The glacial and interstadial sediments at the Burn of Benholm, Kincardineshire: evidence for onshore pre-Devensian ice movement in northeast Scotland

Pebbly clays and diamictons containing marine shell fragments and peat lens es exposed beneath subglacially deposited Late Devensian till at the Burn o f Benholm provide new insights into the glacial history of Quaternary seque nces in eastern Scotland. The peat yielded pollen of interstadial affinity (including Bruckenthalia spiculifolia) and non-finite radiocarbon dates. Co mparisons with other pre-Late Devensian pollen records in northern Scotland suggest that the peat lenses are remnants of an Early Devensian interstadi al deposit, of Oxygen Isotope Substage 5c or 5a age. Reworked faunal assemb lages in the shelly sediments include Quaternary marine molluscs of low bor eal aspect, as well as Mesozoic and Palaeozoic microfossils. Amino acid rat ios from fragments of Arctica islandica suggest that the shells are of Oxyg en Isotope Stage 9 age or older. The fabric acid composition of the shelly sediments are consistent with their emplacement as deformation till during the onshore movement of glacially transported rafts of marine sediment. Fol ded and sheared contacts between the shelly deposits, peat lenses and the o verlying Late Devensian till indicate that the fossiliferous sediments were glacitectonised during the main Late Devensian glaciation, when ice moved from Strathmore and overrode the site from the southwest. British Geologica l Survey. (C) NERC 2000.