|Computer Code:||KC||Preferred Map Code:||KC|
|Status Code:||Full, pending ratification|
|Age range:||Kimmeridgian Age (JD) — Kimmeridgian Age (JD)|
|Lithological Description:|| Onshore:
Mudstones (calcareous or kerogen-rich or silty or sandy); thin siltstone and cementstone beds; locally sands and silts.
In the Southern North Sea, the Kimmeridge Clay Formation comprises dark brown-grey to black, organic rich, fissile mudstone with occasional hard, thin carbonate-cemented horizons. The mudstone comprises fissile grey to brown-grey, shelly mudstone; bituminous mudstone; oil-shale and thin, paler, calcareous mudstone.
In the Central and Northern North Sea, the formation comprises dominantly of dark-grey brown to black, non-calcareous to weakly calcareous, partly fissile, moderately to highly organic-rich mudstone with local, thin laminae and streaks of siltstone and sandstone. Sandstone and conglomerate is interbedded with the mudstone at various levels and have been given member status. Thin, fine grained, sometimes cross-laminated, un-named sandstones also occur locally. Sandstone members are:
Birch Sandstone Member
Burns Sandstone Member
Claymore Sandstone Member
Dirk Sandstone Member
Magnus Sandstone Member
Ptarmigan Sandstone Member
Ribble Sandstone Member
|Definition of Lower Boundary:|| Onshore:
In the type area, at the base of the Inconstans Bed, which also marks the Oxfordian-Kimmeridgian Stage boundary.
In the Southern North Sea, the lower boundary is a sharp downward change from dark mudstone (Kimmeridge Clay Formation, Offshore) to paler, more calcareous, silty mudstone (Woodward Formation).
In the Central and Northern North Sea, the Kimmeridge Clay Formation frequently overlies mudstone of the Heather Formation so that the boundary is difficult to identify without biostratigraphical control. Although there is a sharp down-section decrease in gamma-ray values and, sometimes, an increase in velocity and/or generally a decrease in resistivity at the lower boundary in some well sections, in others there are several log-markers that can be misinterpreted as the boundary. There is locally a downward colour change to paler mudstone, a decrease in organic content and increase in thin limestone beds. Where the Kimmeridge Clay overlies the Piper or Fulmar formations, the lower boundary is the downward change from organic-rich mudstone to sandstone, accompanied by a decrease in gamma values and an increase in velocity.
|Definition of Upper Boundary:|| Onshore:
At the base of the 'Portland Sand'. In the type area, this has traditionally, but not unanimously, been taken at the base of the Massive Bed, which also marks the Kimmeridgian-Portlandian stage boundary. In other areas, taken where silty/sandy mudstones pass up into argillaceous sandstones/siltstones (possibly marked by a spring-line) or, where non-sequential, at the base of the Upper Lydite Bed.
In the Southern North Sea, the upper boundary of the Kimmeridge Clay Formation is often truncated by erosion. Mudstone, sandstone or chalky lithologies overlie the dark brown-grey to black, organic rich, fissile mudstones of the Kimmeridge Clay Formation (Offshore). Generally organic-poor, non-fissile, calcareous mudstones (Valhall Formation) overlie dark brown-grey to black, organic rich, fissile mudstones (Kimmeridge Clay Formation, Offshore). Where two mudstones are juxtaposed, the boundary may be unrecogniseable without biostratigraphical control. In some areas sandstone (Spilsby Sandstone Formation, Offshore) overlies the organic-rich mudstones of the Kimmeridge Clay Formation (Offshore).
In the Central and Northern North Sea, the boundary is placed at the downward change from marls, calcareous mudstone, sandstone or limestone (Cromer Knoll Group) to dark grey mudstone. This is represented on geophysical logs by a downward increase in gamma values and decrease in velocity. Locally a more continuous sandstone succession occurs, and although the boundary is difficult to define, there is commonly a downward change from thickly bedded and/or calcareous sandstones to relatively thinly bedded sandstones.
To c. 500 m
Up to 260 m in the Southern, 300 m in the Central and 1400 m in the Northern North Sea.
|Geographical Limits:|| Onshore:
(Outcrop) - Dorset to North Yorkshire.
Offshore the Formation is considered to extend from the Kimmeridgian to the Late Ryazanian, and forms part of the Humber Group.
Southern North Sea Quadrants 41, 42, 43, 47, 48, 51 and 52. Central and Northern North Sea Quadrants 1-3, 7-9, 12-22, 28-30 and 209-211.
