Fluid migration along faults and gypsum vein formation during basin inversion: An example in the East Walanae fault zone of the Sengkang Basin, South Sulawesi, Indonesia

Abstract

In this study, field, petrographic, and sulfur isotope investigations were conducted for gypsum veins that were formed in the sedimentary rocks of the Walanae Formation in the Sengkang basin, South Sulawesi, Indonesia. Four types of gypsum veins developed in the study area: (1) veins sub-parallel or parallel to bedding, (2) veins perpendicular to bedding, (3) vein networks that fill in complex fractures, and (4) veins that surround carbonate concretions. Their internal structures suggest that fibrous gypsum in these veins grew antitaxially from both sides of the median zone toward the vein walls. Judging from the structural relationships of the orientation of veins with the Sengkang anticline, these gypsum veins were most likely formed as a result of hydraulic fractures or layer-parallel compression within a high fluid pressure environment triggered by the activation of the East Walanae fault under the E-W lateral compression during the Pleistocene basin inversion. The relatively wide range of sulfur isotope values indicates that sulfur in gypsum veins was delivered by the fluids that reacted with framboidal pyrites in the sedimentary rocks.