Seismic stratigraphy and sedimentary facies analysis of the pre- and syn- Messinian Salinity Crisis sequences, onshore Nile Delta, Egypt.

Relatore: Prof. Andrea Moscariello (Universita' di Ginevra)

Data e luogo: Il seminario si svolgera' giovedi 6 settembre 2018 alle ore 14.30 in aula Ruffini.

Riassunto: 

This study provides the first sedimentological and biostratigraphic evidence integrated with seismic stratigraphy in support of the high-resolution definition of the Messinian sequence outline in the onshore Nile Delta. The distribution, pattern and architecture of the Messinian facies deposited before, during and after the Messinian salinity crisis (MSC) have been investigated. The pre-MSC Qawasim Formation is represented by parallel oblique seismic reflectors which display an overall lobate-shaped geometry interpreted as northward prograding deltaic facies. The vertical upward and lateral northward increase in seismic amplitude is consistent with the coarsening and shallowing upward sedimentary facies. The pre-MSC facies typically comprises the sediments of prograding coarse-grained braid delta system that pass from prodelta, distal sand bars into subaqueous proximal delta-front distributary channels and mouthbars and subaerial delta-plain distributary channels.

The MSC Abu Madi Eonile canyon-infill facies consists of three un its: a seismically chaotic lower-infill unit followed by continuous, vertically variable amplitude reflectors of the middle- infill unit and capped by the upper-infill unit of dominantly low-amplitude reflectors. The lower unit corresponds to the subaerial gravity-flow facies formed concurrently with the incision by subaerial landslides, debris avalanches and collapse of the unstable canyon-walls. The middle-infill unit is dominated by fluvial facies and comprises a lower aggradational phase of single-story channel -fill facies followed by prograditional coarsening upward fluvial channel- belt complexes. The upper infill-unit consists of retrogradational estuarine facies and encompasses a fining upward sequence passes from tidally and marine-influenced fluvial channel to tidal sand bars and restricted tidal flat facies.