THE PETROLOGY AND PETROGRAPHY OF MIDDLE PLEISTOCENE VOLCANICS: KAPTHURIN FORMATION, KENYA

Pleistocene Kapthurin Formation (0.8-0.2 Ma) outcrops near Lakes Bogoria and Baringo, in the East African Rift System. The volcaniclastic sequence is punctuated by volcanic members (Lower Kasurein “Basalt”, Lake Baringo Trachyte, Upper Kasurein Basalt and Grey Tuff) that are critical for stratigraphic correlation. The texture, mineralogy, and geochemistry are being documented by optical microscopy and electron probe analysis. Incomplete exposure of members requires petrographic correlation across the Kapthurin Basin. Ambiguities of age and composition in Gray Tuff and L. Kasurein “Basalt” were resolved, however the sequence of volcanics is more complex then previously recorded. Identification and classification of the main members have been changed according to modal and geochemical composition.