Influence of trough currents on Permian reef-shoal belts and reef-capping dolomite reservoirs, Damaoping Block,...

Large Late Permian reef-shoal mounds and supergiant gas fields have been identified along the margin of the Kaijiang-Liangping trough on the Upper Yangtze Platform. However, the underlying mechanisms of their concentration along the trough margin remain unclear. Herein, the Damaoping Block at the eastern trough end is used as a case study to examine how trough currents influence the development of reef-shoal mounds and reef-cap reservoir distribution. Results show that enhanced seismic facies analysis can identify individual reef-shoal mounds in low-amplitude reef-shoal zones and map small-scale reef-cap dolomite reservoirs. Sponge reefs occur in neritic water below the normal wave base because of upwelling. Rear reef-shoal mounds align directionally and become less developed toward the platform interior, with their orientation following the trough axis-indicating upwelling direction. Nutrient- and oxygen-rich cold bottom currents and upwelling helped sustain the preferential development and directional distribution of reef-shoal complexes, and indirectly controlled dolomite reservoir distribution on reef tops. This study establishes a methodological framework for reconstructing carbonate sedimentary systems and characterizing small-scale reef-shoal facies reservoirs, and provides evidence for deep-water bottom currents and upwelling on the Permian Yangtze Platform, which may contribute to future discussion of Late Permian thermohaline circulation.