Tracing Provenance of Mesolithic and Neolithic Pottery Along the Nile River by Trace Elements and Sr Isotope Analysis

The aim of this research is to define the provenance of Mesolithic and Neolithic pottery found in some prehistoric sites in Central-Sudan. The study focuses on the analysis of both local raw materials (clay and temper) and ceramic artefacts. In particular, this research is orientated towards the application of Sr isotope analysis (87Sr/86Sr) to pottery characterised by similar pastes in terms of bulk chemical and petrographic composition. Moreover, the possibility of using Sr isotope analysis in provenance studies of pottery in Central Sudan is here investigated. The analysed samples have been found in several Mesolithic and Neolithic sites located along the Nile River across Central-Sudan and on an area located western of the river, in ancient times connected to the Nile by a tributary. The full set of samples includes both raw materials and pottery sherds. A total of 29 clays have been collected between 2013 and 2014 along the Nile system, covering a distance of nearly 1600 km, while during 2015 campaign six more samples have been added to the set of samples. Raw materials are described by a total of 35 geological samples, including clays, sands and rocks. As regards pottery, the initial selection criteria have been discussed with the archaeologist, Sandro Salvatori, and lead to the creation of a set of samples made by Mesolithic sherds found at Al Khiday (16-D-5) characterized by both quartz-tempered paste and decorative motifs that have a wide spatial-temporal distribution in Central Sudan (Rocker stamp dotted zigzag and Rocker stamp plain zigzag). Later, the set have been increased by adding Neolithic quartz-tempered pottery coming from both Al Khiday (16-D-5) and other regions where the same decorative motifs have been found, and in particular from: i) the Wadi Soba area, located along the Blue Nile and particularly the sites of Sheikh Mustafa and Al Mahalab supplied four sherds; ii) the Wadi Howar region lies in southern fringe of the Sudanese Eastern Sahara, and three samples from the site of Ennedi Erg have been studied. Lastly, the study was integrated with the analysis of K-feldspar-tempered pottery that has been found in several prehistoric archaeological sites of central Sudan, included Al Khiday. While raw materials and quartz-tempered pottery have been ground as is usual, pastes of K-feldspar-tempered pottery were micro-drilled in order to collect only the fine matrix and remove the K-feldspar inclusions. The issue regarding K-feldspar provenance is still under debate: it is usually found in combination with specific ceramic decorations (incised wavy line, rocker stamp dotted zigzag packed, alternating pivoted stamp) but its geological origin is attributable to outcrops of granite-like rocks (granite, syenite, and related ring complexes) that lies only in relatively small areas far away from Al Khiday sites (about 80-100 km), as the nearest location where they outcrop. Therefore, movement of raw materials or finite objects? The answer to this issue is very important to define social structure, relationships and exchange patterns within Mesolithic hunter-gatherer-fisher communities of central Sudan. As regards pottery studies, usually the localisation of the supply zone (the zone where people had direct access to the source of raw material/s) and therefore the definition of the provenance area are based on the presence of specific minero-petrographic markers if the ceramic production is committed to coarse pastes. If the pastes are of fine manufacture, the supply zone is identified by geochemical characteristics belonging to specific reference groups (e.g. production wastes). Nevertheless, in many cases the lack of specific traits of both lithological and geochemical nature prevents the resolution of important issues concerning pottery provenance. In the particular case study of Al Khiday, the presence of abundant quartz in the pastes causes a strong dilution effect also on trace elements potentially useful as markers of provenance. In cases where the coarse fraction of a ceramic is composed entirely of quartz (SiO2), which does not contains significant amounts of Rb or Sr, the Sr isotopic composition of the ceramic is derived almost entirely from the clay fraction. For this reason, the region of Central-Sudan is a suitable area where to apply this analytical method. The application of Sr isotopic analysis in ceramic provenance study rests on the premise that the geological origins of the minerals in ceramic pastes are not entirely obscured by processes associated with ceramic production. The comparison between the isotopic fingerprint of clays deposited by the Nile River across the central-Sudan and that of pottery coming from aforementioned prehistoric archaeological sites helped in the interpretation of provenance and production. Some supply zones have been excluded while others turned out to be more than plausible. Nevertheless, the study of pottery through Sr isotope analysis must face also the fact that the ceramic vessels were used in daily life and were subject to contamination by solid and liquid food. The comparison of Sr isotope signatures obtained from clay and pottery yielded information about the mixing processes of Nile sediments along the areas of interest and about some possible supply zones for raw materials used in pottery production. Because of the contamination of the sherds, which is evident analysing the bulk Sr contents, it is possible to make only some hypothesis about pottery provenance but all this information considerably contributed to the reconstruction of the material culture of Mesolithic and Neolithic populations of central Sudan