Origin of Subsurface Brines in the Sichuan Basin

Abstract Subsurface brines in the Sichuan Basin occur within sedimentary rocks ranging in age from Sinian to Cretaceous, especially within rocks of Triassic age. The chemical and isotopic compositions of the brines and general geological considerations suggest that the Sichuan Basin brines are derived from waters of different origin. Water in brines from Upper Cretaceous clastic reservoirs in Anren, and from basin margin aquifers of Lower Jurassic, Triassic, and Cambrian age are modern meteoric in origin. Salinity in these brines is from dissolution of salt‐bearing formations. Lower Jurassic and Upper Triassic clastic aquifers contain a mixture of meteoric water and brines from older rocks based on isotopic data. Brines in Middle and Lower Triassic carbonate aquifers originated from sea water and are residual brines left after evaporite precipitation. Brines from the Upper Sinian carbonate aquifer in Weiyuan originated from sea water mixed with magmatic waters.