Clay Mineral and Major Element Geochemical Features and Their Paleoclimate Significance in Nenjiang Formation 1st and 2nd Members,Eastern Margin of Songliao Basin
Chen Jiquan;Gao Yuan;Qin Jianming;Qin Zuohuan;Xi Dangpeng;Zhong Hanting;Shi Zhongye;School of Earth Sciences and Resources,CUGB;State Key Laboratory of Biogeology and Environmental Geology,CUGB;Institute of Sedimentary Geology,Chengdu University of Technology;
The Songliao Basin eastern margin Nenjiang Formation 1st and 2nd members as a whole is a set of dark mudstone deposits,also a major source rock horizon. To study its paleoclimate and paleoenvironment is conducive to understand later Cretaceous land paleoclimate features and continental organic matter formation and preservation process. The paper has carried out mineralogical and major element geochemical analyses for Nenjiang Formation 1st and 2nd members strata of the Yuewangcheng section,Songliao Basin eastern margin,and then discussed their paleoclimate significance. The results have shown that the bulk rock minerals have mainly quartz,plagioclase,K-feldspar etc.,clay minerals have mainly montmorillonite (average 84%),illite the second (average 15%),almost no kaolinite and chlorite. Clay minerals present lamellar micro-morphology and uneven margin; montmorillonite has poorer crystallinity,indicates its weathered terrigenous deposit origin. Based on clay mineral major element computed chemical weathering index is 71-73. In comparison with upper crust and granodiorite average composition,its elemental composition is allitic,indicated moderate chemical weathering. Combined with available new data of paleoclimate proxy indices and clay mineral chemical composition,the paper considered that during the deposition of Nenjiang Formation 1st and 2nd members in Songliao Basin,the climate in the provenance had been mainly temperate-subtropical semihumid climate.
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