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Geological notes and local details for 1:10 000 sheet: SP 81 NW Bierton. Part of 1:50 000 Sheets 219 (Buckingham) 202 (Leighton Buzzard), 237 (Thame) and 238 (Aylesbury). British Geological Survey Technical Report WA/88/42

By A J M Barron

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British Geological Survey Onshore Geology Series Technical Report WA/88/42

Bibliographical reference:Barron, A. J.M. 1988. Geological notes and local details for 1:10 000 sheet: SP 81 NW Bierton British Geological Survey Technical Report WA/88/42

British Geological Survey Natural Environment Research Council

©NERC copyright 1988 Keyworth, Nottingham, British Geological Survey 1988

Author: A J M Barron BSc British Geological Survey Keyworth Nottingham NG12 5EE

Introduction

This report covers the area of 1:10 000 Geological sheet SP 81 NW, immediately north of Aylesbury in Buckinghamshire. The ground was originally surveyed at the 1:10 560 scale by A C G Cameron and A J Jukes-Browne in 1896 and 1897. The area south of grid line 16 and east of 818 (County Series 1:10 560 sheets Bucks 28 SE/E and Bucks 29 SW) was revised by C Reid in 1910. The area was also surveyed at the 1:25 000 scale by C R Bristow as part of a PhD thesis (Bristow, 1963). The present survey was carried out by A J M Barron in 1988. Palaeontological determinations of material from the Jurassic were made by B M Cox.

The River Thame and a parallel un-named tributary, called here the Hardwick stream, run from north-east to south-west across the area and their valleys divide it into three parts: in the north-west the ground rises from the village of Hardwick and the Hardwick stream towards Whitchurch which is on the adjacent map to the north (SP 82 SW). In the central part the village of Weedon stands on the western end of a ridge rising to 120 m (the Weedon ridge of this report) and part of the village of Aston Abbotts is on high ground rising to 135 m in the extreme north-east. The hamlet of Rowsham is immediately north of the Thame in the extreme east of the area. The large village of Bierton stands on a plateau in the south-east part of the area astride the A418 Aylesbury to Leighton Buzzard road. In the extreme south are the northern outskirts of Aylesbury.

Parallel reports covering adjacent areas are:

SP 82 SW Whitchurch (R J Wyatt)

SP 71 NE Fleet Marston (M G Sumbler) SP 81 NE Wingrave

SP 81 SW Aylesbury

Geological sequence

Solid formations

Jurassic

Ampthill Clay Formation

The Ampthill Clay Formation crops out in the bottom of a shallow valley in the extreme west. It consists of about 15 m of mid to dark grey mudstone with thin marl and siltstone beds, fossiliferous throughout, but only the uppermost 4 m of the Formation crop out in this area.

The Formation gives rise to a heavy grey-brown clay soil with scarce oysters, including Deltoideum delta, fragments of which were found 200 m south of the pumping station [SP 8006 1965].

A borehole near Datchet House (Appendix 1, (SP81NW/4)) proves 4.00 m of greenish grey and brown mottled silty clay with shell fragments. The surface level of this borehole is not consistent with the site given by the grid reference; the site may be further west in which case the lower beds proved will include the Ampthill Clay.

The outcrop of the Ampthill Clay in the extreme north-west, indicating an apparent reduced total thickness of the Kimmeridge Clay is anomalous, and may result from valley bulging (see Superficial Structures).

Kimmeridge Clay Formation

The Kimmeridge Clay Formation crops of over the greater part (about 19 km2) of the present area. It consists of between 21 and 35 m of mid to dark grey mudstone, silty in parts, with several thin impersistent limestone beds (cementstones) mainly in the lower part. These consist of mid grey, very hard, argillaceous, fine-grained limestone, with calcite veins in places, forming beds no more than 0.2 m thick and some may be nodular indicating a diagenetic origin. To the south-west in the district around Thame, the Kimmeridge Clay includes fine-grained sand beds in its upper part (see for example Barron, 1988), but in this area the only sand beds seen (north of Groveway Farm [SP 8244 1866] and north-west of Lower Burston Farm [SP 8335 1957] consist of less than l m of grey finely sandy clay and are of very limited extent. It is thought that the beds equivalent to the uppermost 7m of the Kimmeridge Clay in the BGS Hartwell Borehole (Gallois and Cox, in prep.) and the uppermost 9 m of the Formation in the BGS Brill Borehole (Barron, 1988, Cox, in prep.) which comprise the upper part of the Hartwell Clay of Hudleston (1880) and the whole of the 'Wheatley Sands' (in Brill) of Arkell (1947) are absent in this area being cut out by the unconformity at the base of the Portland Beds (B M Cox, pers. comm.).

The two cementstone beds shown on the map have been identified by their fauna and lithology from specimens (see Appendix 3). The lower one is Bed (KC) 30 of Gallois and Cox (1976), the upper one comprises the lower doggers of Oates (in prep.) which is in the process of being related to the standard sequence of Gallois and Cox (1979).

The Kimmeridge Clay gives rise to a heavy grey-brown silty clay soil. At shallow depth (0.5 m) it is usually grey, mottled with orange which assists in distinguishing it from the Gault.

There are no permanent exposures within the Kimmeridge Clay but it is regularly exposed in temporary sections. Where a gas pipeline trench crossed a brook south-west of Aston Abbotts (Appendix 2, Locality A) bluish grey clay and mudstone were seen and in a recently dug channel intended to divert the River Thame at Watermead (Locality B), over 0.6 m of grey clay and blue grey mudstone were observed.

