Preliminary Analysis of Color Variations of Sand Deposits in the Western Desert of Egypt

Astronaut observations and photographs of color variations in the Western Desert of Egypt are related to both iron oxide coalings on individual grains and the presence of locally derived material in the sand deposits. The results of four field trips, to Baharîya Oasis, Sîwa Oasis, Khârga and Dakhla Oases, and the Great Sand Sea, enable more detailed interpretations of colors photographed during the Apollo-Soyuz mission. The northern region of the Western Desert has the highest percentage of calcareous grains originating from local limestone outcrops. Samples from the central part of the Western Desert contain numerous iron-rich grains originating from the iron deposits of Baharîya and are locally enriched in shale fragments from the Dakhla Shale. Sands of the Great Sand Sea are relatively homogeneous, quartz-rich deposits that vary little in percentage of minor components. Although these results are preliminary, they indicate the need for more detailed field investigations of the causes of color variations; such investigations are currently underway. INTRODUCTION ably from place to place (ref. 1), Both mappingand handheld-camera photographs obtained on the same mission confirmed that these color variations abound on both regional and local scales. It was also shown that these color variations probably reflect compositional variations of the exposed surfaces (ref. 2). For these reasons, an investigation was planned to document the causes of color variations in sand deposits, which are an important component of desert surfaces. The Western Desert of Egypt was selected for this study because (1) this desert was used as a test site for the investigation of variations in color as seen in ASTP photographs and (2) a team of Egyptian geologists served as team members of the ASTP Earth Observations and Photography Experiment and were able to plan and participate in the collection of field data. This report must be considered as preliminary. The number of samples reported on here is only a fraction of the samples collected. Additional information is being gathered and analyzed by the research team members at Ain Shams University, Cairo, Egypt. This research is continuing under the auspices of a joint research project between Ain Shams University and the Smithsonian Institution, Visual observations made by the astronauts of the Apollo-Soyuz Test Project (ASTP) indicated that the colors of desert surfaces varied consider^National Air and Space Museum, Smithsonian