Abstract:

The upper Permian Dalong Formation in the Lower Yangtze Region with black shales is potential for hydrocarbon source
rock. Little attention has been paid to this issue. In order to improve the understanding about it, we conducted a comprehensively
combined study of petrology and organic geochemistry based on three recently-discovered Dalong black shales outcrops in the southern
Anhui province, with the aim to characterize the development and hydrocarbon potential of the Dalong black shales. The results show
that the black shales developed widely in all the three outcrops, including the Niushan (Xuancheng City), Caicun (Jingxian County) and
Changqiao (Jingxian County). Lithology of the shales is variable from chert to calcareous shale, as well as siliceous mudstone.
Stratigraphic correlation and sedimentology of the shales imply that the study area has been subjected to a complete sequence of marine
transgression and regression and the black shales generally developed in the environment of deep seawater under reducing, restricted
and undercompensated conditions. The results from the study of petrology and organic geochemistry show that the Dalong black shales

are rich in organic with the average total organic carbon content being around 2.0%. In terms of kerogen types, the organic matter is
primarily II2 and III. Combined with the high to over maturation of organic matter, we propose that the regional exploration should be
focused on natural gas reservoir. Based on the comparison of the distribution of Mesozoic-Cenozoic igneous rocks and black shales in
the study area, we infer that the over maturation of organic matter may be primarily influenced by large-scale magmatism in South
China during the Mesozoic to Cenozoic period. Thus, petroleum exploration potential can also be considered in the areas where there
was no/little significant influence of magmatism (e.g., the Jingxian-Guangde area). These results and understanding can also provide
highlights for the fundamental geological study of the black shales in this region.

Key words: DalongFormation;blackshales;sourcerock;hydrocarbonresource;Permian;SouthernAnhuiprovince;LowerYangtzeRegion