NEW EVIDENCE FOR THE TIMING OF AEOLIAN SAND SUPPLY TO THE ALGODONES DUNEFIELD AND EAST MESA AREA, SOUTHEASTERN CALIFORNIA, USA

Results are presented from a preliminary investigation undertaken to p rovide insight into the timing and causes of aeolian sand supply and d une dynamics within the East Mesa-Algodones dunefield area of southeas tern California. Samples for radiocarbon and optically stimulated lumi nescence (OSL) dating were collected from a number of sites along a we st-east transect extending from the 12 m shoreline of palaeolake Cahui lla to the central part of the Algodones dunefield. The western Algodo nes dunefield is underlain by weathered aeolian sands which yielded an OSL age of c. 31 ka, confirming earlier estimates of the timing of du nefield initiation. These deposits are largely buried by unweathered a eolian sediments which gave OSL ages of c. 3.1 ka and <0.4 ka. These a ges correspond quite closely with radiocarbon and OSL ages obtained fr om deposits within, and immediately overlying, the former lake shoreli nes, providing support for the hypothesis that the shorelines acted as an important source of aeolian sediment. Dates from within the Algodo nes suggest an average long-term eastward movement of the dunefield of c. 16.6 m ka(-1). individual transverse megadunes are indicated to ha ve moved southeastwards at an average rate of 2-5 m a(-1) over the las t 100-200 yr, an order of magnitude higher than previous estimates bas ed on process studies.