Organic matter enrichment in basin periphery: A case study of Wufeng-Longmaxi shale, Marcellus shale, and Ohio shale

Our study investigates organic matter (OM) enrichment at the peripheries of marine basins, contrasting with prior research focused on central regions. We analyze three shale formations at three distinct deposition sites: the Marcellus (M) shale near an orogenic belt, and the Wufeng-Longmaxi (WL) shale, the Ohio (O) shale adjacent to a forebulge uplift. By examining factors such as redox conditions, clastic input, paleoproductivity, sedimentary facies and geological activities, we identify that the OM enrichment in shale (M shale) near the orogen resulted from significant inputs of river detritus and semi-deep shelf environment. Additionally, local enrichment is primarily influenced by volcanic ash sedimentation. The shale (O shale) at the distal end of the forebulge shows high OM concentration due to its stable deep-water shelf environment. Local enrichment in this area is caused by sediment re-sedimentation and glaciation. Similarly, the shale (WL shale) at the proximal end also exhibits a high OM concentration due to its stable deep-water shelf environment. In this case, volcanic ash deposition and transgression are responsible for the local enrichment. Our findings reveal how paleogeography and geological activities impact OM enrichment in basin peripheries, while also offering insights into evaluating shale gas reservoirs.