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

Abstract

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.

Marine and terrestrial environmental change during the MIS 5–4 transition (southern North Sea area)

“…The depositional setting of the BB Fm was previously interpreted as either freshwater dominated (Oele, 1971), or transitional from brackish lagoonal to freshwater (Cameron et al, 1989;Zagwijn, 1983). More recently, it has been interpreted to represent a shallow-marine depositional setting with high terrestrial input (Eaton et al, 2020;Laban, 1995;Waajen et al, 2024). Several depositional phases in the BB Fm are distinguished on 2D high-resolution seismic profiles (Eaton et al, 2020;Missiaen et al, 2021, Waajen et al, 2024.…”

“…More recently, it has been interpreted to represent a shallow-marine depositional setting with high terrestrial input (Eaton et al, 2020;Laban, 1995;Waajen et al, 2024). Several depositional phases in the BB Fm are distinguished on 2D high-resolution seismic profiles (Eaton et al, 2020;Missiaen et al, 2021, Waajen et al, 2024. Initially, pollen studies suggested deposition occurred around late MIS 5e and MIS 5d (Laban & Mesdag, 1995;Zagwijn, 1983), while luminescence ages from vibrocores show a range between 85 and 55 ka, corresponding to MIS 5a -MIS 3 (Limpenny et al, 2011;Wessex Archaeology, 2018, Waajen et al, 2024.…”

“…Several depositional phases in the BB Fm are distinguished on 2D high-resolution seismic profiles (Eaton et al, 2020;Missiaen et al, 2021, Waajen et al, 2024. Initially, pollen studies suggested deposition occurred around late MIS 5e and MIS 5d (Laban & Mesdag, 1995;Zagwijn, 1983), while luminescence ages from vibrocores show a range between 85 and 55 ka, corresponding to MIS 5a -MIS 3 (Limpenny et al, 2011;Wessex Archaeology, 2018, Waajen et al, 2024. Recent dating of the BB Fm from a set of cores east of the Brown Bank ridge, at the flank of the tidal scour 'Het Gat' (site FG; Fig.…”

“…The southern North Sea basin holds records covering the MIS 5 -MIS 4 transition, documented in the Brown Bank Formation (BB Fm; Waajen et al, 2024). As the southern North Sea is a relatively flat, shallow shelf sea, it is sensitive to minor climate and sea-level variations.…”

“…We target the BB Fm to produce a new integrated palaeoenvironment and palaeoclimate framework for the transition from MIS 5 to MIS 4 and show biotic and abiotic environmental response to rapid cooling in a shallow-marine area. We analyse both marine and terrestrial biotic and abiotic environmental proxies on previously optically stimulated luminescence (OSL)-dated cores from the BB Fm (Waajen et al, 2024) to reconstruct the marine environment (including salinity), terrestrial input and the vegetation of the hinterland. This study also provides the first reconstruction of Early Weichselian air temperature for the North Sea region, using temperature-sensitive branched glycerol dialkyl glycerol tetraethers (GDGTs; Dearing Crampton-Flood et al, 2020;Weijers et al, 2007) and pollen-based transfer functions (Chevalier et al, 2020).…”