Bouri Formation

The Bouri Formation is a sequence of sedimentary deposits that is the source of australopithecine and Homo (that is, hominin) fossils, artifacts, and bones of large mammals with cut marks from butchery with tools by early hominins. It is located in the Middle Awash Valley, in Ethiopia, East Africa, and is a part of the Afar Depression that has provided rich human fossil sites such as Gona and Hadar.

The Bouri Formation stretches down much of the length and breadth of the Bouri "peninsula", which projects across the dry bed of the Afar Depression. The Formation is sufficiently eroded to expose three geological members or layers: the Hatayae, the Dakanihylo, and the Herto. Human remains with signs of having been prepared for burial have been found in the Upper Herto layers.

The Bouri "peninsula" is a geological fault-raised horst that diverts the Awash River, forming a partial dam and creating Lake Yardi; and it contains the Bouri Formation. The peninsula is about 4 km wide by 10 km long, and lies in a NNW-SSE direction in the Quaternary-period rift zone in the southern part of the Afar Depression (Afar Triangle).

The Bouri Formation is a sediment area some 80 m thick that stretches down much of the length and breath of the peninsula. The formation consists of three geological units, called members, from which fossils and artifacts of different periods of human evolution have been excavated. They are: the lowest member, named Hatayae, or the Hata, dated to 2.5 millions of years ago (mya)—and in which fossils of Australopithecus garhi were found; the Dakanihylo, or Daka, member, one (1) mya—fossils of Homo erectus were found; and the Herto member, Lower layer at 260 kya, and Upper layers at 160 to 154 kya—fossils of Homo sapiens idaltu were found.

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