Etude des roches magmatiques birrimiennes de la region de Sonfara-Laminia-Medina Foulbe (Senegal oriental)

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Diversity of the Palaeoproterozoic granitoids of the Kédougou inlier (eastern Sénégal): Petrographical and geochemical constraints

International audienceField, petrographical and geochemical studies of the Palaeoproterozoic granitoids of the Kédougou inlier (Eastern Sénégal) allow to define four compositional types: (i) the Layered Plutonic Complex consisting of sodic calc-alkaline granitoids defining a trend from Opx-, Cpx- and amphibole-bearing layered gabbros to amphibole-bearing tonalite; the latter shows similarities with adakite-like rocks; (ii) amphibole-bearing granitoids with TTG features occurring as composite batholiths and as isolated oval-shaped plutons cross cutting the entire Birimian metavolcanic and metasedimentary formations; (iii) potassic granitoids defining a trend from Opx-, Cpx-bearing gabbros to amphibole-bearing monzodiorite and preferentially emplaced within the calc-alkaline metavolcanites; (iv) peraluminous biotite-bearing granitoids emplaced within the metasediments of the upper part of the Birimian lithostratigraphical pile. The granitoid suites were emplaced within a time interval of about 80 Ma from about 2160 Ma (emplacement of the LPC) to 2080 Ma (emplacement of the youngest plutons such as the amphibole-bearing TTG granitoid or the pyroxene- and K-feldspar-bearing granitoids). The granitoid suites were emplaced in an immature arc environment [Dia, A., Van Schmus, W.R., Kröner, A., 1997. Isotopic constraints on the age and formation of a Palaeoproterozoic volcanic arc complex in the Kedougou inlier, eastern Senegal, West Africa. J. Afr. Earth Sci. 24 (3), 197 213]. Parental magmas were probably derived from the partial melting of a mantle wedge above a subduction zone. Tonalite magmas of distinctive composition were probably produced by partial melting of the subducting slab itself. They could characterize the early stage of the slab-melting, precursor of the TTG magmatism. The close association of calc-alkaline, trondhjemitic and peraluminous granitoids and the successive emplacement of granitoid groups more and more enriched in K2O recognized in the Kédougou inlier is typical of the Paleoproterozoic granitoid series from West Africa

K–Ar mineral ages and thermal history of magmatic and metamorphic Paleoproterozoic units from the northern part of Kedougou inlier, West African Craton (eastern Senegal).

International audienceThe northern part of the Kedougou Kenieba Inlier (Eastern Senegal) is composed of Palaeoproterozoic volcano-plutonic and volcano-sediment areas cross-cut by differentiated plutonic bodies of gabbroic to granitic composition. They are emplaced in an arc-type environment and accreted during the Eburnean Orogeny. We present here new K–Ar ages obtained on several plutons from different mineralogical phases, each characterized by a different closure temperature for the K–Ar system. Ages from hornblende, between 2013 ± 29 and 2141 ± 30 Ma, constrain the cooling history of the magma bodies through the 550 °C isotherm. They are slightly younger than U–Pb ages previously obtained from the same units, attesting of a rapid cooling, tectonically controlled, of about 7 °C/Myr. Ages obtained on biotite minerals range from 1955 ± 28 to 1893 ± 27 Ma, suggesting that from 550 to 325 °C, cooling rate decreased to about 3 °C/Myr. Significantly younger ages ranging from 1704 ± 24 to 1615 ± 23 Ma have been obtained on plagioclase and microcline. They can be interpreted in terms of either a slow cooling with a rate of only 1 °C/Myr, from about 1.9 to 1.6 Ga, or either reflecting the occurrence of a rather limited thermal event younger than 1.7 Ga. Since no age younger than 2.0 Ga has previously been obtained for plutonic rocks from the early Birimian in the West African Craton, ages of 1.7–1.6 Ga obtained here from feldspars might be the first evidence for a regional re-heating event having occurred in the East–North Kedougou Kenieba inlier

Composition nutritionnelle et apport énergétique du fruit de Maerua pseudopetalosa, aliment de soudure au Sénégal

