Evolution of a carbonate delta generated by gateway-funnelling of episodic currents

Abstract

Cool-water carbonate sedimentation has dominated Mediterranean shelves since the Early Pliocene. Skeletal sand and gravel herein consist of remains of heterozoan organisms, which are susceptible to reworking due to weak early cementation in non-tropical waters. This study documents the Lower Pleistocene carbonate wedge of Favignana Island (Italy), which prograded from a 5 km wide passage between two palaeo-islands into a perpendicular, 10 to 15 km wide strait between the palaeo-islands at one side and Sicily at the other during the Emilian highstand (1·6 Ma to 1·1 Ma). The clinoformed carbonate wedge, which is 50 m thick and 6 km long, formed by east/south-east progradation of a platform on the submarine sill by currents that were funnelled between the two palaeo-islands. Platform-slope clinoforms evolved from initial aggradation (thin and low-angle) into a progradation phase (thick and high-angle). Both clinoform types are characterized by a bimodal facies stacking pattern defined by sedimentary structures created by: (i) subaqueous dunes associated with dilute subcritical currents; and (ii) upper-flow-regime bedforms associated with sediment-laden supercritical turbidity currents. Focusing of episodic currents on the platform by funnelling between the islands controlled the downstream formation of a sediment body, here named carbonate delta. The carbonate delta interfingers with subaqueous dune deposits formed in the perpendicular strait. This study uses a reconstruction of bedform dynamics to unravel the evolution of this gateway-related carbonate accumulation.