The BGS Lexicon of Named Rock Units — Result Details

Cerdic Formation

Computer Code: CERD Preferred Map Code: notEntered
Status Code: Full
Age range: Toarcian Age (JT) — Toarcian Age (JT)
Lithological Description: The Cerdic Formation comprises dominantly dark grey marine mudstones with sporadic, thin argillaceous limestones. Where the formation is most complete, it passes upwards into fine-grained sandstones and siltstones at the top (Phillips Member).
Definition of Lower Boundary: The lower boundary is defined by a downwards change from mudstones to silty, sandy and occasionally ferruginous and oolitic limestone (Ida Formation). The boundary coincides with a marked downwards increase in velocity and a decrease in gamma values.
Definition of Upper Boundary: The upper boundary is erosional. It is usually marked by a downwards change from clastic facies (Wroot Formation) to mudstones, with a corresponding sharp downwards increase in gamma values and decrease in velocity. Where the upper part of the Cerdic formation is more complete, and the Phillips Member is present, the boundary is placed at a downwards change from paralic sandstones (Wroot Formation) to shallow marine sandstones and siltstones.
Thickness: Up to c. 120 m.
Geographical Limits: Southern North Sea Basin (quadrants 41-43, 46-49, and 51-53).
Parent Unit: Lias Group (LI)
Previous Name(s): Lias Group (LI)
Alternative Name(s): Whitby Mudstone Formation
Stratotypes:
Type Section  North Sea well 47/29- 1 between 878 and 997 m (Lott and Knox, 1994). 
Reference Section  North Sea well 42/29a- 1 between 559 and 590 m (Lott and Knox, 1994). 
Reference Section  North Sea well 48/11b- 4 between 1116.5 and 1221 m (Lott and Knox, 1994). 
Reference Section  North Sea well 49/12a- 7 between 1699 and 1804 m (Lott and Knox, 1994). 
Reference(s):
Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable