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Wieloetapowa dolomityzacja w sukcesji triasu dolnego i środkowego serii wierchowej (Tatry Zachodnie, Polska)

Jaglarz P.

Przegląd Geologiczny

2012

Vol. 60, nr 5

284-293

The paper is focused on multi-stage dolomitization process in the Lower-Middle Triassic succession of the High-Tatric series from the Western Tatra Mts. Lower and Middle Triassic bedded dolostones have several features indicating their early-diagenetic (synsedimentary) origin: preservation of sedimentary structures, fine-grained fraction (except redeposited deposits), relatively high concentration of siliciclastics, pseudomorphs after sulfates, lack of benthic fauna (except storm deposits). This can also be identified by presence of teepee structures and solution-collapse breccias. The sedimentological features and δ13C values may lead to conclusion that bedded dolostones were formed in the hypersaline environment, within supra- to interitidal zone. The part of bedded dolostones (mainly Early Triassic and latest Middle Triassic age) were formed during dilution of hipersaline waters by periodic fresh-water inputs. Positive correlation between δ13C and δ18O in dolomitized calcarenites suggests dolomitization with the influence of mixed meteoric and marine (hypersaline) waters. That dolomitization process took place during relatively early stage of burial diagenesis at marine regression times. The δ13C values of dolomitized calcilutites, as well as mosaic and saddle dolomitic cements suggest the dolomitization by solutions of marine origin. The lack of correlation between δ13C and δ18O indicates high temperature of these solutions. The values of δ18O indicate the temperature formation of dolomitic mosaic cements at 45-65°C. Calcilutites were dolomitized at 70-80°C, and saddle dolomite cements were formed in similar thermal conditions (70–85°C). Hydrothermal dolomitization is dated on Middle Triassic time.