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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40Ar/39Ar dating of Plio-Pleistocene Drill Cores from East Africa

East Africa provides the opportunity to acquire unique evidence toward understanding the influence of climate and environmental change on the evolution of the human lineage and technology during the Plio-Pleistocene. The Hominin Sites and Paleolakes Drilling Project (HSPDP) has extracted a total of 2 km of sediment drill core from the Rift Valley of East Africa, in paleolake basins adjacent to fossil hominin and archaeological sites of major significance. 40Ar/39Ar dating and chronology modeling of four of these sites will be discussed. Sites in the southern Kenya Rift will be compared to outcrop geology of the Olorgesailie area, which exhibits some of the earliest Middle Stone Age archaeology.

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Alan Deino, Berkeley Geochronology Center, California.

Alan Deino is a geochronologist at the Berkeley Geochronology Center, Berkeley, California. His career has been devoted to the application of the 40Ar/39Ar dating method to problems of volcanology, tectonics, climate change, faunal evolution, and hominin origins on several continents, but with recurring emphasis on East Africa.

 

 

 

Date: 14/06/2017, 16:00 h – 17:00 h

Location: Room 0.40, Biozentrum (Building 301), Zülpicher Str. 47a, Cologne
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Investigating sediment thicknesses with geophysics in the East-African Rift Valley

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When aiming at the reconstructing of the paleoclimate, applied geophysical techniques can assist with the identification and definition of possible paleoenvironmental archives such as sedimental deposits.

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In 2014 and 2015, a group of geophysicists from the University of Cologne investigated

Marc Seidel, PhD Candidate in A2

Marc Seidel, PhD Candidate in A2

three sedimentary basins within the East ­African Rift Valley using 2D transient electromagnetics (TEM) and electrical resistivity tomography (ERT). Lake Chew Bahir (“Salty lake” in Amharic, approx. 500 m a.s.l.) is a 30 km x 70 km saline mudflat that episodically fills with water during rainy season. According to airborne gravity and seismic reflection data, the thickness of its sedimentary deposits is assumed to be of several kilometers. Therefore, the basin potentially provides sedimentary archives that extend far beyond the Quaternary. The source area of Bisare River is located within the Hobitcha Caldera near Wolaita Sodo in southern Ethiopia. Former sedimentological results indicate a continuous sedimentation process and Tephra layers. The double crater system of the Dendi Lakes is located at Mount Dendi (3,270 m asl) 80 km west of Addis Ababa. First drillings revealed holocene deposits within the lake sediments. Our results indicate sediment thicknesses comprising quaternary sediments.

The recorded data was processed using the software AarhusInv from the Hydrogeophysics Group of the University of Aarhus, Denmark. Here, all data and models are inverted as one system, producing layered solutions with laterally smooth transitions. The models are regularized through lateral constraints that tie interface depths or thicknesses and resistivities of adjacent layers. These inversion schemes are well suited for data taken in sedimentary environments.

Event Information:

Date, Time: 27/06/2016, 14:00 h – 14:45 h

Location: Room S12, Seminargebäude (Building 106), Universitätsstraße 37 , Cologne

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