--> Carpathian Foredeep Basin (Miocene, Poland and Ukraine): Significance of Evaporite Deposition

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Carpathian Foredeep Basin (Miocene, Poland and Ukraine): Significance of Evaporite Deposition

Abstract

The Carpathian Foredeep – the largest foredeep basin in Europe - developed during the early and middle Miocene as a peripheral flexural foreland basin in front of the advancing Carpathian front. There were three periods of intense foreland subsidence: during the early Miocene, early Badenian, and late Badenian to Sarmatian times. The Carpathian Foredeep basin is subdivided into two parts: inner and outer. The inner foredeep is located at the front and beneath the Carpathian Overthrust and is characterized by strongly folded Eggenburgian-Badenian strata. In the Ukraine, evaporites (halite and potash) are important constituent of the sedimentary column. The outer foredeep is filled by generally undisturbed, flat lying Middle Miocene marine deposits a few hundred meters to 5 km thick. Evaporites (initiated to form 13.81 Ma) are prime marker beds and are included into two formations: Wieliczka Formation, 30–100 m thick, composed of chlorides with siliciclastic intercalations accompanied by tuffites and bentonites and occurring close to the Carpathian orogen, and Krzyzanowice Formation, 10-55 m thick gypsum and anhydrite. Study of foraminifers occurring in marls underlying the Badenian gypsum strongly suggests oxygenation and productivity changes in the Carpathian Foredeep Basin prior to the Badenian salinity crisis. In turn, the composition of benthic foraminifer assemblages and their C isotopic values indicate nutrient-rich waters and mesotrophic to eutrotrophic environments in surface waters, and low oxygenation at the sea floor, during deposition of marly deposits related to the transgression that stopped the basinwide evaporite deposition. There occur benthic and planktonic foraminifera in the marly intercalation sandwiched in Badenian gypsum originated in environment of an evaporitic shoal (<1 m deep) what indicates a major short-lived (few thousand years) seawater flooding event (with seawater rise >50 m) in the previously isolated Carpathian Foredeep. A distinctive decreasing trend of 87Sr/86Sr ratios from western Ukraine to southern Poland as observed in the gypsum is due to a consistent direction of a brine inflow during gypsum crystallization (typical cyclonic circulation controlled by the Coriolis effect). Paleogeographical gradient and rapid, well-documented environmental changes controlled by eustatic and tectonic changes cause that in particular the northern part of the Carpathian Foredeep is regarded as a model example of dynamic stratigraphy.