SEDIMENTOLOGY AND AGE OF THE SNOW WATER LAKE DUNE FIELD, NORTHEASTERN NEVADA

This study investigated the sedimentology, stratigraphy, geochemistry, and age of a representative section in the dune field associated with the Snow Water Lake playa in northeastern Nevada. The playa covers an area of ~16 km² and is flanked by prominent clusters of compound dunes rising up to 12 m above the playa surface (elevation of 1705 m). GIS analysis reveals that the total dune volume above the playa elevation is 9x10⁶ m³; therefore, the dunes represent a layer of sediment ~50 cm thick deflated from the playa surface. Field reconnaissance reveals that the dunes consist primarily of grayish-brown clayey-silt with minor (5-10%) sand-sized grains of quartz and feldspar. The dunes are sparsely vegetated, and undisturbed dune surfaces are covered with a low-density crust of sun-baked clayey-silt.

An exposure along an arroyo at the eastern end of the playa provided access to the sediments comprising the dunes. The section stands ~2.5 m tall and reveals three prominent facies. A basal unit of dense silt relatively rich in sand is overlain abruptly by sticky, finer sediment. This middle unit grades upward into a loose clayey-silt with sparse sand grains that extends to the surface. An obvious carbonate-enriched horizon at a depth of ~40 cm marks the extent of soil development. Samples were collected from the basal unit (n=1) and from the uppermost unit (n=3), taking care to remain below the carbonate.

Grain size analysis with laser scattering confirms that the sediments of the middle and upper facies are fine-grained, with a mean of ~10 μm and average sand/silt/clay of 2/81/18. Clay content is greatest near the base of the upper facies. In contrast, the basal unit contains 42% sand and has a mean grain size of 172 μm. Geochemical analysis with ICP-MS indicates that the middle and upper facies are notably consistent, whereas the basal unit is more distinct. To constrain the age of these sediments, two samples, one from the basal layer and one from the upper facies, were dated with optically stimulated luminescence (OSL) using the single-aliquot regenerative (SAR) protocol. Results indicate that these sediments were deposited during the last two centuries. These ages suggest the possibility that Snow Water Lake desiccated as a result of agricultural water diversions following European settlement in the 1800s, leading to dune formation.