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Day 25 (July 20, 2011): Puzzle of the Paleo-channel

July 20, 2011

While I’ve been away in western Kenya, the researchers at Olorgesailie welcomed to camp a member of our field team – John Yellen.  John, who just arrived in Kenya from the U.S., is Alison’s husband and has been doing archeological research in Africa for many years. This morning, I received the following update from Katie about the work going on at Olorgesailie:

Looking down onto the excavation floor, many artifacts sit on small dirt pedestals. The 2 meter squares, outlined with twine and nails, are labeled F7, F8, G7, and H7.

One of the dense areas of artifacts uncovered at site BOK-2
Today, Alison and Katie took John to BOK-2 to show him the latest finds in the excavation.  For the past few years, BOK-2 has progressed in this manner:  Just as everyone thought the excavation was about to reach the end of the artifact concentration, another interesting assemblage of stone tools would be discovered.  This has been the case for 2011!

The most recently uncovered assemblage, however, is unique.  First of all, the sheer concentration of artifacts is astonishing.  Kamula Kawaya, one of our crew members, uncovered over 150 artifacts in just one meter square – which makes it the densest tool assemblage from BOK-2.

Four men are sitting in the corner of an excavation site using hammer and picks to unearth fossils and stone tools

The crew excavates the wall neighboring the newly uncovered assemblage
The distribution of the artifacts is also peculiar.  It consists of a dense patch of artifacts in the middle, with less dense areas trailing out on both ends. Based on the pattern, it is clear that the formation of artifacts continues into the excavation wall. Luckily, the wall was only the side of a test trench dug some years before, and which had been left standing for geology purposes. To uncover the remaining lithics, the crew only had to patiently excavate the wall down to the newly discovered artifact level.

Yet every excavation adds questions as well as answers – and new questions now have to be asked at BOK-2.  Why was the stone assemblage so concentrated in this newly discovered layer of the excavation?  Was the assemblage originally at the bottom of an paleo-river or stream channel, where water had transported the lithics? A channel is a narrow passage where water runs, usually carrying with it sediments and other materials.  Or was the assemblage the result of human agency, in which the toolmakers repeatedly visited or occupied the channel during the dry season?  If so, why did they come so often to the spot we now refer to as BOK-2? To answer these questions, we need to know more about the stratigraphy, the order and position of the layers in which the stone tools were found.

When Rick returns, he’ll be bringing geologist – Kay Behrensmeyer – with him, who has been leading the study of the Olorgesailie sediments for many years.  One other question about BOK-2 is whether the paleo-channel that contains the finds at this site is lying directly on top of the older Olorgesailie Formation.  If so, then this Middle Stone Age excavation is near an end, and Alison will have completed the discovery of the finds at this site.

For now, Alison, Katie, John and the crew have their hands full preparing for the biggest lift of the season. The crew meticulously excavates around each artifact while Katie is writing over 500 bags to archive each new find. Alison is photographing and mapping out the location of artifacts in each square. We look forward to learning more about the finds at this excavation!