Volcanism, tectonism, sedimentation, and the paleoanthropological record in the Ethiopian Rift System

The Ethiopian Rift System consists of basins that are in different stages of evolution. Some of the rift-related basins in southwestern Ethiopia are half-grabens that have not evolved to symmetrical rifts since the initiation of rifting here in the middle Miocene. These basins contain fossiliferous Pliocene–Pleistocene volcaniclastic sediments and volcanic rocks and have been occupied by early hominid populations. The Afar and the Main Ethiopian Rifts are symmetrical, with both margins fully developed. Several paleoanthropological localities, ranging in age from the Quaternary to the Pliocene, were discovered within these rift basins. The discovery of Australopithecus afarensis (the “Lucy” species) at Hadar and Ardipithecus ramidus and Australopithecus garhi in the Middle Awash makes the region the most prolific early hominid area in the world. Many of the known Pliocene–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 the volcanic and tectonic activities that were responsible for the formation of the rift basins and coeval sedimentation created ideal environments for the proliferation of life and the preservation of faunal and floral remains. Volcanic and tectonic activities created plateaus and mountains; most of the sediments in the basins were derived from these topographic highs located within and outside the rift valleys. Volcaniclastic sediments and volcanic ash were responsible for the quick burial and preservation of fossils during diagenesis. 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.

[1]  T. White,et al.  Chronostratigraphy of the Miocene–Pliocene Sagantole Formation, Middle Awash Valley, Afar rift, Ethiopia , 1999 .

[2]  E. Vrba,et al.  Environment and behavior of 2.5-million-year-old Bouri hominids. , 1999, Science.

[3]  B. Latimer,et al.  Australopithecus garhi: a new species of early hominid from Ethiopia. , 1999, Science.

[4]  W. Hart,et al.  New age constraints on the timing of volcanism and tectonism in the northern Main Ethiopian Rift southern Afar transition zone (Ethiopia) , 1998 .

[5]  T. White,et al.  The first skull of Australopithecus boisei , 1997, Nature.

[6]  J. Fleagle,et al.  Age of Australopithecus afarensis from Fejej, Ethiopia , 1996 .

[7]  J. Damuth,et al.  Rapid morphological change in Miocene marsupials and rodents associated with a volcanic catastrophe in Argentina , 1995 .

[8]  A. Walker,et al.  New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya , 1995, Nature.

[9]  T. White,et al.  Age of early hominids , 1995, Nature.

[10]  Tim D. White,et al.  Ecological and temporal placement of early Pliocene hominids at Aramis, Ethiopia , 1994, Nature.

[11]  Tim D. White,et al.  Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia , 1994, Nature.

[12]  E. Vrba,et al.  African Homo erectus: old radiometric ages and young Oldowan assemblages in the Middle Awash Valley, Ethiopia. , 1994, Science.

[13]  E. Vrba,et al.  New discoveries of Australopithecus at Maka in Ethiopia , 1993, Nature.

[14]  Jon E. Kalb.  Refined Stratigraphy of the Hominid-Bearing Awash Group,Middle Awash Valley, Afar Depression, Ethiopia , 1993 .

[15]  K. Verosub,et al.  New data from Hadar (Ethiopia) support orbitally tuned time scale to 3.3 MA , 1993 .

[16]  A. A. Ekdale.  Taphonomy: Releasing the data locked in the fossil record , 1993 .

[17]  G. Woldegabriel,et al.  Late Eocene–Recent volcanism and faulting in the southern main Ethiopian rift , 1993, Journal of the Geological Society.

[18]  T. White,et al.  The earliest Acheulean from Konso-Gardula , 1992, Nature.

[19]  Tim D. White,et al.  Kesem-Kebena : A Newly Discovered Paleoanthropological Research Area in Ethiopia , 1992 .

[20]  Tim D. White,et al.  Fejej: a new paleoanthropological research area in Ethiopia , 1991 .

[21]  G. Woldegabriel,et al.  Geology, geochronology, and rift basin development in the central sector of the Main Ethiopia Rift , 1990 .

[22]  W. Hart,et al.  Basaltic volcanism in Ethiopia: Constraints on continental rifting and mantle interactions , 1989 .

[23]  F. Brown,et al.  Stratigraphic context of fossil hominids from the Omo group deposits: northern Turkana Basin, Kenya and Ethiopia. , 1989, American journal of physical anthropology.

[24]  B. Zanettin,et al.  Volcanic cycles and magmatic evolution in northern Turkana (Kenya) , 1987 .

[25]  S. Tait,et al.  Explosive volcanism: Inception, evolution and hazards , 1987 .

[26]  J. Aronson,et al.  Chow Bahir rift: A “failed” rift in southern Ethiopia , 1987 .

[27]  S. Berhe,et al.  Geology, geochronology and geodynamic implications of the Cenozoic magmatic province in W and SE Ethiopia , 1987, Journal of the Geological Society.

