MID-HOLOCENE DEBRIS-FLOW AND LAKE STAND EVENTS AT SILURIAN LAKE, MOJAVE DESERT, CALIFORNIA

Landscape changes associated with Holocene climate variability are chronicled in few places in the Mojave Desert. We describe evidence for paired debris-flow fan building and a short-lived lake stand in the northern Silurian Valley that provides evidence for a ~6.5 ka wet period.

Silurian Lake is a gently north-sloping playa in the Salt Creek drainage between Silver Lake, the terminal basin of the Mojave River, and Death Valley. Because Silurian Lake is a wide low-gradient part of Salt Creek, it should not have experienced sustained deep standing water. However, beveled gravel platforms around the playa and two bars composed of thinly bedded gravel and sand attest to the presence of a lake. The platforms and bars possess a weak pavement and underlying sandy A_v horizon, as do mid- to early-Holocene alluvial fan surfaces in the vicinity. Downstream 1.6 km from Silurian Lake, tributary Kingston Wash drains into Salt Creek through a channel cut into a debris-flow fan covering about 50 km³. The debris flow was emplaced as a single event, and exhibits soil development similar to other Holocene fans.

Infrared stimulated luminescence (IRSL) ages on fine-grained (4-11 µ) feldspars in the wash sediments immediately under the debris-flow fan, in a Silurian Lake bar, and in other fan deposits are all about 6.5 ± 0.5 ka. Coarse grained feldspars (90-125 µ) from these same deposits, also dated with IRSL, give an average age of 6.3 ± 0.4 ka. The apparent coincidence of ages in fans, bars, and debris flows indicates that Silurian Lake may have experienced a brief lake stand when Kingston Wash and other fans built into Salt Creek, clogging the drainage downstream from the playa for a period of years to a few decades. These related geomorphic events may indicate a wet period that was of local or regional extent.