Neogene stratigraphic evolution of a tectonically controlled continental shelf: the example of the Lampedusa island

Abstract

Lampedusa Island represents a key-area due to its central position within the Sicily Channel and the whole Mediterranean region. The acquisition and interpretation of sixteen “sparker-system” seismic lines allowed a refined reconstruction of the sedimentary architecture of the Lampedusa continental shelf and the detailed timing of its tectonic evolution, providing a contribution to the geodynamic processes affecting this sector of the Sicily Channel.The offshore profiles show five seismic facies, which have been compared with the onshore succession. The older seismic unit (S1) was correlated with the pre-rift Cala Pisana Mb. of the Lampedusa Fm., separated by the overlain Capo Grecale Mb. (=S2) by an erosional surface, identified with the offshore TU (=Tortonian Unconformity) horizon, passing upward to the Vallone della Forbice Mb. (=S3) through a gradual, concordant boundary (Upper Tortonian Boundary=UTB). Capo Grecale and Vallone della Forbice Mbs., and thus the S2 and S3 units, represent the syn-rift deposits, recording the Late Miocene extensional tectonic activity. The effects of the strong erosional phase connected with the Mediterranean Salinity Crisis of Messinian age, are visible in all the seismic lines coinciding with a high impedance irregular surface (MH=Messinian Horizon), above which a further seismic unit (S4) develops. This latter, constituted by reflections onlapping the substratum, in the lower part, and prograding in the upper one, does not find an onshore correspondence, but has been attributed to the post-Messinian (Zanclean) transgression, followed by the subsequent regressive phase (Piacenzian-Gelasian). The uppermost seismic unit (S5), unconformably covering the older substratum, through the Early Pleistocene Unconformity (=EPU horizon) corresponds to the Pleistocene-Holocene onshore deposits. The seabed (top of S5) shows regular morphologies in the southern sector, while in the northern sector it is cut by erosive channels connected to strong streams on the bottom.From a structural point of view, the southern sector recorded an extensional tectonic phase, giving rise to normal faults involving units from S1 to S3, sutured by the MH and the overlain deposits. In the northern sector, the tectonic phase continued until the Pliocene, also involving the S4 unit.The reconstructed tectonic setting well fits the more general setting of the Sicily Channel Rift Zone, where main WNW-ESE faults were active during the Late Miocene and until the Pliocene age, generating small depositional areas, bounded by second-order NNW- SSE normal faults.