Suitability of Paleosols from the early Miocene Kiahera Formation, Rusinga Island, Kenya for Stable Isotopic Analysis

Abstract

Climate change and concurrent environmental changes play an important role in understanding biological evolution through time, because climate change may be a stressor that promotes flora and fauna adaptations. Nearly a century of geological and paleontological study on Rusinga Island, Lake Victoria, Kenya, has made it a touchstone for understanding early Neogene floral and faunal evolution. This is because sediments that were deposited between ca. 20-17 Ma, during the early Miocene, are famous for the presence of the early ape, Ekembo, as well as more than 100 species of mammals. The basal Kiahera Formation has largely been understudied, but recent preliminary work suggests it contains an abundance of fossil soils (paleosols), as well as uniquely preserved fossils. Here we report on the clay mineralogy of four different paleosols within the Kiahera Formation using x-ray diffraction (XRD) analysis. Preliminary XRD analysis reveals samples dominated by illite, kaolinite, and mixed layer clay minerals. In particular, sample LM17KF contained an abundance of clay minerals, no evidence of diagenetic alteration, and the desired two clay mineral suite of illite and kaolinite. This sample was determined to be the most robust candidate for future stable isotopic analysis. These results advance our ability to quantitively assess climate on the island, particularly in a formation that is important for its small mammal communities. Furthermore, this work, suggests there are phyllosilicates that are appropriate for 18O analysis which may result in our better understanding the role the East African monsoon played in the environment during this time.