Distal tephras of the eastern Lake Victoria basin, equatorial East Africa: correlations, chronology and a context for early modern humans

Abstract

a b s t r a c tThe tephrostratigraphic framework for Pliocene and Early Pleistocene paleoanthropological sites in East Africa has been well established through nearly 50 years of research, but a similarly comprehensive framework is lacking for the Middle and particularly the Late Pleistocene. We provide the first detailed regional record of Late Pleistocene tephra deposits associated with artifacts or fossils from the Lake Victoria basin of western Kenya. Correlations of Late Pleistocene distal tephra deposits from the Wasiriya beds on Rusinga Island, the Waware beds on Mfangano Island and deposits near Karungu, mainland Kenya, are based on field stratigraphy coupled with 916 electron microprobe analyses of eleven major and minor element oxides from 50 samples. At least eight distinct distal tephra deposits are distinguished, four of which are found at multiple localities spanning >60 km over an approximately north to south transect. New optically stimulated luminescence dates help to constrain the Late Pleistocene depositional ages of these deposits. Our correlation and characterization of volcaniclastic deposits expand and refine the current stratigraphy of the eastern Lake Victoria basin. This provides the basis for relating fossil-and artifact-bearing sediments and a framework for ongoing geological, archaeological and paleontological studies of Late Pleistocene East Africa, a crucial time period for human evolution and dispersal within and out of Africa.

Reconstruction of Late Pleistocene Paleoenvironments Using Bulk Geochemistry of Paleosols from the Lake Victoria Region

“…More recently, this research has expanded to include the deposits around the region known as Karungu ∼40 km to the south near the town of Sori (Figure 1; Beverly et al, 2015a,b;Blegen et al, 2015;Faith et al, 2015). Abundant fossils and MSA artifacts have long been reported from Karungu and Rusinga and Mfangano Islands (Pickford, 1984;Owen, unpublished manuscript), but until recently only limited geological mapping and reconstructions of the paleoclimate or paleoenvironment have been conducted.…”

“…Abundant fossils and MSA artifacts have long been reported from Karungu and Rusinga and Mfangano Islands (Pickford, 1984;Owen, unpublished manuscript), but until recently only limited geological mapping and reconstructions of the paleoclimate or paleoenvironment have been conducted. Karungu and Rusinga and Mfangano Islands were originally mapped by Oswald (1914), Kent (1942), Van Couvering (1972), Whitworth (1961), and Pickford (1984) and have been more intensively mapped by Beverly et al (2015a,b), Blegen et al (2015Blegen et al ( , 2016, and Tryon et al (2010Tryon et al ( , 2012Tryon et al ( , 2014.…”

“…Tephra deposits can be correlated between sites on the basis of geochemical compositional similarity and have been dated by multiple radiometric methods (Tryon et al, 2010;Beverly et al, 2015b;Blegen et al, 2015Blegen et al, , 2016). Four named tuffs are used to correlate the sections between Rusinga Island and Karungu: Wakondo, Nyamita, Nyamsingula, and Menengai.…”

“…Here we present data from stratigraphy, micromorphology (petrography), and bulk geochemistry from six Late Pleistocene sites from northeastern Lake Victoria in Kenya that were deposited between 94 and 36 ka Beverly et al, 2015b;Blegen et al, 2015). These sites sample an approximately 55 km-long north to south transect along the eastern margin of the modern lake: Rusinga Island (n = 2), Mfangano Island (n = 1), and Karungu (n = 4) (Figure 1; Tryon et al, 2014Tryon et al, , 2016Beverly et al, 2015a,b;Blegen et al, 2015;Faith et al, 2015;Garrett et al, 2015).…”

“…These sites sample an approximately 55 km-long north to south transect along the eastern margin of the modern lake: Rusinga Island (n = 2), Mfangano Island (n = 1), and Karungu (n = 4) (Figure 1; Tryon et al, 2014Tryon et al, , 2016Beverly et al, 2015a,b;Blegen et al, 2015;Faith et al, 2015;Garrett et al, 2015). These deposits are all part a sequence of late Pleistocene deposits around the northeastern margin of Lake Victoria and the stratigraphy is dominated by paleosols, freshwater tufa, fluvial deposits, and volcaniclastic deposits (tuffs) that can be geochemically correlated between outcrops (Tryon et al, 2010Van Plantinga, 2011;Beverly et al, 2015a,b;Blegen et al, 2015Blegen et al, , 2016Faith et al, 2015). The objectives of this study are to: (1) use field and micromorphological observations of paleosols and bulk geochemical proxies for paleoenvironment and paleoclimate to reconstruct a series of paleo-CZs across the northeastern margin of Lake Victoria, (2) provide additional context for fossil fauna and MSA sites, and (3) integrate observations and MAP estimates into other Late Pleistocene reconstructions of regional paleoclimate and paleoenvironment to better understand their impact on human evolution and dispersal.…”