The strata exposed in the excavation of the artificial lake at Watermead [SP 822 157] were measured and collected by M J Oates in 1987 (see Figure 1, pers. comm.) and he records over 15 m of Lower and Upper Kimmeridge Clay which are currently being correlated with the Hartwell Borehole. A largely intact Plesiosaur skeleton was collected and is being prepared for display in the Aylesbury Museum.

The Formation was proved in many of the boreholes in the area (Appendix 1) and is generally described as grey clay, sometimes silty or containing shells, limestone beds and selenite within 10 m of the surface.

Portland Formation

The main outcrop of the Portland Formation is around Bierton, comprises a broad tabular outlier covering about 1 km2, and is the only outcrop in which sub-division of the Formation has been possible. To the south-east at Burcott [SP 842 151] there is an outcrop of the Formation sandwiched between the Kimmeridge Clay and Gault, and at the eastern end of Bierton is a long narrow outcrop preserved in a shallow syncline; the East Bierton Syncline of Bristow (1963). The Formation also crops out on the upper slopes of the Weedon ridge and around Hardwick Hill Farm [SP 812 199] cm the slopes of the hill rising to Whitchurch.

The sequence at the surface in the area around Bierton is as follows:

The uppermost unit is equivalent to the Creamy Limestones of Blake (1880) or Upper Limestone of Bristow (1963) and crops out only around Great Lane [SP 834 155]. The sand bed below is probably equivalent to the Crendon Sands of Buckman (1925–27). Its mapped outcrop is restricted to the ground north-west of Church Farm where sand was augered and it was traced 600 m to the north-west along a concave geomorphological feature which is associated with a sandy soil.

The shelly sandy oolitic limestone unit underlying the sand has the broadest outcrop around Bierton and is probably equivalent to the Aylesbury Limestone of Woodward (1895) or Rubbly Limestone of Blake (1880). It contains numerous fossils including large ammonites and bivalves (see Appendix 3, specimens AMB 460–463).

In the Bierton area this unit is exposed in a disused quarry at Dunsham Farm (Appendix 2, Locality F) and was seen in temporary exposures at Church Farm (Locality G) and in Burcott (Locality H).

The lowest unit of the Portland Formation in the Bierton area is the Portland Sand Member and comprises orange brown calcareous silt, sandy over much of the area, glauconitic and incorporating the shiny black phosphate and chert 'lydite' pebbles. It is thought to be weakly cemented in places and to be equivalent to Bristow's 'Lower Portland Sand' (1963). Sherlock gives an account of Ward and Cannon's brick pit [SP 839 157] (1922, p.7)

Bristow (1963, p.52) interprets this description as indicating contemporaneous erosion at the base of bed 2 and the loss of the 'Lower Portland Sand'. However, as bed 2 can be traced throughout the area this is not thought to be the case but that it is the weakly-cemented representative of the Portland Sand. The Portland Sand Member was also seen in temporary exposures at Church Farm (Locality G) and Burcott (Locality H).

The Portland Formation preserved in the East Bierton Syncline [SP 843 163] includes light brown fine-grained sand, orange brown glauconitic silt and pale grey pelletal limestone. The Formation is not exposed in this area but all these lithologies were encountered by augering and were seen in burrows. Jukes-Browne (in Sherlock, 1922, p.7) recorded '4 feet of hard oolitic limestone' in a pond at the cross-roads [SP 8454 1589]. Limestone was reported at 0.75 m in house foundations at Corner Farm [SP 8458 1583]. Bristow (1963, p.56) described the following section 'alongside the new road [SP 846 160]':

The Rubbly Limestone containing: Protocardia dissimile (J de C Sowerby), Pecten lamellosus Sowerby), Ostrea sp. and Serpula sp."

A trace of limestone was seen in an auger hole on the base of the Gault outlier north of Bierton [SP 8402 1700] but no Portland outcrop could be traced around this knoll.

Away from Bierton, undivided Portland Formation has been mapped on the Weedon ridge; overlain by Gault east of the Weedon Fault and cut out by the unconformity at the base of the Gault at the eastern end of the ridge [SP 826 183] (see also Structure). The beds consist of khaki and orange-brown very fine-grained sandy silty glauconitic clay overlain by buff and pale grey fine-grained sandy Shelly limestone. These lithologies were seen in the soil, in auger samples and were seen in spoil from trenches at Weedon Lodge [SP 8200 1805] (Locality D) and Weedon Lodge Farm [SP 8186 1795] (Locality E). At Groveway Farm, mustard-coloured loose fine to medium-grained sand contained soft sandy limestone debris and a large ammonite fragment was seen dug from a fox earth [SP 8238 1825] and about 1.0 m of limestone is exposed in a ditch 180 m to the west [SP 8219 1827] (Locality C and Appendix 3, specimen AMB 459). Khaki and orange brown very silty clay with sand grade glauconite and a little buff glauconitic limestone debris was seen in a burrow near Chestnuts Farm [SP 8167 1805]. There are several pits in the Formation but it is exposed in none of them. Around Lilies [SP 8112 1843] limestone was seen in the soil in several places.

Pale grey sandy glauconitic limestone and orange-brown glauconitic sand were seen in the soil on the outcrop of the Formation around Hardwick Hill Farm [SP 812 199]. Pale yellow-brown glauconitic fine-grained sand was dug in rabbit burrows 100 m east of the farm [SP 8132 1995]. Both this outcrop and those around Weedon may have been affected by cambering lowering the ends of spurs (see Superficial Structures).

