Supplementary materials for thesis ""The Toarcian oceanic anoxic event: organic and inorganic geochemical anomalies in organic-carbon-rich mudrocks from the North Yorkshire Coast, UK and Dotternhausen Quarry, SW Germany"
This dataset comprises the contents of a CD-ROM which was attached to the thesis when it was submitted in 2003. For more information, please refer to "The Toarcian oceanic anoxic event: organic and inorganic geochemical anomalies in organic-carbon-rich mudrocks from the North Yorkshire Coast, UK and Dotternhausen Quarry, SW Germany" via ORO.
High-resolution organic and inorganic chemostratigraphic profiles have been determined for Toarcian (Lower Jurassic) marine successions of organic-carbon-rich mudrocks from the Yorkshire coast (UK) and Dotternhausen Quarry (SW Germany). This data has been used to understand the nature of the environmental changes and the most plausible mechanism(s) during the Toarcian oceanic anoxic event (OAE, exaratum ammonite Subzone). Possible mechanisms include gas-hydrate release, oxygen minimum zone expansion and oceanic overturn.
Total organic-carbon, total sulfur, total nitrogen and other organic parameters (Rock-Eval pyrolysis) infer that denitrifying/euxinic palaeoredox conditions existed in the sediments and bottom waters during the OAE with conditions becoming less anoxic/euxinic after the end of the exaratum Subzone. The 6‰ negative δ 13Corg excursion is confirmed in Yorkshire and Germany and its relationship to the long-term change established. Correlation between Yorkshire and Germany indicates that several carbonate horizons are equivalent and that diagenetic conditions were similar. Inorganic element abundances have been determined using a combination of X-ray fluorescence and refined Laser ablation ICP-MS techniques. Inorganic elements can be divided into those that have a detrital affiliation (e.g. Si, Al and Ti) and those that are seawater derived or have a biologi cal association (e.g. Cu, V and Mo). Some detrital elements such as Zr and Nb show evidence for hydrodynamic sorting related to a relative sea-level rise that produces a decrease in Zr and Nb during deposition of the bifrons Zone. The Mo/Cu ratio changes from low in the exaratum Subzone to high in the overlying falciferum Subzone. It is suggested that the relatively low levels of Mo/Al2O3, Ni/Al2O3 and Re/Al2O3, in the sedimentary deposits formed during deposition of exaratum Subzone is due to a high sedimentation rate.
The relatively fast sedimentation rates inferred during deposition of the exaratum Subzone are most likely a consequence of increased of continental weathering rates and primary productivity. This supports the hypothesis that the trigger for the Toarcian OAE is massive gas-hydrate dissociation associated with a rise in mean global temperature and an increase in chemical weathering.
