THE TURKANA BASIN AS A PROVING GROUND FOR PALEOENVIRONMENTAL PROXIES

The Turkana Basin has been a “proving ground” for developing paleoenvironmental proxies of terrestrial environments. This comes from the long-term interest in mammalian evolution, especially hominin evolution. The basin has had almost continuous sedimentation through the past 5 million years and numerous volcanic ash layers provide superb chronology and correlations within the basin. Starting in the early 1970s my involvement has included mapping, dating, correlation, and development of environmental proxies. Those proxies include using carbon isotopes in paleosols to quantify the fraction and C₃ and C₄ biomass contributing the ecosystems, and then enhancing that measure to estimate the fraction of woody cover on the landscape which is critical to hypotheses about hominin habitats and their use of the landscape. The Turkana basin was the first place where paleosols were used to estimate the mean temperature of paleosol carbonate formation using “clumped isotopes”; soil temperature monitoring showed that higher than mean annual temperatures were expected for soil carbonates that form at depths of 10s of centimeters in soils. Interest in diet evolution in mammals led to extensive isotope studies of mammalian lineages and showed that some modern taxa have diets different than their direct ancestors. The morphology-independant nature of stable isotopes allows the testing of traditional paleontological diet assumptions. Oxygen isotopes in mammals has the potential to quantify water deficit at the ecosystem scale using both comparisons of coeval taxa and also using 17-Oxygen within single taxa. Questions concerning seasonality spurred research into isotope incorporation during tooth formation; the isotope mixing of the time input signal can be addressed using inverse methods and Bayesian modeling. All of these proxies had important impetus from questions about environment of the Turkana Basin.