Purbeck Formation

The Purbeck Formation crops out only in the fault block north-west of Dunsham Farm [SP 8260 1606] to [SP 8299 1540] where it underlies the Whitchurch Sand Formation. It consists of about 2 m of pale silty clay, cream marl and off-white, fine-grained shelly limestone containing minute freshwater gastropods.

Whitchurch Sand Formation

The Whitchurch Sand Formation crops out in the faulted block west of Bierton [SP 827 159] to [SP 833 150], overlying the Purbeck Formation, and also north-east of Hardwick Hill Farm [SP 8133 1999], overlying the Portland, where it forms part of the outcrop around Whitchurch.

The name Whitchurch Sands was proposed by Casey and Bristow (1964) for deposits of ferruginous sand recorded between the Portland or Lower Purbeck and the Lower Greensand or Gault in the South Midlands. In this district they were previously called Shotover Sands (Blake, 1893) or Shotover Iron Sands (Davies, 1899, p.40). Now known as the Whitchurch Sand Formation, the problem of its age is not yet resolved (see Barron, 1988) and for present purposes it is attributed to the Portlandian Stage and the Jurassic.

In the present area the Formation is comprised of up to about 4 m of interbedded pale grey smooth clay and pale grey and orange-brown medium-grained sand with subordinate orange-brown ironstone beds. The outcrop in Bierton was almost certainly down-faulted prior to the deposition of the Gault (see Structure). On Cameron's 1897 fieldslip he notes 'sand pit' in two places near Dunsham Farm [SP 8310 1522] and [SP 8327 1506] and Reid recorded the following at the north-western pit: 'ferruginous loamy moulding sand and thin bed ironstone with ool (?) grains' which he nevertheless included in the Portland outcrop.

Cretaceous

Gault

The Gault crops out on the high ground in the north-east of the area, on the top of the Weedon ridge, as an outlier [SP 842 170] between Bierton and Rowsham and in the south-east where the tract comprises part of the main outcrop of Gault north of the Chiltern Hills.

The Gault consists of up to about 33 m of dark grey silty mudstone in this area, with thin glauconitic sandy horizons and phosphatised nodules and fossils. It weathers to very pale grey, (Appendix 2, Locality L) and at the surface it gives rise to a very heavy grey brown silty clay soil with black and grey phosphatised fragments, which distinguish it from the Kimmeridge Clay.

There is a substantial unconformity beneath the Gault in this area. In the north-east it rests directly on the Kimmeridge Clay, the Portland, Purbeck and Whitchurch Sand being absent. The junction has been placed with the aid of fossil evidence. At the eastern end of the Weedon ridge the Portland Formation is absent beneath the unconformity and around Bierton the junction is notably angular; as much as 10 m of beds being cut out over less than l km (see Structure).

A large number of phosphatised fossils were collected from the Gault outcrop, mainly ammonite fragments, but at the time of writing these were yet to be identified.

Drift

Quaternary

Till (Boulder Clay)

Deposits of till or boulder clay cap the Gault outcrop in the north-east. The largest deposit around and to the west of Aston Abbotts [SP 83 19] and [SP 84 19] is up to 12 m thick and is overlain by Glacial Sand and Gravel. Two smaller deposits cap hills near Fox Covert [SP 848 195] and 1km north of Rowsham [SP 849 190]. The deposits consist of grey and brown stony clay, sandy-in parts, especially in the upper part, the stones consisting of flints, sandstone and quartz pebbles and a little chalk. The base stands at between 120 and 131m OD.

A deposit of orange brown flinty silty clay occurs 500 m east of Hardwick Hill Farm [SP 8172 1999] on the edge of the area. This is also thought to be Till.

A borehole 900 m west of The Abbey (Appendix 1, (SP81NW/18)) penetrated 10.6 m of till consisting of blue grey silty clay with stones at the base, beneath Glacial Sand and Gravel.

The deposits may have been affected slightly by cambering (see Superficial Structures).

Glacial Sand and Gravel

Deposits of Glacial Sand and Gravel cap the hill in the extreme north-east around Aston Abbotts. They consist of up to 10 m of pale orange to light brown medium-grained silty sand with brown flint gravel and brown sandstone ('Bunter') pebbles in places. The base stands at between 127 and 133 m OD. A borehole (Appendix 1, (SP81NW/18)) a kilometre west of Aston Abbotts proved 1.5 m of brown clay (? made ground) on 3.1mof silty sand. The sand and gravel overlies till, the upper part of which is fairly sandy, but the junction is marked in many places by springs or seepages (see Water Supply). The base is slightly uneven, this could be due to minor cambering of the outer ends of spurs (see Superficial Structures) but is more likely the result of channelling.

Glaciofluvial Sand and Gravel

Deposits of brown stony sandy clay capping hills and spurs in the western part of the area are described as Glaciofluvial Sand and Gravel. They are distinguished from the Glacial Sand and Gravel overlying Till around Aston Abbotts by their lower elevation (maximum 97 m, minimum 82 m), by their poorly-sorted nature and by their resemblance to a system of high-level river terrace deposits collectively inclined towards the south-west. Their coarseness and elevation distinguishes them from the recent river terrace deposits. The deposits consist of brown and grey brown sandy to very sandy clay with varying amounts of flints, quartz and sandstone pebbles, ironstone fragments and limestone gravel. They are at their thickest, stoniest and sandiest immediately west of the A413 near Uppings Farm [SP 807 178] where they are thought to reach 2 m in places. The deposits feather off at the edges, notably south of Uppings Farm [SP 802 172] where the boundary is very approximate. Over much of the outcrop of the deposits grey clay can be seen in the soil. This is thought to have been brought to the surface at least partly by cryoturbation.

