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

The Brown Bank Formation (BB Fm) is a clay-rich sedimentary unit that is distributed over a large area in 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 of interpretations on the depositional environment and age of the BB Fm. In this study we combine high-resolution 2D acoustic reflection profiles and multiproxy sedimentological, geochemical and geochronological analyses of three vibrocores, to provide a detailed description and a new age assessment for the BB Fm at its type locality, adjacent to the 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-energy conditions in an increasingly compartmentalised marginal marine environment. Elevated terrestrial organic input shows that the Rhine–Meuse delta was situated relatively close-by. Luminescence ages indicate that the sediments of the BB Fm in our cores were deposited during the Weichselian Odderade interstadial (MIS5a, ca. 80 ka) and earliest parts of the Early Pleniglacial (MIS4, ca. 70 ka), which is later than previously reported in the literature.