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Stratigraphy and geochronology of the late Miocene Adu-Asa Formation at Gona, Ethiopia

Kleinsasser, Lynnette L. and Quade, Jay and McIntosh, William C. and Levin, Naomi E. and Simpson, Scott W. and Semaw, Sileshi (2008) Stratigraphy and geochronology of the late Miocene Adu-Asa Formation at Gona, Ethiopia. In: The Geology of Early Humans in the Horn of Africa. Special papers (Geological Society of America). No.446. Geological Society of America , Boulder, CO, pp. 33-65. ISBN 9780813724461.

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The Gona area includes many rich fossil localities that are of great consequence to the study of human evolution. The Adu-Asa Formation, containing the oldest of these fossils, consists of nearly 200 m of fossil-bearing sedimentary rocks in thin (≤30 m), laterally variable sections interlayered with abundant basaltic lava flows. These volcanic and sedimentary rocks dip gently to the east and are repeated by north-northwest–trending, mostly west-dipping normal faults that accommodate extension in the Afar Rift. The volcanic rocks in the Adu-Asa Formation are strongly bimodal. Basaltic lavas and tuffs are abundant, but we have also identified a rhyolite center and seven different silicic, or dominantly silicic, tuffs. Of these tuff units, we were able to identify four major tuffs across the Adu-Asa Formation at Gona by combining geochemical comparisons with detailed stratigraphic sections through fossil-bearing deposits: the Sifi, the Kobo'o, the Belewa, and the Ogoti Tuffs. New ^(40)Ar/^(39)Ar dates of these and other tuffs, as well as basalt flows, indicate that the formation spans the period from 5.2 Ma to 6.4 Ma, although the oldest deposits within the Gona Paleoanthropological Research Project (GPRP) area have yet to be thoroughly surveyed. Known fossil localities within the Adu-Asa Formation at Gona are grouped into three temporal clusters, ranging in age from ca. 6.4 Ma to ca. 5.5 Ma.

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Additional Information:© 2008 Geological Society of America. Accepted 17 June 2008. We thank K. Schick and N. Toth at the Center for Research into the Archaeological Foundations of Technology (CRAFT) for their support of this project, and Ambacho Kebeda, Soloman Kebede, Haptewold Habtemichael, and Yonas Beyene for help with permits. We also thank Authority for Research and Conservation of Cultural Heritage of the Ministry of Culture and Tourism of Ethiopia for the field permit. Financial support was provided by the LSB Leakey Foundation, National Geographic, Wenner-Gren Foundation, and the Revealing Hominid Origins Initiative (RHOI)/National Science Foundation (SBR-9910974 and Behavorial and Cognitive Sciences [BCS] Award 0321893). Matt Heizler, Nelia Dunbar, Lisa Peters, Ariel Dickens, Melanie Everett, Steve Frost, Bill Hart, Mike Rogers, and Dietrich Stout are warmly acknowledged for all their help and interesting scientific exchanges. Our special thanks go to Asahmed Humet and many other Afars who in various ways facilitated this research. Kleinsasser also thanks the Department of Geosciences at the University of Arizona and the Bert Butler Foundation for funding, as well as Ken Domanik, Eric Seedorff, Joaquin Ruiz, and Christa Placzek for their generous assistance.
Funding AgencyGrant Number
LSB Leakey FoundationUNSPECIFIED
National GeographicUNSPECIFIED
Wenner-Gren FoundationUNSPECIFIED
Revealing Hominid Origins Initiative (RHOI)UNSPECIFIED
Subject Keywords:tephrostratigraphy; Gona Adu-Asa Formation; 40Ar/39Ar dating; Ardipithecus ramidus; Ardipithecus kadabba
Series Name:Special papers (Geological Society of America)
Issue or Number:446
Record Number:CaltechAUTHORS:20150203-144755649
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Official Citation:Lynnette L Kleinsasser, Jay Quade, William C McIntosh, Naomi E Levin, Scott W Simpson, and Sileshi Semaw Stratigraphy and geochronology of the late Miocene Adu-Asa Formation at Gona, Ethiopia Geological Society of America Special Papers, 2008, 446, p. 33-65, doi:10.1130/2008.2446(02)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54333
Deposited By: Tony Diaz
Deposited On:04 Feb 2015 01:20
Last Modified:03 Oct 2019 07:56

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