July 28, 2004
Today was the last day of the Geology Field Course, and this morning I was able to listen in on a few of the students' final presentations. One project they've been working on during the past three weeks is to compare the geology and fauna of lower Member 11 between Locality A and Locality B. As you may recall, we divide up the Olorgesailie region into localities, with Locality A in the central part of the basin, and Locality B nestled close to the foothills of Mt. Olorgesailie to the south.
Kay has taught the students the basics of how to record each geologic layer, and a really fun part of the course for the students was the chance to look for fossils in the two localities. Lower Member 11 is between two pumice layers, the lower one dated 662,000 years old, and the upper 601,000 years old. The students noted that the sediments in Locality A are thicker, which could mean that this locality was closer to the ancient lake. The thinner amount of sediment in Locality B, then, would indicate an area further from the central, deeper part of the basin. But there's a problem! The thicker deposits of Locality A show more evidence of alteration by vegetation - that is, soils developed in this area due to the growth of plants on stable terrain. Couldn't this mean that this area was further from the lake, not closer?
The plot thickened as the students then turned their attention to the fossils found on the surface in these two localities. It turns out that Locality B, closer to the foothills of Mt. Olorgesailie, produced more fossil bones of hippopotamuses and turtles - animals that like water - while more land-loving animals like antelopes and pigs were found in Locality A. The balance of the evidence, both geologic and fossil, is that there was more water in Locality B than Locality A.
But these students are really clever! They noted that we're not sure yet whether the watery environment of Locality B was mainly lake or a series of streams and small rivers that would have been attractive to the hippos and turtles. In Locality B, we see evidence of lake deposits and of channels carved into the lower deposit (Member 10) and then filled up with sediment. So the students were really keen on excavating! We need more information about where exactly in the sediment layers the fossil bones are coming from. The fossils eroded out and lying on the surface of the lower Member 11 slope give a first good idea about the possible difference in environment from one place to another and from one time to another. But careful digging and recording is needed to tell us whether the hippos and turtles in Locality B and the antelopes and pigs from Locality A were living, dying, and becoming fossils at the same time.
I was really happy to hear the conclusions drawn by these excellent students! They've learned a lot about being really precise and careful when studying the geologic layers and finding fossils. Oh, yes, another thing: they did a marvelous job of discovering handaxes (see photo) and other stone tools during their survey. I think next year, we'll do a lot of slow and detailed digging of lower Member 11 in the two localities.