Afar depression

The Afar Depression in Ethiopia (O Figure 11.2) is one of the world's hotspots in two ways. The temperature can climb up to more than 45°C during daytime in the endless plains of the Afar, and fieldwork is a great challenge in the extreme African sun. Still, for paleoanthropologists and paleontologists who deal with the evolution of early humans, this investigation can be of great interest since the area of about 150,000 km2 bears some of the richest hominid sites in the world. In that

O Figure 11.2

The outlines of the Afar depression in the northeast of Ethiopia draw a triangle of about 150,000 km2. This huge basin contains fossiliferous sediments ranging in age from the Upper Miocene to recent times. The most famous hominid localities in the Afar triangle are Hadar and the Middle Awash area. The Omo Valley is located far south in the main rift, where the Omo river crosses the border into Kenya. The fossil-rich area of Koobi Fora belongs to the Lake Turkana localities in Kenya, where thick sediment deposits surround the recent Lake. Olduvai and Laetoli are positioned within the eastern branch of the EARV, while the Chad Basin reflects an intracratonic depression about 2,500 km west of the Great Rift Valley with widespread deposits of the ancestral Lake Chad

context, the Afar Depression contains fossils from the earliest time interval of humankind, 5-6 Ma, right up to the youngest.

Since the beginning of the 1970s, the Afar Triangle has been in the spotlight of international paleoanthropological field research. Numerous hominid findings, like the skeleton of the famous "Lucy," come from here. Paleontological work in Ethiopia started in 1902, when the Frenchman Robert de Bourg de Bozas discovered fossil-rich deposits in the lower Omo Valley north of the Kenyan boundary (O Figure 11.2).

Nevertheless, the first fossil hominid from Ethiopia, a lower jaw, was discovered only in 1933, in a cave close to Dire Dawa in the east. Likewise in 1933, the French paleontologist Camille Arambourg lead an expedition to the fossiliferous sediments of the Omo river (Arambourg 1933). Although no hominid remains were discovered during the fieldtrip, the team collected numerous animal fossils (Arambourg 1947). In 1967, an Ethiopian-American-French-Kenyan Team under the direction of Clark Howell and Yves Coppens, and with the collaboration of Camille Arambourg, started the intensive search for hominid fossils in the Omo region (Arambourg et al. 1967; Arambourg and Coppens 1968a, b; Coppens et al. 1976). Up to 1973, they recovered several hominid remains in the Usno, Mursi and Shungura formations in the Omo River Basin. This initiated a "homi-nid-rush'' in Ethiopia, which continues today.

When the French geologist Maurice Taieb in 1970 announced the discovery of fossil-rich deposits at Hadar, further north in the Afar depression, the search for hominid remains shifted into the Afar region (Taieb et al. 1972, 1974). It was at Hadar that Donald Johanson and his team found the most complete A. afarensis skeleton in 1973. Inspired by a Beatles song, they named it "Lucy" (Johanson and Edey 1981). From 1975 to 1978, the American geologist Jon Kalb explored with his colleagues of the "Addis Abeba Rift Valley Research Mission in Ethiopia'' (RVRME) the sediments in the "Middle Awash'' region (Kalb et al. 1982a, b), where they have documented one of the best known lithological sequences in the Afar Triangle containing fossil evidence of human evolution. The sediments cover a time-span of more than 6 Myr. Intercalated volcanic ash and lava horizons permit the absolute dating of sandwiched river and lake deposits, and thereby provide a unique insight into the evolutionary history of humankind. Since the early 1990s Tim White and his "Middle Awash Research Project'' have investigated successfully in these deposits. They have collected a large mammal assemblage including numerous hominid fossils, like the first remains of Ardipithecus ramidus (White et al. 1994). Since spring 2000, the international PAR-Team (Paleoanthropological Research Team), under the direction of Horst Seidler, has investigated deposits further south of the "Middle Awash'' in a fossil-rich area in the Somali region, called Galili, about 100 km north of the Awash railway station and town in the vicinity of the rift shoulder (Macchiarelli et al. 2004).

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