Authigenic silicates and Quaternary paleolimnology: Examples from Olduvai Gorge, Tanzania, and the Kenya Rift

The Third Fault, Olduvai Gorge, Tanzania, showing the stratigraphy of the Olduvai Basin.

 

The paleoclimatic framework of human evolution is central to the study of human origins. Several East African basins offer excellent examples of how authigenic silicates may be used in paleoenvironmental reconstructions, particularly when biotic indicators are absent or diagenetically modified.

In a Pleistocene section at Olduvai Gorge, Mg depletion in authigenic clays indicate freshening events occurring over a generally saline and alkaline environmental background. Five of the six events observed occurred at peak climatic precession, correlating with December insolation at 20°S. Peak amplitude of geochemical variation preceded the ca. 1.84 Ma eccentricity maximum by ~20 k.y., suggesting that eccentricity modulation was unexpectedly weak in this interval, or that other factors affected the water balance or geochemical record. 

Dan Deocampo, Georgia State University

Preliminary work has been carried out on deposits of the Lake Magadi, Koora Graben, and Baringo Basin cores obtained by the international Hominin Sites and Paleolakes Drilling Project. In these cores, authigenic clay minerals do not show much variation in chemistry, as these basins did not persist in the window of conditions of salinity and silica availability to promote authigenic clay precipitation. Instead, zeolites produced by alteration of volcaniclastic materials give insight into relative salinity conditions. In particular, different zeolites host different cations (i.e. Na, K, Ca) that provide clues as to cation ratios in the paleolake water. Major transitions of zeolite assemblages are observed in each basin, indicating salinity fluctuations. 

Authigenic silicates provide datasets that can add an important component to multi-proxy paleoenvironmental records from lake basins.

Dr. Deocampo is Professor and Chair of the Department of Geosciences at Georgia State University, in Atlanta.  He conducts geological research around the world, including in Europe, East Africa, and North America. He has published over 30 peer-reviewed scientific publications and has attracted funding support from the U.S. National Science Foundation, the U.S. Geological Survey, the Petroleum Research Fund, and the Departments of Transportation in both California and Georgia. He collaborates with environmental and public health scientists, anthropologists, biologists, chemists, geographers, and others to conduct research on both basic and applied research topics. Dr. Deocampo is an expert in the mineralogy and geochemistry of near surface environments, including soils, sediments, and aquatic systems, and is a Fellow of the Geological Society of America. 

Date: 30/06/2017, 10:00 h – 11:00 h

Location: Room 0.024, Biozentrum (Building 304), Zülpicher Str. 47b, Cologne


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