| The significant discoveries in Paleogene oil and gas exploration in the Sanmenxia Basin have not only expanded the exploration prospects of the region but also promoted a renewed understanding of the hydrocarbon source rock geological conditions in the Neogene basin of the southern Ordos margin. This study evaluates the hydrocarbon potential of two sets of black mud shales developed in the Paleogene Oligocene Xiao ""an Formation at the Mitangou section of the Sanmenxia Basin using a combination of multiple parameters. The results indicate that the upper black mud shales of the Oligocene Xia"" an Formation exhibit substantial thickness and high organic carbon content, with organic matter primarily of Type II? and partially Type I and Type II?. In contrast, the lower black mud shales are relatively thinner, with slightly lower organic carbon content and organic matter predominantly of Type II?, containing minor amounts of Type III. Influenced by regional tectonic uplift during the late Paleogene, the thermal evolution of the source rocks remains generally low. Analysis of triterpene and gamma waxane indices reveals that the lower black mud shales formed in relatively shallow oxidized environments, while the upper ones developed under high-salinity reducing-to-strong-reducing conditions. These findings align with existing crude oil analysis results from the Sanmenxia and Weihe Basins, confirming the upper black mud shales of the Oligocene Xia ""an Formation as the primary source rock system. Based on the "sink-controlled oil accumulation and source rock accumulation" principle for faulted basins, the study concludes that the Neogene basin of the southern Ordos margin should prioritize the Oligocene Xia"" an Formation and equivalent stratigraphic levels as key exploration targets. Currently, drilling activities in these target systems are scarce and located far from hydrocarbon-producing depressions, while the deep depression areas and surrounding regions hold significant exploration potential. |