TERRESTRIAL COSMOGENIC NUCLIDE GEOCHRONOLOGY OF STRATIFIED MIDDLE STONE AGE ARTIFACT ASSEMBLAGES, NORTHERN MALAWI RIFT, EAST AFRICA
Large MSA assemblages have been excavated from 7 sites along the hangingwall; additional artifacts and observations have been recovered from 21 trenches within the sedimentary surfaces including sampling for terrestrial cosmogenic nuclide (TCN) dating, optically-stimulated luminescence (OSL) dating, and characterization of sediment composition and morphology.
Two independent methods allow us to date these surfaces: (1) depth profiles, using 10Be and stable 21Ne—the latter extends our dating ability into the Pliocene; (2) burial isochrons, which rely on TCN pair 26Al/10Be—inherited concentration of nuclides in samples recovered at depth (~2-3m) are used to measure burial ages up to 5 Ma.
We use a recent innovation in the field of TCN dating: the isochron approach, used to converge on a best-fit burial date by iteratively correcting for estimates of post-burial production. This approach allows more flexibility than conventional burial dating to account for factors such as post-burial TCN production. Previous estimates of deposition rates and other a priori knowledge of absolute dates within a stratigraphic column allow a more efficient approach to the calculation of a burial date. Our approach uses independent constraints on the geologic setting in concert with reasonable estimates of the depositional environment to more quickly constrain uncertainties in the calculation of an age.