The BGS Lexicon of Named Rock Units — Result Details

Portskerra Conglomerate Member

Computer Code: PSKA Preferred Map Code: notEntered
Status Code: Full
Age range: Eifelian Age (DI) — Eifelian Age (DI)
Lithological Description: A pebble and boulder conglomerate, typically containing rounded to subangular clasts of Moine psammite, Reay diorite and some granitic rocks in a matrix of greenish grey fine- to medium-grained sandstone. The unit is locally intercalated with thin beds of grey nodular limestone of the Aryleive Limestone Bed.
Definition of Lower Boundary: The unit rests unconformably, directly on Caledonian igneous or Precambrian Moine (basement) rocks as the basal unit of the Bighouse Formation on the Middle Old Red Sandstone unconformity.
Definition of Upper Boundary: Overlain by an interbedded, sandstone-dominated rhythmic sequence of sandstones, siltstones and laminated carbonate mudstones (fish beds) of the Baligill Limestone Member of the Bighouse Formation.
Thickness: Typically 5 - 10m, and locally more than 40m
Geographical Limits: Onshore and immediate offshore of the Dounreay area, Caithness, northern Scotland.
Parent Unit: Bighouse Formation (BIGH)
Previous Name(s): Basal Conglomerate (-1130)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Jetty in Portskerra Harbour. 
Type Area  Portskerra Harbour, about 400m north of the centre of Portskerra village, Sutherland. Trewin, 1993. 
Reference Section  Sea cliff exposures at Red Point, 2.5km northwest of Reay village, Caithness. 
Reference(s):
British Geological Survey. (In preparation, to be published in 2005). Bedrock geology. Scotland Special Sheet (Dounreay).1:25 000. 
British Geological Survey. 2003. Bedrock and superficial deposits. Scotland Sheet 115E (Reay).1:50 000. 
Donovan, R N. 1975. Devonian lacustrine limestones at the margin of the Orcadian Basin, Scotland. Journal of the Geological Society of London, Vol.131, 489-510. 
Trewin, N H. 1993 Old Red Sandstone basin margin deposits at Red Point, Port Skerra and Baligill. 157-166 in Trewin, N H and Hurst, A [editors], Excursion guide to the geology of eastern Sutherland and Caithness. [Edinburgh: Scottish Academic Press.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S115