marls and marly chalks with firm white chalk. Thin gritty, silty chalk beds act as markers in the sequence.

Definition of upper boundary: Conformable. The upper surface is redefined as the bedding plane beneath the lowest of the marls in the Plenus Marls Member in the overlying Holywell Nodular Chalk Formation. (Note that the Plenus Marls Member is now considered as part of the overlying formation thus providing a consistent datum throughout the Chalk Group of England and the North Sea).

Definition of lower boundary: Conformable in full sequences. The lower boundary is placed at the erosional contact at the base of the ‘Cast Bed’ (Southern Province) or the Totternhoe Stone (Transitional Province) in southern England. The former is the direct equivalent of Bed C1 of Gale (1995). The formation oversteps onto older formations over the Mid Dorset Swell where the preceding West Melbury Marly Chalk Formation is absent. The basal unit here is termed the Cenomanian Basement Bed (Drummond, 1970).

Thickness: Generally in the range 35 to 50 m in the Southern Province with the most expanded successions (up to 75 m exceptionally) in the area of West Sussex, East Hampshire and the Isle of Wight. Thins markedly to the west and is at its least over the Mid Dorset Swell where as little as 10 m may be preserved.

Distribution: Throughout the Southern Province and the Transitional Province of England.

Previous names: Broadly equivalent to the ‘Grey Chalk’ of the traditional scheme. Most of the Zig Zag Chalk Member, (but without the Plenus Marls) of Bristow, Mortimore and Wood (1997). Equivalent to the upper part of the East Wear Bay Chalk Formation and the Abbots Cliff Chalk Formation of Robinson (1986).

Parent: Grey Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Acanthoceras rhotomagense to Calycoceras guerangeri Zones.

References: Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore and Wood, 1997.

Totternhoe Stone Member

Name: The Totternhoe Stone of the traditional scheme and implicitly of member status within the Zig Zag Chalk Formation herein.

Type section: Totternhoe Stone Quarry [SP 980 222] west of Dunstable. Now forms the lowest part of the much larger encircling Lime Workings. Regarded as an expanded atypical sequence, almost 5 m thick (Aldiss, 1990).

Primary reference section: In the Hitchin district the Green Lagoon [TL 1978 3486], near Arlesey is in thin ‘shelf’ facies. The western face of the disused Chalk Quarry near the redeveloped Fairfield Hospital site shows an atypical ‘channel’ development (Hopson, 1992). Blue Lagoon [TL 1972 3444], Arlesey has about 1.0 m in typical shelf facies.

Formal subdivision: None. Informal quarrying terms used at the type site.

Lithology: A distinctly harder unit in the Grey Chalk Subgroup (Lower Chalk). Typically brownish-grey, fine-grained calcarenite. Has been described as ‘sandy’ because of coarse fossil fragments, not because of quartz sand grains. Thin to thickly bedded. Phosphatic in part with dark brown pellets a few millimetres across, up to nodules several centimetres across. Fossiliferous. Locally used as building stone.

Definition of upper boundary: Commonly indistinct conformable boundary with the overlying strata of the Zig Zag Chalk Formation (Lower Chalk, Grey Chalk unit). Upward reversion to softer, finer grained more typical chalk or marly chalk. May be difficult to locate, even in sections.

Definition of lower boundary: Commonly indistinct conformable boundary with the underlying West Melbury Marly Chalk Formation (Lower Chalk, Chalk Marl unit) but there may be an erosion surface with concentration of phosphatic pebbles in base of Totternhoe Stone above. May be difficult to locate, even in sections.

Thickness: Between 0.3 and 6.0 m in the Hitchin district. Typically 1–2 m thick but expanded sequences in synsedimentary channels may be up to 6 m thick.

Distribution: Known from Berkshire, Hertfordshire and Cambridgeshire where the Southern Province and Transitional Province overlap.

Previous names: Equivalent to the Cast Bed of the basinal successions in the Southern Province. Called the Chilton Stone on the Abingdon Sheet (253) (see entry under that title).

Parent: Zig Zag Chalk Formation (unit is the basal member of formation).

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Acanthoceras rhotomagense Zone, Turrilites costatus Subzone.

References: Aldiss, 1990; Hancock, 1972; Hopson, 1992; Hopson, Aldiss and Smith, 1996; Jukes-Browne and Hill, 1887; Penning and Jukes-Browne, 1881; Rawson,et al., 1978; Whitaker, 1865b.

2.1.1.3 Beer Head Limestone Formation

Name: First proposed by Jarvis and Woodroof (1984) to replace the Cenomanian Limestone of Smith (1957, 1965) ((Figure 5b), Column 5) but is redefined herein to exclude their Pinnacles Member which is equivalent to the Plenus Marls Member elsewhere. It was not mapped separately in south Devon but is traceable on coastal sections.

Type section: Hooken Cliffs, [SY 210 881] to [SY 227 878], Devon.

Primary reference section: Beer Head [SY 227 879], and Wilmington Quarry [SY 209 997], Devon.

Formal subdivision: None herein but defined as comprising the Pounds Pool Sandy Limestone, Hooken Nodular Limestone and Little Beach Bioclastic Limestone members of the Beer Head Limestone Formation of Jarvis and Woodroof (1984).

Lithology: Complex thin sequence of bedded coarse calcareous sandstone, bioclastic limestone, calcarenite and shelldetrital limestone, with a distinct nodularity and well-developed hardgrounds. Glauconitic and phosphatic. Includes the Wilmington Sand Member in calcarenite facies.

Definition of upper boundary: Disconformable at the surface of the Humble Point Hardground with the Pinnacles Member (of Jarvis and Woodroof, 1984), which is the sub-Plenus Marls Member erosion surface.

Definition of lower boundary: Disconformable on the burrowed Small Cove Hardground of the Upper Greensand Formation.

Thickness: Up to 10.4 m at Hooken Cliffs.

Distribution: Confined to the area south of the Mid Dorset Swell in Dorset.

Previous names: Directly equivalent to the Chloritic Marl of Meyer (1874), the Chalk Marl of Jukes-Browne and Hill (1896) and the Cenomanian Limestone of Smith (1965). Correlates with the Pounds Pool Sandy Limestone, Hooken Nodular Limestone and Little Beach Bioclastic Limestone members of the Beer Head Limestone Formation of Jarvis and Woodroof (1984).

Parent: Grey Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Mantelliceras mantelli to Calycoceras geurangeri zones.

References: Mortimore, Wood and Gallois, 2001.

2.1.2 White Chalk Subgroup

Name: First proposed in Rawson, Allen and Gale (2001) as part of the agreed standard for the Chalk Group of England.

Type section: None defined for the whole subgroup. Full succession visible under favourable conditions in the Isle of Wight and on the Sussex and Kent coast in the Southern Province where the constituent formations have their type sections. Can be considered as defined by reference to the type sections of the constituent formations in the Northern Province.

Primary reference section: Isle of Wight and the coastal successions of Sussex (Mortimore, 1986) and Kent (Robinson, 1986) in the Southern Province. The numerous stratotypes for the constituent formations in the Northern Province (Wood and Smith, 1978).

Formal subdivisions: Divided in the Southern Province into the Holywell Nodular Chalk Formation, New Pit Chalk Formation, Lewes Nodular Chalk Formation, Seaford Chalk Formation, Newhaven Chalk Formation, Culver Chalk Formation and the Portsdown Chalk Formation. In the Northern Province the subgroup comprises the Welton Chalk Formation, Burnham Chalk Formation, Flamborough Chalk Formation and the Rowe Chalk Formation.

Lithology: Chalk with flints. With discrete marl seams, nodular chalk, sponge-rich and flint seams throughout. Typology of flints and incidence of marl seams is important for correlation.

Definition of upper boundary: Unconformable beneath Palaeogene/Quaternary basal unconformity onshore in the UK. Conformable beneath Danian age Maureen Formation in parts of the North Sea. Elsewhere unconformable.

Definition of lower boundary: Conformable on the Grey Chalk Subgroup. Placed at the lowest bed in the Plenus Marls Member at the base of the Holywell Nodular Chalk Formation (Southern Province) and at the base of the same member in the Welton Chalk Formation (Northern Province). (Note that the Plenus Marls Member is now considered as part of this subgroup thus providing a consistent datum throughout the Chalk Group of England and the North Sea).

Thickness: Variable depending on degree of post-Cretaceous erosion and the relative development of its constituent formations. Onshore the thickest development is within the Hampshire/Sussex area of the Southern Province, where up to 470 to 515 m of strata are preserved; the most chronostratigraphically complete succession is in Norfolk but is thought there to be only some 350 m thick; within the Northern Province up to 500 m are preserved but the thickest succession is within the North Sea area where about 800 to 1100 m are preserved.

Distribution: The subgroup is known throughout the onshore outcrops in England and offshore in the Southern, Central and Northern North Sea areas.

Previous names: None directly equivalent, but the Sussex White Chalk Formation (with excludes the lowest Plenus Marls Member) of Mortimore (1986) is the closest match. Includes the Middle Chalk Formation and Upper Chalk Formation of Bristow, Mortimore and Wood (1997).

Parent: Chalk Group.

Age and biostratigraphy: Upper Cretaceous, Cenomanian to Maastrichtian (onshore UK). Metoicoceras geslinianum to Belemnitella mucronata s.l. zones and into Belemnella spp. zones where the highest Campanian and Maastrichtian chalks are encountered. Up to basal Danian (basal Paleocene) in the North Sea Basin.

References: The subgroup is first defined herein, with the term only published in Rawson, Allen and Gale (2001).

2.1.2.1 Holywell Nodular Chalk Formation

Type section: Beachy Head [TV 59 95] and Holywell [TV 603 973] section west of Eastbourne, Sussex.

Primary reference section: The Plenus Marls Member type site at Merstham [TQ 295 542] of Jefferies (1963) is now obscured. Robinson (1986) used Shakespeare Cliff [TR 307 398] in Kent as a reference section. The thickest onshore sequence is seen at Eastbourne adjacent to the Holywell Cafe [TV 602 967]. The Melbourn Rock was originally defined at Melbourn in Cambridgeshire where the type site is now poorly exposed in a car park beneath a building. A replacement type section is taken at Ashwell Quarry [TL 2687 3945] on the Biggleswade sheet (see Hopson et al., 1996). The Melbourn Rock Bed or Beds were defined by Mortimore (1986) and Robinson (1986) at Gun Gardens [TV 588 964] and Akers Steps [TR 297 394] respectively. Chinor [SU 754 994] in Oxfordshire.

Formal subdivision: Includes the Plenus Marls Member and the Melbourn Rock Member. Comprises a number of laterally persistent and named marl and flint beds in Mortimore (1986) that can be recognised outside the Sussex area over much of southern England.

Lithology: Generally hard nodular chalks with thin flaser marls and significant proportions of shell debris in part. Base marked by the interbedded coloured marl and chalk succession characteristic of the Plenus Marls Member (a term applicable in both the Southern and Northern Provinces). The Melbourn Rock Member above the base can be distinguished by its lack of shell material.

Definition of upper boundary: Conformable. Taken at the Gun Gardens Main Marl in the expanded sequences of the Southern Province and at the highest shell detrital bed in mapping terms.

Definition of lower boundary: Conformable. Base of the formation taken at the bedding plane immediately below the lower marl bed in the Plenus Marls Member. (Note that the Plenus Marls Member is now considered as part of this formation thus providing a consistent datum throughout the Chalk Group of England and the North Sea).

Thickness: In thicker successions this formation is generally 25 to 35 m thick. It thins rapidly into the Transitional Province of the North Downs, Berkshire Downs and the Chilterns (10 to 15 m) and is almost absent in the south-west of Dorset and in Devon.

Distribution: Known throughout the Southern Province, within the Chilterns and northward into East Anglia in the Transitional Province.

Previous names: Previously known as the Holywell Nodular Chalk Member of Bristow, Mortimore and Wood (1997), under which name it did not include the Plenus Marls. Equivalent to the Plenus Marl Beds, Lower and Middle Holywell Beds of Mortimore (1986); and the Plenus Marls Formation and lower part of the Shakespeare Cliff Member of the Dover Chalk Formation (Robinson, 1996). Includes the Melbourn Rock (Ballard Head Member of Gale, 1996). The name, as applied erroneously by Shephard-Thorn, 1988, referred to the whole of the condensed succession representing the Holywell Nodular Chalk Formation in East Kent.

Parent: White Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Cenomanian (uppermost) to Turonian. Metoicoceras geslinianum to Mytiloides spp. zones (the inferred top of the Mammites nodosiodes Zone).

References: Mortimore, 1986; Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore and Wood, 1997.

Plenus Marls Member

Name: Traditionally known as the Plenus Marls and defined by Jefferies (1963). Defined herein at member level marking the basal unit of the Holywell Nodular Chalk Formation.

Type section: Merstham Greystone Limeworks in Surrey [SU 295 542].

Primary reference section: Numerous throughout Southern and Northern Province see Jefferies (1963).

Formal subdivision: None herein but finely divided into eight beds of widespread geographical distribution by Jefferies (1963).

Lithology: Interbedded coloured marl and chalk.

Definition of upper boundary: Conformable at the bedding plane above the highest marl below the hard nodular limestone of the Melbourn Rock Member.

Definition of lower boundary: Conformable beneath the lowest marl on the underlying Zig Zag Chalk Formation. Sequence constitutes the lowest member of the Holywell Nodular Chalk Formation and the White Chalk Subgroup (see also the definition for the Northern Province).

Thickness: Usually in the range 1 to 1.5 m but known to be up to 3.0 m at the Holywell Cafe cliff section in Eastbourne.

Distribution: Widespread within the Southern, Transitional and Northern provinces (see additional entry for Northern Province) and offshore in the North Sea area. Forms the most characteristic downhole geophysical signature in the whole of the Chalk Group.

Previous names: Plenus Subzone in various Survey publications; Belemnite Marls.

Parent: Holywell Nodular Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Metoicoceras geslinianum Zone.

References: Jefferies, 1963.

Melbourn Rock Member

Name: Recognition of the Melbourn Rock in the Cambridgeshire and Chiltern areas formed the basis on which the traditional tripartite scheme for the Chalk of southern England was erected by the Geological Survey (Jukes-Browne and Hill, 1903). It is herein regarded as of member status within the lower part of the Holywell Nodular Chalk Formation.

Type section: Named after Melbourn, in Cambridgeshire where two pits are described. The Melbourn Lime-kiln Pit and a second ‘a quarter of a mile distant’ both at the southern end of Melbourn. The type site is in a car park beneath a modern industrial building developed in the old (?) lime-kiln pit and is now in poor condition and the full sequence cannot be seen. A substitute type section and essentially the new stratotype is described in the Hitchin memoir (p. 47) at Ashwell [TL 2697 3945] where the full sequence from the Plenus Marls to well above the Melbourn Rock can be seen in a clean section.

Primary reference section: Numerous throughout the Southern and Transitional Province. Chinor in Oxfordshire, Folkestone–Dover in Kent, Eastbourne–Beachy Head in Sussex, Compton Bay on the Isle of Wight.

Formal subdivision: None

Lithology: Hard to very hard off-white, blocky fractured chalk with numerous nodular chalk beds and thin anastomosing marls.

Definition of upper boundary: Conformable but difficult to place in the Transitional Province where it is usually considered to be at a horizon of less hard flaggy chalks with significant anastomosing marls. This is probably equivalent to the Meads Marls succession of the Southern Province and Mortimore (1986) places the boundary at the Meads Marl 1 in Sussex.

Definition of lower boundary: Conformable on the highest marl seam of the Plenus Marls Member. This is the Foyle Marl of Mortimore (1986).

Thickness: About 3 m in the classic Chiltern area but noted to be between 2 and 7 m in the Hitchin Memoir (Hopson et al., 1996) and a range of 2.7 to 4 m is given in Mortimore (1986).

Distribution: Known throughout the Southern and Transitional provinces and forms the most readily identifiable geomorphological features in unexposed ground.

Previous names: Melbourn Rock as used in many BGS publications and external papers. Equivalent to part of the Grit Bed of Price (1877).

Parent: Holywell Nodular Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Cenomanian to Turonian. Metoicoceras geslinianum, Neocardioceras juddi and basal Mytiloides spp. zones.

References: Hill and Jukes-Browne, 1886; Hill, 1886.

2.1.2.2 New Pit Chalk Formation

Type section: Gun Gardens [TV 588 964] and Beachy Head [TV 576 953] sections in Sussex.

Primary reference section: Akers Steps [TR 297 394], Kent; Compton Bay [SZ 350 855].

Formal subdivisions: None herein but contains a number of laterally persistent and named marl and flint beds in Mortimore (1986) which can be recognised outside the Sussex area over much of southern England.

Lithology: Principally blocky, white firm to moderately hard chalk with numerous marls or paired marl seams. Flint occurs sporadically in the upper part in the deeper basin areas of the Southern Province. In some localities flint, in seams, occurs to the base of the formation most notably over structural highs, towards the margins of the outcrop and within the Transitional Province.

Definition of upper boundary: Conformable at the base of Glynde Marl 1 in Sussex, but one of the higher marls elsewhere although invariably in the interval Glynde Marls to Southerham Marls in the Southern Province. The mapping boundary is placed at the appearance of nodular chalks and significant flint development within that range of marls. In the Transitional Province the formation expands in response to the later inception of nodularity and hardground development (characteristic of the Lewes Nodular Chalk Formation) such that the upper boundary is diachronous here and placed below the ‘Chalk Rock Member’ at the Reed Marl (the lateral equivalent of the Bridgewick Marls of the Southern Province).

Definition of lower boundary: Conformable at the bedding plane immediately below the Gun Gardens Main Marl (the Lulworth Marl of Gale, 1996) in the standard Sussex succession. The mapping boundary is placed at the highest shell-detrital chalk and at the incoming of sporadic flints. In the Transitional Province the top of these shell-detrital chalks is at the Odsey Marl (See Hopson et al., 1996).

Thickness: Typically between 35 and 50 m but is as little as 10 to 25 m metres thick in Wiltshire, north Hampshire and Berkshire over synsedimentary structural highs. The formation expands in the Transitional Province where it is thought to be up to 75 to 80 m thick.

Distribution: Known throughout the Southern Province, within the Chilterns and northward into East Anglia in the Transitional Province.

Previous names: Known as the New Pit Chalk Member prior to Rawson et al. (2001). Also the upper and thicker part of the traditional Middle Chalk. Equivalent to the Upper Holywell Beds and New Pit Beds of the Ranscombe Chalk Member (Mortimore and Pomerol, 1996); and the upper part of the Shakespeare Cliff Member and Aycliff Member of the Dover Chalk Formation (Robinson, 1986).

Parent: White Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Turonian. The greater part of the Terebratulina lata Zone.

References: Mortimore, 1986; Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore and Wood, 1997.

2.1.2.3 Lewes Nodular Chalk Formation

Name: First proposed in Rawson, Allen and Gale (2001) as part of the agreed standard for the Chalk Group of England. Replaces the mapping member of the same name proposed in Bristow, et al. (1997). The term Lewes Nodular and Flinty Chalk Member was used by Mortimore (1987) as part of his Sussex White Chalk Formation and adapted to Lewes Nodular Chalk Member within the Upper Chalk Formation by Bristow, Mortimore and Wood (1997).

Type section: The type sites for the Lewes Chalk as defined by Mortimore (1986) are at the Caburn Pit [TQ 447 089], Navigation Pit [TQ 426 099] and on the coast between Beachy Head [TV 576 953] and Light Point [TV 566 954], all in Sussex.

Primary reference section: Compton Bay [SZ 350 855] and Whitecliff Bay [SZ 638 854] on the Isle of Wight; White Nothe [SY 764 813] in Dorset; Akers Steps [TR 298 394] and Langdon Stairs [TR 341 422] near Dover, Kent; the Aston Rowant (Stokenchurch) M40 cutting [SU 728 965] to [SU 740 965] Oxfordshire; Kensworth Chalk Pit [TL 015 197] in Bedfordshire.

Formal subdivision: Includes the Chalk Rock Member, the Kensworth Nodular Chalk Member and the Top Rock Bed. Includes a number of laterally persistent and named marl, hardground and flint beds in Mortimore (1986) that can be recognised outside the Sussex area over much of southern England.

Lithology: Composed of hard to very hard nodular chalks and hardgrounds (which resist scratching by finger-nail) with interbedded soft to medium hard chalks (some grainy) and marls; some griotte chalks. The softer chalks become more abundant towards the top. Nodular chalks are typically lumpy and iron-stained (usually marking sponges). Brash is rough and flaggy or rubbly, and tends to be dirty. First regular seams of nodular flint, some large, commence near the base and continue throughout.

Definition of upper boundary: Conformable at the Shoreham Marl 2 which is equivalent to the East Cliff Marl 2 in Kent and also identified at the Anstey Quarry [TL 395 329] south of Royston, in the Transitional Province. In the field, this is the most difficult boundary to place precisely because of the gradual upward transition in predominant lithology, with interbeds of hard chalk in soft chalk and vice versa. The most positive criterion is the incoming of abundant thick-shelled inoceramid debris (Platyceramus) in soft chalks, although this may not be applicable everywhere. The presence of a susseccion containing carious flints within the low Seaford Chalk and high Lewes Chalk is a helpful field indicator of the boundary.

Definition of lower boundary: Conformable at the base of Glynde Marl 1 in Sussex, but one of the higher marls elsewhere although invariably in the interval Glynde Marls to Southerham Marls in the Southern Province. The mapping boundary is placed at the appearance of nodular chalks and significant flint development within that range of marls.

In the Transitional Province the formation is condensed in response to the later inception of nodularity and hardground development such that the lower boundary is diachronous here and placed below the ‘Chalk Rock Member’ at the Reed Marl (the lateral equivalent of the Bridgewick Marls of the Southern Province).

Thickness: The formation is thickest in the basinal successions of the Southern Province in east Hampshire and Sussex where it attains c. 35 to 60 m in the east and up to 80 m in west. The formation thins towards the margins of the outcrop and over synsedimentary structural highs.

Distribution: Known throughout the Southern Province, within the Chilterns and northward into East Anglia in the Transitional Province.

Previous names: Lewes Nodular and Flinty Chalk Member of Mortimore (1986) in Sussex and the Lewes Nodular Chalk Member (Bristow et al., 1997). Equivalent to the Akers Steps Member of the Dover Chalk Formation and the St Margarets Member of the Ramsgate Chalk Formation of Robinson (1986) in Kent. Forms the lowest part of the traditional Upper Chalk.

Parent: White Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Turonian to Coniacian. Top Terebratulina lata, Sternotaxis plana (now Plesiocorys plana) and Micraster cortestudinarium zones.

References: Mortimore, 1986; Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore and Wood, 1997.

Chalk Rock Member

Name: Described as the Chalk Rock in the traditional scheme as exemplified in Jukes-Browne and Hill (1904). The term Chalk Rock Formation was adopted in Bromley and Gale (1982) and later as a member in Gale, Wood and Bromley (1987). Defined herein as a member within the Lewes Nodular Chalk Formation.

Type section: Ogbourne Maizey. Old farm west of Ogbourne Maizey, 3 km north of Marlborough, Wiltshire.

Primary reference section: Noted at 55 sites throughout the ‘Transitional’ and Southern Provinces in Bromley and Gale (1982).

Formal subdivision: None herein but is divided into a number of named hardgrounds (of bed status) in Bromley and Gale (1982).

Lithology: Very hard chalk and chalkstone, some nodular, including mineralised hardground surfaces, and marl seams.

Definition of upper boundary: Where the Hitch Wood Hardground is developed the boundary is placed at the flint nodule horizon that marks the base of the overlying nodular chalk unit. In other areas, at the Pewsey Hill Hardground or the Ogbourne Hardground.

Definition of lower boundary: The diffuse lower limit of cementation of the lowest bed of chalkstone at this level.

Thickness: Between 4 and 5 m where fully developed.

Distribution: Known throughout the Southern Province and in the Chiltern area of the Transitional Province.

Previous names: Chalk Rock (CkR). Chalk Rock Formation.

Note 1

Although Bromley and Gale's (1982) definition of the Chalk Rock is accepted, it is BGS practice to include the unit in the Upper Chalk of the traditional scheme and as a constituent part of the Lewes Nodular Chalk Formation in the new scheme. Thus the Chalk Rock is reduced in rank from formation (Bromley and Gale, 1982) to member.

Note 2

Gale, Wood and Bromley (1987) treat the Chalk Rock as a member of the ‘White Chalk Formation’ (= Middle and Upper Chalk of BGS). Equivalent to part of the Kingston Beds of Mortimore (1986) and part of the St Margarets Member of Robinson (1986).

Parent: Lewes Nodular Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Turonian. Sternotaxis plana (now Plesiocorys plana) Zone.

References: Whitaker, 1861; Bromley and Gale, 1982; Jukes-Browne and Hill, 1904; Gale, Wood and Bromley, 1987.

Kensworth Nodular Chalk Member

Name: First used and defined in the Hitchin Memoir (Hopson, Aldiss and Smith, 1996)

Type section: Kensworth Chalk Quarry [TL 017 197], near Dunstable, Bedfordshire.

Primary reference section: Reed Chalk Pit [TL 3595 3704], south of Royston, Hertfordshire.

Formal subdivision: Includes the Top Rock Bed

Lithology: Very hard nodular chalk and chalkstone, including mineralised hardground surfaces.

Definition of upper boundary: Conformable at the top of a succession of obviously indurated chalks within the Lewes Nodular Chalk Formation overlying the Chalk Rock Member. Note that this does not necessarily coincide with the top of the Top Rock Bed.

Definition of lower boundary: Conformable at the top of the Chalk Rock Member above the flint nodule horizon marking the top of the Hitchwood Hardground.

Thickness: About 2.5 to 4 m in Hitchin and Leighton Buzzard districts.

Distribution: Known within the Leighton Buzzard and Hitchin areas of the Chilterns.

Previous names: None

Parent: Lewes Nodular Chalk Formation.

Age and biostratigraphy: Upper Cretaceous Turonian and Coniacian. Sternotaxis plana (now Plesiocorys plana), Micraster cortestudinarium zones.

References: Hopson, Aldiss and Smith, 1996; Shephard-Thorn, Moorlock, Cox, Allsop and Wood, 1994.

Top Rock Bed

Name: The name was first used by Penning and Jukes-Browne (1881) to describe a distinctive bed(s) of hardground and nodular chalk development at a distinctly higher stratigraphical level than the Chalk Rock.

Type section: Reed Pit [TL 3595 3704] near Royston in Cambridgeshire.

Primary reference section: Kensworth [TL 017 197] (Leighton Buzzard); Hitch Wood Hill End [TL 1973 2398] (Hitchin).

Formal subdivision: None

Lithology: Hard cream limestone with scattered brownish phosphatic nodules commonly green-coated at the top. Mineralised hardground or chalkstone bed.

Definition of upper boundary: Conformable at the hardground surface marked by the change from mineralised hard chalkstone to soft white smooth chalk.

Definition of lower boundary: Conformable within the Kensworth Nodular Chalk Member at an indistinct boundary marking a significant increase in nodularity between 2 and 3 m above the uppermost hardground of the Chalk Rock Member.

Thickness: From 0.8 to 1.0 m in Cambridgeshire. And from 0.3 m to 1.0 m in the Chilterns to where it is essentially confined.

Distribution: The Chilterns within Hertfordshire and possibly Buckinghamshire.

Previous names: Forms part of the Kensworth Nodular Chalk Member.

Parent: Lewes Nodular Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Turonian to Coniacian. Micraster cortestudinarium Zone.

Penning and Jukes-Browne, 1881; Brighton, 1928; Worssam and Taylor, 1969.

2.1.2.4 Seaford Chalk Formation

Name: First proposed in Rawson, Allen and Gale (2001) as part of the agreed standard for the Chalk Group of England. The term Seaford Chalk Member was used by Mortimore (1987) as part of his Sussex White Chalk Formation and adopted as Seaford Chalk Member within the Upper Chalk Formation by Bristow, Mortimore and Wood (1997).

Type section: Seaford Head [TV 496 976] in Sussex.

Primary reference section: Light Point, through Birling Gap [TV 553 959] to the Seven Sisters and numerous other sites in Sussex; Whitecliff Bay [SZ 638 854] on the Isle of Wight; in a number of discontinuous sections between Hope Point [TR 379 463] and White Ness [TR 397 710] in Kent; Ballard Point [SZ 048 813] and White Nothe [SY 764 813] in Dorset.

Formal subdivision: Includes the Stockbridge Rock Member in the Hampshire Downs area. Includes a number of laterally persistent flint and marl beds named in Mortimore (1986) that can be traced outside Sussex in the Southern and Transitional provinces.

Lithology: Firm white chalk with conspicuous semi-continuous nodular and tabular flint seams. Hardgrounds and thin marls known from the lowest beds.

Definition of upper boundary: Conformable at the Buckle Marl 1 in the Sussex succession. The incoming of common Zoophycos flints and the presence of the zonal Uintacrinus socialis crinoid at the base of the Newhaven Chalk Formation are useful indicators in the field.

Definition of lower boundary: Conformable at the base of Shoreham Marl 2 in Sussex that marks the change from regularly spaced nodular and grainy chalk beds of the upper Lewes Nodular Chalk Formation to smooth white chalks. This marl is equivalent to the East Cliff Marl 2 in Kent and which is also identified at the Anstey Quarry [TL 395 329] south of Royston, in the Transitional Province.

In the field, this is the most difficult boundary to place precisely as it falls in the sequence where the predominance of interbeds of hard chalk reduces in favour of soft chalk. The most positive criterion is the incoming of abundant thick-shelled inoceramid debris (Platyceramus) in soft chalks, although this may not be applicable everywhere. The presence of a succession containing carious flints within the low Seaford Chalk and high Lewes Chalk is a helpful field indicator of the boundary. Geomorphologically the formation characteristically forms long even dipslope crests.

Thickness: Generally in the range 50 to 80 m in the basinal successions of Sussex and Hampshire within the Southern Province. Equivalent beds in Kent are in the range 55 to 60 m. Over considerable areas of southern England the thickness of this unit is limited by erosion beneath the sub-Palaeogene unconformity.

Distribution: Known throughout the Southern Province, within the Chilterns and northward into East Anglia in the Transitional Province.

Previous names: Seaford Member of Mortimore (1986) and as adapted in Bristow et al., (1997). Broadly equivalent to the Broadstairs Member of the Ramsgate Chalk Formation of Robinson (1986) in Kent.

Parent: White Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Coniacian to Santonian. Micraster coranguinum Zone.

References: Mortimore, 1986; Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore and Wood, 1997.

Stockbridge Rock Member

Name: Described in the Winchester Sheet Explanation (Booth, 2002) and Farrant (2001).

Type section: Type area only in the Stockbridge district. Ongoing research in progress but the unit is identified from its characteristics porcellanous limestone brash in the field.

Primary reference section: Poor exposure in a silage pit at Beech Farm, Nether Wallop [SU 2845 3537].

Formal subdivision: None

Lithology: Very hard, locally porcellanous, creamy white chalk, grainy in part with abundant sponge spicules.

Definition of upper boundary: Conformable at the top of the uppermost bed of very hard chalk.

Definition of lower boundary: Conformable at the change from soft white smooth chalk to very hard chalk. Placed within the higher part of the Seaford Chalk Formation.

Thickness: Not known in detail but estimated to be 2 to 3 m. Member may be a number of such beds of hard chalk between 5 and 10 m below the mapped base of the Newhaven Chalk Formation.

Distribution: Occurs in the high part of the Seaford Chalk Formation in the Winchester, Stockbridge area of Hampshire and westwards within the Bourne and Avon valleys near Salisbury. Central Hampshire and Wiltshire in the Southern Province. May extend northwards into Berkshire.

Previous names: Informally described as the Winchester Hardground. May be the lateral equivalent of the Whitway Rock. The member occurs at about the level of the Barrois Sponge Bed and the Clandon Hardground of the North Kent succession.

Parent: Seaford Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Santonian (?). Micraster coranguinum zone.

References: Farrant, 1999, 2000.

2.1.2.5 Newhaven Chalk Formation

Name: First proposed in Rawson, Allen and Gale (2001) as part of the agreed standard for the Chalk Group of England. The term Newhaven Chalk Member was used by Mortimore (1987) as part of his Sussex White Chalk Formation and adopted as the Newhaven Chalk Member within the Upper Chalk Formation by Bristow, Mortimore and Wood (1997).

Type section: Seaford Head [TV 496 976] in Sussex.

Primary reference section: Newhaven [TV 446 999] to Brighton [TQ 338 033] cliff’s Sussex; Paulsgrove Pit [SU 635 065] on Portsdown; Whitecliff Bay [SZ 638 854] on the Isle of Wight; White Ness [TR 397 710] to Foreness Point [TR 383 717] and Margate [TR 354 714] on the Thanet Coast in Kent; Ballard Point [SZ 048 813] and White Nothe [SY 764 813] in Dorset.

Formal subdivision: Informally includes a number of laterally persistent flint and marl beds named in Mortimore (1986) that can be traced outside Sussex in the Southern and Transitional provinces.

Lithology: Composed of soft to medium hard, smooth white chalks with numerous marl seams and flint bands, including abundant Zoophycos flints (notably at levels near the base). The formation is known to contain distinct phosphatic chalks of limited lateral extent. Equivalent beds, the Margate Chalk of north Kent, are marl-free and contain little flint.

Definition of upper boundary: Placed at the Castle Hill Marl 2 in the type locality at Seaford Head, Sussex where there is some evidence of a reduction in marl thickness over a structural high. In expanded trough areas a higher set of marls, the Pepper Box Marls, are well developed and the boundary is taken at this level.

Definition of lower boundary: Conformable at the Buckle Marl 1 in the Sussex succession. The incoming of common Zoophycos flints and the presence of the zonal Uintacrinus socialis crinoid at the base of the Newhaven Chalk Formation are useful indicators in the field.

Thickness: From 45 to 75 m in the basinal sequences of the Southern Province. Limited by sub-Palaeogene erosion over large areas of southern Britain.

Distribution: Known throughout the Southern Province northward to the Pewsey/Kingsclere structure and as limited outliers north of this structure. Its presence within the Chilterns and northward into East Anglia in the Transitional Province is not well known.

Previous names: Newhaven Chalk Member of Mortimore (1986) and as adopted in Bristow et al. (1997). Broadly equivalent to the Margate Chalk Member of the Ramsgate Chalk Formation of Robinson (1986) in Kent.

Parent: White Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Santonian to Campanian. Uintacrinus socialis, Marsupites testudinarius, Uintacrinus anglicus and Offaster pilula Zones.

References: Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore and Wood, 1997.

Margate Chalk Member

Name: Defined in Robinson (1996). Herein taken as the modified classification in Bristow, Mortimore and Wood (1997).

Type section: North Foreland [TR 398705] to Foreness Point [TR 385 717] and Palm Bay [TR 380 715] on the Isle of Thanet, north Kent.

Primary reference section: As above

Formal subdivision: None herein. Informally includes a number of laterally persistent flint and marl beds named in Robinson (1986) which can be traced outside Kent in the Southern and Transitional provinces where they are correlated with the named beds of Mortimore (1986)

Lithology: Marl-free smooth white chalk with little flint, weakly developed indurated iron-stained sponge beds.

Definition of upper boundary: Limited by sub-Palaeogene erosion surface in the Isle of Thanet.

Definition of lower boundary: Conformable at the surface immediately above the Barrois Sponge Bed in Thanet (Robinson, 1986).

Thickness: Up to 24 m in the North Foreland to Foreness Point and Palm Bay sections on the Isle of Thanet in north Kent.

Distribution: Confined to the Thanet area of Kent and possibly northwards into Essex and southern East Anglia.

Previous names: Margate Member of the Ramsgate Chalk Formation of Robinson (1986). The ‘Margate Chalk’ of Whitaker (1865a, 1872). Margate Chalk Formation definition in BGS lexicon. Lateral equivalent of the greater part of the Newhaven Chalk Formation. The lateral extent of this member is not known and may well be confined to the Thanet area although there are indications of this lithology in Essex.

Parent: Newhaven Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Santonian to basal Campanian. Micraster coranguinum, Uintacrinus socialis, Marsupites testudinarius and Uintacrinus anglicus zones.

References: Bristow, Mortimore and Wood, 1997; Robinson, 1986; Dowker, 1870; Gale, Wood and Bromley, 1987; Mortimore, Wood and Gallois, 2001.

2.1.2.6 Culver Chalk Formation

Type section: Whitecliff Bay [SZ 638 854] on the Isle of Wight.

Primary reference section: Scratchell’s Bay [SZ 296 847] on the Isle of Wight; Ballard Point [SZ 048 813] in Dorset.

Formal subdivision: Is divided into the Tarrant Chalk Member and the Spetisbury Chalk Member. Informally includes a number of laterally persistent flint and marl beds named in Mortimore (1986) that can be traced outside Sussex in the Southern and Transitional provinces.

Lithology: Soft white chalk, relatively marl free with flint seams. Flints are generally large and in the upper part tabular.

Definition of upper boundary: Conformable at the Portsdown Marl (Mortimore, 1986).

Definition of lower boundary: Conformable. As defined in Mortimore (1986), the base of the Culver Chalk lies low in the quadrata Zone, at the Castle Hill Marl. Strong marls commonly occur for several metres above the Castle Hill Marls, up to and including the Pepper Box Marls which are now taken as the base.

Thickness: From 65 to 75 m and exceptionally 90 m but can be significantly less where synsedimentary channelling occurs.

Distribution: Limited to Sussex, Hampshire, Wiltshire and Dorset and as widely spaced outliers to the north in the Southern Province. Its occurrence and distribution beneath the Quaternary deposits of East Anglia in the Transitional Province is not well known.

Previous names: Culver Chalk Member of Mortimore (1986) and as adopted in Bristow et al., (1997). Includes the Tarrant Chalk and Spetisbury Chalk members.

Parent: White Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Campanian. Gonioteuthis quadrata Zone.

References: Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore and Wood, 1997.

Tarrant Chalk Member

Name: Defined in Bristow, Mortimore and Wood (1997) as a stand-alone member in the Upper Chalk Formation. Modified in Rawson et al., (2001) and herein as a member within the Culver Chalk Formation.

Type section: Old pit at the foot of The Cliff, Tarrant Rushton, (see Barton, 1991). Whitecliff Bay [SZ 638 854] on the Isle of Wight.

Primary reference section: Whitecliff Bay [SZ 638 854] on the Isle of Wight.

Formal subdivision: None herein. Informally includes a number of laterally persistent flint and marl beds named in Mortimore (1986) that can be traced outside Sussex in the Southern and Transitional provinces.

Lithology: Soft white chalk with relatively widely spaced, but large, flint seams.

Definition of upper boundary: Conformable (but see note below on thickness). Inferred to be at the Whitecliff Flint at the boundary between the Sompting and Whitecliff beds of Mortimore (1986).

Definition of lower boundary: Conformable. As defined by Mortimore (1986), the base of the Culver Chalk lies low in the quadrata Zone, at the Castle Hill Marl. Strong marls commonly occur for several metres above the Castle Hill Marls, up to and including the Pepper Box Marls which are now taken as the base. Approximately coincident with the Arundel Sponge Beds.

Thickness: From 35 to 45 m in Sussex, about 30 m in Dorset, but can be considerably reduced where synsedimentary channelling occurs.

Previous names: None

Parent: Culver Chalk Formation.

Age and biostratigraphy Upper Cretaceous, Campanian. Gonioteuthis quadrata Zone.

References: Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore and Wood, 1997; Barton, 1991.

Spetisbury Chalk Member

Name: Defined in Bristow, Mortimore and Wood (1997) as a stand-alone member in the Upper Chalk Formation. Modified in Rawson et al., (2001) and herein as a member within the Culver Chalk Formation.

Type section: Bushes Pit, Bushes Farm, and 1.25 km north-north-west of Winterborne Zelstone. Whitecliff Bay [SZ 638 854] on the Isle of Wight.

Primary reference section: Whitecliff Bay [SZ 638 854] on the Isle of Wight.

Lithology: Firm white flint with regular large flint seams, some tabular in the lower part and of Zoophycus type in the upper part.

Definition of upper boundary: Conformable at the Portsdown Marl 1 in the Farlington Redoubt on Portsdown and at Whitecliff Bay, Isle of Wight.

Definition of lower boundary: Conformable (but see note below on thickness). Inferred to be at the Whitecliff Wispy Marls (at Whitecliff Bay) at the boundary between the Sompting and Whitecliff beds of Mortimore (1986).

Thickness: About 30 m at Whitecliff Bay thought to be as thick as 45 m in Dorset and around 35 m in Hampshire.

Distribution: Limited to Sussex, Hampshire, Wiltshire and Dorset and as widely spaced outliers to the north of the Pewsey/Kingsclere structure in the Southern Province. Its possible occurrence and distribution beneath the Quaternary deposits of East Anglia in the Transitional Province is not well known.

Previous names: None

Parent: Culver Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Campanian. Gonioteuthis quadrata zone.

References: Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore and Wood, 1997; Barton, 1991.

2.1.2.7 Portsdown Chalk Formation

Name: First proposed in Rawson, Allen and Gale (2001) as part of the agreed standard for the Chalk Group of England. The term Portsdown Member was first used in Mortimore (1986) as part of his Sussex White Chalk Formation and adapted to the Portsdown Chalk Member of the Upper Chalk Formation by Bristow, Mortimore and Wood (1997).

Type section: Whitecliff Bay [SZ 638 854] on the Isle of Wight.

Primary reference section: Scratchell’s Bay [SZ 296 847] on the Isle of Wight.

Formal subdivision: Includes the Studland Chalk Member. Informally includes a number of laterally persistent flint and marl beds named in Mortimore (1986) that can be traced outside Sussex in the Southern and Transitional provinces.

Lithology: Composed of white chalk with marl seams (particularly in the lower part) and flint bands, although less flinty than the Culver Chalk Formation. The lowest part (up to and including the Farlington Marls at the base of the mucronata Zone) contains several belts rich in inoceramid shell debris, as well as isolated marl seams and pairs of marl seams that likewise contain much inoceramid shell debris. The highest part is essentially marl-free and termed the Studland Chalk ‘Member’ of Gale, Wood and Bromley (1987).

Definition of upper boundary: As defined the upper boundary of the formation is the sub-Palaeogene erosion surface. The boundary with the Studland Chalk Member (sensu Gale et al., 1987) is conformable at a marly bed with included marl above which the chalk is marl-free in the Alum Bay/Scratchell’s Bay section on the Isle of Wight and at ‘the lower horizon of yellow-stained chalk on Old Harry Rock’ in Studland Bay, Dorset (Gale et al., 1987). In the Transitional Province the upper boundary is undefined but it is noted (Mortimore, Wood and Gallois, 2001) that the ‘highest chalk of the Isle of Wight and Dorset’ is equivalent to beds within the Weybourne Chalk Member as formalised by Johansen and Surlyk (1990). These higher beds are informally termed the ‘Norwich Chalk’ and ‘Trimmingham Chalk’.

Definition of lower boundary: Conformable at the Portsdown Marl 1in the Farlington Redoubt on Portsdown and at Whitecliff Bay, Isle of Wight.

Thickness: Around 62 m at Whitecliff Bay but elsewhere thought to be thicker but limited by the sub-Palaeogene erosion surface.

Distribution: Limited to Sussex, Hampshire, Wiltshire and Dorset close to the Palaeogene cover in the Southern Province. Its possible occurrence and distribution beneath the Quaternary deposits of East Anglia in the Transitional Province is not well known.

Previous names: Portsdown Chalk Member of Mortimore (1986) and as adopted in Bristow et al., (1997).

Parent: White Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Campanian. Topmost Gonioteuthis quadrata and Belemnitella mucronata zones.

References: Rawson, Allen and Gale, 2001; Bristow et al., 1999; Bristow, Mortimore, and Wood, 1997.

Studland Chalk Member

Name: The term Studland Chalk was used by Gale, Wood and Bromley (1987) to describe their highest Campanian chalks at Handfast Point in Studland Bay, it is considered as a member herein.

Type section: Studland Bay between Old Harry Rocks [SZ 0055 825] and the Palaeogene contact [SZ 045 824].

Primary reference section: Alum and Scratchell’s Bay [SZ 296 847] Isle of Wight. Dorset coast at Studland.

Lithology: Marl-free, soft chalk with large irregular flints.

Definition of upper boundary: The sub-Palaeogene unconformity in the Southern Province. Relationship to the Upper Campanian and Maastrichtian chalks of the north-east Transitional Province is poorly understood due to poor exposure.

Definition of lower boundary: Conformable at a marly bed with included marl, above which the chalk is marl-free in the Alum Bay/Scratchell’s Bay section on the Isle of Wight and at ‘the lower horizon of yellow-stained chalk on Old Harry Rock’ in Studland Bay, Dorset (Gale et al., 1987). It is not discernible from the published literature whether these two beds are in the same stratigraphic position. This doubt, together with the lack of exposure and geomorphological expression of the member has led to the BGS reverting to the original concept of the Portsdown Chalk Member (Bristow, Mortimore and Wood, 1997). This is also the position stated in Rawson, Allen and Gale (2001) and thus the Portsdown Chalk Formation covers all of the chalk up to the sub-Palaeogene erosion surface.

Thickness: Up to 23 m preserved beneath the sub-Palaeogene unconformity in Alum Bay on the Isle of Wight.

Distribution: Limited to the Isle of Wight and the Swanage area of Dorset in the Southern Province.

Previous names: Studland Chalk of Gale et al., (1987) as adopted informally in Bristow et al., (1997). Perhaps partly equivalent to the informal ‘Norwich Chalk’ as applied in north Norfolk. Perhaps now considered as a Member within the Portsdown Chalk Formation.

Parent: Portsdown Chalk Formation or White Chalk Subgroup.

Age and biostratigraphy Upper Cretaceous, Campanian. Belemnitella mucronata

s.l. zone.

References: Bristow, Mortimore and Wood, 1997; Rawson, Allen and Gale, 2001; Bristow et al., 1999.

2.1.2.8 Upper Campanian and Maastrichtian Chalk in the Transitional Province

These chalks do not fit within the formal framework applied to the Southern Province and no attempt has been made to correlate these informal units with the upper part of the Flamborough Chalk Formation nor the Rowe Formation of the Northern Province with which they broadly share some characteristics and age. The Upper Campanian chalks are informally designated as the ‘Norwich Chalk’ as much of the succession has been long studied in numerous pits around Norwich. Peake and Hancock (1961, 1970) split this succession into a number of named units that were tentatively delimited during the survey of the Norwich Sheet 161 and published as a diagram within the memoir (Cox et al., 1989). The Maastrichtian chalks have become known informally as the Trimmingham Chalk and are described in glacially deformed ‘erratics’ (of considerable size) on the coast between Overstrand and Trimmingham. Again a number of units were given names. Both sets of informal names were given member status in Johansen and Surlyk (1990). All of the succession was investigated in the Trunch Borehole (TG23SE/8) [TG 2933 3455]) that was published in the Great Yarmouth Memoir (Arthurton et al., 1994). No firm conclusion has been reached regarding formal nomenclature for these beds since their distribution under a thick Quaternary cover has not been determined. It is recommended that reference to these units be made informally using the Norwich and Trimmingham terms until such time as they can be formally attributed. The development of the terminology applied to this succession is given in (Figure 5c).

Chapter 3 Northern Province Chalk nomenclature

In the Northern Province the Chalk Group has been in use informally for a number of years. Its first formal use was by Rhys (1974) ((Figure 11), Column 1) to cover the Chalk in the North Sea and by Wood and Smith (1978) ((Figure 6), Column 5) to cover the whole of the Chalk succession in the Northern Province but this also included the Red Chalk (now excluded from the definition as the Hunstanton Formation). Rawson et al., (1978) ((Figure 6), Column 6) used the term Chalk Formation to cover the whole of the Chalk (Cenomanian to Maastrichtian). Rawson et al., (2001) ((Figure 3), Column 11) formalised the terminology, agreed at the November 1999 meeting, using Chalk Group to cover a lower Grey Chalk Subgroup and a higher White Chalk Subgroup. In the Northern Province the Grey Chalk Subgroup is synonymous with the Ferriby Chalk Formation whilst the White Chalk Subgroup includes the Welton Chalk, Burnham Chalk, Flamborough Chalk and Rowe Chalk formations.

The Chalk Group of England has traditionally been divided into three major units, the Lower, Middle and Upper Chalk (Jukes-Browne and Hill, 1903, 1904; and earlier workers, see History of Research above). The separation of Middle and Upper Chalk was based on the recognition of the Chalk Rock at the boundary in the Southern Province. Unfortunately, this marker bed does not occur in the Northern Province, and consequently the classification is difficult to apply and unsatisfactory for this region. Thus, although the main part of the Chalk succession, as originally mapped by the Geological Survey in the 19^th century, was divided into three, the Middle Chalk–Upper Chalk boundary lay at a somewhat indefinite horizon (the base of the Sternotaxis plana (now Plesiocorys plana Zone) within the median unit of ‘Chalk with Flints’ ((Figure 6), Column 3 and (Figure 6), Column 4). To resolve these problems a revised classification was introduced by Wood and Smith (1978) ((Figure 6), Column 5) and the scheme used herein is based on their account, as modified by subsequent work (Figure 6).

Jeans (1980) ((Figure 5c), Column 3) retained the term Lower Chalk for the succession present across northern England (Norfolk, Lincolnshire and Yorkshire), and introduced a series of members within this division, based on sedimentary cycles that he first identified on the Yorkshire Coast (Belchford, Dalby/Stenigot, Bigby, Candlesby, Nettleton, Louth and Flixton members). Jeans et al., (1991) used two of these terms (Louth, Flixton) in the succession at Dover, Kent, effectively taking a nomenclature established in the thin succession of the East Midlands Shelf, south, into the Anglo-Paris Basin. His members have not been used significantly in subsequent papers.

The ‘Lower Chalk’ of north Norfolk, Lincolnshire and Yorkshire is different to that further south, as it is characterised by hard chalks with low clay content. Most workers endorse the use of the Ferriby Chalk Formation for this unit. The only significantly different usage is by Jeans, who uses Lower Chalk from north to south, and throughout he applies (member status equivalent) lithological units that are approximately equivalent to the successions identified by Robaszynski et al., (1998) in southern England.

Wood and Smith (1978) ((Figure 6), Column 5) divided the Chalk Group of the Northern Province into four formations, in ascending order, the Ferriby Chalk, Welton Chalk, Burnham Chalk and Flamborough Chalk formations, typically some 25, 50, 150 and 260 m in thickness respectively. In the updated scheme used in this account, the basal part of their Ferriby Formation is treated as a separate unit named the Hunstanton Formation (about 3 m thick) and excluded from the Chalk Group. Above the Flamborough Chalk Formation an additional unit, the Rowe Chalk Formation, is recognised beneath the drift cover of Holderness (Figure 6). These six units are based on gross lithological characteristics, such as the presence or absence of flints, and thus the classification can be easily applied in exposures and has the potential for use in field mapping. Given some initial knowledge of the stratigraphical context, the units (with the local exception of the Hunstanton Formation) are potentially recognisable on the basis of geophysical borehole logs alone.

Because the boundary between the Northern and Southern provinces is somewhat diffuse, the Chalk Group in southern Lincolnshire acquires many of the characters of the Southern Province succession. Nevertheless, it is convenient to apply the same Northern Province stratigraphical terminology to the whole of this region. In south Norfolk, to the south of The Wash, the Southern Province terminology is used (but see proviso discussed in Section 3 above and note the use of the term Ferriby Formation as noted above). In the thicker Chalk succession in the Southern North Sea, the same Northern Province units can be recognised though a different nomenclature is used; the Rødby, Hidra, Herring, Lamplugh and Jukes formations correspond approximately with the Hunstanton, Ferriby Chalk, Welton Chalk, Burnham Chalk and Flamborough Chalk formations onshore (Lott and Knox, 1994) ((Figure 11), Column 4), and the Rowe Formation is fully developed (note that the Chalk Group as defined in Lott and Knox, 1994, also includes the Ekofisk Formation of basal Palaeogene age throughout the North Sea). BGS Lexicon-style definitions of the component formations of the Chalk Group in Yorkshire and Lincolnshire are given below. The development of the terminology, thickness, distribution and full member and bed description of the formations is discussed in Sumbler (1999) and, within the context of the scheme approved at the November meeting, is summarised below.

The Hunstanton Formation, commonly referred to as the Red Chalk, is of Lower Cretaceous (Albian) age. Partly because of this, its lithostratigraphical classification has been controversial. Wood and Smith (1978), Gaunt et al., (1992), Berridge and Pattison (1994) and Sumbler (1996) all regarded it as a part of the Ferriby Chalk Formation (Hunstanton Chalk Member), but many other workers have treated it as a separate formation (e.g. see discussion of Wood and Smith, 1978), or even as a member, included in one discussion with the underlying Carstone (e.g. Kelly and Rawson, 1983). Recent works (Rawson, 1992; Gallois, 1994; Owen, 1995, Mitchell, 1995a), whilst disagreeing over the precise nomenclature or indeed whether or not it forms a part of the Chalk Group, all treat it as a distinct formation. The consensus in the meeting held at BGS Keyworth in November 1999 was that it was a formation, but not part of the newly defined Chalk Group, and as defined it is older than the major hiatus at the base of the Cenomanian.

The Hunstanton Formation is present throughout Yorkshire and Lincolnshire, and extends southwards to the type locality of Hunstanton [TF 67 40] on the north Norfolk coast, but only a few kilometres south it passes into mudstones of the Gault Formation (Gallois, 1994). At Hunstanton, it comprises about 1 m of reddish brown, sandy chalk or limestone with marl seams; its top is defined by an erosion surface that marks the striking change in colour with the overlying off-white chalks (Owen, 1995).

North of The Wash, the Hunstanton Formation thickens substantially, averaging about 3 m over the East Midlands Shelf, e.g. at South Ferriby Quarry [SE 99 20] (Gaunt et al., 1992; fig 3), an important reference section that is more typical of the formation in general than is the type section at Hunstanton and may be better regarded as a replacement type section therefore. It comprises marls and both rubbly and massive chalks that are mainly a distinctive pink to brick-red colour caused by disseminated hematite. It overlies the Carstone Formation with the contact between the two formations commonly gradational, although non-sequential with phosphatised burrows in places.

A thin 1 m succession more like that at Hunstanton, is developed over the Market Weighton High where it also includes the few centimetres of the Carstone (Jeans, 1973) and rests unconformably on Jurassic mudstones. A thick (24 to 30 m) and more complete succession, overlying the Speeton Clay, is developed in the Cleveland Basin (strictly a term applicable to the Jurassic strata only but commonly used as a shorthand for the thicker Cretaceous strata north of the Flamborough – Dowsing Fault Zone, succession that have affinities to the Central North Sea Basin), in the cliffs at Speeton [TA 165 751] (Wright, 1963; Jeans, 1973, 1980; Neale, 1974; Mitchell, 1995a), and possibly in boreholes inland around Fordon. The top of the formation as now defined is marked by a well-defined burrowed horizon (Mitchell, 1995a).

The succession at Hunstanton has been divided into a number of units based on criteria such as lithology and fossil assemblages (Andrews, 1983; Owen, 1995). The sections at South Ferriby Quarry (Morter, in Gaunt et al., 1992), and Speeton (Mitchell, 1995a) have likewise been subdivided, a correlation between the three sites, and a formal nomenclature, is suggested by Mitchell (1995a).

The Ferriby Chalk Formation corresponds approximately to the Lower Chalk of many previous accounts, although some included the sub-Black Band marls (now Plenus Marls Member) at the top. Rawson et al., (2001) exclude the Plenus Marls Member from this formation. Its type locality is South Ferriby Quarry [SE 9915 2045] (Wood and Smith, 1978; Gaunt et al., 1992).

The Ferriby Chalk Formation is dominated by grey, marly chalk, which weathers to buff in exposures, and gives rise to rather marly soils. It is flint-free throughout, and was mapped as ‘Chalk without Flints’ by the Geological Survey in the 19^th century. As well as marly chalks with some discrete marl bands, ‘gritty’ bioclastic chalks and hard, cemented chalks occur, defining a number of sedimentary rhythms (Jeans, 1980). This rhythmicity is thought to have been climatically controlled and related to periodic variations in the Earth’s orbital and rotational parameters (Milankovitch cycles; e.g. Gale, 1995). Most of the named marker beds can be traced throughout the Northern Province and have been used to define seven members (Jeans, 1980), although these members have not gained widespread use. The marker beds are, in ascending order, the Paradoxica Bed (or Sponge Bed; the Belchford Member of Jeans, 1980; the Crowe’s Shoot Member of Mitchell, 1995a); the Lower Inoceramus Bed; the Upper Inoceramus Bed; the Lower Orbirhynchia Bed; the Totternhoe Stone (the Grey Bed of Hill, 1888) (note that the erosion surface beneath this marker bed is recognised in the Southern Province as the base of the Zig Zag Member); Upper Orbirhynchia Bed (Jeans, 1980); the Lower Pink Band; the Nettleton Pycnodonte Bed (formerly Gryphaea Band); the Nettleton Stone (the Nettleton Member or ‘Three-feet-six-inch Bed’ of Jeans, 1980; the ‘Jukes-Browne Band’ of Murray, 1986); and the Upper Pink Band.

Apart form its lowest beds; the Welton Chalk Formation is dominated by massive or thickly bedded chalk containing flint nodules (as distinct from tabular flints). It comprises the lower part of the unit of ‘Chalk with Flints’ shown on early geological maps and corresponds approximately with the Middle Chalk of earlier accounts (Jukes-Browne and Hill, 1904), though the latter excluded the basal beds (Plenus Marls Member) of the Welton Chalk Formation. Rawson et al., (2001) ((Figure 3), Column 11) in unifying the base of the White Chalk Group, in both the Northern and Southern provinces, at the base of the Plenus Marls Member effectively included the Plenus Marls Member within the Welton Chalk Formation, thus defining the base of this formation at the sub-plenus erosion surface.

The correlation of the Plenus Marls and Black Band members within the base of the Welton Chalk Formation has been ‘one of the most contentious and unresolved issues in English Chalk stratigraphy’ (Wood and Mortimore, 1995). This contention has rested on the placing of the distinctive Black Band and associated beds of the Northern Province with respect to the Plenus Marls of Jefferies (1963) in the Southern Province.

The succession is a thin but complex unit of yellow-brown to green coloured marls and marly chalk with at least two distinct ‘black’ marl bands marking anoxic depositional conditions. They generally form a hollow at outcrop corresponding to the base of the formation. This marly succession can be recognised in boreholes from its distinctive geophysical log signature. The member is generally about 0.5 to 1.4 m thick but is much thinner in south Lincolnshire.

The earliest references to this succession all describe, in varying levels of detail, multicoloured (including black) laminated or shaly clay (Judd, 1867; Blake, 1878; Dakyns and Fox-Strangways, 1886; Dakyns et al., 1886) and the term ‘black band’ came into use. Hill (1888) described ‘the zone of Belemnitella plena’ which always included ‘dark grey, in places almost black’ marl in the centre of a thin marly succession. Rowe (1904) described the ‘black band’ at Speeton [TA 19 74] and regarded it as the Yorkshire equivalent of the Plenus Marls. Wright and Wright (1942), quoting the section published in Hill (1888), used the ‘Black Band’ to cover their Bed 7 (an amalgamation of Beds 9 to 11 of Hill). In so doing formally extending the term to include the marly beds above and below the black band itself.

Wood and Smith (1978) treated this thin succession (their ‘Basal Beds’) as the lowest unit of the Welton Chalk Formation. They reserved the formal name of the Black Band for the bed of ‘dark laminated marl lying in the middle of a complex of marls’ and this classification was generally accepted. Jeans (1980) used the name ‘Flixton Member’, and Whitham (1991) the term ‘Plenus Marls complex’ to cover the same interval. Wood and Mortimore (1995) preferred the term ‘Variegated Beds’ to cover the ‘standard Black Band succession of eastern England (Northern Province)’ to avoid confusion. Dodsworth (1996) has divided the succession into eight units (Beds A to H) that can be correlated across the region.

The base of the succession (and thus of the Welton Chalk Formation) rests upon an erosion surface (see above) that is often highly irregular, and may be stained with iron minerals and glauconite. The belemnite Actinocamax plenus (now Praeactinocamax plenus) has been recorded (Jefferies, 1963; Whitham, 1991, Gaunt et al., 1992) from the basal beds (A and B of Dodsworth, 1996). This demonstrates the equivalence of this part of the succession to the Plenus Marls as developed in Southern England. The Black Band (Beds C, D and E of Dodsworth, 1996) in the middle or upper part of the succession is generally 20 or 30 cm thick. The Black Band comprises very dark grey to black or purplish bituminous marl indicating nearly anaerobic bottom conditions (the so-called Oceanic Anoxic Event) at the Cenomanian-Turonian stage boundary (Hart and Bigg, 1981). However, higher parts of the member (the Black Band proper and above) post-date the youngest part of the Plenus Marls of the south, being equivalent to the basal part of the Melbourn Rock (the Meads Marls succession) (Jefferies, 1963; Wood and Mortimore, 1995).

Wood et al., (1997) described an expanded Cenomanian-Turonian Boundary succession in new excavations at Melton Ross Quarry. They described a ‘Central Limestone’ (equivalent to Bed A of Dodsworth, 1996 in the standard Lincolnshire succession), which they also equated with the Plenus Marls Bed 3 of Jefferies (1963). The succession below, and hitherto unrecorded in the literature, they divided into Beds I to VII and equated to Jefferies Beds 1 and 2. The Central Limestone (divided by them into Beds 1 to 4) and beds above (Beds 5 to 10) they regarded as equivalent to the standard Lincolnshire succession previously described by Dodsworth (1996). Bed 7 (a to c) they equated to the Black Band sensu stricto (Beds C to E of Dodsworth, 1996). Bed 5 of Wood et al., (1997) contains the belemnite from which the Plenus Marls takes its name but it is not stated whether they believe their Bed 6 to be equivalent to the higher Plenus Marls succession or to the post-plenus succession.

The Black Band does not occur south of the neighbourhood of Louth (Bower and Farmery, 1910; Wood, 1980; Hart et al., 1993; Dodsworth, 1996), so that the succession in the south of the region is much like that of Southern England.

Thus, to achieve equivalence between the provinces, the term Plenus Marls Member as applied to the Northern Province should be restricted to those beds beneath the Black Band. The Black Band and marl beds above up to the incoming of inoceramid debris are equivalent to part of the Melbourn Rock Member of the Southern Province and perhaps demands the status of a separate Black Band Member (proposed herein).

The Welton Chalk Formation above the Plenus Marls and Black Band members corresponds with the lower half of the unit of ‘Chalk with Flints’ shown on early geological maps of the region. In full successions the Black Band Member (herein defined, see below) is succeeded by several metres of gritty chalks containing abundant shells and shell debris of the inoceramid bivalve Mytiloides labiatus, the zonal index fossil. These beds correspond with the upper part of the Melbourn Rock and the overlying part of the Holywell Nodular Chalk Formation of the Southern Province. At Speeton, Mitchell (2000) has named this 2.2 m thick unit the Buckton Member.

Above these basal shelly chalks, the bulk of the Welton Chalk Formation is composed of pure, white chalk with flint. It is 43 m thick at the type locality (Whitham, 1991) thinning slightly to the south. This unit is thicker on the Yorkshire coast where Mitchell (2000) recorded about 51 m. There are conspicuous flint bands and marl seams, of bed status, forming important markers (Wood and Smith, 1978; Gaunt et al., 1992; Whitham, 1991).

The Melton Ross Marl, about two-thirds up in the Welton Chalk Formation is the most prominent marker in sections and boreholes, and being identified with the Southerham Marl of Sussex (Mortimore and Wood, 1986), is crucial in the framework of inter-province and regional correlation.

The Burnham Chalk Formation is characterised by thinly bedded chalk with common tabular and semi-tabular (discontinuous) flint bands. It forms the upper part of the ‘Chalk with Flints’ of early geological maps, or the lower part of the Upper Chalk of Jukes-Browne and Hill (1904). The chalk in the lower part of the formation is particularly hard, and forms a conspicuous outstanding feature, facilitating mapping of the base of the formation in the drift-free areas.

The type locality for the base of the formation is the disused Burnham Lodge Quarry [TA 0685 1720] south of Barrow upon Humber. The succession in the overlying beds has been pieced together from various quarries and boreholes, particularly those drilled at Killingholme [TA 16 19] (Wood and Smith, 1978; Gaunt et al., 1992; Berridge and Pattison, 1994; Whitham, 1991).

As in the Welton Chalk Formation, marl seams and flint bands form widespread marker horizons, in addition to several bands of thinly laminated chalk which are also useful for correlation. The chalks become softer in the southern part of the Province, indicative of the transition towards the Southern Province succession.

The lowest few metres of the formation are characterised by hard chalk and thick, closely spaced, tabular flints, and equates with part of the Brandon Flint Series of Norfolk (this series is the flint maximum within the upper Turonian and is further equated with the ‘Basal Complex’ in Kent and the succession from the Bridgewick to BoPeep flints in Sussex thus demonstrating this part of the lower Lewes Nodular Chalk Formation is equivalent to the mapped base of the Burnham Chalk Formation). Rare specimens of the ammonite Hyphantoceras reussianum (Orbigny) from the beds just below and above the Wootton Marls (Gaunt et al., 1992; Whitham, 1991), suggest an approximate equivalence to the Chalk Rock Member within the Lewes Nodular Chalk Formation in the Southern Province.

The Little Weighton Marls or the ‘Conoco Marls’ of Barker et al., (1984), are three thin marl seams (typically 2 cm) within 2 to 3 m of chalk. The lower two of the three marls are thought to correlate with the paired East Cliff or Shoreham Marls of the Southern Province. The upper of these two marls (corresponding with Little Weighton Marl 2) is taken to mark the base of the Hagenowia rostrata Zone, which corresponds approximately with the base of the Micraster coranguinum Zone of the Southern Province. The irregular semi-tabular Eppleworth Flint, about 30 cm thick and generally about 65 to 70 m above the base of the formation, is probably the most substantial flint band in the entire succession, possibly equating with the East Cliff Semitabular or Seven Sisters Flint of the Southern Province (Mortimore and Wood, 1986).

The succeeding beds are massive chalk with marl partings and small lenticular and nodular flints with two notable markers: the De la Pole Flint and the Middleton Marl (or East Halton Marl). The higher beds of the Burnham Chalk Formation are poorly known inland except from boreholes and typically contain pale grey lenticular flints, and bands of small nodular flints, often associated with thin marly laminae. A notable marker bed, 26 m above the Middleton Marl, proved in a borehole [TA 1732 1905] at Killingholme is a carious tabular flint overlain by chalk with Inoceramus shell debris (Berridge and Pattison, 1994). Several boreholes in this area prove a white, or incipient flint, some 14 m higher. This appears to be the highest substantial flint in the succession and it therefore defines the top of the formation. At Flamborough Head, and in the cliffs to the north, the topmost flint is known as the High Stacks Flint (Whitham, 1991). Inland in a quarry section at Langtoft [SE 973 512] (Whitham, 1991) it remains uncertain whether or not the topmost flint is at the same stratigraphical horizon, but it seems unlikely.

The Flamborough Chalk Formation is the youngest formation recognised in the Chalk exposed at outcrop in this region. It is essentially flint-free, and comprises the upper unit of ‘Chalk without flints’ mapped by the Geological Survey in the 19^th century. Much of the succession is also generally less hard than the chalk in the underlying Burnham Chalk Formation, being lithologically similar to the chalks of southern England.

The cliffs constituting the type section of the Flamborough Chalk Formation are described by Lamplugh (1895), Rowe (1904), Neale (1974), Rawson and Whitham (1992), Whitham (1992; 1993) and Mitchell (1994; 1995b). The succession is difficult to measure accurately, because of cliff falls, minor structures and some gaps in exposure, and it is likely that all these accounts contain minor errors. The most complete and detailed description is by Whitham (1993), who introduced names for various marker beds. However, because of the lack of comparative sections elsewhere, it remains uncertain how laterally persistent these named markers are, or to what degree the stratigraphy of the designated type section is representative of the formation on a regional basis.

At the type section, the formation comprises white, flint-free chalk with numerous regularly spaced marl seams typically 1 to 3 cm thick. Some of the thicker marls named as marker horizons are seen to vary greatly in thickness, or split into multiple bands when traced laterally over fairly short distances, and this inevitably complicates correlation with sections elsewhere. Whitham (1993) subdivided the succession at the type section into three members, the South Landing, Danes Dyke and Sewerby members, which have somewhat different lithological characteristics.

The South Landing Member, about 21 m thick, comprises hard chalk with sporadic thin marl seams. The base of the member (and of the Flamborough Formation) is marked by the top of the High Stacks Flint, seen on the foreshore near High Stacks, Flamborough Head [TA 258 704]. About 3 m above is the High Stacks Marl, a 2 cm thick, grey, silty marl marker, with a thinner marl about 1 m below. This marker has not been observed at Langtoft Quarry [TA 012 661] north of Driffield, which also exposes the basal beds of the Flamborough Chalk Formation (Whitham, 1991), but it is unclear whether this indicates that the marl is discontinuous, or whether the base of the flint-free Flamborough chalks lies at a different horizon there. At the top of the member, a 1 m bed of relatively fossiliferous chalk with inoceramids, echinoids, and sponges, is overlain by the South Cliff Marl (Whitham, 1993), and regarded by him as being several metres below the top of the member. However, according to Mitchell (1994), it is the same as the East Nook Marl at the base of the succeeding Danes Dyke Member.

The Danes Dyke Member is about 67 m thick and comprises thinly bedded, alternating hard and soft chalk with stylolites, and with common marl seams (86 in total), some of which are named (see Witham, 1993; Mitchell, 1994). It is less hard than the underlying South Landing Member, and the marls are far more abundant. The lowest are the three East Nook Marls, which occur in the basal few metres of the member. The base is marked by East Nook Marl 1, a grey, rather chalky marl seam, 2 to 3 cm thick. The peculiarly shaped echinoid Hagenowia occurs fairly commonly in the chalks associated with these three marls, indicating the H. rostrata Zone. The base of the succeeding Uintacrinus socialis Zone, between 40 and 45 m thick, is defined by the first appearance of the zonal crinoid a few metres above. The Marsupites testudinarius Zone occurs in the upper third of the member above the lower of the Maidlands Upper Marls pair.

The Sewerby Member constitutes the highest chalks exposed on the coast. Massive chalk dominates the sequence although the lower part comprises thinly bedded chalk with stylolites, much like the bulk of the underlying Danes Dyke Member. Marl seams are somewhat less common than in the Danes Dyke Member. About 71.5 m of beds are seen on the coast with (probably) slightly higher horizons being represented in quarries inland, although precisely how these inland sections relate to the coast is not certain.

The lowest of the Danes Dyke Upper Marls marks the base of the member. Plates of the zonal crinoid Marsupites are common at some levels in the chalk associated with these marls, and in the succeeding 5 m or so. A bed with abundant inoceramid shell debris about 13 m above the base of the member was formerly taken as the base of the Sphenoceramus (Inoceramus) lingua Zone, but these beds are now assigned to the Uintacrinus anglicus Zone, defined by the range of that crinoid (Mitchell, 1995b), and taken as the basal zone of the Campanian Stage.

Inland, quarries at Bessingby [TA 164 669] (Whitham, 1993) and at various localities around Bridlington (Rowe, 1904; Wright and Wright, 1942) expose chalk with marl bands that lie at a slightly higher stratigraphical level than those on the coast. A section at White Hill Reservoir [TA 165 713], Bridlington (Wright and Wright, 1942) is thought to have exposed the youngest chalk represented at outcrop inland. These beds probably belong to the Gonioteuthis quadrata Zone (Figure 2).

The Rowe Chalk Formation are the youngest chalks of the region and occur in the coastal area of Holderness, where it is concealed beneath glacial drift deposits up to 50 m thick. Southwards from Hornsea, the total thickness of chalk strata above the Burnham Chalk Formation is approximately 300 to 350 m. Microfaunal evidence from boreholes indicates that the beds here extend into the Belemnitella mucronata Zone, and specimens of the index belemnite have been found in the tills which cover the chalk of this area (Wood, 1980). Chippings and geophysical data from hydrocarbon wells in the Hornsea area would suggest that the largely flint-free chalks typifying the Flamborough Chalk Formation are about 260 to 280 m thick and are overlain by about 70 m of flint-bearing chalk. These flinty strata, and still higher beds, continue eastwards beneath the North Sea where they have been named the Rowe Formation (Lott and Knox, 1994). The base is thought to lie approximately at the base of the Belemnitella mucronata Zone.

A digest of the development of terminology in the Northern Province is given in (Figure 6) and the lithostratigraphical units recommended for use on maps and in memoirs are listed in (Table 3).

3.1 Chalk Group

for definition see Section 2.1

3.1.1 Grey Chalk Subgroup

For definition see Section 2.1.1

3.2.1.1 Ferriby Chalk Formation

Name: The Ferriby Chalk Formation was first proposed by Wood and Smith (1978) as a replacement for the Lower Chalk as applied to the Northern Province. This paper included the Hunstanton Chalk Member (Red Chalk) at the base of the formation that is excluded by later workers (e.g. Mitchell 1991, 1993). Herein the term also excludes the Hunstanton Formation.

Type section: South Ferriby Quarry [SE 9915 2045] (Gaunt et al., 1992).

Reference section: Speeton Cliffs [TA 162 752] to [TA 192 744] (Wright, 1968; Mitchell, 1995a).

Formal subdivision: None herein but the formation includes a number of named units that are considered of bed status (see Wood and Smith, 1978). Jeans (1980) proposed a scheme of seven members but this has not gained widespread use in the literature.

Lithology: Grey, soft, marly, flint-free chalk, typically weathering buff in exposures; locally includes pinkish bands; some harder, gritty, shell-debris-rich beds, and thin discrete marl seams.

Definition of upper boundary: Uneven erosion surface that may be stained with iron minerals and glauconite, at the top of a succession of marly chalk (Ferriby Chalk Formation) and a little way above the so called Upper Pink Band (of bed status). This surface is succeeded by a thin unit of marls and marly chalks (the Plenus Marls Member, Welton Chalk Formation), which generally forms a topographical slack at outcrop. This facilitates the mapping of the top of Ferriby Chalk Formation, which is also readily recognised from geophysical log signature in boreholes.

Definition of lower boundary: At an erosion surface, locally developed on a hardground, overlain by nodular chalk (lowest Cenomanian) of Paradoxica (or Sponge) Bed or, in the Cleveland Basin, the flaser-bedded white chalks with red or purple marls of the Crowe’s Shoot Member (Gaunt et al., 1992; Mitchell, 1995a).

Thickness: The formation is typically about 20 to 25 m thick throughout the southern part of the region. It thins to 10 to 15 m over the Market Weighton High (Jeans, 1973) and its extension to Hornsea. It thickens immediately at the margin of the Cleveland Basin to the north, being 33 to 35 m thick on the coast at Speeton (Wright, 1963; Jeans, 1980), and possibly 50 m or more in boreholes inland near Fordon.

Distribution: Throughout Yorkshire and Lincolnshire.

Previous names: ‘Chalk without Flints’ or ‘Lower Chalk’ of early Geological Survey maps, but excluding Plenus Marls; Ferriby Chalk Formation (in some cases this includes the basal unit now separated as the Hunstanton Formation).

Parent: Chalk Group.

Age and biostratigraphy Upper Cretaceous, Cenomanian (Mantelliceras mantelli to Calycoceras guerangeri Zone).

References: Wood and Smith, 1978; Gaunt et al., 1992; Whitham, 1991.

3.1.2 White Chalk Subgroup

For definition see Section 2.1.2

3.1.2.1 Welton Chalk Formation

Name: The Welton Chalk Formation was proposed by Wood and Smith (1978).

Type section: Melton Bottoms (Welton Wold) Quarry [SE 970 282] near North Ferriby, Yorkshire (Gaunt et al., 1992; and Whitham, 1991).

Reference section: Bempton and Buckton coastal cliffs between North Landing and Speeton [TA 239 721] to [TA 165 750] (because of inaccessibility and structural complications, the section has never been described in detail, but see for example Rowe, 1904; Neale, 1974; Rawson and Whitham, 1992).

Formal subdivision: Includes at its base the Plenus Marl Member and the Black Band Member both defined herein. There are many named marl and flint bands throughout the succession that are used to divide the formation. They are all of bed status.

Lithology: White, massive or thickly bedded chalk with common flint nodules (‘burrow-form flints’) but generally lacking tabular flint bands; sporadic marl seams including the Plenus Marls Member (‘Black Band’ sensu lato) at the base.

Definition of upper boundary: Marked change from massive, rubbly-weathering chalks below, to harder, thinly bedded or nodular chalk (Burnham Chalk Formation) above. This horizon is found just below the Ravendale Flint, a tabular or semi-tabular flint up to 0.25 m thick, which is the lowest such flint in the Chalk Group and base of the chalk unit in which such flint bands are common.

Definition of lower boundary: Base of Plenus Marls Member, a unit of buff to green and grey marls and marly chalks, typically 0.5 m thick, but up to 1.4 m in Cleveland Basin. This rests on an uneven erosion surface that may be stained with iron minerals and glauconite, at the top of a succession of marly chalk (the Ferriby Chalk Formation). The marly basal beds generally form a topographical slack at outcrop, which facilitates the mapping of the base of the formation, and can also be recognised from their geophysical log signature in boreholes.

Thickness: The formation is approximately 53 m thick in the Burnham–Melton Ross area in the central part of the region, and at the type locality of Melton Bottoms or Welton Wold Quarry [SE 970 282]. It is thinner in the south, the equivalent beds averaging about 33 m in north Norfolk (Peake and Hancock, 1970) ((Figure 5c), Column 2). It also may thin slightly across the Market Weighton High, perhaps to as little as 40 m in places, but thickens again into the Cleveland Basin where the gamma-ray log of the Fordon No 2 borehole [0689 7360] suggests it is about 55 m thick. Whilst Rowe (1904; see also Neale, 1974) suggests it is about 68 m thick in the Bempton and Buckton cliff sections between Flamborough and Speeton, according to Mitchell (2000) it is only 55 m (cf. Fordon) at Speeton, its most northerly outcrop. Curiously, however, at Thornwick Bay, at the south-eastern end of this section, measurement of the upper and greater part of the formation (see Whitham, 1991, ((Figure 6), Column 7); Mitchell 2000) shows that it is slightly expanded relative to Speeton, suggesting a total of at least 60 m there. This may indicate an eastward thickening towards the offshore extension of the Cleveland Basin, or an error in one or other of these sections, possibly related to structural complications.

Distribution: Throughout Yorkshire and Lincolnshire.

Previous names: ‘Chalk with Flints’ (lower part) of early Geological Survey maps. Middle Chalk plus uppermost part (Plenus Marls) of Lower Chalk.

Parent: Chalk Group.

Age and biostratigraphy: Upper Cretaceous, Cenomanian (Metoicoceras geslinianum Zone) to Turonian (Terebratulina lata Zone).

References: Wood and Smith, 1978; Gaunt et al., 1992.

Plenus Marls Member

Name: The Plenus Marl Member as defined in Sumbler (1999) included beds A to H of Dodsworth (1996) and thus contained the Black Band. It is herein proposed to redefine the term to include only beds A and B of Dodsworth with the higher beds C to H forming the newly proposed formal term Black Band Member (see below). In so doing the Plenus Marl Member as defined in the Northern Province is the direct equivalent of the member as described for the Southern Province.

Type section: Melton Ross Quarry, Lincolnshire [TA 082 112].

Reference section: South Ferriby Quarry, Lincolnshire [SE 9915 2045]. Melton Bottom upper quarry [SE 970 280] the stratotypes for the whole Welton Chalk Formation.

Formal subdivision: None

Lithology: Thinly bedded dark-coloured calcareous mudstone (marl) overlain by rubbly limestone and calcareous silty beds followed by a higher calcareous mudstone siltstone (marl).

Definition of upper boundary: Conformable at the base of the Black Band (the ‘Main Black Band’ of Wood et al., 1997), the lowest unit of the Black Band Member.

Definition of lower boundary: An uneven erosion surface that may be stained with iron minerals and glauconite, at the top of a succession of marly chalk (the Ferriby Chalk Formation). This member and the newly proposed Black Band Member above, generally form a topographical slack at outcrop, which facilitates the mapping of the base of the Welton Chalk Formation, and can also be recognised from its higher gamma-ray geophysical log signature in boreholes.

Thickness: About 1.15 m at type site but to as little as 0.25 m elsewhere.

Distribution: Not known in detail but it is suspected that this member forms part of the succession formerly identified as the Black Band in boreholes and seismic sections.

Previous names: Equivalent as defined herein to the Plenus Marls (Member) of Jefferies (1963) and the Plenus Marls Member as defined herein in the Southern Province. Equivalent to Beds A and B of Dodsworth (1996). Lower part of the Flixton Member of Jeans (1980). Lower part of the Plenus Marls Member of Witham (1991). Lower part of the Basal Beds including the Black Band in Gaunt, Fletcher and Wood, (1992). Lower part of the Variegated Beds of Wood and Mortimore (1995) also referred to as the ‘expanded standard Black Band Succession’ by Wood et al., (1997).

Parent: Welton Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Cenomanian (Metoicoceras geslinianum Zone).

References: Dodsworth, 1996; Sumbler, 1999; Wood and Mortimore, 1995; Wood, Batten, Mortimore and Wray, 1997.

Black Band Member

Name: The Black Band Member is formally proposed herein. It is equivalent to beds C to H of Dodsworth (1996) and together the Black Band (bed) itself and superposed Variegated Beds of Wood and Mortimore (1995).

Type section: South Ferriby Quarry, Lincolnshire [SE 9915 2045].

Reference section: Melton Ross Quarry, Lincolnshire [TA 082 112]. Melton Bottom upper quarry [SE 970 280] the stratotype for the whole Welton Chalk Formation.

Formal subdivision: None

Lithology: Interbedded black or very dark carbonaceous calcareous mudstone (the Black Band) and variegated calcareous mudstone (marl) succession terminating in the ‘sticky green clay’ (Wood and Mortimore, 1995).

Definition of upper boundary: Conformable at the junction between a sticky green clay (Bed 6 i.e. the top of the ‘Variegated beds, in fig 4, Wood and Mortimore, 1995) and an extremely condensed succession of shell-detrital limestones with some thin very dark ‘marl’ seams.

Definition of lower boundary: Thickness

Generally about 0.5 to 0.6 m but up to 1.4 m in the Cleveland Basin.

Distribution: A well-known marker throughout the Northern Province and in the offshore areas.

Previous names: Equivalent, as defined herein, to the Melbourn Rock Member (Meads Marls) in the Southern Province.

Equivalent to Beds C and H of Dodsworth (1996). Upper part of the Flixton Member of Jeans (1980). Upper part of the Plenus Marls Member of Witham (1991). Upper part of the Basal Beds including the Black Band in Gaunt, Fletcher and Wood, (1992). Upper part of the Variegated Beds of Wood and Mortimore (1995) also referred to as the ‘expanded standard Black Band Succession’ by Wood et al., (1997).

Parent: Welton Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Cenomanian (Neocardioceras juddi zone) to Turonian (Mytiloides spp. Zone).

References: Dodsworth, 1996; Sumbler, 1999; Wood and Mortimore, 1995; Wood, Batten, Mortimore and Wray, 1997.

3.1.2.2 Burnham Chalk Formation

Name: The Burnham Chalk Formation was proposed by Wood and Smith (1978).

Type section: Burnham Lodge Quarry [TA 0685 1720] near Barrow upon Humber, Lincolnshire (Gaunt et al., 1992).

Reference section: Coastal cliffs north-west of Flamborough Head [TA 259 705] to about [TA 175 748] (this section has never been described in detail, but see e.g. Rowe, 1904; Neale, 1974; Rawson and Whitham, 1992, a, b).

Formal subdivision: None herein but there are many named marl and flint bands throughout the succession that are used to divide the formation. They are all of bed status.

Lithology: White, thinly bedded chalk with common tabular and discontinuous flint bands; sporadic marl seams.

Definition of upper boundary: Top of highest flint band within a flint-rich unit of chalk (i.e. Burnham Chalk Formation) succeeded by flint-free chalks (i.e. Flamborough Chalk Formation); at Flamborough Head, this is the High Stacks Flint, but elsewhere may be at a somewhat different horizon. Change particularly marked on borehole sonic velocity logs.

Definition of lower boundary: Marked change from massive, rubbly-weathering chalks below, to harder, thinly bedded or nodular chalk above. This horizon lies just below the Ravendale Flint, a tabular or semi-tabular flint up to 0.25 m thick that is the lowest such flint in the Chalk Group and base of the chalk unit in which such flint bands are common. The lowest few metres of the formation comprise hard chalks and thick, closely spaced, tabular flint which produce a topographic feature by which the base of the formation can be mapped, and a characteristic geophysical log signature enabling its identification in boreholes.

Thickness: The formation is about 130 m thick; equivalent beds in north Norfolk are approximately 100 m thick (based on Wood et al., 1994), suggesting thinning of the Burnham Chalk Formation in the south of the region. North of the Humber, the Burnham Chalk Formation is 140 m thick (Whitham, 1991) but thins to 85 to 100 m over the Market Weighton High. A complete section of the formation is exposed in the cliffs north of Flamborough Head, from Selwicks Bay to North Landing where Rowe (1904) recorded a thickness of 105 m. However, bed-by-bed measurements of the lower part of the formation indicate that it is thicker, perhaps 160 m for the whole formation. The difference in these figures suggests that the top of the formation in the Cleveland Basin (as defined by the presence of flints) lies at a lower horizon than in the south, perhaps just above the Middleton Marl (based on preliminary correlation of geophysical logs).

Distribution: Known throughout the Northern Province.

Previous names: ‘Chalk with Flints’ (upper part) of early Geological Survey maps. Upper Chalk (lower part).

Parent: Chalk Group.

Age and biostratigraphy: Upper Cretaceous, Turonian to Santonian (Sternotaxis plana (now Plesiocorys plana) to Micraster coranguinum zones).

References: Wood and Smith, 1978; Gaunt et al., 1992; Whitham, 1991.

3.1.2.3 Flamborough Chalk Formation

Name: Flamborough Chalk Formation was proposed by Wood and Smith (1978).

Type section: Cliff section Sewerby Steps and High Stacks, Flamborough Head [TA 201 687] to [TA 259 705] (Whitham, 1993; Mitchell, 1994, 1995b).

Reference section: Atwick No 2 (1973) borehole (TA15SE/9) [TA 1835 5171], from about 122 m to about 385 m.

Formal subdivision: None herein. Divided into three members by Whitham (1993) that are in ascending order the South Landing Member, Danes Dyke Member and the Sewerby Member. There are many named marl units of bed status.

Lithology: White, well-bedded, flint-free chalk with common marl seams (typically about one per metre). Stylolitic surfaces and pyrite nodules are common.

Definition of upper boundary: Base of lowest flint of succeeding thick, flint-rich unit (i.e. Rowe Formation).

Definition of lower boundary: Top of highest flint band of underlying thick, flint-rich unit of chalk (i.e. Burnham Chalk Formation); in type section this is the High Stacks Flint but elsewhere may be at a somewhat different horizon.

Thickness: The type section, between Flamborough Head and Sewerby, exposes the basal about 160 m of the formation. Equivalent, and probably slightly higher beds (extending up to about 220 m above the base of the formation, according to Whitham, 1993) crop out inland, in the northernmost part of the Yorkshire Wolds, near Driffield. Even higher beds occur beneath drift in the Holderness region where the formation, in boreholes, appears to total about 265 m thick.

Distribution

Known throughout the Northern Province.

Previous names: ‘Chalk without Flints’ of early Geological Survey maps. Upper Chalk (pars).

Parent: Chalk Group.

Age and biostratigraphy: Upper Cretaceous, Santonian to Campanian (Gonioteuthis quadrata Zone).

References: Wood and Smith, 1978; Whitham, 1993; Mitchell, 1994.

3.1.2.4 Rowe Chalk Formation

Name: The Rowe Formation was first proposed by Lott and Knox (1994) for flint bearing chalks above the Flamborough Chalk Formation offshore. This term was adopted in Sumbler (1999) and is modified herein to Rowe Chalk Formation.

Type section: Borehole 49/24-1, 635 m to 840 m depth (Offshore, Southern North Sea; see Lott and Knox, (1994).

Reference section: Atwick No 2 (1973) borehole (TA15SE/9) [TA 1835 5171], from about 41 m to about 122 m.

Formal subdivision: None

Lithology: White, flint-bearing chalk with sporadic marl bands.

Definition of upper boundary: Unconformably overlain by Quaternary deposits onshore: offshore apparently conformably succeeded by Palaeogene deposits (Lott and Knox, 1994).

Definition of lower boundary: Basal flint band of thick unit of flint bearing chalk above thick flint-free unit of Flamborough Chalk Formation; recognised on the basis of downhole geophysical logs.

Thickness: About 80 m preserved onshore; up to about 380 m offshore.

Previous names: Not previously named onshore, thus implicitly included in Flamborough Chalk Formation

Parent: Chalk Group

Age and biostratigraphy: Upper Cretaceous, Campanian (Belemnitella mucronata Zone) onshore, extending into Maastrichtian offshore.

References: Sumbler, 1996, 1999; Lott and Knox, 1994.

Chapter 4 Scotland Chalk nomenclature (Scottish Chalk Province)

Judd (1878) ((Figure 7), Column 1) proposed the first comprehensive lithostratigraphy for the Cretaceous of western Scotland in the third of his extensive papers on the strata of the western coast and islands. Whilst recognising that there were ‘very rapid and remarkable changes in thickness and character’ he divided the widely spaced successions into four members (numbered I to IV down sequence) representing two marine and estuarine phases of sedimentation. The members in ascending order were Glauconitic Greensand (IV), White Sandstone or Lower Estuarine Series (III), Chalk with bands of flint or Upper Chalk (II) and Sandstones with white marls or Upper Estuarine Series (I). He considered Member IV to be unequivocally of Cenomanian (or mistakenly equivalent to the Upper Greensand) age, Member II contained Belemnitella mucronata and was equivalent to the greater part of the White Limestone of Ireland, thus placing his White sandstone or ‘Lower Estuarine series’ (III) as the equivalent to the whole or part of the Chalk of England. He tentatively placed his sandstones and white marls or ‘Upper Estuarine series’ (I) in the Cretaceous but suggested that it may well prove to be of younger ‘Tertiary’ age. His terms of Upper and Lower Estuarine Series are completely different from the Jurassic strata of the same names. He also suggested thicknesses for his members based on the known exposures as follows: VI a maximum of 60 feet (18.3 m), III an average of 100 feet (30.5 m), II a minimum of 10 feet (3.1 m) and I a minimum of 20 feet (6.1 m) (Figure 7).

Subsequent work by Survey officers and others up to the 1920s added to the number of known localities beyond those mentioned by Judd. The principal localities for the Cretaceous of Western Scotland are shown in (Figure 8). Much of this work is to be found in the memoirs of the Survey (e.g. Bailey and Anderson, 1925; Lee and Bailey, 1925) and other papers (see Bailey, 1924; Scott, 1928) ((Figure 7), Column 2 and (Figure 7), Column 3) where a tripartite sequence was described similar to that of Judd but with the proviso that Judd’s highest unit (I) was essentially ignored or regarded as of ‘Tertiary’ age. This work was summarised briefly in Lee and Pringle (1932) ((Figure 7), Column 4) within a synopsis of all of the Mesozoic rocks of Scotland. A variety of slightly different terms were used (some with the informal epithet of member or with a locality descriptor). For example in those memoirs and papers the White Sandstone (III) became closely associated with the Loch Aline locality thus creating the term Loch Aline White Sandstone or Glass Sand (this latter term being used because of the rock’s exceptional purity and its use in the optical industry). Humphries (1961) comprehensively described the White Sandstone of Loch Aline.

Rawson et al., (1978) ((Figure 7), Column 5) introduced the formal term of Morvern Greensand Formation, and so implied that the overlying Loch Aline Glass Sand was also of formational level. The beds above the Loch Aline Glass Sand Formation were unnamed units of ‘chalk and greensand’ and ‘chalk’.

Braley (1990) described the Cretaceous rocks of northwest Scotland and developed the formal terminology, down to member level, outlined in Lowden, et al., (1992) and in (Figure 7), Column 6 herein. She introduced the term Inner Hebrides Group to cover all of the Cretaceous beds, and the thin Paleocene(?) sediments, beneath the basalts in the region. However, there are serious problems with the dating of the various units within the sequence.

Hancock (2000) introduced the term Gribun Conglomerate Formation to cover the highest beds, of Maastrichtian(?) age, in the Gribun section on the Isle of Mull. This should not be confused with the Gribun Chalk Formation (Lowden et al., 1992) which they determined to be of Turonian(?) age. Emeleus (1997) used part of this scheme to describe the rocks encountered on Eigg, including the Laig Gorge Beds of Hudson (1960).

Most recently the succession of Cretaceous rocks in the Inner Hebrides Group, at SSSI and other sites in the northwest of Scotland has been the subject of review as part of the Geological Conservation Review (GCR) Series funded by the Joint Nature Conservation Committee. The GCR volume, the British Upper Cretaceous Stratigraphy (Mortimore, et al., 2001), ((Figure 7), Column 7) gives a comprehensive account of the sequence, formalises the nomenclature, partly in accordance with Braley (1990) but makes significant changes to the chronology, and corrects earlier correlations. It goes further and suggests correlation with the sequences exposed in Northern Ireland. This document is considered as the standard for the Inner Hebrides Group (see (Figure 7)). Recommended lithostratigraphical units are listed in (Table 4).

These entries are formalised following the review of Upper Cretaceous nomenclature in Mortimore, Wood and Gallois (2001) that provides the most up-to-date and comprehensive study of these rocks following on from the work of Braley (1990). The equivalent terms used in BGS products are also shown. With the limited and widely spaced outcrops it is inevitable that there is still some debate as to the exact correlation of each of the condensed successions known and indeed the prospect of further successions coming to light that will alter our understanding cannot be discounted. Whilst the Cenomanian age for the basal beds is firmly established, the sparse fauna and degree of reworking can only suggest that Turonian, Santonian and Campanian sedimentary rocks remain. Depositional environments can be difficult to establish and it is by no means certain that a single basin with related sediments can be demonstrated. This problem is of course compounded by the degree of diagenesis suffered by the succession beneath the thick Paleocene basalt cover.

4.1 Inner Hebrides Group

Name: The Inner Hebrides Group was formally proposed by Braley (1990). See also Lowden, Braley, Hurst, and Lewis, (1992) and Mortimore, Wood, and Gallois, (2001) in which volume a number of the correlations in the earlier work are adjusted and the dating of the sequence refined.

Type section: At various localities for the constituent formations in the Inner Hebrides and Morvern. Principal exposures are at Beinn Iadain and Loch Aline Mine in Morvern, at Gribun, Carsaig and Auchnacraig on Mull, at Clach Alasdair and Laig Gorge on Eigg and Strathaird on Skye.

Primary reference section: At the type sites of the constituent formations and members.

Formal subdivisions: Divided into seven formations and a number of constituent members. These are from the oldest: the Morvern Greensand Formation; Lochaline White Sandstone Formation; Coire Riabhach Phosphatic Formation; Gribun Chalk Formation; Feorlin Sandstone Formation; Strathaird Limestone Formation (including the Clach Alasdair Conglomerate Member and Laig Gorge Sandstone Member) and the Beinn Iadain Mudstone Formation. This latter probably principally of basal Palaeogene in age. A description is included herein for completeness.

Lithology: Glauconitic sandstones, pure silica sands, silicified chalks, flints and conglomerates.

Definition of upper boundary: Unconformable beneath the Paleocene lavas or conformable (?) beneath the Beinn Iadain Mudstone Formation of presumed Paleocene age.

Definition of lower boundary: Unconformable at the erosion surface below the Morvern Greensand Formation.

Thickness: The group comprises a highly condensed sequence and is variable in thickness depending on the relative development of its constituent parts. The group may be as little as a few metres thick but is between 10 to 15 m on Mull and between 11 to 22 m in Morvern.

Distribution: Known from the Inner Hebrides islands of Mull, Eigg, Skye, Scalpay, Soay and Raasay and also from the Morvern district of the Scottish mainland.

Previous names: Generally the Cretaceous rocks of the Inner Hebrides have been described using that title or, because of their limited outcrop, as individual constituent units attached to a locality i.e. Morvern Greensand. Some of these gained greater acceptance and were applied more widely.

Parent: None

Age and biostratigraphy: Upper Cretaceous, Cenomanian to early Campanian.

References: Braley, 1990; Lowden, Braley, Hurst and Lewis, 1992; Mortimore, Wood and Gallois, 2001.

4.1.1 Morvern Greensand Formation

Name: In older literature known as the Cenomanian Greensand, Greensand and Cenomanian Greensand Member. Designated the Morvern Greensand in Rawson et al., (1978) and given formation status in Braley (1990).

Type section: In Braley (1990) are two sections given on Beinn Iadain as [NM 6917 5490] and [NM 6965 5645] the former presumed to be the section described in Judd (1878) and Lee and Bailey (1925). Mortimore et al., (2001) give their locality as Beinn Iadain, Morvern [NM 670 541] to [NM 689 528] and also a site called Beinn na H-Uamha at [NM 68].

Primary reference section: Loch Aline Borehole No. 10 [NM 6890 4695] and Auchnacraig Cliff [NM 7440 2989] in Braley (1990) and Alt na Teangaigh [NM 453 328], Isle of Mull, Mortimore et al., (2001).

Formal subdivision: None

Lithology: Glauconitic calcareous sandstone, white to pale greenish. Some gritty beds and calcareous inclusions up to cobble size. Conspicuously shelly (mainly oysters) in parts.

Definition of upper boundary: Conformable with the Lochaline White Sandstone Formation. However Braley (1990) and Lowden et al., (1992) regarded the Lochaline White Sandstone Formation as a member within this formation and considered the upper boundary as unconformable with the Gribun Chalk Formation.

Definition of lower boundary: Unconformable on various Jurassic and Triassic strata.

Thickness: From 0.3 to 13.4 m in Rawson et al., (1978).

Distribution: Known from the Morvern district and the Isle of Mull.

Previous/equivalent names: Greensand in the literature. Cenomanian Greensand (map code of h or h5) as on Ardnamurchan 52W, Strontian 52E, Iona 43, Mull 44. Glauconitic Sandstone (? Greensand) (map code of GSM or MorG) as on Staffa 43N, Ross of Mull 43S. Greensand of Morvern obsolete Dic_Strat entry (code of GSM). Morvern Greensand (h5) as on Eastern Mull 44W, Lismore 44E and in general informal use in the literature.

Parent: Inner Hebrides Group.

Age and biostratigraphy: Upper Cretaceous, Cenomanian

References: Rawson et al., 1978; Lee and Pringle, 1932; Braley (1990); Lowden, Braley, Hurst and Lewis, 1992; Mortimore, Wood and Gallois, 2001.

4.1.2 Lochaline White Sandstone Formation

Name: The Loch Aline Glass Sand of Rawson et al., (1978) and the Lochaline Sandstone Member in Braley (1990). The formation as named above proposed by Mortimore et al., (2001).

Type section: Lochaline Mine adit section [NM 6800 4535], Morvern.

Primary reference section: Loch Aline three sections given in Braley (1990) at waterfalls around the loch [NM 6935 4595], [NM 6869 4665], [NM 6935 4535], Beinn Iadain [NM 6917 5490] and [NM 6965 5645] all in the Morvern district. At various sites in Mull e.g. Auchnacraig Cliff [NM 7440 2989] in Braley (1990) and Alt na Teangaigh [NM 453 328] in Mortimore et al., (2001).

Formal subdivision: None

Lithology: Very pure white to pale yellow brown well-sorted medium-grained quartz sandstone. Massive with laminated and shelly beds to base. Most comprehensively described by Humphries (1961) at its type site.

Definition of upper boundary: Unconformable beneath the Gribun Chalk Formation or Coire Riabhach Phosphatic Formation.

Definition of lower boundary: Conformable (?) on the Morvern Greensand Formation.

Thickness: Up to 40 feet (12.2 m) on the west side of Loch Aline according to Humphries (1961).

Distribution: Known from the Morvern district and the Isle of Mull.

Previous/equivalent names: Loch Aline Glass Sand (Loch Aline) (map code of h5’) as on Lismore 44E, Eastern Mull 44W. White Sandstone (map code of h5’) as on Iona 43. White Sandstone (?Loch Aline Glass Sand) (map code of LAWS) as on Staffa 43N. Loch Aline White Sandstone.

Parent: Inner Hebrides Group.

Age and biostratigraphy: Upper Cretaceous, Cenomanian; Turonian to Santonian in Mortimore et al., (2001).

References: Braley, 1990; Lowden, Braley, Hurst and Lewis, 1992; Mortimore, Wood and Gallois, 2001. (In this volume a number of the correlations in the earlier works are adjusted and the dating of the sequence refined. The term Lochaline White Sandstone Formation appears first in this volume as one of the adjustments to the terminology and correlation of the sequence of Braley, 1990).

4.1.3 Coire Riabhach Phosphatic Formation

Name: The name first appears in Mortimore et al., (2001) and is substantially unrecognised in previous descriptions.

Type section: Stream section on the west bank of Coire Riabhach [NM 697 564] on the north-east flank of Beinn Iadain.

Primary reference section: As above

Formal subdivision: None

Lithology: Up to five beds of glauconitic sand with phosphate nodules and fossil casts.

Definition of upper boundary: Unconformable (or a non-sequence at an erosion surface) with the overlying Gribun Chalk Formation.

Definition of lower boundary: Conformable (or a non-sequence at an erosion surface) with the underlying Lochaline White Sandstone Formation.

Thickness: Usually less than one metre.

Distribution: Limited to the Beinn Iadain area.

Previous names: None

Parent: Inner Hebrides Group.

Age and biostratigraphy: Upper Cretaceous, Coniacian to Santonian in Mortimore et al., (2001).

References: Mortimore, Wood and Gallois, 2001. (In this volume a number of the correlations in the earlier works are adjusted and the dating of the sequence refined. The term Coire Riabhach Phosphatic Formation appears first in this volume as one of the adjustments to the terminology and correlation of the sequence proposed by Braley, 1990).

Note: Because of its relative thinness it is questionable as to whether this bed is a ‘mappable’ unit and as such worthy of formational status, however it is prominent in sections logged in Morvern and may prove the correlative of the basal unit of the Gribun Chalk Formation as mapped on Mull where glauconite is seen in the sequences associated with erosional surfaces. It may also be a key link with the Northern Ireland succession where Mortimore et al., correlate it with the Cloghfin Sponge Formation at the base of the Ulster White Limestone Group.

4.1.4 Gribun Chalk Formation

Name: The Gribun Chalk Formation was formally proposed by Braley (1990).

Type section: The Gribun Boulder [NM 457 357] and Gribun Stream Boulder [NM 456 355], Isle of Mull.

Primary reference section: Clachandhu Boulders [NM 4550 3533], [NM 4550 3531], [NM 4550 3528] and at Allt na Teangaidh [NM 453 328] near Gribun, Isle of Mull.

Formal subdivision: None

Lithology: Silicified Chalk. Reworked Chalk and conglomerate as (?) debris flow. Flinty in part.

Definition of upper boundary: Unconformable with the Clach Alasdair Conglomerate Member of the Strathaird Limestone Formation or Beinn Iadain Mudstone Formation (basal Paleocene age).

Definition of lower boundary: Unconformable on the Coire Riabhach Phosphatic Formation or the Lochaline White Sandstone Formation.

Thickness: About 5 m at Gribun, about 1 m elsewhere.

Distribution: Principally on the island of Mull and within the Morvern district.

Previous/equivalent names: —

Parent: Inner Hebrides Group.

Age and biostratigraphy: Upper Cretaceous, Cenomanian in Lowden et al., (1992); Santonian in Hancock, (2000); Santonian to Campanian in Mortimore et al., (2001).

References: Braley, 1990; Lowden, Braley, Hurst and Lewis, 1992; Mortimore, Wood and Gallois, 2001.

4.1.5 Strathaird Limestone Formation

Name: The Strathaird Limestone Formation was formally proposed by Braley (1990).

Type section: Strathaird [NG 5365 1790], Skye.

Primary reference section: Laig Gorge [NM 4735 8750] on Eigg, Camasunary [NG 5181 1775], and two sections at Allt Eoghainn, Strollamus [NG 5965 2645] on Skye, An Leac headland, Soay Sound [NG 4400 1695], and numerous localities of the Clach Alasdair Conglomerate Member on Mull.

Formal subdivision: Includes the Clach Alasdair Conglomerate Member and the Laig Gorge Sandstone Member.

Lithology: Dark grey micritic limestone and two clastic members. A basal Laig Gorge Sandstone member and the Clach Alasdair Conglomerate Member.

Definition of upper boundary: Unconformable below the Beinn Iadain Mudstone Formation or at an erosion surface beneath the Palaeogene basalts.

Definition of lower boundary: Unconformable upon the Gribun Chalk Formation and Feorlin Sandstone Formation.

Thickness: From 2 to 6 m on Eigg, 2.5 m on Skye and 2 m of the Clach Alasdair Conglomerate Member on Mull.

Distribution: Throughout the Inner Hebrides islands but poorly represented in Morvern.

Previous names: Part of the Silicified Chalk and its derivative names in earlier accounts.

Note: Hancock (2000), confusingly, used the term Gribun Formation or Gribun Conglomerate Formation to describe rocks above the Chalk (silicified Chalk) of? Santonian age which is the named Gribun Chalk Formation. This unit is probably equivalent to the Strathaird Limestone Formation (in part) of Braley (1990) or the Clach Alasdair Conglomerate Member of Mortimore, Woods and Gallois (2001). Probably the same beds as Hancock's (2000) Gribun Chalk. Probably equivalent to the Laig Gorge Limestone Member (LAGL) as mapped on the Rum Sheet 60 where Braley (1990) uses the name Strathaird Limestone Formation.

Parent: Inner Hebrides Group.

Age and biostratigraphy: Upper Cretaceous, Turonian.

References: Braley, 1990; Lowden, Braley, Hurst and Lewis, 1992. This Formation is not mentioned in Mortimore, Wood and Gallois (2001) although the Clach Alasdair Conglomerate Member is used for the beds intervening between the Gribun Chalk Formation and the Ben Iadain Mudstone Formation.

4.1.5.1 Clach Alasdair Conglomerate Member

Name: The Clach Alasdair Conglomerate Member was formally proposed by Braley (1990).

Type section: Clach Alasdair [NM 4540 8831], Eigg.

Primary reference section: Caisteal Sloc nam Ban [NM 431 312] in the Wilderness and Allt na Teangaidh [NM 453 328] on Mull. Strathaird [NG 5365 1790] on Skye.

Formal subdivision: None

Lithology: Conglomerate (principally silicified chalk clasts) with a coarse sandstone matrix.

Definition of upper boundary: Top of member not seen at the type site at Clach Alasdair on Eigg nor at Strathaird on Skye. May be unconformable beneath the Ben Iadain Mudstone Formation at Gribun, Allt na Teangaidh, Mull (Mortimore, Wood and Gallois, 2001).

Definition of lower boundary: Unconformable on beds attributed to the Morvern Greensand at the Clach Alasdair type site on Eigg (Braley, 1990), and unconformable on the Strathaird Limestone Formation at the type site of that unit on Skye. Considered to rest on the Gribun Chalk Formation elsewhere according to Mortimore, Wood and Gallois (2001).

Thickness: Only 0.5 m at Strathaird and 0.4 m at Clach Alasdair in Braley (1990) and up to 2.5 m at Caisteal Sloc nam Ban, Mull in Mortimore, Wood and Gallois (2001).

Distribution: Known throughout the Inner Hebrides Eigg, Skye and Mull and in Morvern.

Previous names: None

Parent: Strathaird Limestone Formation.

Age and biostratigraphy: Upper Cretaceous, Turonian, but considered to be Campanian in age by Mortimore, Wood and Gallois (2001).

References: Braley, 1990; Lowden, Braley, Hurst and Lewis, 1992; Mortimore, Wood and Gallois, 2001. In this volume a number of the correlations in the earlier works are adjusted and the dating of the sequence refined.

4.1.5.2 Laig Gorge Sandstone Member

Name: The Laig Gorge Sandstone Member was formally proposed by Braley (1990).

Type section: Laig Gorge [NM 4735 8750] on Eigg.

Primary reference section: Strathaird [NG 5365 1790] on Skye.

Formal subdivision: None

Lithology: Medium- to coarse-grained poorly sorted sandstones and conglomerates.

Definition of upper boundary: Unconformable at an erosion surface above a coarse very poorly sorted conglomerate with the grey micritic limestones of the remainder of the Strathaird Limestone Formation at Strathaird on Skye but apparently conformable at a burrowed horizon with the same limestones at Laig Gorge on Eigg.

Definition of lower boundary: Unconformable on the Gribun Chalk Formation but considered absent in Mull and Morvern by Mortimore, Wood and Gallois (2001). This is the basal unit of the Strathaird Limestone Formation according to Braley (1990).

Thickness: Measures 3.0 m at Laig Gorge, Eigg.

Distribution: Known on the islands of Eigg and Skye.

Previous names: None

Parent: Strathaird Limestone Formation.

Age and biostratigraphy: Upper Cretaceous, Turonian.

4.1.6 Feorlin Sandstone Formation

Name: The Feorlin Sandstone Formation was formally proposed by Braley (1990) as part of the Beinn Iadain Mudstone Formation but is considered as a formation in its own right beneath the Beinn Iadain Mudstone Formation and questionably beneath the Clach Alasdair Conglomerate Member by Mortimore et al., (2001).

Type section: Feorlin Cottage [NM 5317 2225] at Carsaig, Mull.

Primary reference section: Caisteal Sloc nam Ban [NM 431 312] in the Wilderness on Mull.

Formal subdivision: None

Lithology: Slightly glauconitic sandstone with silicified chalk pebbles.

Definition of upper boundary: Conformable with the rest of the Ben Iadain Mudstone Formation (Braley, 1990) or questionably beneath the Clach Alasdair Conglomerate Member (Mortimore, Wood and Gallois, 2001).

Definition of lower boundary: Unconformable on the Strathaird Limestone Formation when considered as the basal member of the Ben Iadain Mudstone Formation (Braley, 1990), or on the Gribun Chalk Formation or Morvern Greensand (Mortimore, Wood and Gallois, 2001) as a formation in its own right.

Thickness: About 8.5 m is attributed to these beds at Caisteal Sloc nam Ban in the Wilderness on Mull.

Distribution: Known from the island of Mull.

Previous names: None

Parent: Inner Hebrides Group.

Age and biostratigraphy: Upper Cretaceous or Paleocene.

Note: The Feorlin Sandstone Formation of Mortimore, Wood and Gallois (2001) is considered to be a formation in its own right and forming part of the Upper Cretaceous sequence (or possibly Paleocene). At the Caisteal Sloc nam Ban section on the Isle of Mull the formation is shown beneath the Clach Alasdair Conglomerate Member (which elsewhere in Mortimore et al., (2001) is shown as Santonian to Maastrichtian in age) itself within the Strathaird Limestone Formation. Braley (1990) considers the unit to be a member within the Ben Iadain Mudstone Formation of Paleocene or younger age.

4.1.7 Beinn Iadain Mudstone Formation

Name: The Beinn Iadain Mudstone Formation was formally proposed by Braley (1990).

Type section: Beinn Iadain Section A of Braley (1990) [NM 6917 5490] in Morvern.

Primary reference section: Allt na Teangaidh [NM 453 328] on Mull.

Formal subdivision: Considered by Braley (1990) to include the Feorlin Sandstone Member.

Lithology: Mudstone and siltstone, shaly and micaceous, red to purplish in colour but bleached white in places considered to be ‘argillised ash’ by Mortimore et al., (2001). Organic rich and sandy in lower part.

Definition of upper boundary: Disconformable at a sharp contact beneath Paleocene lavas.

Definition of lower boundary: Unconformable above an erosive contact with underlying conglomerates of the Clach Alasdair Conglomerate Member.

Thickness: Some 2.5 m at Allt na Teangaidh on Mull, about 1.9 m at Feorlin tributary section [NM 5317 2225], 0.92 m at the type site on Beinn Iadain.

Distribution: Known from Morvern and the island of Mull.

Previous names: Considered by Braley (1990) to be equivalent to the ‘Upper Estuarine Series’ of Judd (1878).

Parent: Inner Hebrides Group.

Age and biostratigraphy: Upper Cretaceous or Paleocene.

Chapter 5 Statement on Northern Ireland Chalk nomenclature (Ulster Cretaceous Province)

The classification of Cretaceous rocks in Northern Ireland dates from 1786 when Whitehurst (1786) made comments on the outcrop using the term ‘White Limestone’. Sampson (1814) demonstrated that this White Limestone was underlain by a succession of greensands, conglomerates and marls. Essentially, these workers established the two-fold division of the Cretaceous.

Portlock (1843) suggested three divisions of the strata introducing the terms Upper Chalk (equivalent to the White Limestone), an intermediate unit the Lower Chalk (Glauconitic Chalk) and a lower unit termed the Greensands. Bryce (1853) divided the ‘greensands’ into three, and this three-fold division was also recognised by Tate (1865) ((Figure 9), Column 1). The work of Tate was the first appraisal of the faunal and lithological characteristics of the full Cretaceous sequence and its comparison to the English and French schemes. In his appraisal of the biozones present he recognised that most of the Middle Chalk of England was unrepresented in Northern Ireland and reverted to a two-fold division of the strata into the ‘Hibernian Greensand’ and ‘Upper Chalk’ formations. Further division equivalent to ‘member’ status formalised the terms, in ascending order, of Glauconitic Sands, ‘Grey Marls and Yellow Sandstones with Chert’, ‘Chloritic Sands and Sandstones’, as subdivisions of the Hibernian Greensand; and the ‘Chloritic Chalk’ and ‘White Limestone’ (or ‘Hard Chalk’) as subdivisions of the Upper Chalk (Figure 9).

Gault (1878) and Hume (1897) ((Figure 9)/2) added refinements and corrections to the work of Tate based on more extensive fieldwork. Hume (1897) produced a comprehensive description and correlation for the whole of Northern Ireland and divided the outcrop into five geographical ‘divisions’ each with its own character, thus essentially being the first to recognise the structural control on sedimentation in the Province. He also suggested the term ‘Antrim Beds’, in his ‘eastern division’, for the Chloritic Sands (sensu Tate). Reid (1958) introduced the terms ‘Upper Glauconitic Sandstone’ and ‘Lower Glauconitic Sandstone’ to cover Hume’s Antrim Beds and the older Zone of Exogyra columba, thus separating the Cenomanian (Lower) from the ?late Turonian and Senonian (Upper) strata. The outcrop and principal localities of the Ulster Cretaceous are shown in (Figure 10).

Hancock (1961) ((Figure 9), Column 3) made a complete re-assessment of the Cretaceous of north-east Ireland. He attempted to simplify terminology and included Tate’s and Hume’s Chloritic Sands and Chloritic Chalk in his ‘Upper Glauconitic Beds’ of the ‘Hibernian Greensands’. In so doing Hancock amalgamated the glauconite rich beds of post-Cenomanian age despite there being a second major diachronous break within the succession. Hancock’s Hibernian Greensands ‘Formation’ also included the ‘Yellow Sandstone’ and ‘Glauconite Sands’ each respectively equivalent to the Grey Marls and Yellow Sandstones and the Glauconitic Sands of Tate and Hume.

Extensive work by staff of the Geological Survey (Wilson and Robbie, 1966; Manning et al., 1970; Fowler and Robbie, 1961) led to a significant systematic reappraisal of the Cretaceous of Northern Ireland. The Belfast memoir (Manning et al., 1970) ((Figure 9), Column 4) offers the fullest account and maintained the White Limestone and Hibernian Greensand divisions. They further divided the Hibernian Greensand into ‘Cenomanian Greensands’ (equivalent to the Yellow Sandstones and Grey Marls, and Glauconitic Sands of previous authors), the ‘Cenomanian/Turonian Greensands’ (including the new terms of ‘Glauconitic Sands and Sandstones’ and ‘Quartzose Sand’) and the ‘Senonian Greensands’ (presumably equivalent to the Upper Glauconitic Beds of Hancock, 1961). The White Limestone was divided, in ascending order, into a basal ‘Conglomerate Bed’, ‘Chalk with derived Glauconite’, ‘Lower White Limestone’ and an ‘Upper White Limestone’ (this latter being subdivided into four named beds).

Reid (1971) ((Figure 9), Column 5) summarised the earlier papers and gave an indication of the spatial variability of the Cretaceous succession across the Province in his (Figure 2). Fletcher (1977) ((Figure 9), Column 6) introduced a comprehensive nomenclature for the Cretaceous of northeast Ireland and formalised the terms of the ‘Hibernian Greensands Formation’ and the ‘Ulster White Limestone Formation’. The Hibernian Greensands Formation was redefined with respect to the proposals by Tate (1865) and Hancock (1961) and he confined the term to the glauconitic sands and related clastic deposits. He excluded the ‘Glauconitic Chalk’ from the formation regarding this as a local, structurally controlled, facies of a number of his Ulster White Limestone Formation members.

Fletcher (1977) divided the Ulster White Limestone Formation into fourteen members on the basis of their lithological character, correlation of marker bands and their spatial distribution (see Fletcher, 1977; Fig.8). His work is the standard for the succession mapped in Northern Ireland and is used on the subsequent map publications on the geology of the Province.

Griffith and Wilson (1982) ((Figure 9), Column 7) gave formal names to the ‘members’ of the Hibernian Greensands first defined but unnamed by Fletcher (1977).

There is an argument for upgrading Fletcher’s system, elevating his members to formations permitting the introduction, in future years, of chalk and glauconitic chalk members within each of his presently constituted members. In so doing the Ulster White Limestone and Hibernian Greensands would then be considered as groups or subgroups depending on whether it was felt that an over-arching group term should be applied to the Cretaceous of the province. The use of the term Chalk Group (in the sense of its use in England and the North Sea) would provide uniformity to the Upper Cretaceous of the whole of the UK but may not be appropriate because of the distinct clastic nature of the lower half of the succession. It is recommended herein that the terms Hibernian Group and Ulster White Limestone Group be introduced with Fletcher’s member being elevated to formation status.

Within the lexicon there are only full formal descriptions for the two formations (now groups), each of the members (formations) are registered as code only. In consequence an attempt has been made to outline the main Lexicon entry-style information for each of Fletcher’s units below. The lithostatigraphical units used on maps and memoirs are listed in (Table 5).

Prior to this report there was no formal ‘group’ level nomenclature for the Northern Ireland succession. The term Chalk Group could be utilised to cover all of the deposits of the Upper Cretaceous in the Province despite the lower part of the sequence being predominantly in ‘greensand facies’. However it may prove preferable, and suggested herein, to raise the status of each of the presently defined formation and member level entries to group and formation respectively. In so doing formalising the framework and permitting greater flexibility to future workers on the succession at the member level.

5.1 Hibernian Greensands Group

(See note above concerning the adoption of Hibernian Greensand Group as the formal notation for this succession of units).

Name: The name was first proposed by Tate (1865) as Hibernian Greensand. Hancock (1961) used the term Hibernian Greensands. Hibernian Greensands Formation was adopted in BGS publications and in Fletcher (1967). Elevated to Group status herein.

Type section: Numerous exposures of the constituent formations (see formal subdivisions below for reference to those divisions) in the Midland (East Antrim) Basin and Southern Uplands district.

Primary reference section: Cloghfin Port [J 483 938], Magheramorne Borehole [J 433 975] and area, Collin Glen [J 269 702] district south-west of Belfast, Kilcoan Old Quarry [J 461 985] on Island Magee.

Formal subdivisions: Divided into four members as in the BGS memoir (e.g. Griffith and Wilson, 1982). It is proposed herein that the group be divided at the formation level in ascending order, the Belfast Marls Formation, the Island Magee Siltstones Formation, the Collinwell Sands Formation and the Kilcoan Sands Formation.

Lithology: Glauconitic ‘marls’, argillaceous siltstones and calcareous sandstones, and quartzose sands. Succession divided into four formations noted above.

Definition of upper boundary: Unconformable at a major regional erosional break. Overlain by various members of the Ulster White Limestone Group.

Definition of lower boundary: Unconformable on a variety of older formations at a major regional erosinal break at the base of the Belfast Marls Member.

Thickness: About 21 m to 22 m in the Carrickfergus, Larne, Antrim and Belfast sheet areas.

Distribution: Throughout Northern Ireland. As a thin basal Cretaceous unit over structural highs and in the North Antrim Basin, where the group is undivided. Fullest development in the Midland Valley (East Antrim Basin) and the Southern Uplands as defined in Fletcher (1977) where group is divided.

Previous names: ‘Mulatto’ a collective term for the greensands, conglomerates and marls beneath the White Limestone (Whitehurst, 1786); the ‘Greensands’ of Portlock (1843); Hibernian Greensand of Tate (1865); part of Hibernian Greensands as defined by Hancock (1961); the Upper and Lower Hibernian Greensands of Reid (1971). Hibernian Greensand Formation in BGS publications and Fletcher (1967).

Parent: None

Age and biostratigraphy: Upper Cretaceous, Cenomanian to Santonian. Various basal Upper Cretaceous zones up to Micraster coranguinum Zone.

References: Fletcher, 1967, 1977; Griffith and Wilson, 1982.

The following entries, in stratigraphical order from the base, for the formations of the Hibernian Greensands Group form part of the Lexicon derived from its precursor Dic_Strat (as code only entries). They are not shown individually upon maps of Northern Ireland but are described in various publications from the province (see note above concerning the adoption of Hibernian Greensand Group as the formal notation for this succession of beds thus raising the rank of each of the following from member status).

5.1.1 Belfast Marls Formation

Name: The Belfast Marls Member was first used in Griffith and Wilson (1982). The term is upgraded to formation status herein.

Type section: Cloghfin Port area [J 483 938] where three exposures of the formation occur, Woodburn Glen South and 503 m north-west of Knock Lodge.

Primary reference section: Carrs Glen near Belfast [J 311 793], in a borehole near Magheramorne [J 433 975]. Numerous localities on the Larne, Antrim, Carrickfergus and Belfast sheet areas (see Griffith and Wilson, 1982, p.48, fig.16A).

Formal subdivisions: None

Lithology: Pale grey strongly bioturbated silty marls with a scattering of dark green glauconite grains (not exceeding 40%). Transitional ‘zone’ at the top contains relatively little glauconite. Fossiliferous with concentrations in discreet laterally continuous shell-beds.

Definition of upper boundary: Conformable, junction arbitrarily drawn at the base of the lowest persistent hard calcareous siltstone of the overlying Island Magee Siltstones Formation. This junction appears at the top of a transitional zone showing an upward decrease in glauconite content.

Definition of lower boundary: Unconformable, oversteps various older units.

Thickness: Maximum thickness of a little less than 3.0 m known from a borehole near Magheramorne [J 433 975] in the Larne (Sheet 21) area. Minimum thickness of 1.6 m over the Knockagh Axis north of Belfast.

Distribution: East Antrim Basin and Southern Uplands area of Northern Ireland.

Previous names: Glauconitic Sands of Tate (1865) and subsequent workers. Belfast Marls Member.

Parent: Hibernian Greensand Group.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Mantelliceras mantelli to basal Acanthocerus rhotomagense Zone.

Reference: Griffith and Wilson, 1982.

5.1.2 Island Magee Siltstones Formation

Name: The Island Magee Siltstones Member was first used in Griffith and Wilson (1982). The term is upgraded to formation status herein.

Type section: Collin Glen [J 269 702] (Belfast area), Cloghfin [J 483 938] (Carrickfergus area), Magheramorne area [J 430 980] (Larne area).

Primary reference section: Kilcoan Old Quarry [J 4610 9850] and numerous localities on the Larne, Antrim, Carrickfergus and Belfast sheet areas (see Griffith and Wilson, 1982, p.48, fig.16A).

Formal subdivisions: None

Definition of upper boundary: Disconformable with the Collinwell Sands Formation and unconformable with the Kilcoan Sands Formation beneath the so-called Turonian non-sequence of the Hibernian Greensands Group.

Definition of lower boundary: Conformable with the Belfast Marls Formation with the boundary arbitrarily taken at the base of the first upwardly occurring hard calcareous siltstone above the transitional top of the preceding formation.

Lithology: Hard and soft grey siltstones and marls (calcareous siltstones) that weather to a pale yellow colour.

Distribution: East Antrim Basin and the Southern Uplands area of Northern Ireland.

Thickness: A maximum of 8.0 m in the Magheramorne area and a minimum of 0.67 m over the Knockagh Axis north of Belfast.

Previous names: The Grey Marls and Yellow Sandstones with Chert of Tate (1865) and Reid (1971); Yellow Sandstones of Hume (1897) and Hancock (1961); Yellow Sandstones and Grey Marls of Manning, Robbie and Wilson (1970). Island Magee Siltstones Member.

Parent: Hibernian Greensands Group.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Acanthoceras rhotomagense Zone.

Reference: Griffith and Wilson, 1982.

5.1.3 Collinwell Sands Formation

Name: The Collinwell Sands Member was first used in Griffith and Wilson (1982). The term is upgraded to formation status herein.

Type section: The formation is best developed south-west of Belfast and was described from a type area around Collin Glen [J 269 702] in terms of the old Glauconitic Sands. This site is reported in Manning, Robbie and Wilson (1970) to be obscured by landslips. The member was named after the quarry at Collinwell [J 269 701] nearby.

Primary reference section: Kilcoan Old Quarry [J 461 985] and numerous localities on the Larne, Antrim, Carrickfergus and Belfast sheet areas (see Griffith and Wilson, 1982, p.48, fig.16A).

Formal subdivisions: None

Lithology: Pale green to grey coarse-grained unconsolidated sands with some glauconite. Becomes whitish and poorly glauconitic in the Carrickfergus district.

Definition of upper boundary: Unconformable at an erosion surface with younger Kilcoan Sands Formation beneath the so-called Turonian non-sequence within the Hibernian Greensands Group; and beneath the erosion surface at the base of the Ulster White Limestone Group.

Definition of lower boundary: Disconformable at an erosional surface upon the Island Magee Siltstones Formation.

Thickness: Maximum of 2.4 m at Rungill Burn in the Carrickfergus district.

Distribution: Fully developed in the area south-west of Belfast within the East Antrim Basin and Southern Uplands area. Elsewhere in Northern Ireland the formation may be represented in the condensed successions of the undivided Hibernian Greensands Group.

Previous names: Part of the Glauconitic Sands of Tate (1865); part of the Chloritic Sands and Sandstones of Hume (1897); lower part (‘Basement Sands’) of the Upper Glauconitic Beds of Hancock (1961); part of the Lower Hibernian Greensands of Reid (1971); the Quartzose Sand (part of the Cenomanian/Turonian Greensands) of Manning, Robbie and Wilson (1970). Collinwell Sands Member in BGS publications.

Parent: Hibernian Greensands Group.

Age and biostratigraphy: Upper Cretaceous, Uppermost Cenomanian and Turonian. Rhynchostreon suborbiculatum Zone.

References: Fletcher, 1967; Griffith and Wilson, 1982.

5.1.4 Kilcoan Sands Formation

Name: The Kilcoan Sands Member was first used in Griffith and Wilson (1982). The term is upgraded to formation status herein.

Type section: The old cutting to the old Kilcoan Quarry [J 4610 9850] west Island Magee.

Primary reference section: Numerous localities on the Larne, Antrim, Carrickfergus and Belfast sheet areas (see Griffith and Wilson, 1982, p.48, fig.16A).

Formal subdivision: None

Lithology: Pale green glauconitic sands thought largely to be derived from the Collinwell Sands Formation. Three conspicuous Inoceramus bands divide the succession into three unequal parts.

Definition of upper boundary: Disconformable at an erosion surface beneath various younger members of the Ulster White Limestone Group.

Definition of lower boundary: Disconformable at an erosion surface above the mid-Hibernian Greensands ‘unconformity’. Rests on each of the older formations in the group and overlaps onto pre-Cretaceous strata over the most positive structural highs.

Thickness: Up to 7.3 m at Kilcoan.

Distribution: Fully developed in the Island Magee area and within the East Antrim Basin and Southern Uplands area. Elsewhere in Northern Ireland the formation may be represented in the condensed successions of the undivided Hibernian Greensands Group.

Previous names: Part of the Chloritic Sands and Sandstones of Tate (1865) and Hume (1897); part of the Upper Glauconitic Beds of Hancock (1961); The Upper Hibernian Greensands of Reid (1971); Senonian Greensands of Manning, Robbie and Wilson (1970). Kilcoan Sands Member.

Parent: Hibernian Greensands Group.

Age and biostratigraphy: Coniacian to Santonian. Micraster cortestudinarium to Micraster coranguinum zones.

References: Fletcher, 1967; Griffith and Wilson, 1982.

5.2 Ulster White Limestone Group

(See note below concerning the adoption of Ulster White Limestone Group as the formal notation for this succession of units)

Name: The White Limestone of Hancock (1961). Ulster White Limestone Formation proposed in Fletcher (1967, 1977). Elevated to group status herein.

Type section: Numerous exposures of the constituent formations (see formal subdivisions below for reference to those divisions) with no one site containing all of the stratigraphical elements included within the group.

Primary reference section: Many individual type sections for the component formations of the group.

Formal subdivisions: Fletcher (1967, 1977) proposed fourteen members which are herein considered as formations, in ascending order; the Cloghfin Sponge Formation, Galboly Chalk Formation, Cloghastucan Chalk Formation, Creggan Chalk Formation, Boheeshane Chalk Formation, Larry Bane Chalk Formation, Ballintoy Chalk Formation, Glenarm Chalk Formation, Garron Chalk Formation, Portrush Chalk Formation, Ballymagarry Chalk Formation, Tanderagee Chalk Formation, Port Calliagh Chalk Formation and Ballycastle Chalk Formation. He informally divided the succession into a Pre-Larry Bane Chalk White Limestone, Larry Bane Formation and Post-Larry Bane Chalk White Limestone parts. The two divisions above and below the Larry Bane Chalk Formation are regarded as subgroups herein but their name is shortened by the omission of the white limestone descriptor.

Lithology: Principally limestones (hardened chalks) with subordinate flint, marl, sponge bed, hardground, conglomeratic and fossil acme bands, with glauconite grains where formations become condensed over structural highs.

Definition of upper boundary: Eroded contact where the group is overlain by the Palaeogene Antrim Basalts or Quaternary deposits.

Definition of lower boundary: Rests disconformably on various members of the Hibernian Greensands Formation and oversteps (unconformable) onto older pre-Cretaceous rocks. Internal overstep within the group principally at the level of the Post-Larry Bane White Limestone Subgroup (informal term defined below) places successively higher formations at the base of the group over structural highs at the margins of the principal basins.

Thickness: Highly variable dependant on the position within structurally controlled basins environments of which five were named by Fletcher (1977) as the Hebridean Basin (presumably incorporating his Londonderry Shelf and North Antrim Basin), the Highland Border (also termed the Dalradian Massif), the Midland Valley (usually termed the East Antrim Basin) and the Southern Uplands. Up to 150 m+ of ‘White Limestone’ was encountered in the Aughrimderg Borehole [H 880 685] (Wilson, 1972, p.56) but the thickest and most complete development at outcrop is found on the North Antrim coast where 120 m of beds are present, although not at any one locality. The Geological Society Special Report on the Cretaceous (Rawson et al., 1978) gives a value of 130 m.

Distribution: Throughout Northern Ireland. Fullest development in the North Antrim Basin with significant successions in the Midland Valley (East Antrim Basin) and the Southern Uplands as defined in Fletcher (1977).

Previous names: Upper Chalk (White Limestone) and Lower Chalk (Glauconitic Chalk) by Portlock (1843); Upper Chalk divided into an upper White Limestone (or Hard Chalk) and a lower Chloritic Chalk (or Basement bed of the White Limestone) by Tate (1865); Reid (1958) included a ‘Basal Conglomerates’ within Tate’s definition of the Chloritic (correctly termed Glauconitic) Chalk. Ulster White Limestone Formation of BGS publications and Fletcher (1977).

Parent: None

Age and biostratigraphy: Upper Cretaceous, Santonian to Maastrichtian. Uintacrinus socialis to Belemnitella occidentalis occidentalis (see Wood, 1967) zones.

References: Fletcher, 1967, 1977; Griffith and Wilson, 1982.

The following entries, in stratigraphical order from the base, for the subgroups and formations of the Ulster White Limestone Group form part of the Lexicon derived from its precursor Dic_Strat (as code only entries). They are not shown individually upon maps of Northern Ireland but are described in various publications from the province (see note above concerning the adoption of Ulster White Limestone Group as the formal notation for this succession thus raising the rank of each of the following).

5.2.1 Pre-Larry Bane Chalk Subgroup

Name: Proposed as the Pre-Larry Bane Chalk White Limestone by Fletcher (1977) as an informal term to cover the Santonian and lower Campanian Chalks below the lowest of three distinctive and traceable erosion surfaces marking the Larry Bane Chalk Formation.

Type section: Defined at the type sections of its constituent formations. East Antrim Depositional Basin around Glenarm [D 310 150] and marginally less well developed in the North Antrim Basin in the White Park Bay [D 027 440] area.

Primary reference section: White Park Bay [D 027 440].

Formal subdivisions: Fletcher (1977) proposed five members that are herein considered as formations. They are in ascending order the Cloghfin Sponge Formation, Galboly Chalk Formation, Cloghastucan Chalk Formation, Creggan Chalk Formation, and the Boheeshane Chalk Formation.

Lithology: Chalk with flints and a basal glauconitic arenaceous member.

Definition of upper boundary: Taken at the base of the Larry Bane Chalk Formation where it is marked by the lower of three persistently strong erosion surfaces.

Definition of lower boundary: Rests unconformably on the Hibernian Greensands Formation within the deep depositional basins and on a variety of older deposits as the subgroup oversteps onto the bounding structural highs.

Thickness: Amounts to 37.19 m from type sites of constituent members and 26 m in the East Antrim Depositional Basin south of Glenarm.

Distribution: Present in the East Antrim and North Antrim basins overstepped by the Ballintoy Chalk Formation and higher units over structural highs.

Previous names: None formally but may be considered as equivalent to those defined as ‘Beds earlier than the zone of Belemnitella mucronata’ by Hancock (1961). This group of sediments are usually easily recognised by the presence above of the characteristic Larry Bane Chalk Formation and is reported (Fletcher, 1977) to be recognisable within downhole geophysical logs.

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Santonian to Campanian. Uintacrinus socialis to Gonioteuthis quadrata and basal Belemnitella mucronata zones.

References: Fletcher, 1977; Griffith and Wilson, 1982.

5.2.1.1 Cloghfin Sponge Formation

Name: The Cloghfin Sponge Beds Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded herein as a formation and the name altered to the Cloghfin Sponge Formation.

Type section: As defined in Fletcher (1967) on the shore [J 4760 9110] near Whitehead and Hillsport, Island Magee.

Primary reference section: Restricted to the south-east Antrim region between Little Deer Park near Glenarm and Castle Dobbs. Other principal exposures near Kilcoan [J 461 985] and Cloghfin Port [J 483 938].

Formal subdivisions: None but divided informally into Beds A B and C by Fletcher (1967).

Lithology: Chalk and chalk conglomerate/breccia, glauconitic, with conspicuous hexactinellid sponge psuedomorphs. Three separate beds recognised (A, B, C) each with characteristic shape variants of the irregular echinoid Echinocorys.

Definition of upper boundary: The exact relationship with the overlying Galboly Chalk Formation is not certain (Fletcher, 1978 p. 8 para. 2). It is taken at a well-developed separation plane below which the beds contain arenaceous ‘contamination’.

Definition of lower boundary: Everywhere the base rests unconformably upon eroded Hibernian Greensand Group successions. In the most complete Hibernian Greensands Formation sequences (Kilcoan [J 461 985]) the base of the Clochfin Sponge Formation is 4.27 m above the conspicuous Inoceramus Bands.

Thickness: As defined in the type site the beds are 1.4 m thick.

Distribution: Limited to the East Antrim Basin Northern Ireland.

Previous names: Cloghfin Sponge Beds Member (note the term Beds is removed from the new name designation to remove ambiguity). Equivalent to the ‘Spongiarian Zone’ of Hume (1897) and later called the ‘Sponge Bed’ by Hancock (1961).

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Santonian. Uintacrinus socialis Zone in part.

References: Fletcher, 1967, 1977.

5.2.1.2 Galboly Chalk Formation

Name: The Galboly Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Roadside ‘pillar’ south of Garron Point Irish Grid Reference [D 301 245] but this site is noted in Fletcher (1977) as being within an unstable residual block near to the main road. An alternative type section can be built up from foreshore blocks or from the indifferently exposed old quarry at Milltown [D 255 243].

Primary reference section: Milltown [D 255 243] and in central Murlough Bay [D 200 401].

Formal subdivisions: None

Lithology: Chalk, with some flint bands and ‘incipient flints’. Marl partings common to base with some glauconite.

Definition of upper boundary: At a prominent bedding plane (an erosion surface in part) immediately above a zone of wavy and disturbed bedding. Overlain by the Cloghastucan Chalk Formation.

Definition of lower boundary: The exact relationship with the underlying Cloghfin Sponge Formation is not certain (Fletcher, 1978 p. 8 para 2). It is taken at a well-developed separation plane above which the beds contain no appreciable arenaceous ‘contamination’.

Thickness: Measures 5.85 m at its type section.

Distribution: Known throughout the North Antrim and East Antrim Basins and part of the Southern Upland, Highland Border and northern Londonderry Shelf. Absent elsewhere.

Previous names: Galboly Chalk Member.

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Santonian. Uintacrinus socialis Zone (in part).

References: Fletcher, 1967, 1977.

5.2.1.3 Cloghastucan Chalk Formation

Name: The Cloghastucan Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Fallen blocks on the foreshore north of Garron Point [D 301 245], and in Red Bay and Murlough Bay on either side of the Highland Border Ridge.

Primary reference section: Restricted to the North Antrim and East Antrim (Midland Valley) basins, and overlaps, and is itself overlapped (at the Benvan track [D 2000 413]) onto the Highland Border Ridge (Massif). In the North Antrim Basin the formation is continuous from Murlough Bay to the Portrush-Downhill area but diminishes between Oweynamuck and Portbraddan with a concomitant loss of flints. South of the Highland Border Ridge the formation is first seen at Altmore Burn [D 237 228], is absent around Dooray Bridge but attains its maximum thickness on the south side of Red Bay. It overlaps in the south against the Southern Uplands and is absent south of Castle Dobbs.

Formal subdivisions: Contains within it the Oweynamuck Flint Band.

Lithology: Limestone (chalk), with an overall ‘gritty’ texture and with some flint bands (mainly small and ‘spindle-shaped’) most notably the coalescing nodular flint course termed the Oweynamuck Flint Band (of bed status defined at the eastern bluff in White Park Bay [D 029 448]). Beds of green-coated chalk pebbles at some levels. Common brachials and calyx plates of Marsupites.

Definition of upper boundary: The upper limit is taken at the top of a thin (0.15 m) wavy bedded unit underlying Creggan Chalk Formation chalks rich in Inoceramus debris. The wavy bedded unit contains a marked increase in Inoceramus compared to the rest of the Cloghastucan Chalk Formation.

Definition of lower boundary: At the type site, the boundary is at a prominent bedding plane immediately above a wavy bedded unit at the top of the underlying Galboly Chalk Formation. Outside the type area the basal contact is disconformable and the junction is marked by an erosion surface with glauconitised chalk pebbles, which includes rolled sponge psuedomorphs.

Thickness: Thin succession of 2.33 m thickness at its type site. Absent over structural highs and overlapped by succeeding members.

Distribution: Present in the North Antrim and East Antrim basins and parts of the Highland Border and Southern Uplands areas. Absent over the Londonderry shelf.

Previous names: Cloghastucan Chalk Member. The Marsupites White Limestone (Reid, 1964).

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Santonian. Marsupites testudinarius Zone.

References: Fletcher, 1967, 1977.

5.2.1.4 Creggan Chalk Formation

Name: As first published called the Ballykeel Chalk in Fletcher (1967). The Creggan Chalk Member was first proposed in Fletcher (1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Gortin Quarry, Creggan [D 277 187]. The type section of the Ballykeel Chalk in Fletcher (1967) is on the south-east coast of Island Magee at [J 9710 4860].

Primary reference section: Best developed in the North Antrim and Midland Valley Basins particularly in the down-warp areas around Garron and Hillsport. Other localities within these basins to note are at White Park Bay, Boheeshane Bay and Murlough Bay in North Antrim, in Church Bay on Rathlin Island and along the East Antrim coast (Midland Valley Basin). This formation is more widely spread than all older formations overlapping significantly onto the Londonderry Shelf to near Dungiven, onto the Highland Border Ridge as seen at Carneighaneigh Quarry, and onto the Southern Uplands as far south as Collinwell in south Belfast. The stromatolitic surface becomes very prominent in the Southern Uplands area where it was formerly known by the quarrying term ‘mulatto’.

Formal subdivisions: None

Lithology: Limestone (chalk), with common Inoceramus fragments (up to 20%) and many small burrow-fill flints scattered throughout. The upper part contains several green-coated pebble horizons that coalesce towards the basin margins to form a single conspicuous hardground with rolled and mineralised fossils most notably belemnites and echinoid steinkerns. Glauconitic in marginal overlap facies where the uppermost beds/surfaces are attenuated, gritty, glauconitic and algal-topped (stromatolitic).

Definition of upper boundary: Taken at the highest of several green-coated chalk pebble beds within the Inoceramus-rich limestone. This unit is termed the Bendoo Pebble Bed (of member? status) in the North Antrim Basin. Overlain by the Boheeshane Chalk Formation.

Definition of lower boundary: Taken at the point in the succession where there is a sudden increase in Inoceramus fragments. At Creggan this occurs 0.23 m above the Oweynamuck Flint Band within the top of the Cloghastucan Chalk Formation.

Thickness: Measures 3.45 m at the type locality.

Distribution: North Antrim and East Antrim basins and the Southern Upland area. Oversteps onto the Highland Border area and a limited northern part of the Londonderry Shelf.

Previous names: Creggan Chalk Member.

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Campanian. Lower part of Offaster pilula Zone.

References: Fletcher, 1967, 1977.

5.2.1.5 Boheeshane Chalk Formation

Name: The Boheeshane Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Boheeshane Bay [D045 450] in North Antrim Basin.

Primary reference section: Best developed in the North Antrim and East Antrim (Midland Valley) basins. It is overlapped by younger chalk members towards the structural highs. The Whitehead Flint Band is displayed at the reference section at the old quarry (a landfill site) at Whitehead [J474 913].

Formal subdivisions: Includes the Whitehead Flint Band and is informally divided into units A, B and C.

Lithology: Limestone (chalk), with common massive flint bands and tabular flints. Some green-coated chalk pebble beds near the base and as a prominent bed associated with sponges in the middle of the sequence. Hard pellet chalk in softer matrix is common at some levels. Divided into three main ‘beds’ (A, B and C) each further divided into numbered ‘units’. Each ‘bed’ separated by marked bedding planes that are locally emphasised by weathering. A number of notable fossil acmes throughout. Considered to be much finer-grained than older gritty members and termed ‘White Chalk’ by Wolfe (1968). A distinctive massive flint band, which marks the upper limit of Gonioteuthis, is termed the Whitehead Flint Band (of bed status) whose type reference section is the old quarry at Whitehead [J 474 913].

Definition of upper boundary: Taken at the well-developed erosional surface at the base of the Larry Bane Chalk Formation.

Definition of lower boundary: Base defined by reference to the terminal pebble bed of the Creggan Chalk Formation and the stromatolitic ‘mulatto’ surface in marginal areas.

Thickness: Combined thickness at the type site of 24.19 m. Bed A

8.33 m, Bed B 8.69 m and Bed C 7.17 m.

Distribution: North Antrim and East Antrim basins part of the Southern Uplands area and over parts of the Highland Border and Londonderry Shelf areas.

Previous names: Boheeshane Chalk Member.

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Campanian. Gonioteuthis quadrata and basal Belemnitella mucronata zones. From Applinocrinus [Saccocoma] cretaceus Subzone (quadrata Zone).

References: Fletcher, 1967, 1977.

5.2.2 Larry Bane Chalk Formation

Name: The Larry Bane Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Larry Bane Bay [D 058 452]. Specifically in the cliff section [D 0500 4500] 400 metres north-north-east of Ballintoy in the North Antrim Basin.

Primary reference section: North Antrim Basin particularly Carrickarade to Portbraddan and in the East Antrim Basin.

Formal subdivisions: Informally divided into units A and B, which are said to have a characteristic one-third (A) to two-thirds (B) thickness relationship throughout the province.

Lithology: Limestone (chalk) with numerous flint bands. Shell debris abundant with distinct ‘pellet’ or fragmentary limestone clasts evident on weathered surfaces. Three persistent erosion surfaces divide the Larry Bane Chalk Formation into two ‘Beds’ (A and B). These surfaces may be treated as marl seams. Very large belemnites are a prominent feature of this formation.

Definition of upper boundary: Conformable at an upper prominent erosion surface/marl beneath the Ballintoy Chalk Formation. Overlapped by younger members at margins of structural highs.

Definition of lower boundary: Conformable at lower prominent erosion surface/marl resting on Boheeshane Chalk Formation.

Thickness: Totals 7.29 m at type site with Bed A 2.44 m and Bed B

4.85 m thick. This 1:2 ratio of bed thickness is considered to be characteristic of the whole Larry Bane Chalk Formation outcrop.

Distribution: Known throughout the North Antrim and East Antrim (Midland Valley) basins of Northern Ireland.

Previous names: Larrybane Chalk of Fletcher (1967); Larry Bane Chalk Member.

Parent: Ulster White Limestone Group.

Age and biostratigraphy Upper Cretaceous, Campanian. Belemnitella mucronata Zone.

References: Fletcher, 1967, 1977.

5.2.3 Post-Larry Bane Chalk Subgroup

Name: Proposed by Fletcher (1977) as the Post-Larry Bane Chalk White Limestone as an informal term to cover the upper Campanian and Maastrichtian Chalks above the highest of three distinctive and traceable erosion surfaces marking the top of the Larry Bane Chalk Formation.

Type section: Ballycastle area [D 115 420], North Antrim Basin.

Primary reference section: Cliff and quarry sections around Ballycastle [D 114 420]; Whiterocks [C 893 409] and Garron Point [D 301 239].

Formal subdivisions: Fletcher (1977) proposed eight members that are regarded as formations herein. They are in ascending order the Ballintoy Chalk Formation, Glenarm Chalk Formation, Garron Chalk Formation, Portrush Chalk Formation, Ballymagarry Chalk Formation, Tanderagee Chalk Formation, Port Calliagh Chalk Formation and the Ballycastle Chalk Formation

Lithology: Limestone (chalk) with layers of nodular, tabular and ‘paramoudra’ type flints.

Definition of upper boundary: Placed at the erosion surface at the top of Ulster White Limestone Group succession beneath Palaeogene Antrim basalt.

Definition of lower boundary: Placed at base of Ballintoy Chalk Formation at the top of the Larry Bane Chalk Formation where it is marked by the upper of three persistently strong erosion surfaces.

Thickness: A total of 89.28 m from type sites of constituent members, but the full thickness is very variable due to pre-Palaeogene Basalts erosion.

Distribution: Known throughout Northern Ireland. Its major development is in the North Antrim, East Antrim and Southern Upland basins. Oversteps onto structural highs.

Previous names: None formally but may be considered as the partial equivalent to those defined as ‘Beds of the zone of Belemnitella mucronata’ by Hancock (1961). This group of sediments are usually easily recognised by the presence, in sections, of the characteristic underlying Larry Bane Chalk Formation and is reported by Fletcher (1977) to be recognisable within downhole geophysical logs.

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Upper Campanian to Maastrichtian. Belemnitella mucronata to Belemnella occidentalis zones.

References: Fletcher, 1967, 1977; Griffith and Wilson, 1982.

5.2.3.1 Ballintoy Chalk Formation

Name: The Ballintoy Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: The type section is taken on gently dipping rock platforms in Ballintoy Harbour [D 040 456] in the North Antrim Basin. More accurate measurements are achieved from Larry Bane Head and Quarry to the east. The maximum development of the member was formerly visible in air-weathered cliffs in White Bay. The type section was defined by Fletcher in his 1967 thesis is at White Bay [D 3280 1510].

Primary reference section: North Antrim and Midland (East Antrim) basins and on the eastern Londonderry Shelf. The member is continuous around the outcrop from Portrush to north Belfast.

Formal subdivisions: The highest unit within the formation is named the Altachuile Breccia (member). The whole formation is divided informally from the base into A and B units.

Lithology: Limestone (chalk) with small flints scattered in the lower part and small discontinuous tabular flints in the upper part. The formation can be divided two ‘beds’ (A and B) separated by conspicuous separation planes. The formation is terminated by the ‘wavy-bedded’ Altachuile Breccia (member).

Definition of upper boundary: Conformably succeeded by the Glenarm Chalk Formation above the Altachuile Breccia (member).

Definition of lower boundary: Conformably overlies ‘Bed’ B of the Larry Bane Chalk Formation. Oldest of the post-Larry Bane Chalk ‘Subgroup’.

Thickness: Totals 12.65 m at its type site with Bed A 9.65 m and Bed B 3.00 m.

Distribution: Principal outcrop is within the North Antrim and East Antrim (Midland Valley) basins. Oversteps the Larry Bane Formation onto the Southern Uplands, Highland Border and the northernmost part of the Londonderry Shelf.

Previous names: White Bay Chalk of Fletcher (1967); Ballintoy Chalk Member.

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Campanian. Belemnitella mucronata Zone sensu lato.

References: Fletcher, 1967, 1977.

5.2.3.2 Glenarm Chalk Formation

Name: The Glenarm Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Old quarry at Parishagh [D 304 156], half a mile north-west of Glenarm in the Midland Valley (East Antrim) Basin.

Primary reference section: Cliff sections at White Rocks near Portrush and in the quarry at Larry Bane Head in the northern depositional basin. The sections around Glenarm in the Midland Valley Basin. At Kilwaughter [D 354 008] and Ballycarry [J449 943].

Formal subdivisions: Includes the North Antrim Hardgrounds (of member status) and is informally divided into units A to D from the base.

Lithology: Limestone (chalk), with flints ranging from small nodular at the base through nodular to tabular flints in the middle part of the succession to massive nodular at the top. The formation can be divided into four ‘Beds’ (A to D) by subdivision on bedding planes. In the North Antrim Basin the formation includes two well-developed hardgrounds, the North Antrim Hardgrounds (of member? status) and the succession is therefore incomplete. In the Midland Valley (East Antrim) Basin only limited wavy bedding and scattered green glauconitised pebbles indicate interrupted sedimentation. This area is regarded as the ‘standard’.

Definition of upper boundary: Weathered-out bedding plane below conspicuously shelly wavy-bedded chalk at the base of the conformable Garron Chalk Formation.

Definition of lower boundary: Base delimited by a prominent weathered-out bedding plane immediately above the Altachuile Breccia (member) of the Ballintoy Chalk Formation.

Thickness: Some 8.10 m at the type area.

Distribution: Maximum development in the East Antrim (Midland Valley) Basin and found over the Highland Border High and well developed in the North Antrim Basin. Becomes attenuated including several non-sequences and overstepped by younger formations across the Londonderry Shelf and in the Southern Uplands Belfast district.

Previous names: Glenarm Chalk of Fletcher (1967); Glenarm Chalk Member.

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Campanian. Belemnitella mucronata Zone sensu lato.

References: Fletcher, 1967, 1977.

5.2.3.3 Garron Chalk Formation

Name: The Garron Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Cliff section just north of the Post Office at Garron Point [D 301 239].

Primary reference section: Whiterocks and Larry Bane Head in the North Antrim Basin. Portaneevy [D 063 444] on the north coast, Portantonnish on Rathlin Island and Ballysillan Quarry [J 305 778] show the characteristic giant ‘flint-circles’.

Formal subdivisions: None but divided informally into Units A to C from the base.

Lithology: Limestone (chalk) with characteristic giant flints (‘massive flint rolls’) and significant Inoceramus fragments. Is divided into three ‘Beds’ (A to C).

Definition of upper boundary: Conformable with Portrush Chalk Formation at a bedding plane above wavy-bedded sediment with small nodular flints.

Definition of lower boundary: Conformable on the Glenarm Chalk Formation at a bedding plane, above which wavy-bedded conspicuously shelly chalk with corals and bryozoa occurs.

Thickness Wood (in Wilson, 1972). The term ‘Green Beds’ is utilised

Some 9.65 m in type section.

Distribution: North Antrim Basin, East Antrim (Midland Valley) Basin and over structural highs with the exception of the southern and western Londonderry Shelf. Oversteps younger beds over structural highs.

Previous names: Garron Chalk of Fletcher, 1967; Garron Chalk Member.

Parent: Ulster White Limestone Group.

Age and biostratigraphy Upper Cretaceous, Campanian. Belemnitella mucronata Zone sensu lato.

References: Fletcher, 1967, 1977.

5.2.3.4 Portrush Chalk Formation

Name: The Portrush Chalk Member was first proposed in Fletcher (1967, 1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Taken at the south-facing wall of the older and deeper Ballymagarry Quarry [C 890 408], i.e. immediately above the main cave which passes beneath the Portrush to Bushmills Road. Sliddery Cove Cliffs [C 890 410] east of Portrush.

Primary reference section: Garron Point [D 301 2390] in East Antrim Basin.

Formal subdivision: Includes the South Antrim Hardgrounds (of member status) and informally divided into units A to D from the base.

Lithology: Limestone (chalk) with many tabular flint bands and Inoceramus debris in upper part. In the south Antrim area (Southern Uplands High) there are important hardground non-sequences of green-coated chalk pebbles called the South Antrim Hardgrounds (of member status).

Definition of upper boundary At a prominent bedding plane above Inoceramus-rich chalk with tabular flint.

