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 sediments 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 paleochemical properties of lake sediments analyzed by inductively coupled plasma optical emission spectrometry and inductively 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 occupations return during this exorheic/freshwater lake phase.

Lake-level changes and hominin occupations in the arid Turkana basin during volcanic closure of the Omo River outflows to the Indian Ocean – comment on the published paper by Boës et al. Quaternary Research (2018), Vol. 91.2, 892–909

“…In conclusion, once published, we believe fully that our results are free to be reused by colleagues; thus, we acknowledge Boës et al (2018) for their confidence in incorporating our work. Our main concern, however, remains that our data were not properly transcribed.…”

“…Third, the transformation of our original geological section raises suspicions and fosters a more critical view of their hypothesized lake-level curve ( fig. 6A, 6B, and 9B in Boës et al, 2018). At least for the time interval between 1.95 and 1.72 Ma, the highstand does not coincide with an insolation maximum at 65°N; a perfect example is the 1.78 Ma insolation peak that rather coincides with a lowstand (Fig.…”

“…In a recent paper, Boës et al (2018) propose a reconstruction of paleolake water-level changes in the Turkana Depression from ca. 2.4 to 1.7 Ma.…”

“…1). Boës et al (2018) propose two general transgressions, the first ca. 1.93-1.88 Ma and a second ca.…”

“…1.82-1.78 Ma ( fig. 6B and 9B in Boës et al, 2018). These are separated by two general regressions from ca.…”