Pre-salt clastic systems in the Herodotus Basin, SE Mediterranean Sea

Abstract

This study is focused on the architectural characteristics of the offshore extension of a late Messinian deep-sea fan system through the analysis of a large set of multichannel seismic-reflection profiles. A 2 km thick Messinian Salinity Crisis sequence occurs on top of a clastic system, indicating that even during the maximum sea-level drop, this part of the basin was still a marine setting. The top of the clastic system is characterized by a sharp surface on which several shear surfaces within the overlying Messinian salt terminate. This is attributed to the northward gliding of the Messinian mobile salt layer from the Nile cone to the deep Herodotus basin. Mapping the base of the clastic system, it is concluded that the bathymetry on which it evolved was complex, forming valley-like structures in the southern half of the study area. The sediment source of this clastic system is interpreted to have originated from the Nile River through gravity flows during the early stages of the Messinian Salinity Crisis that resulted in thick deposits at the deepest parts of the Herodotus basin. Medium to high amplitude discontinuous reflections with multiple sudden terminations representing local (channel-like) to broader-scale erosional surfaces characterize the late Messinian clastic system. Such a seismic character, in combination with its confined nature, indicates the development of a submarine channel complex set. On the other hand, towards the north, the convex top surface of the clastic system and discontinuous internal reflections, exhibit in multiple occasions, bidirectional downlap geometries that point to the basinward evolution of the channel complex set into a lobe complex set at the most unconfined parts of the basin. This clastic system is time equivalent to the fluvio-deltaic deposits of the Abu Madi Formation of the Nile Delta region.