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对四川盆地二叠系和三叠系接触关系的认识长期存在较大分歧。通过对钻井、岩心等资料的研究发现,蜀南地区长兴组钻进过程中出现大量钻具放空现象,岩心上见大量的溶沟、溶缝、溶洞及岩溶角砾。综合分析认为蜀南地区长兴组与飞仙关组并非连续沉积,其间存在沉积间断,长兴组古岩溶作用发育,形成了长兴组顶部古岩溶不整合。泸州古隆起的持续发展和二叠纪末期一次重大海退引起的长时期暴露溶蚀是蜀南地区长兴组古岩溶形成的关键。古岩溶对碳酸盐岩的储集性能具有较强的优化改造能力,古岩溶不整合面可以作为油气长距离运移的优质通道,岩溶斜坡带是油气成藏的有利区带。长兴组顶部古岩溶不整合的发现为区内二叠系和三叠系非整合接触找到了直接证据,对今后蜀南地区乃至四川盆地长兴组的油气勘探具有指导意义。
There are long-standing differences on the understanding of the contact between Permian and Triassic in the Sichuan Basin. Through the study of drilling and core data, it is found that a large number of drilling tools have been emptied during the drilling process of Changxing formation in the southern Sichuan region. A large number of ditches, dissolved seams, karst caves and karst breccias were found in the core. The comprehensive analysis shows that the Changxing Formation and the Feixianguan Formation in the Shunan area are not continuously deposited with depositional discontinuities and paleokarstification in the Changxing Formation and the formation of the paleokarst unconformity at the top of the Changxing Formation. The continuous development of the Luzhou paleouplift and the prolonged exposure and erosion caused by a major regression of the end of Permian are the key to the formation of paleokarst in the Changxing Formation in the southern Sichuan area. Paleokarst has a strong ability to optimize the reservoir properties of carbonate rocks. Paleokarst unconformity can be used as a good channel for long-distance migration of oil and gas. Karst slope zone is a favorable zone for hydrocarbon accumulation. The discovery of the unconformity of paleokarst at the top of Changxing Formation has found direct evidence for the non-integrated contact of Permian and Triassic in the area, which is of guiding significance to the future exploration of hydrocarbon in Changxing Formation in Sichuan Province and even in Sichuan Basin.