ABSTRACT
The sediments deposited in Tule Lake, California can be described in terms of a four-component system of clastic material, CaCO3, organic matter and diatom debris. Samples of a 330-m core, representing deposition in Tule Lake during the last three million years, were analyzed for concentrations of 24 major, minor, and trace elements as well as organic carbon and carbonate carbon. Q-mode factor analysis of the geochemical data provides a geochemical zonation of the core based on four principal element associations. Association 1 is essentially a basic igneous rock association and groups those samples with relatively high concentrations of Ti, Zn, Ce, La, Al, Co, Cu, Ni, Y, Ba, Cr, Pb, and Sc. This component makes up an average of about 70% of the sediment deposited in Tule Lake, and represents the inorganic clastic fraction derived mainly from erosion of basic igneous rocks in the drainage basin, with minor additions from acidic volcanic ash derived from within and outside the drainage basin. Association 2 groups those sediments that are rich in siliceous biogenic debris and organic matter. The average organic carbon concentration in the Tule Lake sediments is 2.5%, with a maximum of 7.6%. The average concentration of biogenic SiO2, estimated from the total SiO2 content and SiO2/Al2O3 ratio, is about 25% with a maximum of about 60%. Association 3 is based on the content of CaCO3 and associated elements Mg and Sr. The maximum concentration is 42%, but the average is only 2.5%, and most of the carbonate-rich beds occur near the top of the sediment section between 50 and 130 m. Association 4 is weak, but appears to reflect variations in redox conditions within the lake as indicated by relatively high concentrations of Fe, Mn, Sc, V, and P.
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