Anomalinoides dividens bioevent at the Badenian/Sarmatioan boundary – a response to paleogeographic and paleoenvironmental chnages

Abstract

Recent investigations on the microfauna at the Badenian / Sarmatian boundary (Middle Miocene) showed interesting characters of the Anomalinoides dividens foraminifera assemblages. Several taxonomic aspects are considered in order to clarify the meaning of different stratigraphic approaches. A possible planktonic or pseudo-planktonic life of the species is suggested by micropaleontologic, paleogeographic and paleoenvironmental data. INTRODUCTION Anomalinoides dividens a foraminifer species described by Łuczkowska (1967) is considered as an index taxon for the regional biostratigraphy of the Paratethyan area. Its acme characterizes the base of the Sarmatian; therefore the Anomalinoides dividens Biozone was introduced in order to trace the boundary between Badenian and Sarmatian deposits. Recent sedimentologic and micropaleontologic investigations showed new possibilities to interpret the paleoenvironmental conditions around the Badenian / Sarmatian boundary. MATERIAL AND METHODS Most of the studied specimens of Anomalinoides dividens come from the micropaleontological collection of Romgaz S.A. Mediaş, now in the custody of the Department of Geology of Babeş-Bolyai University. The specimens were collected from exploration wells drilled during the last decades in the Transylvanian Basin. Individual specimens were studied by using the JEOL JSM 5510LV scanning electron microscope in the Department of Biology, Babeş-Bolyai University. The micropaleontological record was correlated with sedimentological data gathered from cores, well logs and seismic profiles (Krézsek & Filipescu, in press).