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Part III. Regional Studies in the Gregory Rift Valley |
The geological setting of the Kilombe Acheulian site is described. A single horizon yields a prolific artifact assemblage from an erosion gully floor 200 m N–S and E–W. The sequence is underlain by deeply weathered phonolite lava upon which a red-brown clay wash has accumulated. The artifact horizon lies on the almost planar clay surface and is sealed beneath pale weathered pumice tuff exhibiting weak palaeosols. The upper part of the sequence commences with a three banded tuff, that appears to have been deposited in still water, succeeded by reworked tuffs cut by several deep channels of fluviatile origin and overlain by a coarse ash flow tuff. The underlying phonolite is dated at 1.7 m.y. by K-Ar and the palaeomagnetic polarity of the three banded tuff is reversed suggesting an age in excess of 0.7 m.y. The Acheulian assemblage lies between these two limiting dates.
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