Hydrologic and climatic implications of stable isotope and minor element analyses of authigenic calcite silts and gastropod shells from a mid-Pleistocene pluvial lake, Western Desert, Egypt

Abstract

Authigenic calcite silts at Wadi Midauwara in Kharga Oasis, Egypt, indicate the prolonged presence of surface water during the Marine Isotope Stage 5e pluvial phase recognized across North Africa. Exposed over an area of ∼ 4.25 km2, these silts record the ponding of water derived from springs along the Libyan Plateau escarpment and from surface drainage. The δ18O values of these lacustrine carbonates (− 11.3‰ to − 8.0‰ PDB), are too high to reflect equilibrium precipitation with Nubian aquifer water or water of an exclusively Atlantic origin. Mg/Ca and Sr/Ca of the silts have a modest negative covariance with silt δ18O values, suggesting that the water may have experienced the shortest residence time in local aquifers when the water δ18O values were highest. Furthermore, intra-shell δ18O, Sr/Ca, and Ba/Ca analyses of the freshwater gastropodMelanoides tuberculataare consistent with a perennially fresh water source, suggesting that strong evaporative effects expected in a monsoonal climate did not occur, or that dry season spring flow was of sufficient magnitude to mute the effects of evaporation. The input of a second, isotopically heavier water source to aquifers, possibly Indian Ocean monsoonal rain, could explain the observed trends in δ18O and minor element ratios.

A humid corridor across the Sahara for the migration of early modern humans out of Africa 120,000 years ago

“…25 for a review). Palynological studies as well as dated tufas and lacustrine sediments indicate an even more significant extension of wetter conditions during the pluvial of 130-120 ka (9)(10)(11)(12)(13)(14). These inferences are consistent with the fact that the orbital insolation forcing of climate was more pronounced during MIS 5e than during the Holocene (15), and Global Climate Models confirm that the resultant northward displacement of the ITCZ (and associated ''greening'' of the Sahara) would have been more extreme during MIS 5e than during the Holocene (28).…”

“…There is widespread evidence for episodes of significantly more humid conditions over much of the Sahara itself in the past (9)(10)(11)(12)(13)(14), driven by orbital insolation-induced African monsoon maxima (15). The most recent of these so-called pluvials occurred during the early Holocene (Ϸ10-5 ka), when decorated pottery and other archives attest to a flourishing Neolithic civilization in the heart of what is now desert (16).…”

Causal links between Nile floods and eastern Mediterranean sapropel formation during the past 125 kyr confirmed by OSL and radiocarbon dating of Blue and White Nile sediments

“…8 shows phases of high Nile floods, as determined in this study, in relation to dated intervals of sapropel formation in the East Mediterranean during the last 125 kyr. Sapropel 5 (124 kyr) was synchronous with major flooding and the creation of an enormous seasonal lake in the White Nile valley (Barrows et al, 2014) and with a prolonged wet phase at~125 kyr at Kharga Oasis in the Western Desert of Egypt (Kieniewicz and Smith, 2007). The final stages of the White Nile mega-lake and its regression dated to 109 kyr, after which it never filled to such a high level.…”

Paleoenvironmental reconstruction and water balance of a mid-Pleistocene pluvial lake, Dakhleh Oasis, Egypt

“…Where available, lake sediments can act as valuable archives of paleoenvironmental information, capable of constraining some of these poorly resolved parameters. Their faunal assemblages (e.g., Churcher et al, 1999;Ghetti et al, 2002), geochemistry (e.g., Hay and Kyser, 2001;Leng and Marshall, 2004), paleohydrology (e.g., Talbot, 1990;Li and Ku, 1997;Kieniewicz and Smith, 2007), and inferred water balance (e.g., Kutzbach, 1980;Bergonzini et al, 1997;Hoelzmann et al, 2000;Jones et al, 2007) can provide centennial-to millennialscale records of surface environmental conditions and serve as ground truth for global circulation models (GCMs).…”

“…In contrast with the early to mid-Holocene, the pluvial phase coeval with marine isotope stage (MIS) 6/5e seems to have been particularly pronounced in the Western Desert; it is documented by extensive tufa deposits in Kharga and Kurkur Oases (e.g., Crombie et al, 1997;Smith et al, 2007) and lacustrine carbonates in Kharga, the Great Sand Sea, and Bir Sahara-Bir Tarfawi (Fig. 1;McKenzie, 1993;Pachur and Wuennemann, 2002;Kieniewicz and Smith, 2007). Available estimates of MIS 5e precipitation in the Western Desert from faunal evidence and GCMs are 400-500 mm/yr (Kowalski, 1993;Wendorf et al, 1993) and >2 mm/d (Prell and Kutzbach, 1987), which suggest that pluvial conditions were not as humid as those in modern equatorial Africa (Griffi ths, 1971;Nicholson, 2000).…”