Petrology of Late Precambrian-Cambrian Quartzose Sandstones in the Eastern Mojave Desert, Southeastern California
ABSTRACT Petrographic and radiographic analyses were conducted on oriented samples of Late Precambrian-Cambrian quartzose sandstones collected from five cratonal and five miogeoclinal stratigraphic sections in the eastern Mojave Desert, southeastern California. Twelve petrographic variables were measured in each of 494 samples. Cratonal sandstones are dominantly subarkose, whereas miogeoclinal sandstones are subarkose and quartzarenite in almost equal proportions. Sediments were derived chiefly from granitic rocks, gneiss, and schist as well as older sedimentary and metasedimentary rocks. The cratonal source areas were to the east and southeast. Samples collected from six northern sections within the Cordilleran frontal thrust belt have a higher content of undulatory quartz and silica cement and are partially recrystallized when compared with samples from four southern sections. Polynomial time-trend analysis showed considerable variation in mineral composition with thickness at each stratigraphic section. Areal variation of total quartz was estimated from analysis of variance models. The difference was not highly significant for the Stirling Quartzite. Depositional history was inferred for each formation on the basis of petrography, clasticity and sedimentary structures. The Johnnie Formation fines upward, which suggests a marine transgression or change from open to partially restricted shelf environments. The Stirling Quartzite coarsens upward and consists largely of prograding mature shelf sands or deposits of migrating bars and barrier beaches. The Wood Canyon Formation is dominantly subtidal with local evidence for intertidal deposition.