...Ian McDougall; Francis H. Brown; Paulo M. Vasconcelos; Benjamin E. Cohen; David S. Thiede; Michael J. Buchanan Abstract Six tuffaceous beds within the Omo Group of the Omo–Turkana Basin have been dated using the 40 Ar/ 39 Ar single crystal total fusion method on anorthoclase, yielding eruption ages...

...IAN McDOUGALL; FRANCIS H. BROWN Abstract The Omo–Turkana Basin of northern Kenya and southern Ethiopia developed in the northern Kenya Rift about 4.3 Ma ago in the Early Pliocene. Nearly 800 m of sediments, included within the Omo Group, crop out in the basin. Numerous rhyolitic tuffs...

... of tuffs that is derived is consistent with 40 Ar/ 39 Ar ages reported separately, and provides the stratigraphic framework for interpreting those ages. Further, new correlations are established to the Konso Formation in southern Ethiopia. As drainage from the Ethiopian Rift to the Omo–Turkana Basin...

...Ian McDougall; Francis H. Brown Abstract The Plio-Pleistocene Koobi Fora Formation, about 560 m thick, crops out east of Lake Turkana and is part of the much larger depositional system of the Omo–Turkana Basin. The upper half of the Koobi Fora Formation from just below the KBS Tuff to above...

... in a northeasterly direction. About 4.3 Ma ago, in the Pliocene, the Omo–Turkana Basin formed in the northern part of the Kenya Rift in relatively low country between the Kenya and Ethiopia domes, where the sediments of the Omo Group accumulated. The domes are often regarded as related to underlying mantle plumes...

...BEREKET HAILEAB; FRANCIS H. BROWN; IAN McDOUGALL; PATRICK N. GATHOGO Abstract A little before 4 Ma ago, deposition of Pliocene and Pleistocene strata described as the Omo Group began in the Turkana and Omo basins of northern Kenya and southern Ethiopia. Soon after, basaltic magma erupted as thin...

... our ancestors’ paleobiology. In eastern Africa, the Ngorongoro Volcanic Highlands, Omo-Turkana Basin, and Awash Valley contain many paleontological sites that have produced a comprehensive fossil record of human origins and exhibited the geologic setting of the last six million years. Allia Bay...

..., 1994 ) ( Figs. 3 and 4 ). The seismically and volcanically active Turkana-Omo rift is to the east of the Lotikipi-Kibish rift, and it branches northward into the North Omo and Usno basins ( Figs. 3 and 4 ). Geological Society of America 2000 Phonolite flows from eruptive centers...

.... 2006 ). A number of Turkana Basin tuffs contain pumice clasts that host feldspar (typically anorthoclase) crystals, which are the primary target for 40 Ar/ 39 Ar geochronology. Ages are available for c. 40 Omo Group tuffs, ranging from 4.23 ± 0.01 (2 σ ) Ma (unnamed tuff, Apak Member...

... sequences that enable the evaluation of climatic influences on hominin evolution ( F ig . 3 ). During the Plio–Pleistocene, magmatism and faulting migrated eastward to the basins of the Omo-Turkana Rift, the current locus of subsidence and magmatism. A phase of magmatism and faulting at 3–2 Ma along...

... it existed primarily as a fluvially-dominated rift basin. During relatively short time intervals, rift lakes formed in the basin, including the most recent, modern Lake Turkana, which is fed primarily by the Omo River draining from the Ethiopian Highlands to the south. The Omo River is hypothesized...

.... 2016 ). 1, Koro Toro (Chad); 2, Northern Awash Basin (Ethiopia); 3, Middle Awash Basin (Ethiopia); 4, Fejej (Ethiopia); 5, Turkana Basin (Omo, Koobi Foora, West Turkana, Kanapoi, and Allia Bay; Kenya); 6, Lothagam (Kenya); 7, Laetoli (Tanzania); 8, Makapansgat (South Africa); 9, Sterkfontein...

... Kenya:Los Angeles County Natural History Musuem Contributions in Science , 498 . 9 – 20 . Feibel , C.S. , Brown , F.H. , and McDougall , I. , 1989 , Stratigraphic context of fossil hominids from the Omo Group deposits, Northern Turkana Basin, Kenya and Ethiopia : American Journal...