A potential global chronostratigraphic boundary for the base of the middle Viséan

Cozar, pedro and Somerville, Ian D and Hounslow, Mark W (2023) A potential global chronostratigraphic boundary for the base of the middle Viséan. Newsletters on stratigraphy: 0746.

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Abstract

: High-resolution foraminiferal biostratigraphy of carbonate strata below the Holkerian Substage in three sections of the Southern Cumbria Shelf allows the recognition of the Cf5α and Cf5β subzones. The most complete section, almost free of dolomitization is recorded at Grubbins Wood, whereas at the White Scar Quarry and Barker Scar sections, minor hiatuses or condensed intervals are recorded at the base of one or both subzones, respectively. In contrast, Grubbins Wood has the most limited exposure, whereas White Scar Quarry shows, extensive exposure of this interval, especially of the basal horizons of the subzones, compared to Barker Scar. The Barker Scar section could be retained as a Holkerian unit stratotype for Britain, if the base of the Holkerian is repositioned to the base of Cf5β, using White Scar as a parastratotype to fill the absence of data and hiatuses at Barker Scar due to dolomitization. The rich foraminiferal assemblages in the studied interval suggest a close correlation with other regional substages around the World, and further investigation in those other countries would facilitate the establishment of a worldwide chronostratigraphic horizon at the base of the ‘mid Viséan’. Owing to the hiatuses detected in Barker Scar and White Scar, for this scenario, the Grubbins Wood section would be more suitable for establishment of a mid Viséan boundary and Holkerian boundary stratotype.