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AMS-14C Chronology of a Lacustrine Sequence from Lake Langano (Main Ethiopian Rift): Correction and Validation Steps in Relation with Volcanism, Lake Water and Carbon Balances

Published online by Cambridge University Press:  18 July 2016

Elisabeth Gibert ,
Yves Travi ,
Marc Massault ,
Jean-Jacques Tiercelin  and
Tesfaye Chernet
Elisabeth Gibert*
Affiliation:
FRE 2566-ORSAYTERRE, CNRS-UPS, Equipe ≪Hydrologie, Paléohydrologie et Paléoenvironnement≫, Université Paris-Sud, Bâtiment 504, F-91405 Orsay cedex, France
Yves Travi
Affiliation:
Laboratoire d'Hydrogéologie, Département de Géologie, Faculté des Sciences d'Avignon, 33 rue Louis Pasteur, F-84000 Avignon, France
Marc Massault
Affiliation:
FRE 2566-ORSAYTERRE, CNRS-UPS, Equipe ≪Hydrologie, Paléohydrologie et Paléoenvironnement≫, Université Paris-Sud, Bâtiment 504, F-91405 Orsay cedex, France
Jean-Jacques Tiercelin
Affiliation:
UMR 6538 “Domaines Océaniques”, Institut Universitaire Européen de la Mer, Place Nicolas Copernic, F-29280 Plouzané, France
Tesfaye Chernet
Affiliation:
Laboratoire d'Hydrogéologie, Département de Géologie, Faculté des Sciences d'Avignon, 33 rue Louis Pasteur, F-84000 Avignon, France
*
Corresponding author. Email: egibert@geol.u-psud.fr.
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Abstract

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Located in the Ziway-Shala Basin of the Main Ethiopian Rift, Lake Langano is part of an asymmetric half-graben, defined by a series of north-northeast-trending faults in the tectonically active zone of the rift. A 15-m deep succession of organic homogeneous muds, silts, bioclastic sands, and pyroclastic layers was cored in 1994. The definition of a certified radiocarbon chronology on these deposits required the indispensable establishment of modern hydrological and geochemical balances. The isotopic contents of the total dissolved inorganic carbon (TDIC) of surface water clearly show the influence of a deep CO2 rising along the main fault crossing the lake basin. The 5.8 pMC disequilibrium existing in 1994 with the atmosphere likely produces the aging of authigenic materials developing at the lake surface. However, with a mean residence time of ~15 years, this apparent 14C aging of Lake Langano water still integrates the 14C produced by the nuclear tests in the 1960s. Reconstructing the natural 14C activity of the lake TDIC allows for the quantification of the deep CO2 influence, and for the correction of AMS-14C datings performed along the core. The correction of the AMS-14C chronology defined on Lake Langano allows for a better understanding of paleohydrological changes at a regional scale for at least the last 12,700 cal BP.

Type
Articles
Information
Radiocarbon , Volume 44 , Issue 1 , 2002 , pp. 75 - 92
Copyright
Copyright © 2002 by the Arizona Board of Regents on behalf of the University of Arizona 

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