Early Priabonian Mesophyllum dominated coralline algal assemblage from coastal upwelling settings (Central Carpathian Paleogene Basin, Slovakia)

The studied transgressive deposits record the imprints of the coastal upwelling affecting the distribution of the shallow-water benthic assemblage in the early Priabonian Central Carpathian Paleogene Basin (CCPB). Our inferences are based on the study of benthic and planktonic assemblages, with special emphasis on the coralline algal (CRA) system, and the facies development at the Štrba locality. We have observed the development of cool-water carbonates on warm-water carbonate platforms. Coralline algal assemblage predominated through hapalidialids, rhodalgal and bryomol grain associations; specific microborings and calcareous nannoplankton in the Štrba locality are indicative of cool-water, while nummulite banks and hermatypic corals from adjacent and distant sites within the basin are indicative of warm-water carbonates. The last mentioned are indicative of oligotrophic and euphotic settings, while nannoplankton, bryozoans and mollusks suggest mesotrophic conditions. Given the above, our results show the heterogeneous distribution of sea water temperature and nutrients that are characteristic for recent seasonal wind or eddy-driven coastal upwelling ecosystems (e.g. in the Mediterranean Sea). Upwelled cold and nutrient-enriched water enhanced the expansion of suspension feeders and favoured the growth of cool-water CRA with gametophytic phases. In the seasons without upwelling, nummulits could thrive in warm-water settings. This mechanism well explain why extensive nummulit banks were developed in adjacent sites but were not in the Štrba locality. The section is topped by bryozoan marlstone with glaucony. This lithofacies indicates the deepening of the basin. Here we were not able to discriminate between agents causing nutrification (e.g. upwelling, river plumes or gradual cooling) and the associated mesotrophication of the environment during the climatic deterioration documented across the CCPB.