Les phytolithes, marqueurs des environnements mio-pliocènes du Tchad. Reconstitution à partir du signal environnemental des phytolithes dans l'Afrique subsaharienne actuelle

Ce mémoire présente l'étude du signal phytolithique de sédiments mio-pliocènes du Tchad(Afrique Centrale) datés entre 7-2 Ma, et contemporains des Homininés anciens Sahelanthropustchadensis et Australopithecus bahrelghazali. Une calibration de la relation plantes-phytolithes-solspour l'Afrique tropicale subsaharienne actuelle a d'abord été réalisée pour apprécier la signatureenvironnementale des phytolithes dans le registre fossile. L'analyse des assemblages phytolithiques de98 espèces de graminées (Poaceae) a permis d'élaborer trois nouveaux indices phytolithiques à partirde 43 types propres aux Poaceae. Testés sur une base de 57 sols/sédiments modernes du Tchad, cesindices permettent de tracer les associations graminéennes aquatiques du Lac Tchad, les associationsmésophytiques des milieux humides soudaniens, et les associations xérophytiques des milieux secssahéliens. L'analyse des assemblages phytolithiques des sols/sédiments actuels considérés dans leurensemble a permis d'évaluer le potentiel de ce proxy à caractériser la physionomie des formationssoudano-sahéliennes modernes. La calibration a été appliquée à l'étude d'un enregistrementsédimentaire discontinu du Lac Tchad (6-2 Ma) (forage de Bol, 13N/14E) et à celle de 18 niveauxpaléontologiques du Djourab (7-3.5 Ma) (16N/17E). Les résultats indiquent la présence de savanesintermédiaires à fermées et de zones de végétation aquatique dominantes à 7 Ma dans le Djourab, puisde savanes plus ouvertes et sèches à 3.5 Ma. Une phase de bas niveau lacustre est enregistrée entre3.6-2.8 Ma à Bol, et un pic d'aridité à 3.2 Ma. Enfin, les résultats montrent l'existence de graminéesen C4 au Tchad depuis 7 Ma.This thesis dissertation is dedicated to the study of the phytolith signal of Mio-Pliocenesediments from Chad (Central Africa) dated between 7-2 Ma, and contemporary to the early Homininspecies Sahelanthropus tchadensis and Australopithecus bahrelghazali. A calibration work studyingthe relationship plants-phytoliths-soils in modern sub-Saharan tropical Africa was carried out in orderto assess the environmental significance of the phytolith signal in the fossil record. Phytolithassemblages produced by 98 sub-Saharan grass species (Poaceae) were analyzed and the results led tothe development of three new phytolith indices defined from 43 types specific to Poaceae. Tested on adatabase of 57 modern soil/sediment samples from Chad, these indices allow drawing aquatic grassassociations of Lake Chad, mesophytic grass associations of wetlands from the Sudanian domain, andxerophytic grass associations of drylands from the Sahelian domain. The analysis of modern soilphytolith assemblages (total assemblages) was used to assess the potential of this proxy to characterizethe physiognomy of the Sudano-Sahelian vegetation types. The calibration had been applied to thestudy of a discontinuous sedimentary record from Lake Chad (6-2 Ma) (Bol core, 13N/14E) and of18 paleontological levels from the Djourab (7-3.5 Ma) (16N/17E). The results indicate thedominance of intermediate to closed savannas and areas of aquatic vegetation at 7 Ma in the Djourab,and more open and dry savannas at 3.5 Ma. A limited lacustrine stage is recorded between 3.6-2.8 Maat Bol, and a shift of aridity at 3.2 Ma. Finally, the results show the existence of C4 grasses in Chadsince 7 Ma.POITIERS-SCD-Bib. électronique (861949901) / SudocSudocFranceF

Earliest Porotic Hyperostosis on a 1.5-Million-year-old Hominin, olduvai gorge, Tanzania.

Meat-eating was an important factor affecting early hominin brain expansion, social organization and geographic movement. Stone tool butchery marks on ungulate fossils in several African archaeological assemblages demonstrate a significant level of carnivory by Pleistocene hominins, but the discovery at Olduvai Gorge of a child's pathological cranial fragments indicates that some hominins probably experienced scarcity of animal foods during various stages of their life histories. The child's parietal fragments, excavated from 1.5-million-year-old sediments, show porotic hyperostosis, a pathology associated with anemia. Nutritional deficiencies, including anemia, are most common at weaning, when children lose passive immunity received through their mothers' milk. Our results suggest, alternatively, that (1) the developmentally disruptive potential of weaning reached far beyond sedentary Holocene food-producing societies and into the early Pleistocene, or that (2) a hominin mother's meat-deficient diet negatively altered the nutritional content of her breast milk to the extent that her nursing child ultimately died from malnourishment. Either way, this discovery highlights that by at least 1.5 million years ago early human physiology was already adapted to a diet that included the regular consumption of meat

Paleoenvironmental insights by stable isotopes and phytoliths at Simbiro III Monumental Section (~1.2-1.3 Ma) (Melka Kunture, Upper Awash, Ethiopia) (Abstract)

Depto. de Prehistoria, Historia Antigua y ArqueologíaFac. de Geografía e HistoriaTRUEpu

The European Modern Pollen Database (EMPD) project

Modern pollen samples provide an invaluable research tool for helping to interpret the quaternary fossil pollen record, allowing investigation of the relationship between pollen as the proxy and the environmental parameters such as vegetation, land-use, and climate that the pollen proxy represents. The European Modern Pollen Database (EMPD) is a new initiative within the European Pollen Database (EPD) to establish a publicly accessible repository of modern (surface sample) pollen data. This new database will complement the EPD, which at present holds only fossil sedimentary pollen data. The EMPD is freely available online to the scientific community and currently has information on almost 5,000 pollen samples from throughout the Euro-Siberian and Mediterranean regions, contributed by over 40 individuals and research groups. Here we describe how the EMPD was constructed, the various tables and their fields, problems and errors, quality controls, and continuing efforts to improve the available dat

Signal pollinique et climat de mousson en Inde du Sud

This study investigates the relationship between the pollen signal of evergreen, semi-evergreen and deciduous forests in southwest India and the current monsoon climate. Detailed analysis of 180 soil surface samples collected between 8°-16°N and 0-1400 m altitude enables us to discriminate 9 of the 15 floristic types distinguished by plant mapping. Interpretation of the factorial analyses indicates that the differences in composition between the pollen spectra are the result of climatic constraints on the current vegetation. Temperatures of 20°C and 15°C in the coldest month condition the existence of low-, medium- and high-altitude tropical forests. Annual rainfall, below or above 2,500 mm/year, determines whether vegetation is deciduous or evergreen. The impact of water stress induced by the dry season and assessed by the humidity coefficient E/PE, was also studied. E/PE values of 65% and 75% define the climatic space for different subtypes of evergreen and deciduous vegetation. These new climatic thresholds, responsible for significant changes in pollen rain composition and vegetation, will be incorporated into a future version of the BIOME model. Our research on India thus contributes to the improvement of vegetation models for tropical regions. In addition, current quantitative data on 30 pollen taxa as markers of temperature, 23 of rainfall and 39 of humidity coefficient have been used to develop Pollen-Climate transfer functions by multiple regression. An application to two cores from the Arabian Sea indicates a 50% reduction in rainfall, a 20% increase in water stress and a 2°C reduction in temperature during the Glacial Maximum at latitutes 13°-15°N, in line with modelled fluctuations in the past monsoon.Ce travail étudie la relation entre le signal pollinique des forêts sempervirentes, semi-sempervirentes et décidues du Sud-Ouest de l’Inde et le climat de mousson actuel. L’analyse détaillée de 180 échantillons de surface de sol collectés entre 8°-16°N et entre 0-1400 m d’altitude permet de discriminer 9 des 15 types floristiques distingués par la cartographie végétale. L’interprétation des analyses factorielles indique que les différences de composition entre les spectres polliniques sont le résultat de contraintes climatiques sur la végétation actuelle. Les températures du mois le plus froid de 20°C et 15°C conditionnent l’existence des forêts tropicales de basse, moyenne et haute altitude. La pluviométrie annuelle, inférieure ou supérieure à 2500 mm/an détermine le caractère décidu ou sempervirent de la végétation. L’impact du stress hydrique induit par la saison sèche et évalué par le coefficient d’humidité E/PE, a aussi été étudié. Les valeurs 65% et 75% de E/PE définissent l’espace climatique de différents sous-types de végétations sempervirentes et décidues. Ces nouveaux seuils climatiques, responsables de changements importants dans la composition de la pluie pollinique et dans la végétation, seront intégrés dans une prochaine version du modèle de BIOME. Nos recherches sur l’Inde contribuent donc à l’amélioration des modèles de végétation pour les régions tropicales. De plus, les données quantitatives actuelles de 30 taxons polliniques marqueurs de la température, 23 de la pluviométrie et 39 du coefficient d’humidité ont permis d’élaborer par régression multiple, des fonctions de transfert Pollen – Climat. Une application à deux carottes de la Mer d’Arabie, indique une pluviométrie réduite de moitié, un stress hydrique augmenté de 20% et une température réduite de 2°C pendant le Maximum Glaciaire aux latitutes 13°-15°N, en accord avec les fluctuations modélisées de la mousson passée

Signal pollinique et climat de mousson en Inde du Sud

This study investigates the relationship between the pollen signal of evergreen, semi-evergreen and deciduous forests in southwest India and the current monsoon climate. Detailed analysis of 180 soil surface samples collected between 8°-16°N and 0-1400 m altitude enables us to discriminate 9 of the 15 floristic types distinguished by plant mapping. Interpretation of the factorial analyses indicates that the differences in composition between the pollen spectra are the result of climatic constraints on the current vegetation. Temperatures of 20°C and 15°C in the coldest month condition the existence of low-, medium- and high-altitude tropical forests. Annual rainfall, below or above 2,500 mm/year, determines whether vegetation is deciduous or evergreen. The impact of water stress induced by the dry season and assessed by the humidity coefficient E/PE, was also studied. E/PE values of 65% and 75% define the climatic space for different subtypes of evergreen and deciduous vegetation. These new climatic thresholds, responsible for significant changes in pollen rain composition and vegetation, will be incorporated into a future version of the BIOME model. Our research on India thus contributes to the improvement of vegetation models for tropical regions. In addition, current quantitative data on 30 pollen taxa as markers of temperature, 23 of rainfall and 39 of humidity coefficient have been used to develop Pollen-Climate transfer functions by multiple regression. An application to two cores from the Arabian Sea indicates a 50% reduction in rainfall, a 20% increase in water stress and a 2°C reduction in temperature during the Glacial Maximum at latitutes 13°-15°N, in line with modelled fluctuations in the past monsoon.Ce travail étudie la relation entre le signal pollinique des forêts sempervirentes, semi-sempervirentes et décidues du Sud-Ouest de l’Inde et le climat de mousson actuel. L’analyse détaillée de 180 échantillons de surface de sol collectés entre 8°-16°N et entre 0-1400 m d’altitude permet de discriminer 9 des 15 types floristiques distingués par la cartographie végétale. L’interprétation des analyses factorielles indique que les différences de composition entre les spectres polliniques sont le résultat de contraintes climatiques sur la végétation actuelle. Les températures du mois le plus froid de 20°C et 15°C conditionnent l’existence des forêts tropicales de basse, moyenne et haute altitude. La pluviométrie annuelle, inférieure ou supérieure à 2500 mm/an détermine le caractère décidu ou sempervirent de la végétation. L’impact du stress hydrique induit par la saison sèche et évalué par le coefficient d’humidité E/PE, a aussi été étudié. Les valeurs 65% et 75% de E/PE définissent l’espace climatique de différents sous-types de végétations sempervirentes et décidues. Ces nouveaux seuils climatiques, responsables de changements importants dans la composition de la pluie pollinique et dans la végétation, seront intégrés dans une prochaine version du modèle de BIOME. Nos recherches sur l’Inde contribuent donc à l’amélioration des modèles de végétation pour les régions tropicales. De plus, les données quantitatives actuelles de 30 taxons polliniques marqueurs de la température, 23 de la pluviométrie et 39 du coefficient d’humidité ont permis d’élaborer par régression multiple, des fonctions de transfert Pollen – Climat. Une application à deux carottes de la Mer d’Arabie, indique une pluviométrie réduite de moitié, un stress hydrique augmenté de 20% et une température réduite de 2°C pendant le Maximum Glaciaire aux latitutes 13°-15°N, en accord avec les fluctuations modélisées de la mousson passée

Vegetation of Northern Tanzania during the Plio-Pleistocene: A synthesis of the paleobotanical evidences from Laetoli, Olduvai, and Peninj hominin sites

International audienc

Phytoliths of East African grasses: An assessment of their environmental and taxonomic significance based on floristic data

International audienceRelations between phytolith occurrences. taxonomy, and habitat are assessed for 184 East African grass species through the re-analysis of two qualitative surveys of phytolith types in leaf epidermis. This is done in conjunction with data on grass subfamily, photosynthetic pathway, and requirement for light and moisture compiled from floras and the literature. This survey includes ca 79% of the grass genera listed in the flora of tropical East Africa. It aims to further investigate the potential for grass short cell phytoliths to characterize the environment, and therefore improve reconstructions of past vegetation and climate in Africa. In this analysis, we identified ca 60 phytolith types (within the main categories Rondel, Trapeziform Short Cell, Bilobate, Cross, Polylobate, Saddle, and Trapeziform Sinuate) reported to occur in 10 grass subfamilies (Pharoideae, Bambusoideae, Ehrhartoideae, Pooideae, Danthonioideae, Arundinoideae, Chloridoideae. Centothecoideae, Panicoideae, and Incertae Sedis Streptogyna). These subfamilies include hydrophytic, helophytic, mesophytic and xerophytic species, with C3 or C4 photosynthetic pathways, and with affinities for shade, open, or semi-shade habitats. Analysis of phytolith occurrences shows that few morphotypes are restricted to some species only. However, there are morphological variations (of size and number of lobes) within the main phytolith categories Rondel, Bilobate, and Cross, which could additionally be considered to improve environmental and taxonomical interpretation of phytolith assemblages. The Rondel phytolith with a base diameter >15 mu m was only reported in C3-Pooideae, while the Rondel with a base diameter of <15 mu m occurs in several grass subfamilies (including Pooideae). Bilobates with long shanks between the two lobes are most frequently reported in xerophytic species, while Bilobates with short shanks are most frequently reported in mesophytic grass species. Finally, three-lobed crosses are reported only in Panicoideae and Chloridoideae, all being C4, light-loving species. A correspondence analysis confirms already known relationships between 1) Saddle forms, C4 pathway, open and xeric habitats, 2) Bilobates, Crosses, Polylobates, shaded and hydric habitats, 3) Trapeziform Sinuates and Pooideae. Of major implication for palaeoenvironmental reconstructions in East Africa, we found that the Trapeziform Sinuate phytoliths mark the presence of C3-grasses in the Afromontane zone, whereas the Rondels alone do not because they also occur in many C4 species of the Chloridoideae subfamily. We also establish that collapsed saddles are not diagnostic for Bambusoideae closed-habitat grasses since they occur in xerophytic species of the Chloridoideae, characteristic of several open habitats. In conclusion, this study contributes to better characterize Afromontane vegetation and better discriminate mesic and xeric vegetation types in East Africa. It also brings caution for future phytolith studies that rely on the presence of diagnostic types instead of phytolith assemblage analysis to trace the presence of particular taxa and/or environments in East Africa

Grass inflorescence phytoliths of useful species and wild cereals from sub-Saharan Africa

International audienceDendritic phytoliths that precipitate in grass inflorescences are often used in archaeology to trace the use of cereals (i.e. grasses harvested for their edible grain) and their domestication by early human societies. High amounts of these morphotypes are sometimes interpreted in terms of cereal accumulation in archaeological contexts. In sub-Saharan Africa, few cereals were domesticated during the mid-Holocene, but many wild grasses are still largely harvested by modern societies for food. The harvesting of wild cereals is also considered as one of the first stages toward early grass domestication. To evaluate how well dendritic phytoliths and/or other phytoliths produced in the grass inflorescences could help trace the use of wild cereal grains in sub-Saharan Africa, we analyzed the phytolith content of 67 African species (including 20 wild cereals), and 56 modern soils. We used test-value analysis and ANOVA to evaluate how well grass inflorescences could be distinguished from leaf/culm parts based on their phytolith content. We also measured the abundances of these phytoliths in natural soils from sub-Saharan Africa to provide a benchmark percentage abundance above which anthropogenic accumulation may be suspected in archaeological deposits. Our results confirm that, although rondel type phy-toliths are abundant, only the dendritic phytolith morphotype is exclusive to the grass inflorescences. Yet, dendritic phytoliths do not occur in all species. They happen to be most frequent and found in greatest abundance (>34% relative to total phytolith count) in Panicoideae grasses (Sehima ischaemoides, Sorghastrum stipoides, and Sorghum purpureo-sericeum), and in one Eragrostideae species (Eragrostis squamata), which are not considered cereals. Inflorescences of the wild African cereals studied here do not happen to be particularly rich in dendritics (>3% relative to sum of grass silica short cell phytoliths plus dendritics are likely to indicate anthropogenic accumulation of grass inflorescences. Yet, the absence or low abundance of dendritic phytoliths in archaeological deposits may not always indicate the absence of anthropogenic accumulation of grass inflorescence material