International audienceNutritive composition and energy contribution of the fruit of Maerua pseudopetalosa, a food extender in Senegal. Abstract-Introduction. The foods known to be used in times of food shortage, the majority of which are fruits, are identified all over the world such as in Australia, in Sudan, in Senegal, in America, in Sahel and in Chad. The work carried out on these fruits often concerns their nutritive values. In Senegal, Maerua pseudopetalosa (Gil & Gil-Ben) De Wolf, a species of the Capparidaceae family, provides consumable fruits to the native populations for the lean period. No scientific study has yet reported the nutritive composition and energy contribution of this species' fruit. Our study evaluated its contribution of nutritive elements. Materials and methods. Mature fruits of M. pseudopetalosa were collected in June 2007 and May 2008 in the neighborhoods of the villages of Kéniéba and Koussane, in the area of Tam-bacounda in Senegal. The almonds were dried and crushed for the requirements of various samples. Ashes, protein, sugars, fat and mineral elements were determined by standardized traditional methods of analysis. Results and discussions. Our results show that the fruit of M. pseudopetalosa is rich in iron (26.8-45.9 mg·kg-1), potassium (1098-1342 mg·kg-1) and protein (19.26-22.06%). However, the amino acid profile testifies to the poor nutritional quality of its protein. Conclusion. Our analysis shows that, despite everything, the M. pseudopetalosa fruit constitutes an excellent source of nutrients and can validly make up certain deficiencies, especially in periods of food shortage. Senegal / Maerua pseudopetalosa / fruits / proximate composition / mineral content / food supply Composition nutritive et apport énergétique du fruit de Maerua pseudopetalosa, aliment de soudure au Sénégal

K-Ar mineral ages and thermal history of magmatic and metamorphic Palaeoproterozoic units from the northern part of Kedougou Kenieba Inlier, West African Craton (Eastern Senegal)

International audienc

K-Ar mineral ages and thermal history of magmatic and metamorphic Palaeoproterozoic units from the northern part of Kedougou Kenieba Inlier, West African Craton (Eastern Senegal)

International audienc

Shellfishing and shell midden construction in the Saloum Delta, Senegal

International audienceThe Saloum Delta, Senegal, is renowned for its vast shell middens which date to at least 5000 BP and in many cases, also contain numerous burials. Though archaeological work has been conducted here for over 70 years, the focus has been on obtaining radiocarbon dating sequences and rescue excavation; little is known in detail about the middens or the people who built them. Today, the Sereer Niominka people of the Saloum Delta continue to collect and trade shellfish using traditional methods. This has offered an opportunity to observe these processes in practice, and examine the archaeological footprints they produce. These ethnoarchaeological observations have provided new perspectives on the development of large shell middens that will contribute to a better understanding of the archaeological landscape here and will also be of relevance to midden-rich environments, more widely

Amas et sites coquilliers du delta du Saloum (Sénégal) : Passé et présent

International audienceThe three main branches of the Saloum delta: the Saloum in the north (110 km), the Diombos (30 km) and the Bandiala in the south (18 km) are joined by numerous small channels, locally called “bolons”. They create many islands that are bordered by dense mangrove and comprise three ecological zones: maritime, amphibious and continental. The delta comprises an area of around 500,000 ha and is inhabited by human communities that have been involved in maritime activities for well over two millennia. These include the exploitation of shellfish including the bivalves oyster, Crassostrea gasar, and cockle (Arca senilis) as well as the gastropods “Yett” (Cymbium spp.) and “Touffa” (Murex spp., Thais spp.), and the cuttlefish (Sepia officinalis), all of which proliferate in the Delta. Artificial shell mounds comprising bivalves and gastropods provide evidence for a human presence in the Delta for well over 2000 years. In some cases, the shell mounds have also been reused as burial grounds and contain many remains of the ancient fisher-collector inhabitants. The Saloum delta is: (1) an exceptional archaeological landscape with many hundreds of sites, and several periods of excavation, including 1939 (J. de Saint-Seine, M. Yvetot, T. Monod), 1951-1956 (H. Bessac, R. Mauny, G. Thilmans and C. Descamps), in 2000 (H. Bocoum, A. Camara, C. Descamps, E. Dioh, M. Gueye, A.A. Seck, G. Thilmans); (2) an archaeological heritage comprising shell mounds which support many baobab trees (Adonsonia digitata). In some cases, these trees become “sacred forests or woods” where ritual activities take place near modern villages; (3) a rich natural heritage containing shell mounds that have become refuges for wildlife especially birds, and flora…; (4) a cultural landscape comprising enduring traditions that are thousands of years old, based on shellfish harvesting and fishing, in a fragile natural environment of great biodiversity. It is one of the few places in the world where traditional shellfishing still survives. Researchers from Cheikh Anta Diop University in Dakar (A. Camara, E. Dioh, M. Guèye, M. Sall) and a team from the Autonomous University of Barcelona (UAB) (K. Hardy, R. Piqué, J. Marti) have been conducting ethnoarchaeological research on the Atlantic coast and the Gokehor bolon since 2010. The focus of the work is to document the distribution of the archaeological shell middens, conduct excavations, obtain samples for radiocarbon dating and record the cultural traditions associated with the current collection of shell middens. There are many features of this research that will be of interest to archaeologists, as well as contributing data in palaeoclimatology, archaeozoology and malacology in a delta inscribed on UNESCO's World Heritage List in 2011 on the basis of criteria III, IV and V.Les trois bras principaux du delta du Saloum : le Saloum au Nord (110 km), le Diombos (30 km) et le Bandiala au Sud (18 km) s’emboîtent par une infinité de petits canaux, appelés localement « bolons ». Ils créent de nombreuses îles bordées d’une mangrove dense qui font apparaître trois ensembles écologiques : un domaine maritime, un domaine insulaire et amphibie et un domaine continental. S’étendant sur environ 500 000 ha, le delta est habité par des communautés humaines qui y mènent, depuis plus de deux millénaires, des activités basées sur des ressources halieutiques dont une bonne partie concerne l’exploitation des mollusques : huîtres (Crassostrea gasar), les « Yett » (Cymbium spp.), les « Touffa » (Murex spp., Thais spp.) et les arches (Arca senilis) ainsi que les seiches (Sepia officinalis) qui prolifèrent dans ce biotope. Témoins d’activités dont les plus anciennes remontent dans le delta à plus de 2000 ans, des milliers d’amas de coquilles de bivalves et de gastéropodes constituent des vestiges archéologiques. Ces restes de consommation ont été aussi réutilisés comme éléments de construction de nécropoles, de tumulus funéraires par d’anciens pêcheurs-collecteurs. Le delta du Saloum est : (1) un paysage archéologique exceptionnel constitué de centaines de sites dont certains ont fait l’objet de fouilles en 1939 (J. de Saint-Seine, M. Yvetot, T. Monod), en 1951-1956 (H. Bessac, R. Mauny, J. Figuie), en 1971-1973 (G. Thilmans et C. Descamps), en 2000 (H. Bocoum, A. Camara, C. Descamps, E. Dioh, M. Guèye, A.A. Seck, G. Thilmans) ; (2) un patrimoine archéologique réutilisé par les populations d’aujourd’hui pour leurs espaces peuplés de baobabs (Adonsonia digitata) comme des « forêts ou bois sacrés » pour des libations et des sacrifices à faible distance des villages actuels ; (3) un patrimoine naturel avec des amas devenus des niches, des refuges pour la faune en particulier les oiseaux et la flore ; (4) un paysage culturel d’une tradition millénaire toujours vivante privilégiant un mode de vie basé sur la cueillette des coquillages et sur la pêche, dans un milieu naturel fragile d’une grande biodiversité et l’un des rares endroits au monde où les pratiques de collecte des coquillages survivent. Des chercheurs de l’Université Cheikh Anta Diop de Dakar (A. Camara, E. Dioh, M. Guèye, M. Sall) en collaboration avec une équipe de l’Université Autonome de Barcelone (K. Hardy, R. Piqué, J. Marti) mènent depuis 2010 des recherches ethnoarchéologiques dans la bordure atlantique et du bolon de Gokehor pour compléter les inventaires, les fouilles, les datations, les traditions culturelles associées de près ou de loin à la collecte actuelle des coquillages. Les intérêts de ces recherches sont multiples pour les informations archéologiques, paléoclimatiques, archéozoologiques, malacologiques dans un delta inscrit en 2011 sur la Liste du patrimoine mondial de l’UNESCO sur la base des critères III, IV et V