Mixed-water dolomitization in a transgressive beach-ridge system, Eocene Catalan Basin, NE Spain

Abstract

Summary Dolomitization occurs at the top of alluvial fan deposits in the SE margin of the Eocene Catalan Basin, NE Spain. The dolomitized rocks occur just below erosion terraces which show a step-like disposition on the continental sediments and on which shallow marine facies (beach-ridge systems and reefs) are developed. Petrography shows that diagenesis in the continental sediments mainly originated under meteoric water influence, while in beach-ridge systems and reef carbonates there is evidence of early diagenesis in a marine environment. All the nearshore sediments (from alluvial fan to reefs) record a distinct geochemical pattern where a progressively more marine influence parallels the regional trend in facies across the ancient shoreline. Petrographic and geochemical data suggest that mixing of meteoric and marine waters in the sediments representing the continental-to-marine transition caused dolomitization at the top of the alluvial fan deposits. Unlike most mixing-zone dolomites, in this case mixing took place when shallow marine sedimentation took place on erosional surfaces causing the inflow of marine waters that mixed with meteoric porewaters.