The BGS Lexicon of Named Rock Units — Result Details

Portavadie Sand And Silt Member

Computer Code: PRTS Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: At Portavadie: soft to hard, grey to dark grey, poorly sorted silty sand and sandy silt with subangular to angular clasts up to 200mm across, particularly in the upper 1.5m. Gravel and cobbles were more common above -4m OD in the generally matrix supported sediment. Brown staining was noted at the unconformity with the overlying Flandrian sand. Seaweed and plant fragments were present at one or two horizons and the intact marine shells were of arctic aspect. At Ardyne Units 3 and 4 of Peacock (1997) consisted of very poorly sorted, pebbly clayey silt and silty sand 2.5m-2.9m thick. Crude interbeds of pale brownish grey sand are present in places along with pockets and lenticles of similar throughout.The top of the unit is more sandy and with crude lamination. Clasts up to 80mm across are scattered through the member but are more common near the top. These are generally sub-rounded to sub-angular in shape and of metamorphic lithologies (psammite, quartz-schist and phyllite). Intact marine shells of arctic affinities are also present.
Definition of Lower Boundary: The Portavadie Sand and Silt Member of the Clyde Clay Formation rests with angular unconformity on older Quaternary sediments. It normally rests unconformably on either the Linwood Clay or the Paisley Clay Members of the Clyde Clay Formation.
Definition of Upper Boundary: The Portavadie Sand and Silt Member of the Clyde Clay Formation is overlain unconformably by younger Quaternary sediments, normally the Gourock Sand Member of the Clydebank Clay Formation of the British Coastal Deposits Group.
Thickness: Veneer to over 3m.
Geographical Limits: The Portavadie Sand ad Silt Member of the Clyde Clay Formation is recognised in the Firth of Clyde and Loch Fyne.
Parent Unit: Clyde Clay Formation (CLYD)
Previous Name(s): Clyde Beds (-1375)
Portavadie Formation (-4850)
Alternative Name(s): none recorded or not applicable
Partial Type Section  Ardyne Platform Construction Site, Elf Pit. 
Type Area  Portavadie Platform Construction Yard; temporary sections 
Peacock, J D. 1997. Ice rafted sediments of Loch Lomond Stadial age in western Scotland. Scottish Journal of Geology, 33, 51-57. 
Peacock, J D and Wilkinson, I P. 1978. Late-Glacial and post-Glacial marine environments at Ardyne, Scotland and their significance in the interpretation of the history of the Clyde sea area.Report of the Institute of the Geological sciences 78/17 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable