A new subsurface record of the Pliensbachian–Toarcian, Lower Jurassic, of Yorkshire

Abstract

Here, we describe the upper Pliensbachian to middle Toarcian stratigraphy of the Dove's Nest borehole, which was drilled near Whitby, North Yorkshire, in 2013. The core represents a single, continuous vertical section through unweathered, immature Lower Jurassic sedimentary rocks. The thickness of the Lias Group formations in the Dove's Nest core is approximately the same as that exposed along the North Yorkshire coast between Hawsker Bottoms and Whitby. The studied succession consists of epeiric-neritic sediments and comprises cross-laminated very fine sandstones, (oolitic) ironstones, and argillaceous mudstones. Dark argillaceous mudstone is the dominant lithology. These sediments were deposited in the Cleveland Basin, a more subsident area of an epeiric sea, the Laurasian Sea. We present a set of geochemical data that includes organic carbon isotope ratios ( δ 13 C org ) and total organic carbon (TOC). The δ 13 C org record contains a negative excursion across the Pliensbachian–Toarcian boundary and another in the lower Toarcian that corresponds to the Toarcian Oceanic Anoxic Event (T-OAE). Below the T-OAE negative excursion, δ 13 C org values are less 13 C-depleted than above it. We find no evidence of a long-term δ 13 C org positive excursion. TOC values below the T-OAE negative excursion are lower than above it. Sedimentary evidence suggests that, during much of the Pliensbachian–Toarcian interval, the seafloor of the Cleveland Basin was above storm wave-base and that storm-driven bottom currents were responsible for much sediment erosion, transport, and redeposition during the interval of oceanic anoxia. The abrupt shifts observed in the δ 13 C org record (lower Toarcian) are likely to reflect the impact of erosion by storms on the morphology of the δ 13 C record of the T-OAE. Supplementary material: stratigraphic and geochemical data [organic carbon isotope ratios ( δ 13 C org ) and total organic carbon (TOC)] are available at https://doi.org/10.6084/m9.figshare.c.6154436