Old chalk, new tricks: revisiting the Lower Cretaceous carbonates of the Danish Central Graben

The Lower Cretaceous (upper Hauterivian–Albian) pelagic and hemipelagic carbonates of the Tuxen and Sola Formations in the Danish Central Graben, North Sea, constitute one of the oldest chalk successions recorded globally, but have received less attention than the Upper Cretaceous–Danian Chalk Group. This paper presents an updated depositional model for the succession drawn from synthesis of the latest published sedimentological and stratigraphic results, and correlation of 11 wells in the Valdemar, Boje, Adda and Tyra Fields. Four depositional sequences, deposited on a relatively deep subphotic shelf, record c. 20 Myr of transgressive–regressive cycles, including: (1) late Hauterivian–earliest Barremian highstand and differential subsidence, resulting in aggradation across a westward-dipping ramp; (2) early Barremian eastern (Adda Field) inversion causing plateau condensation, sediment bypass and sourcing of gravity flows, followed by lowstand-controlled basin isolation and associated anoxia (Munk Marl Bed), and finally late Barremian tectonic quiescence and highstand with deposition of clean reservoir chalk; (3) latest Barremian lowstand causing filling of local depocentres, interrupted by early Aptian transgression-controlled anoxia during the global Oceanic Anoxic Event 1a (Fischschiefer Member), and finally late Aptian highstand; and (4) latest Aptian–earliest Albian lowstand causing local erosion and heightened influx of clay.