Datations radiométriques de l'extinction des grandes faunes pléistocènes au Pérou.

International audienceThe discovery in northern Peru of fossil deposits belonging to large mammals allows the dating of the extinction of this fauna. The method based on desequilibrium within the uranium family (230Th/234U) was used. The extinction occurred at the end of the Pleistocene (15-16 Kyrs Cal BP) and is contemporaneous with the beginning of the deglaciation. Moreover, this dating, compared with the results of excavations of palaeo-indian "Paijan" sites, indicates that human groups in Peru did not play a significant role in the extinction of this large fauna.Les restes osseux découverts dans les gisements paléontologiques à grands mammifères du Pérou ont pu être datés par la méthode fondée sur les déséquilibres de la famille de l'uranium (230Th-234U). L'extinction de cette grande faune coïncide avec la fin du Pléistocène et le début de la déglaciation (15-16 Ka Cal BP). La chronologie et les fouilles menées dans les gisements paijaniens montrent que les groupes humains préhistoriques au Pérou ne semblent pas avoir joué un rôle significatif dans cette extinction qui semble être la conséquence de changements climatiques importants dans cette région

Carbonisation de brais en milieu géométriquement limité (application aux composites carbone-carbone granulaires)

ORLEANS-BU Sciences (452342104) / SudocSudocFranceF

: Radiometric dating of the extinction of the large Pleistocene fauna in Peru

The discovery in northern Peru of fossil deposits belonging to large mammals allows the dating of the extinction of this fauna. The method based on disequilibrium within the uranium family (230Th234U) was used. The extinction occurred at the end of the Pleistocene (15-16 kyrs Cal BP) and is contemporaneous with the beginning of the deglaciation. Moreover, this dating, compared with results of excavations of palaeo-lndian " Paijân " sites, indicates that human groups in Peru did not play a significant role in the extinction of this large faunaLes restes osseux découverts dans les gisements paléontologiques à grands mammifères du Pérou ont pu être datés par la méthode fondée sur les déséquilibres de la famille de l'uranium (230Th/234U). L'extinction de cette grande faune coïncide avec la fin du Pléistocène et le début de la déglaciation. (15-16 000 ans Cal BP). La chronologie et les fouilles menées dans les gisements paijaniens montrent que les groupes humains préhistoriques au Pérou ne semblent pas avoir joué un rôle significatif dans cette extinction qui semble être la conséquence de changements climatiques importants dans cette région

四极杆电感耦合等离子体质谱仪 测定动物牙化石中 Ｕ和 Ｔｈ同位素

International audienceOver the past two decades TIMS and MC-ICP-MS have become the main techniques used for high-precision of 230 Th/U dating studies.Recently,a relatively simply and cheap technique for U-Th isotopic analysis was developed by using Inductively Coupled Plasma-Quadrupole Mass Spectrometry(ICP-QMS).With precisions about 0.3 % and 1 % for U and Th isotope analyses,this technique has the ability to estimate sample’s 230 Th/U age with 1 % ~10 % uncertainty.In this work,we use this new technique analyzed four fossil teeth coming from the Acheulian site of Venosa Loreto,southern Italy,where the faunal remains indicate an early Middle Pleistocene age.The previously published purification procedure of U and Th by UTEVA resins was modified for the fossil teeth.The UTEVA resins can efficiently extract U but not Th from the HNO3 solution of dental samples,in the presence of large amount of phosphates.In the present work,Th was allowed to co-precipitate with iron,then was loaded on anion exchange resin column in 7N HNO3 condition.In such strong HNO3 solution Th will be fixed onto the column,and can be diluted by 6N HCl.The U-Th isotope analysis with ICP-QMS was carried out on each dental tissue(enamel,dentine and cementum)of fossil teeth and yielded data with precision on average of 0.3 % and 0.6 % for 238 U and 232 Th contents,and of 0.3 % and 0.8 % for activity ratios of 234 U/238 U and 230 Th/238 U at 2σ uncertainty level,respectively.Our results show that U-contents in fossil teeth can be as high as 1000 ppm,but may differ from tissues by 1~2 orders of magnitude.On the other hand,for each tooth,dental tissues show substantial dispersion( >2σ)in their activity ratios of 234 U/238 U and 230 Th/238 U,consequently leading to scattered 230 Th/U dates,ranging from 139±2ka to 425±48ka.Fossil teeth thus are not ideal targets for 230 Th/U dating because of their open-system behavior,but the measured present-day U-Th isotopic information is useful for simulation of U-uptake histories experienced by dental tissues,and a combination of U-series and ESR analyses on fossil teeth seems a better way for age estimation

La faune du Pléistocène supérieur - Holocène ancien de la Toca da Pena (Piauí, Brésil) - étude paléontologique

