Calcareous concretions yield the first U/Th date for the Late Devensian raised marine strata of eastern Scotland

Abstract

Synopsis This paper presents the first application of U-series disequilibria dating to the Late Devensian raised marine strata of Scotland. The Errol Clay Formation (ECF) is an extensive deposit of laminated glaciomarine silty-clays found offshore from and within the Firths of eastern Scotland. The stratigraphic significance of these deposits lies in their diachronous deposition following the retreat of the Late Devensian ice sheet, and local glaciotectonization following the readvance of the Younger Dryas. In spite of their importance to an understanding of the deglaciation of Scotland, the paucity and poor preservation of biogenic material have hitherto hampered radiocarbon dating of these sediments. A working clay pit at Gallowflat [NO 211 209], in the inner Firth of Tay, provided access to a 5.3 m section of the ECF. A characteristic feature of the lower ECF is that the basal sub-units are rich in calcareous concretions, believed to have formed rapidly at the sediment water interface during glaciomarine sedimentation. Eight individual concretions were hand-picked from the 1.4 m concretion rich sub-unit, 0.5 m above the Devensian till, yielding a U-Th age of 14.2 ±0.9 ka (2σ) using the total-dissolution isochron method. This date accords with the few 14 C dates presently available and offers a new approach to establishing the dynamics of the ECF deglaciation record.