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34-681: Between 1970-1985 the age of the tuff was the subject of intense academic dispute, with a variety of dates proposed by different geochemical and paleontological laboratories. This dispute came to be known as the KBS Tuff Controversy. The KBS Tuff has been described as "the Turkana Basin ’s most celebrated tephrostratigraphic marker." The KBS Tuff was first reported and described by Kay Behrensmeyer (hence "KBS", Kay Behrensmeyer Site) in sediments that belong to Omo Group deposits in southern Ethiopia and northern Kenya . Within this larger group,

68-513: A great fault. Thomson returned in 1883, traveling through the rift valley in Kenya from Mount Longonot to Lake Baringo . Describing the valley around this lake he said: "Imagine if you can a trough or depression 3300 feet above sea level, and twenty miles broad, the mountains rising with very great abruptness on both sides to a height of 9000 feet". John Walter Gregory visited central Kenya in 1893 and again in 1919. His 1896 book The Great Rift Valley

102-500: A large endorheic basin , a drainage basin with no outflow centered around the north-southwards directed Gregory Rift system in Kenya and southern Ethiopia. The deepest point of the basin is the endorheic Lake Turkana , a brackish soda lake with a very high ecological productivity in the Gregory Rift. A narrower definition for the term Turkana Basin is also in widespread use and means Lake Turkana and its environment within

136-492: A series of horst and graben structures, and led to approximately 1 km of sedimentary deposits at the center of the basin every 1 million years. Sedimentary records , which become more sparse and discontinuous at greater distance from the basin center, suggest that the basin has alternated between fluvial and lacustrine regimes throughout the Plio-Pleistocene , primarily as a result of continued volcanic activity first to

170-700: A single, continuously evolving " anagenetic " lineage, hominin fossil remains become extraordinarily diverse in East Africa 2.5 million years ago, with numerous species of robust australopithecine and early human ancestors found first in the Turkana Basin, and ultimately in South Africa as well. The earliest putative evidence for stone tool use among human ancestors is found within the Turkana Basin. Gregory Rift The Gregory Rift ( Ufa la Gregori , in Swahili )

204-633: Is considered a classic. Gregory was the first well-known European to use the term "rift valley", which he defined as "a linear valley with parallel and almost vertical sides, which has fallen owing to a series of parallel faults". In 1913 the German geologist Hans Reck made the first European study of the strata in the Olduvai Gorge to the west of the Crater Highlands. He brought a large collection of mammalian fossils back to Berlin. In 1928 Louis Leakey ,

238-719: Is the eastern branch of the East African Rift fracture system. The rift is being caused by the separation of the Somali Plate from the Nubian Plate , driven by a thermal plume . Although the term is sometimes used in the narrow sense of the Kenyan Rift , the larger definition of the Gregory Rift is the set of faults and grabens extending southward from the Gulf of Aden through Ethiopia and Kenya into Northern Tanzania , passing over

272-612: The Gombe basalts in the Koobi Fora formation to the east and with the Lothagam basalts further south; this event created a lake in the center of the basin and apparently established the modern, continuous depositional system of the Turkana Basin. Deposition in the Turkana Basin overall is driven primarily by subsidence , a result of rifting between the Somali and Nubian plates that has created

306-558: The Miocene world was more lush than the Pliocene . Some herbivores, like horses , responded rapidly to the spread of C4 grasslands , while other herbivores evolved more slowly, or developed a number of different responses to an increasingly arid landscape. Evolutionary studies of the Turkana Basin have found what may be major intervals of faunal turnover after the Miocene as well, most notably in

340-560: The 1,300 kilometres (810 mi) wide East African Plateau . Large shield volcanoes near the margins of the craton and in the adjacent Mozambique belt issued large volumes of basaltic to trachytic magmatism between five and one million years ago, with faulting around 1.2 million years ago. Volcanic activity started in the central Ethiopian plateau around 30 million years ago, long before rifting began. The first period of activity deposited flood basalts and rhyolites from 500 metres (1,600 ft) to 2,000 metres (6,600 ft) thick. Uplift of

374-658: The Argon-Argon 2.6 Ma Tuff. Another problem that emerged was that the 2.6 Ma date for the KBS Tuff, provided by Fitch and Miller, made alignment of the Koobi Fora (east Turkana) geochronology with the Omo (north Turkana) geochronology impossible. The conflict was resolved after geochemist Garniss Curtis and his student Thure E. Cerling conducted independent investigations of the age of the KBS Tuff using Argon-Argon and Potassium-Argon dating at

