RECONSTRUCTING PALEOENVIRONMENT USING SOIL CARBONATE ISOTOPIC DATA FROM THE HOLOCENE GALANA BOI FORMATION, TURKANA, KENYA

The Turkana Basin in northwest Kenya provides a remarkable window to the paleoenvironmental trends for the late Pleistocene to the early Holocene of the region. The creation of a detailed stratigraphic history is key to fully understanding the basin’s environmental history, namely the end of the African Humid Period. This study used oxygen and carbon isotopes from soil carbonates from the Kabua Gorge. The Kabua Gorge located on the western side of Lake Turkana, around 12 km south of the town Kalokol. The carbonate nodule samples originate from the Galana Boi Formation. This formation is composed of marginal lacustrine deposits ranging from deltaic to fluvial environments. The carbonate nodules from this study are from an organic-rick back shale unit within the formation. An AMS radiocarbon date was collected from mollusk shell fragments within this same unit and yielded an age of 7350 +/- 75 Cal BP, which places these sediments to the middle of the African Humid Period. The nodules were crushed to a fine powder then weighed and run through Hamilton College’s mass spectrometer for isotopic data collection. The δ¹⁸O values range from -4.06‰ to -1.55‰ and the δ¹³C values range from -4.67‰ to -2.29‰. In order to connect our data to the basinal trends, this study used previously published isotopic data from soil carbonates across the basin. The data collected in this study is most similar to isotopic data collected by Levin et al., 2011 from the Upper Burgi member from the Koobi Fora formation, found of the eastern side of Lake Turkana. This association is a function of the similarities of the depositional environments of the Kalokal River and Omo River associated with the Galana Boi Formation and the Upper Burgi member, respectively. However, the isotopic data from the Upper Burgi has a much larger spread. This could be due to an increased variation of vegetation in the larger depositional system of the Omo River. Most vegetation found in Eastern Africa is either classified as C₃ or C₄. In this study collected mixed signals showing the presence of both C₃ and C₄ vegetation. The relationship established in this study between the Galana Boi formation and the Upper Burgi is significant as it helps link environmental similarities between space and time.