La Geocronología del yacimiento pleistocénico de Lezetxiki (Arrasate, País Vasco) : Crítica de las dataciones existentes y algunas nuevas aportaciones

El yacimiento pleistocénico de Lezetxiki se sitúa en la provincia de Gipuzkoa, en el País Vasco peninsular. El depósito ha sido objeto de intentos de datación mediante métodos alternativos. En efecto, resulta muy importante establecer un cuadro geocronológico para este yacimiento excepcional, en el que han sido localizados restos humanos fósiles asociados a elementos faunísticos e industrias humanas. En este artículo se presenta un estado de la cuestión acerca de las diferentes analíticas y estudios que se han aplicado en Lezetxiki, tanto geológicos y paleoambientales, como tecnotipológicos. Tras esta presentación pluridisciplinar, se procede a efectuar una recopilación exhaustiva de las dataciones efectuadas sobre diversos tipos de muestra y diferentes métodos radiométricos

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

: New radiometric dating from the marine terraces of Corinthia, Northern Peloponnese, Greece

Two interpretations are usually proposed for the Corinthian flight of terraces: faulting or flexuration, of a single or* fewkueis, or stepping of numerous cut-and-fill shorelines. In this paper, U/Th radiometric data confirm the diachronism of the terraces and a previously proposed correlation with the isotopic stratigraphy. While they support the morphological criteria used in this correlation, thèse data strengthen the calibration of the whole flight of Corinthian Terraces, allow one to appreciate the evolution of the uplift rate and confirm the hypothesis of an uplift beginning before 600 kyr in this part of the Aegean Arc.Deux interprétations sont classiquement données de l'étagement de terrasses de Corinthie : multiplication par failles ou flexures d'un ou de quelques niveaux, ou emboîtement de paléorivages de plus en plus jeunes. Dans cette note, des données radiométriques (U/Th) confirment le diachronisme de l'êtagement et une corrélation des terrasses avec la stratigraphie isotopique proposée antérieurement. En validant les critères morphologiques utilisés dans cette corrélation, les datations confortent la calibration de la totalité de l'étagement des terrasses de Corinthie, permettent d'apprécier l'évolution des taux de surrection et appuient l'hypothèse d'un début du soulèvement avant 600 ka dans ce secteur de l'arc Égéen

Stability of some centres in quartz

Electron spin resonance (ESR) is a promising dating method for Quaternary sediments. A preliminary ESR analysis was done on quartz grains extracted from sediments baked by lava-flows of Massif Central (France). For this type of sample, zeroing occurs during heating. To test the reliability of the method, the palaeodoses were determined from centres (Al and Ti) and compared with those obtained by the thermoluminescence (TL) method.The annealing temperature and sunlight have an effect upon the stability and the behaviour of the different ESR signals. An attempt to correlate ESR signals and the red TL peak is made in terms of the variation of these two factor

Datation absolue des planchers stalagmitiques de la Grotte du Vallonnet à Roquebrune-Cap-Martin (Alpes-Maritimes) France, par la résonnance de spin électronique (ESR)

International audienceAbsolute dating of thé stalagmitic floors of Vallonnet Cave at Roquebrune-Cap-Martin (Alpes-Maritimes) France, by thé electronic spin résonance method (ESR). Two of Vallonnet Cave's stalagmitic floors are dated by thé electronic spin résonance method (ESR) for thé purpose of dating thé deposit of this cave. For thé base of thé closing stalagmitic floor an âge of 910 000 ± 60 000 years is obtained. For thé top of thé lower stalagmitic floor, an âge of 1 370 000 ±120 000 years is obtained. Given that thé entire deposit of this cave is included between thèse two stalagmitic layers, thé âge of thé continental deposit which contains lithic industry and fauna is between 910 000 ± 60 000 and 1 370 000 ±120 000 years. Thèse âges agrée with thé âges estimated from thé fauna and paleomagnetism.Dans le but de dater le remplissage de la grotte du Vallonnet, deux planchers stalagmitiques de cette grotte ont été datés par la méthode de la résonance de spin électronique (ESR). Pour la base du plancher de fermeture, un âge de 910 000 ± 60 000 ans a été obtenu. Pour le sommet du plancher stalagmitique inférieur, un âge de 1 370 000 ±120 000 ans a été obtenu. Etant donné que tout le remplissage de cette grotte se trouve entre ces deux planchers stalagmitiques, l'âge du remplissage continental qui renferme l'industrie lithique et la faune est compris entre 910 000 ± 60 000 ans et 1 370 000 ±120 000 ans. Ces âges sont en accord avec les âges estimés par la faune et le paléomagnétisme

