245 Archaeological Geology (Posters)

Wednesday, 3 November 2010
8:00 AM - 6:00 PM
Hall D

STRATIGRAPHY AND ESR DATING FOR PALEOLAKE DEPOSITS ASSOCIATED WITH MIDDLE PALEOLITHIC ASSEMBLAGES IN THE SELIMA SANDSHEET, SOUTHERN EGYPT

Paper number: 245-8
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

Although presently in the hyperarid southeastern Sahara, Bir Tarfawi, Egypt, contains Middle Paleolithic and Acheulean artefact assemblages associated with lacustrine sedimentary remnants. At three localities, E-86-2, E-86-3, and E-86-4, artefact assemblages characterized by high Levallois indices, which resemble the Denticulate Mousterian, occur in strata deposited under wetter climate conditions. At these open-air sites, the stratigraphy reflects different lateral and vertical depositional facies related to changing hydrologic conditions. At all the localities, dark hydromorphic sands containing the freshwater snail Melanoides tuberculata and Middle Paleolithic artefacts gradationally overlie white sands. The dark sands interfinger with sediment containing higher carbonate concentrations (typically calcareous sands) that represent a transgressive paleolake phase. At E-86-2, this sequence underlies sands with lenses of gravel, artefacts, Melanoides, and Gazella dorcas tooth fragments.

At E-86-2, a TL date of 60 ± 15 ka for laminated sand interpreted as paleolake beach deposits hints that the upper layers in this sequence may represent deposition during Oxygen Isotope Stage (OIS) 4. At E-86-3, Melanoides tuberculata from the dark sand containing Middle Paleolithic artefacts were dated using electron spin resonance (ESR). The shells' stratigraphic context indicate that they were not likely buried by more than 10 m of sediment. Assuming a time-averaged cosmic dose rate and an early U uptake model, i.e., that the shells gained most of their U rapidly after deposition, yields a minimum possible age of 66 ± 7 ka. The linear U uptake model provides a median age of 82 ± 9 ka, while the recent U uptake model sets the maximum possible age at 98 ± 11 ka. Hence, the associated artefacts were deposited near the paleolake at E-86-2 in the early Late Pleistocene. This age suggests that the wetter climatic phases associated with the paleolake during OIS 5 or 4 may have enabled biologically modern humans to migrate into, and through, the eastern Sahara.