The Middle Awash Research Project is an international, multidisciplinary scientific study, whose objective is establishing an accurate geological information for elucidating human origins and evolution within the framework of the tectonic, volcanic, and sedimentological processes in the southern Afar Rift since the late Miocene. The project is funded primarily by the National Science Foundation; and the Los Alamos researchers are funded by the Institute of Geophysics and Planetary Sciences (IGPP) at Los Alamos National Laboratory (LANL) as part of the University of California, Berkeley - LANL Research Collaboration Program.
The Main Ethiopian, the Gulf of Aden, and the Red Sea Rifts meet at a triple junction in the Afar depression where a proto-oceanic crust is developing by rifting and drifting of the Arabian, Somalian, and the African continental blocks (Fig. 1). The Afar Rift forms a triangular depression that is characterized by widespread horst and graben structures and along-axis segmentation with variable intensity of tectonic activity and volcanic eruption that decrease toward the Main Ethiopian Rift. Unlike the central Afar rift floor, the southern part is dominated by late Miocene to Quaternary lacustrine and fluvial sedimentary rocks with recent volcanic and tectonic activities confined to a narrow axial zone which is marked by basaltic lava fields, fissures, nested cinder cones, silicic centers, horsts and grabens. Recent studies in the Middle Awash region of the southern Afar indicate uplifted and faulted late Miocene basaltic flows distributed within the rift floor and along marginal grabens. These volcanic rocks and associated sediments appear to decrease in age toward the axial zone. Geochemical and geochronological analyses are carried out to document spatial and temporal distributions of these lava fields and tectonic features to determine the history of lithospheric and volcanotectonic processes in the southern part of the Afar Rift. Volcanic rocks interbedded with fluvial and lacustrine sedimentary rocks provide temporal information about rate of subsidence and sedimentation and the overall history of basin development. The sedimentary rocks are rich in fossils and systematic studies are being conducted to assess the impact of these geologic processes on faunal, including hominid evolution.
Most of the Miocene and Plio-Pleistocene paleoanthropological localities that have given us information about our ancestors are concentrated in the East African Rift System. This is not a coincidence, because volcanic and tectonic activities that were responsible for the formation of the rift basins, plateau, and coeval sedimentation were responsible for creating dynamic environments for the proliferation of life and the preservation of faunal and floral remains within the confines of the rift. Volcanic and tectonic activities related to rift evolution created plateaus and mountains; most of the sediments in the basins were derived from these topographic highs located within and outside the rift valleys. Lavas, volcaniclastic sediments, and tephra were responsible for the quick burial and preservation of fossils. Water-rock interactions during burial diagenetic processes involving silicification, calcification, zeolitization, feldspathization, clay formation, and pedogenesis all played roles in fossil preservation in the volcaniclastic sediments. Volcanic rocks interbedded with the fossiliferous sediments also provide temporal information about geologic processes, faunal evolution, paleoenvironment, and early hominid behavior and lithic technology.
Current knowledge of the paleontology, paleoenvironment and paleoecology of latest Miocene Eastern Africa is scanty because of limited fossiliferous sedimentary deposits. The few known late Tertiary fossiliferous sedimentary rocks of the region have yielded important information on the origin and early evolution of numerous taxonomic groups. However, there are numerous gaps in the fossil record that represent an important time period (10-5 million years) pertinent to the understanding of the pongid/hominid split and the extinction and appearance of numerous taxa. The Middle Awash valley contains late Miocene fossiliferous sedimentary sequences that can fill this gap. Detailed geological, paleontological, paleoenvirnmental and paleoecological studies in the Middle Awash fluvial and lacustrine fossiliferous sedimentary rocks are addressing the environment-related evolutionary issues.
