Early Pleistocene lake formation and hominin origins in the Turkana–Omo rift

• Magnetostratigraphic records of the Turkana–Omo rift.
• New observations on the timing and cause of lake formation in East Africa.
• Paleo-Lake Lorenyang expanded diachronously at 2.14–1.95 Ma.
• Volcano-tectonism damming the SE Turkana basin coincided with lake formation.
• Case study provides some contrasts to climate-based interpretations of hominin evolution and lake formation in East Africa.

Prior research has correlated the formation of Plio-Pleistocene lakes in East Africa to global/regional climate changes and interpreted the lacustrine basins as significant settings of hominin evolution. Paleo-Lake Lorenyang from the Turkana–Omo rift is important to these issues, as its marginal deposits contain some of, if not the earliest currently known specimens of Acheulian stone tools and African Homo erectus. Magnetostratigraphic and sedimentological evidence indicates that the oldest preserved paleo-Lake Lorenyang deposits are dated at 2.148–2.128 Ma and derive from the NW Turkana basin, predating those from the Omo basin by ∼100 kyr and the NE Turkana basin by ∼190 kyr. Apparently, the lake expanded asynchronously in the rift, potentially due to a volcano-tectonic influence on the location of drainage networks, depositional slopes, or topographic elevation differences within and between the basins at the time of flooding. The onset of the lake temporally coincides with the eruption of basalt lava flows dated to 2.2–2.0 Ma that blocked the southeast outlet of the Turkana basin. This provides a plausible mechanism for hydrologic closure and lacustrine basin formation through volcano-tectonic impounding. It also points to a non-climatic cause for the initial formation of paleo-Lake Lorenyang at ∼2.14 Ma. First appearances for African H. erectus (∼1.87 Ma) and Acheulian tools (∼1.76 Ma) in the Turkana–Omo rift postdate the lake's initial formation by about 270 kyr and 380 kyr, respectively. Such timing differences contrast with studies that correlate all three to the 400-kyr-eccentricity maximum at 1.8 Ma. Although the Turkana–Omo rift is just one example, it does provide alternative insights to views that link climate, hominin evolution, and lake formation in East Africa.