MAGNETOSTRATIGRAPHY AND SEDIMENTARY EVOLUTION OF THE LATE MIOCENE TO EARLY PLEISTOCENE SEDIMENTS, QUSEIR REGION, EGYPTIAN RED-SEA

An integrated sedimentological and magnetostratigraphic study has allo wed a detailed understanding of the late Miocene to early Pleistocene evolution of the sediments in the Quseir region of the Egyptian Red Se a coast. Palaeomagnetic samples were collected from sections in six wa dis, covering the Shagara Formation, the Gabir and Samh members of the Wardan Formation, and the Abu Dabbab Formation evaporites. Remanence properties are carried by magnetite, haematite and goethite. The chara cteristic remanence is typically carried by detrital magnetite and hae matite, with more recent overprints predominantly associated with haem atite and goethite, produced by the weathering of diagenetic pyrite. T he magnetostratigraphy has allowed the following detailed age assignme nts for the lithostratigraphic units. The Shagara Formation ranges in age from late Pliocene (late Piacenzian) to middle Pleistocene (0.6-2. 5 Ma). The Gabir Member is latest Messinian to earliest Piacenzian in age (approximate to 3.5-5.5 Ma) and the Samh Member, late Tortonian to mid-Messinian (approximate to 6.0-7.5 Ma). The age of the top of the Abu Dabbab Formation is probably mid-Tortonian (approximate to 8 Ma). Disconformities occur between all the lithostratigraphic units, with a local angular unconformity between the Shagara and Wardan Formations. Lowstands in global sea level appear to have a strong influence on th e timing of these disconformities. Characteristic mixed alluvial and r eef facies of the Shagara formation are a response to the ephemeral we tter climate following the initiation of northern hemisphere glaciatio n at approximate to 2.4 Ma, enhanced by rift-margin uplift of basement complexes to the west. This tectonic activity was concentrated in the early Piacenzian. The marine Gabir Member was deposited during the ea rly Pliocene and latest Messinian high-sea-level stands. The late Tort onian/early Messinian age and sedimentological character of the Samh M ember indicates this unit was affected by marine flooding events, whic h ultimately produced, during drawdown phases, the off-shore Zeit Form ation evaporites in half-graben depocentres.