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Dinaride evaporite mélange : Diagenesis of the Kosovo polje evaporites

The Dinaride evaporite mélange is composed of evaporites and associated sedimentary and magmatic formations of Permian to Triassic age and fl oored by the various Adriatic carbonate platform units. The tectonic history of the Dinaridic evaporite mélange is related to long term burial and Palaeogene to Neogene exhumation processes. Evaporite rocks of the Kosovo polje deposits are associated with carbonates, clastic and minor albitized, subvolcanic, neutral to basic rocks. They are capped by a clayey Quaternary cover of variable thickness, and a several metres thick cavernous carbonate breccia-rauhwacke. Evaporite rocks show two distinct facies: laminated evaporite-carbonate, composed of evaporite and dolomicrite (± organic matter, pyrite, halite) intercalations, and evaporite-carbonate breccia, composed of fragments of laminated evaporites, carbonate and siltite, cemented by massive gypsum ± sulfur, occurring at the shallower levels and related to the emplacement. The Quaternary cover is composed of 47 – 88% clayey material, comprising illite, kaolinite and most likely vermiculite, 9 – 49 % carbonate and 3 – 4% evaporite minerals. The thickness of the evaporite rehydration zone correlates negatively with the thickness of the overlying Quater nary cover and with the amount of clayey material within it. Rauhwacke are composed of partly dedolomitized dolostone and leached gypsum fragments, cemented with late stage calcite. Diagenetic processes are related to early diagenesis and the burial phase began with the formation of diagenetic halite from an oversaturated subsurface or surface (lagoon) brine, and was followed by the biochemical reduction of evaporite sulphate to sulfide and formation of pyrite within organic-rich carbonate laminae. These processes triggered early dolomitization (in a shallow burial realm), and the formation of idiomorphic planar-e type of dolomite crystals at temperatures below 50 – 60°C. Planar dolomite suppressed diagenetic halite. With an increase in burial depth, gypsum dehydrates to anhydrite and when temperatures exceed ~50 °C, precipitation of fine grained non-planar-a type of dolomite began. Halite molds are partly replaced with non-planar-a type of dolomite. During regional uplift and exhumation, anhydrite rehydrated to gypsum under the influence of low-temperature undersaturated fl uid (meteoric water), whereas hydrogen-sulfi de oxi diz ed to elementary sulfur, observed as cement in the evaporite-carbonate breccia. Rauhwacke at the uppermost part of the deposit are formed by severe tectonic movements associated with the gypsum-driven dedolomitization process.

evaporite mélange; burial; emplacement; diagenesis; gypsum-anhydrite transition zone; Kosovo polje evaporites; Dinarides

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