Paper No. 18-14
Presentation Time: 4:50 PM
A GRAIN SIZE TRANSECT OF BADWATER BASIN, DEATH VALLEY, CA
Death Valley, CA is a well-known closed basin with a xeric environment. The Death Valley Fault Zone is a right lateral-moving fault in California. It runs from a connection with the Furnace Creek Fault Zone south to a junction with the Garlock Fault. Materials eroded from the bounding mountain chains are focused in the center of the basin. These sediments are transported by gravity, wind, and water with sporadic times of alluviation. On occasion, portions of the valley floor flood dissolving evaporite minerals which are later concentrated by evaporation. Other than these and rare episodes, the floor of Death Valley is covered in sediment and in some locations desiccation polygons. Analysis of the stratigraphy in Death Valley provides a wealth of information on paleoclimate in the region and shows both arid and wet conditions through time. Here, we characterize the modern grain size distributions of clastic materials at 10 sites using 40 samples within the Badwater Basin. The data set forms an east west transect across the center portion of the valley floor. Since evaporite minerals are abundant but their grain size results from crystallization conditions, we focus on the grain size of clastic minerals in the basin. We measured grain size of the clastic fraction after precipitates and organic matter was removed using a pretreatment procedure. Samples were disaggregated with sonication and a hexametaphosphate solution and grain size was measured using a Coulter LS 13 320. We focus on the grains sizes contained within desiccation polygons but also present additional samples for context. We examine multiple samples from different locations within individual desiccation polygons, from the edges and centers and compare these with samples along an 8-kilometer transect. The most abundant grain size range was between 0.4 to 150µm. The grain size distributions from multiple samples taken at each of the 10 sites were mostly consistent, suggesting that the grain sizes detected are representative of a given site location. In the transect, the average grain size across the playa is finest in the middle furthest from the alluvial fans. This research provides a snapshot of the grain sizes, environment, and spatial distribution of grain sizes on the modern playa floor which may help future interpretation of sedimentary records in the basin.