Throats of Olduvai
The throats of Olduvai constitute one of the most important complexes of prehistoric sites of East Africa. They delivered faunal lithic industries, vestiges and Hominidé S Fossile S whose ages lie between 1,8 million years and 400.000 years before the present. They also gave their name to the Oldowayen, period of the beginning of the Paléolithique inferior characterized by industries relatively not very elaborate.
Geographical location and geological contextThe throats of Olduvai notch the western slope of the valley of the Rift, in the plain of the Serengeti, in the north of Tanzania and near the border Kenya and in an protected area: the Surface of conservation of Ngorongoro.
- the presence of a lake allowed at the origin a practically continuous Sédimentation on the last two million years and a relatively fast burial of many faunal and lithic remainders;
- the intense volcanic activity, which involved the deposit throughout the sequence of various levels of volcanic ash likely to be dated;
- the setting at the day of this long sequence by the erosion related to the streaming, involving the digging of the throats which notched the various layers while making them available. The long sequence of Olduvai was subdivided in various horizons or Beds .
If the place were sometimes regarded as the “cradle of humanity”, one should not lose sight of the fact that the prehistoric human groups were probably present in many areas of Africa but that Olduvai, a conjunction of favorable factors allowed the conservation then the redécouverte and the study of direct or indirect testimonys of their existence.
History of researchIf the site is known since 1911, the essence of research took place as from 1931, under the direction of Mary and Louis Leakey.
In 1959, the discovery of a cranium of Australopithecus boisei , the “Zinjanthrope”, involved an intensification of work of ground which continued until 1973. Many other vestiges of Hominides were thereafter discovered, of which the bones of OH 7, the Holotype of Homo habilis .
The archeology of Olduvai is described in many publications, including two monographs published under the direction of Mary Leakey, one in 1971 for Beds I and II, the other in 1994 for Beds III, IV and Maseks.
ChronostratigraphyParadoxically, the base of the sequence provided dates surer than the posterior formations: a level of Basalt and a level of Tuf located under Bed I gave dates of about 1,8 million years before the present (Datation with potassium-argon).
The magnetic polarity of the volcanic sediments provided the chronological elements most reliable for the remainder of the sequence. The inversion Brunhes/Matuyama, classically regarded as the limit between Pleistocene lower and average and gone back to 0,7 My, is probably towards the top of Bed IV. Most of Bed II, Bed III and the lower part of Bed IV are thus of magnetic polarity opposite. Although they were set up during the opposite period of Matuyama, Bed I and bases it of Bed II have a normal polarity between approximately 1,7 and 1,85 My: this positive episode which is used from now on as reference mark in the paleomagnetic scales received the name of “event of Olduvai”.
Material fault likely to provide ages radionumeric, Beds III, IV and Masek are gone back by the Paléomagnétisme and estimates based on the rates to sedimentation. The deposits of Bed III would correspond to the period 1,15 - 0,8 My and those of Bed IV at period 0,8 - 0,6 My. Beds Masek would be former to 0,4 My while Beds Ndutu and Naisiusiu, of age higher pleistocene, would be contemporary formation of the Throat itself. According to a recent reinterpretation of the paleomagnetic data, Beds Maseks could be definitely older and fall under the episode of normal magnetic polarity of Jaramillo.
Principal industriesThe industries put at the day with Olduvai were divided into three categories by Mary Leakey:
- the Oldowayen, of which it is the site éponyme. Present in Bed I and a site of the medium of Bed II, it comprises many rollers cut (51%), spheroids, the “discoidal ones”, tools on glare S and of rare proto- Biface S.
- developed Oldowayen itself is subdivided in three sub-groups. Developed Oldowayen, limited to the base of Bed II, is as its name indicates it regarded as a demonstration derived from Oldowayen, with less cut rollers, more thedouble-side ones, but always deprived of truths Biface S. Oldowayen developed B falls under continuity: it comprises some rare double-side low-size and an increasing proportion of tools on glares. It is especially known in the upper part of Bed II. Oldowayen developed C, identified in the upper part of Bed IV, comprises an increased proportion of double-side (7,2%) and many small tools on glares.
- the Acheuléen appears in Olduvai in the middle of Bed II around 1,3 My. It is obviously characterized by the importance of the group of “double-side” (double-side + Hachereau X) which is however decreasing to the profit of small the tools on glare.
The principal raw materials used with Olduvai are volcanic rocks (Basalte, trachyandesite, Phonolite, nephelinite) and Quartzite S. the Gneiss was also employed in an anecdotic way. At the present time, all these materials level in a radius of 13 km around the junction of the two branches of the Throats.
- Leakey, L.S.B. (1951), Olduvai Gorges (Tanganyika) - off has carryforward one the evolution the hand-axis culture in Beds I-IV , Cambridge, University Close, 164 p.
- Leakey, M.D. (1971), Olduvai Gorge - vol. 3: Excavations in Beds I and II, 1960-1963 , Cambridge, Cambridge University Close, 306 p.
- Leakey, M.D. (1994), Olduvai Gorges - vol. 5: Excavations in Beds III, IV and the Masek Beds, 1968-1971 , Cambridge, with the coll of D.A. Roe, Cambridge University Close, 327 p.
- Animation explaining the formation of the deposits of Olduvai
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