Lake-level changes and hominin occupations in the arid Turkana basin during volcanic closure of the Omo River outflows to the Indian Ocean.

Abstract

In the East African Rift, the western margin of Lake Turkana (northern Kenya) exposes Mio-Plio-Pleistocene lake sedi- ments with dated volcanic horizons constraining basin dynamics at the astronomical time scale. Since the late Pliocene, coastal archaeological sites have formed within the lacustrine dynamics. Here, lake levels are reconstructed from 2.4 to 1.7 Ma using sedimentary facies and water/depth-controlled sediment association. The lacustrine stratigraphy is measured with a total station, and cyclostratigraphy is derived from tephrochronology. The water depths are evaluated from paleo- chemical properties of lake sediments analyzed by inductively coupled plasma optical emission spectrometry and induc- tively coupled plasma mass spectrometry. Our reconstruction highlights that Lake Turkana rose during 100 ka insolation/ eccentricity maxima periods in response to higher monsoonal inputs of the Omo River. However, Lake Turkana also expanded through an insolation minimum at 2.17–1.95 Ma. This asynchronous lake phase coincides with volcanic closure of the Omo River and Lake Turkana outflow sill to the east and the Indian Ocean. An archaeological hiatus occurs during this endorheic lake phase, and alkalinity increases at the beginning of the hiatus. The lake rose again during insolation/ eccentricity maxima at 1.9–1.7 Ma, and a new outflow sill opened to the west and the Nile basin. Hominin coastal occupa- tions return during this exorheic/freshwater lake phase.