The BGS Lexicon of Named Rock Units — Result Details

Sellafield Member

Computer Code: SELF Preferred Map Code: notEntered
Status Code: Full
Age range: Anisian Age (TA) — Anisian Age (TA)
Lithological Description: The dominant lithology is a red-brown, weathering to orange-brown, fine-grained, well-sorted sandstone with well-rounded grains of aeolian origin. It is commonly cross-bedded. This aeolian dune facies is interbedded with an interdune facies comprising well-cemented fine- to medium-grained, poorly sorted sandstone with common wavy silty laminae. Small-scale convolutions, loading and dewatering structures are common.
Definition of Lower Boundary: The lower boundary is taken at the sharp upward change from fine- to coarse-grained fluvial sandstone in the underlying undivided Helsby Sandstone Formation to medium-grained, aeolian sandstone. In borehole geophysical logs it is marked by an upward decrease in gamma-ray values and an upward increase in mean interval transit time in the sonic log. Both log signatures are more serrated than in the underlying part of the Helsby Sandstone Formation.
Definition of Upper Boundary: The upper boundary is not seen but will be marked by the incoming of dominantly red-brown mudstones and siltstones of the Mercia Mudstone Group.
Thickness: The thickest known sequence is 176.42 m, in the Sellafield 13B Borehole.
Geographical Limits: The member only occurs at outcrop between Drigg and Sellafield on the Cumbrian coast. Very scarce exposures in the Sellafield–Seascale–Drigg area.
Parent Unit: Helsby Sandstone Formation (HEY)
Previous Name(s): Kirklinton Sandstone (-4998)
Ormskirk Sandstone Formation [Obsolete Name And Code Use: HEY] (OMS)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  River Calder, Cumbria (Barnes et al., 1994). 
Reference Section  Seascale Scar, Cumbria (Gregory, 1915). 
Type Section  0-176.42 m in the Sellafield 13B Borehole, Cumbria (BGS Registered Number NY00SW/42). 
Reference(s):
Dixon, E E L, Maden J, Trotter, F M, Hollingworth, M A and Tonks, L H. 1926. The geology of the Carlisle, Longtown and Silloth District. Memoir of the Geological Survey of England and Wales. 
Institute of Geological Sciences, 1977.1:50.000 Geological Sheet 84 (Wigan) 
Ambrose, K, Hough, E, Smith, N J P and Warrington, G. 2014. Lithostratigraphy of the Sherwood Sandstone Group of England, Wales and south-west Scotland. British Geological Survey Research Report, RR/14/01. 
Gregory, J W. 1915. A deep bore at Seascale in Cumberland. Geological Magazine, Vol. 52, 146-149. 
Barnes, R P, Ambrose, K, Holliday, D W, and Jones N S. 1994. Lithostratigraphical subdivision of the Triassic Sherwood Sandstone Group in west Cumbria. Proceedings of the Yorkshire Geological Society, Vol. 50, 51-60. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable