Abstract

A 65-m-long core taken at the margin of Pyramid Lake, Nevada, has a well-preserved record of sedimentary features for the period 150,000 to 20,000 years before present. These features are grouped into four categories: subaerial deposits, deposits with wave-formed features, bioturbated mud, and laminated mud. The sedimentary features occur in a series of asymmetric, 1-to-3-m-thick sequences that reflect shallowing lake conditions. Sedimentary features also constitute asymmetric decimeter-scale vertical successions that also suggest shallowing lake sequences. The asymmetry is attributed to higher sedimentation rates during falling lake levels when sediment deposited during the higher lake levels was washed into the falling lake. These asymmetric cyclic sediment patterns are interrupted by subaerial features or wave-formed sand deposits that mark zones of sediment loss. δ¹⁸O and TIC values provide a measure of the hydrologic balance of the lake with heavier δ¹⁸O values reflecting closed-basin conditions. Heavy δ¹⁸O values are coincident with subaerial and sandy wave-formed sedimentary features. Light δ¹⁸O values are commonly coincident with bioturbated muds, indicating spill from Pyramid Lake into one of three adjacent lake basins. Many laminated intervals have heavy δ¹⁸O values, which may reflect coalescence of several lake basins. The combined use of sedimentary features and δ¹⁸O values allows, to a first approximation, the resolution of millennial-scale climatic changes in nonlaminated deposits.

Sedimentary features also provide information about relative lake depth, changing sedimentation rates, loss of section, and homogenization by bioturbation, all of which affect the sampling density and interpretation of other climatic proxies.