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2004 Field Season: Day 9
July 1, 2004
Bernie is dusty and desperate for a shower after collecting samples of diatoms from several portions of the Olorgesailie Formation. His goal is to figure out the conditions of the ancient lake and how the lake changed through time. The diatoms are a terrific clue about this. They are single-celled algae that have a silica skeleton easily preserved in sediments. They are very small, many being <0.01 mm. When viewed under a microscope, diatoms fossils are incredibly beautiful, since their skeletons show diverse patterns of slits and holes arranged in intricate ways. It turns out that patterns help distinguish between the several thousands of species of diatoms. Bernie drew pictures of several species of diatoms common to the Olorgesailie Formation - see the photos at the bottom of the page.
Diatoms first appeared in ocean deposits during the Cretaceous Period (see our web site page on Geologic Time). Lacustrine (or lake-living) diatoms, such as those at Olorgesailie, first appeared during the Miocene, about 15 million years ago. Their value to Bernie's work lies in the fact that different species of diatoms live under different environmental conditions. Some diatoms are found only in deep water, while others live in shallow water. Several species live as epiphytes on reeds and other aquatic plants. When these occur in large numbers in the fossil record they suggest swampy settings. Diatoms are also valuable indicators of water chemistry and are able to provide information on water pH, conductivity, and silica levels, and can also provide useful information about the water nutrients such as phosphorus.
At Olorgesailie, Bernie uses the fossil diatoms preserved in layers of white sediment to provide a detailed record of environmental change in the ancient lake, particularly water pH, conductivity, water depth, and the presence of reeds and other aquatic plants. He already has some data from earlier work that suggest a variable fresh to alkaline lake (Member 1) that gave way to a relatively deep, freshwater, environment (M2). Data from parts of the middle Members indicate that the lake sometimes became very alkaline, before returning to fresher conditions in the younger layers. But there are gaps in the earlier work, which was done before our team found out that the Olorgesailie record spans many hundreds of thousands of years. The aim of Bernie's work is to fill these missing parts of the lake story at Olorgesailie.