The BGS Lexicon of Named Rock Units — Result Details

Cornelly Oolite Formation

Computer Code: CNLL Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Holkerian Substage (CQ)
Lithological Description: Thick bedded, cross bedded, pale grey ooid grainstones with scattered beds of medium grey fine-grained skeletal packstone. Compound ooids of pisolitic proportions common. Thin mudstone associated with the palaeokarstic surface at the top of the Cefnyrhendy Oolite Member, present in the northeast of the Vale of Glamorgan.
Definition of Lower Boundary: The base of the formation is gradational and taken at the incoming of a predominantly oolitic grainstone sequence above the skeletal packstones or skeletal/oolitic packstone/grainstones of the underlying High Tor Limestone Formation.
Definition of Upper Boundary: The top of the formation is taken at the base of the first bed of calcite mudstone of the overlying Stormy Limestone Formation occuring above the ooid grainstones and subordinate skeletal packstones of the Cornelly Oolite Formation.
Thickness: 135m in the west of the Vale of Glamorgan, thickening to 180m in the eastern part of the Vale of Glamorgan.
Geographical Limits: Central and western Vale of Glamorgan [ST 00 74]. Passes eastwards into undivided Hunts Bay Oolite Subgroup. Present in Gower [SS 50 90] and Pembrokeshire [SM 99 01], but not mapped.
Parent Unit: Hunts Bay Oolite Subgroup (HBO)
Previous Name(s): Seminula Oolite [Obsolete Name And Code: Use CNLL] (SMO)
Alternative Name(s): none recorded or not applicable
Partial Type Section  South face of Cornelly Quarry, 250m north of Mount Pleasant Farm, South Cornelly, Vale of Glamorgan. Top third of the unit is seen, which comprises ooid grainstones and skeletal packstones. Lower contact with the High Tor Limestone Formation is not visible, but the upper contact with the Stormy Limestone Formation is exposed. 
Wilson, D, Davies, J R, Fletcher, C J N, and Smith, M. 1990. The Geology of the South Wales Coalfield, part VI the Country around Bridgend. Memoir of the British Geological Survey, 1:50 000 Geological Sheets 261 and 262 (England and Wales). 
George, T N, 1933. The Carboniferous Limestone Series in the west of the Vale of Glamorgan. Quarterly Journal of the Geological Society of London, Vol.89, 221-271. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: