Chronostratigraphy of the Miocene–Pliocene Sagantole Formation, Middle Awash Valley, Afar Rift, Ethiopia
Chronostratigraphy of the Miocene–Pliocene Sagantole Formation, Middle Awash Valley, Afar rift, Ethiopia Paul R. Renne* Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California 94709 and Department of Geology and Geophysics, University of California, Berkeley, California 94720 Giday WoldeGabriel Los Alamos National Laboratory, Los Alamos, New Mexico 87545 William K. Hart Department of Geology, Miami University, Oxford, Ohio 45056 Grant Heiken Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Tim D. White Laboratory for Human Evolutionary Studies, Museum of Vertebrate Zoology and Department of Integrative Biology, University of California, Berkeley, California 94720 ABSTRACT 1999). The sediment deposited in these basins is largely volcaniclastic in ori- gin and is interbedded with mafic lava and compositionally bimodal tephra The Sagantole Formation comprises more than 200 m of lacustrine, that are products of intermittent volcanism related to the Afar plume. The alluvial, and volcaniclastic sediments, plus compositionally bimodal Afar and the Main Ethiopian rift, covering an area of ~3.5 × 105 km2,began tephras and basaltic lavas, exposed in a domelike horst named the to form at least by 25 Ma (Moore and Davidson, 1978; Berhe et al., 1987; Central Awash Complex in the southwestern Afar rift of Ethiopia. The WoldeGabriel et al., 1990, 1991, 1992; Ebinger et al., 1993; Yemane et al., Sagantole Formation is widely known for abundant vertebrate faunas, 1999), and thick accumulations of sediment, lava, and tephra have been sub- including the 4.4 Ma primitive hominid Ardipithecus ramidus. New sequently deposited into the subsiding rift basins. In the Middle Awash re- lithostratigraphic data are used to subdivide the Sagantole Formation gion of the southern Afar rift, faulting, uplift, differential subsidence, and ero- into the Kuseralee, Gawto, Haradaso, Aramis, Beidareem, Adgantole, sion have produced windows into one such rift-basin succession.
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