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《Geoscience》 2018-01
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Geochemical Characteristics and Genetic Interpretation of Laminated Shales of the Third Member of Hetaoyuan Formation in the Biyang Depression of Nanxiang Basin

GUO Laiyuan;LIU Zhengjun;XIE Xinong;Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education,China University of Geosciences( Wuhan);Zhanjiang Branch,CNOOC Ener Tech-Drilling & Production Co.;Henan Oilfield Company,SINOPEC;  
The occurence of black and white stripes of laminated shales is a very important and common phenomenon in sedimentary rocks. The X-ray fluorescence core scanner has been used for testing laminated shale samples from the fifth layer in the Biyang Depression. The analysis results show that some chemical elements of the lacustrine lamina,such as Sr,CaO,K_2O,SiO_2,TiO_2,Fe_2O_3,Al_2O_3 and Cu,show obvious regular changes in the black and white laminae. That is,the Sr and CaO contents in the white laminae are significantly higher than those in the black laminae,and the contents of K_2O,SiO_2,TiO_2,Fe_2O_3,Al_2O_3 and Cu in the black laminae are significantly higher than those in the white laminae. The formation machanism of laminae is analyzed combined with the boron element and paleoredox proxies and paleoclimate proxies,and the result suggeststhat these laminated shales would have mainly developed in the brackish-saline and semiarid-arid stratified water. Microscopic investigation also reveals that the black stripes are mainly composed of a high proportion of organic matters and argillaceous sediments,while white stripes are mainly composed of the calcite,gypsum,quartz,dolomite and other minerals. The black and white laminated material components are closely related with a terrigenous supply and authigenic minerals formed in a saline enviroment. The occurence of different elements between the black and the white reveals the different mineral compositions as well as seasonal rhythm changes in the continental lake basin. Therefore,core scanning provides a new effective method to evaluate geochemical characteristics of the laminated shale and its formation mechanism.
【Fund】: 国家重大油气专项(2016ZX0534-002-003);; 中国地质调查局油气基础性公益性地质调查项目(DD20160185)
【CateGory Index】: P618.13
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