The BGS Lexicon of Named Rock Units — Result Details

Dudgeon Formation

Computer Code: DGSL Preferred Map Code: notEntered
Status Code: Full
Age range: Ladinian Age (TD) — Carnian Age (TC)
Lithological Description: The Dudgeon Formation consists largely of mudstones but a concentration of halite in the upper part of the sequence, mainly in parts of quadrants 47, 48, 49, 52 and 53, constitutes the Keuper Halite Member; thin halite beds also occur lower in the formation. The mudstones are red, red-brown, orange-red, and green; some silty interbeds and thin beds of anhydrite, and grey to buff dolomite occur.
Definition of Lower Boundary: The base of the Dudgeon Formation is marked by a downward change from a mudstone sequence with some silty interbeds, thin anhydrites, dolomites and traces of halite, to a sequence in which rather similar mudstones are distinguished by the presence of more numerous and more prominent beds of grey and buff coloured dolomite. The boundary corresponds to a downhole decrease in gamma-ray values and an increase in velocity at a regionally consistent log-marker that is slightly below the level selected by Rhys (1974) in the type section (49/21-2).
Definition of Upper Boundary: Where the Keuper Halite Member occurs, the top of that unit, at the downward change from Triton Formation mudstones to halite, marks the top of the Dudgeon Formation. This boundary corresponds with an abrupt downward decrease in gamma-ray values and a slight increase in velocity. Elsewhere, the boundary is marked by a downward change from rather uniform, red-brown mudstones, with thin anhydrites, of the Triton Formation, to the more varied red, red-brown, orange-red, and green mudstones, with some silty beds, thin anhydrites and dolomites, of the Dudgeon Formation. Here, the boundary corresponds to a downhole change to gamma-ray and velocity values that are generally lower and higher respectively than in the overlying Triton Formation and which form the top of a slightly 'waisted' log profile.
Thickness: The formation is thickest in the Sole Pit Basin, with a maximum of 350 m present at the southern end of that basin. The formation thins abruptly westwards across the Dowsing Fault Zone, indicating syndepositional movement in that fault zone, and is less than 100 m thick on the South Hewett Shelf and the East Midlands Shelf. To the north of quadrants 47, 48 and 49 thicknesses are also less than 100 m (Cameron, 1993). The formation is partially eroded on the western margin of the Cleaver Bank High and farther north, on the southern flank of the Mid North Sea High.
Geographical Limits: The Dudgeon Formation is present throughout quadrants 47 and 48, much of quadrants 41, 42, 43 and 44, and parts of 49, 52 and 53.
Parent Unit: Haisborough Group (HAI)
Previous Name(s): Dudgeon Saliferous Formation (-859)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 49/21- 2 (Rhys, 1974): 882-1161.5 m (2893-3810 ft) below KB (revised base). The base of the formation in this section has been revised from 1158.5 m (3800 ft) (metric conversion revised) (Rhys, 1974) to the level of a regionally consistent log-marker. 
Reference Section  North Sea well 42/29- 3: 1555-1659.5 m (5102-5444 ft) (Johnson et al., 1994). 
Reference Section  North Sea well 47/05a- 2: 1262.5-1438 m (4142-4718 ft) (Johnson et al., 1994). 
Reference Section  North Sea well 53/02- 2: 610-932.5 m (2001-3059 ft) below KB drilled depths, 605.5-892.5 m (1987-2928 ft) true vertical depths (Johnson et al., 1994). 
Reference(s):
Johnson, H, Warrington, G and Stoker, S J. 1994. 6. Permian and 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. 
Cameron, T D J. 1993. 4. Triassic, Permian and pre-Permian 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. 
Geiger, M E, and Hopping, C A. 1968. Triassic stratigraphy of the southern North Sea Basin. Philosophical Transactions of the Royal Society of London B254, 1-36. 
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. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable