TY  - JOUR
A1  - Deino, A. L.
A1  - Dommain, René
A1  - Keller, C. B.
A1  - Potts, R.
A1  - Behrensmeyer, A. K.
A1  - Beverly, E. J.
A1  - King, J.
A1  - Heil, C. W.
A1  - Stockhecke, M.
A1  - Brown, E. T.
A1  - Moerman, J.
A1  - deMenocal, P.
A1  - Deocampo, D.
A1  - Garcin, Yannick
A1  - Levin, N. E.
A1  - Lupien, R.
A1  - Owen, R. B.
A1  - Rabideaux, N.
A1  - Russell, J. M.
A1  - Scott, J.
A1  - Riedl, S.
A1  - Brady, K.
A1  - Bright, J.
A1  - Clark, J. B.
A1  - Cohen, A.
A1  - Faith, J. T.
A1  - Noren, A.
A1  - Muiruri, V.
A1  - Renaut, R.
A1  - Rucina, S.
A1  - Uno, K.
T1  - Chronostratigraphic model of a high-resolution drill core record of the past million years from the Koora Basin, south Kenya Rift: Overcoming the difficulties of variable sedimentation rate and hiatuses
JF  - Quaternary science reviews : the international multidisciplinary research and review journal
N2  - The Olorgesailie Drilling Project and the related Hominin Sites and Paleolakes Drilling Project in East Africa were initiated to test hypotheses and models linking environmental change to hominin evolution by drilling lake basin sediments adjacent to important archeological and paleoanthropological sites. Drill core OL012-1A recovered 139 m of sedimentary and volcaniclastic strata from the Koora paleolake basin, southern Kenya Rift, providing the opportunity to compare paleoenvironmental influences over the past million years with the parallel record exposed at the nearby Olorgesailie archeological site. To refine our ability to link core-to-outcrop paleoenvironmental records, we institute here a methodological framework for deriving a robust age model for the complex lithostratigraphy of OL012-1A. Firstly, chronostratigraphic control points for the core were established based on 4 Ar/39Ar ages from intercalated tephra deposits and a basal trachyte flow, as well as the stratigraphic position of the Brunhes-Matuyama geomagnetic reversal. This dataset was combined with the position and duration of paleosols, and analyzed using a new Bayesian algorithm for high-resolution age-depth modeling of hiatus-bearing stratigraphic sections. This model addresses three important aspects relevant to highly dynamic, nonlinear depositional environments: 1) correcting for variable rates of deposition, 2) accommodating hiatuses, and 3) quantifying realistic age uncertainty with centimetric resolution. Our method is applicable to typical depositional systems in extensional rifts as well as to drill cores from other dynamic terrestrial or aquatic environments. We use the core age model and lithostratigraphy to examine the inter connectivity of the Koora Basin to adjacent areas and sources of volcanism. (C) 2019 Elsevier Ltd. All rights reserved.
KW  - Pleistocene
KW  - Paleolimnology
KW  - East Africa
KW  - Sedimentology
KW  - Radiogenic isotopes
KW  - Bayesian modeling
KW  - paleosol
KW  - Tephrostratigraphy
KW  - Magnetostratigraphy
KW  - Kenya Rift
Y1  - 2019
U6  - https://doi.org/10.1016/j.quascirev.2019.05.009
SN  - 0277-3791
VL  - 215
SP  - 213
EP  - 231
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Melnick, Daniel
A1  - Garcin, Yannick
A1  - Quinteros, Javier
A1  - Strecker, Manfred
A1  - Olago, Daniel
A1  - Tiercelin, Jean-Jacques
T1  - Steady rifting in northern Kenya inferred from deformed Holocene lake shorelines of the Suguta and Turkana basins
JF  - Earth & planetary science letters
N2  - 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.
KW  - continental rifting
KW  - East Africa
KW  - lake shorelines
KW  - Holocene extension
KW  - isostatic rebound
Y1  - 2012
U6  - https://doi.org/10.1016/j.epsl.2012.03.007
SN  - 0012-821X
VL  - 331
IS  - 10
SP  - 335
EP  - 346
PB  - Elsevier
CY  - Amsterdam
ER  -