Isimila Prehistoric Site, Tanzania: Comparative Faunal Datings and ESR, with a Reassessment

More than sixty years ago, 1957-58 University of Chicago excavations at the Isimila Prehistoric Site in the Southern Highlands of Tanzania exposed a sequence of Pleistocene deposits that included Earlier Stone Age aggregates. Now, the available correlations with extinct fauna from other dated East African localities and preliminary electron spin resonance (ESR) estimates indicate that the Isimila Formation was deposited over a much longer time range than originally proposed. As originally noted, Earlier Stone Age 'large cutting tools' or LCT's found in the upper Lisalamagasi Member are more refined than are those found in the Sands units of the lower Lukingi Member. This suggests a correlation with Kalambo Falls Prehistoric Site for the upper member, with new OSL dating at ca. 400-500 ka. The new faunal correlations and ESR estimates indicate that the lower member was deposited between 500 and 900 ka, during the later Early Pleistocene to the early Middle Pleistocene. A reassessment of Isimila including unpublished excavation data raises questions about the Pleistocene human occupations and their palaeoenvironments on the Highlands Plateau.