Late MIS5a in the southern North Sea: new chronostratigraphic insightsfrom the Brown Bank Formation

Abstract

The Brown Bank Formation (BB Fm) is a clay‐rich sedimentary unit that is distributed over a large areain the southern North Sea. It is easily recognisable in 2D acoustic reflection profiles, forming sets of subparallel high‐amplitude reflections. Previous studies have provided only fragmentary information on the facies, and a variety ofinterpretations on the depositional environment and age of the BB Fm. In this study we combine high‐resolution 2Dacoustic reflection profiles and multiproxy sedimentological, geochemical and geochronological analyses of threevibrocores, to provide a detailed description and a new age assessment for the BB Fm at its type locality, adjacent tothe Brown Bank ridge. At the study site, the BB Fm shows morphologically well‐preserved submarine sand dunes,deposited in a high‐energy shelf setting, overlain by organic‐rich silty clays that were deposited under lower‐energyconditions in an increasingly compartmentalised marginal marine environment. Elevated terrestrial organic inputshows that the Rhine–Meuse delta was situated relatively close‐by. Luminescence ages indicate that the sediments ofthe BB Fm in our cores were deposited during the Weichselian Odderade interstadial (MIS5a, ca. 80 ka) and earliestparts of the Early Pleniglacial (MIS4, ca. 70 ka), which is later than previously reported in the literature.