(Table 1) Elemental composition, pyrite-Fe and degree of pyritisation in Upper Pliensbachian and Lower Toarcian sediments from the costal section of Yorkshire

Profiles of Mo/total organic carbon (TOC) through the Lower Toarcian black shales of the Cleveland Basin, Yorkshire, United Kingdom, and the Posidonia shale of Germany and Switzerland reveal water mass restriction during the interval from late tenuicostatum Zone times to early bifrons Zone times, times which include that of the putative Early Toarcian oceanic anoxic event. The degree of restriction is revealed by crossplots of Mo and TOC concentrations for the Cleveland Basin, which define two linear arrays with regression slopes (ppm/%) of 0.5 and 17. The slope of 0.5 applies to sediment from the upper semicelatum and exaratum Subzones. This value, which is one tenth of that for modern sediments from the Black Sea (Mo/TOC regression slope 4.5), reveals that water mass restriction during this interval was around 10 times more severe than in the modern Black Sea; the renewal frequency of the water mass was between 4 and 40 ka. The Mo/TOC regression slope of 17 applies to the overlying falciferum and commune subzones: the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years. The more restricted of the two intervals has been termed the Early Toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to NW Europe. Crossplots of Re, Os, and Mo against TOC show similar trends of increasing element concentration with increase in TOC but with differing slopes. Together with modeling of 187Os/188Os and d98Mo, the element/TOC trends show that drawdown of Re, Os, and Mo was essentially complete during upper semicelatum and exaratum Subzone times (Mo/TOC regression slope of 0.5). Drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of Re, Os, and Mo, via a low-salinity surface layer, created isotopic excursions of up to 1.3 per mil in d98Mo and up to 0.6 per mil for 187Os/188Os. Restriction thereby compromises attempts to date Toarcian black shales, and possibly all black shales, using Re-Os chronology and introduces a confounding influence in the attempts to use d98Mo and initial 187Os/188Os for palaeo-oceanographic interpretation.

对英国约克郡克利夫兰盆地下托阿尔阶黑色页岩以及德国、瑞士波西多尼亚页岩中的钼（Molybdenum, Mo）/总有机碳（Total Organic Carbon, TOC）剖面展开分析，结果揭示了细肋菊石带晚期至双肋菊石带早期这一时间段内的水体封闭状态——该时段恰好涵盖了被认为的早托阿尔期海洋缺氧事件。克利夫兰盆地的Mo与TOC浓度交叉散点图呈现出两组线性阵列，其回归斜率（ppm/%）分别为0.5与17。斜率为0.5的阵列对应半盔菊石亚带和隆脊菊石亚带上部的沉积物。该数值仅为现代黑海沉积物Mo/TOC回归斜率（4.5）的十分之一，表明此时期的水体封闭程度约为现代黑海的10倍，水体更新周期介于4至40千年之间。斜率为17的阵列对应上覆的镰形菊石亚带和普通菊石亚带，该数值显示此时期的水体封闭程度相对较弱，水体更新周期介于10至130年之间。此前将封闭程度更高的这一时期定义为早托阿尔期海洋缺氧事件，但本研究表明该事件实为西北欧局域性盆地封闭所引发。铼（Rhenium, Re）、锇（Osmium, Os）与Mo分别与TOC的交叉散点图呈现出类似趋势：元素浓度随TOC含量升高而增加，但斜率各不相同。结合187Os/188Os与δ98Mo的模拟结果，上述元素/TOC趋势表明，在半盔菊石亚带和隆脊菊石亚带时期，Re、Os和Mo的水相耗竭作用已基本完成（对应Mo/TOC回归斜率为0.5）。水体封闭使得受限水体对淡水混合引发的同位素变化更为敏感：通过低盐度表层水体输入的陆源Re、Os和Mo，造成了δ98Mo最高可达1.3‰、187Os/188Os最高可达0.6‰的同位素偏移。因此，水体封闭现象会干扰利用铼-锇年代学对托阿尔阶黑色页岩（乃至所有黑色页岩）进行定年的尝试，并为利用δ98Mo和初始187Os/188Os开展古海洋学解释的研究引入混杂影响因素。