|Parent Unit:||Ancholme Group (AMG)|
|Previous Name(s):|| Oaktree Clay
Oaktree Soil (-4725)
Cemetery Beds [Obsolete Name And Code: Part Of KC] (CE)
|Alternative Name(s):||none recorded or not applicable|
|Type Section||North Sea well 47/15-1 at 885-919 m depth. Rhys (1974); Lott and Knox (1994).|
|Reference Section||North Sea well 47/9b-4 at 756-875 m depth. Lott and Knox (1994).|
|Reference Section||North Sea well 47/10-1 at 1147-1334 m depth. Lott and Knox (1994).|
|Reference Section||North Sea well 47/18-1 at 545-738 m depth. Lott and Knox (1994).|
|Reference Section||North Sea well 48/17a-2 at 792-981.5 m depth. Lott and Knox (1994).|
|Reference Section||North Sea well 211/28-5 at 3133.5-3308.5 m depth. Richards et al. (1993).|
|Reference Section||North Sea well 3/1-2 at 3338-3535 m depth. Richards et al. (1993).|
|Reference Section||North Sea well 11/30-2 at 969.5-1638.5 m depth. Richards et al. (1993).|
|Reference Section||North Sea well 16/13a-3 at 4285.5-4672.5 m depth. Richards et al. (1993).|
|Reference Section||North Sea well 30/8-1 at 3700-3990 m depth. Richards et al. (1993).|
|Type Area||Coastal cliffs and landslips, Black Head to Osmington Mills, Dorset (continuous with two other areas as described).|
|Type Area||Coastal cliffs and landslips, Ringstead Bay, Dorset (continuous with two other areas as described).|
|Type Area||Coastal cliffs and foreshore, Brandy Bay to Chapman's Pool, Dorset (continuous with two other areas as described).|
|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. Lithostratigraphic nomenclature of the UK North Sea. [British Geological Survey, Nottingham]|
|Rhys, G H. 1974. A proposed standard lithostratigraphic nomenclature for the southern North Sea and an outline structural nomenclature for the whole of the (UK) North Sea. Report of the Institute of Geological Sciences, 74/8.|
|Bowen, J M. 1975. The Brent Oil-Field. In: Woodland, A W (ed.) Petroleum and the contineental shelf of North-West Europe, 353-361. [Heyden & Son, London]|
|Deegan, C E and Scull, B J. 1977. A standard lithostratigraphic nomenclature for the Central and Northern North Sea. Report of the Institute of Geological Sciences, 77/25; NPD Bulletin No.1.|
|Maher, C E and Harker, S D. 1987. Claymore OIlfield. In: Brooks, J and Glennie, K W (eds.) Petroleum Geology of North West Europe, 835-845. [Graham & Trotman, London]|
|Webster, T, 1816. Geological observations on the Isle of Wight. 117-238 in Englefield, H. Description of the principal picturesque beauties, antiquities and geological phenomena of the Isle of Wight. [London: Payne and Foss.]|
|Blake, J F, 1875. On the Kimmeridge Clay of England. Quarterly Journal of the Geological Society of London, Vol.31, 196-233.|
|Gallois, R W and Cox, B M, 1976. The stratigraphy of the Lower Kimmeridge Clay of eastern England. Proceedings of the Yorkshire Geological Society, Vol.41, 13-26.|
|Cox, B M and Gallois, R W, 1979. Description of the standard stratigraphical sequences of the Upper Kimmeridge Clay, Ampthill Clay and West Walton Beds. 68-72 in Geological investigations for the Wash Water Storage Scheme. Gallois, R W. Report of the Institute of Geological Sciences, No.78/19.|
|Cope, J C W, 1980. Kimmeridgian correlation chart. 76-85 in A correlation of Jurassic rocks in the British Isles. Part Two: Middle and Upper Jurassic. Special Report of the Geological Society of London, No.15.|
|Cox, B M and Gallois, R W, 1981. The stratigraphy of the Kimmeridge Clay of the Dorset type area and it's correlation with some other Kimmeridgian sequences. Report of the Institute of Geological Sciences, No.80/4.|
|Wignall, P B. 1990. Benthic palaeoecology of the late Jurassic Kimmeridge Clay of England. Special Papers in Palaeontology, No.43.|
|Herbin, J P, Geyssant, J R, Melieres, F, Muller, C, Penn, I E and The Yorkim Group. 1993. Variation of the distribution of organic matter within a transgressive system tract: Kimmeridge Clay (Jurassic), England. 67-100 in Source rocks in a sequence stratigraphic framework. American Association of Petroleum Geologists Studies in Geology, No.37|
|Horton, A, Sumbler, M G, Cox, B M and Ambrose, K, 1995. Geology of the country around Thame. Memoir of the British Geological Survey, Sheet 237 (England and Wales).|
|Smith, W, 1815. A delineation of the strata of England and Wales with part of Scotland. [London: W Smith.]|
|Smith, W. 1817. Strata identified by organized fossils, Part 3. [London.]|
|Turner, C.C., Cohen, J.M., Connell, E.R. & Cooper, D.M. 1987. A depositional model for the South Brae Oilfield. In Brooks, J. & Glennie, K.W. (eds) Petroleum Geology of North West Europe, 853-864. [Graham & Trotman, London]|
|Riley, L A, Roberts, M J and Connell, E R. 1989. The application of palynology in the interpretation of Brae Formation stratigraphy and reservoir geology in the South Brae Field area, British North Sea. In: Collinson, J.D. (ed.) Correlation in hydrocarbon exploration, 339-356. [Graham & Trotman, London]|
|Price, J, Dyer, R, Goodall, I, Mackie, T, Watson, P and Williams, G. 1993. Effective stratigraphical subdividion of the Humber Group and the Late Jurassic evolution of the U.K. Central Graben. In: Parker, J.R. (ed.) Petroleum geology of Northwest Europe: Proceedings of the 4th Conference, 443-458. [Geological Society, London]|
|Lott, G K and Knox, R W O'B. 1994. 7. Post-Triassic of the Southern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. [British Geological Survey, Nottingham].|
|Arkell W J, 1933. The Jurassic System in Great Britain [Oxford: Clarendon Press.]|
|1:50K maps on which the lithostratigraphical unit is found, and map code used:|
|E102 E103 E115 E128 E129 E145 E159 E173 E187 E188 E204 E205 E219 E220 E236 E237 E238 E252 E253 E254 E266 E268 E281 E282 E298 E299 E313 E327 E341 E342 E343 E055 E064 E065 E072 E081|