Developing a Record of Quaternary Climatic Oscillation for the Eastern Sahara through Analysis of Fossil-spring Tufas and Lacustrine Deposits, Western Desert, Egypt

Washington University, Saint Louis MO

Investigators

Abstract

This grant develops a climate chronology for the Quaternary of the Eastern Sahara and to constrain the conditions of humid-phase environments in the Sahara via survey, mapping, and analysis of fossil-spring and lacustrine deposits in the currently hyperarid Western Desert of Egypt. The spring carbonates, or tufas, are datable by Uranium-series and Electron Spin Resonance techniques, and directly record times of increased precipitation in North Africa. The environmental conditions of these humid phases are reconstructed via the stable-isotope geochemistry of tufas, lacustrine carbonates, and gastropod-shell aragonite, among other proxies. Data from survey and geochemical analyses of lacustrine sediments are used to build hydrologic- and isotopic- balance models of lacustrine hydrochemical evolution. These models generate quantitative estimates of climatic variability during the lifespan of the pluvial -phase lakes. Data thus obtained is used to test the hypothesis that Saharan pluvial phases have occurred more frequently than interglacial maxima, as a response to orbital precession- and obliquity-based fluctuations in the African Monsoon. The establishment of a precise, detailed climate chronology for the Eastern Sahara allows for detailed comparison with regional climate records (Mediterranean and Atlantic cores, East African Rift Valley lake cores), which aids in piecing together climate linkages. The projected precision of the U-series dates also permits direct comparison with orbital parameters, in order to test insolation-based mechanisms for generating rainfall in North Africa, or to identify non-orbital climatic fluctuations in the region. The climatic history obtained by the research could additionally be used to test hypotheses regarding the role of the North African landmass in global carbon and methane budgets over the course of the Quaternary. The 'greening' of such a substantial area as the Sahara, as well as the formation of extensive lakes throughout the Sahara would generate significant feedbacks to the climate system. Finally, a better understanding of the frequency and intensity of North African pluvial phases would allow for a re-evaluation of the extent to which the Sahara acted as a barrier to the dispersal of modern humans out of Africa during the Quaternary Period, an important concern in human origins research. Broader impacts of the proposed work include the fostering of cooperation and collaboration with Egyptian scientists through the hosting of a short course on field techniques in Quaternary geology and geomorphology in Dakhleh Oasis. This work forms the basis of a Ph. D. for one of the PI.s female graduate students. The climate chronology is deposited with the web-based World Data Center for Paleoclimatology database, allowing widespread use. Samples collected during field work become part of a course on paleoenvironmental reconstruction.