The Lower Jurassic is characterized by multiple intervals of organic-rich sediment deposition likely related to high carbon injection into the atmosphere (CO2 and/or CH4) and associated environmental changes, such as global warming, sea level changes, accelerated hydrological cycles and continental weathering. These changes resulted in perturbations in the carbon cycle which are recorded as C isotope excursions (CIE) of organic (Corg) and/or inorganic (Ccarb) carbon in black shale or carbonate archives. Even though such CIE are recorded in basins worldwide, it is still poorly understood to what extent regional or global driving forces resulted in enhanced deposition of organic matter and if (or to which degree) this correlates with an areal expansion of seafloor anoxia at global scales.
Here we propose to investigate the coupled Mo-U isotope (+ trace element) signatures of black shales from three different basins of the European epicontinental seaways (EES), i.e. the Cheshire basin, that was recently intersected by the Prees-2 drilling (and earlier by Mochras Farm) and the Northwest German Basin (sampled by the Schandelah drill core). We focus on selected time intervals, such as e.g. the Triassic-Jurassic- (T-J) boundary incl. the lower Hettangian and the Pliensbachian-Toarcian (Pl-To) boundary incl. the T-OAE), both of which were characterized by significantly negative CIEs, global warming and a first- or second order mass extinction, respectively. For the latter time interval we also consider the Southwest German Basin (sampled by SEPIA Metzingen drill cores). The Mo and U isotope signatures in black shales are both depending on local depositional conditions, such as water mass mixing time scales, water column H2S and metal sources. Their combined use, however, together with concentrations and ratios of redox-sensitive trace element and TOC, provides extremely powerful means to characterize water-circulation timescales within and connection between the different investigated basins.
In a complementary approach, we furthermore propose to investigate the U isotope signatures of selected Lower Jurassic shallow-marine carbonates from Morocco and Portugal. We want to focus here in particular on the Pl-To and T-OAE and consider earlier findings for the T-J boundary. Marine carbonates are ideal archives for the U isotope composition of paleo-seawater that can be used to estimate the areal expansion of seafloor anoxia at global scales. With these complementary investigations, we expect to unravel to what extent the observed Lower Jurassic CIE and enhanced black shale formation in the EES, were driven by global or regional environmental changes. These findings will be ground-breaking for subsequent investigations about the linkage of carbon cycle perturbations and seafloor anoxia expansion in deep time and for projections to the future.