The BGS Lexicon of Named Rock Units — Result Details

Harris Member

Computer Code: HARR Preferred Map Code: notEntered
Status Code: Full
Age range: Rhaetian Age (TR) — Rhaetian Age (TR)
Lithological Description: The Harris Member is composed almost entirely of reddish brown, red, brownish grey, and waxy green to greenish grey mudstones and minor siltstones, but there are occasional laminae of white and purple mudstone, and stringers and thin beds of sandstone and argillaceous limestone. The mudstones are micromicaceous, and locally contain traces of pyrite. They are typically slightly calcareous, and include sporadic units of highly calcareous mudstone, grading to marl. Most of the sandstone beds are less than 1 m thick; they are white, pale grey, pale brown or greenish grey, moderately or poorly sorted, and very fine, fine or medium grained. Some sandstone beds are highly micaceous; others are reported to contain traces of glauconite. The sporadic, thin limestone beds are white, pale grey or pale brown, and have microcrystalline or cryptocrystalline textures.
Definition of Lower Boundary: The Harris Member rests on sheet sandstones and interbedded mudstones and sandstones (Lewis Member) in and around the Beryl Field; elsewhere, it rests on undifferentiated sandstones and mudstones of the Cormorant Formation. The base of the member is taken at the top of the highest significant sandstone bed, and coincides with a marked downward change to lower, more variable gamma-ray values.
Definition of Upper Boundary: The Harris Member is either conformably overlain by the Jurassic Statfjord Formation (Banks Group) (e.g. 9/13a-22) or, more commonly, unconformably overlain by younger Jurassic or Cretaceous strata. The contact with the Statfjord Formation is generally transitional, and taken at a downward change to a higher, less erratic gamma-log response, representing a gross lithological change from relatively sandy to relatively argillaceous sediments. In most sections, the wireline-log break coincides approximately with the downward incoming of common red beds. Where the boundary is unconformable, the colour change and wireline-log markers are usually sharply defined. In some sections, the colour change is masked by reduction of the primary red beds to green or greenish grey beds, but the boundary can still be detected by a downward change to mudstones with a more waxy texture.
Thickness: The member is between 30 m and 250 m thick.
Geographical Limits: The member is widely distributed across the centre of the Beryl Embayment.
Parent Unit: Cormorant Formation (CORM)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 9/13-A2: 3162-3254 m (10373-10675 ft) below KB (Cameron, 1993). 
Reference Section  North Sea well 9/12a- 8: 2977.5-3082 m (9769-10111 ft) (Cameron, 1993). 
Reference(s):
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. 
Clemmensen, L B. 1987. Complex star dunes and associated aeolian bedforms, Hopeman Sandstone Formation (Permo-Triassic), Moray Firth Basin, Scotland. In: Frostick, L E and Reid, I (eds.) Desert sediments: ancient and modern. Geological Society, London, Special Publication No.35, 213-231. 
Frostick, L E, Linsey, T K, and Reid, I. 1992. Tectonic and climatic control of Triassic sedimentation in the Beryl Basin, northern North Sea. Journal of the Geological Society, London 149, 13-26. 
Knutson, C A, and Munro, I C. 1991. The Beryl Field, Block 9/13, UK North Sea. In: Abbotts, I L (ed.) United Kingdom oil and gas fields 25 years commemorative volume. Geological Society, London, Memoir No. 14, 33-42. 
Steele, L E, and Adams, G E. 1984. A review of the Northern North Sea's Beryl Field after seven years' production. In: 1984 European Petroleum Conference, London. Society of Petroleum Engineers of AIME, Paper No. 12960. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable