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Show HONORS COLLEGE SPRING 2013 CORRELATION OF ASH LAYERS FROM THE ISINYA, KARIANDUSI, AND OLORGESAILIE FORMATIONS, SOUTHERN KENYA Hannah Durkee (Francis H. Brown) Department of Geology and Geophysics University of Utah Isinya, Kariandusi, and Olorgesailie are archeological sites in the southern Rift Valley of Kenya. Thick diatomite deposits at Kariandusi and Olorgesailie suggest that the formations are related in age. Members of the Olorgesailie Formation are numbered from the base to the top, with Member 1 dated at 992 ka, Member 5 dated at 974 ka, and Member 9 dated at 747 ka, determined by the 40Ar/39 method on feldspar from tuffs in the sequences. At Kariandusi, there are two ages of 960 and 980 ka. Glass phase compositions were obtained on samples from volcanic ash layers from each of the sites by electron microprobe analysis. Based on the data obtained, tephrostrati-graphic correlations can be made at five levels. In particular, four sets of samples from the upper layers of Kariandusi, below the archeological site, correlate with samples from Olorgesailie Member 4 and Member 2 that lie between ash layers dated at 992 ka and 974 ka. Furthermore, samples from Isinya also correlate with an ash layer in Olorgesailie Member 4, showing that they are of similar age, ~ 960 ka. This is the first age estimate available for Isinya. The direct correlations show that diatomites were deposited at the same time in sites approximately 120 km apart but which now differ in elevation by -700 m. It remains to determine whether the diatomites at these different elevations were deposited in the same water body, in which case those at Kariandusi have moved up at an average rate of 0.73 mm/yr, or whether they were originally deposited at different elevations. The ash layers have also been compared with analyses of obsidian samples from southern Kenya, and some may originate from the area south of Lake Naivasha. t NAKURU * » * » ~ ^ Kariandusi 05 S \ Lake 4^p \ Naivasha \ ^=TT1 **-•'NAIROBI • Olorgesailie K 50 km r^lsenya Lake I \ ^Ma„aM365l I 37QE \ 3?SE CORRELATIONS OF ASH LAYERS AT SOUTHERN KENYA SITES „ 070pl|B.8y«> L. -070p2(86ye> 116 IB Bye! KEYTOUTHOLOGY m S3 m • m m -**- E&J \\ ««*.».*.« P u * * . * , * . *, Sdndvopc LamJruicd tltuionr Poorly KtftttJ d*yitorw Ajrhllnh OtJtomli* dtpoUt TuffbodlttwirMn dUtomkt 1MJ-Tuir«riuny* |
