Late Ryazanian black shales in the Southern North Sea Basin and their lithostratigraphical significance

SUMMARY The basal beds of the Speeton Clay Formation in Yorkshire and BGS Offshore Borehole 81/43, Beds E and D8 of late Ryazanian age, are in poorly fossiliferous, carbonate-free, organic-rich Kimmeridge Clay type facies. Above Bed D8 there is a rapid transition to carbonate-rich sediments with a lower organic carbon content and increasingly diverse faunal and palynofloral assemblages. In the Northern and Central North Sea basins similar coeval facies changes are represented by the Kimmeridge Clay Formation/Valhall Formation boundary.