Application of seismic geomorphology to carbonate rocks: A case study of the Cambrian Longwangmiao Formation in the Gaoshiti-Moxi area, Sichuan Basin, China

Seismic data are an integrated reflection of the sedimentary interfaces and processes of paleo formations. In this study, seismic geomorphology was applied to analyze and reconstruct the paleogeomorphology of the sedimentation of the Cambrian Longwangmiao Formation in the central Sichuan area by combining three-dimensional (3D) seismic data, a large amount of drilling data, logging data, cores and thin sections. It is believed that the thickness of the Cang-2 member reflects the paleogeomorphology during the sedimentation of the Longwangmiao Formation. Forward seismic modeling was used to select the seismic physical attributes sensitive to the Cang-2 member, which were then used to reconstruct the paleogeomorphology during the sedimentation of the Longwangmiao Formation. The results of this study show that the larger the amplitude of the bottom trough of the Longwangmiao Formation, the higher the landform during the sedimentation period. Therefore, the Caledonian paleo-uplift had already taken shape before the sedimentation of the Longwangmiao Formation, creating a paleo-geomorphologic pattern containing two uplifts and one depression. The geo-morphologic distribution controlled the development of the shoals and reservoirs. The geomorphic highlands not only contained shoals with large areas and thicknesses but were also susceptible to superimposed syngenetic and quasi-syngenetic exposures, which provided preferential flow channels for atmospheric fresh water in the later period and caused the reservoirs to be subjected to more intense karstification. Due to the differences in the potential energy of the topography, the quality of the reservoirs in the NW slope zone is the best, followed by that in the NW high zone and the SE sub-high zone, while the shoals and reservoirs of the sedimentary geomorphic lowlands are poorly developed.