The BGS Lexicon of Named Rock Units — Result Details

Darwin Formation

Computer Code: DARW Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Pliensbachian Age (JE) — Toarcian Age (JT)
Lithological Description: Lenticular bedded, grey siltstones and fine-grained sandstones, heavily bioturbated locally to produce structureless sandy siltstones. Very fine- to coarse-grained sandstones occur in thin (c. 0.6 m), sharp based beds. Thicker (c. 1.3 m) well laminated, rippled and occasionally bioturbated, very fine-grained sandstones also occur. Sandstones are most common in the middle part of the formation. The heterolithic nature of the formation results in an erratic gamma-ray profile.
Definition of Lower Boundary: The lower boundary is defined by a downwards passage from siltstones (Darwin Formation) to sandstones (Nansen Formation) and a marked decrease in gamma values.
Definition of Upper Boundary: The upper boundary is defined by a downward passage from interbedded sandstones, siltstones and coals (Pentland Formation) to siltstones. The boundary coincides with a marked increase in gamma values.
Thickness: 0 to 80 m.
Geographical Limits: Beryl Embayment and Viking Graben, in North Sea quadrant 9.
Parent Unit: Dunlin Group (DUNL)
Previous Name(s): Amundsen Formation (AMND)
Burton Formation (BURT)
Dunlin Group (DUNL)
Lower Beryl Floating Sand Grain Unit (-5183)
Lower Beryl Shale (-5184)
Upper Formation (-5185)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea Well 9/13-19 between 3564.5 and 3608 m below KB (Richards et al., 1993). 
Reference Section  North Sea Well 9/8a-10 between 3951.5 m and 4018 m (Richards et al., 1993). 
Reference Section  North Sea Well 9/14b-2B between 4618 and 4666 m (Richards et al., 1993). 
Reference Section  North Sea Well 9/19-5A between 3767 and 3842 m (Richards et al., 1993). 
Reference(s):
Richards, P C. 1989. Lower and Middle Jurassic sedimentology of the Beryl Embayment, and implications for the evolution of the northern North Sea. Unpublished Ph.D. thesis, University of Strathclyde. 
Richards, P C. 1991. The evolution of Lower Jurassic coastal plain and fan delta sediments in the Beryl Embayment, North Sea. Journal of the Geological Society, London, 148, 1037-1047. 
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] 
Richards, P C. 1990. The early to mid-Jurassic evolution of the northern North Sea. In: Hardman, R F P and Brooks, J (eds.) Tectonic events responsible for Britain's oil and gas reserves. Special Publication of the Geological Society, London, No.55, 191-205. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable