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

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 (in The geology of early humans in the Horn of Africa, Jay Quade (editor) and Jonathan G. Wynn (editor))
Special Paper - Geological Society of America (2008) 446: 33-65

Abstract

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 (< or =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 (super 40) Ar/ (super 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.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 446
Title: Stratigraphy and geochronology of the late Miocene Adu-Asa Formation at Gona, Ethiopia
Title: The geology of early humans in the Horn of Africa
Author(s): Kleinsasser, Lynnette L.Quade, JayMcIntosh, William C.Levin, Naomi E.Simpson, Scott W.Semaw, Sileshi
Author(s): Quade, Jayeditor
Author(s): Wynn, Jonathan G.editor
Affiliation: University of Arizona, Department of Geosciences, Tucson, AZ, United States
Affiliation: University of Arizona, Department of Geosciences, Tucson, AZ, United States
Pages: 33-65
Published: 2008
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
ISBN: 978-0-8137-2446-1
References: 31
Accession Number: 2009-060442
Categories: StratigraphyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: NSF grants SBR-9910974 and BCS-0321893
Illustration Description: illus. incl. sect., strat. cols., 8 tables, sketch maps
N11°04'60" - N11°15'00", E40°10'00" - E40°19'60"
Secondary Affiliation: University of South Florida, USA, United StatesNew Mexico Bureau of Geology and Mineral Resources, USA, United StatesUniversity of Utah, USA, United StatesCase Western Reserve University, USA, United StatesIndiana University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200933
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