Some more images showing the mixed-up nature of the upper rocks in the exposure of Hunts Bay Oolite Subgroup of the Carboniferous Limestone in the cliffs at the west end of Broughton Bay on the Gower Peninsula – illustrating the irregular fracture patterns, rough textures and combinations of rock type within the formation.
In the British Geological Survey (BGS) Lexicon of Named Rock Units regarding Hunts Bay Oolite Subgroup, the rock is described:
Mainly ooidal limestones, with subordinate skeletal, peloidal and oncolitic limestones and calcite mudstones. Mainly dolomitised on the southeast and east crop of the South Wales Coalfield.
Definition of the Lower Boundary:
The base of the Subgroup is gradational and taken at the incoming of a predominantly oolitic grainstone sequence, locally with units of calcite mudstone, above the skeletal packstones or skeletal/peloidal/oolitic packstone/grainstones of the underlying High Tor Limestone Formation.
Definition of the Upper Boundary:
In the Vale of Glamorgan the top is taken at the sharp contact, defined by a palaeokarstic surface, between the heterolithic lithologies of the Subgroup and the overlying partially dolomitised sandy skeletal packstones and the calcareous sandstones of the Pant Mawr Sandstone Member [Oxwich Head Limestone Formation]. In the Gower and Pembrokeshire it is taken at the palaeokarstic surface separating the heterolithic lithologies of the Subgroup from the mottled and pseudobrecciated skeletal packstones of the overlying Oxwich Head Limestone Formation.
What do all these geological terms mean? I’m away to consult with the Oxford Dictionary of Earth Sciences!
Waters C N, Waters R A, Barclay, W J, and Davies J R (2009) A lithostratigraphical framework for the Carboniferous successions of southern Great Britain (onshore), British Geological Survey Research Report RR/09/01, NERC, Keyworth, Nottingham.
Willoughby, C (1996) Environments of Deposition in the Carboniferous Limestone of South East Gower, Bsc Geology Thesis, University of Wales, Aberystwyth.
Wilson, D, Davies, J R, Fletcher, C J N, and Smith M. (1990) Geology of the South Wales Coalfield, Part VI, the country around Bridgend. Memoir of the British Geological Survey, Sheets 261 and 262 (England and Wales).
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