@article{OwenMuiruriLowensteinetal.2018, author = {Owen, Richard Bernhart and Muiruri, Veronica M. and Lowenstein, Tim K. and Renaut, Robin W. and Rabideaux, Nathan and Luo, Shangde and Deino, Alan L. and Sier, Mark J. and Dupont-Nivet, Guillaume and McNulty, Emma P. and Leet, Kennie and Cohen, Andrew and Campisano, Christopher and Deocampo, Daniel and Shen, Chuan-Chou and Billingsley, Anne and Mbuthia, Anthony}, title = {Progressive aridification in East Africa over the last half million years and implications for human evolution}, series = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {115}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, number = {44}, publisher = {National Academy of Sciences}, address = {Washington}, issn = {0027-8424}, doi = {10.1073/pnas.1801357115}, pages = {11174 -- 11179}, year = {2018}, abstract = {Evidence for Quaternary climate change in East Africa has been derived from outcrops on land and lake cores and from marine dust, leaf wax, and pollen records. These data have previously been used to evaluate the impact of climate change on hominin evolution, but correlations have proved to be difficult, given poor data continuity and the great distances between marine cores and terrestrial basins where fossil evidence is located. Here, we present continental coring evidence for progressive aridification since about 575 thousand years before present (ka), based on Lake Magadi (Kenya) sediments. This long-term drying trend was interrupted by many wet-dry cycles, with the greatest variability developing during times of high eccentricity-modulated precession. Intense aridification apparent in the Magadi record took place between 525 and 400 ka, with relatively persistent arid conditions after 350 ka and through to the present. Arid conditions in the Magadi Basin coincide with the Mid-Brunhes Event and overlap with mammalian extinctions in the South Kenya Rift between 500 and 400 ka. The 525 to 400 ka arid phase developed in the South Kenya Rift between the period when the last Acheulean tools are reported (at about 500 ka) and before the appearance of Middle Stone Age artifacts (by about 320 ka). Our data suggest that increasing Middle- to Late-Pleistocene aridification and environmental variability may have been drivers in the physical and cultural evolution of Homo sapiens in East Africa.}, language = {en} } @misc{BraunAldeiasArcheretal.2019, author = {Braun, David R. and Aldeias, Vera and Archer, Will and Arrowsmith, J. Ramon and Baraki, Niguss and Campisano, Christopher J. and Deino, Alan L. and DiMaggio, Erin N. and Dupont-Nivet, Guillaume and Engda, Blade and Feary, David A. and Garello, Dominique I. and Kerfelew, Zenash and McPherron, Shannon P. and Patterson, David B. and Reeves, Jonathan S. and Thompson, Jessica C. and Reed, Kaye E.}, title = {Reply to Sahle and Gossa: Technology and geochronology at the earliest known Oldowan site at Ledi-Geraru, Ethiopia}, series = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {116}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, number = {41}, publisher = {National Acad. of Sciences}, address = {Washington}, issn = {0027-8424}, doi = {10.1073/pnas.1911952116}, pages = {20261 -- 20262}, year = {2019}, language = {en} } @article{DeinoSierGarelloetal.2019, author = {Deino, Alan L. and Sier, Mark Jan and Garello, Dominique and Keller, B. and Kingston, John and Scott, Jennifer J. and Dupont-Nivet, Guillaume and Cohen, Andrew}, title = {Chronostratigraphy of the Baringo-Tugen-Barsemoi (HSPDP-BTB13-1A) core-Ar-40/Ar-39 dating, magnetostratigraphy, tephrostratigraphy, sequence stratigraphy and Bayesian age modeling}, series = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, volume = {532}, journal = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0031-0182}, doi = {10.1016/j.palaeo.2019.109258}, pages = {16}, year = {2019}, abstract = {The Baringo-Tugen-Barsemoi 2013 drillcore (BTB13), acquired as part of the Hominin Sites and Paleolakes Drilling Project, recovered 228 m of fluviolacustrine sedimentary rocks and tuffs spanning a similar to 3.29-2.56 Ma interval of the highly fossiliferous and hominin-bearing Chemeron Formation, Tugen Hills, Kenya. Here we present a Bayesian stratigraphic age model for the core employing chronostratigraphic control points derived from Ar-40/Ar-39 dating of tuffs from core and outcrop, Ar-40/Ar-39 age calibration of related outcrop diatomaceous units, and core magnetostratigraphy. The age model reveals three main intervals with distinct sediment accumulation rates: an early rapid phase from 3.2 to 2.9 Ma; a relatively slow phase from 2.9 to 2.7 Ma; and the highest rate of accumulation from 2.7 to 2.6 Ma. The intervals of rapid accumulation correspond to periods of high Earth orbital eccentricity, whereas the slow accumulation interval corresponds to low eccentricity at 2.9-2.7 Ma, suggesting that astronomically mediated climate processes may be responsible for the observed changes in sediment accumulation rate. Lacustrine transgression-regression events, as delineated using sequence stratigraphy, dominantly operate on precession scale, particularly within the high eccentricity periods. A set of erosively based fluvial conglomerates correspond to the 2.9-2.7 Ma interval, which could be related to either the depositional response to low eccentricity or to the development of unconformities due to local tectonic activity. Age calibration of core magnetic susceptibility and gamma density logs indicates a close temporal correspondence between a shift from high- to low-frequency signal variability at similar to 3 Ma, approximately coincident the end of the mid-Piacenzian Warm Period, and the beginning of the cooling of world climate leading to the initiation of Northern Hemispheric glaciation c. 2.7 Ma. BTB13 and the Baringo Basin records may thus provide evidence of a connection between high-latitude glaciation and equatorial terrestrial climate toward the end of the Pliocene.