@article{SierLangereisDupontNivetetal.2017, author = {Sier, Mark J. and Langereis, Cor G. and Dupont-Nivet, Guillaume and Feibel, Craig S. and Joordens, Josephine C. A. and van der Lubbe, Jeroen Fiji. and Beck, Catherine C. and Olago, Daniel and Cohen, Andrew}, title = {The top of the Olduvai Subchron in a high-resolution magnetostratigraphy from the West Turkana core WTK13, hominin sites and Paleolakes Drilling Project (HSPDP)}, series = {Quaternary geochronology : the international research and review journal on advances in quaternary dating techniques}, volume = {42}, journal = {Quaternary geochronology : the international research and review journal on advances in quaternary dating techniques}, publisher = {Elsevier}, address = {Oxford}, organization = {WTK Science Team Members}, issn = {1871-1014}, doi = {10.1016/j.quageo.2017.08.004}, pages = {117 -- 129}, year = {2017}, abstract = {One of the major challenges in understanding the evolution of our own species is identifying the role climate change has played in the evolution of hominin species. To clarify the influence of climate, we need long and continuous high-resolution paleoclimate records, preferably obtained from hominin-bearing sediments, that are well-dated by tephro- and magnetostratigraphy and other methods. This is hindered, however, by the fact that fossil-bearing outcrop sediments are often discontinuous, and subject to weathering, which may lead to oxidation and remagnetization. To obtain fresh, unweathered sediments, the Hominin Sites and Paleolakes Drilling Project (HSPDP) collected a \&\#8764;216-meter core (WTK13) in 2013 from Early Pleistocene Paleolake Lorenyang deposits in the western Turkana Basin (Kenya). Here, we present the magnetostratigraphy of the WTK13 core, providing a first age model for upcoming HSPDP paleoclimate and paleoenvrionmental studies on the core sediments. Rock magnetic analyses reveal the presence of iron sulfides carrying the remanent magnetizations. To recover polarity orientation from the near-equatorial WTK13 core drilled at 5°N, we developed and successfully applied two independent drill-core reorientation methods taking advantage of (1) the sedimentary fabric as expressed in the Anisotropy of Magnetic Susceptibility (AMS) and (2) the occurrence of a viscous component oriented in the present day field. The reoriented directions reveal a normal to reversed polarity reversal identified as the top of the Olduvai Subchron. From this excellent record, we find no evidence for the 'Vrica Subchron' previously reported in the area. We suggest that outcrop-based interpretations supporting the presence of the Vrica Subchron have been affected by the oxidation of iron sulfides initially present in the sediments -as evident in the core record- and by subsequent remagnetization. We discuss the implications of the observed geomagnetic record for human evolution studies.}, 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{GarcinJungingerMelnicketal.2009, author = {Garcin, Yannick and Junginger, Annett and Melnick, Daniel and Olago, Daniel O. and Strecker, Manfred and Trauth, Martin H.}, title = {Late Pleistocene-Holocene rise and collapse of the Lake Suguta, northern Kenya Rift}, doi = {10.1016/j.quascirev.2008.12.006}, year = {2009}, language = {en} } @article{MelnickGarcinQuinterosetal.2012, author = {Melnick, Daniel and Garcin, Yannick and Quinteros, Javier and Strecker, Manfred and Olago, Daniel and Tiercelin, Jean-Jacques}, title = {Steady rifting in northern Kenya inferred from deformed Holocene lake shorelines of the Suguta and Turkana basins}, series = {Earth \& planetary science letters}, volume = {331}, journal = {Earth \& planetary science letters}, number = {10}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2012.03.007}, pages = {335 -- 346}, year = {2012}, abstract = {A comparison of deformation rates in active rifts over different temporal scales may help to decipher variations in their structural evolution, controlling mechanisms, and evolution of sedimentary environments through time. Here we use deformed lake shorelines in the Suguta and Turkana basins in northern Kenya as strain markers to estimate deformation rates at the 10(3)-10(4) yr time scale and compare them with rates spanning 10(1)-10(7) yr. Both basins are internally drained today, but until 7 to 5 kyr lake levels were 300 and 100 m higher, respectively, maintained by the elevation of overflow sills connecting them with the Nile drainage. Protracted high lake levels resulted in formation of a maximum highstand shoreline - a distinct geomorphic feature virtually continuous for several tens of kilometers. We surveyed the elevation of this geomorphic marker at 45 sites along >100 km of the rift, and use the overflow sills as vertical datum. Thin-shell elastic and thermomechanical models for this region predict up to similar to 10 m of rapid isostatic rebound associated with lake-level falls lasting until similar to 2 kyr ago. Holocene cumulative throw rates along four rift-normal profiles are 6.8-8.5 mm/yr, or 7.5-9.6 mm/yr if isostatic rebound is considered. Assuming fault dips of 55-65, inferred from seismic reflection profiles, we obtained extension rates of 3.2-6 mm/yr (including uncertainties in field measurements, fault dips, and ages), or 3.5-6.7 mm/yr considering rebound. Our estimates are consistent, within uncertainties, with extension rates of 4-5.1 mm/yr predicted by a modern plate-kinematic model and plate reconstructions since 3.2 Myr. The Holocene strain rate of 10(-15) s(-1) is similar to estimates on the similar to 10(6) yr scale, but over an order of magnitude higher than on the similar to 10(7) yr scale. This is coherent with continuous localization and narrowing of the plate boundary, implying that the lithospheric blocks limiting the Kenya Rift are relatively rigid. Increasing strain rate under steady extension rate suggests that, as the magnitude of extension and crustal thinning increases, the role of regional processes such as weakening by volcanism becomes dominant over far-field plate tectonics controlling the breakup process and the transition from continental rifting to oceanic spreading.}, language = {en} } @article{GarcinMelnickStreckeretal.2012, author = {Garcin, Yannick and Melnick, Daniel and Strecker, Manfred and Olago, Daniel and Tiercelin, Jean-Jacques}, title = {East African mid-Holocene wet-dry transition recorded in palaeo-shorelines of Lake Turkana, northern Kenya Rift}, series = {Earth \& planetary science letters}, volume = {331}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2012.03.016}, pages = {322 -- 334}, year = {2012}, abstract = {The 'wet' early to mid-Holocene of tropical Africa, with its enhanced monsoon, ended with an abrupt shift toward drier conditions and was ultimately replaced by a drier climate that has persisted until the present day. The forcing mechanisms, the timing, and the spatial extent of this major climatic transition are not well understood and remain the subject of ongoing research. We have used a detailed palaeo-shoreline record from Lake Turkana (Kenya) to decipher and characterise this marked climatic transition in East Africa. We present a high-precision survey of well-preserved palaeo-shorelines, new radiocarbon ages from shoreline deposits, and oxygen-isotope measurements on freshwater mollusk shells to elucidate the Holocene moisture history from former lake water-levels in this climatically sensitive region. In combination with previously published data our study shows that during the early Holocene the water-level in Lake Turkana was high and the lake overflowed temporarily into the White Nile drainage system. During the mid-Holocene (similar to 5270 +/- 300 cal. yr BP), however, the lake water-level fell by similar to 50 m, coeval with major episodes of aridity on the African continent. A comparison between palaeo-hydrological and archaeological data from the Turkana Basin suggests that the mid-Holocene climatic transition was associated with fundamental changes in prehistoric cultures, highlighting the significance of natural climate variability and associated periods of protracted drought as major environmental stress factors affecting human occupation in the East African Rift System. (}, language = {en} }