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408-575: The Baringo – Bogoria half-graben from 500 metres (1,600 ft) to 1,000 metres (3,300 ft) thick and in the Afar depression up to 100 metres (330 ft) thick. The first well-known European geologist to explore the region was Joseph Thomson , a member of an expedition in 1879–1880 sponsored by the Royal Geographical Society of Britain. From his observations he deduced the existence of

442-753: The Berkeley Geochronology Laboratory. Curtis and Cerling found that the material dated by the Cambridge team actually belonged to two separate tuffs, which they estimated at 1.8 and 1.6 Ma. This date was confirmed by Potassium-Argon dating conducted by Ian McDougall, and later Fission-Track dating conducted by Andy Gleadow. Turkana Basin The greater Turkana Basin in East Africa (mainly northwestern Kenya and southern Ethiopia , smaller parts of eastern Uganda and southeastern South Sudan ) determines

476-570: The Ethiopian plateau began around this time or soon after. Between 30 million and 10 million years ago synrift shield volcanoes deposited from 1,000 metres (3,300 ft) to 2,000 metres (6,600 ft) of additional material over the Ethiopian flood basalts. Rifting in Ethiopia began about 18 million years ago in the southwest and 11 million years ago in northern parts of the Main Ethiopian Rift as

510-625: The Himalayas. This belt runs from Ethiopia through Kenya, Tanzania and Mozambique . The rift is widest at the northern end in the Afar region, narrowing to a few kilometers in northern Tanzania, then splaying out in the North Tanzania Divergence. The Gregory Rift has shoulders rising over 3,000 metres (9,800 ft) above sea level, 1,000 metres (3,300 ft) above the inner part of the graben. The Tanzanian portion includes Mount Kilimanjaro ,

544-640: The KBS has been found in the Shungura Formation in southern Ethiopia, In the Nachukui Formation on the west side of Lake Turkana in northern Kenya, and in the Koobi Fora Formation on the east side of Lake Turkana. Argon-argon dating has placed the age of the KBS Tuff at 1.869 ± 0.021 Ma. This age estimate is supported by independent fission track and K/Ar dating methods. KBS is situated above

578-470: The KBS tuff separates distinct sedimentary members of the Nachukui and Foobi Fora formations. In the Nachukui (western) formation, KBS divides the older Kalochoro from the younger Kaitio member. In the Koobi Fora formation, it separates the older Burgi from the younger KBS member. The KBS Tuff marks a transition in the Turkana Basin from a stable to a fluctuating lake, partly filled by a river and delta system to

612-644: The Turkana grits like the Lapurr Sandstone and are dominated by eastward flowing fluvial sequences draining into the Indian Ocean; later formations from the Oligocene and Miocene are characterised by similar fluvial regimes that are not however unified under a single geological group or system . Approximately 4.2 million years ago (Ma), the region experienced widespread and significant volcanism , associated with

646-410: The anthropologist, visited Berlin, where he saw that some of Reck's materials were artifacts . Leakey began exploring Olduvai in the 1930s and collecting material that has led to the site being recognized as an important center of early hominin occupation. Volcanism and rifting started in Kenya in the northern region of Turkana between 40 and 35 million years ago and then spread north and south. To

680-568: The center of the Turkana Basin and is flanked by the Chalbi Desert to the east, the Lotakipi Plains to the north, Karasuk to the west and Samburu to the south. Included within these regions are desert scrub, desert grass and shrubland, and scattered acacia or open grasslands. The only true perennial river is the Omo River in Ethiopia, in the northern part of the basin, which discharges into

714-563: The confines of the Gregory Rift in Kenya and Ethiopia. This includes the lower Omo River valley in Ethiopia. The Basin in the narrower definition is a site of geological subsidence containing one of the most continuous and temporally well controlled fossil records of the Plio-Pleistocene with some fossils as old as the Cretaceous . Among the Basin's critical fossiliferous sites are Lothagam , Allia Bay , and Koobi Fora . Lake Turkana sits at

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748-651: The east, and later to the south of the basin. Fossil records in the basin help establish much of what is known about African faunal evolution in the Neogene and Quaternary . As in other regions, the end-Miocene Messinian aridification crisis and global cooling trend seem to have influenced fossil assemblages in the Turkana Basin, either through migrations or de novo evolutionary events . Fossilized leaves characteristic of more mesic landscapes, faunal community compositions, and increase " C4 " or arid-adapted plant contribution to herbivore carbon intake, all suggest that

