GARVEY, TIMOTHY P., Groundwater Technology Inc., Ventura, CA, GEORGE C. DUNNE, and A. EUGENE FRITSCHE, Department of Geological Sciences, California State University, Northridge, CA

ABSTRACT: Depositional Environments and Paleogeographic Significance of Mesozoic Volcanic and Volcaniclastic Strata in the Southern Inyo Mountains, East-Central California

Exposed on the west flank of the southern Inyo Mountains in east-central California is a 3200-m-thick (10,500-ft-thick) section of Triassic(?) and Jurassic (pre-148 Ma) volcanic and volcaniclastic rocks. The section is divided into three stratigraphic intervals on the basis of the lithosomes predominant in each of the intervals.

The lowest of the three stratigraphic intervals contains thick-bedded, clast- and matrix-supported volcanic- and limestone-containing conglomerate, mafic and intermediate volcanic flow rocks, and minor sandstone, siltstone, and fine-grained pyroclastic tuff. Rocks in the lower stratigraphic interval were deposited on two separate coalescing alluvial fans that evolved alongside one or more active volcanoes.

The middle stratigraphic interval consists of laterally continuous intermediate and felsic volcanic flow rocks, intermediate to felsic pyroclastic tuff, and local interbeds of volcanic breccia, conglomerate, and sandstone. Rocks in the middle interval were deposited in a low-relief, distal alluvial fan/"volcanic apron" environment.

The upper stratigraphic interval contains bedded, clast-supported conglomerate and cross-bedded sandstone that were deposited in poorly confined, shallow braided channels on a fluvial plain. The upper interval also contains siltstone with mudcracks as well as shale that represents deposition in overbank, and perhaps lacustrine, environments.

These three stratigraphic intervals are significant because they represent the oldest preserved depositional environments that existed during the onset and evolution of uplift, volcanism, and epiclastic sedimentation on the eastern (landward) side of the Sierran continental-margin arc that extended along western North America during much of the Mesozoic and Cenozoic.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.