Around Uppings Farm [SP 804 179] and south-west of Weedon Hill [SP 809 158] the deposit stands at at least two levels. This indicates at least two periods of deposition separated by spells of downcutting. The material is thought to have been deposited, by high-energy braided meltwater streams.

River Terrace Deposits

Spreads of brown silty clay, generally sandy and stony, flank the alluvial tracts of the River Thame and Hardwick stream. They comprise deposits with flat terrace-like tops generally sloping towards the river and downstream. The terraces stand at two distinct levels; a lower level (distinguished provisionally here as First Terrace) between just above and 3 m above the floodplain and a higher level (provisionally Second Terrace) between 3 and 8 m above the floodplain in the Thame valley, and between 2 and 4 m above in the Hardwick valley. There appears to be no clear lithological distinction between the deposits of the different terraces; the proportions of sand and gravel are quite variable throughout as is the grade of the clasts, and the lithologies and relative abundances of the stones are generally similar to that seen in a section at Watermead ((Appendix 2), Locality B) with flints being most common, followed by sandstone and quartz pebbles, and rarer ironstone and limestone debris.

The river terrace deposits were penetrated in several boreholes in the area (Appendix 1), mainly around the north side of Aylesbury (SP81NW/7), (SP81NW/11), (SP81NW/12), (SP81NW/15), (SP81NW/36), (SP81NW/42), (SP81NW/44), (SP81NW/45), (SP81NW/49) and (SP81NW/51) in which they are described variously as silty clay, stony sandy clay, gravelly sand and gravel. In boreholes for the A413 improvement scheme (SP81NW/190) and (SP81NW/23) and the Lakeside village development (SP81NW/67) and (SP81NW/83) the First Terrace deposits were proved.

Alluvium

The River Thame, the Hardwick stream and most of their tributaries are flanked by alluvial tracts composed of grey-brown silty clay with sand and gravel lenses and lag deposits. The floodplain of the Thame is generally between 100 and 200 m wide but at the western margin [SP 800 159] broadens to 800 m. That of the Hardwick stream is generally about 50 m wide, broader in places.

There is a large spread of alluvium east of Grendon Hill Farm [SP 830 167] consisting of about a metre of sandy clay on sand which is linked to the Thame floodplain but has probably been formed by winter flooding.

Alluvial deposits are exposed in only one place: about a metre of sandy clay and sand with gravel was seen in a new cut at Watermead ((Appendix 2), Locality K).

A number of boreholes penetrate alluvial deposits ((Appendix 1), (SP81NW/2), (SP81NW/37), (SP81NW/38), (SP81NW/39), (SP81NW/52), (SP81NW/53), (SP81NW/55), (SP81NW/56), (SP81NW/58), (SP81NW/62), (SP81NW/63), (SP81NW/65), (SP81NW/73), (SP81NW/76), (SP81NW/79), (SP81NW/84), and (SP81NW/90) – (SP81NW/94)) proving it to be around 2 m thick in the Hardwick valley and up to 3.3 m in the Thame valley.

Colluvial Deposits (Hillwash)

Deposits of brown sandy silty clay, stony in places, plaster the sides and lie in the bottoms of many of the valleys in the area. They are shown as colluvial deposits; possible evidence was seen of solifluction in one borehole (see below) but it is possible that many of the deposits may be in part periglacial and therefore bona fidehead. The deposits consist of material derived from formations and drift deposits upslope from their present position. Thus in the valley near Lower Burston Farm [SP 843 185] the colluvial material consists of sandy stony clay derived mainly from the Gault, Till and Glacial Sand and Gravel.

Around the Watermead site [SP 82 16] the deposits are very sandy clay derived from the Portland Formation and Kimmeridge Clay. In the bottoms of valleys the deposits may reach 2 m in thickness but elsewhere are probably no more than 1 m thick, although around the Watermead site several boreholes and trial pits ((Appendix 1), (SP81NW/72), (SP81NW/74), (SP81NW/78, (SP81NW/81), (SP81NW/86), (SP81NW/98), (SP81NW/101), (SP81NW/102), (SP81NW/104), (SP81NW/109) and (SP81NW/110)) penetrate colluvial deposits showing them to be up to 1.7 m thick here. One pit (SP81NW/102) apparently shows a gravel pocket within weathered Kimmeridge Clay which suggests that cryoturbation may have taken place, indicating a periglacial environment.

Structure

The regional dip in this area is less than half a degree to the SSE, and this is only slightly modified in places by faulting, folding and superficial structures (see below).

The only folding visible in the outcrop pattern is the shallow syncline north-east of Bierton (the East Bierton Syncline of Bristow, 1963) which has preserved Portland Formation in a NNW–SSE trending structure formed prior to the deposition of the Gault. The early Cretaceous earth movements also produced gentle anticlines on either side with similar trends. Subsequent erosion truncated the anticlines, being responsible for the absence of the Portland Formation south-west of Corner Farm [SP 844 156] and, if the anticline is projected NNW, to the east of Groveway Farm [SP 826 183], its eastern equivalent being responsible for their absence north-east of Grove Farm [SP 847 162] and beneath the Gault in the knoll [SP 842 170] west of Cane End Farm. Dips on the limbs of these folds are thought to be less than one degree.

