Stratigraphic Correlation and Geochronology of Varved Sediments from Lake Malawi, East Africa
2001-01-29
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Stratigraphic Correlation and Geochronology of Varved Sediments from Lake Malawi, East Africa
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2001-01-29
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Five nine-m long piston cores and 16 multi-cores less than 60 cm long were obtained for a paleoclimate study from Lake Malawi in East Africa, and have provided the first high-resolution geochronology of varved lake sediments from the southern tropics. The establishment of this 22,000-year sedimentation chronology is essential to the construction of a paleoenvironmental history of Lake Malawi, and so that results obtained from subsequent work on sediment chemistry and diatom content of the cores can be expressed on a well-dated basis. The cores were stratigraphically correlated using volcanic ash beds and magnetic susceptibility measurements, and were dated using lead-210 assay, radiocarbon and varve counts. Interpretation of the stratigraphy and geochemistry suggests that Lake Malawi experienced a lowstand during the Last Glacial Maximum (LGM); however, the presence or absence of varves does not seem to be dependent on lake level. Thickness was measured on varves spanning the last 600 years on one of the cores. Spectral analysis of a time series constructed from these measurements exhibit periodicities in the 3-4 yr, 8 yr and 17 yr range, suggesting an El Nino/Southern Oscillation (ENSO) type signal or some as yet unknown forcing mechanism. Trace element from discrete ash layers within the cores provided a unique geochemical fingerprint for each tephra, which is useful for correlation of other cores in the absence of varves or other stratigraphic markers.
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A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Sylvia Lee Barry in partial fulfillment of the requirements for the degree of Master of Science, January 2001.
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Barry, Sylvia Lee. (2001). Stratigraphic Correlation and Geochronology of Varved Sediments from Lake Malawi, East Africa. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/212498.
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