Contextes et âge des nouveaux restes dentaires humains du Pléistocène moyen de la carrière Thomas I à Casablanca (Maroc)

Abstract

Contexts and age of the new dental human fossils from Middle Pleistocene deposits at Thomas Quarry I (Casablanca, Morocco) – The Thomas Quarry I locality became famous in 1969 with the discovery of a human half-mandible in a cave. From 1988 onwards, modern controlled excavations took place within the framework of the Franco-Moroccan co-operative project “ Casablanca.” The stratigraphy of Thomas I Quarry is complex and represents several major episodes of coastal sedimentation that are dated to the final Lower and early Middle Pleistocene on the basis of a detailed regional lithostratigraphical and microfaciological study and form the Oulad Hamida Morpho-stratigraphic Unit. Within this MSU, some lithostratigraphic units fossilize a polyphase palaeo-shoreline in which caves have developed. A continental sediment series dated to the Middle and Upper Pleistocene on lithostratigraphical and biochronological evidence and by OSL is preserved in the Hominid Cave (GH). The top of the GH general stratigraphy shows a red complex with abundant microfauna (stratigraphic unit 1). Below this, a multilayer dripstone floor interbedded with loose red sands (stratigraphic units 2-3) caps the lower stratigraphic units (4 and 5). Stratigraphic unit 4 contains artefacts, fauna and hominid fossils and rests on collapsed eolianite blocks imbedded in coarse sands which form stratigraphic unit 5 ; this lowermost intertidal unit fossilizes a notch in the polyphase shoreline. The Acheulean lithic assemblage recovered by recent excavations in GH stratigraphic unit 4 is similar to the series collected at the time of the discovery of the first Homo fossil in 1969. It is 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 flint nodules derive from the phosphatic plateau of the Meseta hinterland and were carried to the ocean by wadis. The assemblage consists of chopper-cores (mainly unifacial unidirectional cores with a retouched cutting edge) and cores, semi-cortical flakes obtained by direct and bipolar knapping, along with rare handaxes made from large flakes or from flat pebbles, handaxe-like cores, hammerstones and anvils. Stone knapping was mainly oriented towards flake production and a few handaxes were probably imported to the site. A rich mammalian macrofauna supplemented by the addition of a few reptiles and birds is associated with the lithics in GH stratigraphic unit 4. The abundance and diversity of carnivores attest to their use of the cave. The most common species is a middle-size canid, with enlarged crushing part of the dentition. The fauna indicates an open woodland environment and suggests an age younger than Tighenif in Algeria, but the remoteness of this latter site, its distance from the seashore, and the fact that it is an open-air site may account for some of the differences. Preliminary taphonomic analysis of the megafauna indicates that the carcasses were processed by carnivores. Cut-marks are still absent from this assemblage despite the association with refitted lithic artefacts, which raises the question of any human role in the bone accumulations. Similar cases of accumulations created by humans, carnivores and porcupines have already been described in the Mediterranean area. However, the studied assemblage comes from inside the cave, whereas any human occupation may well have been concentrated closer to the entrance. Geological studies have demonstrated that unit 4 containing the assemblage results from several sedimentary processes having possibly mixed artefacts with bones previously accumulated by predators. Between 1994 and 2005, four teeth of Homo were recovered in stratigraphic unit 4, a right upper premolar (ThI 94 OA 23-24), another right upper premolar (ThI 95 SA 26 no 89), a first left upper incisor (ThI 95 SA 26 no 90) and a left upper premolar (ThI 2005 PA 24 no 107). The teeth are larger than those of modern humans and show moderate to heavy wear Laser ablation ICP-MS dating combining tESR and U-series data for modelling U-uptake has given an US/ ESR age of 501 ka for a human premolar while new OSL measurements yielded an age of 420 ± 34 ka for sediments immediately above the dated tooth and 391 ± 32 ka below. Nevertheless, biostratigraphy and lithostratigraphy point to greater antiquity, towards the base of the Middle Pleistocene. + 94 − 76