}, language = {en} } @article{BergnerStreckerTrauthetal.2009, author = {Bergner, Andreas G. N. and Strecker, Manfred and Trauth, Martin H. and Deino, Alan L. and Gasse, Francoise and Blisniuk, Peter Michael and Duehnforth, Miriam}, title = {Tectonic and climatic control on evolution of rift lakes in the Central Kenya Rift, East Africa}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2009.07.008}, year = {2009}, abstract = {The long-term histories of the neighboring Nakuru-Elmenteita and Naivasha lake basins in the Central Kenya Rift illustrate the relative importance of tectonic versus climatic effects on rift-lake evolution and the formation of disparate sedimentary environments. Although modem climate conditions in the Central Kenya Rift are very similar for these basins, hydrology and hydrochemistry of present-day lakes Nakuru, Elmenteita and Naivasha contrast dramatically due to tectonically controlled differences in basin geometries, catchment size, and fluvial processes. In this study, we use eighteen C-14 and Ar-40/Ar-39 dated fluvio-lacustrine sedimentary sections to unravel the spatiotemporal evolution of the lake basins in response to tectonic and climatic influences. We reconstruct paleoclimatic and ecological trends recorded in these basins based on fossil diatom assemblages and geologic field mapping. Our study shows a tendency towards increasing alkalinity and shrinkage of water bodies in both lake basins during the last million years. Ongoing volcano-tectonic segmentation of the lake basins, as well as reorganization of upstream drainage networks have led to contrasting hydrologic regimes with adjacent alkaline and freshwater conditions. During extreme wet periods in the past, such as during the early Holocene climate optimum, lake levels were high and all basins evolved toward freshwater systems. During drier periods some of these lakes revert back to alkaline conditions, while others maintain freshwater characteristics. Our results have important implications for the use and interpretation of lake sediment as climate archives in tectonically active regions and emphasize the need to deconvolve lacustrine records with respect to tectonics versus climatic forcing mechanisms.}, language = {en} } @article{TrauthMaslinDeinoetal.2010, author = {Trauth, Martin H. and Maslin, Mark A. and Deino, Alan L. and Junginger, Annett and Lesoloyia, Moses and Odada, Eric O. and Olago, Daniel O. and Olaka, Lydia A. and Strecker, Manfred and Tiedemann, Ralph}, title = {Human evolution in a variable environment : the amplifier lakes of Eastern Africa}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2010.07.007}, year = {2010}, abstract = {The development of rise Cenozoic East African Rift System (EARS) profoundly re-shaped the landscape and significantly increased the amplitude of short-term environmental response to climate variation. In particular, the development of amplifier lakes in rift basins after three million years ago significantly contributed to this exceptional sensitivity of East Africa to climate change compared to elsewhere on the African continent. Amplifier lakes are characterized by tectonically-formed graben morphologies in combination with an extreme contrast between high precipitation in the elevated parts of the catchment and high evaporation in the lake area. Such amplifier lakes respond rapidly to moderate, precessional-forced climate shifts, and as they do so apply dramatic environmental pressure to the biosphere. Rift basins, when either extremely dry or lake-filled, form important barriers for migration, mixing and competition of different populations of animals and hominins. Amplifier lakes link long-term, high-amplitude tectonic processes and short-term environmental fluctuations. East Africa may have become the place where early humans evolved as a consequence of this strong link between different time scales. (C) 2010 Elsevier Ltd. All rights reserved.}, language = {en} } @article{TrauthMaslinDeinoetal.2008, author = {Trauth, Martin H. and Maslin, Mark A. and Deino, Alan L. and Strecker, Manfred and Bergner, Andreas G. N. and D{\"u}hnforth, Miriam}, title = {High- and low-latitude forcing of Plio-Pleistocene African climate and human evolution}, doi = {10.1016/j.jhevol.2006.12.009}, year = {2008}, abstract = {The late Cenozoic climate of East Africa is punctuated by episodes of short, alternating periods of extreme wetness and aridity, superimposed on a regime of subdued moisture availability exhibiting a long-term drying trend. These periods of extreme climate variability appear to correlate with maxima in the 400-thousand-year (kyr) component of the Earth's eccentricity cycle. Prior to 2.7 Ma the wet phases appear every 400 kyrs, whereas after 2.7 Ma, the wet phases appear every 800 kyrs, with periods of precessional-forced extreme climate variability at 2.7-2.5 Ma, 1.9-1.7 Ma, and 1.1-0.9 Ma before present. The last three major lake phases occur at the times of major global climatic transitions, such as the onset of Northern Hemisphere Glaciation (2.7-2.5 Ma), intensification of the Walker Circulation (1.9-1.7 Ma), and the Mid-Pleistocene Revolution (1.0-0.7 Ma). High-latitude forcing is required to compress the Intertropical Convergence Zone so that East Africa becomes locally sensitive to precessional forcing, resulting in rapid shifts from wet to dry conditions. These periods of extreme climate variability may have provided a catalyst for evolutionary change and driven key speciation and dispersal events amongst mammals and hominins in East Africa. (C) 2007 Elsevier Ltd. All rights reserved.}, language = {en} }