Regional onset of Holocene drying period estimated from sand deposit analyses in Kharga Oasis, Western Desert, Egypt

Abstract

Desertification in North Africa has progressed rapidly over the past 6000 years. The occupation of Egypt by the Achaemenid Persians and Romans occurred even in hyperarid climates. Understanding the process of environmental changes on a regional scale may improve knowledge of how people developed technologies and adapted to the natural environment during a significant drying period. This study explored past environmental indicators from a sand profile at the foot slope of a Nubia sandstone ridge in Kharga, Western Desert, Egypt. The particle size distribution, free Fe oxide content, and mineralogical properties of magnetic spherical grains were analyzed alongside radiocarbon dating. Magnetic spherical grains, predominantly black with goethite as the primary mineral phase, exhibited micromorphological features resembling fungal durable structures. The presence of black-brown pigmented grains containing Mn and Fe indicated microbial activity in relatively humid environments. The ratio of Mn-type to Fe-type grain content has been proposed as a proxy for past environmental conditions preserved in sand deposits. A comprehensive analysis of the sand profile revealed an abrupt drying event around 5400 BCE, followed by a slight humid recovery around 4400 BCE in the Kharga Oasis.