Late Jurassic–Early Cretaceous marine deoxygenation in NE Greenland

The Late Jurassic–Early Cretaceous interval represents a prolonged marine deoxygenation period particularly in the Boreal–Arctic basins, the controlling factors of which remain poorly understood. Two drill cores totalling >450 m cover the Kimmeridgian–Barremian succession in contrasting locations in an evolving half-graben system (basin centre and near the footwall crest) in Wollaston Forland, NE Greenland; they provide an exceptional c. 20 myr long window into palaeoenvironmental development and changes in redox conditions within a detailed tectonostratigraphic framework. Synthesis of a multidisciplinary dataset including sedimentology, inorganic geochemistry and previously published organic geochemistry indicates that, despite continuous black mudstone accumulation from the Kimmeridgian to the Ryazanian, seafloor anoxia was intermittent in the Kimmeridgian, whereas more sustained anoxia or euxinia occurred in the middle Volgian–early Ryazanian. Correlation to reported contemporaneous successions along the Greenland margin indicates that protracted rifting and generation of localized seafloor topography were among the major drivers both of seafloor deoxygenation and current funnelling and amplification during the Jurassic–Cretaceous transition. Consequently, distribution of seaway current activity and dysoxia, anoxia and euxinia varied spatially, allowing fully oxygenated and anoxic pockets to coexist.