Differentiation of Lake Lahontan sediments in western Nevada by grain size parameters

Abstract

Textural parameters of Pleistocene sediments from the Lake Lahontan Basin were studied from outcrops in the Truckee River Canyon, Carson Valley, Rye Patch Dam, and Wadsworth areas. Two stratigraphic sections of Lake Lahontan strata, including Eetza, Wyemaha and Sehoo formations were measured and sampled near Wadsworth. Parameters calculated from the gram size data, partially based upon statistical equations established by Foik and Ward (1957), include mean diameter, standard deviation, skewness, kurtosis, and the coarsest 5 percent. These parameters, in conjunction with field observations, are used to differentiate the following depositional environments: aeolian, sub- aerial, fluviatile, beach, shallow-water nearshore, transitional shoreline to offshore, offshore, and turbidite. Where no single parameter can be used to discriminate environments, a combination of parameters could be used. Graphs of mean diameter versus coarsest 5 percent, mean diameter versus standard deviation, and mean diameter versus skewness are most indicative of environment in lacustrine settings. Kurtosis is of little value. Sorting generally is poor within water-laid sediments, and no sediment studied has better than moderate sorting.