Geochemical characteristics and genesis of T/P boundary clay and event clay in Da-fang aera, Guizhou Province
Geochemical characteristics and genesis of T/P boundary clay and event clay in Da-fang aera, Guizhou Province
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发表时间：
2016
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通讯作者：
T. Mei;Zhao Bing;Zhou Bingyang;Zhang Xiao-shi
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作者：
T. Mei;Zhao Bing;Zhou Bingyang;Zhang Xiao-shi
贵州大方地区广泛分布着二叠、三叠系地层。在二叠系与三叠系交界处发现粘土层，厚度12~ 14 cm。在边界粘土之上有3~4层厚5~ 18 cm的火山事件粘土。二叠系与三叠系界线粘土中K_2O和MgO含量较高，事件粘土和火山事件粘土位于松子坎段底部。稀土元素特征也相似。边界粘土和事件粘土均与火山活动有关，表现为Eu亏损。边界粘土的Eu亏损比事件粘土明显，部分事件粘土还表现出Ce亏损。边界粘土和事件粘土的构造背景与活动大陆边缘长英质火山灰存款有关，而与砂堡湾段和九鸡滩段泥质物源区为长石砂岩不同。除Th、Y、Nb、Cd、Ga、In、Ta等微量元素含量远高于事件粘土外，其余微量元素含量与事件粘土相近。由此推断，边界粘土中可能存在少量宇宙事件物质。
The Permian and Triassic strata are widely distributed over Dafang area, Guizhou Province. Clay at the boundary between Permian and Triassic was discovered which is 12~14cm in thickness. There are 3~4 beds of volcanic event clay above the boundary clay which are 5~18cm in thickness. K2O ang MgO are relatively high in boundary clay between Permian and Triassic, event clay and volcanic event clay lie at the bottom of Songzikan Member. Their REE characteristics are also similar to each other. Boundary clay and event clay are both related to volcanic activity, as shown by Eu deficiency. Eu deficiency of boundary clay is more obvious than that of event clay, and some of this clay also show Ce deficiency. Tectonic background of boundary clay and event clay is related to felsic volcanic ash deposit in active continental margin, which is different from things of mud of Shabaowan Member and Jiujitan Member whose source area was feldspar arenite. Most of the trace elements in boundary clay are similar to those in event clay except Th, Y, Nb, Cd, Ga, In and Ta which are much higher than in volcanic event clay. It is thus inferred that there might have existed a little material from cosmic event in boundary clay.