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サンブルピテクスの生息した960万年前のサンブル丘陵

実吉玄貴（島根大学）

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The Miocene Namurungule Formation yielding the Samburupithecus kiptalami in the lower part of the formation crops out on the northern Kenya Rift, representing basin fill that developed in association with Miocene rifting. The formation is characterized by large volume of volcaniclastics supplied passively by pyroclastic fall, pyroclastic flow and lahar. Facies analysis reveals that this formation consists mostly of lacustrine delta deposits with minor alluvial fan deposits as its base. The alternation of sandstone beds with wave generated structure and massive mudstone beds with rootlets implies that the seasonal lake level change had been influenced in this basin. The rarity of fluvial channel fill deposits and the mainly of volcaniclastics in the lower part of the formation can also be explained by the immaturity of the drainage system. These evidences suggest that Samburupithecus kiptalami had been transported to short distance from around basin.

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