Volcanism in Association with the Prelude to Mass Extinction and Environment Change Across the Permian-Triassic Boundary (PTB), Southern China
Volcanism in Association with the Prelude to Mass Extinction and Environment Change Across the Permian-Triassic Boundary (PTB), Southern China
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DOI：
10.1346/ccmn.2011.0590505
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发表时间：
2011-10
影响因子：
2.2
通讯作者：
H. Hong;S. Xie;X. Lai
中科院分区：
文献类型：
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作者：
H. Hong;S. Xie;X. Lai
为了更好地了解沉积物的物源以及与二叠-三叠系生物危机相关的环境变化，采用X射线衍射和差示扫描量热法（DSC）对中国南方梅山剖面和峡口剖面的二叠-三叠系界线沉积物进行了粘土矿物学对比研究。结果表明，梅山火山爆发前大规模绝灭的24 e碎屑岩层的粘土矿物组成为56%的伊蒙混合层（I-S）、39%的伊利石和5%的高岭石。在652°C时测得的脱羟基效应表明，该层的I-S和伊利石主要含有与火山成因有关的顺空（cv）层。该脱羟作用事件与峡口P257层有关。白色粘土层25也对应于梅山的主要灭绝事件，含有95%的I-S和5%的高岭石，在DSC曲线中，在676°C具有强吸热效应，在514°C具有较弱的吸热效应。这些结果归因于I-S粘土中cv层的脱羟基作用，表明白色粘土层中的I-S来自火山灰的海相蚀变，与夏口牙形石相关粘土（P258）一致。（牙形刺是牙齿状的微化石，通常用作PTB地层学的年龄指标。在梅山的黑色粘土层（26层）和夏口的牙形石相关的黑色粘土层（P259 b）中，方解石和伊利石含量的增加可能表明在较冷和较干旱的条件下，侵蚀过程较强。在一个标志着大规模灭绝主要情节前奏的床中发现的火山物质加强了火山活动和大规模灭绝之间的时间联系。
In order to better understand the provenance of the sediments and environmental change associated with the Permian-Triassic (P/T) biotic crisis, a comparative clay mineralogical study of the Permian-Triassic boundary (PTB) sediments between the Meishan section (the Global Stratotype Section and Point of the PTB) and the Xiakou section, southern China, was undertaken using X-ray diffraction and differential scanning calorimetry (DSC). The results showed that clay minerals of the packstone bed 24e, in which the preludial mass extinction occurred at Meishan, consist of 56% mixed-layer illite-smectite (I-S), 39% illite, and 5% kaolinite. A dehydroxylation effect was measured at 652°C, indicating that I-S and illite of this bed contain mainly cis-vacant (cv) layers related to volcanic origin. The dehydroxylation event correlates with bed P257 at Xiakou. The white clay bed 25 also corresponding to the main extinction event at Meishan contains 95% I-S and 5% kaolinite, with a strong endothermic effect at 676°C and a weaker one at 514°C in the DSC curve. These results are attributed to dehydroxylation of cv layers in I-S clays, suggesting that I-S in the white clay bed was derived from marine alteration of volcanic ash, in agreement with the conodont-correlated clay (P258) at Xiakou. (Conodonts are tooth-like microfossils and are usually used as an indicator of age in PTB stratigraphy.) Increases in chlorite and illite contents in the black clays (bed 26) at Meishan and the conodont-correlated black clay layer (P259b) at Xiakou probably indicate stronger erosional processes under cooler and more arid conditions. Volcanic materials found in a bed which marked the prelude to the main episode of mass extinction reinforce the temporal link between volcanism and the mass extinction.