Reappraisal of Arundian–Asbian successions of the Great Scar Limestone Group across northern England

Abstract

The correlation of disparate mid- to late Viséan platform carbonate successions of the Great Scar Limestone Group across northern England formerly relied heavily upon a coral and brachiopod biozonation scheme erected in the early 20th century. This subsequently guided the development of a regional chronostratigraphic scheme some sixty years later that continues to be used to the present day, broadly coinciding with development of new lithostratigraphical nomenclatures, different for each distinct structural area. Correlation problems encountered within these lithostratigraphic units from study of their foraminiferal assemblages, as well as critical analysis of the stratotype sections for the Holkerian and Asbian substages, questions the veracity of the long-established coral and brachiopod biostratigraphy. This study appraises the lithostratigraphical and biostratigraphical relationships of late Arundian to late Asbian limestones across the Askrigg and Alston blocks, the Stainmore Trough and flanks of the Lake District Block. It considers the correlation and potential rationalisation of lithostratigraphic units, comments on revisions to the definition of the Holkerian and Asbian substage stratotypes and the suitability of the various biostratigraphical guide fossils.

A late Asbian (Mississippian) stratotype for England: Trowbarrow Quarry, Cumbria, UK

“…The new formation and biozone interpretations from Waters et al . (2021) are shown in the right‐hand columns. Abbreviation : lst., limestone.…”

“…In addition, lithological features change notably from blocks to troughs in the region (Waters et al . 2021), which hinders correlation.…”

“…junceum , D. septosa , Howchinia and G. bilineatus (Riley 1993; Jones & Somerville 1996; Somerville 2008; Waters et al . 2011 b , 2021). In addition, it is now well known that some other taxa first occur in the Holkerian, such as D. bourtonense , D. llangollensis and A. convexus (Strank 1981; Somerville & Strank 1984 a ; Conil et al .…”

“…In contrast, Waters et al . (2021) considered the formation to be entirely late Asbian. The main problem is that no previous author has specified precisely the horizons where macrofossils were recorded, only the general content, but in some cases they subdivided the lower and upper parts of the quarry (or lower and upper part of the Urswick Limestone).…”

“…The occurrence and distribution of the early Asbian in Britain is currently a debated and uncertain issue (Cózar & Somerville 2020; Waters et al . 2021), and plausibly the early Asbian may represent a hiatus in some regions. This uncertainty is related to the poorly selected stratotype at Little Asby Scar, which, as has been recommended by previous authors (and followed here), should be abandoned for multiple reasons that cannot be resolved.…”