Depositional Setting and Tectonic Background Analysis on Lower  Cambrian Black Shales in the North of Guizhou Province

Key words: 
• black shale /
• trace elements /
• REE /
• depositional setting /
• tectonic setting /
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Abstract: In order to discuss depositional setting and its tectonic background of the black shale and on the base of the researched 20 profiles, we chose 20 samples collected from bottom of lower Cambrian in the north of Guizhou Province to test and analyze clay minerals, Xray diffraction of the rock minerals and trace elements (including REE). Current study shows that the main minerals are quartz whose average content are 55.75%, and clay minerals whose average content are 28.35%, Among which, the average content of illite is 59%,and the main aeceasory mineral is pyrite in the bottom of lower Cambrian in the north of Guizhou Province; ΣREE is very high and the differentiation between LREE and HREE is distinct which LREE is enriched and Eu is postive anomaly and Ce is negative anomaly; the average ratio of WV/(WNi+WV)and U/Th is respectively 0.78 and 3.76 and the depleted Ce together reflect that Black shale in the north of Guizhou Province forms in reduction environment with stable crust, transgression sea climax and open sea area；the enrichment of trace elements Mo,Sb,U,Cd, V,Ba,Tl,Ni,W,Cr,Cs,Cu,Zn,Bi，strongly depleted Sr,Re , positive Eu anomaly and the lower Co/Zn ratio of the Black shale in the north of Guizhou Province are most likely due to a hydrothermal input;. By the contrast of major elements, trace elements and REE parameters , a conclusion can drawn that in research areas source rocks are mainly sedimentary rocks and granitic rocks with a few locallyinvolved basalt components , the tectonic setting is mainly passive continental margin and partly continental island arc because of hydrothermal input.