Marine transgression(s) to evaporite basin: The case of middle Miocene (Badenian) gypsum in the Central Paratethys, SE Poland

Abstract

The middle Miocene Badenian evaporite basin of the Carpathian Foredeep Basin was a saline lake, separated by a barrier from the sea and supplied with seawater seeping through the barrier or overflowing it occasionally in the form of short-lived marine transgressions. Such transgressions could leave behind marine microfossils in marly clay intercalations. One of them (2.3 m thick) occurs in the uppermost part of the sulphate sequence, in the unit ‘o’, in the Babczyn 2 borehole section. It contains marine palynomorphs (dinoflagellate cysts) and foraminiferal assemblages indicating a marine environment. The low-diversity benthic foraminiferal assemblages are dominated by opportunistic, shallow infaunally living species, preferring muddy or clayey substrate for thriving, brackish to normal marine salinity, and inner shelf environment. Dinoflagellate cyst assemblages, although taxonomically impoverished, consist of marine species; euryhaline forms that tolerate increased salinity are missing. Relatively common microfossils found in clay intercalations within gypsum have important palaeogeographical implications: they strongly suggest that there existed an additional inflow channel supplying the Polish Carpathian Basin from the south during the evaporite deposition and afterwards.