MALICSE, ARIEL, Geology Department, Texas A&M Univ., College Station, TX

ABSTRACT: Sedimentary Processes and Facies of Desert Fluvial System: South Death Valley, California

The sedimentary processes and facies of ephemeral streams are among the least understood aspect of desert sedimentology. Few criteria exist that aid in their recognition in the rock record and in the assessment of their potential as hydrocarbon reservoirs. The ephemeral Amargosa River system that flows northward towards Badwater Basin in Death Valley, California, was investigated with the objective of providing these criteria. The study involved detailed descriptions of sedimentary facies using a combination of features observed at the surface, and in trenches and cores.

The fluvial system exhibits a succession of channel patterns and facies that can be divided into proximal, middle, and distal regions. The proximal region has steeply graded (15 m/km), straight braided channels bordered by floodplains. Its facies consist of massive to crudely bedded gravel (longitudinal bar and channel thalweg), cross-bedded coarse sand (thalweg dunes), and planar to ripple laminated fine sand (bar tops and floodplains). This region grades downdip into the low gradient (0.6 m/km) anastomosing streams of the middle region, which consists of straight channels with transverse bars and ripples, meandering channels with muddy mid-channel bars and point bars, and saline mudflats. Its facies consist of massive to cross-bedded sand (transverse bars and thalweg dunes), and wav to cross-laminated silty sand and mud (mid-channel bars, point bars, and floodplain deposits). The anastomosing system shows an overall downdip decrease in its sand to mud ratio, and eventually grade into the nearly flat (0.3 m/km) distal region, where they diverge into a few shallow straight to meandering muddy channels and widespread saline mudflats. Its facies consist of haloturbated mud (saline mudflats), and planar to ripple laminated mud with occasional lenticular sand (sheetflood flats).

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.