T54 From Desert to Delta: Geologic Research and Applications in Egypt in the First Decade of the 21st Century (Posters)

Sunday, 27 October 2013
9:00 AM - 6:30 PM
Hall D

RECONSTRUCTING PALEOENVIRONMENTS IN THE WESTERN DESERT, EGYPT: ESR DATING FRESHWATER MOLLUSCS FROM KHARGA OASIS

Paper number: T54-17
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Kharga Oasis, in Egypt's hyperarid Western Desert, receives ~ 0.7 mm/y precipitation, but suffers > 2 m/y of evaporation, ensuring that it now lacks naturally occurring standing water. Large tufa deposits ranging from a few hectares to > 10 km2 in area, such as at Midauwara, Matana, and Bulaq, dot the edge of the Libyan Plateau. Paleolithic artefacts occur associated with lacustrine deposits in the tufa mounds. Freshwater molluscs in intercallated tufas and lacustrine silts indicate that sufficient potable water existed to support hominins, a diverse fauna, and locally lush vegetation at times in the Pleistocene. Along with Pleistocene fossils, archaeological finds have included artefacts from Earlier Stone Age, Middle Stone Age, including the Aterian, Later Stone Age, and younger cultural materials lying in gravel lags, within sedimentary deposits, and on the older geomorphic surfaces. At Wadi el Midauwara, a tufa mound complex covering ~ 25 km2 has grown during at least four different pluvial events. Tufa dammed small ponds and lakes from 1-5 m2 to 1.5 km2in area that trapped calcareous lacustrine silt. At Matana and Bulaq, smaller tufa mounds also house hominid artefacts and freshwater snails. Dating these lacustrine sediment deposits pinpoints the pluvial events that enabled hominin habitation in, and migration through, the eastern Sahara.

Electron spin resonance (ESR) can date aragonitic molluscs ranging from ~ 5 ka to > 2 Ma. From Midauwara, > 50 Melanoides tuberculata and Gyraulus samples were dated with standard ESR using time-averaged sediment and cosmic dose rates. In some units, multiple gastropod populations from different times were preserved as a temporally mixed deposit, while several other sites appear to only preserve a single population. Snail dates suggest that fresh water existed sporadically at Bulaq and Matana during Marine (Oxygen) Isotope Stages (MIS) 2 and 4. At Midauwara, however, standing freshwater existed during the MIS 7/6 and 6/5e boundaries, and repeatedly in MIS 5-2. Thus, the times for the standing freshwater correlate best with times that, globally, were neither fully interglacial nor fully glacial. During the earliest Pleistocene, at ~ 2.4 ± 0.4 Ma, molluscs and freshwater also existed at Midauwara, which may have enabled the first hominin migration out of Africa via the Western Desert.