Biostratigraphy of Jurassic–Cretaceous boundary strata in the Terschelling Basin, The Netherlands

Abstract

SUMMARY The Jurassic–Cretaceous boundary beds in the Scruff Greensand Formation from Dutch sector North Sea wells L06-2 (between 2245.36 m and 2262.76 m) and L06-3 (between 2028.90 m and 2037.80 m) have yielded both ammonite faunas and abundant marine and terrestrial palynomorphs. Ammonite endemism in Europe was intense at the Jurassic–Cretaceous boundary. This means that pan-European correlations of Jurassic–Cretaceous boundary beds based on macrofossils are problematical. The ammonite faunas of wells L06-2 and L06-3 provide the most extensive and complete marine macrofossil record so far across the Volgian–Ryazanian (Jurassic–Cretaceous) boundary in the Spilsby Province and the North Sea Basin. The Primitivus, Preplicomphalus, Lamplughi, Runctoni and Kochi Zones have been identified. In both wells, the occurrences of the dinoflagellate cyst Gochteodinia virgula mean that the successions are no older than latest mid-Volgian. The dinoflagellate cyst associations of L06-2 are indicative of the late Volgian/early Ryazanian. The range tops of Gochteodinia virgula and Amphorula expirata are revised as a result of correlations with the ammonite zonation. Dinoflagellate cyst floras in L06-3 are indicative of the latest Volgian–? earliest Ryazanian. In particular, the co-occurrence of Batioladinium? gochtii and Gochteodinia virgula at 2030.60 m in well L06-3, together with ammonite data, indicates that this horizon is of latest Volgian (Lamplughi Zone) age. Both wells contain reworked palynomorphs, including recycled older Late Jurassic dinoflagellate cysts. In addition, the palynological assemblages yield relatively diverse sporomorph associations. The sporomorph succession of both wells is used to establish an ammonite-calibrated sporomorph chronostratigraphy. Comparison with other studies suggests that the Jurassic/Cretaceous boundary occurs within the Cherty ‘Freshwater’ Beds of the Purbeck Limestone Group in Dorset, southern England, and within the Serpulite Member of Germany.