Museum

TUKUL 2: Geology and Volcanology

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Stratigraphy

Melka Kunture stratigraphy

The deposits are located downstream from the Melka Kunture ford and stretch several kilometers along both banks of the upper reaches of the Awash and to the east of a fault that created a graben which was later filled in with Pleistocene sedimentary and  volcanic deposits. In the highlands (2,000 m) there are extensive areas covered with consolidated volcanic ash (ignimbrites), which was itself often covered with brownish-black surface clay, the so called Holocenic black-cotton-soil. The Melka Kunture Formation dates to the Pleistocene. The earliest deposits, ten or so metres thick, probably date to 1.7-1.6 Myr and are presumably preserved under the present level of the Awash. The geological history of the site is characterized by alternating sedimentary or volcanic phases and erosive phases. Tectonic influences cannot be ruled out. According to M. Taieb, the repetition of the fluvio-lacustrine cycles is due to the presence of numerous faults, although also the influence of climatic factors must be taken into consideration. According to J. Chavaillon the most important factors were variations in climate, although with an appreciable tectonic activity towards the end of the Acheulean. The sedimentary deposits are composed of gravels and conglomerates, pebbles, sand and clay; those of volcanic origin consist of relatively clayey tuffs and mainly of a thick layer of ignimbrites incised by the course of the Awash. Six main cycles of erosion-sedimentation tell the geological history of this site and the alternating phases of human presence at Melka Kunture.


The Awash

Cycles of erosion-sedimentation

Six main cycles of erosion-sedimentation tell the geological history of this site and the alternating phases of human presence at Melka Kunture. 

Cycle 1 - The lowest deposits of Melka Kunture, the top of which is represented by the Oldowan sites of Gombore I D-B and Garba IV F-E (1.7-1.6 Myr) with remains of Homo erectus

Cycle 2 - Erosion of the preceding deposits, visible at Gombore, was followed by clayey sediments forming a fossil beach. 

Cycle 3 - Following the erosion phase, the base of the Garba IV D-C levels are visible, following the fluvio-lacustrine sediments,  towards the top of the volcanic ash (Tuff A dated to 1.3-1.1 Myr) overlain by archaeological levels referable to the ancient Acheulean (Garba XII J). 

Cycle 4 - Erosive phases of variable extent followed by deposits of different origin (0.9-0.4 Myr) envelop the levels of Simbiro III and Garba XII H-D at their base, then those of Gombore II (Middle Acheulean with remains of a skull of Homo erectus) and, in the end portion, the level of  Garba I (Upper Acheulean). 

Cycle 5 - An extensive erosion phase, followed by deposits of sand, gravel and ferrugineous deposits incised and destroyed the top of the preceding cycle. Here there are levels dating to the late Acheulean with remains of a skull of Homo sapiens (about 200.000 years). 

Cycle 6 - This incision phase was apparently caused by a new activity of the ancient faults, followed by an accumulation of slope deposits and a sedimentation of clay and sand, which have preserved remains referable to the Middle Stone Age. The entire Melka Kunture Formation was covered by brownish-black alluvial clays which were contemporaneous with human frequentation during the Late Stone Age. 

A strong erosive phase (20 m or more) followed the arrival of the first productive societies, and brought to light the deposits of the preceding periods, creating a landscape similar to that of the present day.


The Awash

 

 

 

 

 


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