Lake Cycles and Sediments: Locality 80, Olduvai Gorge, Tanzania

Studies have shown that Bed I and Lower Bed II (1.92Ma- 1.76Ma) of Paleolake Olduvai at Locality 80 are primarily composed of the authigenic lacustrine clay minerals illite, smectite, and interlayered illite-smectite. X-ray fluorescence analysis and the sedimentation rates of Hay and Kyser (2001) were used to identify four apparent lake cycles beginning and ending with saline alkaline phases. Peaks in Al2O3/MgO ratios, and TiO2 and P2O5 abundances occur at approximately the same elevations within the stratigraphic section. Low values in these three parameters indicate saline alkaline conditions whereas high values represent fresh water conditions. Lake Cycles (LC) 1 and 4 completed in approximately 44,000 years and 42,000 years respectively, which is similar to the 41k.y. year cycle associated with Earth?s obliquity. Lake Cycles 2 and 3 span approximately 24,000 years and are similar to the 21k.y. precession cycle.