Paleoclimate reconstruction from pedogenic carbonates from the early Miocene Wayando and Kiahera Formations, Rusinga and Mfangano Islands, Lake Victoria, Kenya and the impact on early ape evolution

Abstract

Changes to climate and resulting changes to ecosystems are thought to be stressors leading to evolutionary adaptions. Early Miocene deposits on Rusinga and Mfangano Islands, Kenya, are ideal for studying the impact of environment on evolution and adaptation within early apes. Despite decades of geological and paleontological research there, however, paleoclimate reconstructions have been conflicting, ranging from open and arid to closed and ever-wet environments. Here, we present results from paleosol-bearing deposits in the two oldest fossiliferous units, the Wayando Formation, on Mfangano Island and Kiahera Formation on Rusinga Island. Results show that the Wayando Fm. contains interbedded ashes, groundwater nodules, and carbonate-forming fossil soils (paleosols). In modern soils, pedogenic carbonate is found in environments where evapotranspiration is greater than precipitation – common in semi-arid to arid environments. Results from the Kiahera Fm. show a more violent volcanic history, with volcanic brecca common in the lower units. In the upper Kiahera Fm. there are common paleosols containing vertic features which are in modern soils with seasonal water budget surpluses and deficits. Some paleosols contain pedogenic nodules, though they are much better developed then those found in the Wayando Formation. These formations with semi-arid to arid climate and possibly season climates differs sharply from paleoclimate and habitat reconstructed for the younger Hiwegi Fm., which include woodlands and closed-canopy forests. These results add to a growing body of data showing that Rusinga Group strata contain a wide variety of paleoenvironments in which Ekembo and other early Miocene catarrhines were living.