July 22, 2011
Sometimes solving archeological puzzles requires a step back in order to see the big picture.
Our second stratigraphic question at hand regards a layer of sediment at BOK-2: is the gray sandy layer at the base of the excavation, part of the Olorgesailie Formation, or is it in the younger Oltulelei Formation? Answering this question is vital if we are to understand the age of the site and the geological context in which the stone tools have been found. To figure out the answer, we had to take a look outside the site.
While the BOK-2 excavation focuses on the concentration of stone tools within a relatively small area, our project has pioneered the need to look beyond each specific dig to understand the larger landscape. In this case, it means tracing the BOK-2 channel out to the side in an effort to follow the ancient erosion surface and sediment fills of the channel across a long distance. Geological studies of this type involve observing not only individual layers, but more importantly, a series of layers and the relationships among them. Layers of sediment are not always superimposed in a neat cake-layer fashion. More often than not in the Oltulelei Formation, the layers are discontinuous and reflect a complex juxtaposition of sediments deposited in old river channels, floodplains, and swamps that developed as the landscape varied from place to place and as it changed over time. Careful observation of the different types of sediment and how they relate to each other enable geologists to reconstruct the larger context of the archeological finds.
This is exactly what Kay and Naomi did. Up to a hundred meters away from BOK-2, they traced the sediments into a large trough, the bank of which clearly depicts continuous stratigraphy. The stratigraphy shows exactly where the transition from the Olorgesailie Formation to the Oltulelei Formation occurs. By carefully studying this and other outcrops where the transition was visible, Kay and Naomi were able to determine that the gray sandy sediment at the base of the BOK-2 excavation was actually part of the Olorgesailie Formation. This realization is surprising and helps us think about the artifacts at BOK-2 in a different way. Knowing that this gray sediment at the base of the excavation is much older than the sediments containing the artifacts helps explain why we find no artifacts within it.