Electron Spin Resonance (ESR) Dating of Hominid-Bearing Deposits in the Caverna delle Fate, Ligure, Italy

Stalagmitic floors interstratified with Mousterian deposits from the Caverna delle Fate (Italy) have been dated by the electron spin resonance (ESR) method. Three samples dated fall between 60,000 and 74,000 yr and indicate the age of the Mousterian deposits. They are in good agreement with eges determined by nondestructive "y-ray spectrometry of the human remains from 231Pa/235U and 230Th/234U ratios, which are, respectively, 75,000+21000 -14000 and 82,000 +36000 - 25000 These dates are consistent with the morphological characteristics of the bones as Neanderthal remains

Impact de la néotectonique quaternaire sur la dynamique sédimentaire du Saïs (Maroc) : du bassin d'avant fosse pliocène au plateau continental quaternaire

Au passage du Néogène au Quaternaire, la région du Saïs a connu un changement important dans l’évolution géodynamique, marqué par une intense activité néotectonique qui a permis un changement radical de la géomorphologie du Saïs. Notre étude a permis de retracer l’histoire géologique de cette région depuis le Néogène.– Au Miocène supérieur, le Saïs correspond à un bassin marin d’avant fosse lié au sillon sud rifain situé à la limite sud du Prérif en cours de surrection. Son comblement se fait par des faciès marins profonds. Il s’agit d’une séquence majeure de dépôts essentiellement marneux à intercalations de turbidites lenticulaires gréseuses. La régression du Pliocène inférieur et moyen permet le dépôt de faciès paradeltaïques marquant ainsi les derniers dépôts marins dans le bassin du Saïs.– Au Pliocène terminal, le Saïs, ainsi comblé, forme un bassin endoréique correspondant à un palier simple sur le profil du paléofleuve de Sebou qui l’alimente. Nous avons situé l’exutoire du PaléoSebou dans la partie est du bassin, au droit de la ville de Fès. La sédimentation est détritique terrigène de type fluviatile sur les bordures du bassin. Elle est carbonatée et évaporitique de type lacustre au centre du bassin.– Au Quaternaire, on observe un changement radical dans l’évolution du Saïs. Il s’agit de la réactivation néotectonique majeure du front sud rifain et des flexures du Moyen Atlas traduisant ainsi une phase de compression N-S à NNW-SSE. Cette phase a permis la création de nouveaux reliefs sur les bordures du Saïs et la surélévation de ceux préexistants. Le système de rampes du front sud rifain permet le chevauchement, vers le sud, des rides de Zalagh et de Tghat sur les formations pliocènes du Saïs. Notre travail montre pour la première fois que le Saïs n’est plus un bassin situé entre deux chaînes, mais plutôt un plateau surélevé attaché au versant nord de la chaîne du Moyen Atlas. De ce fait, le drainage du réseau hydrographique se fait, désormais, du sud vers le nord perpendiculairement à la direction générale du Saïs. Les formations du Pliocène et leur substrat miocène subissent une érosion intense qui se traduit par des incisions dépassant les 100 m. Actuellement, la plaine de Saïs correspond à la partie médiane du bassin versant de Sebou située entre la partie amont dans le Moyen Atlas et le point bas exutoire situé dans le Prérif et la plaine du Gharb.Le passage du Pliocène au Quaternaire est marqué par une nouvelle phase tectonique qui a permis un changement radical dans la géomorphologie du Saïs et de ses bordures atlasiques et rifaines.Saïs is located between Rif and Middle Atlas chains; its Quaternary evolution corresponds to an inversion in dynamics compared to its evolution in Miocene and Pliocene times. We defined three major stages: – Upper Miocene: the Saïs is a foreland deep marine basin located at the southern limit of Pre-Rif during its uplift. The sequence includes more than 1 km of marls with interbedded turbidite sands. The structural style analysis shows that NE and NW extensional faults are responsible for graben formation towards the Saïs basin centre. This extensional system is contemporary with an advance towards the south of preriffian ridges ramps existing in the northern part of basin. The simultaneity of the extensive and compressive structures is typical of the foreland basins. The last marine deposits in the Saïs basin are littoral and paradeltaic sandy marls. The ultimate filling in Saïs basin, of Lower and Middle Pliocene age, is due to the marine regression in the South riffian basin.– Upper Pliocene evolution: the Saïs basin, thus filled, formed a continental basin corresponding to a simple stage on profile of the Sebou palaeoriver. We define the discharge system of PalaeoSebou in the eastern part of basin near Fez. Sedimentation is dominated by conglomerates of fluvial origin on the edges of the basin; it is evaporatic and lacustrine carbonate towards the basin centre. The climate was hot and humid. The northern part of the basin shows a syntectonic character expressed by flexural faults that affected the fluvial conglomerates. This deformation reflects an episode of mobilization of the preriffain ridges ramp of Tghat and Zalagh. – Quaternary evolution: The culmination of Saïs area is made by the progress of preriffian ramp who overrides on Pliocene deposits of the northern edge of Saïs. The preriffian ridges migrate towards the south by Zalagh, Sebou and Sidi Hrazem ramps. The southern riffian front “FSR” towards the south in the plain reorganized a change of course of the Sebou palaeoriver. This deformation translates NS to NNW-SSE compressional strain and allows reactivation of the preexisting Miocene structures and the neo-formation of new structures. A change in the evolution of Saïs results also of major neotectonic reactivation of the flexures of North Middle Atlas. This new structural state allows the rise of the Saïs who becomes elevated plain related to the northern middle atlasic catchment basin. Saïs Pliocene formations and their Miocene substrate are subjected to intense erosion whith fluvial incisions exceeding 100 m. Currently, the Saïs plain corresponds to the median part of the Sebou catchment basin located between the middle Atlas upstream and Prerif downstream. This last paroxysmal strain has been also described in the Pre-Rif (Faugères, 1978; Ait Brahim&Chotin, 1983; Chalouan et al., 2000, 2003) and in the south of Middle Atlas (Charroud 2002; Charroud et al., 2006). It is interpreted as being the result of the crustal readjustment under Alboran, Rif and Atlas (Frizon de Lamotte et al., 2004), where shoshonitic volcanism produced in the eastern external Betico-Riffian zones is replaced by the alkaline volcanism (Calvert et al., 2000). The role of crustal readjustment to explain the culmination of Saïs is proven for atlasic chain (Teixell et al., 2003; Arboleya et al., 2004; Ayarza et al., 2005)