Definition of lower boundary: Conformable, on the Garron Chalk Formation, at a bedding plane beneath a prominent continuous tabular flint.

Thickness: About 14.28 m in the type section.

Distribution: Found consistently throughout the province but is generally absent from much of the East Antrim (Midland Valley) Basin due to pre-Palaeogene basalt erosion. Oversteps onto older strata over the Londonderry Shelf.

Previous names: Portrush Chalk of Fletcher (1967); Portrush Chalk Member. Is equivalent to the Cardiaster Beds described by as a mappable unit in Manning et al., (1970) for the South Antrim Hardgrounds.

Parent: Ulster White Limestone Group.

Age and biostratigraphy Upper Cretaceous, Campanian. Belemnitella mucronata Zone sensu lato.

References: Fletcher, 1967, 1977.

5.2.3.5 Ballymagarry Chalk Formation

Name: The Ballymagarry Chalk Member was first proposed in Fletcher (1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Ballymagarry Quarry [C 889 407].

Primary reference section: The western side of Port More [D 073 439] and Downhill in north Derry. Found throughout the Londonderry Shelf, North Antrim Basin and Southern Uplands High. Absent from the Midland Valley (East Antrim) Basin and Highland Border High.

Formal subdivisions: None but informally divided into units A to C from the base.

Lithology: Limestone (chalk) with extremely large flat lying and near-continuous flint bands. Divided into three ‘Beds’ (A to C) separated by well-marked bedding planes.

Definition of upper boundary: Marked by the base of the prominent continuous flint band termed the Long Gilbert Flint Band within the Tanderagee Chalk Formation.

Definition of lower boundary: Conformably overlies the Portrush Chalk Formation at a level of a well-marked bedding plane immediately below the inception of large flat lying and near continuous flint nodules.

Thickness: About 10.95 m at its type site.

Distribution: Absent from the Highland Border High and East Antrim Basin presumably by pre-Palaeogene erosion.

Previous names: Ballymagarry Chalk Member.

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Campanian. Belemnitella mucronata Zone sensu lato.

References: Fletcher, 1977.

5.2.3.6 Tanderagee Chalk Formation

Name: The Tanderagee Chalk Member was first proposed in Fletcher (1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Long Gilbert Quarry, Ballymagarry [C 889 407], south wall of the western part of the quarry.

Primary reference section: Numerous in the North Antrim Basin, the southern Londonderry Shelf and in the Southern Uplands. It is seen in sections between Magheralin and Trummery, Groganstown and the ‘Hairpin Bend’ region of Ballysillan, Ballycastle to Ballintoy, Portbraddan to Downhill and between Carmean and Stewartstown.

Formal subdivision: Includes the Long Gilbert Flint Band (of bed status) and informally divided into units A to E from the base.

Lithology: Limestone (chalk) with flint bands. Divided into five ‘Beds’ (A to E). Abundant belemnites in lower ‘Bed’ A and by an acme of crinoid debris in ‘Bed’ C. Elsewhere asteroid and crinoid debris common.

Definition of upper boundary: Conformable, with the overlying Port Calliagh Chalk Formation, at a bedding plane below a ‘belt of complex flints’.

Definition of lower boundary: Conformable, on the Ballymagarry Chalk Formation, at a bedding plane immediately below the thick continuous tabular Long Gilbert Flint Band where this exists. Or at the same bedding plane marking the faunal change from the Ballymagarry Chalk Formation fauna.

Thickness: About 7.63 m at type site.

Distribution: Outcrops in the Southern Uplands area, the North Antrim Basin and in the southern part of the Londonderry Shelf. Absent in the East Antrim Basin, the Highland Border High and northern Londonderry shelf due to pre-Palaeogene erosion.

Previous names: Tanderagee Chalk Member.

Parent: Ulster White Limestone Group.

Age and biostratigraphy Upper Cretaceous, Maastrichtian. Belemnella lanceolata Zone?

References: Fletcher, 1977.

5.2.3.7 Port Calliagh Chalk Formation

Name: The Port Calliagh Chalk Member was first proposed in Fletcher (1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: Port Calliagh [D 112 420] inlet west of Castle Point near Ballycastle, north Antrim and to the east under Castle Point.

Primary reference section: Ballymagarry Quarry and around Ballycastle Harbour in the North Antrim Basin, in three quarries on the western Londonderry Shelf region, at Whiterock in Belfast and in Small and Hayes Quarry north-east of Lurgan.

Formal subdivision: None but informally divided into units A to F from the base.

Lithology: Limestone (chalk) with numerous flint bands displaying large, tabular and complex habit.

Definition of upper boundary: Conformable at a prominent weathered-out bedding plane at the top of ‘Bed’ F with the Ballycastle Chalk Formation.

Definition of lower boundary: Conformable on the Tanderagee Chalk Formation at the lowest ‘separation plane’ immediately beneath the ‘belt of complex flints’ seen in the Ballycastle section.

Thickness: Some 12.40 m at the type site.

Distribution: Outcrops in the Southern Uplands area (in isolated areas), the North Antrim Basin and in the southern part of the Londonderry Shelf. Absent in the East Antrim Basin, the Highland Border High and northern Londonderry Shelf due to pre-Palaeogene erosion.

Previous names: Port Calliagh Chalk Member. Forms the lower part of the Ballycastle White Limestone (Wood, 1967).

Parent: Ulster White Limestone Group.

Age and biostratigraphy Upper Cretaceous, Maastrichtian. Belemnella lanceolata Zone.

References: Fletcher, 1967, 1977.

5.2.3.8 Ballycastle Chalk Formation

Name: The Ballycastle Chalk Member was first proposed in Fletcher (1977) and adopted in BGS publications subsequently. It is regarded as a formation herein.

Type section: West of Ballycastle Pier [D 120 415].

Primary reference section: Ballymagarry Quarry, Castle Point Quarry and cliffs and foreshore eastward to Ballycastle.

Formal subdivision: None but informally divided into units A to G from the base.

Lithology: Limestone (chalk) with nodular flint bands which have a carious habit in the upper part of the formation. Divided into seven ‘beds’ (A to G).

Definition of upper boundary: Erosional contact with Palaeogene basalts or Quaternary deposits.

Definition of lower boundary: Conformable on the Port Calliagh Chalk Formation at a prominent weathered-out bedding plane at the top of ‘Bed’ F of that lower formation and characterised by tabulate flints.

Thickness: Some 13.72 m at type site.

Distribution: Limited to the Ballymagarry and Ballycastle areas by pre-Palaeogene erosion.

Previous names: Forms the upper part of the Ballycastle White Limestone of Wood (1967). Ballycastle Chalk Member.

Parent: Ulster White Limestone Group.

Age and biostratigraphy: Upper Cretaceous, Maastrichtian. Belemnella occidentalis Zone.

References: Fletcher, 1967, 1977.

Chapter 6 Note on the Chalk Group nomenclature in the UK Offshore sector

Investigations into the hydrocarbon prospectivity of the North Sea has led to the development from an early, essentially downhole geophysical log and seismic, stratigraphy into a more refined lithostratigraphical nomenclature based not only on geophysical data but on biostratigraphy, cuttings and type cores. In the UK sector the first comprehensive lithostratigraphical schemes were established by Rhys (1974) ((Figure 11), Column 1) in the Southern North Sea and by Deegan and Scull (1977) ((Figure 11), Column 2) in the Central and Northern North Sea (east of the Shetland Islands and southwards). The terms, developed in those early studies, have been expanded with a considerable body of stratigraphical evidence and piecemeal additions were made such that the meaning of many lithostratigraphical terms became blurred. The ‘BGS under the auspices of the UKOOA (UK Offshore Operators Association)’ published a rationalisation of this nomenclature in seven volumes (under the editorship of Knox and Cordey) with Volume 2 (Johnson and Lott, 1993) ((Figure 11), Column 3), and Volume 7 (Lott and Knox, 1994) ((Figure 11), Column 4) covering the Cretaceous strata of the Central and Northern North Sea, and the Southern North Sea respectively.

Three similar volumes were produced by BGS to cover the UK sector North-west Margin with Volume 1 giving a correlation of the pre-Tertiary lithostratigraphy (Ritchie, Gatliff and Riding, 1996) ((Figure 11), Column 5). This covered the area west of the Shetland Islands southward to the Orkneys Islands.

The most recent review of the stratigraphy of the offshore sector is contained in The Millennium Atlas: petroleum geology of the central and northern North Sea published by the Geological Society of London in 2002 (Surlyk et al., 2003). This contains a comprehensive overview of the stratigraphy within the Danish, Norwegian and UK sectors of the hydrocarbon-producing regions of the North Sea, north of latitude 55° 20´ N, and updates the UKOOA and BGS volumes.

Data is also held within the Offshore Regional Reports of the BGS published between 1990 and 1996 although in general the terminology used reflects their compilation prior to the UKOOA volumes.

A detailed discussion is beyond the scope of this report but a correlation of the lithostratigraphical units given in the UKOOA publications is given in (Figure 11) for completeness. Two aspects of the offshore terminology should be noted.

The Hunstanton Formation is considered to be of Albian age and equivalent to the Rødby Formation in the Cromer Knoll Group.

In general the Hidra Formation and its lateral equivalents correlate roughly to the Grey Chalk Subgroup or Ferriby Chalk Formation with the Plenus Marl Formation and/or the Black Band at the base of the Herring Formation (and lateral equivalents) marking the base of the White Chalk Subgroup. However it should be noted that the use of the terms Plenus Marl Formation and Black Band within the offshore sector is confused and they are not necessarily mutually exclusive. Indeed in correlation charts the Black Band is shown spanning the Cenomanian/Turonian boundary and must therefore include the entirely Cenomanian Plenus Marls Member as defined onshore. It follows therefore that where the Black Band defines the base of the Herring Formation this may or may not include the Plenus Marls succession and similarly the Plenus Marl Formation may encompass the Black Band. It is quite possible therefore that the topmost part of the Hidra Formation should be considered as equivalent to the very basal White Chalk Subgroup.

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Appendix 1 — BGS geological sheet areas in England and Scotland showing Upper Cretaceous strata

This list encompasses all of the Geological Survey sheets within Great Britain with units of the Upper Cretaceous delimited. The ‘date’ indicates the published date of the latest edition, though in many cases the date of survey is much earlier. Provisional editions (P) are based principally on a desk revision incorporating available data. The Chalk nomenclature schemes used to divide the rocks are given as follows:- Scotland Traditional (ST); England and Wales Traditional (EWT); England and Wales Revised (EWR); England and Wales fully compliant with agreed terminology (EWFC); [Northern Province (NP); Southern Province (SP)]. An indication of the upgrading of terminology required to conform to the framework herein is indicated in the notes column. The PDG Programme was the 10-year forward look for the BGS surveying programme, until 2005. It was replaced by a new programme in April 2005. OOP indicate sheets out of print.

Terminological schemes used on 1:50 000 geological maps in Scotland.

Sheet name	Sheet No.	Date	Scheme used	Notes
Iona	S43	1954	ST	Minor name revision
Staffa (P)	S43N	1996	ST	Minor name revision
Ross of Mull	S43S	1999	ST	Minor name revision
Eastern Mull	S44W/ pt.44E	1992	ST	Reprinted without revision
Lismore	S44E	1992	ST	Reprinted without revision
Ardnamurchan	S52W	1977	ST	Minor name revision
Strontian	S52E	1977	ST	Minor name revision
Rum	S60	1994	ST	Minor name revision
Minginish	S70	2001	ST	Minor name revision
Minginish	S70	1964	ST	Minor name revision
Broadford	S71W	1976	ST	Minor name revision

Terminological schemes used on 1:50 000 geological maps in England.

Sheet name	Sheet No.	Date	Scheme used	Notes
Pickering (P)	53	2001	EWRNP	Minor revision required
Scarborough (P)	54	1998	EWRNP	Minor revision required
Flamborough &	55/65	1986	EWRNP	Minor revision required
Bridlington (P)	63	1983	EWT	In PDG programme
York
Great Driffield (P)	64	1993	EWRNP	Minor revision required
Selby	71	1973	EWT	In PDG programme
Beverley (P)	72	1995	EWRNP	Minor revision required
Hornsea (P)	73	1998	EWRNP	Minor revision required
Kingston upon Hull	80	1983	EWRNP	Minor revision required
Patrington	81/82 pt 90	1991	EWRNP	Minor revision required
Brigg	89	1982	EWRNP	Minor revision required
Grimsby	90/91	1990	EWRNP	Minor revision required
Louth (P)	103	1999	EWRNP	Minor revision required
Mablethorpe (P)	104	1996	EWRNP	Minor revision required
Horncastle (P)	115	1995	EWRNP	Minor revision required
Skegness (P)	116	1996	EWRNP	Minor revision required
The Wash	129	1997	EWT	Revision required
Wells-next-the-Sea	130	OOP	EWT	In PDG programme
Cromer	131	2003	EWFCSP	Compliant to formation
Mundelsey & Walsham	132 & 148	1998	EWT concealed	Nomenclature revision
King’s Lynn & The Wash	145/pt 129	1978	EWT	Nomenclature revision required
Fakenham (P)	146	1999	EWRSP	Minor revision required
Aylesham	147	OOP	EWT	In PDG programme
Wisbech	159	1995	EWT	Nomenclature revision required
Swaffham (P)	160	1998	EWRSP	Minor revision required
Norwich	161	1975	EWT	Nomenclature revision required. In PDG programme
Great Yarmouth	162	1990	EWT concealed	Nomenclature revision required
Ely	173	1980	EWT	Nomenclature revision required
Thetford	174	OOP	EWT	In PDG programme
Diss	175	1989	EWT	Nomenclature revision required
Lowestoft	176	1996	EWFCSP concealed	Compliant at group level
Huntingdon	187	1975	EWT	Nomenclature revision required
Cambridge	188	1981	EWT	Nomenclature revision required
Bury St Edmunds	189	1982	EWT	Nomenclature revision required
Eye (P)	190	1995	EWT	Nomenclature revision required
Saxmundham	191	1996	EWT concealed	Nomenclature revision required
Biggleswade	204	2001	EWRSP	Minor revision required
Saffron Walden	205	2002	EWRSP	Minor revision required
Sudbury	206	1991	EWT	Nomenclature revision required
Ipswich (P)	207	1990	EWT concealed	In PDG programme (2010)
Woodbridge & Felixstowe	208 & 225	2001	EWSP	Minor revision required
Leighton Buzzard	220	1992	EWT	Nomenclature revision required
Hitchin	221	1995	EWT	Nomenclature revision required
Great Dunmow	222	1990	EWT	Minor revision required
Braintree	223	1982	EWT concealed	Minor revision required
Colchester	224	OOP	EWT concealed	Minor revision required
Thame	237	1994	EWT	Nomenclature revision required
Aylesbury	238	1923	EWT	Nomenclature revision required. In PDG programme
Hertford	239	1978	EWT	Nomenclature revision required. In PDG programme
Epping	240	1981	EWT concealed	Nomenclature revision required
Chelmsford	241	1975	EWT concealed	Nomenclature revision required
Swindon	252	1974	EWT	Nomenclature revision required
Abingdon	253	1971	EWT	Nomenclature revision required
Henley-on-Thames	254	1980	EWT	Nomenclature revision required
Beaconsfield	255	2005	EWFCSP	New sheet
North London	256	1994	EWT	Nomenclature revision required
Romford	257	1996	EWT concealed	Nomenclature revision required
Southend & Foulness	258/259	1976	EWT concealed	Nomenclature revision required
Marlborough	266	1974	EWT	Nomenclature revision required. In PDG programme
Newbury (Hungerford)	267	1947*	EWT	Nomenclature revision required. *New sheet in press 2005 (EWFCSP)
Reading	268	2000	EWRSP	Minor revision required
Windsor	269	1999	EWRSP	Nomenclature revision required
South London	270	1998	EWT	Nomenclature revision required
Dartford	271	1998	EWRSP	Minor revision required
Chatham	272	1977	EWT	Nomenclature revision required. In PDG programme (2008)
Faversham	273	1974	EWT	Nomenclature revision required. In PDG programme (2010)
Ramsgate	274	1980	EWT	Nomenclature revision required
Frome	281	2001	EWRSP	Minor revision required
Devizes	282	1959	EWT	Nomenclature revision required. In PDG programme (2005)
Andover	283	1975	EWT	Nomenclature revision required. In PDG programme (2007)
Basingstoke	284	1978	EWT	Nomenclature revision required. In PDG programme (2008)
Guildford	285	2001	EWRSP	minor revision required
Reigate	286	1978*	EWT	*New sheet in press, minor revision
Sevenoaks	287	1971	EWT	In PDG programme
Maidstone	288	1976	EWT	Nomenclature revision required
Canterbury	289	1982	EWT	Nomenclature revision required
Dover	290	1977	EWT	Nomenclature revision required
Wincanton	297	1996	EWRSP	Minor revision required
Salisbury	298	2005	EWFCSP	New sheet
Winchester	299	2002	EWFCSP	New sheet
Alresford	300	2000	EWRSP	Minor revision required
Sheet name	Sheet No.	Date	Scheme used	Notes
Folkestone & Dover	305 &306	1974	EWT	Nomenclature revision required
Wellington	311	1976	EWT	Nomenclature revision required. In PDG programme
Yeovil	312	1958	EWT	Nomenclature revision required
Shaftsbury	313	1994	EWRSP	Minor revision required
Ringwood	314	2004	EWFCSP	New sheet
Southampton	315	1987	EWT	Nomenclature revision required
Fareham	316	1998	EWRSP	Minor revision required
Chichester & Bognor	317 & 332	1996	EWRSP	Minor revision required
Brighton & Worthing	318 & 333	1984*	EWT	*New sheet in press 2005 (EWFCSP)
Lewes/Eastbourne	319/334	1979*	EWT	*New sheet in press 2005/6 (EWFCSP)
Sidmouth	326 & 340	2005	EWFCSP	New sheet
Bridport	327	1977	EWT	Nomenclature revision required. In PDG programme
Dorchester	328	2001	EWRSP	Minor revision required
Bournemouth	329	1991	EWT	Nomenclature revision required
Lymington	330	1975	EWT	Nomenclature revision required. In PDG programme (2009)
Portsmouth	331	1994	EWT	Nomenclature revision required
West Fleet	Pts. 341	2001	EWRSP	Minor revision required
and Weymouth	& 342
Swanage	pts 342	2000	EWFCSP	Minor revision required
	& 343
Isle of Wight	Pts. 330,	1976	EWT	Nomenclature revision required.
	331, 344,			In PDG programme (2010)
	& 345

It should be noted that the BGSs hold all of its 1:50 000 scale geological linework in digital fully attributed format within a dataset called DigMapGB-50. Version 1 was launched in 2002 and had anticipated some nomenclature changes within sheet areas that were being revised prior to that date. Version 2 has been released recently and incorporates many revisions to the Chalk nomenclature and linework. This data will be incorporated into the printed dataset, as new editions, when individual sheets come up for reprinting.

The BGS is also compiling a 1:10 000 scale dataset, DigMapGB-10. At present coverage is restricted to those areas where newly acquired geological linework (since the mid 1990s) is available. This includes a considerable part of the Chalk outcrop particularly in Southern England. The dataset is expanding rapidly as new areas are mapped and where the BGS is commissioned to digitise its historical map dataset held at various scales and projections.

Appendix 2 — Nomenclature terms used on published 1:50 000 scale BGS geological sheets in England and Scotland (S)

This table incorporates all of the terms used to describe and divide the Upper Cretaceous successions shown on the published 1:50 000 scale maps currently available (listed by number). The terms that are recommended for use in the framework described in this report are given in bold.

Redundant terms in normal type have been given an equivalent term within the framework, where such a term is discernible and meaningful. It is recommended that these replacement terms are used when maps come up for revision.

Terms used on BGS 1:50 000 geological maps in England and Scotland (S).

Term used	50K sheet number (s) on which term appears	Equivalent term in framework
Blandford Chalk	313	Seaford Chalk and Newhaven Chalk formations undivided
Brandon Flint Series	175	Bed or member as yet undefined within the Lewes Nodular Chalk Formation
Burnham Chalk	55 & 65, 80, 81 & 82 and pt 90, 89, 90 & 91	Burnham Chalk Formation
Burnham Formation	73, 103	Burnham Chalk Formation
Cambridge Greensand	173, 175, 187, 188, 189, 204, 205, 206, 221	Cambridge Greensand Member Equivalent to the Melbury Sandstone Member and the Glauconitic Marl Member
Cenomanian Greensand	S52E, S52E, S43, S44	Morvern Greensand Formation
Chalk	208 & 225, 256, 331	Chalk Group
Chalk (Flamborough, Burnham and Welton Chalks), undifferentiated	104	The major part of the White Chalk Subgroup
Chalk Group	257, 268, 269, 281, 297, 299, 300, 313, 316, 317 & 332, 328, 341 & 342, 343 & 342	Chalk Group defined within the Northern and Southern provinces in England
Chalk Group, undivided	176	Chalk Group defined within the Northern and Southern provinces in England
Chalk Marl	187, 267, 283, 284	Part of the Grey Chalk Subgroup. All of the West Melbury Marly Chalk Formation and the lower part of the Zig Zag Chalk Formation
Chalk Rock	175, 188, 189, 204, 205, 206, 220, 221, 237, 238, 239, 253, 254, 267, 282, 283, 312, 327, 331	Chalk Rock Member, part of the Lewes Nodular Chalk Formation
Chalk with flints (Middle Chalk)	63	Equivalent to part of the Welton Chalk Formation and Burnham Chalk Formation
Chalk without flints (Lower Chalk)	63	Equivalent to the Ferriby Chalk Formation and the lowest part of the Welton Chalk Formation
Chilton Stone	253	Equivalent to the Totternhoe Stone Member of the Zig Zag Chalk Formation
Culver Chalk Formation	299, 314, 343 & 342	Culver Chalk Formation. Includes the Tarrant Chalk Member and the Spetisbury Chalk Member where these are discernible
Ferriby Chalk	55 & 65, 80, 81 & 82 pt 90, 89, 90 & 91, 104,116	Ferriby Chalk Formation
Ferriby Chalk Formation	54, 64, 72, 115	Ferriby Chalk Formation
Ferriby Formation	73, 103	Ferriby Chalk Formation
Flamborough Chalk	55 & 65, 80, 81 & 82 pt 90, 90 & 91	Flamborough Chalk Formation
Flamborough Chalk Formation	54, 64, 72	Flamborough Chalk Formation
Flamborough Formation	73	Flamborough Chalk Formation
Glauconitic Marl	237, 254, 289, 299, 300, 316, 317 & 332	Glauconitic Marl Member of the West Melbury Marly Chalk Formation
Glauconitic sandstone (= Greensand)	S43N, S43S	Morvern Greensand Formation
Grey Chalk Subgroup	299, 314	Grey Chalk Subgroup. Includes the Zig Zag Chalk Formation and the West Melbury Marly Chalk Formation in the Southern Province; is equivalent to the Ferriby Chalk Formation in the Northern Province
Hard Bed	328	Informally named part of the
Holywell Chalk	271, 313	Newhaven Chalk Formation
		Holywell Nodular Chalk Formation, originally excluded the Plenus Marls Member
Holywell Nodular Chalk	297, 300, 316, 317 & 332	Holywell Nodular Chalk Formation, originally excluded the Plenus Marls Member
Holywell Nodular Chalk Formation	204, 205, 281, 299, 314, 328, 341 & 342, 343 & 342	Holywell Nodular Chalk Formation. Includes the Plenus Marls Member and the Melbourn Rock Member
Horizon of Chalk Rock	284, 286	Chalk Rock Member, part of the Lewes Nodular Chalk Formation
Hunstanton Chalk Formation	64, 72	Hunstanton Formation no longer part of the Chalk Group
Hunstanton Formation	54	Hunstanton Formation no longer part of the Chalk Group
Hunstanton Member	73,103	Hunstanton Formation no longer part of the Chalk Group
Laig Gorge Limestone	S60	Informal term for a bed within the Laig Gorge Sandstone Member equivalent in age to the Lochaline White Sandstone Formation
Lewes Chalk	271,313	Lewes Nodular Chalk Formation
Lewes Nodular Chalk	297	Lewes Nodular Chalk Formation
Lewes Nodular Chalk and Seaford Chalk Members, undifferentiated	205	Undivided Lewes Nodular Chalk and Seaford Chalk formations
Lewes Nodular Chalk Formation	204, 299, 314, 343 & 342	Lewes Nodular Chalk Formation. Includes the Chalk Rock Member
Lewes Nodular Chalk Member	268, 281, 300, 316, 317 & 332, 328, 341 & 342	Lewes Nodular Chalk Formation
Loch Aline Glass Sand (Loch Aline)	S44W pt 44E, S44E	Lochaline White Sandstone Formation
Lower Beds (Chalk Marl)	188	Equivalent to the West Melbury
Marly Chalk Formation		Equivalent to the Grey Chalk
Lower Chalk	53, 129, 132 & 148, 145 & pt 129, 159, 161, 162, 173, 175, 187, 188, 189, 190, 206, 207, 220, 221, 222, 237, 238, 239, 240, 252, 253, 254, 257, 266, 267, 268, 269, 270, 271, 272, 273, 274, 282, 283, 284, 286, 287, 288, 289, 290, 297, 300, 305 & 306, 311, 312, 313, 315, 316, 317 & 332, 318 & 333, 319, 327, 329, 330, 331, 334	Subgroup (West Melbury Marly Chalk Formation and Zig Zag Formation) with the inclusion of the Plenus Marls Member of the succeeding Holywell Nodular Chalk Formation
Lower Chalk (grey chalk)	284	Equivalent to the Grey Chalk Subgroup with the inclusion of the Plenus Marls Member of the succeeding Holywell Nodular Chalk Formation
Lower Chalk Formation	146, 160, 204, 205, 281, 328, 341 & 342	Equivalent to the Grey Chalk Subgroup with the inclusion of the Plenus Marls Member of the succeeding Holywell Nodular Chalk Formation
Lower Chalk without flint	71, 327	Equivalent to the Ferriby Chalk Formation and the lowest part of the Welton Chalk Formation on 71. Equivalent to the Grey Chalk Subgroup with the inclusion of the Plenus Marls Member on 327
Melbourn Rock	129, 145 & pt 129, 175, 188, 189, 204, 205, 206, 220, 221, 237, 238, 252, 253, 254, 267, 282, 283, 284, 285, 286, 287, 288, 289, 305 & 306, 312, 318 & 333, 319, 331, 334	Melbourn Rock Member of the Holywell Nodular Chalk Formation
Melbourn Rock Member	299, 314	Melbourn Rock Member of the Holywell Nodular Chalk Formation
Melbourne Rock	272, 273	Melbourn Rock Member of the Holywell Nodular Chalk Formation
Melbury Sandstone	297, 313	Melbury Sandstone Member of the West Melbury Marly Chalk Formation. Equivalent to the Glauconitic Marl Member. Initially attributed to the Upper Greensand Formation
Melbury Sandstone Member	281	Melbury Sandstone Member of the West Melbury Marly Chalk Formation. Equivalent to the Glauconitic Marl Member. Initially attributed to the Upper Greensand Formation
Middle Chalk	129, 132 & 148, 145 & 129 161, 162, 175, 188, 189, 190, 206, 207, 221, 222, 223, 237, 238, 239, 240, 252, 253, 254, 257, 266, 267, 268, 269, 270, 271, 272, 273, 274, 282, 283, 284, 285, 286, 287, 288, 289, 290, 297, 300, 305 & 306, 311, 312, 313, 315, 316, 317 & 332, 327, 329, 330, 331	Equivalent to the lowest part of the Lewes Nodular Chalk Formation, the New Pit Chalk Formation and the Holywell Nodular Chalk Formation(with the exclusion of the Plenus Marls Member)
Middle Chalk and Lower Chalk	Isle of Wight pts 330, 331, 344, 345	Basal Lewes Nodular Chalk Formation to the base of the Chalk Group
Middle Chalk Formation	146, 160, 204, 205, 281, 328, 341 & 342	Equivalent to the New Pit Chalk Formation and the Holywell Chalk Formation with the exclusion of the Plenus Marls Member
Middle Chalk with flint	71	Lower Burnham Chalk Formation and most of the Welton Chalk Formation
Morvern Greensand	S44W pt 44E, S44E	Morvern Greensand Formation
Morvern Greensand Formation	S70	Morvern Greensand Formation
New Pit Chalk	271, 297, 313	New Pit Chalk Formation
New Pit Chalk Member	204, 205, 281, 300, 316, 317 & 332, 328, 341 & 342	New Pit Chalk Formation
New Pit Chalk Formation	299, 314	New Pit Chalk Formation
Newhaven Chalk Formation	299, 314, 343 & 342	Newhaven Chalk Formation
Newhaven Chalk Member	316, 317 & 332, 328, 341 & 342	Newhaven Chalk Formation
Plenus Marl	273	Plenus Marls Member of the Holywell Nodular Chalk Formation
Portsdown Chalk Formation	299, 314, 343 & 342	Portsdown Chalk Formation
Portsdown Chalk Member	316, 317 & 332, 328, 341 & 342	Portsdown Chalk Formation
Red Chalk	53, 55 & 65, 63, 71, 80, 81 & 82 pt 90, 89, 90 & 91, 115, 129, 145 & pt 129, 146	Hunstanton Formation
Red Chalk (Hunstanton Member)	104, 116	Hunstanton Formation
Rowe Formation	73	Rowe Chalk Formation
Sandstone and limestone with flint	S44
Seaford and Newhaven (undivided)	328, 341 & 342, 343 & 342	Seaford Chalk Formation and Newhaven Chalk Formation
Seaford and Newhaven Chalk, undivided		undivided
Seaford Chalk	297	Seaford Chalk Formation
Seaford Chalk Formation	299, 314, 343 & 342	Seaford Chalk Formation
Seaford Chalk Member	281, 300, 316, 317 & 332, 328, 341 & 342	Seaford Chalk Formation
Seaford to Spetisbury, undivided	343 & 342	Seaford Chalk, Newhaven Chalk and Culver Chalk formations undivided
Siliceous and glauconitic sandstone	S52W, S52E	Morvern Greensand Formation
Silicified Chalk	S43	Gribun Chalk Formation
Silicified Chalk (= Gribun Chalk)	S43N	Gribun Chalk Formation
Silicified limestone with flint (Torosay)	S44W & pt 44E, S44E	Gribun Chalk Formation
Spetisbury Chalk	313	Spetisbury Chalk Member
Spetisbury Chalk Member	299, 314, 316, 317 & 332, 328, 341 & 342, 343 & 342	Spetisbury Chalk Member of the Culver Chalk Formation
Stockbridge Rock Member	299	Stockbridge Rock Member of the Seaford Chalk Formation
Tarrant and Spetisbury Chalk (undivided)	328	Culver Chalk Formation
Tarrant Chalk	313	Tarrant Chalk Member
Tarrant Chalk Member	299, 300, 314, 316, 317 & 332, 328, 341 & 342, 343 & 342	Tarrant Chalk Member of the Culver Chalk Formation
Top Rock	204, 206, 220, 221	Top Rock Bed within the Lewes Nodular Chalk Formation
Totternhoe Stone	145 & 129, 173, 175, 188, 189, 204, 205, 206, 220, 221, 237, 254	Totternhoe Stone Member at the base of the Zig Zag Chalk Formation
Uintacrinus Band	273	Bed within the Newhaven Chalk Formation (Margate Chalk Member)
Upper and Middle Chalk	241	White Chalk Subgroup excluding the Plenus Marls Member
Upper and Middle Chalk, undivided	318 & 333, 319, 334	White Chalk Subgroup excluding the Plenus Marls Member
Upper Beds	188	Part of the Zig Zag Chalk Formation
Upper Chalk	132&148, 161, 162, 175, 188,189, 190, 191, 206, 207, 220, 221, 222, 223, 237, 238, 239, 240, 253, 254, 257, 266, 267, 268, 269, 270, 271, 272, 273, 274, 282, 283, 284, 285, 286, 287, 288, 289, 290, 297, 300, 305 & 306, 311, 312,313, 315, 316, 317 & 332, 327, 329, 330, 331, IoW pts 330 331 344 345	Equivalent to most of the Lewes Nodular Chalk Formation (from the base of the Chalk Rock Member) and the succeeding formations up to the pre-Palaeogene unconformity. Term includes the highest chalks in East Anglia
Upper Chalk Formation	146, 160, 204, 205, 281, 328, 341 & 242	Equivalent to the Lewes Nodular Chalk Formation and the succeeding formations up to the pre-Palaeogene unconformity.
Upper Chalk with flint	71	Equated with the Burnham Chalk Formation
Upper Cretaceous limestone	S71W	Inner Hebrides Group and sandstone
Upper Cretaceous undivided	S43N	Inner Hebrides Group
Welton Chalk	55 & 65,80, 81 & 82 pt 90, 89, 90 & 91,116	Welton Chalk Formation
Welton Chalk Formation	115	Welton Chalk Formation
Welton Chalk and Burnham Chalk Formations, undiv	54, 64, 72
Welton Formation	73, 103	Welton Chalk Formation
West Melbury Chalk	313	West Melbury Marly Chalk Formation
West Melbury Marly Chalk	297	West Melbury Marly Chalk Formation
West Melbury Marly Chalk Member	204, 205, 281, 300, 316, 317 & 332, 328	West Melbury Marly Chalk Formation
West Melbury Marly Chalk Formation	299, 313	West Melbury Marly Chalk Formation. Includes the Melbury Sandstone Member, the Glauconitic Marl Member and the Cambridge Greensand Member as its basal unit.
White Chalk Subgroup	299, 314, 343 & 342	White Chalk Subgroup. Includes the Lewes Nodular Chalk Formation and formations above in the Southern Province; the Welton Chalk Formation and formations above in the Northern Province
White Sandstone	S43	Lochaline White Sandstone Formation
White Sandstone (=Loch Aline Glass Sand)	S43N	Lochaline White Sandstone Formation
Zig Zag Chalk	297, 313	Zig Zag Chalk Formation
Zig Zag Chalk Member	204, 205, 281, 300, 316, 317 & 332, 328, 341 & 342, 343 & 342	Zig Zag Chalk Formation
Zig Zag Chalk Formation	299, 313	Zig Zag Chalk Formation. Includes the Totternhoe Stone Member and Cast Bed as its basal unit.

