Organic matter enrichment in a terrestrial-marine transitional environment driven by global/regional climate recorded in the Upper Permian succession from the Qiangtang Basin, northern Tibet

Abstract

Compared to organic matter (OM) accumulation in marine environments, OM enrichment mechanism in terrestrial-marine transitional environments remain unclear. The Late Permian was an important coal-forming period in China. Late Permian coal-bearing mudstones are important petroleum source rocks in the Qiangtang Basin. In this study, the coal-bearing rocks in the Late Permian Nayixiong Formation from the Qiangtang Basin are selected to address OM accumulation process in transitional environments. Our work demonstrates three-stage climatic changes during the deposition of coal-bearing sedimentary rocks: stages I, II and III, corresponding to a semi-warm and semi-humid climate, warm and humid climate, and cold and arid climate, respectively. Based on degree of pyritization (DOP), enrichment factor (EF) of elements, the Late Permian coal-bearing rocks were deposited under oxic-dysoxic environments. Low excessive barium (Baxs) and biogenic silica (Sibio) contents in the coal-bearing rocks indicates a low primary productivity. We suggest that warm and humid conditions, freshwater and terrestrial plants input are the primary factors controlling OM accumulation during the Late Permian coal-bearing deposition. We summarized a global/regional climate-driven model for OM accumulation in transitional environments. The warming climate created a habitable environment for both terrestrial and marine organisms. Subsequent freshwater input brought abundant nutrients and terrestrial OM to the aqueous system to build high OM accumulation.