Surface sediment samples from 32 sites in Pyramid Lake, Nevada, have been studied to investigate the sources and distribution of carbon within a large, terminal lake basin. The origins of organic and inorganic carbon in the sediments of this lake are predominantly from in-lake sources. Dilution of these sedimentary materials by land-derived elastic components occurs near the mouth of the Truckee River, the only perennial river entering the lake. Total organic carbon (TOC) concentrations and CaCO 3 concentrations and delta 18 O values increase while organic matter C/N atomic ratios and delta 13 C values decrease with increasing distance from the river mouth as the proportion of river-derived components decreases. Aragonite precipitates from lake water and dominates CaCO 3 deposition in most parts of the lake, except near underlake springs, where calcite precipitates. TOC concentrations increase as water depth increases, reflecting grain sorting as smaller particles are resuspended and focused toward the deep basin center.

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