The BGS Lexicon of Named Rock Units — Result Details

Ayrshire Bauxitic Clay Member

Computer Code: ABC Preferred Map Code: ABC
Status Code: Full
Age range: Namurian Stage (CN) — Langsettian Substage (CA)
Lithological Description: A pale grey to buff clayrock, of massive habit with conchoidal fracture, hard and compact. Texture ranges from fine-grained to ooidal, pisolitic and coarsely clastic. Mineralogically, "bauxitic in the chemical sense of containing more Al2O3 than can be accommodated with SiO2 to give kaolinite". The bauxitic clay may be considered a flint clay. The member may also contain sphaerosiderite, plant fragments, tree trunks and include beds of seatrock, coal and mudstone.
Definition of Lower Boundary: Taken at lithological change from olivine basalt of the underlying Troon Volcanic Formation. The base is gradational from basalt through clayrock rich in sphaerosiderite to bauxitic clay. The base is considered to be stratiform, although it might be obscured by later lateritic weathering or diagenesis and some in situ alteration of basalt to bauxitic clay might have occurred.
Definition of Upper Boundary: Taken at the base of the Lower Coal Measures; in Ayrshire this is marked by the Raise Coal seam that lies immediately above the Ayrshire Bauxitic Clay.
Thickness: To about 20m
Geographical Limits: Limited to north Ayrshire and parts of central Ayrshire
Parent Unit: Passage Formation (PGP)
Alternative Name(s): none recorded or not applicable
Type Section  Saltcoats shore. 
Browne, M A E, Dean, M T, Hall, I H S, McAdam, A D and Monro, S K, 1995. A review of the lithostratigraphy of the Carboniferous rocks of the Midland Valley of Scotland. BGS Technical Report, WA/95/25R. 
Monro, S K, 1982. Sedimentation, Stratigraphy and Tectonics of the Dalry Basin, Ayrshire. Unpublished PhD Thesis, University of Edinburgh. 
Monro, S K. 1999. Geology of the Irvine District. Memoir of the British Geological Survey, Sheet 22W and part of 21E (Scotland). 
Browne, M A E, Dean, M T, Hall, I H S, McAdam, A D Monro, S K and Chisholm, J I. 1999. A lithostratigraphical framework for the Carboniferous rocks in the Midland Valley of Scotland. British Geological Survey Research Report, RR/99/07. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S022 S014 S014 S022