Organic Matter Enrichment of Black Shale under Tectonic Transformation of the Wulalike Formation in the western margin of Ordos Basin, China

Different tectonic settings affect organic matter enrichment by influencing sedimentary environments. The formation, preservation, and enrichment patterns of organic matter in the Wulalike Formation are still unclear. The influence of the ancient tectonic pattern and sedimentary environment of the Wulalike Formation are summarized to provide insights into the organic matter enrichment through analysis methods such as tectonics, petrology, mineralogy, and geochemistry. The abundance of organic matter is low and heterogeneous vertically in the bulk of the Wulalike Formation. The Wulalike Formation was formed during a tectonic transformation, during which it transitioned from an active continental margin to a passive continental margin. It was at high sedimentation rates that the organic matter content was diluted by the input of clastic sediments. The terrestrial inputs increased through time. The preservation conditions of organic matter were disrupted by the increasing oxygen content with the increase of terrestrial inputs. The level of ancient productivity is gradually decreasing, and the hydrocarbon-generating organisms are a combination of floating algae and benthic algae. The enrichment pattern of organic matter in the Wulalike Formation is controlled by regional structures, dominated by sedimentation rate, terrestrial input, and preservation conditions, supplemented by primary productivity levels. The organic matter accumulation model proposed in this study will provide theoretical support for the exploration of shale gas in northern China.