The main trend of the faulting is also NNW–SSE and has been detected mainly within the Portland Formation outcrops. Faulting is believed to both pre-date and post-date the deposition of the Gault; the system of faults around Dunsham Farm [SP 830 153] has preserved a block of the Purbeck and Whitchurch Sand formations, not seen beneath the Gault anywhere else around Bierton, but the faults in east Bierton and Weedon affect the Gault outcrop and therefore must post-date it.

The main Weedon Fault, running from near Lilies Farm [SP 8110 1863] to south of Chestnuts Farm [SP 8163 1770] throws down to the east along its middle section but subsidiary faults, thought to belong to a later period of faulting, have caused the sense of throw to be reversed along the northern part near Lilies Farm and the southern part [SP 8150 1792] east of Stockaway.

Superficial structures

Cambering is thought to have affected the outer ends of spurs capped by both the Portland Formation and the hilltop glacial drift. The process involves softer beds, such as clay, being squeezed out or washed out from beneath harder or permeable strata and the gradual lowering of the overlying strata (see Hollingworth, Taylor and Kellaway, 1944 and Horswill and Horton, 1976). This is thought to have profoundly affected the Kimmeridge Clay and Portland Formations around Manor Farm, Weedon [SP 814 184] and Hardwick Hill Farm [SP 812 199] and the Sand and Gravel and Till south of The Abbey, Aston Abbotts [SP 845 196] to only a minor degree may have been much more profoundly affected.

Clay strata at the bottom of valleys may be affected by a process known as valley bulging in which they are squeezed upward above their original level. This may have taken place north-west of Hardwick [SP 801 198] and in the Hardwick valley [SP 825 199] affecting the Ampthill and Kimmeridge Clay formations.

Landslip

Minor slips have occurred on the steep slopes of Gault in the valley by Fox Covert [SP 845 195] and [SP 846 194]. The drift deposits overlying the Gault in this area are sufficiently durable to allow the development of steep slopes in the clay formations and the included sandy beds conduct water to spring and seepage lines (see Water Supply) providing lubrication to shear planes within the underlying clay. The mapped landslips are not extensive but any part of the steeper slopes around Aston Abbotts may be susceptible to slippage. An analogous situation occurs around the Weedon ridge and north-east of Hardwick where the Portland beds are both durable and permeable. Landslips within the outcrop of the underlying Kimmeridge Clay were not detected but may have taken place and have been blended back into the slope by human activity. The steeper parts of these slopes may also be still susceptible.

Made Ground (and Landscaped Ground)

There are several minor areas of made ground or fill in this area; some constructed as dams for ponds or sludge tanks for instance near Aston Abbotts [SP 8396 1995], [SP 8442 1944] near Lower Burston Farm [SP 8425 1875] and near Dunsham Lane [SP 8276 1509]; some are spoil from or within pits or quarries, for instance near Burston Hill Farm [SP 8331 1844] and [SP 8366 1879] and at Dunsham Farm [SP 8311 1523].

There is a small area of made ground near Dunsham Lane [SP 8240 1519] at the site of demolished farm buildings, and a length of abandoned railway embankment about 0.5 m high in the extreme south-east [SP 8490 1505]. Considerable earthworks exist at the abandoned village sites at Lower Burston Farm [SP 841 188] and south-west of Weedon Hill [SP 806 157] together with Civil War earthworks at the latter location.

The major deposits of made ground are much more recent; areas of landfill, presumably mainly domestic refuse deposited on the floodplain, fringe the northern outskirts of Aylesbury [SP 800 153] to [SP 822 152]. Some of these have been filled up level with the river terrace and are now built over and the southern boundary is difficult to place precisely, notably around Beresford Avenue [SP 8139 1513].

At a site east of the A413 road, just north of the Aylesbury outskirts and now called Watermead [SP 821 155] a combined residential and recreation development was under construction at the time of survey (1988). Considerable landscaping had already taken place including the excavation of an extensive artificial lake. Spoil from this operation (Kimmeridge Clay and drift deposits) had been utilised to raise ground level in several places but principally to construct a substantial 20 m high conical mound. The River Thame has also been diverted around the north and west sides of the mound.

Economic geology

Most of the formations and deposits in this area have been dug for materials at one time or another although there are no major extraction sites now in use.

There are a few minor pits in the Kimmeridge Clay outcrop, and the largest pit in the area is Ward and Cannon's brick pit in Bierton [SP 839 158] (seeSherlock 1922, p.7) which was dug through the Portland Formation to extract Kimmeridge Clay for brickmaking. On a field slip, Reid noted in 1910 'lydite bed 2' (0.6 m), dark blue very sandy clay 8' (2.4 m) (dug to 25' (7.6 m))' at this site.

The Portland Formation outcrops are pockmarked with pits particularly around Dunsham Farm [SP 830 153], Barnett House [SP 837 158] along Rowsham Road [SP 843 162] and around Weedon [SP 81 18]. The Portland Stone has been used as a rough building stone and the sand beds for various purposes. However, the softer fine-grained limestones were used in the past as a vernacular construction material known as 'witchett', involving burning the stone and mixing it with water as a poor-quality mortar.

Material for witchett was probably also dug from the Purbeck in pits north-west of Dunsham Farm [SP 8294 1550].

The Whitchurch Sand was dug around Dunsham Farm [SP 8273 1586], [SP 8310 1522] and [SP 8327 1506] for sand. Reid notes its use as moulding sand on his 1910 field slip, Bristow (1963, p.53) reports its use as building sand for Aylesbury Prison –– they both record it as being from the Portland.

