Possible isotopic fractionation of argon in source obsidians and archeological artifacts from Kulkuletti, Ethiopia

Despite uniform geochemistry ⁴⁰Ar/³⁹Ar ages of 0.6, 1.25, and 1.3 Ma on obsidians from a source flow (Worja) and from archeological artifacts at the sites of Kulkuletti (near Gademotta, Ethiopia) have been interpreted to suggest that they derive from different source flows of different ages. A further suggestion is that the magmatic source of the obsidian flows was chemically homogeneous between 1.3 Ma and 0.6 Ma. Chemical analysis of these obsidians indeed suggests that they derive from a single flow. Reexamination of the argon isotopic data reveals that argon isotopes may have been fractionated within the flow, so that the assumption of an atmospheric ⁴⁰Ar/³⁶Ar ratio of 295.5 is inappropriate to use for computing ages. Three groups of data are apparent, and internally all yield ages near 1.3 Ma if the intercept value for ⁴⁰Ar/³⁶Ar from an isotope correlation plot is used for computation instead of using the atmospheric ratio. The Soret thermal diffusion effect provides a possible mechanism of fractionation of argon within the obsidian flow that is of approximately the right magnitude to explain the observations by in-diffusion of already fractionated atmospheric argon.     

Variability in Ethnographic Hidescraper Use among the Hadiya of Ethiopia: Implications for Reduction Analysis

The contemporary use of flaked stone tools provides a rare opportunity to study various aspects of lithic technology. Variables that must be inferred in archaeological contexts can be observed and more easily studied in ethnographic ones. The Hadiya hideworkers of southern Ethiopia, like a few other groups in this region, still retain the tradition of making and using obsidian scrapers on a daily basis for hide-working activities. This ethnoarchaeological study demonstrates how differential access to raw material and the resultant procurement strategies result in intra-group variability in scraper-use intensity. Results show that raw material acquisition costs, which are difficult to identify in archaeological assemblages, represent significant impacts on tool use life and curation.     

Source provenance of obsidian artifacts from the Early Stone Age (ESA) site of Melka Konture,Ethiopia

The source provenance of 10 Early Stone Age artifacts from the localities in Melka Konture has been determined by EDXRF. Results show that the early to mid-Pleistocene makers of the artifacts derived the raw material from a source located in their proximity, supporting the previously proposed short distance transport of raw material for the time period.     

Forensic Ar/Ar dating: a provenance study of Middle Stone Age obsidian artifacts from Ethiopia

Obsidian sourcing based on geochemistry is widely applied to reconstruct commerce patterns and dissemination of early hominid groups. Due to problems concerning potential intra-source variability or homogeneity of a geological source over large areas, parameters additional to this classical approach are desirable. Here we present the first ⁴⁰Ar/³⁹Ar investigation of Middle Stone Age (MSA) obsidian artifacts (i.e. debitage pieces) for this purpose, as well as of potential geological obsidian sources from Ethiopia. With the present pilot study we demonstrate that ⁴⁰Ar/³⁹Ar geochronology represents a reliable and powerful tool for archaeological provenance studies complementary to the geochemical approach and more recently applied techniques like fission track counting or Mössbauer spectroscopy. Two independent sets of debitage and potential source rock samples were dated by the ⁴⁰Ar/³⁹Ar method. Debitage pieces from the Kulkuletti excavation site and obsidian samples from the nearby obsidian outcrop Worja (central Ethiopia) exhibit basically identical age ranges as well as similar Ca/K and Cl/K ratios, supporting the debitage/source rock relationship previously inferred on geochemical grounds. A second small set of geochemically characterized debitage samples from the Porc Epic cave and potential source rocks from an obsidian outcrop at Kone (Eastern Ethiopia) however have different ⁴⁰Ar/³⁹Ar ages and Ca/K and Cl/K ratios. These results contradict the previous conclusion about a debitage/source rock relationship of the Porc Epic and Kone samples made on the basis of geochemistry [A. Negash, M.S. Shackley, Archaeometry 48 (2006) 1]. Additional sampling at the Kone outcrop as well as of other obsidian occurrences in the greater area is needed to unambiguously pinpoint the origin of these obsidian tools.