Multidisciplinary geological studies in the Middle Awash valley have established the region as one of the world’s most important paleontological sites with the discovery of a partial skeleton of the most ancient hominids (4.4 million years) known--Ardipithecus ramidus, Australopithecus afarensis (>3.9 to 3.4 million years), and many other recently discovered hominid remains that are being cleaned and studied for publications. More than 5000 other fossil specimens have been collected from these sedimentary rocks during the last seven field seasons. With full geological and paleoenvironmental understanding of the time period (5.3-3.9 million years) represented by the rocks of the Central Awash complex adjacent to the current axial rift zone of the floor, an effort is being made to extend this study deeper in time into late Miocene (10-5 million years) along the western rift margin. Moreover, the late Pliocene and Pleistocene sedimentary rocks exposed within the rift floor are also being investigated.
Research in the Middle Awash region of the southern Afar Rift has now established a reliable stratigraphic sequence between the present and the late Miocene (≤10 million years) using multiple approaches such as biochronology, tephrochemistry and tephrochronology, 40Ar/39Ar dating, and paleomagnetism. The overall geologic research is related to the understanding of lithospheric process, volcanic and tectonic activities, basin development, sedimentation processes, paleoenvironment, and temporal constraints on the fossil record in the Middle Awash rift floor and the adjacent western rift margin of the southern Afar Rift (Fig. 1).
Selected Publications Related to Research
Clark, J.D., Asfaw, B., Harris, J.W.K., Walter, R.C., White, T.D. and Williams, M.A.J. Paleoanthropological discoveries in the Middle Awash Valley, Ethiopia. Nature, 307:423-428, 1984.
Clark, J.D., deHeinzelin, J., Schick, K., Hart, W., White, T.D., WoldeGabriel, G., Walter, R.C., Suwa, G., Asfaw, B., Vrba, E. and H. -Selassie, Y. African Homo erectus: Old Radiometric Ages and Young Oldowan Assemblages in the Middle Awash Valley, Ethiopia. Science, 264:1907-1910, 1994.
White, T.D. Pliocene hominids from the Middle Awash, Ethiopia. Courier Forschungsinstitut Senckenberg, 69:57-68, 1984.
White, T.D., Suwa, G., Hart, W.K., Walter, R.C., WoldeGabriel, G., de Heinzelin, J., Clark, J.D., Asfaw, B., and Vrba, E. New discoveries of Australopithecus at Maka, Ethiopia. Nature, 366:261-265, 1993.
White, T.D., Suwa, G. and Asfaw, B. Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia. Nature, 371:306-312, 1994.
White, T. D., G. Suwa, and B. Asfaw, Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia. Nature, 375, p. 88, 1995.
Renne, P. R., G. WoldeGabriel, W. K. Hart, G. Heiken, and T. D. White, Chronostratigraphy of the Miocene-Pliocene Sagantole Formation, Middle Awash Valley, Afar Rift, Ethiopia. Geological Society of America (1999, in press).
WoldeGabriel, G., T. D. White, G. Suwa, P. Renne, J. de Heinzellin, W. K. Hart, and G. Heiken, Ecological and temporal placement of early Pliocene hominids at Aramis, Ethiopia. Nature, 371, 330-333, 1994.
WoldeGabriel, G., P. Renne, T. D. White, G. Suwa, J. de Heinzelin, W. K. Hart, and G. Heiken, Age of Early hominids. Nature, 376, 558-559, 1995.
WoldeGabriel, G., G. Heiken, T. D. White, B. Asfaw, W. K. Hart, and P. Renne, Volcanism, tectonism, sedimentation, and the paleoanthropological record in the Ethiopian Rift System, Volcanic Hazards and Disasters in Human History. Geological Society of America Special Paper 385, 2000.
Figure 1. Digital elevation map of the Main Ethiopian Rift (MER) and the Afar Rift showing the location of the Middle Awash tectonic transition zone. The different parts of the rift systems are labeled and represent SMER (southern MER), CMER (central MER), NMER (northern MER). Map is modified from Hayward and Ebinger (1996).