Geochemical analysis of organic matter and inorganic sediments preserved within lake deposits provides a record of changes in environmental conditions, within and around a lake. Thirty samples were collected at 2 cm increments from an outcrop at Fossil Lake, Oregon. Fossil Lake has been extensively studied for the collection and description of a large diversity of fossils. However, a thorough geochemical analysis of the sediments is lacking. My thesis research tested the concentrations of elements in the inorganic fraction of the sediments and the bulk elemental geochemistry to determine the sources of material preserved within the lake sediments. These sediments, dated to ~10 to 13 ka, were analyzed for stable organic carbon (δ13C) and nitrogen (δ 15N) isotope data, C/N ratios, and elemental concentrations. Carbon to nitrogen ratios reflect algal vs. terrestrial organic matter sources. Variations in paleo-productivity and organic matter sources are also indicated by nitrogen stable isotope composition. Stable carbon isotopic composition is used to interpret changes in terrestrial plant species (C3 vs. C4 ). The new geochemical data suggest short-term trends in lake productivity higher in the section due to increased precipitation and also, it reveals changes in lake water chemistry as a result of wash-in of minerals in and around the lake. The results show that the amount of carbon in the Fossil Lake sediment is attributable to an allochtonous source. This indicates a mixing of aquatic algae with minor terrestrial input. The upper section (10–0 cm depth) is richer in organic carbon and considered to be a high lake stand period. During this time the influx of materials to the lake increased, likely a result of increased precipitation. The general trend showing increased %C, decreased δ13C, and no significant change in the C/N ratio correspond to increased lake productivity during the late Pleistocene.
|Commitee:||Borrok, David, Duex, Timothy, Hargrave, Jennifer|
|School:||University of Louisiana at Lafayette|
|School Location:||United States -- Louisiana|
|Source:||MAI 57/01M(E), Masters Abstracts International|
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