Early Pleistocene habitat in Member 1 Olorgesailie based on paleosol stable isotopes

Stable carbon and oxygen isotope values from soil carbonates were used to d etermine the vegetation context of archaeological sites and local climatic conditions represented in a similar to 0.99 Ma paleosol that is exposed lat erally in the Olorgesailie basin, southern Kenya rift valley. As part of th is landscape-scale project, samples of an upper Member 1 paleosol were anal yzed along nearly 4 km of outcrop in three adjacent parts of the basin. Mod em East African soil and plant community analogs are used to interpret. the isotope ratios. The carbon isotopic composition of the paleosol carbonates indicates that the area supported a local biomass of about 75-100% C-4 pla nts during the period of soil formation. After averaging the data for each trench, an open C-4 grassland is represented by half of the carbon values, with wooded grassland more abundant across the paleolandscape than it is in the area now. This vegetational reconstruction is supported by the mammali an faunal assemblage, which has a high percentage of grazers. Although the relatively small sample size outside the main excavation area precludes fir m characterization of vegetational diversity across the basin in upper Memb er 1 times, eastern and western localities in the study area may have had m ore woody C-3 plants than the widely sampled zone in between. Oxygen isotop es indicate that the lowland basin was slightly cooler and moister than tod ay's semi-arid climate, with greater annual rainfall. Archaeological traces have a virtually continuous distribution across the paleolandscape, but va ry in density of occurrence. With the strong evidence for C-4 grassland as the primary vegetation context across most of the study area, no habitat pr eference by the Acheulean toolmakers at Olorgesailie is shown in our initia l comparison between carbon isotope values and stone/bone densities. (C) 19 99 Academic Press.