1999 Field Season: Day 11

July 5, 1999

Back to work today, after yesterday's R'n'R.

We hit our target at Site 15 today; the paleosol layers that contained the elephant fossils we originally excavated. Just within this layer we began uncovering fossils very different from those above. While the microfauna are present in this layer as well, we are uncovering bones of large grazing animals, which is consistent with the switch from diatom-rich sediments to soils. We are going to excavate the layers following the contours of sediments from here on out, instead of sticking to arbitrary 5 cm thick spits. This is done to ensure that artifacts and fossils are properly assigned to the correct sedimentary environment, as well as to aid our attempts to reconstruct the landscape of the basin at this period. Continued excavation should soon uncover the level with the curious stone cobbles.

New fossils of large grazing animals at Site 15.
New fossils at Site 15.

Our microfuana project continues, with our concentration shifting to the sieving of samples from several of last year's fossil sites. Bags of sediment taken from the excavations are analyzed for both fragments of bone and stone tools. A useful byproduct of our microfaunal analysis is that small flakes of stone tool, which would have ordinarily gone unnoticed, can also be recovered at the same time as the bone. Thus we not only can reconstruct ancient environments with our efforts, but also determine if a sufficiently large number of stone tools are going unnoticed to warrant careful examination of all of the previously excavated sediment.

Jennifer Clark and Chris Bolton search for tiny bones in the dirt from the excavations.

The transit expedition to place three datum points in Locality B, which we had tentatively planned for today, had to be postponed until tomorrow. While checking the data from the test run, we noticed a 7 cm discrepancy between the elevation values we were reading on our instruments and those we had recorded. While a 7 cm error may not seem like a whole lot at distances of over a football field in length, remember our instrument is sensitive to changes of only 5 mm, at distances of up to a kilometer. We were worried that the transit might need adjustment. So today we tested the transit and the team at two known points in our camp. They were able to gauge the elevations of the test points to within 3 mm, well within the confidence limit of the machine. We believe that there has been some disturbance in the position of one of the test datums we used. Since we haven't visited these transit sites in nearly 6 years, it is possible that some movement due to small earthquakes has occurred that has altered the elevation of one or both of the points to create the error we were noticing. The important thing is that the transit works.

Testing the transit.