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.%下扬子地区上二叠统大隆组黑色岩系是区域潜在的烃源层,但过去关注较少.为加深对该问题的认识,本文以新近在皖南地区发现的3条剖面为例,通过详细的岩石学和有机地球化学综合研究,讨论了大隆组黑色岩系的发育特征及油气资源潜力.结果表明,宣城牛山、泾县蔡村和泾县昌桥三条剖面中大隆组黑色岩系均稳定发育,岩石类型包括硅质岩、钙质泥岩和硅质泥岩等.综合地层对比和沉积学研究结果,发现研究区在大隆期经历了一个完整的海进—海退的沉积旋回,黑色岩系主要发育于深水、还原滞留、欠补偿的海洋环境.岩石学和有机地球化学研究结果显示该地区大隆组黑色岩系的有机质丰度高,有机碳含量平均在2.0%左右,有机质类型以Ⅱ2和Ⅲ型为主,并普遍进入高过成熟演化,因此区域勘探应以天然气勘探为主.对比研究区大隆组黑色岩系与中新生代火成岩的分布关系,推测大隆组黑色岩系中有机质的高过成熟演化可能与华南中新生代大规模的岩浆作用影响有关,因此在未受/少受影响的地区(例如泾县—广德一带),也可能存在一定的原油资源潜力.这些认识还可供区域黑色岩系基础地质研究参考.
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