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Biostratigraphy and palaeoenvironments of the Ballagan Formation (Lower Carboniferous) in Ayrshire

Mike Stephenson, Mark Williams, Alison Monaghan, Sarah Arkley and Richard Smith
Biostratigraphy and palaeoenvironments of the Ballagan Formation (Lower Carboniferous) in Ayrshire
Scottish Journal of Geology (December 2002) 38, Part 2: 93-111

Abstract

A local palynostratigraphical subdivision for the Ballagan Formation in Ayrshire is established, based on the Heads of Ayr coastal section. The lower part of the formation is characterized by a low-diversity CM Biozone Colatisporites-dominated assemblage, while the upper part is characterized by high-diversity assemblages containing Acanthotriletes cf. macrogaleatus and Radiizonates mirabilis, and assemblages dominated by Leiosphaeridia and algal palynomorphs. Sedimentological analysis of the lower part of the formation suggests deposition in an arid coastal floodplain environment. Up sequence, there is a gradual reduction in sandstones, suggesting reduced fluvial influence. The Ballagan Formation yields ostracodes indicative of marginal marine and brackish environments, which supports the sedimentological interpretation. The lower part of the formation contains species that are typical of the Tournaisian Beyrichiopsis glyptopleuroides-Eriella Biozone, providing a stratigraphical tie with the CM Biozone assemblage. The upper part of the formation yields ostracodes that elsewhere have been reported from the Visean, but Lycospora pusilla, the index taxon for the Visean Pu palynomorph Biozone, was not recovered. Two age interpretations can be offered for this part of the section: either late Tournaisian or early Visean. A late Tournaisian-early Visean age for the Ballagan Formation would imply that L. pusilla is so rare in the lower parts of its range that dense sampling failed to recover it. By contrast, a Tournaisian age for the entire Ballagan Formation at the coast implies recalibration of some ostracode ranges. Above the Ballagan Formation, mid-Visean palynomorph assemblages from the Lawmuir Formation allow the Heads of Ayr volcanic vent to be dated in the range late Tournaisian-mid-Visean, implying correlation with the Clyde Plateau Volcanic Formation.


ISSN: 0036-9276
EISSN: 2041-4951
Coden: SJGEAX
Serial Title: Scottish Journal of Geology
Serial Volume: 38, Part 2
Title: Biostratigraphy and palaeoenvironments of the Ballagan Formation (Lower Carboniferous) in Ayrshire
Affiliation: British Geological Survey, Nottingham, United Kingdom
Pages: 93-111
Published: 200212
Text Language: English
Publisher: Scottish Academic Press, Edinburgh, United Kingdom
References: 39
Accession Number: 2003-027476
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendices
Illustration Description: illus. incl. strat. cols., geol. sketch maps
N55°28'00" - N55°28'00", W04°37'60" - W04°37'60"
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data from The Geological Society, London, London, United Kingdom
Update Code: 200309
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