CORRELATION AND RELATIVE DATING OF FAN SURFACES IN DEATH VALLEY USING SOIL PROPERTIES

In the past correlating and dating geomorphic surfaces in arid environments has been difficult due to a lack of appropriate dating techniques or material for dating. The development of cosmogenic and optically stimulated luminescence dating methods has significantly advanced our ability to date arid geomorphic surfaces and these methods are widely applied. In a recent study of fan surfaces in Death Valley, ten depth profile ages were obtained from the Qai surface. The data indicated that the Qai surface ranges in age from 100 ka to 40 ka with an average age of 70ka. An alternative interpretation is that the Qai fan was deposited in two discrete episodes, from 90-80 ka and 60-50 Ka ( Machette et al., 2008). Soil properties have been widely used estimate relative ages of arid geomorphic surfaces so a possible test of these two scenarios could be provided by analyzing the soil properties at each cosmogenic dating site. Soil samples from each site were analyzed for typical measures of arid soil development such as CaCO3, gypsum and soluble salts and particle size. None of these parameters consistently increased with cosmogenic age, instead of their accumulation in the soil profiles was determined by dust and salt fluxes from the playa in the valley floor. Steep pedogenic gradients are common in arid environments and they can significantly impact correlation and relative dating of geomorphic surfaces.