Students begin leveled profile exercise atop the cut-bank above GaJi12.



Ancient terrestrial beach with cultural material, GaJi12, Koobi Fora Spit.  

Context of Archaeological Remains

  Amid the eroding lacustrine deposits and their many fossils, emergent beach horizons are briefly exposed before being deflated by wind erosion. These horizons are made of oxidized, yellow-brown sands that are frequently cemented just enough to resist erosion for a brief time, forming shelves above shallow blowouts such as you see here. Not the dark, silty clay horizon that covers this horizon on the left, the casts of roots from shore-side vegetation, and the wing of the vertebra that is protruding from the base of the sandy layer. The top of the vertebra is just barely exposed below the white end of the marker.

As you can see from the down-stream striations, the wind has been exposing this surface from right to left. Where the striated surface ends, note the hummock-like topography of garyer colored sand. This is wind-blown sand that is accumulating in the bottom of the blow-out. It is in such blow-outs that most cultural materials are found, with small numbers of specimens recovered from the yellow sand horizons at blow-out margins.

Close-up of a vertebra, GaJi12, Koobi Fora Spit

Close-up from the photograph, above.

Close-up of a vertebra, GaJi12, Koobi Fora Spit

  Here is the same vertebra after a further day of wind erosion. Note the top of the specimen higher in the erosion face.

Rib <i>in situ</i>, Gaji12, Koobi Fora Spit.

  The first of three photos showing the erosion of a rib over a five day period. Notice that the rib was broken and displaced after burial.

Rib <i>in situ</i>, Gaji12, Koobi Fora Spit.

  As the blowout deepens, the end of the rib is dislodged.

Rib <i>in situ</i>, Gaji12, Koobi Fora Spit.

  Despite considerable erosion, the larger rib fragment is still left in situ. This is because the uncemented beach sands below the slightly cemented occupation layer are more easily removed by the wind, which blows parallel to the erosion face, from the foreground to the background in this picture.

Mandible <i>in situ</i>, GaJi12, Koobi Fora Spit.

  Here the slightly cemented sands that form the crust of the occupation horizon have been broken and moved aside, probably by footfall, revealing the front half of a mandible just beneath. There is a large of resident Topi that moves on and off the spit every day. Their regular passage promotes surface erosion in bands parallel to the shore.

<i>In situ</i> specimen damaged by footfall, GaJi12, Koobi Fora Spit.

  Note the fresh fractures on this in situ specimen, also caused by footfall.

Harpoon fragment on erosional pavement, GaJi12, Koobi Fora Spit.

  At the base of the cut-bank, there is a wide pavement of coarse rubble concentrated from four to five meters of eroded deposits. Stone artefacts are common in this rubble, but only dense pieces of fossilized bone survived exposure as the lag concentrate formed over a period of about three decades. Among these, are a few harpoons such as the one seen here as it was found about 20 meters from the base of the cut bank.

Harpoon beneath sandstone slab, GaJi12, Koobi Fora Spit.

  Harpoon found beneath a sandstone slab about 330 meters out from the cut bank. When the slab was lifted, the harpoon was fully exposed in the wind-eroded area that undercut the slab. So it was not quite in situ. In 1993, this scatter of artefacts was about 50 meters long and 20 meters wide. Over the next three years, the scatter grew to a width of 30 meters and a length of 90 meters.

Horn core and grindstone from older Iron Age scatter, GaJi12, Koobi Fora Spit.

  Grindstone fragment and horn core with cut marks found together in an older Iron Age scatter at GaJi12.

Iron Age pot sherd <i>in situ</i>, Gaji12, Koobi Fora Spit.

  This Iron Age sherd was discovered just as the artefact horizon was starting to be exposed.

Iron Age pot sherd <i>in situ</i>, Gaji12, Koobi Fora Spit.

  When exposed further, we can see that the sherd is in a cemented sand with a very thin coating of clay.

Iron Age pot sherd <i>in situ</i>, Gaji12, Koobi Fora Spit.

  This Iron Age sherd is still held in place by a ramp of sand on it's sheltered lee side.

Iron Age pot sherd <i>in situ</i>, Gaji12, Koobi Fora Spit.

  Side-view of the sherd showing the nature of the back ramp.

Iron Age pot sherd <i>in situ</i>, Gaji12, Koobi Fora Spit.

  Here is another more-or-less in situ Iron Age sherd. It is hard to tell if it was stepped on and pressed into a near-vertical position, or if it has been "walking" upwind as its pedestal was eroded on the windward side. Notice the carbonized material on the surface of the sherd.

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