Tephrostratigraphy of the eastern Lake Victoria Basin including the Nyanza Rift, Kenya: Building a stratigraphic and chronological framework for modern human evolution

Abstract

Modern human evolution in Africa over the last ∼300 kyr is complex, with a variety of behavioral and biological changes appearing at different times and places. Explaining this pattern, as well as its relationship to paleoenvironmental circumstances, requires chronological and stratigraphic control of the paleoanthropological record. This study employs tephrostratigraphy, the chemical correlation of volcanic ashes (tephras), to provide chronostratigraphic context for modern human evolution in the Middle Pleistocene–Holocene of equatorial East Africa. This work geographically expands the eastern Lake Victoria Basin tephrostratigraphic framework over an area >16,000 km2. Geochemical comparisons show that most eastern Lake Victoria Basin tephras are derived from the volcanoes of the Central Kenyan Rift. New tephra correlations in the eastern Lake Victoria Basin incorporate 11 terrestrial localities throughout the Nyanza Rift as well as the V95–1P sediment core from the Ugandan waters of Lake Victoria. The spatial expansion of the eastern Lake Victoria Basin tephrostratigraphy also extends the previously documented ∼94–36 ka chronology of the tephra sequence to encompass most of the last ∼240 kyr. Tephra correlations presented here provide new ages for previously excavated, but undated, archaeological sites including Songhor (GqJe-1) = >94 ka, Simbi (GrJe-2) = 45–36 ka, and Muguruk (GqJc-1) where the correlation of a ∼49–36 ka tuff may help constrain the age for some or all of the site’s multiple archaeological levels. The tephrostratigraphy presented here thus constitutes a necessary step in expanding a Middle Pleistocene–Holocene chronostratigraphic framework across equatorial East Africa, which is fundamental to future studies on modern human evolution and behavioral change through time.