Timing and intensity of groundwater movement during Egyptian Sahara pluvial periods by U-series analysis of secondary U in ores and carbonates

Abstract

Wet climatic episodes are known to have prevailed in the Egyptian Sahara several times during the late Quaternary, most recently during the Holocene 8000 yr ago. Earlier wet episodes have been recognized as having occurred during the past 300,000 yr and have been dated by U-series methods in speleothems and in lake travertines. We show here that the times of enhanced groundwater movement can also be determined by 230Th/234U dating of secondary U in ores of uranium, iron, and phosphate. We also present evidence that such acceleration of groundwater movements is indicated by relatively low 234U/238U activity ratios in the secondary uranium. Our new data show that pluvial periods in Egypt occurred during marine oxygen isotope stages 4, 5, 6, and 7 and therefore are consistent with the view that the wet episodes are the results of migration of the tropical monsoonal belt driven primarily by the 23,000-yr precession cycle of the Milankovich curve, modulated by the 100,000-yr eccentricity cycle.

Micromorphological approach to polycyclic pedogenesis on the Messak Settafet plateau (central Sahara): Formative processes and palaeoenvironmental significance

“…Finally, considering our data in the context of Quaternary climate changes we notice that palaeopedological indicators point to confirm the time correspondence between interglacial conditions at temperate midlatitudes and pluvial episodes in subtropical arid regions (Crombie et al, 1997;Burns et al, 2001;Osmond and Dabous, 2004). Notwithstanding that, the modern Sahara seems to show an anomalous behaviour (Cremaschi and Zerboni, in press): the dismantling of the mid-latitude glaciers could be considered typical of an interglacial, but the modern expansion of the desert may correspond to environmental conditions more consistent for a glacial phase.…”

Middle Palaeolithic find spots with Nubian cores from the Southern Negev and the Arava, Israel

“…Past climatic records indicate that during glacial and interglacial periods between MIS 6 and MIS 4 the central Negev was mostly dry (Amit et al 2006;Vaks et al 2007), whereas short humid episodes (Negev Humid Periods, (2017) NHP), possibly resulting from a northern shift of the African Monsson system, occurred during interglacial times (Blome et al 2012;Kutzbach & Liu 1997;Larrasoaña et al 2013;Torfstein et al 2015;Vaks et al 2010). The last of the NHP (NHP-1) is dated to 142-109 ka and was synchronous with pluvial periods in the Sahara, the Egyptian Desert and the Arabian Peninsula (Osborne et al 2008;Osmond & Dabous 2004;Petit-Maire et al 2010;Rosenberg et al 2011;Yehudai et al 2017;Vaks et al 2006;. Terrestrial corridors between the Negev and Arabia, along which there were sufficient water sources, have been suggested to exist during MIS5 (Breeze et al 2016).…”

Palaeoclimate in the Saharan and Arabian Deserts during the Middle Palaeolithic and the potential for hominin dispersals

“…The 76e68 ka humid period is predominantly indicated by 19 dates that show a spatial distribution ranging from the eastern to the central and north-west Sahara (Fig. 4B), but are concentrated in the east, with speleothems from Wadi Sannar Cave and Djara Cave in Egypt (Osmond and Dabous, 2004), tufa from Kharga Oasis (Osmond and Dabous, 2004) and Kurkur Oasis, Egypt (Crombie et al, 1997), travertine from Oued Noun in Morocco (Weisrock et al, 2008), lacustrine sediments from the Western Desert of Egypt and Sudan at Bir Sahara East and Bir Tarfawi (Wendorf et al, 1993), the Selima Sandsheet, Wadi Hussein and Wadi Arid (Szabo et al, 1995) and Algeria at Kadda (Causse et al, 1988) as well as and fluvial sediments from Wadi Zewana in Libya (Rowan et al, 2000).…”