Quantitative analysis of Upper Miocene Mediterranean reef carbonates: A tool for reconstructing palaeoenvironmental gradients

During latest Miocene times the Mediterranean Sea was linked exclusively to the Atlantic Ocean, just as it is today. This configuration could have likely resulted in a pronounced longitudinal environmental gradient, with warm and highly oligotrophic waters in the east, and cooler, less oligotrophic conditions in the west (a scenario resembling modern conditions). This setting provides a natural laboratory to test the effectiveness of quantitative microfacies analysis in tracking palaeoenvironmental gradients. Two approaches were compared: the presence/absence of carbonate producers assessed on the basis of literature data and a quantitative skeletal assemblage analysis of reef sites spanning the Western, Central, and Eastern Mediterranean. While the presence/absence approach only offers a broad environmental overview, the quantitative analysis better differentiate between the eastern and western settings. The Eastern sector displays a higher relevance of symbiont-bearing foraminifera, suggesting warmer conditions. In contrast, the western sector is comparatively richer in heterotrophic organisms, likely reflecting a higher nutrient availability and cooler water. These results support the reliability of quantitative microfacies analysis and provide a framework for comparing reef-bearing, carbonate systems across the Mediterranean within climatic homogeneous time intervals. Both approaches suggest that these carbonate factories represent subtropical, modern-like, biotic assemblages adapted to the cooler, oligotrophic, and likely semi-restricted conditions that were prevalent prior to the Messinian Salinity Crisis.