DMP VIII. Palaeohydrology and palaeoenvironment.

Ahmed S El-Hawat

The January 2009 fieldwork season conducted geomorphological and palaeoenviromental surveys in as yet unexplored parts of the Lake Megafazzan Basin, as well as continuing research in the Wadi al-Hayat and Ubari Sand Sea. Lake Megafazzan sediments were investigated at two sites on the eastern margin of the basin. At the first site, east of Tamessah, 24 m of stratigraphy was investigated and found to consist of a lacustrine carbonate unit at the base progressing into a fluvial unit and then an upper carbonate unit. The sediments were sampled for magnetostratigraphy and cosmogenic nucleide dating in order to determine their age. Similar studies were undertaken in the vicinity of the Arial Agricultural Project, where 31 m of section were logged and sampled. Here the sediments were quite different, being composed of a deltaic sequence consisting of stacked channels and palaeosols, thought to represent the outflow delta of the palaeolake. Many new Holocene lake sediment deposits were discovered and sampled in the Wadi al-Hayat and the Ubari Sand Sea, including a 5 m section through Jarma Playa that appears to record the last arid-humid cycle. Lake Gabr 'Awn and the moat round Old Jarma were cored in order to gather a detailed picture of recent palaeoenvironmental change. Finally, we implemented a pilot geophysical survey to test the ability of state-of-the-art Ground Penetrating Radar (UltraGPR) technology for detecting and mapping buried palaeolake sediments under the dunes of the Ubari Sand Sea. The UltraGPR was found to be very effective, detecting palaeolake sediments as much as 60 m beneath the surface. Preliminary results suggest such sediments underlie much of the region.