Geochemical Characteristics and Controlling Factors of Organic Matter Enrichment in the Bagong Formation Source Rocks, Eastern Qiangtang Basin

Abstract

The Upper Triassic successions in the Qiangtang Basin are critical targets for petroleum exploration, yet the key factors controlling OM (organic matter) enrichment in the Bagong Formation source rocks remain unclear. The source rock characteristics and sedimentary environments of the Bagong Formation in the Upper Triassic from well QS9 in the eastern North Qiangtang Basin were analysed through organic geochemistry and major and trace element data, and the factors governing OM enrichment were identified. The results reveal that the TOC content ranges from 0.29% to 2.20% (avg. 1.13%). Organic matter from land plants and plankton is characterized by type II₂ kerogen but is close to type III kerogen. Organic matter is thermally mature to highly mature. The palaeoclimate shifted from hot with intense weathering to warm with humid moderate weathering. The depositional environments were marine and oxic–suboxic water conditions, with oxidation in the lower part and suboxidation in the upper part. OM enrichment is controlled by the evolution of the sedimentary environment (climate, sea level, and clastic input) and local reducing conditions. This conclusion provides a clear scientific basis for petroleum exploration and high-quality source rock prediction of the Bagong Formation source rocks in the study area.

Keywords

organic matter enrichment / sedimentary environment / source rocks / geochemistry / Bagong Formation / Qiangtang Basin

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2025 Geological Society of China