Appendix 3 — Redundant terms on BGS maps and other schemes used in the Southern Province

There are a number of entries that appear in the BGS Lexicon and within commonly quoted references that need to be understood in terms of the lithostratigraphic framework presented herein. Lexicon style entries are given for terms that have appeared on BGS maps but are now considered to be redundant. A further set of terms from four of the principal references concerned with the definition of the Chalk are also given.

The following entries cover terms utilised on BGS maps and, mostly, those that appear in the Lexicon. For the most part these are now redundant terms and frequently poorly defined with respect to formal lithostratigraphies or unit status. Their closest equivalent term in the new Chalk Stratigraphy is given if possible. They are shown in alphabetical order.

A3.1 Blandford Chalk Member

Name: The term Blandford Chalk Member was used by Bristow et al. (1995) to describe the succession between the Lewes Nodular Chalk and Tarrant Chalk of the Shaftsbury area where they could not distinguish the Seaford Chalk and Newhaven Chalk members.

Type section: General area around Blandford Forum, Dorset.

Primary reference section: Old railway cutting on the military sidings, Blandford, (see Bristow, et al., 1995).

Formal subdivision: None but now regarded as the Seaford and Newhaven Chalk formations undivided.

Lithology: Firm, smooth, white flinty chalk; some thin marl seams present.

Definition of upper boundary: Conformable at the incoming of soft to firm smooth white chalk with conspicuous large flint seams and including the fauna indicative of the quadrata zone.

Definition of lower boundary: Conformable at the change from hard nodular chalk, to firm smooth chalk.

Thickness: Between 75 to 90 m in the Shaftsbury area.

Distribution: Confined to the Shaftsbury Geological Sheet 313 area.

Previous names: None but would now be considered to be an amalgamation of the Seaford Chalk Formation and the Newhaven Chalk Formation undivided. Term is redundant except for its use on the Shaftsbury sheet area.

Parent: White Chalk Subgroup.

Age and biostratigraphy: Upper Cretaceous, Coniacian, Santonian and basal Campanian. Micraster coranguinum to Offaster pilula zones.

References: Barton, 1991; Bristow et al., 1995; Gaster, 1944; Bristow, 1990a; Mortimore, 1986.

A3.2 Brandon Flint Series

Name: First called the Horizon of the Brandon Flint Series in Hewitt (1935) and used as the Brandon Flint Series in the Bury St Edmunds memoir (Bristow, 1990b).

Type section: Named after Grimes Graves flint mines near Brandon.

Primary reference section: Skertchly (1879) refers to pits at Lingheath (Brandon Park), Santon Downham, Broomhill, Icklingham and Elvedon.

Formal subdivision: None but divided into a number named flint and marl beds.

Lithology: Massive bedded chalks with marl seams and tabular and nodular flints.

Definition of upper boundary: Conformable below the hard yellow nodular chalk of the Chalk Rock.

Definition of lower boundary: Conformable, below the lowest major flint seam (the Rough and Smooth Blacks), which occur below the Grimes Graves Marl. A position that is regarded as marking the base of the plana zone.

Thickness: Between 12 and 15 m at Lingheath (Skertchly, 1879; Bristow, 1990b).

Distribution: Central East Anglia around Bury St. Edmunds within the Transitional Province. Its extent is not mapped.

Previous names: Brandon Flints

Parent: Lewes Nodular Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Turonian. Sternotaxis plana (now Plesiocorys plana) zone.

References: Skertchly, 1879; Hewitt, 1935; Bristow, 1990b.

A3.3 Chalk Marl

Name: Informal term as part of the terminology for used in the traditional scheme as exemplified in Jukes-Browne and Hill (1903) but in existence prior to that date.

Type section: Folkestone in Kent, Compton Bay on the Isle of Wight.

Primary reference section: See above

Formal subdivision: None but contains some informally named units.

Lithology: Rhythmically bedded marly chalk (argillaceous limestone) and marl (silty calcareous mudstone) with no flint.

Definition of upper boundary: Disconformable beneath the erosion surface at the base of the Totternhoe Stone (see also Chilton Stone) of the Transitional Province as defined by Jukes-Browne and Hill (1903) and its lateral equivalent of the ‘Cast Bed’ of the Southern Province.

Definition of lower boundary: Conformable at an indistinct horizon at the contact between the ‘Chloritic’ Marl (Glauconitic Marl) and the Chalk Marl as defined in Jukes-Browne and Hill (1903). In modern usage this would equate to the top of the Glauconitic Marl Member (Southern Province) or the Cambridge Greensand Member (Transitional Province).

Thickness: Generally in the range 15 to 40 m throughout the Southern and Transitional Provinces. Becomes thin or absent in basin margin situations such as the mid-Dorset Swell and in Devon.

Distribution: The term was used widely within the Southern and Transitional provinces to denote the lower part of the Lower Chalk.

Previous names: Longstanding term from the Traditional scheme of Chalk nomenclature, Lower Chalk (Chalk Marl), also referred to as the Lower Beds (Chalk Marl) on the Cambridge Sheet (188). The unit is approximately equivalent to the West Melbury Marl Chalk Formation and the basal Zig Zag Chalk Formation but with important differences as to the definition of its lower and upper boundaries.

Parent: Not definable in new terminology; forms part of the Lower Chalk of the traditional scheme.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Mantelliceras mantelli to Acanthoceras rhotomagense zones.

References: Jukes-Browne and Hill (1903), for its usage by the Geological Survey, but the term had been in existence for some considerable time prior to that publication in both Survey publications and in journals.

A3.4 Chilton Stone

Name: First used by Jukes-Browne (1889) to denote a bed that was equated to the Totternhoe Stone of the Chilterns.

Type section: Railway cutting east of Chilton, Oxfordshire.

Primary reference section: As above

Formal subdivision: None

Lithology: Brownish grey limestone. Rough to the touch (‘gritty’) with many phosphatic nodules.

Definition of upper boundary: Commonly indistinct conformable boundary within the Zig Zag Chalk Formation (Lower Chalk, Grey Chalk unit). Upward reversion to softer, finer grained more typical chalk or marly chalk. May be difficult to locate, even in sections.

Definition of lower boundary: Commonly indistinct conformable boundary with the underlying West Melbury Marly Chalk Formation (Lower Chalk, Chalk Marl unit) but there may be an erosion surface with a concentration of phosphatic pebbles in its base. May be difficult to locate, even in sections.

Thickness: Some 0.6 m at its type site in the cutting east of Chilton on the Didcot to Newbury railway line.

Distribution: Limited to a small area of Berkshire.

Previous names: Equivalent to the Totternhoe Stone of the Chilterns and regarded as the most south-westerly outcrop of that unit.

Parent: Zig Zag Chalk Formation.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Acanthoceras rhotomagense Zone.

References: Jukes-Browne, 1889; Jukes-Browne and Hill, 1889.

A3.5 Lower Chalk

Name: The term is used for the lowest part of the traditional tripartite scheme of the Chalk (Jukes-Browne and Hill, 1903) and as used is equivalent to a formation.

Type section: In the Chiltern Hills. It was this area utilised to define the Lower Chalk in much of the early literature (Hill and Jukes-Browne, 1886; Jukes-Browne and Hill, 1903).

Primary reference section: Compton Bay, Isle of White Beachy Head to Eastbourne in Sussex Folkestone towards Dover in Kent.

Formal subdivision: Divided into the Glauconitic Marl, Chalk Marl, Totternhoe Stone (where present), Grey Chalk, ‘White Bed’ and Plenus Marls in the traditional scheme.

Lithology: A grey marly chalk with marl content decreasing upwards. No flint. Comprises a thin basal bed of glauconitic marl (Glauconitic Marl, Melbury Sandstone or Cambridge Greensand) overlain by more typical Lower Chalk sequence that is usually divided into a lower ‘Chalk Marl’(see West Melbury Marly Chalk Formation entry) with rhythmic alternations of chalk and marl, and an upper ‘Grey Chalk’ (see Zig Zag Chalk Formation entry) separated by a distinctive hard band (Cast Bed or Totternhoe Stone). (See entries for Grey Chalk and White Chalk Subgroups).

Definition of upper boundary: Conformable at the top of the highest marl within the Plenus Marls Member. (Refer to entries for Zig Zag Chalk and Holywell Nodular Chalk Formations).

Definition of lower boundary: At an unconformity at the base of the Glauconitic Marl, Melbury Sandstone or Cambridge Greensand ‘members’ at the base of the West Melbury Marly Chalk Member (see reference to the Grey Chalk Subgroup and West Melbury Marly Chalk Formation).

Thickness: Between 45 and 100 m in the Southern and Transitional provinces. Thinner sequences known towards the margins of the Chalk basin and over synsedimentary highs.

Distribution: Throughout the Southern and Transitional provinces and prior to Wood and Smith (1978) used in the Northern Province.

Previous names: Lower Chalk, formerly applied throughout the Chalk outcrop in England but now only used to describe those chalks within the Southern and Transitional provinces beneath the Melbourn Rock in the traditional scheme. Has constituent parts of the Glauconitic Marl, Chalk Marl, Totternhoe Stone (where present), Grey Chalk, ‘White Bed’ and Plenus Marls. Its use is not recommended for descriptive purposes and should be replaced by the term Grey Chalk Subgroup (but see definition) or the constituent formations within the new scheme.

Lower Chalk (Grey Chalk).

Lower Chalk Formation as used in Bristow, Mortimore and Wood (1997) in an early version of the new Chalk stratigraphy, is the direct equivalent of the Lower Chalk of the traditional scheme.

Lower Chalk without flints as used on the Selby Sheet (71) and Chalk without flint as on the York Sheet (63). (Revision of these sheets will follow the Northern Province terminology). This term is also prevalent in the 19^th century literature where it can include the lower flint-free part of the traditional Middle Chalk depending on the author and the area within which the chalks are described.

Lower Beds (Chalk Marl, h5a1) and Upper Beds (h5a2) as utilised on the Cambridge Sheet (188) to denote those beds below and above the Totternhoe Stone.

Parent: Chalk Group.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Mantelliceras mantelli to Metoicoceras geslinianum zones.

References: Penning and Jukes-Browne, 1881; Rawson et al., 1978.

A3.6 Lower Chalk Formation

Name: This term was erected by Bristow, Mortimore and Wood (1997) to cover the interval of their West Melbury Marly Chalk Member and Zig Zag Chalk Member in recognition of the widespread use of the Lower Chalk in the traditional scheme. Its use is not recommended and is now redundant.

Type section: At the type sections of its constituent members.

Primary reference section: Compton Bay, Isle of White Beachy Head to Eastbourne in Sussex Folkestone towards Dover in Kent.

Formal subdivision: Divided into the West Melbury Marly Chalk Member and the Zig Zag Chalk Member.

Age and biostratigraphy: Upper Cretaceous, Cenomanian. Mantelliceras mantelli to Metoicoceras geslinianum zones.

Lithology: A grey marly chalk with marl content decreasing upwards. No flint. Comprises a thin basal bed of glauconitic marl (Glauconitic Marl, Melbury Sandstone or Cambridge Greensand) overlain by a more typical Lower Chalk sequence that is usually divided into a lower ‘Chalk Marl’ (see West Melbury Marly Chalk Formation entry) with rhythmic alternations of chalk and marl, and an upper ‘Grey Chalk’ (see Zig Zag Chalk Formation entry) separated by a distinctive hard band. (Cast Bed or Totternhoe Stone). (See entries for Grey Chalk and White Chalk subgroups).

Definition of upper boundary: Conformable at the top of the highest marl within the Plenus Marls Member. (Refer to entries for Grey Chalk Subgroup, White Chalk Subgroup, Zig Zag Chalk and Holywell Nodular Chalk Formations).

Definition of lower boundary: At an unconformity at the base of Glauconitic Marl, Melbury Sandstone or Cambridge Greensand ‘members’ at the base of the West Melbury Marly Chalk Member (see reference to Grey Chalk Subgroup and West Melbury Marly Chalk Formation).

Thickness: From 45 to 100 m in the Southern and Transitional provinces. Thinner sequences known towards the margins of the Chalk basin and over synsedimentary highs.

Distribution: Throughout the Southern and Transitional provinces.

Previous names: Lower Chalk of the traditional scheme.

Chalk without flints used on the York Sheet (63) and Lower Chalk (without flints) used on the Selby Sheet (71). Sheet due for revision when the newer Yorkshire/Lincolnshire terminology will be applied (Hunstanton and Ferriby Chalk formations). This term is also prevalent in the 19^th century literature where it can include the lower flint-free part of the traditional Middle Chalk depending on the author and the area within which the chalks are described.

Lower Chalk (Grey Chalk).

Parent: Chalk Group

Age and biostratigraphy: Upper Cretaceous Cenomanian. Mantelliceras mantelli to Metoicoceras geslinianum zones

References: Bristow, Mortimore and Wood, 1997; Rawson et al., 1978.

A3.7 Middle Chalk

Name: The term is used for the middle part of the traditional tripartite scheme of the Chalk (Jukes-Browne and Hill, 1903) and as used is equivalent to a formation.

Type section: Chiltern area used to define the Lower Chalk in much of the early literature (Hill and Jukes-Browne, 1886).

Primary reference section: Compton Bay, Isle of White; Beachy Head to Eastbourne in Sussex; and Folkestone towards Dover in Kent.

Formal subdivisions: Included the Melbourn Rock as its basal unit.

Lithology: White pure chalk with some flint seams and very shelly beds. Comprises from its base: hard indurated chalk with flaser marls (Melbourn Rock) to exceptionally shelly chalk with flints into chalk with well defined marl seams.

Definition of upper boundary: Bedding plane beneath the Chalk Rock in the Chilterns (Transitional Province) and beneath the equivalent beds containing the ‘reussianum fauna’ elsewhere in the Southern Province.

Definition of lower boundary: Conformable at the base of Melbourn Rock above highest marl within Plenus Marls.

Thickness: Between 75 and 95 m in the Southern and Transitional provinces. Thinner sequences are known towards the margins of the Chalk basin and over synsedimentary highs.

Distribution: Throughout the Southern and Transitional provinces.

Previous names: Chalk with few flints.

Chalk with flints (Middle Chalk) on the York Sheet (63) and Middle Chalk with flint on the Selby Sheet (71). Sheets due for revision when the newer Yorkshire/Lincolnshire terminology will be applied (Hunstanton and Ferriby Chalk formations). This term is also prevalent in the 19^th century literature where it can include the lower flint-free part of the traditional Middle Chalk depending on the author and the area within which the chalks are described.

Parent: Chalk Group.

Age and biostratigraphy: Upper Cretaceous Cenomanian and Turonian. Neocardioceras juddii to Terebratulina lata zones.

Reference

Penning and Jukes-Browne, 1881.

A3.8 Middle Chalk Formation

Name: This term was erected by Bristow, Mortimore and Wood (1997) to cover the interval of their Holywell Nodular Chalk Member and New Pit Chalk Member in recognition of the widespread use of the Middle Chalk in the traditional scheme. Its use is not recommended and is now redundant.

Type section: At the type sections of its constituent members.

Primary reference section: Compton Bay, Isle of White; Beachy Head to Eastbourne in Sussex; and Folkestone towards Dover in Kent.

Formal subdivision: Includes the Melbourn Rock as its basal unit.

Lithology: White pure chalk with some flint seams and very shelly beds. Comprises from base: hard indurated chalk with flaser marls (Melbourn Rock) to exceptionally shelly chalk with flints into chalk with well defined marl seams. The Holywell Nodular Chalk Member and New Pit Chalk Member are its constituent parts.

Definition of upper boundary: Coincident with the base of the Lewes Nodular Chalk Member. Conformable at the incoming of nodular chalk and regular flint seams.

Definition of lower boundary: Conformable at the base of the Melbourn Rock.

Thickness: From 75 to 95 m in the Southern and Transitional provinces. Thinner sequences known towards the margins of the Chalk basin and over synsedimentary highs.

Distribution: Throughout the Southern and Transitional provinces.

Previous names: Middle Chalk of the traditional scheme. Chalk with few flints. Chalk with flints (Middle Chalk) on the York Sheet 63 and Middle Chalk with flints on the Selby Sheet 71. Sheets due for revision when the newer Yorkshire/ Lincolnshire terminology will be applied. This term is also prevalent in the 19^th century literature.

Parent: Chalk Group

Age and biostratigraphy: Upper Cretaceous Cenomanian and Turonian. Neocardioceras juddii to Terebratulina lata zones.

References: Bristow, Mortimore and Wood, 1997; Rawson et al., 1978.

A3.9 Red Chalk

Name: The term Red Chalk is of great antiquity being used since the middle of the 19^th century. It has been used generally subsequently often including Hunstanton in its title. Now redefined as the Hunstanton Formation.

Type section: Hunstanton Cliff [TF 6725 4130] to [TF 6786 4238], north Norfolk (Owen, 1995; Gallois, 1994).

Primary reference section: South Ferriby Quarry [SE 9915 2045], Lincolnshire (Gaunt et al., 1992).

Formal subdivision: None

Lithology: Rubbly to massive chalks with marl bands; typically pink to brick-red in colour (due to disseminated hematite), but locally upper part grey due to secondary alteration of the iron minerals. Commonly sandy, particularly in lower part.

Definition of upper boundary: Erosion surface, locally developed as a hardground, overlain by nodular chalk (lowest Cenomanian) of Paradoxica (or Sponge) Bed or (in Cleveland Basin) Crowe’s Shoot Member (Mitchell, 1995); this horizon (the base of the Lower Chalk in Norfolk, or elsewhere of the Ferriby Formation) may or may not correspond with the upper limit of red chalks.

Definition of lower boundary: Sharp or [apparently] gradational boundary of marly chalks with ferruginous sandstones of Carstone Formation in the Transitional Province, Lincolnshire and Yorkshire or (in Cleveland Basin) with mudstone of Speeton Clay Formation; commonly marked by a line of phosphatic nodules (burrow-fills).

Thickness: About 1 m at type section in Norfolk, typically 3 m in Lincolnshire and south Yorkshire, thinning over Market Weighton High but expanding up to about 30 m in Cleveland Basin with about 24 m in cliffs at Speeton.

Distribution: North Norfolk, Lincolnshire and Yorkshire in the Northern Province.

Previous names: Red Chalk; Red Chalk Member as part of the Ferriby Formation as per Wood and Smith (1978); Red Chalk (Hunstanton Member) as above. Hunstanton Limestone; Hunstanton Red Rock; Hunstanton Chalk Formation; Hunstanton Red Chalk Formation (Owen, 1995); Hunstanton Chalk Member (Wood and Smith, 1978).

Parent: Not definable in the new terminology, as the Hunstanton Formation it is a stand-alone unit excluded from the Chalk Group. Part of the Ferriby Chalk Formation of Wood and Smith (1978).

Age and biostratigraphy: Lower Cretaceous, Albian.

References: Owen (1995), as modified herein (see entry for Hunstanton Chalk Formation).

A3.10 Uintacrinus Band

Name: A term used on the Faversham and Ramsgate geological sheets to denote a mappable boundary within the Upper Chalk.

Type section: Graves in St Peters churchyard [TR 3779 6862].

Primary reference section: Top of Cliff at Foreness Point (see Rasmussen, 1961).

Formal subdivision: None

Lithology: Soft white chalk with some flints.

Definition of upper boundary: At the incoming of the Offaster pilula index fossil.

Definition of lower boundary: At the incoming of the zonal index fossil.

Thickness: From 2 to 3 m at the top of the Zone of Marsupites testudinarius as originally defined in Kent.

Distribution: Confined to the Faversham and Ramsgate geological sheets.

Previous names: None

Parent: Newhaven Chalk Formation.

Age and biostratigraphy Upper Cretaceous, Campanian. Uintacrinus anglicus Zone.

Reference

Shephard-Thorn, 1988.

A3.11 Upper Chalk

Name: The term is used for the highest part of the traditional tripartite scheme of the Chalk (Jukes-Browne and Hill, 1903) and as used is equivalent to a formation.

Type section: Type areas of East Kent Cliffs, Sussex Cliffs, Isle of Wight and Dorset cliffs.

Primary reference section: See above

Formal subdivision: Includes the Chalk Rock as its basal unit.

Lithology: Generally soft white chalk with flints and marl seams throughout. Variation in the relative proportions of marl and flint seams indicative of major constituent units. Hard nodular chalks at base.

Definition of upper boundary: Unconformable and limited by the pre-Palaeogene erosion surface.

Definition of lower boundary: Conformable and placed at the base of the Chalk Rock in the Transitional Province and at the lowest nodular chalk containing the Hyphantoceras reussianum fauna in the Southern Province, or at the base of the ‘Basal Complex’ in East Kent. When used in the Northern Province the boundary is at a horizon marking the base of the Sternotaxis plana (now Plesiocorys plana) Zone.

Thickness: Variable depending on degree of post-Cretaceous erosion and the relative development of its constituent formations. Onshore the thickest development is within the Hampshire/Sussex area of the Southern Province, where up to about 470 to 515 m of strata are preserved; the most chronostratigraphically complete succession is in Norfolk but is thought there to be only some 350 m thick; within the Northern Province up to 500 m are preserved but the thickest succession is within the North Sea area where about 800 to 1100 m are preserved.

Distribution: Throughout the Southern and Transitional provinces.

Previous names: Upper Chalk with flint of BGS usage and is also prevalent in the 19^th century literature.

Substantially equivalent to the Upper Chalk Formation of Bristow, Mortimore and Wood (1997), and the White Chalk Subgroup of Rawson, Allen and Gale (2001).

Parent: Chalk Group.

Age and biostratigraphy: Upper Cretaceous, Turonian to Maastrichtian. Sternotaxis plana (now Plesiocorys plana) Zone to highest belemnite zones preserved.

Reference

Jukes-Browne and Hill, 1903, 1904.

A3.12 Upper Chalk Formation

Name: This term was erected by Bristow, Mortimore and Wood (1997) to cover the interval of their Lewes Nodular Chalk Member to the Portsdown Chalk Member in recognition of the widespread use of the Upper Chalk in the traditional scheme. It use is not recommended and is now redundant.

Type section: At the type sections of its constituent members.

Primary reference section: Compton Bay, Isle of White; Beachy Head to Eastbourne in Sussex and Folkestone towards Dover in Kent.

Formal subdivision: Includes the Lewes Nodular Chalk Member, Seaford Chalk Member, Newhaven Chalk Member, Tarrant Chalk Member, Spetisbury Chalk Member and Portsdown Chalk Member.

Definition of upper boundary: Unconformable and limited by the pre-Palaeogene erosion surface.

Definition of lower boundary: Conformable, coincident with the base of the Lewes Nodular Chalk Member (of Bristow, Mortimore and Wood, 1997) and the Lewes Nodular Chalk Formation (of Rawson, Allen and Gale, 2001). It is placed at the incoming of hard nodular chalks and regular well-developed flint seams. This horizon is known to be diachronous in the Southern and Transitional provinces.

Thickness: Variable depending on degree of post-Cretaceous erosion and the relative development of its constituent formations. Onshore the thickest development is within the Hampshire/Sussex area of the Southern Province, where up to about 470 to 515 m of strata are preserved; the most chronostratigraphically complete succession is in Norfolk but is thought there to be only some 350 m thick; within the Northern Province up to 500 m are preserved but the thickest succession is within the North Sea area where about 800 to 1100 m are preserved.

Distribution: Throughout the Southern and Transitional provinces.

Previous names: Upper Chalk. Upper Chalk with flints.

Parent: Chalk Group.

Age and biostratigraphy: Upper Cretaceous, Turonian to Maastrichtian. Terebratulina lata Zone to highest belemnite zones preserved.

References: Bristow, Mortimore and Wood, 1997; Rawson et al., 1978.

The following is a list of terms appearing in the major lithostratigraphical papers. They are terms that are infrequently utilised in BGS descriptive texts. An attempt has been made to give the relevant parent unit or approximate correlative term within the New Chalk Stratigraphy. For the most part these terms can be considered as being at member or bed level.

A3.13 Mortimore (1986)

This paper essentially deals with the beds attributable to the Middle and Upper Chalk of the Traditional Scheme for which he adopted the term the Sussex White Chalk Formation and which he further divided into six members. The units so described are designated from his study of the thicker ‘basinal’ chalk successions exposed on the coast and in large inland sites in the South Downs, the Hampshire/Wiltshire ‘Downs’ and the Isle of Wight. The Lower Chalk of the area was not considered in this paper. The essential elements of this study formed the basis for the mapping scheme whose development resulted in the presently accepted unified scheme (Rawson, Allen and Gale, 2001). It follows that many of the terms described below (i.e. formation, member and bed) would be considered at the next higher level in the unified scheme. Numerous marker flint, marl, hardground and other units at bed level are given codes in the BGS Lexicon for use in borehole coding. They are not defined further in the lexicon and reference should always be made to Mortimore (1986) for their understanding.

Sussex White Chalk Formation

Base is at the junction of the Melbourn Rock and the underlying Plenus Marls as traditionally defined, with the top of the formation limited beneath the sub-Palaeogene erosion surface. Essentially equivalent to the White Chalk Subgroup with the proviso that the Plenus Marls are excluded from the Sussex White Chalk Formation.

Ranscombe Chalk Member

The basal member of the Sussex White Chalk Formation whose lower boundary is coincident with the base of the Melbourn Rock. This unit covers the majority of the Middle Chalk of the traditional scheme and is equivalent to the Holywell Nodular Chalk Formation (excluding the Plenus Marls Member) and the New Pit Chalk Formation. Overlain by the Lewes Nodular and Flinty Chalk Member.

Melbourn Rock The basal unit of the Ranscombe Chalk Member and the Sussex White Chalk Formation. As defined is most closely equivalent to the traditional understanding of the Melbourn Rock of the Chilterns and Thames valley. Base placed at the Foyle Marl.

Holywell Beds As originally defined the beds are divided into Lower, Middle and Upper units whose bases are placed respectively at the Meads Marl 1, Gun Gardens Marl 1 and the Gun Gardens Main Marl. This was modified (Mortimore and Pomerol, 1996) with the Upper unit considered to be equivalent to the lowest part of the New Pit Chalk Member as defined in BGS mapping. With the Melbourn Rock, the Lower and Middle Holywell Beds are equivalent to the Holywell Chalk Member of Bristow, Mortimore and Wood (1997) and with the further addition of the Plenus Marls Member equivalent to the Holywell Nodular Chalk Formation of Rawson, Allen and Gale (2001).

New Pit Beds As originally defined the beds covered the interval from the Malling Street Marls to the Glynde Marl 1. This was modified (Mortimore and Pomerol, 1996) with the upper unit of the Holywell Beds considered to be equivalent to the lowest part of the New Pit Chalk Member, and the top of the Member being taken at the incoming of nodular chalks, as defined in BGS mapping (Bristow, Mortimore and Wood, 1997), which is invariably in the Glynde Marl 4 to Southerham Marl 1 interval. The New Pit Chalk Member so defined is the direct equivalent of the New Pit Chalk Formation of Rawson, Allen and Gale (2001).

Lewes Nodular and Flinty Chalk Member

As originally defined the member covered the interval between the Glynde Marl 1 and the uppermost of the Shoreham Marls including most of the nodular flinty chalks of Turonian and Coniacian age. The member includes an informal Lower and Upper part. This was modified in Mortimore and Pomerol (1996) with the Lower Lewes Nodular Chalk defined as the succession from the inception of nodularity (immediately above the Glynde Marl 4 in Sussex) to the Lewes Marl; and (presumably) the Upper Lewes Nodular Chalk from the Lewes Marl to the Shoreham Marl 2. In total this member has the same definition as the Lewes Nodular Chalk Member of Bristow, Mortimore and Wood (1997) and accords with the definition of the Lewes Nodular Chalk Formation of Rawson, Allen and Gale (2001) as applied to the basinal successions of the Southern Province. The inception of nodularity becomes younger northwards into the Transitional Province i.e. the base of the formation is diachronous up to approximately the level of the Ringmer/Kingston Beds.

