Takeshi Makinouchi

K-Ar ages of miocene hominoidea (Kenyapithecus and Samburupithecus) from Samburu Hills, Northern Kenya

The Neogene volcano-sedimentary succession west of Baragoi and in the Samburu Hills, northern Kenya has yielded over 200 higher primate fossils, comprising the cercopithecoid Victoriapithecus and the hominoids, Nyanzapithecus, Kenyapithecus and Samburupithecus. K-Ar ages have been obtained from lavas and pumices intercalated with the sediments. The Aka Aiteputh Formation with Kenyapithecus and Nyanzapithecus is dated ca 15-14 Ma while the Namurungule Formation with Samburupithecus is ca 9.5 Ma.

Geology of the Nachola Area and the Samburu Hills, West of Baragoi, Northern Kenya

The Nachola area, about 15 kiloinetres west of Baragoi, is underlain by Precambrian Basement Complex, above which come the Nachola Formation of Miocene age, undifferentiated, probably Pleistocene basalts and Alluvium, in ascending order (Figs. 3, 4 and 6). The Nachola Formation consists of basaltic lavas and clastic sediments. Kenyapithecus occurs in the Nachola Formation. The Samburu Hills, about 30 kilometres west of Baragoi, are underlain by the Aka Aiteputh, Namurungule, Kongia, Nagubarat, and Tirr Tirr Formations, grey silts and fluviatile sedinlents, in ascending order (Figs. 3, 4 and 8). The Aka Aiteputh, Kongia, Nagubarat and Tirr Tirr Formations are mainly composed of accumulations of basaltic and trachytic lavas. The Namurungule Formation is of late Miocene age and consists of tuffaceous alternations of sand and mud with intercalations of mud-flow deposits. The Samburu hominoid, a late Miocene hominoid fossil, occurs in the basal part of the Namurungule Formation (Figs. 9, 10,11,12 & 13). The lower part of the Nachola Formation is correlated with the lower part of the Aka Aiteputh Formation. Many faults, trending nearly N-S, cut the volcanics and sediments in the Samburu Hills and Nachola area (Figs. 14 and 15). These faults form synthetic (western margin of the Samburu Hills) and antithetic fault systems accompanying the tectonic line along the eastern border of the Suguta valley.