Palaeoenvironments of the Middle Miocene evaporite-bearing deposits from the Działoszyce Trough, Carpathian Foredeep, Poland, based on microfaunal studies

Abstract

Analysis of microfossil distribution (foraminifera, ostracodes and bolboforms) in evaporite-bearing deposits from the Działoszyce Trough (northern Carpathian Foredeep) has allowed the distinction of three ecozones: the Globigerinoides ecozone (Lower Badenian), the Globigerina ecozone (Middle and Upper Badenian) including an evaporitic horizon, and the Anomalinoides dividens ecozone (Sarmatian). These ecozones are of ecostratigraphical significance and reflect major sea-level changes. The highest stands of sea-level correspond with the Globigerinoides ecozone and the upper part of the Globigerina ecozone, above the evaporites, and they are considered to relate to an influx of oceanic waters. Drastic climatic changes (cooling) and a sea-level fall that weakened bottom water circulation at the boundary between the Globigerinoides and Globigeriau ecozones are considered the major factors which accounted for hypoxia (an oxygen·poor environment) that accompanied evaporitic deposition. The appearance of a specific ostracod assemblage (Xylocythene carpathica Szczechura and ?Microxestoleberis sp.) in Upper Badenian deposits is linked with the occurrence of active submarine hydrocarbon seepages.