Organic matter accumulation under the Middle-Upper Ordovician tectonic transition on the western margin of the North China platform

The tectonic of the Middle and Late Ordovician in the western margin of the north China Platform is complex, and the accumulation models of organic matter of the Wulalike Formation formed during this period are still unclear. Total organic carbon (TOC) content, mineral composition, organic carbon isotope composition, as well as the major and trace elements in the shale samples were all measured in this study. The Wulalike Formation was formed during a tectonic transition from a passive continental margin to an active continental margin. Hydrocarbon-forming organisms are mainly algae. Primary productivity, terrigenous input, and sedimentation rates influence input, dilution, and degradation of organic matter. The degree of degradation, redox, and basin restriction control the preservation of organic matter. The TOC of the Wulalike Formation is determined by the input and preservation degree of organic matter at different sedimentary periods. The organic matter accumulation model in the Wulalike Formation is controlled by regional structures, dominated by sedimentation rate and preservation conditions.