MINERALOGICAL AND GEOCHEMICAL TRENDS FROM MODERN SURFACE AND OUTCROP SAMPLES OF THE SOUTHERN KENYA RIFT

Samples were collected from modern surface and outcrop localities throughout the Southern Kenya Rift for mineralogical and geochemical analysis to characterize the parent material and weathering patterns of fluviolacustrine and volcanogenic sediments in the southern Kenya Rift. This will help support efforts underway by a number of projects in the region that have drilled rift basin sediments in an effort to understand the relationships between terrestrial environmental change and hominin evolution (Cohen et al., 2016; Campisano et al., 2017). A suite of 41 samples from the Koora and Magadi Basins were analyzed for this study, including volcanic material, soils, and volcanogenic sediments. Principle component analysis of X-ray diffraction data revealed four clusters. Principal Component 1 is comprised of mostly trachytic material and minor zeolites and pyroxene; this largely originates in the western part of the region near the Nguruman Escarpment and Nasikie Engida (Little Magadi). Principal Component 2 contains calcite, trona, quartz, feldspathic material, pyroxene, zeolites, magadiite, and other evaporites, mostly contained in samples from the Magadi Basin. Principal Component 3 contains quartz, feldspars, and zeolites, mostly from the Olorgesailie Basin, Ol Kejo Nyiro, and Ol Doinyo Nyokie. Principal Component 4 is comprised of quartz, feldspars, pyroxene, hematite, and magnetite, mostly pedogenic material from the Kiserian region – in the highlands to the north of Koora and Magadi. Geochemical analyses indicate that there is a strong positive correlation between Fe, Al, Ti, and P (detrital); Si and K (sanidine); and Na vs. LOI (trona). There is a strong negative correlation between Na, Al, Fe, and Mn (basalt vs. trachyte source); and Si, Mn vs. LOI (perhaps chert?). These data suggest that the material in the Koora Graben is likely sourced to the north, as well as from Ol Doinyo Nyokie, whereas parent material for Lake Magadi sediments is primarily sourced in the west near the Nguruman Escarpment and to a lesser extent from the east near Ol Doinyo Nyokie. This study will help inform our understanding of sedimentary processes in the southern Kenya Rift by providing insight as to potential sources of parent material for southern Kenya Rift Basins.