There are several small pits on the Gault outcrop notably around Burston Hill [SP 834 185] and north of Rowsham from which clay may have been taken for brickmaking or phosphatic material for 'coprolite' fertilizer.

There are many disused pits in the Glacial Sand and Gravel and Till around Aston Abbotts from which sand and gravel were extracted for construction uses.

There are a couple of pits in the glaciofluvial sand and gravel deposits at Uppings Farm [SP 8036 1811] and north-west of Rectory Farm [SP 8019 1861] from which gravel would have been extracted.

No evidence has been found for exploitation of the river terrace deposits or the alluvium. In the neighbourhood of Aylesbury, no doubt any pits would have been backfilled with refuse and be indistinguishable.

Water supply

The main water bearing strata in this area are the Portland Formation and the sandy drift deposits. However, a well at Grendon Hill Farm [SP 8271 1676] was noted on an old map as containing water at 15 feet (4.6 m) 'large ironstones 1' - 1'6" at base in ... Kimmeridge Clay giving irony water'. This is probably Bed KC 30 of Gallois and Cox (1976). Another well was seen in the Kimmeridge Clay outcrop 500 m west of Rowsham [SP 8442 1788].

Seepages were seen in several places around the Portland Formation outcrop, notably 450 m east of Hardwick Hill Farm. [SP 8168 1999] and near Groveway Farm [SP 8251 1829]. Wells were seen in several places on the Portland outcrop and immediately below the base. A well at Barnett House [SP 8370 1582] was found to be 5.3 m deep with a water level 2.5 m below ground level (May 1988). The water was 1.0 m below ground level in a well in Burcott [SP 8420 1512]. The Uptown Well and pond [SP 8359 1521] by the church in Bierton are just below the base of the Portland Formation and are presumably supplied by spring or pipe. A well at Hardwick Hill Farm [SP 8124 1992] is about 5 m below the Portland base but the water stood at ground level and is thought to be piped in.

The edge of the glacial sand and gravel deposit around Aston Abbotts is marked by a very strong spring line, at the top, the Till is quite sandy so the issues may not be precisely at the. base of the sand and gravel. A spring, reported to be perpetual, was seen west of The Lines [SP 8402 1965] and a strong seepage line 250 m to the east [SP 8428 1962] fed a small brick reservoir [SP 8423 1953].

The surface drainage on the clay formations feeds many ponds, some natural, others formed. or enlarged by man-made banks (see Made Ground).

Appendix 1 Boreholes and trial pits

Abbreviations:

AmC Ampthill Clay Formation

G Gault

OD Ordnance Datum

P1S Portland Sand Member

RTD River Terrace Deposits

c circa (approximately)

