Palaeoenvironmental significance of the clay mineral composition of Olduvai basin deposits,northern Tanzania |
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| Institution: | 1. Universidad de Chile, Departamento de Geología, Plaza Ercilla 803, Santiago, Chile;2. University of Geneva, Department of Earth Sciences, rue de Mairaîchers 13, Geneva, Switzerland;3. Universidad Andres Bello, Facultad de Ingenieria, Salvador Sanfuentes 2357, Santiago, Chile;4. Laboratoire de Pétrologie Magmatique, Université Aix Marseille III, 13397 Marseille Cedex 20, France;5. Universidad de Chile, Departamento de Producción Agrícola, Santiago, Chile (Correo 1004);1. St. Petersburg State University, Institute of Earth Science, V.O., 10 line, 33, St. Petersburg 199178, Russia;2. Leibniz Universität Hannover, Institute of Soil Science, Herrenhäuser Str. 2, D-30419 Hannover, Germany;3. ETH Zurich, Institute for Geotechnical Engineering, CH-8093 Zurich, Switzerland;4. St. Petersburg State Polytechnical University, 29 Politekhnicheskaya, 195251 St. Petersburg, Russia;5. Belgorod State University, ul. Pobedy 85, Belgorod, Russia;1. Department of Economics, University of Dar es Salaam, Dar es Salaam, Tanzania;2. School of International Development and Global Studies, University of Ottawa, 120 University Private, Ottawa ON K1N 6N5, Canada;1. King Abdullah University of Science and Technology, Division of Physical Science and Engineering, Thuwal 23955-6900, Saudi Arabia;2. King Fahd University of Petroleum and Minerals, Collage of Petroleum Engineering and Geosciences, Dhahran 31261, Saudi Arabia;3. Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Brownlow Street, Liverpool L69 3GP, UK;4. The Stone Age Institute, 1392 W Dittemore Road, Gosport, IN 47433, USA;5. GeoZentrum Nordbayern, Friedrich-Alexander-University (FAU) Erlangen-Nürnberg, Schloßgarten 5, 91054 Erlangen, Germany;6. Department of Earth & Atmospheric Sciences, Indiana University, Bloomington, IN 47405, USA |
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| Abstract: | Quaternary deposits in the southeastern part of the Olduvai basin, northern Tanzania, consist of lake margin deposits, followed by a series of fluvial sediments. The clay mineral fraction of the lake margin deposits (Bed I and lower part of Bed II) is composed of smectite and subordinate illite. All smectite is largely dioctahedral and shows indications for a limited degree of irregular interstratification by illite. In the overlying fluvial deposits (Beds II–IV), illite is the most abundant clay mineral. Smectite only occurs in lower parts of the fluvial deposits (up to the middle of Bed III), where it generally shows a high degree of irregular interstratification. Differences in clay mineral composition between the lake margin deposits and the fluvial deposits record differences in sediment source area and degree of alteration. Dioctahedral smectite in the lake margin deposits and the oldest fluvial deposits is derived from a region with volcanic material extending to the east and south of the basin, which also supplies a certain amount of illite. Illite in the fluvial deposits of Bed IV originates from an area with a metamorphic bedrock to the west and north. Alteration of detrital clay minerals resulted in Mg-enrichment of dioctahedral smectite in part of the lake margin deposits and partial illitization of smectite in the older fluvial deposits. Formation of clay minerals during diagenesis or soil development is not documented by analysis of the total clay fraction. |
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