The Santonian–Campanian Boundary Event (SCBE) in Boreal Basins: New geochemical and mineralogical data from the Northern Chalk Province (East Yorkshire, UK)

Abstract

The Upper Cretaceous Flamborough Chalk Formation of the English Northern Chalk Province (Danes Dyke section, East Yorkshire, UK) has been sampled for isotope analyses to test for the expression of the positive carbon-isotope excursion defining the Santonian–Campanian Boundary Event (SCBE) in northern England, and to improve basin-scale correlations between the Boreal and Tethyan realms. Clay mineral investigations have been conducted in order to characterise potential variations in the detrital flux between the top of the Santonian and the base of the Campanian, and to test relationships with the SCBE. In the Flamborough Chalk and in other chalk sections, the Santonian/Campanian boundary is defined by the highest occurrence datum of the crinoid Marsupites. Carbon isotope results in this section indicate the presence of the negative Foreness Event in the upper Santonian, while the SCBE is characterised by a double positive excursion with peaks respectively named ‘a’ and ‘b’. The first peak of the SCBE (a) lies in the uppermost part of the Marsupites Zone and therefore belongs to the upper Santonian. Peak b of the SCBE is located above the highest occurrence of Marsupites and is thus partially included in the Uintacrinus anglicus Zone of the lower Campanian. The clay fraction (<2 μm) analysis of chalks and marl bands reveals dominant smectite-rich clay minerals (e.g. R0 type illite/smectite mixed-layers or IS R0, 95% on average) and subordinate illite (5% on average) through the section. A discrete increase of the illite/IS R0 ratio in the clay fraction, combined with an increase in marl horizons and clay proportions in the bulk insoluble residue, highlight slightly enhanced terrigenous input during the SCBE. Correlation with published key sections in Western Europe shows that the SCBE has a similar chemostratigraphic signature and can be used to refine regional correlations, although it is thicker in the English Northern Province due to higher sedimentation rates in this area.