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

Abstract

Mid-Pleistocene lacustrine sediments exposed as erosional remnants in Dakhleh Oasis in the Western Desert of Egypt provide evidence for a more humid climate than that which persists today. The sediments range in facies from palustrine to fully lacustrine and generally refl ect an increase in water depth upward through the strata. Ironstone spring deposits associated with the lacustrine sediments and modern artesian discharge in the oasis indicate that Nubian aquifer water was probably an important component of the water balance, but the high carbonate content of the lake sediments requires the input of surface drainage derived from the nearby limestone-capped Libyan Plateau. Although defi nitive shorelines have not been observed, a maximum lake size of 1735 km 2 is derived from extrapolation of the elevations of the deposits onto the modern defl ated topography. Theoretical water balance modeling suggests that in addition to the discharge derived from the Nubian aquifer, ~410-860 mm/yr of rainfall would be required over the Dakhleh Oasis drainage basin in order to maintain the lake at hydrologic steady state. The persistence of climatic and hydrologic conditions amenable to maintaining a shallow freshwater lake would have allowed the region to be inhabited by a savanna fauna, as well as early human groups.

Dynamics of Green Sahara Periods and Their Role in Hominin Evolution

“…The scarcer paleoprecipitation estimates available for the Eemian GSP (122–128 kyr BP) [16], [39], [40], [71] point to markedly increased precipitation across North Africa compared to the Holocene GSP (Figure 4a, b), as is evident also from quantifications of monsoonal runoff into the eastern Mediterranean [44], [77] and from modelling data [39]. Eemian GSP paleoprecipitation points to wooded grassland occurrences (10–40% woody cover) across the Sahara, which is supported by the occurrence of tropical humid plants ( Ficus , Celtis , and ferns) and subtropical vertebrate fauna as far north as 23–26°N in the Western Desert [14], [40].…”

“…Paleohydrological modelling of the Dakhla and Chad megalakes suggests MAP values of 410–670 mm/yr [16] and ≥730 mm/yr [39], respectively. Fossil faunas from Bir Tarfawi indicate a MAP value of ≥500 mm/yr [40].…”

Evidence for Pleistocene lakes in the Tushka region, south Egypt

“…Past attempts to reconcile a Nile connection for middle Pleistocene fi sh (Van Neer, 1993) and lacustrine deposits at both Bir Tarfawi (Hill, 2009) and Dakhla Oases (Kieniewicz and Smith, 2009) have relied on a combination of precipitation and groundwater to maintain stable lakes, since estimates of 500 mm/yr precipitation (Wendorf et al, 1993) are insuffi cient to support a standing body of water. Seasonal (or more frequent) fl ooding of the Nile, particularly during pluvial conditions, may well have provided the water necessary for the megalakes proposed here.…”

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

“…In order to assess the role of these periods on the type and production of pedogenic magnetic minerals, it is necessary to recall: (1) the overall environmental conditions during GSPs; (2) the relationship between pedogenic hematite and magnetite/maghemite abundances with respect to presentday precipitation variations (Figure 2) (Lyons et al, 2010(Lyons et al, , 2012; and (3) paleoprecipitation estimates for representative GSPs. Paleoenvironmental reconstructions indicate mean annual precipitation of around 100-300 and 400-600 mm/year throughout the core of the NES during the Holocene (Kuper and Kröpelin, 2006;Larrasoaña et al, 2013) and Eemian GSPs (Kowalski et al, 1989;Kieniewicz and Smith, 2009;Larrasoaña et al, 2013), respectively. These conditions, coupled with overall warmer temperatures and the seasonal nature of monsoonal Saharan precipitation, suggest that pedogenic magnetite/maghemite and hematite production was favored compared to goethite production during most GSPs (Schwertmann and Taylor, 1989;Balsam et al, 2011;Maher, 2011;Quinton et al, 2011).…”

“…For example, short-lived (e.g., 4-8 kyr) past periods of increased monsoonal precipitation in the Sahara, called "green Sahara" periods (GSPs), led to development of lakes and permanent river systems and to the spread of savannah vegetation through the NES (Kuper and Kröpelin, 2006;Drake et al, 2011;Lézine et al, 2011;Larrasoaña et al, 2013). Paleoprecipitation estimates for the Holocene (∼6-11 ka) and Eemian (∼121-128 ka) GSPs, which can be taken as representative of late Pleistocene-Holocene GSPs, indicate mean annual precipitations of around 100-300 mm/year (Kuper and Kröpelin, 2006;Larrasoaña et al, 2013) and 400-600 mm/year (Kowalski et al, 1989;Kieniewicz and Smith, 2009;Larrasoaña et al, 2013) throughout the core of the NES, respectively. Wetter conditions may have prevailed during earlier GSPs (Drake et al, 2008;Geyh and Thiedig, 2008;Larrasoaña et al, 2013).…”