KC Kimmeridge Clay Formation

P1 Portland Formation

P1St Portland Stone Member

S.L. Surface level

2. Gas pipeline borehole 25 [SP 824 195] S.L. + c 86 m OD

4. Gas pipeline borehole 27 [SP 804 197] S.L. + 97.75 m OD

7. Quarrendon housing borehole C4 [SP 8003 1518] S.L. + 72.38 m OD

11. Quarrendon housing borehole-G3 [SP 8006 1533] S.L. + 71.40 m OD

12. Quarrendon housing borehole G5 [SP 8002 1530] S.L. + c72 m OD

15. Quarrendon sports pavilion borehole 2 [SP 8080 1519] S.L. + c76 m OD

18. [SP 8362 1998] S.L. + 134.2 m OD

19. A413 improvement borehole 1 [SP 8171 1565] S.L. + 74.05 m OD

23. A413 improvement borehole 5 [SP 8160 1604] S.L. + 74.43 m OD

26. A413 improvement borehole 8 [SP 8156 1623] S.L. +75.23 m OD

29. A413 improvement borehole 11 [SP 8148 1636] S.L. +84.5 m OD

31. A413 improvement borehole 13 [SP 8143 1645] S.L. + c84.5 m OD

34. A413 improvement borehole 16 [SP 8130 1672] S.L. + c81.1 m OD

36. Haydon Hill Farm Estate borehole 3 [SP 8019 1524] S.L. + 73.06 m OD

37. Haydon Hill Farm Estate borehole 4 [SP 8076 1531] S.L. + 75.13 m OD

38. Haydon Hill Farm Estate borehole 5 [SP 8110 1529] S.L. + 72.82 m OD

39. Haydon Hill Farm Estate borehole 6 [SP 8156 1516] S.L. + 72.39 m OD

42. Haydon Hill Farm Estate trial pit 3 [SP 8018 1513] S.L. + 74.51 m OD

44. Haydon Hill Farm Estate trial pit 12 [SP 8042 1521] S.L. + 73.00 m OD

45. Haydon Hill Farm Estate trial pit 13 [SP 8059 1513] S.L. + 77.51 m OD

49. Haydon Hill Farm Estate trial pit 17 [SP 8099 1524] S.L. + 74.32 m OD

51. Haydon Hill Farm Estate trial pit 19 [SP 8154 1505] S.L. + 73.28 m OD

52. Lakeside Village borehole 1 [SP 8192 1560] S.L. + 73.53 m OD

53. Lakeside Village borehole 2 [SP 8191 1565] S.L. + 73.66 m OD

55. Lakeside Village borehole 4 [SP 8189 1570] S.L. + 73.63 m OD

56. Lakeside Village borehole 5 [SP 8193 1545] S.L. + 73.31 m OD

58. Lakeside Village borehole 7 [SP 8224 1549] S.L. + 72.98 m OD

60. Lakeside Village borehole 9 [SP 8236 1557] S.L. + 74.87 m OD

61. Lakeside Village borehole 10 [SP 8229 1592] S.L. + 75.50 m OD

62. Lakeside Village borehole 11 [SP 8269 1517] S.L. + 73.42 m OD

63. Lakeside Village trial pit 1 [SP 8185 1580] S.L. + 73.75 m OD

65. Lakeside Village trial pit 3 [SP 8194 1573] S.L. + 73.49 m OD

67. Lakeside Village trial pit 5 [SP 8184 1565] S.L. + 73.89 m OD

72. Lakeside Village trial pit 10 [SP 8208 1590] S.L. + 73.9 m OD

73. Lakeside Village trial pit 11 [SP 8205 1578] S.L. + 73.42 m OD

74. Lakeside Village trial pit 12 [SP 8215 1580] S.L. + 73.71 m OD

76. Lakeside Village trial pit 14 [SP 8207 1569] S.L. + 73.37 m OD

78. Lakeside Village trial pit 16 [SP 8230 1574] S.L. + 74.59 m OD

79. Lakeside Village trial pit 17 [SP 8213 1561] S.L. + 73.34 m OD

81. Lakeside Village trial pit 19 [SP 8230 1565] S.L. + 73.0 m OD

83. Lakeside Village trial pit 21 [SP 8184 1542] S.L. + 73.30 m OD

84. Lakeside Village trial pit 22 [SP 8210 1550] S.L. + 73.20 m OD

86. Lakeside Village trial pit 24 [SP 8198 1596] S.L. + c74 m OD

90. Lakeside Village trial pit 28 [SP 8230 1543] S.L. + c73 m OD

91. Lakeside Village trial pit 29 [SP 8227 1533] S.L. +c73 m OD

92. Lakeside Village trial pit 30 [SP 8213 1533] S.L. + c73 m OD

93. Lakeside Village trial pit 31 [SP 8221 1533] S.L. + c73 m OD

94. Lakeside Village trial pit 32 [SP 8225 1544] S.L. + c73 m OD

98. Watermead trial pit 1 [SP 8245 1580] S.L. + 76.84 m OD

101. Watermead trial pit 4 [SP 8243 1567] S.L. + 76.08 m OD

102. Watermead trial pit 5 [SP 8230 1588] S.L. + 74.88 m OD

104. Watermead trial pit 7 [SP 8229 1579] S.L. + 74.54 m OD

109. Watermead trial pit 12 [SP 8233 1559] S.L. + 74.49 m OD

110. Watermead trial pit 13 [SP 8234 1552] S.L. + 74.49 m OD

Appendix 2 Localities

see Appendix 1 for abbreviations.

A. Gas pipe trench stream crossing [SP 8349 1953]

B. River diversion, Watermead [SP 8173 1573]

C. Ditch section, Groveway Farm [SP 18219 18271]

D. Trench along front of Weedon Lodge [SP 8200 1805]

Material dug from trench:

E. Trench, Weedon Lodge Farm [SP 8186 1795]

Material dug from trench:

F. Disused quarry, Dunham Farm [SP 8299 1535]

G. House foundations, Church Farm [SP 8344 1519]

H. Foundations, Burcott [SP 8429 1520]

J. Trench, Fox Covert [SP 8484 1931]

Material dug:

K. River bank section, Watermead [SP 8191 1592]

Appendix 3 Palaeontology

Specimen no. AMB 432

1200 m on 106° from Hardwick Church, Hardwick, Bucks.

[SP 8181 1864]

Silty cementstone (rather dense) with indeterminate shell fragments.

Horizon: Kimmeridge Clay (lower doggers of M J Oates)

Specimen no. AMB 433

1750 m on 094° from Hardwick Church, Hardwick, Bucks.

[SP 8240 1885]

Small, worn piece of silty cementstone with common shell fragments (bivalve and ammonite indeterminate).

Horizon: Kimmeridge Clay (lower doggers of M J Oates)

Specimen no. AMB 434

1700 m on 097° from Hardwick Church, Hardwick, Bucks.

[SP 8234 1876]

Worn piece of cementstone with perisphinctid ammonite fragments/impressions and other indeterminate shell fragments.

Horizon: Kimmeridge Clay (lower doggers of M J Oates)

Specimen no. AMB 435

900 m on 228° from Hardwick Church; Hardwick, Bucks.

[SP 8000 1838]

Worn piece of silty/silty-textured septarian cementstone with several Protocardia.

Horizon: Kimmeridge Clay (KC30 of standard sequence)

Specimen no. AMB 436

2100 m on 133° from Hardwick Church, Hardwick, Bucks.

[SP 8218 1753]

Small piece/chip of silty cementstone with indeterminate small shell fragments (?bivalve).

Horizon: Kimmeridge Clay (lower doggers of M J Oates)

Specimen no. AMB 437

450 m on 250° from Hardwick Church, Hardwick, Bucks.

[SP 8022 1883]

Loose specimen of Laevaptychus.

Horizon: Kimmeridge Clay (KC24 – KC33 of standard sequence)

Specimen no. AMB 438

1220 m on 055° from Hardwick Church, Hardwick, Bucks.

[SP 8166 1967]

Worn, silty, weakly septarian cementstone with scattered serpulid bits and indeterminate shell fragments.

Horizon: Kimmeridge Clay (lower doggers of M J Oates) (Nanogyra virgula recorded nearby)

Specimen no. AMB 439

2000 m on 120° from Hardwick Church, Hardwick, Bucks.

