Use of multiparameter relative-age methods for age estimation and correlation of alluvial fan surfaces on a desert piedmont, eastern Mojave Desert, California

Numerical and calibrated age determinations of the late Quaternary alluvial fan deposits of the Soda Mountains piedmont in the Mojave Desert provide an opportunity to study the utility of the multiparameter relative-age (RA) method for distinguishing and mapping geomorphic surfaces on a desert piedmont. Most RA parameters could not discriminate between deposits of Holocene age, although pavements have formed over locally significant parts of surfaces as young as middle Holocene. Several parameters, including lithologic composition, particle size, soil development, and varnish cover, permit distinguishing between Holocene surfaces and late Pleistocene surfaces. Statistically significant differences in initial particle size and lithology of the deposits, inferred to be the result of complex interaction among hillslope, alluvial fan, and eolian processes and climatic change, create conditions unfavorable for use of most RA techniques. In contrast, soil-profile development and varnish cover data are successful in discrimination among deposits of Holocene and Pleistocene age. This is attributed to the development of pedogenic features and varnish that are strongly dependent on dust influx and to the relatively minor dependence of these features on differences in the depositional character of the fan.