SEDIMENTARY RECORD OF DECADAL TO CENTENNIAL CLIMATE FLUCTUATIONS IN NON-VARVED HOLOCENE LAKES IN THE WESTERN UNITED STATES

The Holocene climate record of non-varved lacustrine deposits was examined in multiple cores from deposits of Pyramid Lake, Nevada, Owens Lake, California, and Bear Lake, Utah. Holocene deposits more than 17 m thick were cored at Owens Lake near the west-central part of the now dry lake floor, at Pyramid Lake (over 6 m thick) in 100 m water depth, and at Bear Lake (over 5 m thick) in 60 m water depth. The sedimentary record of each lake contains variations in sedimentary fabric at 5- to 30-cm intervals that represent time periods of tens to hundreds of years. These sedimentary fabrics are coincident with chemical and biological indicators of changes in the lake depth in response to major changes in the hydrologic balance of precipitation and evaporation. The variations in sedimentary fabric include changes in the relative content of biological or chemical components versus mechanically derived sediment and are attributable to changes in the water chemistry or greater influence of suspended sediment washed into the lake or reworked by wave action; winnowing or mechanical transport of material by wave action, and changes in the burrowing strategy of organisms in response to available oxygen or sediment influx. Most studies of decadal to centennial climate variation in non-glacial lake deposits are conducted on varved sequences to provide strong age control and simple depositional interpretation. The constraints on preservation of varves, however, typically requires small surface area with respect to depth so that those lakes represent small drainage areas and often limited time intervals. Large lakes representing large drainage areas are commonly not varved. Within bioturbated sequences, the loss of resolution due to mixing is less severe than predicted by complete homogenization of laminated material, and suggests that most mixing predates water loss at the surface. Resuspension and erosion by wave action have a more severe impact on the resolution of the climate record.