| Description |
The lowest four members of the Koobi Fora Formation: the Lonyumun Member, the Moiti Member, the Lokochot Member, and the Tulu Bor Member, are exposed in Areas 117, 137 and 116. These deposits include strata that were incorrectly identified as the KBS Tuff and the Surgaei tuff in Findlater's 1976 study. The composite thickness of strata within the study area is approximately 170 m, approximately 100 m of which are deposits of the Lonyumun Member. In addition to these strata, intrusions of Gombe Group basalts are exposed as well as a littoral zone of the lacustrine Galana Boi Formation of Holocene age. A large lake from 4.2-3.99 Ma, a fluvial deltaic system from 3.99-3.40 and a large fluvial system from 3.40-3.06 Ma deposited strata of the Koobi Fora Formation in this region. This observation is consistent with Brown and Feibel's 1991 study. Nine tuffs are exposed in the study area. Two of these tuffs, the Naibar and Aberegaiye Tuff, are newly named in this study. The Naibar Tuff was deposited by fluvial action to the shores of the receding Lonyumun Lake. |
