Geochemical trends through time and lateral variability of diatom floras in the Pleistocene Olorgesailie Formation, southern Kenya Rift Valley |
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| Authors: | RB Owen RW Renaut AK Behrensmeyer |
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| Institution: | a Department of Geography, Hong Kong Baptist University, Kowloon Tong, Hong Kongb Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatachewan S7N 5E2, Canadac Human Origins Program, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, Washington D.C. 20013-7012, USAd Paleontology Section, Department of Earth Sciences, National Museums of Kenya, P.O. Box 40658, Nairobi, Kenyae Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, Washington D.C. 20013, USA |
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| Abstract: | The Olorgesailie Formation (1.2-0.49 Ma) consists of fluvial and lacustrine rift sediments that have yielded abundant Acheulean artifacts and a fossil hominin (Homo cf. erectus). In testing prior understandings of the paleoenvironmental context, we define nine new geochemical zones. A Chemical Index of Alteration suggests increased catchment weathering during deposition of Members 1, 2, 7, 11, and 13. Biophile elements (Br, S) peak in M8-9 and lower M13 possibly reflecting increased input from soil erosion. REE data show that the Magadi Trachytes supplied most siliciclastic grains. Sixteen diatom stages indicate conductivities of 200-16,000 μS cm− 1 and pH of 7.5-9.5 for five deep-water lakes, ten shallow lakes and sixteen wetlands. These results are compared with diatom data from other sections in the basin and show aquatic spatial variability over km-scale distances. Similar floras are traceable over several kilometers for M2, M3 and M9, indicating broadly homogeneous lacustrine conditions during these times, but diatoms in other members imply variable conditions, some related to local tectonic controls. This lateral and temporal variability emphasizes the importance of carrying out stratigraphic sampling at multiple sites within a basin in efforts to define the environmental context relevant to human evolution. |
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| Keywords: | Diatoms Geochemistry Sedimentology Weathering REE data Lakes Olorgesailie East African Rift System |
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