Pleistocene evolution of the eastern Salento continental shelf: Tectonic and/or eustatic controls

Abstract

Sequence stratigraphic interpretation of about 183 nautical miles of single-channel reflection seismic profiles (Sparker 1 kJ) allows us to investigate the Pleistocene stratigraphic record of the continental shelf offshore the eastern Salento area (Apulia, Southern Italy); stratal patterns and depositional sequences in the Middle-Late Pleistocene succession are described. The acoustic substratum consists of Paleocene-Oli-gocene limestones ("Calcari di Castro), cropping out in the coastal cliffs of the Salento region. Three main unconformities (RS1, RS2 and RS3), identified in the whole investigated area, outline the stratigraphic evolution of the eastern Salento continental shelf, which is characterized by Late Pleistocene-Holocene alternating progradational and retrogradationai units, on a wide Middle Pleistocene progra-ding wedge. The above unconformities have been interpreted as erosional surfaces related to the landward shift of the shoreline (ravinement surfaces) during sea level rises. A number of patch-reef shaped algal buildups, recognized by seismic interpretation and sampled by dredging offshore S. Maria di Leuca overlie the youngest erosional surface (RS3, starting from 18 ka). Patch-reef shaped features have been recognized on seismic profiles even at lower stratigraphic levels, namely on RS2 and RS1, thus suggesting similar environmental conditions for the formation of patch reefs and confirming the genetic meaning of the RS. Seismic interpretation and correlation with mainland geology suggest that different factors have controlled the stratigraphic evolution of the Salento continental shelf during the Pleistocene. Tectonic control, relative to the uplift of the Apulian foreland, prevailed in the Middle Pleistocene, producing a wide forced regression prograding wedge which enlarged the shelf of several kilometers. Eustatic sea level changes controlled the stratigraphic evolution during the Late Pleistocene-Holocene, creating 4th order incomplete depositional sequences. Eustatic signal overwhelming the tectonic one may indicate a decrease in the rate of uplift of the Apulian foreland for the last 250 ky.