| Computer Code: |
EMLD |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Bathonian Age (JN)
— Oxfordian Age (JO) |
| Lithological Description: |
The formation comprises very fine- to medium-grained, shelly, bioturbated sandstone and subordinate siltstone, often with a thin basal conglomerate. In many sections, the lower part of the formation is coarser and cleaner than the upper part, but in some sections log signatures indicate upward coarsening. |
| Definition of Lower Boundary: |
The Emerald formation may overlie, lower Jurassic, Upper Palaeozoic, Lower Palaeozoic and Precambrian strata. In some sections (e.g. 2/10-8) the base can be placed between the basal conglomerate Lower Jurassic sandstones and this is shown on geophysical logs by a distinct downward increase in velocity. In other sections there is a down-section change from clean brownish sandstone (Emerald Formation) to red or varicoloured sandstones, siltstones or limestones of Devonian age, accompanied by a downward increase in gamma values and velocity. Where the formation rests on Lower Palaeozoic or Precambrian rocks, there is a downward change from clean sandstone to gneiss and a downward increase in gamma values and decrease in velocity. |
| Definition of Upper Boundary: |
The upper boundary is characterised by a downward change from grey mudstones and siltstones (Heather Formation) to sandstones (Emerald Formation). The boundary is marked by a down-section decrease in gamma values and increase in velocity. |
| Thickness: |
10-30 m (average c. 15 m). |
| Geographical Limits: |
'Transitional Shelf', North Sea quadrants 2 and 3. |
| Parent Unit: |
Humber Group (HMBG)
|
| Previous Name(s): |
Emerald Sandstone
(-5100)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 2/10- 8 at 2706.5-2734 m depth below KB (Wheatley et al., 1987; Richards et al., 1993). |
| Reference Section |
North Sea well 2/15- 1 at 1705-1725 m depth (Richards et al., 1993). |
| Reference Section |
North Sea well 3/11b- 3 at 1672-1686.5 m depth (Richards et al., 1993). |
| Reference(s): |
| Stewart , D.M. & Faulkener, J.G. 1991. The Emerald Field, Blocks 2/10a, 2/15a, 3/11b, UK North Sea. In: Abbotts, I.L. (ed.) United Kingdom oil and gas fields 25 years commemorative volume. Memoir of the Geological Society, London, 14, 111-116. |
| Wheatley, T.J., Biggins, D., Buckingham, J. & Holloway, N.H. 1987. The geology and exploration of the Transitional Shelf area, an area to the west of the Viking Graben. In: Brooks, J. & Glennie, K.W. (eds) Petroleum geology of North West Europe, 979-989. [Graham Trotman, London] |
| Richards, P C, Lott, G K, Johnson, H, Knox, R W O'B. and Riding, J B. 1993. 3. Jurassic of the Central and Northern North Sea. In: Knox, R W O'B and Cordey, W G (eds.). Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
