Sources and Accumulation of Sedimentary Organic Matter in a Closed Lake System: Pyramid Lake, Nevada

Philip A. Meyers, Gabrielle E. Tenzer, and Martin E. Lebo

Pyramid Lake is a saline, terminal lake that has experienced a variety of changes in its aquatic and watershed environments since arrival of European settlers in the mid-1800s. We have examined the organic matter contents of surficial sediments from 32 lake sites and in two ²¹⁰Pb-dated sediment cores to determine their sources and delivery of organic matter. The primary influence on sediment in the southern basin is input from land-derived clastic components by the river. Concentrations of CaCO₃ and total organic carbon, mass accumulation rates of CaCO₃ and total organic carbon, and isotopic compositions of carbonate carbon and oxygen increase with increasing distance from the mouth of the Truckee River, whereas organic C/N atomic ratios and carbon isotopic compositions decrease. Organic C/N ratios, ^dgr¹³C values, and terrigenous/aquatic n-alkane ratios indicate that the proportion of land-derived organic matter in sediments has decreased as agricultural diversion of Truckee River has increased. Elevations in the proportion of land- lant wax and in organic C/N ratios in sediments deposited from 1200-1400 AD suggest that contributions of land-derived organic matter were enhanced at this time, probably because of an interval of regionally wetter climate.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California