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Olorgesailie, Kenya: A Million Years in the Life of a Rift Basin

By
Anna K. Behrensmeyer
Anna K. Behrensmeyer
Department of Paleobiology, MRC 121, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, U.S.A.
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Richard Potts
Richard Potts
Department of Anthropology, MRC 122, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, U.S.A.
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Alan Deino
Alan Deino
Berkeley Geochronology Center, 2455 Ridge Rd., Berkeley, California 94709, U.S.A.
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Peter Ditchfield
Peter Ditchfield
Department of Geology, University of Bristol, Wills Memorial Building. Queens Road, Briston BS8 1RJ, Great Britain
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Published:
January 01, 2002

Abstract

A sequence of lacustrine, volcaniclastic, and alluvial sedimentary deposits that record the past million years of the history in the Olorgesailie Basin, southern Kenya, provide an example of how tectonics, climate, and volcanism affect sedimentation in a rift valley. A series of radiometric dates on volcanic materials through this sequence permits relatively fine-scale calibration of the timing and duration of volcanic input to the depositional system, transgressive-regressive cycles of the lake, and intervals of valley cutting and filling. The Olorgesailie Formation, accumulated between 0.992 and 0.493 Ma, consists of relatively pure diatomites, reworked diatomites, primary volcanic and reworked volcaniclastic units, and alluvial deposits (clays, silts, and sands with several well-developed paleosols) that bear a rich archeological and paleontological record. After 0.493 Ma, increased tectonic activity initiated a series of valley cutting and filling cycles that continue into Recent times. A working hypothesis attributes the formation of the paleolake to a barrier on the southwest side of the basin, large-scale lacustrine versus alluvial phases of the Olorgesailie Formation to variations in subsidence rates operating on a time scale of 104-105 yr, and transgressive-regressive cycles within these sedimentary packages to wet-dry climate cycles on time scales of 103-104 yr. Episodes of volcanism were superimposed on these patterns but did not have significant long-term effects on the depositional system.

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SEPM Special Publication

Sedimentation in Continental Rifts

Robin W. Renaut
Robin W. Renaut
Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
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Gail M. Ashley
Gail M. Ashley
Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854-8066, U.S.A.
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SEPM Society for Sedimentary Geology
Volume
73
ISBN electronic:
9781565761957
Publication date:
January 01, 2002

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