Early middle Miocene paleoenvironmental evolution in southwest Transylvania (Romania): Interpretation based on foraminifera

Abstract

The paleoenvironmental changes produced during the early middle Miocene have been restored based on foraminiferal assemblages collected from the Hațeg Basin in the southwestern part of Transylvania. The identified planktonics suggest a late early Badenian age (Orbulina suturalis: mid-late Langhian) and relatively warm water temperature (high percentages of Trilobatus trilobus together with Trilobatus quadrilobatus, Globigerinella regularis, and Orbulina suturalis). Composition, abundance, diversity, and distribution of the benthic assemblages indicate fluctuations in the paleoecological parameters and nutrient supply in shelf settings. Separating the assemblages based on the preferred life habitat and feeding strategies along with analysis of species distribution using univariate (Fisher Alpha, Shannon, Simpson, Pielou, Hurlbert) and multivariate statistical indices (Bray Curtis distance matrix) aided in interpreting the paleoenvironmental changes along the succession (food content, oxygenation, changes in the hydrodynamics). The results suggest a relatively shallow and well-oxygenated depositional environment with few intervals of increased nutrient supply and decreased oxygen content, warm surface waters as well as a deepening upward trend along the section.