[SP 8238 1795]

Silty/silty-textured septarian cementstone with poorly preserved perisphinctid ammonite fragments and impression.

Horizon: Kimmeridge Clay (upper or lower doggers of M J Oates)

Specimen no. AMB 440

2250 m on 331° from Bierton Church, Bierton, Bucks.

[SP 8252 1725]

Septarian cementstone with shell fragments including Aulacostephanus ex gr. eudoxus (d'Orbigny) and indeterminate bivalves.

Horizon: Kimmeridge Clay (KC30 of standard sequence)

Specimen no. AMB 441

450 m on 196° from Hardwick Church, Hardwick, Bucks.

[SP 8054 1855]

Silty cementstone, weakly septarian, with bivalve fragments and ?serpulid bits.

Horizon: Kimmeridge Clay (?KC30 of standard sequence)

Specimen no. AMB 442

1550 m on 223° from The Abbey, Aston Abbotts, Bucks.

[SP 8341 1887]

Piece of worn, cube-shaped (?septarian) cementstone with scattered small, indeterminate shell fragments.

Horizon: Kimmeridge Clay (upper doggers of M J Oates)

Specimen no. AMB 443

1680 m on 098° from Hardwick Church, Hardwick, Bucks.

[SP 8232 1874]

Piece of silty-textured, septarian cementstone with ?poorly preserved, small shell fragments.

Horizon: Kimmeridge Clay (upper doggers of M J Oates)

Specimen no. AMB 444

1620 m on 099° from Hardwick Church, Hardwick, Bucks.

[SP 8226 1974]

Loose specimen of vertebra (?marine reptile)

Horizon: Kimmeridge Clay (clays between upper and lower doggers of M J Oates)

Specimen nos AMB 445–446

2790 m on 308° from Bierton Church, Bierton, Bucks.

[SP 8142 1699]

Pieces of worn, silty cementstone with perisphinctid fragments.

Horizon: Kimmeridge Clay (lower doggers of M J Oates)

Specimen nos AMB 447– 448

1570 m on 253° from the Abbey, Aston Abbotts, Bucks.

[SP 8296 1959]

Small, worn pieces of septarian cementstone with tiny shell fragments (?including Protocardia).

Horizon: Kimmeridge Clay (lower doggers of M J Oates)

Specimen nos AMB 449–450

1970 m on 257° from The Abbey, Aston Abbotts, Bucks.

[SP 8256 1961]

Piece of silty cementstone with shell fragments/impressions including perisphinctid ammonite, serpulid and indeterminate others, plus a smoother-textured pale cementstone nodule with clean moulds of fossil fragments including perisphinctid ammonite (and nucleus).

Horizon: Kimmeridge Clay (KC30 of standard sequence)

Specimen no. AMB 451

2010 m on 351° from Bierton Church, Bierton, Bucks.

[SP 8333 1726]

Piece of septarian, silty cementstone with poorly preserved perisphinctid ammonites.

Horizon: Kimmeridge Clay (lower doggers of M J Oates)

Specimen no. AMB 452

1890 m on 351° from Bierton Church, Bierton, Bucks.

[SP 8334 1713]

Piece of worn, silty, septarian cementstone with perisphinctid ammonite fragment.

Horizon: Kimmeridge Clay (lower doggers of M J Oates)

Specimen no. AMB 453

1600 m on 201° from Hardwick Church, Hardwick, Bucks.

[SP 8009 1748]

Piece of worn, silty cementstone with indeterminate bivalve fragments.

Horizon: Kimmeridge Clay (KC30 of standard sequence) (associated Nanogyra virgula marked on field slip)

Specimen no. AMB 454

1350 m on 231° from The Abbey, Aston Abbotts, Bucks.

[SP 8342 1917]

Very worn piece of barren, smooth-textured cementstone.

Horizon: Kimmeridge Clay (upper doggers of M J Oates)

Specimen no. AMB 455

1080 m on 242° from The Abbey, Aston Abbotts, Bucks.

[SP 8349 1953]

Loose right valve of Nanogyra

Horizon: ?Upper Kimmeridge Clay

Specimen no. AMB 456

1290 m on 266° from The Abbey, Aston Abbotts, Bucks.

[SP 8318 1991]

Loose right valve of Nanogyra.

Horizon: ?Upper Kimmeridge Clay

Specimen nos AMB 457–458

1930 m on 318° from Bierton Church, Bierton, Bucks.

[SP 8234 1673]

Loose specimens of Nanogyra virgula (Defrance).

Horizon: Kimmeridge Clay (almost certainly Eudoxus Zone (KC24 – KC32)

Specimen no. AMB 459

1700 m on 114° from Hardwick Church, Hardwick, Bucks.

[SP 8219 1827]

Ammonite whorl fragment (very evolute with pavloviid ribbing) in shell-fragmental ?sandy limestone.

Horizon: Portland Formation ?Portland Stone Member (?Aylesbury (Rubbly) Limestone)

Specimen no. AMB 460

1090 m on 358° from Bierton Church, Bierton, Bucks.

[SP 8359 1636]

Broken ammonite (Galbanites?) with scattered lydites and greenglauconitic grains in limestone matrix, also internal mould of

trigoniid.

Horizon: Portland Formation

Specimen nos AMB 461–463

180 m on 245° from Bierton Church, Bierton, Bucks.

[SP 8345 1520]

Bivalves preserved in pale cream-coloured limestone with some sparry calcite (large mytiloid or pterioid, Protocardia dissimilis (J de C Sowerby), cyprinid?).

Horizon: Portland Formation ?Portland Stone Member

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