Paleoenvironment and Hydrocarbon Potential of Salinized Lacustrine Shale with High Terrigenous Input in the Paleogene Biyang Depression (East China): Evidence from Organic Petrography and Geochemistry

Abstract

Salinized lacustrine shale (SLS) represents a frontier in the global quest for unconventional hydrocarbon resources. The impact of terrigenous input, which includes terrigenous organic matter (OM) and detrital matter, on the deposition and hydrocarbon potential of SLS is still controversial. Here, we examine this issue using the newly discovered SLS within the Paleogene Biyang Depression, employing a combination of organic petrographic and geochemical analyses. A high influx of terrigenous input (terrigenous OM and detrital matter) promotes the formation of SLS. On the one hand, terrigenous higher plants emerge as the primary source of OM in the SLS, as indicated by the dominance of terrigenous macerals (e.g., terrigenous liptinite) and the abundance of plant-derived biomarkers (e.g., tricyclic terpanes). Additionally, a portion of the OM may originate from bacteria. On the other hand, the rapid input of detrital matter improves the preservation of OM, resulting in the deposition of SLS with high total organic carbon (TOC) contents and low hydrogen index (HI) values. The findings of this study contribute to a deeper understanding of SLS deposition and provide guidance for regional hydrocarbon exploration.