Abstract

Study of the Soda Mountains in the northeastern Mojave Desert revealed new stratigraphic and structural features of this area. A section of Cambrian to Jurassic rocks in the area displays various features of regional importance. Lower Permian rocks have depositional characteristics indicative of mass-flow deposition, contrasting with underlying shelf strata and platformal rocks exposed in areas to the east. These rocks are similar to deep-water rocks exposed to the north in eastern California. Lower Triassic rocks are named the "Silver Lake Formation" and consist of shallow-water siltstone and carbonate that contain conglomerate with volcanic and gneissic ciasts. These latter rocks record the possible presence of Permian-Triassic igneous and deformational activity in the area.

A complicated deformational history is also evident from this study. We interpret several west-dipping, low-angle faults active during intrusion of middle Cretaceous granitoids to be normal faults rather than thrust faults, as they were originally considered. Structures in the Soda Mountains probably correlate with similar ones in surrounding areas. Collectively, the local structures imply a complicated stress regime during emplacement of the middle Cretaceous plutonic rocks. These new data imply that large thrusts faults placing Paleozoic rocks over Mesozoic rocks are not present in this area. Upper Paleozoic and lower Mesozoic rocks also tie this area to the western Mojave Desert, indicating that strike-slip faults with several hundred kilometers of displacement do not separate the two areas.

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