Expansion and connection of Early Jurassic oceanic anoxia: A complementary approach based on coupled Mo-U isotopes of black shales and U isotope signatures of carbonates

下侏罗纪的特点是多个富含有机物的沉积物沉积可能与高碳注入大气（CO2和/或CH 4）和相关的环境变化，如全球变暖，海平面变化，加速水文循环和大陆风化。这些变化导致碳循环的扰动，记录为黑色页岩或碳酸盐档案中有机碳（Corg）和/或无机碳（Ccarb）的碳同位素偏移（CIE）。尽管世界各地的盆地都记录了这种CIE，但人们仍然不太了解区域或全球驱动力在多大程度上导致有机物沉积增加，以及这是否（或在多大程度上）与全球范围内海底缺氧面积扩大有关。在这里，我们建议调查耦合的Mo-U同位素（+微量元素）签名的黑色页岩从三个不同的盆地的欧洲陆表海航道（EES），即柴郡盆地，这是最近由Prees-2钻井（和更早的Mochras农场）和德国西北盆地（采样的Schandelah钻芯）。我们专注于选定的时间间隔，例如三叠纪-侏罗纪-（T-J）边界，包括。下Hettangian和Pliensbachian-Toarcian（Pl-To）边界，包括T-OAE），两者的特征分别是显著负的CIE、全球变暖和一阶或二阶大灭绝。对于后一个时间段，我们还考虑了德国西南部盆地（由SEPIA Metzingen岩心取样）。黑色页岩中的Mo和U同位素特征都取决于当地的沉积条件，如水团混合时间尺度、水柱H2S和金属来源。然而，它们的结合使用，再加上氧化还原敏感的微量元素和TOC的浓度和比例，提供了非常强大的手段来表征水循环的时间尺度内和不同的调查流域之间的连接。在一个互补的方法，我们还建议调查选定的下侏罗纪浅海碳酸盐岩的U同位素签名从摩洛哥和葡萄牙。我们想在这里特别关注的P1-To和T-OAE，并考虑T-J边界的早期发现。海洋碳酸盐岩是古海水铀同位素组成的理想档案，可用于估计全球范围内海底缺氧的面积扩张。通过这些补充调查，我们希望能够揭示在EES中观察到的下侏罗纪CIE和增强的黑色页岩形成在多大程度上是由全球或区域环境变化驱动的。这些发现将是开创性的碳循环扰动和深海海底缺氧扩张之间的联系的后续调查和对未来的预测。

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.