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Reinterpreting the age of the uppermost ‘Old Red Sandstone' and Early Carboniferous in Scotland

Published online by Cambridge University Press:  20 February 2019

John E. A. MARSHALL*
Affiliation:
School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, European Way, Southampton SO14 3ZH, UK. Email: [email protected]
Emma J. REEVES
Affiliation:
School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, European Way, Southampton SO14 3ZH, UK. Email: [email protected]
Carys E. BENNETT
Affiliation:
School of Geography, Geology and the Environment, University of Leicester, University Road, Leicester LE1 7RH, UK.
Sarah J. DAVIES
Affiliation:
School of Geography, Geology and the Environment, University of Leicester, University Road, Leicester LE1 7RH, UK.
Timothy I. KEARSEY
Affiliation:
British Geological Survey, The Lyell Centre, Edinburgh EH14 4AP, Scotland.
David MILLWARD
Affiliation:
British Geological Survey, The Lyell Centre, Edinburgh EH14 4AP, Scotland.
Timothy R. SMITHSON
Affiliation:
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
Michael A. E. BROWNE
Affiliation:
British Geological Survey, The Lyell Centre, Edinburgh EH14 4AP, Scotland.
*
*Corresponding author

Abstract

In Scotland, the base of the Ballagan Formation has traditionally been placed at the first grey mudstone within a contiguous Late Devonian to Carboniferous succession. This convention places the Devonian–Carboniferous boundary within the Old Red Sandstone (ORS) Kinnesswood Formation. The consequences of this placement are that tetrapods from the Ballagan Formation were dated as late Tournaisian in age and that the ranges of typically Devonian fish found in the Kinnesswood Formation continued into the Carboniferous. The Pease Bay specimen of the fish Remigolepis is from the Kinnesswood Formation. Comparisons with its range in Greenland, calibrated against spores, show it was Famennian in age. Detailed palynological sampling at Burnmouth from the base of the Ballagan Formation proves that the early Tournaisian spore zones (VI and HD plus Cl 1) are present. The Schopfites species that occurs through most of the succession is Schopfites delicatus rather than Schopfites claviger. The latter species defines the late Tournaisian CM spore zone. The first spore assemblage that has been found in Upper ‘ORS' strata underlying the Ballagan Formation (Preston, Whiteadder Water), contains Retispora lepidophyta and is from the early latest Famennian LL spore zone. The spore samples are interbedded with volcaniclastic debris, which shows that the Kelso Volcanic Formation is, in part, early latest Famennian in age. These findings demonstrate that the Ballagan Formation includes most of the Tournaisian with the Devonian–Carboniferous boundary positioned close to the top of the Kinnesswood Formation. The Stage 6 calcrete at Pease Bay can be correlated to the equivalent section at Carham, showing that it represents a time gap equivalent to the latest Famennian glaciation(s). Importantly, some of the recently described Ballagan Formation tetrapods are older than previously dated and now fill the key early part of Romer's Gap.

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Articles
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Copyright © The Royal Society of Edinburgh 2019 

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