Sulfur-isotope study on the mass extinction boundaries

在日本千叶地体的天神丸和丹波地体的Sasayama，获得了横跨二叠纪/三叠纪（P/Tr）界线的以硅质岩为主的连续泥灰岩沉积序列的全岩硫化物的系统硫同位素数据。P/Tr边界的特征是硅质页岩与碳质黑色泥岩的出现，碳质黑色泥岩在外观上类似于全球分布的白垩纪/第三纪（K/T）边界粘土岩。观察到的数据清楚地表明了显著的双峰性。相对于CDT的34 S/32 S比值在整个Hiddle二叠纪（约- 39 - 25%）。并显示出一个显着的增加开始在较低的上二叠世和持续到下三叠世（约- 20至-2%），随着一个暂时的和剧烈的负位移，下降到大致相同的同位素水平，在Hiddle二叠纪，只是在可疑的P/Tr边界（约- 41%至-23%）。有趣的是，同位素漂移的方式跨越P/Tr的边界是在鲜明的对比，最近在日本北海道的Kawaruppu在K/T的边界。高~（34）S/~（32）S组相对于同期海水硫酸盐的表观分馏程度在-25SY. ±-范围内。()10%，这在数量上相当于目前确认的细菌异化硫酸盐还原过程中动力学同位素效应的范围，并且在低-34S/32S组中，该值大多超过该范围，给出了典型地在-45（）SY ±-范围内的值。()10%，这与现代海洋沉积物中通常观察到的相似。目前的数据将提供强有力的证据，一个基本上停滞，缺氧分层的海洋，这大概开始形成在晚二叠世早期，并持续到早三叠世的发展，和爆发的临时大规模混合只是在可疑的P/Tr边界。这种海洋缺氧-缺氧的历史

Systematic sulfur isotope data for whole-rock sulfides have been obtained from the chert-dominated, continuous, pelaqic sedimentary sequences spanning the Permian/Triassic (P/Tr) boundary at Tenjinmaru in the chichibu Terrane and at Sasayama in the Tanba Terrane in Japan. The P/Tr boundary is characterized by the occurrence of siliceous shales in association with a carbonaceous black mudstone which is similar in appearance to the worldwide distributed Cretaceous/Tertiary (K/T) boundary claystone. The obsarved data ciearly demonstrate a significant bimodalism. The 34S/32S ratios with respect to CDT are generally low throughout the Hiddle Permian (ca.-39 to -25 %.) and show a remarkable increase beginning in the lower Upper Permian and persisting into the Lower Triassic (ca.-20 to -2 %.), with a temporary and drastic negative shift, down to roughly the same isotopic level as in the Hiddle Permian, just at the suspected P/Tr boundary (ca.-41 to -23 %.). Interestingly, the mode of isotopic excursion across the P/Tr boundary is in striking contrast to that across the K/T boundary which was recently disclosed at Kawaruppu in Hokkado, Japan. The apparent extent of fractionation, with rospect to contemporaneous seawater sulfate, in the high-34S/32S grouplies within the range of -25(〕SY.+-.〔)10 %, which is quantitatively equivalent to the currently confirmed range of kinetic isotope effect during bacterial dissimilatory sulfate reduction, and that in the low-34S/32S group mostly exceeds this range, giving the values typically in the range of -45(〕SY.+-.〔)10 %, which is similar to what is generally observced in the present-day oceanic sediments. The present data would provide strong evidence for the development of a largely stagnant, anoxic stratified ocean, which presumably began to form in the early Late Permian and persisted into the Early Triassic, and for the outbreak of its temporary massive mixing just at the suspected P/Tr boundary. Such an oceanic oxic-anoxic histor