Abstract:

Karstic rocks of the Huanglong Formation exposed at the margin of the southern Daba Mountain can be divided into four types: slightly-corroded, moderately-corroded porous，intensely-corroded brecciated and intensely corroded and altered secondary calcic karstic rocks. The strontium isotope compositions of various karstic rocks are analyzed systematically and are compared with the rocks without karst corrosion. It is indicated that during the karst formation process, a positive deviation of  ⁸⁷Sr/⁸⁶Sr ratio can be seen from infiltrating fluid belt to active underflow belt while an intense negative deviation appears gradually in the inactive underflow belt. Under the water-rock interaction system of the same karst fluid regime, the matrix are more enriched in  ⁸⁷Sr compared to breccias. However, the secondary calcic karstic rocks are poorly enriched in ⁸⁷Sr when compared with those of dolomitic karstic rocks. The high ⁸⁷Sr/⁸⁶Sr ratios of the varied genetic and differently corroded karstic rocks are caused by the injection of high ⁸⁷Sr groundwater involved in the water-rock interaction and the intense ⁸⁷Sr enrichment of the matrix dolomite. The strontium isotope of different karstic reservoirs can provide meaningful geochemical information for forecasting and evaluating the development and distribution rules of the Huanglong Formation at the margin of southern Daba Mountain in time and space.

Key words: paleokarst reservoirs, strontium isotope, geochemistry, karst fluid, Huanglong Formation, southern Daba Mountain