TY - JOUR
T1 - Stratigraphy and geochronology of the late miocene adu-asa formation at gona, ethiopia
AU - Kleinsasser, Lynnette L.
AU - Quade, Jay
AU - McIntosh, William C.
AU - Levin, Naomi E.
AU - Simpson, Scott W.
AU - Semaw, Sileshi
PY - 2008
Y1 - 2008
N2 - 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 from5.2 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.
AB - 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 from5.2 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.
KW - Adu-Asa Formation
KW - Ardipithecus kadabba
KW - Ardipithecus ramidus
KW - Gona
KW - Tephrostratigraphy
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U2 - 10.1130/2008.2446(02)
DO - 10.1130/2008.2446(02)
M3 - Article
AN - SCOPUS:75449095011
SN - 0072-1077
VL - 446
SP - 33
EP - 65
JO - Special Paper of the Geological Society of America
JF - Special Paper of the Geological Society of America
ER -