Carbonate compounds in some alluvial fans of northern Grass Valley, Nevada

Abstract

The factors influencing the pattern of occurrence of carbonate compounds in some alluvial fans of northern Nevada were investigated. Depths from the land surface to the top of the first carbonate zone were measured in the field along with the pertinent physical characteristics of each fan, including slope, relief, orientation, vegetal cover, and the megascopic petrography of the fan material. Mechanical analyses, insoluble residue studies, and some microscopic mineral identifications were made in the laboratory. The general pattern of carbonate occurrence is most affected by the amount of alkalies adsorbed onto colloidal material in the uppermost zones of the alluvium and by capillary effects which increase in importance as one approaches the valley floor. Local variations, generally restricted to one fan, are caused by variations in alkali content, small differences in the degree of sorting of the material, lateral inflow of water from the adjacent mountains, differences in microclimate due to local relief, and different ages of alluvium.