[28]  A. Wehner,et al.  Evaluation of physical health effects due to volcanic hazards: the use of experimental systems to estimate the pulmonary toxicity of volcanic ash. , 1986, American journal of public health.

[29]  F. Brown,et al.  Revision of lithostratigraphic nomenclature in the Koobi Fora region, Kenya , 1986, Journal of the Geological Society.

[30]  I. Mcdougall.  K-Ar and 40Ar/39Ar dating of the hominid-bearing Pliocene-Pleistocene sequence at Koobi Fora, Lake Turkana, northern Kenya , 1985 .

[31]  F. Brown,et al.  Ages of tuff beds at East African early hominid sites and sediments in the Gulf of Aden , 1985, Nature.

[32]  D. York,et al.  Geochronology, stratigraphy and geochemistry of Cindery Tuff in Pliocene hominid-bearing sediments of the Middle Awash, Ethiopia , 1984, Nature.

[33]  T. White,et al.  Palaeoanthropological discoveries in the Middle Awash Valley, Ethiopia , 1984, Nature.

[34]  F. Brown,et al.  Tuffaceous marker horizons in the Koobi Fora region and the Lower Omo Valley , 1982, Nature.

[35]  P. Mohr,et al.  Quaternary volcanism and faulting at O’A caldera, central ethiopian rift , 1980 .

[36]  D. Rex,et al.  Age of volcanism and rifting in southwestern Ethiopia , 1980, Nature.

[37]  F. Gasse,et al.  Plio–Pleistocene environments at Gadeb prehistoric site, Ethiopia , 1979, Nature.

[38]  J. D. Clark,et al.  Hominid occupation of the East-Central Highlands of Ethiopia in the Plio–Pleistocene , 1979, Nature.

[39]  J. M. Moore,et al.  Rift structure in southern Ethiopia , 1978 .

[40]  R. L. Laury,et al.  Geology of Middle Stone Age Archaeological Sites in the Main Ethiopian Rift Valley , 1975 .

[41]  R. L. Hay.  Chert and its sodium-silicate precursors in sodium-carbonate lakes of East Africa , 1968 .

[42]  K. J. Murata.  Volcanic ash as a source of silica for the silification of wood , 1940 .

[43]  R. Walter,et al.  Age of Lucy and the First Family: Single-crystal 40Ar/39Ar dating of the Denen Dora and lower Kada Hadar members of the Hadar Formation, Ethiopia , 1994 .

[44]  W. Hart,et al.  Tephra sources and correlations in Ethiopia: Application of elemental and neodymium isotope data , 1992 .

[45]  F. Brown,et al.  Correlation of Pliocene and Pleistocene tephra layers between the Turkana Basin of East Africa and the Gulf of Aden , 1992 .

[46]  Arturo S. Daag,et al.  Immediate and long-term hazards from lahars and excess sedimentation in rivers draining Mount Pinatubo, Philippines , 1992 .

[47]  T. White,et al.  Age of volcanism and rifting in the Burji-Soyoma area, Amaro Horst, southern Main Ethiopian Rift: geo- and biochronologic data , 1991 .

[48]  F. Brown,et al.  Correlation of tephra layers from the Western Rift Valley (Uganda) to the Turkana Basin (Ethiopia/Kenya) and the Gulf of Aden , 1991 .

[49]  L. Prévôt,et al.  Phosphates and Fossil Preservation , 1991 .

[50]  Gary A. Smith.  Facies Sequences and Geometries in Continental Volcaniclastic Sediments , 1991 .

[51]  Meave G. Leakey,et al.  Stratigraphy and paleontology of Pliocene and Pleistocene localities west of Lake Turkana, Kenya , 1988, Contributions in science.

[52]  R. Watkins.  Volcano-tectonic control on sedimentation in the Koobi Fora sedimentary basin, Lake Turkana , 1986, Geological Society, London, Special Publications.

[53]  M. Pickford.  Sedimentation and fossil preservation in the Nyanza Rift System, Kenya , 1986, Geological Society, London, Special Publications.

[54]  S. Berhe.  Geologic and geochronologic constraints on the evolution of the Red Sea-Gulf of Aden and Afar depression , 1986 .

[55]  J. Tiercelin.  The Pliocene Hadar Formation, Afar depression of Ethiopia , 1986, Geological Society, London, Special Publications.

[56]  R. L. Hay.  Role of tephra in the preservation of fossils in Cenozoic deposits of East Africa , 1986, Geological Society, London, Special Publications.

[57]  R. Johnson,et al.  Volcano town : the 1937-43 eruptions at Rabaul , 1985 .

[58]  J. D. Rees.  9 – Effects of the Eruption of Parícutin Volcano on Landforms, Vegetation, and Human Occupancy , 1979 .

[59]  T. White,et al.  A new species of the genus Australopithecus (Primates: Hominidae) from the Pliocene of eastern Africa , 1978 .

[60]  H. H. Waldron.  Debris flow and erosion control problems caused by the ash eruptions of Irazu Volcano, Costa Rica , 1967 .