In Africa Acheulian stone tool assemblages are defined by the presence of the handaxe (or biface) and/or other large cutting tools (LCTs) such as cleavers, unifaces, or picks/trihedrals. In the absence of LCTs, an assemblage may still be identified as Acheulean by the presence of particular stone working techniques intended to produce large flake-blanks which are further knapped into LCTs. Among these techniques are the Victoria West, Kombewa, Talbalbal-Tachengit techniques.
Trihedrals in Africa seem to be more numerous during the older and early middle Pleistocene. Many of these ensembles could be called either younger Oldowan or older Acheulian. The assemblages in Konso Gardula , Ethiopia were dated to 1.75 million years. The Nachukui Formation is a geological deposit located on the western shore of Lake Turkana, northern Kenya, that includes archaeological sites dated to the earliest stone tool production in the world. The KS4 ensemble, dated to 1.5 million years is characterized by the presence of pick-like tools with a trihedral or quadrangular section, unifacially or bifacially shaped crude hand-axes, and a few cores and flakes. At 1,5 million years ago, Trihedrals were also present in the Levant at Ubeidiya (Israel), situated on the edge of the western escarpment of the Jordan Rift Valley.
At Sidi Abderrahmane near Casablanca Thomas I quarry unit L exhibits classical Trihedrals dated geochronologically and by OSL to about 1 million years. Trihedrals were still present during OIS 16 at the STIC Quarry (see a Trihedral from STIC from the classic Biberson Publication 1961 on the picture above). Here Handaxes were manufactured mainly on various quartzites available close to the site as pebbles of small to medium size and some blocks as well as a few flint nodules collected in a secondary position from beach deposits.
The site of Arkin 8, on the West margin of the Nile at the Sudanese-Egyptian border is undated. However, the character of the stone-tool industry, dominated by heavy duty tools, cordiform, ovate and lanceolate handaxes, as well as Trihedrals; tentatively aligns it with this early Middle Pleistocene group of sites. Similarly undated, early bifaces and trihedral pieces have recently been recorded for the Fazzan, Libya.
Sites of younger Middle Pleistocene age in Noth Africa and Egypt usually have no Trihedrals. This hold true for the younger localities at Sidi Abderrahman – Cap Chatelier, Grotte d’Ours, and Grotte des Littorines and sites in the Fayum depression (associated with the 40 m lake), the Wadi Midauwara in the Kharga depression, at Bir Tarfawi and Bir Sahara East. Geochronometric dating of the Acheulean deposits in the oases of the western desert suggest a minimum age of 350 k.a. while recent work on the geochronology of the fossil-spring tufas of the Kharga Oasis have provided U-series minimum ages of 300 k.a.
In Europe the presence / absence of Trihedrals seem to be not of much chronical value. For example an Acheulian with some Trihedrals is known all along the middle and lower Guadalquivir basin along the main river and several of its tributaries. The geostratigraphic sequence of the Guadalquivir depression is composed of 14 terraces, dated recently by U/Th and paleomagnetic determinations. Acheulian remains are especially concentrated on the middle terraces, dated not earlier than MIS 11. The most common raw material is quartzite and the local Acheulian is characterized by the presence of bifaces, often showing a trihedral concept, cleavers and tools made from medium and large flakes. A similar position of Trihedrals has been proposed for the Acheulian ensembles at the Manzanares at Madrid.
Trihedrals are part of the classic ensemble at La Micoque, layer N. The age of Layer N will possibly remain unknown. After the lower strata have been consistently dated to a glacial circle at 250-300 k.a. BP, there is a possibility that they are much older than traditionally suggested (http://www.aggsbach.de/2010/08/la-micoque-revisited/). Acheulian Trihedrals are part of the “Chalossien” of France, which has never been dated by modern techniques and are also frequent at some “Micoquian” ensembles of Germany (Bocksteinschmiede, Salzgitter Lebenstedt;http://www.aggsbach.de/2011/02/salzgitter-lebenstedt-an-imprortant-paleolithic-site-in-n-germany/ ). These ensembles were part of the Keilmessergruppen, which are dated securely to the last glaciation.