Hydrocarbon source rocks were developed in the Pingliang Formation of the Middle Ordovician in southern Ordos Basin. Based on test of over 40 outcrop samples from five sections in southern Ordos Basin

we studied the paleosalinity

hydrodynamic conditions and redox conditions during the Pingliang Age of the Middle Ordovician through trace element analysis. Two major paleosedimentary environments are identified: deepwater slope with brackish

weak hydrodynamics and reducing conditions; and carbonate platform with brine

strong hydrodynamics and oxidizingprone and weak reducing conditions. The former was favorable for development of quality hydrocarbon source rocks. By conducting a comprehensive evaluation of the TOC

organic types and maturity

we come to the conclusion that the mudstone at the lower part of the Formation is the major source rocks

which are mediocre to excellent gas source rocks featuring in large thickness

high TOC

favorable kerogen types (sapropeltype predominant) and high maturity. It is therefore suggested that the northern Weibei high be favorable for exploring the lower Paleozoic in southern Ordos Basin.