Prediction of weathering paleokarst reservoirs by combining paleokarst landform with unconformity: A case study of Sinian Dengying Formation in Leshan-Longnüsi paleo-uplift, Sichuan Basin

Abstract

Abstract Based on the research of unconformity type and distribution, and restoration of structural feature of paleo-uplift in the late sedimentary period of Sinian Dengying Formation, the evolution of paleokarst landform and karstic hydrodynamic field during depositional hiatus between the Cambrian and Sinian of Leshan-Longnusi paleo-uplift is revealed to predict weathering paleokarst reservoir of Dengying Formation dynamically and effectively. The restoration of ancient structures shows that salient structures were developed continuously in the west of Weiyuan-Renshou, forming concurrent erosional-overlap unconformity, but in the east of Weiyuan- Renshou line, the palaeostructure high shifted from east of Zizhong-Yingshan to the west, forming inversion erosional-overlap unconformity. On this basis, the ancient karstic hydrodynamic field change caused by the change in paleogeomorphology was analyzed to find out the modes and strength of dissolution for different paleokarst landforms. The study indicates that areas along Hechuan-Dazu, Peng'an-Guang'an-Anyue-Neijiang and north of Renshou experienced strong dissolution, developing multiple sets of karst layers; Dazu-Tongnan-Hechuan area underwent fairly strong dissolution, resulting in fairly developed karst reservoirs; the two ends of the area west of Weiyuan-Lezhi-Xichong-Yilong also experienced certain degree of dissolution, with fairly developed karst reservoirs, whereas the middle of this area experienced weak dissolution, resulting in poor development of karst reservoirs.