WANG Ming-zhen1, WU Chao-dong1,2, WANG Lu-xin1, FANG Ya-nan1, LI Lin-lin1, CHEN Rong1, ZHANG Chen-chen1
1. Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Peking University, Beijing 100871, China;
2. Institute of Oil & Gas, Peking University, Beijing 100871, China
Abstract: This paper analyzes the combination of types, micro-morphology and geochemical features of clay minerals contained in the Jurassic mudstones along the Manasi river in the southern part of Junggar Basin. The Jurassic paleo-climate and paleo-environmental evolution is dicussed based on data of X-ray diffraction, SEM, X-ray fluorescence and ICP-MS. Results show that mudstones are composed of clay minerals, quartz, feldspar and accessory calcite and hematite. Clay mineral assemblages in the mudstones can be divided into two types:one is a mixed-layer of illite-smectite, illite, kaolinite and chlorite, which is distributed in the lower Jurassic strata, the other type is an assemblage of randomly distributed illite and smectite, which is present in the upper Jurassic strata. The crystallinity of clay minerals is low. Illite exists in a filamentous, leaf shape. Montmorillonite shows an irregular distribution of slabs in the surface of clastic particles.Based on the SEM and EDS results, we can conclude that illite/montmorillonite interlayers minerals also exist in pores.The δCe value ranges from 0.9 to 1.3. Eu shows a negative anomaly. All the La/Sc, La/Th, Th/Sc values are higher. This suggests that the provenance is a felsic rock. We conclude that the evolution of the Jurassic climate and sedimentary environment along the southern part of the Junggar Basin can be divided into three stages: during the early Jurassic, the climate was warm and humid, and this area was dominated by fluvial and lacustrine-delta sediments; during the early to middle Jurassic, the climate became relatively warm and arid and this area developed lacustrine sediments; and lastly, from the middle to late middle Jurassic to the late Jurassic, the climate became relatively cold and dry and the sedimentary environment changed to a wide shallow lake basin.
Keywords: paleo-climate paleo-environment CIA CIW
