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Solution-collapse breccias in the upper Olenekian–Ladinian succession, Tatra Mts, Poland

Jaglarz P., Rychliński T.

Annales Societatis Geologorum Poloniae

2018

Vol. 88, No. 4

303--319

The upper Olenekian-Middle Triassic succession of the Tatricum domain (Central Western Carpathians, southern Poland) includes a few horizons of breccias, which are intercalated with early-diagenetic dolostones. On the basis of macroscopic and microscopic (including cathodoluminescence) observations, the paper presents a new interpretation of the genesis of the breccias and their diagenetic history. The rocks studied range from monomictic, cemented mosaic packbreccias to chaotic, unsorted, monomictic, particulate rubble floatbreccias. The processes that preceded the formation of the breccias encompassed the precipitation of evaporites and the early-diagenetic dolomitization of lime muds. The solution-collapse breccias were formed during episodes of cyclic sediment emersions in the upper Olenekian and Middle Triassic, as the result of gradual sediment collapse after karstic dissolution of the intercalated evaporites. After the brecciation process, during diagenesis the rocks were subjected to cementation by sulphate minerals and next, to multi-stage dolomitization. Later tectonic processes led to fracturing and even re-brecciation of the previously formed solution-collapse breccias.

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.