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 provide insight into the timing and causes of aeolian sand supply and dune dynamics within the East Mesa-Algodones dunefield area of southeastern California. Samples for radiocarbon and optically stimulated luminescence (OSL) dating were collected from a number of sites along a west-east transect extending from the 12 m shoreline of palaeolake Cahuilla to the central part of the Algodones dunefield. The western Algodones dunefield is underlain by weathered aeolian sands which yielded an OSL age of c. 31 ka, confirming earlier estimates of the timing of dunefield initiation. These deposits are largely buried by unweathered aeolian sediments which gave OSL ages of c. 3.1 ka and <0.4 ka. These ages correspond quite closely with radiocarbon and OSL ages obtained from deposits within, and immediately overlying, the former lake shorelines, providing support for the hypothesis that the shorelines acted as an important source of aeolian sediment. Dates from within the Algodones suggest an average long-term eastward movement of the dunefield of c. 16.6 m ka−1. Individual transverse megadunes are indicated to have moved southeastwards at an average rate of 2–5 m a−1 over the last 100–200 yr, an order of magnitude higher than previous estimates based on process studies.