Magnetostratigraphy and sedimentary evolution of the late Miocene to early Pleistocene sediments, Quseir region, Egyptian Red Sea

Abstract

An integrated sedimentological and magnetostratigraphic study has allowed a detailed understanding of the late Miocene to early Pleistocene evolution of the sediments in the Quseir region of the Egyptian Red Sea coast. Palaeomagnetic samples were collected from sections in six wadis, 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 characteristic remanence is typically carried by detrital magnetite and haematite, with more recent overprints predominantly associated with haematite and goethite, produced by the weathering of diagenetic pyrite. The magnetostratigraphy has allowed the following detailed age assignments 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 (≈3.5–5.5 Ma) and the Samh Member, late Tortonian to mid‐Messinian (≈6.0–7.5 Ma). The age of the top of the Abu Dabbab Formation is probably mid‐Tortonian (≈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 the timing of these disconformities. Characteristic mixed alluvial and reef facies of the Shagara formation are a response to the ephemeral wetter climate following the initiation of northern hemisphere glaciation at ≈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 early Pliocene and latest Messinian high‐sea‐level stands. The late Tortonian/early Messinian age and sedimentological character of the Samh Member indicates this unit was affected by marine flooding events, which ultimately produced, during drawdown phases, the off‐shore Zeit Formation evaporites in half‐graben depocentres.

Source-to-sink magnetic properties of NE Saharan dust in Eastern Mediterranean marine sediments: review and paleoenvironmental implications

“…Such a model has been suggested for most pedogenic environments (Torrent et al, 2006;Liu et al, 2012a), and is likely responsible for the magnetic enhancement observed in soils from the arid and semi-arid tropical belt (Balsam et al, 2011). This pedogenic pathway is supported by some paleomagnetic studies in northern Sudan and the Red Sea coast that reported maghemite and hematite formation (Bachtadse and Briden, 1991;Lean et al, 1998), but not magnetite formation, under present-day hyper-arid weathering conditions (Lean et al, 1998). Further support for this pedogenic pathway comes from the suggestion that magnetite in Eastern Mediterranean marine sediments appears to be invariably maghemitized to some extent, with the exception of paleooxidation fronts that developed above sapropels where relatively fresher biogenic magnetite formed (Passier and Dekkers, 2002) (Figure 5).…”

“…Goethite is present in a relatively low number of NES rock units (Davies et al, 1980;Bachtadse and Briden, 1991;Abdeldayem, 1996Abdeldayem, , 1999Lotfy and van der Voo, 2007;Lotfy, 2011), and has been reported to occur in some regions under present-day weathering conditions (Lean et al, 1998;Abdeldayem, 1999). The relatively minor abundance of goethite reported in Eastern Mediterranean marine sediments by Balsam et al (2007) seems to support its eolian origin, bearing in mind its less frequent occurrence also in NES source rocks and dust (Lyons et al, 2010(Lyons et al, , 2012.…”

“…Of the main magnetic minerals discussed above, it is worth noting that goethite has been interpreted to form under present-day weathering conditions in Miocene and Quaternary sedimentary rocks from the Qattara depression (Abdeldayem, 1996) and the Red Sea coast, where hematite might also be forming during weathering (Lean et al, 1998). Hematite and maghemite that formed during recent weathering have been reported from Paleozoic volcanic rocks from northern Sudan (Bachtadse and Briden, 1991).…”

“…Magnetite is ubiquitously present in a wide range of volcanic rocks ranging from Precambrian (Reischmann et al, 1992), to Paleozoic (Bachtadse and Briden, 1991), Mesozoic (Lotfy, 2011), and Cenozoic (Hussain and Aziz, 1983;Perrin et al, 2009) in age, and also in igneous, metamorphic, and sedimentary rocks that range in age from Proterozoic (Reischmann et al, 1992) to Paleozoic (Davies et al, 1980) and Mesozoic (Hussain and Aziz, 1983). Magnetite is also the dominant magnetic mineral in Paleogene (Lotfy and van der Voo, 2007), Neogene (Abdeldayem, 1996;Lean et al, 1998), and Quaternary (Lean et al, 1998) sedimentary rocks. Hematite is reported less frequently than magnetite, but still dominates the magnetic mineral assemblages in some Precambrian (Davies et al, 1980), Paleozoic (Bachtadse and Briden, 1991) and Mesozoic (Lotfy, 2011) volcanic rocks and also in sedimentary rocks that range in age from Mesozoic to Quaternary (Hussain and Aziz, 1983;Abdeldayem, 1996Abdeldayem, , 1999Lean et al, 1998;Odah, 2004;Lotfy and van der Voo, 2007;Lotfy, 2011).…”

“…Magnetite is also the dominant magnetic mineral in Paleogene (Lotfy and van der Voo, 2007), Neogene (Abdeldayem, 1996;Lean et al, 1998), and Quaternary (Lean et al, 1998) sedimentary rocks. Hematite is reported less frequently than magnetite, but still dominates the magnetic mineral assemblages in some Precambrian (Davies et al, 1980), Paleozoic (Bachtadse and Briden, 1991) and Mesozoic (Lotfy, 2011) volcanic rocks and also in sedimentary rocks that range in age from Mesozoic to Quaternary (Hussain and Aziz, 1983;Abdeldayem, 1996Abdeldayem, , 1999Lean et al, 1998;Odah, 2004;Lotfy and van der Voo, 2007;Lotfy, 2011). Some of these rocks, such as the Nubian Mesozoic sandstones (Odah, 2004) and some Paleogene and Neogene formations (Abdeldayem, 1999) also contain smaller amounts of magnetite.…”