Age and context of mid-Pliocene hominin cranium from Woranso-Mille, Ethiopia
Résumé
A fossil hominin cranium was discovered in mid-Pliocene deltaic strata in the Godaya Valley of the northwestern Woranso-Mille study area in Ethiopia. Here we show that analyses of chemically correlated volcanic layers and the palaeomagnetic stratigraphy, combined with Bayesian modelling of dated tuffs, yield an age range of 3.804 ± 0.013 to 3.777 ± 0.014 million years old (mean ± 1σ) for the deltaic strata and the fossils that they contain. We also document deposits of a perennial lake beneath the deltaic sequence. Mammalian fossils associated with the cranium represent taxa that were widespread at the time and data from botanical remains indicate that the vegetation in the lake and delta catchment was predominantly dry shrubland with varying proportions of grassland, wetland and riparian forest. In addition, we report high rates of sediment accumulation and depositional features that are typical of a steep topographic relief and differ from younger Woranso-Mille fossil localities, reflecting the influence of active rift processes on the palaeolandscape. Q1 Until recently, field work in the Woranso-Mille area (Afar, Ethiopia) has concentrated on exposures along the Mille River that include more than 120 m of fossiliferous sedimentary and volcanic strata that are between 3.8 and 3.2 million years (Myr) old. East of Korsi Dora (Fig. 1a), sedimentary sequences that are younger than the extra-regional approximately 3.57-Myr-old Kilaytoli tuff 1 have yielded specimens of at least two hominin species, Australopithecus afarensis and Australopithecus deyiremeda 2-5
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