Stratigraphy of the Koobi Fora Formation (Pliocene and Pleistocene) in the Ileret region of northern Kenya

Exposures of Pliocene and Pleistocene deposits in the Ileret region include all eight members of the Koobi Fora Formation and represent at least 533 m of section from the base of the Lonyumun Member to the top of the Chari Mb. This thickness is more than twice that reported by earlier workers (～260 m) and compares well with the composite section of the Koobi Fora Formation (525 m). Thus the Ileret region provides a very complete and representative outcrop of the Koobi Fora Formation. As Koobi Fora Formation member boundaries are placed at the base of specified tuffs, not all member boundaries can be recognized in the Ileret region. For this reason, the stratigraphy is described in terms of the following members (thicknesses in parentheses): Lonyumun (110 m), undifferentiated Moiti and Lokochot (104 m), Tulu Bor (54 m), Burgi (55 m), KBS (74 m), Okote (45 m), and Chari (93 m). Moreover, the boundary between the Okote Member and the KBS Member in the Ileret region is placed at a prominent caliche which must closely approximate the age of the Okote Tuff in its type section.