Restoration and Evolution of the Paleogene (E1f2) Shale Sedimentary Environment in the Subei Basin, China.

Restoring the sedimentary environment of paleolakes is of great significance to the formation of laminated calcareous shale deposited in paleolakes and the prediction of shale oil reservoir distribution. This article focuses on the second section shale of the Paleogene in the Funing Formation in the Gaoyou Sag, Subei Basin, China, and uses X-ray fluorescence diffraction technology and core lithology analysis methods to obtain the content datum of major and trace elements such as Sr, Cu, Ba, Ga, V, and Ni in shale at different depths. Based on the empirical values of Sr/Cu, Sr/Ba, V/(V + Ni), and total organic carbon, paleoenvironmental evolution of the continental shale was determined and studied, including the changes in paleoclimate temperature, paleosalinity, paleowater depth, and strong or weak redox intensity. The research results indicate that the sedimentary environment of the paleolake in the Paleogene Funing Formation, second section, in the Gaoyou Sag is mainly characterized by a dry and hot climate; the salinity of paleolake water is that of stable brackish water, and the entire sedimentary period of the Funing Formation, second section, is dominated by a reduction environment, which is conducive to the preservation of sedimentary organic matter. The frequent changes in the depth of sedimentary water and the alternating dry and hot climate are the main reasons for the development of laminated calcareous shale in the second section of the Paleogene Funing Formation of the Gaoyou Sag and have also contributed to the abundant commercial resources of laminated calcareous shale oil in the second section of the Funing Formation.

The timing of the initial collision between the South and North China blocks constraining from the sediments in the eastern Sichuan Basin.

In this study, detrital zircon U-Pb geochronology, trace element and Hf isotopic compositional data from the Early-Middle Triassic clastic rocks in the eastern Sichuan Basin were obtained to distinguish the sediment provenance and constrain the timing of the initial collision between the South China and North China blocks. Detrital zircons from the Early Triassic Feixianguan Formation clastic rocks yield one major age peak at 2476 Ma and three minor age peaks at 1886, 802 and 304 Ma. These detrital zircons may be derived from the South China Block. Detrital zircons from the Early Triassic Jialingjiang Formation clastic rocks yield multiple age peaks at 979, 856, 392 and 269 Ma, indicating a mixed sediment provenance from the South China Block and Qinling Orogenic Belt. This is the first appearance of the detritus with the Qinling Orogenic Belt affinity in the eastern Sichuan Basin. Detrital zircons from the Middle Triassic Leikoupo Formation clastic rocks yield two centralized age peaks at 447 and ca. 245 Ma. These zircons may mainly be derived from the Qinling Orogenic Belt. The results indicate an abrupt change in the detrital zircon U-Pb provenance from the South China Block to the Qinling Orogenic Belt during the Early-Middle Triassic. Integrating the provenance change and other geological characteristics, we suggest that the initial collision in the eastern Qinling Orogenic Belt occurred in the Early Triassic.