Paper No. 8
Presentation Time: 9:45 AM
GEOMORPHOLOGY, STRATIGRAPHY, AND GEOCHEMISTRY OF SPRING-DEPOSITED IRONSTONES AND ASSOCIATED SEDIMENTS, DAKHLEH OASIS, WESTERN DESERT, EGYPT
Spring, lacustrine and fluvial sediments in the currently hyperarid Western Desert of Egypt record pluvial, or humid, climatic phases which have occurred repeatedly throughout Quaternary time. Spring- and lacustrine-deposited carbonates found in Dakhleh Oasis likely record relatively local rainfall and groundwater recharge along the limestone-capped Libyan Plateau. Iron-rich spring sediments, however, record outflow from the Nubian Aquifer, locally represented by the iron-rich Taref Fm., which is recharged in southwestern Egypt. This interface between local water sources and fossil' groundwater has yet to be investigated, although understanding the role of each of these components to local paleolake recharge is necessary in constructing a complete picture of local climate change through the Quaternary. Towards this end, spring mounds associated with Pleistocene lacustrine sediments of the Lake Balat and Lake Kellis Fms. (following Kleindienst et al. 2004) were mapped using differential GPS, their stratigraphy measured, and their sediments sampled for geochemical analysis. The spring mounds generally consist of small, isolated hills of Cretaceous-age Mut Fm. shales capped by iron-rich silts, sands and iron precipitate, often preserving vegetation casts. These sediments appear to be consistent with deposition at spring vents and at localized iron-rich paludal environments. Latitudinal variations in erosional spring mound morphology and a northward-dipping paleo- landsurface also suggest some structural control over the formation of the springs, as the underlying Taref Fm. forms northward-plunging gentle folds. Understanding the geochemistry of the spring deposits will allow for the characterization of groundwater chemistry and discharge processes during the early stages of the mid-Pleistocene pluvial phase. These data will aid in the paleoecological reconstruction of a landscape that archaeological evidence suggests was utilized by early Acheulian tool-makers as well as later human groups.