International audienceThe site of Toca da Pena corresponds to a small cave located in the limestone massif of Antero, south of the Serra de Capivara and 7 km to the east-north-east of the town of Coronet Jose Dias. Excavations, undertaken between 2008 and 2014, together with some lithic artefacts, have yielded numerous osseous remains. Almost half of them are reported to Scelidodon piauiense, a ground sloth which was the size of a large cattle. This Mylodontidae is associated with Leopardus pardalis, Hippidion, Tayassu pecari, Mazama gouazoubira, Mazama americana and Palaeolama niedae.This faunal association allows us to date this site of the Upper Pleistocene or the Early Holocene. Moreover, the Toca da Pena fauna is very similar to that of Toca do Barrigudo, which is less than one kilometer away and yielded the holotype of the species: Scelidodon piauiense Guerin & Faure, 2004.Le site de la Toca da Pena correspond à une petite grotte qui se trouve dans le massif calcaire d’Antero, au sud de la Serra da Capivara et à 7 km à l’est-nord-est de la ville de Coronel José Dias. Des fouilles entreprises entre 2008 et 2014 ont permis de recueillir, associés à quelques artefacts lithiques, de nombreux vestiges osseux. Près de la moitié d’entre eux sont rapportés à Scelidodon piauiense, un paresseux terrestre de la taille d’un grand bœuf. Ce Mylodontidé est associé à Leopardus pardalis, Hippidion, Tayassu pecari, Mazama gouazoubira, Mazama americana et à Palaeolama niedae. Cette association faunique permet de dater ce site du Pléistocène supérieur ou du tout début de l’Holocène. Par ailleurs, cette faune de la Toca da Pena présente beaucoup de similitude avec celle de la Toca do Barrigudo, qui se trouve à moins d’un kilomètre et d’où provient l’holotype de l’espèce : Scelidodon piauiense Guérin & Faure, 2004

Origin of clays from the Northwestern Black Sea sediments : relatationships with climate

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Kuturbulak revisited - A middle palaeolithic site in Zeravshan river valley, Uzbekistan

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Another sequence, same evidence: human presence at the end of the Pleistocene in America. The Toca da Janela da Barra do Antonião, Piauí, Brazil

The site of Toca da Janela da Barra do Antonião (TJBA) is situated in the calcareous massif of Antero, in the Serra da Capivara National Park, Piauí State, Brazil. The entire rockshelter is more than 150m long, with few meters deep recesses. Part of the site was extensively studied in the 1990s [1]. Our team begun a wide archaeological program in the region in 2008 [2,3], focusing on different archaeological sequences. New archaeological excavations started in TJBA in 2013, at an extremity of the Toca, without possible stratigraphic correlation with previous excavations. After 3 archaeological campaigns, the bedrock was not reached. At the time of writing this abstract (April 2016), the site presents a 1.5 m thick chrono-cultural sequence, inside of which six sedimentary layers and four archaeological levels were identified. All the four archaeological layers delivered lithic and faunal remains. The two archaeological layers at the top of the sequence are separated by a thin sterile sediment layer, but present a cultural homogeneity, and both can be attributed to the Itaparica facies of the region. The two underlying archaeological levels are poorer in lithic artefacts; the lithics can be divided in three categories: small artefacts on quartz, big artefacts on quartz, and hammers. These two lower levels also delivered skeletal remains of a giant sloth corresponding to Eremotherium (megafauna); in particular, it seems that certain bones were used to produce artefacts. Charcoal samples from the upper part of the sequence were radiocarbon dated. In addition, six sediment samples were collected from the profile for luminescence dating. Sand-sized (180-250 μm) and fine (20-41μm) quartz grains were extracted from the samples and prepared following a standard chemical treatment. For all six samples, the quartz OSL signal is bright, reproducible and dominated by the fast component, which indicates good luminescence characteristics for obtaining accurate and precise ages. OSL measurements were performed on both multi-grain and single-grain aliquots. The ages obtained for the two upper archaeological levels (Itaparica) correspond to the beginning of the Holocene. Conversely, the other two archaeological levels are dated to the end of the Pleistocene. Thus, the Toca da Janela da Barra do Antonião constitutes the fifth Pleistocene-Holocene chrono-cultural sequence studied by our team in the region [2,3,4]. As such, it provides new evidence of an ancient human presence in South America, more than 20, 000 years ago.Peer reviewe

De l’utilisation des isotopes stables du carbone dans la datation par la méthode du radiocarbone

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Sur la présence d’ursus arctos au début de l’Holocène dans le Moyen Atlas (Maroc) - datations et implications paléoenvironnementales

International audienceNear Boulmane city, in the limestone formation of El Minchare, the Ifri Oussaïd cave open over the Middle Atlas plateau at 2 075 m high. From 2005 to 2007 excavations provided charcoal associated to bone remains mainly belonging to Ursus arctos, at last 156 identiied bones from ive bears. Paleontological studies describe bear of small size (Ouchaou, 2008). Datations of charcoal from stalagmitic loors above bear bone layer give ages between 5 220 ± 30 and 5 865 ± 30 yrs 14 C BP, while the collagen of a radius bone was dated at 7 300 ± 40 yrs 14 C BP. This date, taking in account the local climatic pattern, conirms the presence of Ursus arctos at the beginning of the Holocene period in North Africa but also point out to the importance of environmental changes in the Middle Atlas and their potential importance for the extinction of Ursus arctos.Dans le Moyen Atlas, près de Boulmane les formations calcaires d'El Minchare abritent une grotte profonde (Ifri Oussaïd) s'ouvrant au-dessus du plateau à 2 075 m d'altitude. Les fouilles de ce site ont livré, de 2005 à 2007, des charbons associés à plusieurs ossements dont au moins 156 restes d'ours brun (Ursus arctos) appartenant à cinq individus. L'étude paléontologique atteste d'un ours de petite taille (Ouchaou, 2008). Les niveaux à charbons de bois scellés dans de petits planchers stalagmitiques situés au-dessus des restes ont donné des dates allant de 5 220 ± 30 à 5 865 ± 30 ans 14 C BP. La datation obtenue directement sur un radius d'ours est de 7 300 ± 40 ans 14 C BP. Cette date, replacée dans le contexte climatique local, conirme la présence d'Ursus arctos au début de l'Holocène moyen en Afrique du Nord, mais souligne aussi l'ampleur des changements environnementaux dans le Moyen Atlas depuis cette époque et leur inluence potentielle sur la disparition d'Ursus arctos de cette région