177 / 2022-02-28 06:50:56

沉积环境与气候对有机质富集的控制：以四川盆地东南部晚三叠世须家河组泥页岩为例

Rhaetian, Sedimentary environment, Climate, Organic-rich sediments, Sichuan Basin

Abstract  The mud shale of the Late Triassic Xujiahe Formation in Sichuan Basin are the important source rocks with high organic matter (OM) abundance and wide distribution. At present, there are few studies on the late Triassic Norian-Rutian-sedimentary environment in southeastern Sichuan Basin, and there have been controversies. Based on the investigation of the Xujiahe section in southeastern Sichuan Basin and the analysis of element geochemistry, the evolution process of the sedimentary environment is reconstructed. Combined with previous studies, the factors that control OM enrichment during the Rhaetian are discussed. The sedimentary system in the study area of the Late Triassic Xujiahe Formation was lacustrine-delta. The ratios of V/Cr, U/Th and Ni/Co indicate that the organic-rich sediments were mainly deposited in a weakly oxidized environment, which is not conducive to the preservation of OM. The chemical index of alteration (CIA) indicates the palaeoclimate. A warm and humid paleoclimate favored the growth of organisms, which could enhance the surfcial biotic productivity. The sedimentation rate in southeast area is much lower than that in western Sichuan depression. Although the OM content of mudstone member of Xujiahe Formation in southeastern Sichuan basin is lower than that of western Sichuan depression in general, the OM content of some layers is well preserved. According to the data analysis, OM enrichment in southeastern Sichuan Basin is mainly affected by redox environment and climate, and is almost not affected by sedimentation rate. The upper part of the third member of Xujiahe Formation has the lowest oxygen content, the warmest and wettest climate, and the highest TOC content. These studies reveal that sedimentary environment and paleoclimate might be responsible for the enrichment of OM in the Xujiahe Formation in southeastern Sichuan Basin.