NEW 40AR/39AR AGE CONSTRAINTS FOR MIDDLE STONE AGE ARCHAEOLOGY AT GADEMOTTA AND KULKULETTI, ETHIOPIA

The emergence of Middle Stone Age (MSA) technology in Africa indicates a significant change in hominid behavior as Acheulean technology, which had been the standard for over 1 My, was replaced in large part by MSA technologies. Although various definitions of the MSA are in use, this transition included the development of the Levallois core-preparation technique, which is thought to require forethought not seen in earlier technologies and is thus indicative of increased cognitive ability in the toolmakers. Moreover, the timing of the first MSA technologies may be coincident with the biological evolution of anatomically modern H. sapiens (McBrearty and Brooks 2000). Evaluation of this possibility relies on precise and accurate geochronology of important MSA and early H. sapiens localities.

Here we present new age constraints on archaeologically rich sediments containing MSA technology at Gademotta and Kulkuletti, near Lake Ziway in the northern part of the Main Ethiopian Rift. Abundant artifacts, made exclusively from locally-derived obsidian, are found in-situ in sedimentary context. Single-crystal total-fusion ⁴⁰Ar/³⁹Ar data indicate two tuffaceous horizons, which bound most of the archaeology at Kulkuletti, are 193 +/- 5 ka (Unit D of Laury and Albritton, 1975) and 298 +/- 11 ka (Unit 10 of same paper). Additional single-crystal, step-heating analyses (in progress) from the lower tuff, which can be traced physically and geochemically to Gademotta, should further constrain the older age. These new ages are significantly older than previous K/Ar work (149 +/- 13 ka and 181 +/- 6 ka, respectively) (Wendorf et al., 1975) and place Gademotta and Kulkuletti among the earliest well-dated MSA sites.