MULTI-PROXY RECONSTRUCTION OF POST-GLACIAL ENVIRONMENTAL CHANGE FROM A CORE OF SOLDIER LAKE, NEVADA

We analyzed a core retrieved from Soldier Lake, a tarn at 2775 m asl in the Ruby Mountains of northeastern Nevada, to reconstruct a record of post-glacial Holocene environmental change. The core penetrated to a depth of 415 cm below the sediment-water interface. Two AMS radiocarbon analyses, one on terrestrial plant material and another on charcoal, indicate that the core extends to at least 9600 cal ka BP. A layer of tephra encountered at a depth of 190 cm was correlated with the Mt. Mazama eruption by geochemical fingerprinting. Multi-proxy laboratory analysis of the core included measurements of magnetic susceptibility (MS), water content, loss on ignition (LOI), grain size distribution (GS), carbon to nitrogen ratio (C/N), and biogenic silica content (bSi). MS values are close to zero in the upper part of the core, rise slightly in the tephra layer (20 x 10^-5 SI units), and increase substantially in the bottom quarter of the core (70 x 10^-5 SI units), reflecting higher levels of inwashing of iron-bearing minerals. Water content values are in excess of 80% near the surface, drop substantially (from 65 to 20%) in a 70-cm interval (from ~216 to 286 cm depth), and increase gradually in the basal sediments (rising back to ~30%). LOI values mimic this trend with values above 30% in the surface sediment, and generally below 10% in the basal sediments. Mean grain size exhibits cyclic variability throughout the record, with values oscillating between 7 and 70 μm. The organic-inorganic transition occurs at a depth of 240 cm, corresponding to an age older than 9600 cal ka BP. Additional radiocarbon dating of pollen concentrates will permit construction of a depth-age model, and analysis of C/N and bSi content will support development of an environmental history that will be compared with other post-glacial lacustrine records from the region.