782-537: The highest mountain in Africa, and the huge caldera of Ngorongoro In the Crater highlands This portion also contains Ol Doinyo Lengai , the world's only active carbonatite volcano. Lakes in the rift other than Lake Turkana are mostly small and shallow, some with fresh water but many being saline. The thickness of lake sediments is mostly unknown. In Lake Turkana they seem to be at most 4 kilometres (2.5 mi) thick, in

816-586: The lake on its northern shore and supplies the lake with more than 98% of its annual water inflow. The two intermittent rivers – which almost alone contribute the remaining 2% of water inflow – are the Turkwel River and the Kerio River in Kenya, in the western part of the basin. Much of the Turkana Basin today can be described as arid scrubland or even desert. The exception is the Omo- Gibe River valley to

850-400: The late Pliocene and early Pleistocene, though later studies have suggested more gradual changes in herbivore community composition throughout this interval. One cause of focus on the late Pliocene and early Pleistocene is the large literature on hominin fossil remains showing an apparent " adaptive radiation " across this boundary. While previous hominin species are considered to be part of

884-544: The local uplifts of the Ethiopian and Kenyan domes. Ancient fossils of early hominins , the ancestors of humans, have been found in the southern part of the Gregory Rift. The Gregory Rift is named in honour of the British geologist John Walter Gregory who explored the geology of the rift in 1892–93 and 1919. The Gregory Rift lies within the Mozambique belt , often considered to be the remains of an orogenic system similar to

918-465: The north and east of the basin. In Koobi Fora, on the eastern side of Lake Turkana, a substantial number of hominin fossils have been found immediately below or above the KBS Tuff. A partial list is provided below, including a few specimens from north and west Lake Turkana. The KBS Tuff was first dated in 1969, after Behrensmeyer discovered stone tools at Koobi Fora in the layer of the Tuff. Argon/Argon dating

952-524: The north. Important towns within the Turkana Basin include Lokitaung, Kakuma, Lodwar, Lorogumu, Ileret and Kargi. The Turkana people inhabit the west of the Basin, the Samburu and Pokot people inhabit the south, and the Nyangatom , Daasanach and Borana Oromo peoples inhabit the north and east. The oldest sedimentary records go back to the Cretaceous , including units previously informally referred to as

986-405: The older Kangaki (2.063 Ma), G-3 (2.188 Ma) and Kalochoro (2.331 Ma) tuffs, and below the younger Malbe (1.843 Ma), Morutot (1.607 Ma) and Lower Ileret (1.527 Ma) tuffs. In some locations tuffs with chemical compositions identical to the KBS tuff have been found in multiple, distinct layers, suggesting that deposition of the layers occurred at various times after eruption. Within Omo group deposits,

1020-606: The opening of the Gregory rift caused the Afar Triple Junction to form. Volcanism from the Middle Pleistocene onward formed a chain of volcanoes along the floor of the rift throughout its length, dividing it into separate valleys. There are some indications that the lithosphere may have thinned below the Gregory rift, although based on basalt geochemistry the lithosphere is at least 75 kilometres (47 mi) thick below

1054-453: The south of Kenya. The Gregory rift is oriented NS, and in the past the minimum horizontal tectonic stress direction was EW, the direction of extension. The alignment of rows of small vents , cones , domes and collapse pits in the Suswa , Silali and Kinangop Plateau regions support this theory. However, data from oil and gas exploration wells in Kenya, vents in volcanic shields to the east of

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1088-484: The south volcanism and rifting happened together, first in other parts of northern Kenya around 30 million years ago, then around 15 million years ago in the central part of the Kenyan Rift , 12 million years ago in southern Kenya and 8 million years ago in northern Tanzania. When rifting reached the Tanzanian Craton , the rift split into the eastern Gregory Rift and the western Albertine Rift , which are separated by

1122-466: Was called into question because efforts to replicate the findings produced KBS Tuff ages ranging from less than 1 to over 220 Ma. A study of pig molar anatomy from the site, by Vincent Maglio and Basil Cooke, suggested an age closer to 2 Ma or even less, using methods of biogeochronology. Similar investigation using antelope remains by Alan Gentry at the British Museum of Natural History also contradicted

1156-521: Was performed by Frank Fitch at Birckbeck College in London and Jack Miller at the University of Cambridge in Cambridge, UK, who found a most likely age of 2.61 Ma for the KBS eruption. This find had important implications for the anthropological community because it provided a very old age for the tools found by Behresmeyer, and for associated crania including KNM-ER 1470, attributed to the genus Homo . The date

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