Sedimentary architecture of the Brown Bank Formation (Dutch sector of the North Sea) reveals consecutive shallow marine depositional phases during the MIS 5-4 transition

Abstract

Major climate cooling transitions have large impacts on the evolution of sedimentary depositional systems of shelf seas and coastal areas. These transitions are rarely preserved because they are prone to erosion during subsequent lowstands or, if preserved, buried too deep to reach with standard ground-truthing methods. As result, the relation between climate cooling and these sedimentary systems is still poorly understood. Severe climate cooling occurred during the Late Pleistocene MIS 5-MIS 4 transition, as captured within the shallow marine deposits of the Brown Bank Formation (Fm), which occurs between 0.1 m and 40 m below the present southern North Sea floor. To improve our understanding of the character and complexity of the depositional system, as well as the environmental response during the rapid climate cooling it portrays, we map the hitherto poorly constrained extent and architecture of the Brown Bank Fm within part of the Dutch sector of the North Sea. We document and map four seismic facies units (BB1-BB4) that are attributed to variations in tidal energy and pro-deltaic sediment supply. Pollen, diatom and mollusc assemblages reveal that the palaeoenvironment remained shallow marine throughout deposition and provide evidence for two cooling phases. The pollen assemblage also indicates that during this period forests changed to open woodlands in this period. Linking the palaeoenvironmental data and new luminescence ages of the four units with the Greenland NGRIP δ¹⁸O_ice chronology, suggests that deposition of the units occurred during a relatively short time. The new analyses from the Brown Bank Fm suggest that the North Sea became disconnected from the Atlantic Ocean at its southern outlet (the Dover Strait) around the start of MIS 5a (ca. 88 ka) and that the floor of the southern North Sea became completely exposed around 72 ka.