Geology of Middle Stone Age Archaeological Sites in the Main Ethiopian Rift Valley

Abstract

Research Article| July 01, 1975 Geology of Middle Stone Age Archaeological Sites in the Main Ethiopian Rift Valley ROBERT L. LAURY; ROBERT L. LAURY 1Department of Geological Sciences, Institute for the Study of Earth and Man, Southern Methodist University, Dallas, Texas 75275 Search for other works by this author on: GSW Google Scholar CLAUDE C. ALBRITTON, JR. CLAUDE C. ALBRITTON, JR. 1Department of Geological Sciences, Institute for the Study of Earth and Man, Southern Methodist University, Dallas, Texas 75275 Search for other works by this author on: GSW Google Scholar Author and Article Information ROBERT L. LAURY 1Department of Geological Sciences, Institute for the Study of Earth and Man, Southern Methodist University, Dallas, Texas 75275 CLAUDE C. ALBRITTON, JR. 1Department of Geological Sciences, Institute for the Study of Earth and Man, Southern Methodist University, Dallas, Texas 75275 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1975) 86 (7): 999–1011. https://doi.org/10.1130/0016-7606(1975)86<999:GOMSAA>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation ROBERT L. LAURY, CLAUDE C. ALBRITTON; Geology of Middle Stone Age Archaeological Sites in the Main Ethiopian Rift Valley. GSA Bulletin 1975;; 86 (7): 999–1011. doi: https://doi.org/10.1130/0016-7606(1975)86<999:GOMSAA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract On a ridge west of Lake Ziway, northernmost of the Galla Lakes, rich Middle Stone Age sites are present in paleosols of the late Pleistocene Gademotta Formation. The underlying rocks are of alkali rhyolite and tuff, the eruption of which commenced over 1 m.y. ago and was climaxed by caldera collapse and explosive ejection of pumiceous tephra. Lower Gademotta sediments consist of tuffaceous laharic mudstone interbedded with thick paleosols developed on unsorted colluvial volcanic detritus. Artifacts are lacking.A paleosol in the middle of the Gademotta Formation contains obsidian tools of Levallois-Mousterian technology, the earliest Middle Stone Age artifacts thus far discovered in the area. This soil was covered by a crystal-rich volcanic ash, which has been dated at ∼ 181,000 yr B.P. Above the ash, in turn, are three superposed paleosols, each with Middle Stone Age artifacts intercalated with water-laid sandstone, and two additional ash beds.Late in the sedimentary history of the Gademotta Formation it was eroded by intermittent streams forming deep gullies which subsequently were aggraded. Perhaps the cutting and filling were related to the fluctuations of an ancient lake whose level may have reached more than 100 m above present Lake Ziway (1,636 m). The consistent occurrence in this region of Middle Stone Age sites — > 35,000 to > 100,000 yr B.P., elevations ≧ 150 m above Lake Ziway — suggests geographic control of human settlement by high lake stands during late Pleistocene time. Topographically lower volcanic hills, which probably formed contemporaneously with Gademotta Ridge, appear not to have been inhabited until the Late Stone Age (< 15,000 yr B.P.) when the lake level was substantially lower. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.