Plio-Pleistocene wood from the Lower Omo Valley, Ethiopia: paleoenvironnemental implications for paleoanthropological and paleontological sites

Plio-Pleistocene sediments of the Shungura Formation in the Lower Omo Valley in Ethiopia, have been intensively prospected for their abundant African fossil fauna, including early hominin remains. In this paper, we present descriptions of 65 wood samples collected in these sediments and dated from 3.6 to 1.7 Ma. Geological studies performed during half a century all over the Turkana Lake Basins now provide precise absolute dates for each of the fossil wood samples we have studied. A total of 17 botanical families, 26 genera and four species are identified, all belonging to tropical taxa. Most of them bring new information that increases present knowledge of the late Cenozoic flora from the tropical lowlands of Ethiopia. Our interpretation of the past environment of the studied area shows the occurrence of a permanent and dense riverine forest, with tall trees and diversified taxa that varied through time. Taxa of humid tropical forests occurred during the Late Pliocene. Deciduous trees indicating seasonal climate attested to variations in the amount of rainfall and the length of dry seasons that persisted throughout the Pleistocene. These changes are discussed in parallel with other indicators such as pollen and fauna. Reconstruction of the past environment at the selected time intervals of fossil wood deposition emphasizes the great diversity of past ecosystems available to early hominins mainly Australopithecus, Paranthropus and Homo found in the Lower Omo valley during this time interval.