Glynde Beds Basal marker is Glynde Marl 1. This interval contains the boundary between the New Pit Chalk and Lewes Nodular Chalk Formations of Rawson, Allen and Gale (2001) as defined in the Southern Province.
Caburn Beds Basal marker — Southerham Marl 1.
Ringmer Beds Basal marker — the Caburn Marl. In the Transitional Province the Caburn Marl is the lateral equivalent of the Reed Marl, which is beneath the inception of nodularity (the Chalk Rock Member) in the Reed Quarry. Known as the Bridgewick Beds (Mortimore, 1983).
Kingston Beds Basal marker — the Bridgewick Marl 1, includes the distinctive fauna of the Chalk Rock Member.
South Street Beds Basal marker — Lewes Marl. Known as Lewes Beds (Mortimore, 1983).
Navigation Beds Basal marker — Snowdrop Flint 1.
Cliffe Beds Basal marker — the upper Navigation Marl.
Hope Gap Beds Basal marker — the top surface of the Cliffe Hardground.
Beeding Beds Basal marker — the top surface of the Hope Gap Hardground.
Light Point Beds Basal marker — the top surface of the Beeding Hardground.
Beachy Head Beds Basal marker — the top surface of the uppermost Light Point Hardground.

Seaford Chalk Member

As originally defined the member covered the interval between the Shoreham Marl 2 and the Buckle Marl 1. This is equivalent to the member concept in Bristow, Mortimore and Wood (1997) and the Seaford Chalk Formation of Rawson, Allen and Gale (2001).

Belle Tout Beds Basal marker — the Shoreham Marl 2
Cuckmere Beds Basal marker — the Seven Sisters Flint.
Haven Brow Beds Basal marker — the Michel Dean Flint. Known as Seaford Head Beds (Mortimore, 1983).

Newhaven Chalk Member

As originally defined the member covered the interval between the Buckle Marl 1 and the Castle Hill Marl 2. This is equivalent to the member concept of Bristow, Mortimore and Wood (1997) with the proviso that in full successions in structural lows additional marls are strongly developed (the Pepper Box Marls) above the Castle Hill Marls. This higher level marks the mapping boundary in this situation.

Splash Point Beds Basal marker — the Buckle Marl 1.
Old Nore Beds Basal marker — the Brighton Marl.
Peacehaven Beds Basal marker — the Old Nore Marl.
Meeching Beds Basal marker — the Peacehaven Marl.
Bastion Steps Beds Basal marker — the Meeching Paired Marl.

Culver Chalk Member

As originally defined the member covered the interval between the Castle Hill Marl 2 and the Portsdown Marl. This is equivalent to the member concept of Bristow, Mortimore and Wood (1997) with the proviso that the mapping base may be slightly lower at the Arundel Sponge Beds or slightly higher at the Pepper Box Marls. It conforms to the definition of the Culver Chalk Formation of Rawson, Allen and Gale (2001).

Castle Hill Beds Basal marker — the Castle Hill Marl 2.
Sompting Beds Basal marker — the Lancing Flint.
Whitecliff Beds Basal marker — the Whitecliff Marl.

Portsdown Chalk Member

As originally defined the member covered the interval from the Portsdown Marl up to the sub-Palaeogene unconformity in the Southern Province. This upper level is some distance (about 8 m) above the Shide Marl as exposed at Whitecliffe Bay on the Isle of White (as in Mortimore, 1986) but younger chalks are known at this locality (Mortimore, Wood and Gallois, 2001) and elsewhere on the Isle of Wight and in Dorset. Gale, Wood and Bromley (1987) introduced the term Studland Chalk of ‘member’ status to define the marl-free soft white chalk with large flints in the upper part of the chalk exposed in Scratchells Bay and Alum Bay and on the Dorset coast in Studland Bay. It is not discernible from the published literature at what level the division of the Portsdown and Studland ‘members’ of Gale, Wood and Bromley (1987) occurs in the highest preserved chalk sequence. This doubt together with the lack of exposure and geomorphological expression of the member has led to the BGS reverting to the original concept of the Portsdown Chalk Member (Bristow, Mortimore and Wood, 1997). This is also the position stated in Rawson, Allen and Gale (2001) and thus the Portsdown Chalk Formation covers all of the chalk up to the sub-Palaeogene erosion surface in the Southern Province.

Redoubt Beds Basal marker — the Portsdown Marl

3.14 Robinson (1986)

This paper describes and erects a lithostratigraphical terminology for the chalk of the North Downs. The paper reclassifies the Lower, Middle and Upper Chalk of the Traditional Scheme on the basis of distinct types of chalk and associations. The succession is divided completely into five formations and nine members with a large part of the lowest formation being undivided at member level. It is not easy to correlate the divisions of Robinson to biostratigraphical terminology without significant knowledge of the literature, however the succession is essentially the same and can be described using the terms as defined in Sussex by Mortimore (1986). Thus the work is largely redundant in terms of the new agreed lithostratigraphical framework.

East Wear Bay Chalk Formation

Defined on the coastal section between Copt Point [TR 242 365], near Folkestone, and Hay Cliff [TR 301 394] where it is approximately 58 m thick. Its base is at the erosional contact beneath the Glauconitic Marl Member and its top is defined as the base of the overlying Hay Cliff Member of the Abbots Cliff Formation and placed at the ‘omission surface beneath the lowest layer containing laminated structures’. The formation is undivided above the Glauconitic Marl Member. The formation is essentially equivalent to all of the Lower Chalk of the Traditional Scheme beneath the Jukes-Browne Bed 7. The ‘Cast Bed’ is present in the succession (but not used to divide the sequence) and demonstrates that the formation is equivalent to all of the West Melbury Marly Chalk Formation and the lower half if the Zig Zag Chalk Formation. Equivalent to the Mantelliceras mantelli Zone to the very basal Acanthoceras jukesbrownei Zone.

Glauconitic Marl Member

This is the basal member of the East Wear Bay Chalk Formation and is defined at Copt Point where it is about 5 m thick. Its top is placed above a nodular bed equated to be that of Bed ‘h’ in Band 1 of Kennedy (1969). Equivalent to the Neostlingoceras carcitanense Subzone.

Abbots Cliff Chalk Formation

The formation (and its constituent members) is named from (and its stratotype is at) the Abbots Cliff path [TR 268 385] where it is 22 m thick. The formation is divided into two members, the lower, Hay Cliff Member being overlain by the Capel-le-Ferne Member. The base is defined at the ‘omission surface beneath the lowest layer containing laminated structures’ and its top coincident with the base of the Plenus Marl Formation. It is equivalent to the Jukes-Browne Bed 7 and ‘White Bed’ (JB Bed 8) of the Traditional Scheme and to the upper half of the Zig Zag Chalk Formation. Equivalent to the Acanthoceras jukesbrownei Zone and Calycoceras guerangeri Zone.

Hay Cliff Member

Indurated calcarenite equivalent to the Jukes-Browne Bed 7 of the Traditional Scheme, basal Acanthoceras jukesbrownei Zone. The base is defined at the ‘omission surface beneath the lowest layer containing laminated structures’.

Capel-le-Ferne Member

Bioturbated soft white Chalk equivalent to the ‘White Bed’ (JB Bed 8) of the Traditional Scheme and the Falling Sands ‘Member’ of Mortimore, Pomerol and Foord (1990) (or ‘Beds’ of Bristow, Mortimore and Wood, 1997). Topmost Acanthoceras jukesbrownei Zone and Calycoceras guerangeri Zone. The top defined as being coincident with the base of the Plenus Marl Formation at the sub-plenus erosion surface of Hill and Jukes-Browne (1886).

Plenus Marl Formation

This unit is directly equated to the Actinocamex plenus (now Praeactinocamax plenus) Subzone of Jefferies (1963) defined at Merstham [TQ 295 542] with the proposal that Shakespeare Cliff [TR 307 398] be designated its primary reference section. Here it is 2.67 m thick. Base marked by the sub-plenus erosion surface with a top above the highest of the Plenus Marl ‘Beds’ of Jefferies (1963), the Foyle Marl of Mortimore (1986). It is equivalent to the Plenus Marls (Jukes-Browne Bed 9) of the Traditional Scheme and the Plenus Marls Member of the Holywell Nodular Chalk Formation in the new scheme. Equivalent to most of the Metoicoceras geslinianum Zone.

Dover Chalk Formation

This formation is divided into three constituent parts; the Shakespeare Cliff, Aycliffe and Akers Steps members, each containing and limited by named marker beds, with the stratotype designated as Akers Steps [TR 297 394] where 66.9 m of beds are present. The base is taken at the base of the Melbourn Rock Beds and the top placed at the Crab Bay Marl. The formation is equivalent to the Bed 4 and Bed 5 units defined by Whitaker, Bristow and Hughes (1872) and most of the Middle Chalk of the Traditional Scheme. It is equivalent to the Holywell Nodular Chalk Member (but not the newly defined formation of that name which includes the Plenus Marls Member), New Pit Chalk Formation and the lower part of the Lewes Nodular Chalk Formation. As defined the formation covers the Neocardioceras juddii to Terebratulina lata Zones.

Shakespeare Cliff Member

The Melbourn Rock Beds (about 12 m) form the lowest part of the Shakespeare Cliffe Member, which terminates upwards at the Warren Marl 1. The member being 26.5 m thick at its stratotype. The member is typically composed of beds of nodular and intraclastic chalk with spectacular concentrations of shell-detrital chalks containing Mytiloides within which the Round Down Marl is the only named marker. This member is equivalent to the ‘Grit Beds’ in the early literature and the Holywell Nodular Chalk Member of Bristow, Mortimore and Wood (1997).

Aycliff Member

This member is 17.5 m thick at its stratotype and comprises essentially flintless white chalk with marl seam and weakly nodular chalk. The lower boundary is placed at the Warren Marl 1, which is the lateral equivalent of the New Pit Marl 1 in the Sussex succession, and the top is placed, rather unsatisfactorily, at the base of the first persistent flint up-sequence from the Maxton Marls. These marls being the lateral equivalent of the Glynde Marls in Sussex. Thus the member is essentially the equivalent of the New Pit Chalk Formation, as defined in Sussex, with the proviso that nodular chalks, characteristic of the Lewes Nodular Chalk Formation, are not encountered in Kent until only a few metres below the Langdon Bay Marls (the Southerham Marls of Sussex) higher still in the succession. The member is entirely within the Terebratulina lata Zone.

Akers Steps Member

This unit is 17.5 m thick at its stratotype at Akers Steps and includes the inception of nodularity as seen in the North Downs successions. The first nodular beds appear approximately 5 m below the Langdon Bay Marls, which are equivalent to the Southerham Marls in the Sussex succession, but the base of the member is placed lower (about 15 m lower) at the first persistent flint below the Lydden Spout Flint. The top of the member is defined as the basal surface of the Crab Bay Marl that is the lateral equivalent of the Caburn Marl in the Sussex sequence. As the inception of nodularity indicates the base of the Lewes Nodular Chalk Formation in mapping terms, the lower part (about 10 m) of this member is to be considered as part of the New Pit Chalk Formation (but is the lateral equivalent of the Glynde Beds of the Sussex chalk). The upper part of the member is equivalent to the Caburn Beds of the Sussex Chalk. The member is entirely within the Terebratulina lata Zone.

Ramsgate Chalk Formation

This formation is divided into three constituent parts, the St Margarets, Broadstairs and Margate members each containing and limited by named marker beds. The stratotype is composite from the Dover to Thanet coast of Kent (see member entries) where about 120 m of beds are seen. The base is taken at the base of the Crab Bay Marl with the top limited by the sub-Palaeogene erosion surface. The formation is equivalent to the Bed 3, Bed 2 (Broadstairs Chalk) and Bed 1 (Margate Chalk) units defined by Whitaker, Bristow and Hughes (1872). The formation covers the highest beds of the Middle Chalk and all of the known Upper Chalk (in the North Downs) of the Traditional Scheme. It is equivalent to the middle and upper part of the Lewes Nodular Chalk Formation, the Seaford Chalk Formation and the lower part of the Newhaven Chalk Formation. As defined the formation covers the Terebratulina lata to Offaster pilula zones.

St Margarets Member

This member is defined at the Langdon Stairs [TR 345 425] stratotype where 38.3 m of beds are encountered. The base is at the Crab Bay Marl (Caburn Marl) and its top placed at the East Cliff Marl 2 (Shoreham Marl 2). The member comprises nodular chalks with mineralised hardgrounds and regular strong nodular flint seams. It is equivalent to the ‘middle’ and ‘upper’ Lewes Nodular Chalk Formation.

Broadstairs Member

Defined at four sites representing a composite stratotype at St Margarets Bay [TR 371 446], Kingsdown Rifle Range [TR 380 473], Pegwell Bay [TR 368 640] and Joss Bay [TR 398 702] where it has a combined thickness of 58.5 m. The base is placed at the East Cliff Marl 2 (Shoreham Marl 2) and its top at the upper surface of the Barrois Sponge Bed. As defined it is the direct equivalent of the Seaford Chalk Formation.

Margate Member

The member is defined at two sites which constitute the composite stratotype at White Ness [TR 396 710] and Foreness Point [TR 384 716] on the Isle of Thanet in Kent where 22.5 m are preserved beneath the sub-Palaeogene erosion surface. The base is at the Barrois Sponge Bed. The member comprises soft white, marl-free, flint-poor chalk. Because of its lithological differences the Margate Member is retained in the new lithostratigraphical scheme within the Newhaven Chalk Formation that is thicker and stratigraphically more extensive (with significant marls) elsewhere.

A3.15 Jarvis and Woodroof (1984)/Jarvis and Tocher (1987)

The succession of Upper Cretaceous sediments in south-east Devon is lithologically distinct principally because of its presumed proximity to the basin margin and synsedimentary structural control. The succession is divided into two formations and six members with numerous named marker beds. In the 1984 paper the highest beds described are from the Beer Roads Flinty Chalk Member up to ‘Rowe’s Two Foot Band’ (Common Hill Marl, locally; or New Pit Marl 1 in the main basin). In the later (1987) paper the the higher part of the Beer Roads Flinty Chalk member and beds equated to the St Margarets and Broadstairs members of the North Downs (Robinson, 1986, see above) succession are described. The whole succession is however better understood by comparison to the Sussex sequence (see Mortimore, 1986; Mortimore, Wood and Gallois, 2001).

Beer Head Limestone Formation

The formation is divided into four members (but each not present everywhere) each defined by lithostratigraphical markers determined from stratotype sections between Branscombe [SY 204 882] and Seaton/White Cliff [SY 233 893] in Devon. Because of the marked lithological differences, condensation and omission in this marginal setting the term is utilised instead of the West Melbury Marly Chalk and Zig Zag formations in BGS descriptive texts with the proviso that the highest, Pinnacles Member is demonstrably equivalent to the Plenus Marls Member and Melbourn Rock Member and therefore excluded from the Beer Head Limestone Formation. Thus the BGS usage accords with the Cenomanian Limestone as adjusted in Smith (1965) and Beds A1, A2 and B of Jukes-Browne and Hill (1903). It is equivalent to the Zig Zag and West Melbury Marly Chalk formations or the Grey Chalk Subgroup.

Pounds Pool Sandy Limestone Member

The ‘stratotype’ for this member is at Pounds Pool Beach [SY 227 881] where it is 3.5 m thick. Its base is placed on the surface of the Small Cove Hardground of the Upper Greensand Formation with its top on the upper surface of the Weston Hardground. The member comprises yellowish brown very coarse calcareous sandstone passing up into indurated sandy bioclastic limestone. Biostratigraphically the member is reported to be in the Neostlingoceras carcitanensis Subzone, Mantelliceras mantelli Zone of the Lower Cenomanian. The member is equivalent to Bed A1 of Jukes-Browne and Hill (1903) and Smith (1965) and the lower part of the West Melbury Marly Chalk Formation.

Hooken Nodular Limestone Member

Named after Hooken Cliffs adjacent to the Beer Stone Adit [SY 219 879] where the member achieves its maximum thickness of 5 m. The base of the member is placed at the upper surface of the Weston Hardground and its top on the upper surface of the King’s Hole Hardground. It is composed of grey, shell-detrital rubbly limestone at various stages of induration. Inland the lateral equivalent of this member is termed the Wilmington Sand Facies (or member of some authors), which is composed of decalcified sand and sandy calcarenite overlain by highly fossiliferous sand with a chalky matrix (‘Grizzle’). Kennedy (1970) regarded this member as being of Mantelliceras saxbii Subzone Mantelliceras mantelli Zone age. There is a major hiatus between this and the succeeding member. The member is equivalent to Bed A2 of Jukes-Browne and Hill (1903) and Smith (1965) and the upper part of the West Melbury Marly Chalk Formation.

Little Beach Bioclastic Limestone Member

The member is thickest (1.75 m) at the Beer Stone Adit but seen to advantage in fallen blocks on Little Beach. It is a greatly condensed and complex bioclastic limestone sequence commencing with the ‘cavernous hardground’. The base is at the King’s Hole Hardground surface and its top at the Humble Point Hardground. Records show the member to be of Turrilites costatus Subzone (Acanthoceras rhotomagense Zone) to Acanthoceras jukesbrownei Zone with reworked material from older zones at the base and therefore is of Middle Cenomanian age. There is a major hiatus between this and the succeeding member. The member is equivalent to Bed B of Jukes-Browne and Hill (1903) and Smith (1965) and to much of the Zig Zag Chalk Formation.

Pinnacles Glauconitic Limestone Member

Named after the Pinnacles, which stand proud of the Hooken Cliffs, the member attains a maximum thickness there of 2.3 m. The member is confined between the top surfaces of the Humble Point Hardground and the Haven Cliff Hardground. Biostratigraphically the member contains a reworked fauna representing a part of the Middle and Upper Cenomanian and an indigenous fauna of Metoicoceras geslinianum Zone with Neocardioceras juddii Zone in the Haven Cliff Hardground. The member is equivalent to Bed C of Jukes-Browne and Hill (1903) and Smith (1965) and the basal Plenus Marls and Melbourn Rock members of the Holywell Nodular Chalk Formation.

Seaton Chalk Formation

The formation is divided into two members each defined by marker beds determined from the White Cliff stratotype between Beer and Seaton [SY 233 886]. The formation is equivalent to the Middle Chalk of the Traditional Scheme and the Holywell Nodular Chalk and New Pit formations of the new scheme.

Connett’s Hole Nodular Chalk Member Eaton Chalk Member

Defined at White Cliff where 13.5 m of beds are preserved. The base is placed at the surface of the Haven Cliff Hardground and the top at the upper surface of the last nodular bed (the Flinty Hardground 5). The member is characterised by nodular chalk with hardgrounds, glauconitic and sandy at the base, and is poorly flinty above the Branscombe Hardground. The Beer Stone, an important architectural freestone, is derived from a particularly pure, grey, fine-grained calcarenite lens in the lower part of the succession. The obvious West Ebb Marl is an important marker in the succession above the Beer Stone. There is a marked non-sequence beneath the Beer Roads Flinty Chalk Member over much of the outcrop that cuts out the highest beds down to the level of the Branscombe Hardground. This hardground itself cuts out the lower part of the succession entirely, to the west, where it sits on the Pinnacles Member. Biostratigraphically it covers the Mytiloides spp. Zone and is equivalent to the Holywell Nodular Chalk Formation.

Beer Roads Flinty Chalk Member

Named after the eastern side of Beer Beach [SY 232 892]. The base is at the surface of the Flinty Hardground 5 and the top at the inception of nodularity a metre or so below the Whitlands Marl on the Pinhay Cliffs (see Jarvis and Tocher, 1987). The member is characterised by soft white chalks with numerous flint and marl seams. Flint is less prominent to the east where the succession becomes more like the New Pit Chalk Formation of Sussex. The distinct marker beds known as Rowe’s Two Foot and Four Foot bands are equated to the New Pt 1 and 2 marls in Sussex. Biostratigraphically the member is equivalent to the Terebratulina lata Zone and thus essentially the New Pit Chalk Formation.

A3.16 Johansen and Surlyk (1990)

This paper dealing principally with the distribution of brachiopods within the upper Campanian and lower Maastrichtian chalk in Norfolk formalises, in lithostratigraphical terms and with some additions, the essentially biostratigraphical work of Peake and Hancock (1970); a paper which also describes the entire chalk succession in the county (see also Brydone, 1908). In this earlier paper these chalks are referred to the ‘Zone of Belemnitella mucronata’, which they equate to the ‘Norwich Chalk’ of previous authors. This Norwich Chalk term is again used, informally but presumably implying formation status, by Mortimore, Wood and Gallois (2001), to cover all of the Chalk of Norfolk above the Portsdown Chalk Formation. The Norwich Chalk (and the stratigraphically higher Trimmingham Chalk) is the lateral equivalent of the Rowe Chalk Formation, as defined, of the Northern Province.

The Basal mucronata Chalk ‘Member’

This is noted as the unit below their formally defined units and the name is taken from Peake and Hancock (1970). Its base is not formally defined but presumed to be at the base of the zonal index belemnite. Peake and Hancock estimate it to be 50 feet (15.2 m) of firm white chalk with frequent flints. Also known as the lower part of the pre-Weybourne Chalk.

This overlies the ‘Basal mucronata chalk’ and is the oldest unit formally described. The base is ill defined within the Belemnitella mucronata sensu stricto Zone (at the base of the Echinocorys marginata approaching subglobosa ‘zone’, Peake and Hancock, 1961,1970). The member is also known as the upper part of the pre-Weybourne Chalk. Peake and Hancock estimate it to be 50 feet (15.2 m) of soft chalks with irregularly scattered flints.

Weybourne Chalk Member

The base of this member is placed at the top of the sponge-bed hardground above Flint Z in the section at Weybourne Hope. Peake and Hancock estimate it to be 75 feet (22.8 m) of chalk with bands of strongly developed flints. It is mostly coincident to the Belemnitella woodi Zone of Christensen (1995, 1999).

Catton Sponge Bed

This is the topmost unit of the Weybourne Chalk Member. The base is marked by the incoming of sponges and its top is placed above the hardground. It varies between 0.3 m and a few metres in thickness and comprises one to three yellow stained hardgrounds and soft chalk with flint.

Beeston Chalk Member

The lower boundary placed at the surface above the Catton Sponge Bed whilst the upper boundary is poorly defined at a hardground on the coast at West Runton. The member comprises soft white chalk with irregular seams of large flints. Together with the Catton Sponge Bed below, the beds cover most of the Belemnitella minor I Zone of Christensen (1995, 1999). Peake and Hancock estimate it to be 75 feet (22.8 m) thick.

Paramudra Chalk Member

The lower boundary is placed at the hardground described above but the top is ill defined in glacially disturbed masses but conventionally placed at the Overstrand Pyramidata Hardground. The member comprises soft white chalk with large vertical, cylindrical ‘Paramudra’ flints and repeated hardgrounds. It is equivalent for the most part with the Belemnitella minor II Zone of Christensen (1995, 1999). Peake and Hancock estimate it to be 75 feet (22.8 m) thick.

Sidestrand Chalk Member

Lower boundary placed at the Overstrand Pyramidata Hardground with the top at the hardground labelled ‘O’ in Peake and Hancock (1970, fig 7). The member includes the Sidestrand Chalk and Porosphaera Beds of Peake and Hancock (1970), which they equated with the Belemnella lanceolata ‘zone’, in the lowermost Maastrichtian. The member is between 10 and 12 m of white soft infrequently nodular chalk with regular flint seams. It forms part of the Belemnella lanceolata, B. psuedobtusa and B. obtusa zones of Christensen (1999).

Trimingham Sponge Beds Member

Lower boundary at the top of the Sidestrand Chalk Member and a top at the marl band (the ‘greasy’ marl) labelled ‘G’ in Peake and Hancock (1970, fig 7). Equivalent to the ‘Sponge Beds’ of Brydone (1908) and Peake and Hancock (1970). The member is 2.9 m of lithified chalk with green-coated pebbles, several erosion surfaces and four flint seams. The boundary between the Belemnella obtusa and B. sumensis zones falls within this member.

Little Marl Point Chalk Member

The lower boundary is at the ‘greasy marl’ with the top at the base of the first soft grey chalk beds labelled ‘A’ by Peake and Hancock (1970, fig 7). This unit is equivalent to the ‘White Chalk with Ostrea lunata’ of Peake and Hancock (1970). Comprises 5 to 6 m of soft white chalk with four flint seams and two marls. Within the Belemnella sumensis Zone of Christensen (1999).

Beacon Hill Grey Chalk Member

Lower boundary bed ‘A’ by Peake and Hancock (1970, fig 7). Equivalent to the ‘Grey Beds’ of Peake and Hancock (1970). The member is at least 5 m thick and comprises grey chalk with five flint bands. Within the Belemnella sumensis Zone of Christensen (1999).

Figures and tables

Figures

(Figure 1) The Upper Cretaceous ‘provinces’ for the United Kingdom.

(Figure 2) Litho- and biostratigraphical correlation chart for the Chalk Group of Southern England.

(Figure 3) Terminology applied to the Chalk of England.

(Figure 4) The Chalk Group provinces of England.

(Figure 5a) The development of the terminology in the Southern Province.

(Figure 5b) The development of the terminology in south-east Devon (Southern Province).

(Figure 5c) The development of the terminology in Norfolk (Transitional Province).

(Figure 6) The development of the terminology in the Northern Province.

(Figure 7) The development of the terminology in the Scottish Chalk Province.

(Figure 8) The Inner Hebrides Scottish Chalk Province.

(Figure 9) The development of the terminology in the Ulster Cretaceous Province.

(Figure 10) The Northern Ireland Cretaceous Province.

(Figure 11) The development of the terminology in the offshore UK Sector.

(Front cover) Chalk cliff and the Pinnacles stacks south of Handfast Point, north-east of Swanage, Dorset.

Tables

(Table 1) The agreed lithological framework from the Chalk Lithostratigraphy meeting held at BGS, Keyworth, on the 3–4 November 1999 (after Rawson, Allen and Gale, 2001).

(Table 2) The lithostratigraphical units used on the 1:50 000 geological maps and within the descriptive memoirs of the Southern and Transitional provinces of England.

(Table 3) The lithostratigraphical units used on the 1:50 000 geological maps and within the descriptive memoirs of the Northern Province of England.

(Table 4) The lithostratigraphical units used on the 1:50 000 geological maps and within the descriptive memoirs of Scotland.

(Table 5) The lithostratigraphical units used on the 1:50 000 geological maps and within the descriptive memoirs of Northern Ireland.

Tables

(Table 2) The lithostratigraphical units used on the 1:50 000 geological maps and within the descriptive memoirs of the Southern and Transitional Provinces of England

Name of Unit	Lexicon code	Map symbol
Beer Head Limestone Formation	None	None
Cambridge Greensand Member	CBG	CGS
Chalk Rock Member	CKR	CkR
Culver Chalk Formation	CUCK	CCk
Glauconitic Marl Member	GLML	GM
Grey Chalk Subgroup	GYCK	GyCk
Holywell Nodular Chalk Formation	HCK	HCk
Kensworth Nodular Chalk Member	KNCK	None
Lewes Nodular Chalk Formation	LECH	LeCk
Margate Chalk Member	MACK	MaCk
Melbourn Rock Member	MR	None
Melbury Sandstone Member	MYS	Mels
New Pit Chalk Formation	NPCH	NPCk
Newhaven Chalk Formation	NCK	NCk
Plenus Marls Member	PLMA	None
Seaford Chalk Formation	SECK	SCk
Spetisbury Chalk Member	SPCH	SpCk
Stockbridge Rock Member	STRK	STRK
Studland Chalk Member	STCK	StCk
Tarrant Chalk Member	TACH	TCk
Top Rock Bed	TRK	TRk
Totternhoe Stone Member	TTST	TtSt
West Melbury Marly Chalk Formation	WMCH	WMCk
White Chalk Subgroup	WHCK	WhCk
Zig Zag Chalk Formation	ZZCH	ZCk

(Table 3) The lithostratigraphical units used on the 1:50 000 geological maps and within the descriptive memoirs of the Northern Province of England

Name of unit

Lexicon code

Map symbol

Black Band Member

None

Burnham Chalk Formation

BCK

BCk

Ferriby Chalk Formation

FYCK

FyCk

Flamborough Chalk Formation

FCK

FCk

Hunstanton Formation

HUCK

HCk*

Plenus Marls Member

PLMA

None

Rowe Chalk Formation

ROWE

Welton Chalk Formation

WCK

WCk

*this is the same map symbol as that used for the Holywell Nodular Chalk Formation of the Southern Province and it is recommended that this Northern Province symbol be changed to HuCk to avoid confusion.

Notes: For definitions of the Chalk Group and its component Subgroups refer to the entries within Section 3 above. An entry is included for the Hunstanton Formation (Red Chalk) because of its historical association with the Chalk Group but from which it is now formally excluded.

(Table 4) The lithostratigraphical units used on the 1:50 000 geological maps and within the descriptive memoirs of Scotland.

Name of unit	Lexicon code	Map symbol
Black Band Member	None	None
Inner Hebrides Group	None	None
Morvern Greensand Formation	MORG	MorG
Lochaline White Sandstone Formation	LAWS	None
Coire Riabhach Phosphatic Formation	None	None
Gribun Chalk Formation	GRIB	UCG
Feorlin Sandstone Formation	None	None
Strathaird Limestone Formation	STRL	None
Laig Gorge Sandstone Member	None	None
Laig Gorge Limestone Member	LAGL	LagL
Clach Alasdair Conglomerate Member	None	None
Beinn Iadain Mudstone Formation	None	None

(Table 5) The lithostratigraphical units used on the 1:50 000 geological maps and within the descriptive memoirs of Northern Ireland

Name of unit	Lexicon code	Map symbol
Ballintoy Chalk Formation	BTC	None
Ballycastle Chalk formation	BCCK	None
Ballymagarry Chalk Formation	BMC	None
Belfast Marls Formation	BLFM	None
Boheeshane Chalk Formation	BHCK	None
Cloghastucan Chalk Formation	CLC	None
Cloghfin Sponge Formation	CSP	None
Collinwell Sands Formation	CLLW	None
Creggan Chalk Formation	CGCK	None
Galboly Chalk Formation	GCK	None
Garron Chalk Formation	GRCK	None
Glenarm Chalk formation	GAC	None
Hibernian Greensands Group	HBG	HBG
Island Magee Siltstones Formation	ISMS	None
Kilcoan Sands Formation	KOS	None
Larry Bane Chalk Formation	LBC	None
Portrush Chalk Formation	PRC	None
Port Calliagh Chalk Formation	PCC	None
Post-Larry Bane Chalk Subgroup	None	None
Pre-Larry Bane Chalk Subgroup	None	None
Tanderagee Chalk Formation	TDC	None
Ulster White Limestone Group	UWLF	UWLF