POTENTIAL USE OF THE E' CENTER AS AN INDICATOR OF INITIAL RESETTING IN TL/ESR DATING OF VOLCANIC MATERIALS

International audienceQuartz inclusions embedded in volcanic materials can be used for dattng Quaternary volcanoes by TL or ESR methods. For these techniques the initial zeroing by heat is assumed. However, this assumption can sometimes be questioned either because the temperature was not high, like in phreatomagmatic deposits, or because of contamination, like in thin tephra layers. Preliminary observations suggested that the présence of thé E' center could be an indicator of poor initial zeroing. This possibility was investigated in the present work. Quartz grains from various geological contexts were studied for comparison. Annealing and régénération of the E' center was explored

Possibilities and limitations of ESR dating applied to Pliocene and Pleistocene units of western central mainland Portugal

Summary: This work aims to give a short description of the applicability of ESR method for dating Pliocene and Pleistocene units of western central mainland Portugal ranging between 2.5 and 0.2 Ma. The vast culminant unit of the sedimentary infill only was previously dated, at the base, in one site. The dating of the topmost deposits of this unit will allow to date the transition from the stage of sedimentary infilling to that of fluvial incision and to understand the controls of this. Only the lower coastal terraces are dated to <ca. 300 ka provided by OSL methods. The ESR dating will support stratigraphic correlations and estimate the local uplift rates and the identification of the main active tectonic structures in central western mainland Portugal

TL and ESR of quartz from the astrobleme of Aorounga (Sahara of Chad)

International audienceThe present work was intended to evaluate the time that elapsed since the meteorite fall that produced-the giant astrobleme of Aorounga (Sahara ot'Chad". For this purpose the TL and ESR dating techniques using the additive dose method were applied to quartz grains extracted f'rom an impactite and from a sandstone shocked and haked during the impact. The ESR Al centre was measured and resulted in an âge or about 800 ka. The red TL and the blue TL showed unusual TL features: the additive dose response curves were marked by an initial saturated part followed by a second rise at around +0.5 kGy: the peaks showed erratic temperature shifts with dose: fading was observed for high temperature peaks. By comparison with previous work using samples baked by lava flows more than 1 Ma ago and presenting some of those features. it was assumed that the minimum age of the astrobleme was of the same order of magnitude. This is in agreement with other observations. A preliminary explanation for those ageing features is proposed. It is suspected that radiation induced traps contribute to the TL of the studied quartz grains. Most probably the "malign-behaviour' of the quartz grains is also connected with shock effects