Environmental cycles in the late Jurassic northwest European epeiric basin: interaction with atmospheric and hydrospheric circulations

Abstract

Despite the large size and the heterogeneity of the northwest European late Jurassic (Kimmeridgian/Lower Tithonian) epeiric basin the sedimentary environment was rather uniform. In general, deposition of mudstones and the microlaminated organic-rich sediments took place under low-oxic to anoxic conditions. Detailed environmental analysis clearly points to a seasonal alternation of aerobic with anaerobic conditions in substrate and bottom water, resulting in one year life-cycles in the benthic environment. The widespread uniformity of facies and the seasonal alternation in the oxygen budget of the benthic environments are best explained by a summer to winter change in the atmospheric circulation of the Northern Hemisphere. This change strongly influenced the oceanographic situation in the northwestern European epeiric basin. Superposed on this one-year cyclicity, three more hierarchical levels of cycles are stratigraphically recorded. They reflect a complex history of orbital-forced, and non-orbital-forced climatic changes and/or eustatic sea-level fluctuations in the late Jurassic.