Pleistocene paleosol development and paleoenvironmental dynamics in East Africa: a multiproxy record from the Homo-bearing Aalat pedostratigraphic succession, Dandiero Basin (Eritrea)

The climatic changes during the Early-Middle Pleistocene transition are a key to understand the ecosystem dynamics that involved the Homo erectus-ergaster distribution. The Aalat pedostratigraphic succession represents a continental archive in the African Rift Valley (Eritrea), where remains of Homo around 1 Ma were identified. High-resolution magnetostratigraphy dated this succession between the base of the Jaramillo subchron and the lower Brunhes chron. Despite the present arid, desert climate, the Aalat section records a persistence of water-driven, fluvio-lacustrine environments, which suggests a major tectonic control on sedimentation, although climate changes are clearly overprinted. Macro- and micromorphological, physico-chemical, mineralogical and geochemical features, up to now poorly available for Pleistocene paleosols in East Africa, depict a poor to moderate degree of development, although calcic and petrocalcic/petrogypsic horizons at different stratigraphic heights indicate phases of geomorphic stability. The concurrent alternation of these horizons with iron-stained layers suggests cyclical changes from dry to wet conditions, which fit well with aeolian dust fluxes and marine isotope stages of glacials and interglacials at higher latitudes. Stable isotope data are consistent with these climatic cycles and suggest a succession of monsoonal and non-monsoonal conditions. The Homo erectus settlement lasted apparently for a short time span, because a long, high-discharge fluvial sedimentation (and/or an aridity phase at the base of the fluvial facies) could have made the area less suitable for human settling and could have hindered preservation of fossils and artifacts.