Implications of geomagnetic field variation for the chronology of the Middle Later Stone Age and Middle Upper Paleolithic transitions

s of the Paleoanthropology Society Meetings Adam’s Mark Hotel, St Louis, Missouri, 1–2 April 1997 0047–2484/97/0400A1+26 $25.00/0/hu970131 ? 1997 Academic Press Limited Implications of geomagnetic field variation for the chronology of the Middle Later Stone Age and Middle Upper Paleolithic transitions Stanley H. Ambrose, Department of Anthropology, University of Illinois, 109 Davenport Hall, 607 S. Mathews Ave., Urbana, Illinois 61801, U.S.A. The transition to ‘‘modern’’ human behavior is marked by the change from the Middle Stone Age (MSA) to the Later Stone Age (LSA) in Sub-saharan Africa and the Middle to Upper Paleolithic (MP/UP) in northern Africa and Eurasia. After the transition, ground bone tools and perforated ornaments become common and resource exploitation and socio-territorial organization patterns begin to resemble those of recent hunter–gatherers. The transition apparently occurred around or earlier than 40,000 BP, which is near the limits of the radiocarbon dating technique. Calibration of Late Pleistocene radiocarbon dates with high precision U-series dating demonstrates radiocarbon dates are 23000 years too young by 30,000 BP. This deviation reflects weakening of the earth’s magnetic field strength. It was weakest at 245–40,000 BP, during the Laschamp geomagnetic reversal event. Cosmogenic nuclide production increased during this event, making radiocarbon dates on materials formed after 244,000 BP up to 3500 years younger than their true age. Older radiocarbon dates are unaffected by this event, so a gap in radiocarbon dates should occur around 42–38,000 BP. The MP/UP transition in the Levant is dated on radiocarbon, TL and U-series to 46–43,000 BP, with a gap in radiocarbon dates after the transition. The oldest European UP sites have radiocarbon dates of 38–40,000 BP, but associated U-series and TL dates indicate the transition occurred around 42–40,000 BP, within the Laschamp event. In eastern Africa, the MSA/LSA transition apparently occurred earlier than 50,000 BP and perforated ornaments are radiocarbon dated to 39,900 BP. This is consistent with a tropical African origin for modern human behavior. Paleoecological implications of faunas associated with hominids in the Turkana Basin, Kenya Anna K. Behrensmeyer, Nancy E. Todd and Richard Potts, Evolution of Terrestrial Ecosystems Program, MRC NHB 121, Smithsonian Institution, Washington, DC 20560, U.S.A. Inferences about the paleoecological requirements of hominids have been based on various methods, including functional anatomy, stable isotope analysis, paleocommunity analysis, and paleoenvironmental context. We report here an approach using a large database to generate testable hypotheses concerning hominid paleoecology based on the association or nonassociation of hominid fossils with remains of other species. An intensive study of published mammalian faunas at 342 localities in the Turkana Basin, northern Kenya, provides a dataset consisting of nearly 3000 species occurrences that was used to examine species associations. Co-occurrences of species in fossil assemblages are subject to many potential taphonomic biases and may not accurately reflect original ecological associations. We use two strategies to overcome this problem: (1) controlling for taphonomic factors known to introduce biases into paleoecological information, such as sedimentary context, body size, and time-averaging, and (2) using the large dataset to isolate trends that are statistically stronger than potential confounding taphonomic processes. As paleoecological indicators, we use species with ecological requirements that can be inferred based on functional anatomy and/or nearest living relatives, such as arboreal monkeys and grazing ungulates. Chi-square tests are used to determine the significance of negative or positive associations. Preliminary results indicate that 2      