Paleoenvironmental dynamics in the southern Pannonian Basin during initial Middle Miocene marine flooding

Abstract

Paleoenvironmental analysis based on foraminiferal distribution has been carried out on 44 sediment bulk samples from the locality Bogutovo selo near Ugljevik (NE Bosnia and Herzegovina). During the Middle Miocene the region was positioned on the southern margin of the Pannonian Basin and the Central Paratethys Sea. The studied section comprises [approximate] 70-m-thick sedimentary succession dominated by marine marls and intercalated in its middle part by a single 14-m-thick limestone package. Marine succession superposes by angle discordance Oligocene coal-bearing deposits. The marker species allow correlation of the lower part of the section with the Early Badenian Upper Lagenidae Zone, whereas for the middle and upper part, the Middle Badenian [Spirorutilus] Zone was inferred. Integrating data from calcareous nannoplankton, the stratigraphic range has been limited to the time interval of 14.36-13.65 Ma (late NN5, late Langhian). The statistical agglomerative techniques applied to benthic foraminiferal distribution suggest the presence of six assemblages showing gradual transition from one to another. Their paleoenvironmental significance points to initial upward deepening of the depositional environment as a result of the Badenian transgression. This trend is interrupted by major sealevel- fall and switch to carbonate platform conditions in the middle part of the section. Subsequent sea-level-rise and increased primary production resulted in progressive reduction of oxygen content at the sea bottom in the upper part of the section. The stratigraphic position in the topmost NN5 Zone implies the correlation of the major sea-level-fall with the glacio-eustatic isotopic event Mi-3b astronomically dated to 13.82 Ma and coinciding with the base of the Serravallian.