The Pre-Windermere Interstadial (Late Devensian) raised marine strata of eastern Scotland and their macrofauna: a review

Abstract

Late Devensian raised marine deposits predating the Windermere Interstadial (c. 13–11 ka BP) are found between the Moray Firth and Berwick. The widely distributed, sparsely fossiliferous Errol Clay Formation of the firths of Forth and Tay was laid down in a high-arctic environment immediately following the retreat of the Late Devensian (Dimlington Stadial) ice. In the Tay Estuary, sedimentation took place under distal glaciomarine to marine conditions at a time when there was a fully marine connection between the Scottish east coast and the then high-arctic Norwegian Sea. On the south shore of the Moray Firth, the similar, but undated Spynie Clay Formation seems to have been laid down in a wholly glaciomarine environment. Part of the macrofauna attributed to the St. Fergus Silt Formation of the NE Scottish coast may have been either misidentified, or is not in situ. The preservation of the fauna and of delicate sedimentary structures indicate that the arctic clays as a whole were laid down rapidly. It is suggested that tidal currents were minimal, and that waves were dampened by sea ice for much of the year. Bones of the ringed seal, Phoca hispida, have been recorded from 12 sites in eastern Scotland. About 40 macrofaunal taxa are present in the Errol Clay Formation, a number similar to that recorded in the Danish Younger Yoldia Clay, which is of comparable age. The faunal nomenclature is updated, and three species ( Cylichna occulta, Retusa obtusa and Lyonsia arenosa) are added to the macrofaunal list for the Errol Clay Formation. Reports of in situ boreal molluscs and of one possibly North American species in the otherwise high-arctic assemblage are not supported by specimens in extant collections. Differential decay of the fauna below the zone of weathering in the Errol Clay Formation may have resulted from early diagenesis. Deposition of the Late Devensian, pre-Windermere Interstadial marine sediments as a whole was probably diachronous, beginning after 15–14 ka BP on the outer coast, but was confined to a short interval (c. 13.5–13 ka BP) at the type site in the Tay Estuary. In the Forth Estuary, the high-arctic marine fauna adjacent to the retreating ice-front may have survived the rapid climatic amelioration (c. 13 ka BP) at the beginning of the Windermere Interstadial (marked by the Main Perth Shoreline) for perhaps a few decades.