Pliocene/pleistocene formations in the lower omo basin, southern Ethiopia

Following a two month geological reconnaissance by one of us (FHB) in 1966, four seasons of fieldwork by members of the Omo Research Expedition has added greatly to our previous, scanty knowledge of the late Cenozoic history of the lower Omo basin in southern Ethiopia. Eduard Suess (in: von Hohnel et al., 1891) was the first to associate the lower Omo basin with the Eastern Rift Valley after the explorations of the Teleki-von Hohnel expedition in 1888 (von Hohnel, 1938). M. Sacchi, geologist with the Bottego expedition, subsequently noted the occurrence of flat-lying, undeformed sediments in the basin and these were reported on by Angelis d'Ossat and Millosevich (Angelis d'Ossat and Millosevich, 1900; Vannutelli and Citerna, 1899). These sediments have since proved to represent an extensive suite of later Pleistocene to recent strata deposited during major northward extensions of Lake Rudolf and of the delta and floodplain of the Omo River (Butzer and Thurber, 1969). E. Brumpt first collected fossils from older, tectonically disturbed sediments in the lower Omo basin when the Bourg de Bozas (Bourg de Bozas, 1903) expedition traversed the area at the turn of the century. Haug (1912, p. 1727) recognized that these specimens were of some importance in the study of the Pleistocene of eastern Africa. Two decades later, the late Prof. C. Arambourg (Arambourg and Jeannel, 1933) made a geological reconnaissance of a part of this area and amassed a substantial collection of vertebrate fossils from these deformed deposits, which he termed the Omo Beds. His pioneer work placed on record the richness and diversity of this fauna which he regarded as of earlier Pleistocene age.