2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 6
Presentation Time: 9:30 AM

Accretionary Pavement Development and Landscape Stability on the Eastern Libyan Plateau, Egypt

ADELSBERGER, Katherine A., Environmental Studies, Knox College, 2 East South St, Galesburg, IL 61401 and SMITH, Jennifer R., Earth & Planetary Sciences, Washington University, 1 Brookings Dr, Campus Box 1169, St Louis, MO 63130, kadelsbe@knox.edu

The Quaternary sedimentary record of the eastern Libyan Plateau, in central Egypt, consists primarily of shallow soils and desert pavement surfaces. Desert soil profiles expose a clast-free silty layer beneath a surface layer of gravel, indicating accretionary pavement development in this region. Measurements of surface clasts reveal variable clast size, density, lithology and orientation among pavement samples, but no spatial relationship has been identified among any of these variables across the study area. Measured pavement characteristics are also unrelated to expected geomorphic controls such as slope gradient. Slopes have no identifiable effect on clast sorting or orientation, indicating minimal to no gravity-driven transport through processes such as overland flow or creep. The presence of meridional cracks in surface clasts indicates the breakdown of clasts at the surface through mechanical weathering; cracks were likely caused by thermal stresses related to diurnal solar variations. The combination of an accretionary pavement surface, a lack of lateral transport of surface clasts, and the in situ mechanical breakdown of clasts at the surface suggests that desert pavements in this region also formed in situ on a laterally stable landscape. The long-term stability of this desert surface makes it an excellent recovery zone for Paleolithic artifacts, which have likely been undisturbed since they were deposited ca. 100 kya and potentially earlier. Taphonomic effects on larger (>2 cm) artifacts are minimal at best, whereas vertical movements of smaller clasts may have been more likely than lateral transport of archaeological materials. Understanding the small-scale formational processes of this desert pavement informs landscape development in the region while providing a taphonomic history for Paleolithic materials recovered at the surface.