BIOMASS PRODUCTIVITY, STABLE ISOTOPE PROXIES, AND LANDSCAPE RECONSTRUCTIONS FROM THE KAPTHURIN FORMATION, KENYA

The Middle Pleistocene of East Africa documents significant technological and biological change, which could be influenced by changing environments (Rightmire 1998; Wood and Collard 1999; McBrearty and Brooks 2000; Henshilwood and Marean 2003). The Kapthurin Formation is a part of the Middle Pleistocene sedimentary sequence of the Kenyan Rift Valley, recording the transition from Acheulean to Middle Stone Age technology, providing an ideal setting to test the relationship between environments and technological change (Leakey et al. 1969; Wood and Van Noten 1986; Tryon and McBrearty 2002). Environmental reconstructions that use landscape perspectives are ideal to test such relationships, because they offer a wider perspective to study the environmental context associated with hominin tool technologies and ranging behaviors (Peters and Blumenschine 1995). Stable isotope analysis provides a unique method for reconstructing past environments, and is independent of taxonomic identifications of fauna and their assumed habitats based on modern distributions. Environmental reconstructions from two time intervals within the Kapthurin Formation, 543 ± 4 ka – 509 ± 9 ka and 509 ± 9 ka – 235 ± 2 ka, calibrated with the ⁴⁰Ar/³⁹Ar method (Denio and McBrearty 2002) indicate differential use of resources among MSA and Acheulean hominins. These reconstructions are based on stable isotope values of carbon (δ¹³C) and oxygen (δ¹⁸O) derived from fossil bovid tooth enamel, pedogenic carbonates, and soil organic carbon. These environmental reconstructions also utilize a new technique for correlating modern biomass productivity with stable isotope values of soil organic carbon. We assess biomass productivity using a a Normalized Differential Vegetation Index (NDVI) extracted from modern landscapes via satellite imagery and stable isotope analyses, and extrapolate these NDVI values for past landscapes. These environmental reconstructions provide rich landscapes to assess the ranging patterns of Acheulean and MSA hominins, and test whether MSA and Acheulean hominins differed in their exploitation of landscapes, environments, and resources.