The Kimmeridge Clay Formation (Upper Jurassic–Lower Cretaceous) of the Norwegian Continental Shelf and Dorset, UK: a chemostratigraphic correlation

The Late Jurassic and Early Cretaceous were characterised by a number of carbon cycle perturbations, of which the temporal and geographic extent are poorly understood. This is due to a scarcity of high-resolution records and difficulties in correlation because of faunal provincialism and insufficiently constrained chronostratigraphy. In the Boreal and Sub-boreal seas of north-western Europe, the Kimmeridge Clay Formation (KCF) was deposited, a source-rock for oil of great economic value. Precise correlation is critical for assessing the nature of widespread organic matter deposition. Here we compare biostratigraphically-constrained organic carbon-isotope records from the Norwegian Continental Shelf with the Kimmeridgian-Tithonian (Upper Jurassic) Kimmeridge Clay Formation of the Dorset type area and with upper Tithonian-Berriasian (Upper Jurassic-Lower Cretaceous) records of Svalbard and Siberia. A number of isotopic excursions have been correlated between the studied cores (four Lundin Norway cores and one Statoil core from the Norwegian Continental Shelf) and from KCF-coeval sections in the Tethyan and Boreal realms. We identify and correlate the Eudoxus Zone positive shift, Hudlestoni Zone short-term negative shift, Volgian Isotopic Carbon Excursion (VOICE) and J/K boundary negative isotope excursion. Whereas physical properties or biostratigraphic data alone usually do not allow precise correlation, our integrated approach enables us to identify and correlate synchronous events amongst interregional sections. In addition, time series analyses of TOC records from two wells reveal cycles that strongly resemble the short-term eccentricity component recorded in Dorset. Correlation to the cyclostratigraphic framework of Dorset provides independent support of our age model, which is based on C-isotope stratigraphy and biostratigraphy. Our regional-scale correlation reflects the consistency of the C-isotope signal in the seas of north-western Europe at the time of deposition, and a high correlation potential across significant distances. In particular, correlation of C-isotope signals in the Early Cretaceous attests to sufficiently open marine conditions in the Greenland-Norwegian Seaway to record global carbon cycle variations despite a sea level lowstand.