Integrated correlation of the Kimmeridge Clay Formation (Late Jurassic‒Early Cretaceous)

: a Boreal‒Tethyan transect

Abstract

The Kimmeridge Clay Formation (Upper Jurassic‒Lower Cretaceous) is a widely deposited mudrock that has a high total organic carbon content and is a major petroleum source rock of the North Sea, Norwegian Sea and Barents Sea. The Late Jurassic and Early Cretaceous were characterised by a number of carbon cycle perturbations and a climatic shift in north-western Europe from relatively humid to arid and back to humid conditions. Precise correlation of the KCF in north-western Europe is critical for assessing the temporal and geographic extent of these events, stratigraphic fidelity, and the nature of widespread organic matter deposition in the region. However, correlation is complicated by faunal provincialism and insufficiently constrained chronostratigraphy. Biostratigraphic data alone generally does not allow precise correlation. An integrated approach (bio-, cyclo- and chemostratigraphy) is applied here to correlate several biostratigraphically-constrained organic carbon isotope (훿¹³C_org) records from the Norwegian Continental Shelf with the (1) Kimmeridgian‒Tithonian (Upper Jurassic) Kimmeridge Clay Formation of the Dorset type area; (2) upper Tithonian‒Berriasian (Upper Jurassic‒Lower Cretaceous) of Svalbard and Siberia; and (3) lower Kimmeridgian of west-central Portugal (Tojeira-1 section), and other Tethyan sites.
Identification and correlation of synchronous C-isotope events amongst inter-regional sections reflects the consistency of the C-isotope signal in the seas of north-western Europe at the time of deposition, and include the mid-Eudoxus Zone, mid-Hudlestoni Zone and early Berriasian negative isotope excursions, and the Volgian Isotopic Carbon Excursion (VOICE). The relationship of these records and other Boreal C-isotope accounts for the Late Jurassic and Early Cretaceous are presented as a 훿¹³C_org stack. In addition, time series analyses of TOC records from wells 7120/2-3 and 16/1-14 reveal cycles that strongly resemble the short-term eccentricity component recorded in the well-studied and relatively complete Dorset section. Implied long-term eccentricity modulation in the Tojeria-1 section is also compared with the cyclostratigraphic framework of SE France.
Cyclostratigraphic correlation provides independent support of the constructed age models for the studied sections, and a basis for understanding the timing and extent of Late Jurassic‒Early Cretaceous climate change. As the clay mineral kaolinite is weathered in humid environments, the Early Cretaceous climatic shift from dry-warm conditions is suggested by its abundance, however, palaeoclimatic inferences from clay mineralogical records are complicated by diagenetic overprinting. Clay mineral assemblages from several well constrained sections from the Norwegian Continental Shelf are presented as a N-S transect of the Norwegian-Greenland Seaway.

Date of Award	Jan 2018
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Andy Gale (Supervisor), David Martill (Supervisor) & Felix M. Gradstein (Supervisor)