The BGS Lexicon of Named Rock Units — Result Details

Overtoun Sandstone Member

Computer Code: OVS Preferred Map Code: OVS
Status Code: Full
Age range: Chadian Substage (CI) — Chadian Substage (CI)
Lithological Description: The lower part of the unit is about 36m thick, and is dominated by grey, fine-grained, thin-bedded or partly concretionary sandstone. There are also intervals of mudstone, up to 3.32m thick, commonly with calcareous concretions and uncommon beds of concretionary limestone or dolomitic limestone (cementstone). The upper part, which is about 20m thick, largely comprises of pale grey, mostly fine-grained sandstone with clasts of carbonate. Unlike the lower part of the member, sandstones with concretions and mudstones are uncommon.
Definition of Lower Boundary: The lower boundary is unconformable and overlies strata of the Ballagan Formation, that are characterised by grey mudstone and dolomitic limestone (cementstone). In the Barnhill Borehole, the base of the member is picked at the top of an interval dominated by grey mudstone with gypsum veins, at 161.48m depth, and overlain by a sequence dominated by thick intervals of sandstone.
Definition of Upper Boundary: The boundary is sharp and picked at a marked change from grey sandstone and mudstone to grey tuff, with volcanic lapillae of the overlying Clyde Plateau Volcanic Formation at 104.89m depth in the Barnhill Borehole. Correlation with the Greenock district, demonstrates that the base of the Clyde Plateau Volcanic Formation is unconformable.
Thickness: 56.6m at the Type Section.
Geographical Limits: The area around Overtoun House, north of the River Clyde near Dumbarton in Strathclyde, Scotland.
Parent Unit: Clyde Sandstone Formation (CYD)
Previous Name(s): Overtoun Sandstone Formation (-3600)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Barnhill Borehole, near Overtoun, BGS borehole NS47NW/2, from 104.9 to 161.5 m depth. 
Reference(s):
Institute of Geological Sciences, 1978. Institute of Geological Sciences boreholes, 1977. Report of the Institute of Geological Sciences, No.78/21. 
Paterson, I B, Hall, I H S & Stephenson, D. 1990. Geology of the Greenock district: Memoir for 1:50000 geological sheet 30W and part of sheet 29E (Scotland). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S030 S030 S030