Multi-phase dolomitization and recrystallization of Middle Triassic shallow marine–peritidal carbonates from the Mecsek Mts. (SW Hungary), as inferred from petrography, carbon, oxygen, strontium and clumped isotope data

Abstract

Abstract Shallow marine to peritidal carbonates of the Triassic Csukma Formation in the Mecsek Mts. of SW Hungary are made up of dolomites, limestones and dolomitic limestones that show evidence of a complex diagenetic history. Integration of petrographic, conventional stable oxygen and carbon isotope, clumped isotope, and strontium isotope data with the paleogeography, paleoclimate, and burial history of the region revealed four major diagenetic stages. Stage 1: The peritidal carbonates were dolomitized penecontemporaneously during the Middle Triassic by refluxing evaporatively concentrated brines. Stage 2: Increasing burial during the Late Triassic–Jurassic resulted in recrystallization of the Kan Dolomite Member in an intermediate burial setting. Stage 3: During the Early Cretaceous seawater was drawn down and circulated through rift-related faults, causing renewed recrystallization of the Kan Dolomite Member as well as dolomitization of the Kozar Limestone Member and the underlying limestones in a deep burial setting, but only in the vicinity of the faults. Stage 4: During the Late Cretaceous and Cenozoic thrusting resulted in tectonic expulsion of basinal fluids and precipitation of multiple saddle dolomite cement phases near the faults. The results of this study imply that the clumped isotope method integrated with other geochemical data can successfully be applied to identify the nature and potential sources of extra-formational diagenetic fluids responsible for dolomitization and recrystallization. This study provides conclusive evidence for multi-phase dolomitization and dolomite recrystallization over several millions of years (Middle Triassic through Early Cretaceous) and several thousands of meters of burial in the Csukma Formation in SW Hungary. Furthermore, this study is the first to identify fault-controlled dolomitization by circulating Cretaceous seawater within Triassic carbonates of central Europe, further supporting the viability of the interpretation of dolomitization by seawater initially drawn down and then geothermally circulated through faults in extensional basins.