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dc.contributor.advisor Pedone, Vicki en Telles, Franky en 2012-09-14T00:21:20Z en 2012-09-14T00:21:20Z en 2005 en 2005-11 en
dc.identifier.uri en
dc.description Includes bibliographical references (leaves 87-93) en
dc.description California State University, Northridge. Department of Geology. en
dc.description.abstract Lake Thetis is a small, hydrologically closed coastal lake located ~240 km north of Perth, Western Australia (30°30'S). The sediment record of Lake Thetis obtained in two cores spans the past ~4100 y and shows changes in sediment type, sedimentation rate, biota, and C and O isotopes that are related to climate change and the evolving nature of the lake. The oldest sediment is dominated by organic-rich sand and accumulated at rates of >20 cm/100 y. During this phase of sedimentation, the control on δ13 C of the lake changed from photosynthesis to addition of isotopically light carbon derived from organic decomposition, shown by the significant decrease in δ13 C in endogenic micrite. The δ18 of endogenic micrite during this phase has an average value of +1.0%o, indicating that it formed from water that had a δ18 value higher than seawater and meteoric water of the region. Therefore during this period of time, evaporation must have slightly exceeded precipitation and inflow. However, the sediment of this interval contains abundant, well preserved diatoms and ostracode species Mytilocypris ambiguosa. These observations constrain the salinity of the lake to be only brackish (<10 g/L). This period likely represents the lowest salinity and largest lake size of the time represented in the cores. Between -4000 y and 3650 y, sand deposition increased and organic-rich sand deposition decreased. Since this time, sand and organic-rich sand (and uncompacted organic-rich sand, i.e., sludge) have accumulated at rates between 3 and 6 cm/100y. The increase in eolian sand brought to the lake suggests that the vegetation in the area surrounding Lake Thetis decreased owing to increasing aridity. Concomitant with the change in sedimentation is the disappearance of Mytilocypris ambiguosa from the sediment record, which signals that the lake reached a salinity level above the biological tolerance of this species. The average size and salinity of the lake have probably similar to those of today for the past -3800 y, particularly after -2770 y when the average δ18 O of the micrite increased from +1%o to its modern value of +2 %o. Today, evaporation greatly exceeds precipitation. The lake water is hypersaline, generally>40 g/L, exceeding the documented tolerance level of Cyprideis australiensis, the only ostracode extant in the lake. Biodiversity is low, indicating that the lake is inhospitable to many species. Superposed on the overall history of increasing salinity and decreasing lake size are small excursions that mark short-term increases and decreases in salinity and lake size. These excursions are recorded in small (-1 %o) changes in δ18 O of micrite and in changes in the abundance of Cyprideis australiensis. The excursions are likely associated with drought/wet cycles in the area of Lake Thetis. Definition of the magnitude and frequency of drought/wet cycles require additional high-resolution temporal and spatial studies. en
dc.description.statementofresponsibility by Franky Telles en
dc.format application/pdf en
dc.format.extent xiii, 145 leaves en
dc.language.iso en en
dc.publisher California State University, Northridge en
dc.rights.uri en
dc.subject Lake Thetis en
dc.subject Western Australia en
dc.subject Geology en
dc.subject.other Dissertations, Academic -- CSUN -- Geology. en
dc.title Sedimentology, paleontology, C and O isotope chemistry, and geochronology of Holocene sediment from Lake Thetis, Cervantes, Western Australia en
dc.type Thesis en
dc.contributor.department Geological Sciences en M.S. en
dc.contributor.committeemember Vazquez, Jorge en
dc.contributor.committeemember Sloan, Jon en
dc.contributor.committeeMember Vazquez, Jorge en
dc.contributor.committeeMember Sloan, Jon en
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