Eocene carbonate clasts in Oligocene siliciclastic sediments of the Trapani Basin (NW Sicily): depositional and stratigraphic significance

Abstract

The ‘Monte Bosco clays and quartz sandstones’, cropping out at Baglio Beatrice near Castellammare del Golfo (Sicily, southern Italy) and belonging to the Pre-Panormide domain, contain planktic and nannofossil assemblages indicating the lower Oligocene, whereas reworked larger foraminifers occurring in turbidites are upper Eocene, and limestone clasts scattered throughout the section and occurring in channelized conglomerates are lower Eocene (Cuisian) in age. The autochthonous benthic foraminiferal assemblages in the hemipelagic marly clay background sediment indicate a well-oxygenated sea floor and show a deepening-upward trend through the succession from a middle to lower bathyal zone. Turbidites are graded and the coarser fraction, at the base of the beds, is composed by scattered tests of shallow-water late Eocene foraminifers reworked into the Oligocene matrix dominated by planktic foraminifers. The latter dominate the finer fraction characterized by the occurrence of quartz grains. The analysis of six limestone clasts revealed the occurrence of four microfacies characterizing a shallow-marine moderate-energy environment, a high-energy vegetated shoal, a high-energy middle-ramp, and the outer-ramp. The investigated clasts are all of a similar age, middle Cuisian, according to the microfossils, which include alveolinids, ornatorotaliids, and Cuvillierina vallensis. The interpreted microfacies suggest a distally steepened ramp source area, although there is no outcrop of such a platform in NW Sicily. The ‘Monte Bosco clays and quartz sandstones’ were deposited along a slope periodically affected by turbidity currents and debris flows, which cannibalized cemented and unlithified Eocene shallow-water carbonate facies.