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