Facies Models and Geometries of the Ragusa Platform (SE Sicily, Italy) Near the Serravallian–Tortonian Boundary

Abstract

Detailed sequence and facies analyses of eleven stratigraphic sections, positioned on two platform to basin transects, on the Ragusa ramp (Sicily, Italy) demonstrates that two facies models must be used to describe the internal architecture of this carbonate edifice near the Serravallian/Tortonian boundary. Seven facies zones, based on the paleobathymetric position of the carbonate-producing biota, have been defined and described for each of these stages. During the late Serravallian, the inner ramp was characterized mainly by small epiphytic biota of the foramol association, whereas the middle ramp was dominated by rhodoliths and minor benthic foraminifera, bryozoans, barnacles, serpulids and echinoids. In contrast, during the early Tortonian, the inner ramp was characterized by a chlorozoan biota (Porites, Halimeda), and the middle ramp by branching Corallinacea and rhodoliths. This seemingly minor modification in the type and locus of carbonate production, and the associated changes in hydrodynamism, had profound consequences on the overall geometry of the platform which evolved from a distally steepened ramp, in the late Serravallian, to a geometry approaching that of flat-topped platform in the early Tortonian.