Chupicuaro archaeological sites: from magnetic survey to excavation (late pre-classic period, Middle Lerma Valley, Guanajuato, Mexico)

Aims of the project The area of Chupicuaro, located in the middle valley of the Lerma river, is regarded as one of the major archaeological targets of central Mexico for the late pre-classic period (600 BC-AD 300). Archaeological investigations in the area have been limited because of a large reservoir constructed in 1948 and severe plundering. Since 1999 a French-Mexican research program has concentrated on broadening knowledge of the local Chupicuaro culture and its development (Faugère & D..

Karstologie et remplissage sédimentaire du gisement pléistocène de Romain-la-Roche (Doubs, France).

19 pagesInternational audienceLe gisement pléistocène du site de Romain-la-Roche (commune de Romain dans le Doubs) correspond au remplissage épikarstique d'un aven affectant les calcaires du Jurassique moyen d'un plateau situé au nord du massif jurassien. Cette cavité, située en dehors de l'extension de la calotte du dernier maximum glaciaire, a été façonnée par un flux hydrologique en liaison avec un drainage de surface qui a vraisemblablement disparu au cours du Pliocène lors d'une phase d'inversion du relief de part et d'autre de la faille normale qui délimite la partie ouest du plateau. Avant son colmatage au cours du Pléistocène la cavité était reliée à un réseau dense de conduits karstiques sous-jacents qui ont été explorés par les spéléologues postérieurement aux opérations de fouilles paléontologiques. La base du remplissage de l'aven est de nature endokarstique et n'a livré aucun matériel paléontologique ou archéologique. Le remplissage épikarstique qui a livré le matériel étudié dans la présente monographie a commencé à se mettre en place au Pléistocène moyen lorsque le toit de la cavité, rattrapé par l'érosion de surface, s'est effondré. L'aven a alors formé un piège karstique d'abord profond et sans échappatoire, puis de plus en plus accessible suite à son comblement et à l'évasement de son ouverture

A new Early Triassic crinoid from Nevada questions the origin and palaeobiogeographical history of dadocrinids

Knowledge of the early evolution of post-Palaeozoic crinoids mainly relies on the well-preserved and abundant material sampled in Triassic Konservat-Lagerstätten such as those from the Anisian Muschelkalk (Middle Triassic) of the Germanic Basin. These crinoid-bearing Lagerstätten have been central to understanding the rapid evolution and diversification of crinoids after the dramatic Permian/Triassic Boundary biological crisis that led the class to near-extinction. The Encrinida are the emblematic crinoids of the Triassic. They are mainly known from rich fossil deposits where their abundant ossicles are at the origin of the extensive crinoidal limestone beds of the German Upper Muschelkalk. So far, they were first represented in the Middle Triassic by the family Dadocrinidae and genus Dadocrinus. In the present work, a new species Dadocrinus montellonis sp. nov., is described based on a well-preserved, almost complete articulated specimen from the Spathian (Lower Triassic) of Nevada (USA). The new species differs from other species of Dadocrinus by its palaeobiogeographic position but also by its earlier stratigraphic occurrence and ancestral morphology. It represents the first reported occurrence of Dadocrinus outside the Germanic Basin prior to the Middle Triassic and also the oldest firm evidence of its presence in the Early Triassic (middle–late Spathian). This discovery sheds new light on the origin of post-Palaeozoic crinoids. It suggests a much wider distribution than commonly assumed for the genus Dadocrinus and implies that the first dadocrinids originated either in the Panthalassa or Tethys oceans, and then dispersed over long distances in a relative short period of time

Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France).

27 pagesInternational audienceSeveral diagenetic models have been proposed for Middle and Upper Jurassic carbonates of the eastern Paris Basin. The paragenetic sequences are compared in both aquifers to propose a diagenetic model for the Middle and Late Jurassic deposits as a whole. Petrographic (optical and cathodoluminescence microscopy), structural (fracture orientations) and geochemical (δ18O, δ13C, REE) studies were conducted to characterize diagenetic cements, with a focus on blocky calcite cements, and their connection with fracturation events. Four generations of blocky calcite (Cal1-Cal4) are identified. Cal1 and Cal2 are widespread in the dominantly grain-supported facies of the Middle Jurassic limestones (about 90% of the cementation), whereas they are limited in the Oxfordian because grain-supported facies are restricted to certain stratigraphic levels. Cal1 and Cal2 blocky spars precipitated during burial in a reducing environment from mixed marine-meteoric waters and/or buffered meteoric waters. The meteoric waters probably entered aquifers during the Late Cimmerian (Jurassic/Cretaceous boundary) and Late Aptian (Early Cretaceous) unconformities. The amount of Cal2 cement is thought to be linked to the intensity of burial pressure dissolution, which in turn was partly controlled by the clay content of the host rocks. Cal3 and Cal4 are associated with telogenetic fracturing phases. The succession of Cal3 and Cal4 calcite relates to the transition towards oxidizing conditions during an opening of the system to meteoric waters at higher water/rock ratios. These meteoric fluids circulated along Pyrenean, Oligocene and Alpine fractures and generated both dissolution and subsequent cementation in Oxfordian vugs in mud-supported facies and in poorly stylolitized grainstones. However, these cements filled only the residual porosity in Middle Jurassic limestones. In addition to fluorine inputs, fracturation also permitted inputs of sulphur possibly due to weathering of Triassic or Purbeckian evaporites or H2S input during Paleogene times

The skeleton of the staghorn coral Acropora millepora: molecular and structural characterization

15 pagesInternational audienceThe scleractinian coral Acropora millepora is one of the most studied species from the Great Barrier Reef. This species has been used to understand evolutionary, immune and developmental processes in cnidarians. It has also been subject of several ecological studies in order to elucidate reef responses to environmental changes such as temperature rise and ocean acidification (OA). In these contexts, several nucleic acid resources were made available. When combined to a recent proteomic analysis of the coral skeletal organic matrix (SOM), they enabled the identification of several skeletal matrix proteins, making A. millepora into an emerging model for biomineralization studies. Here we describe the skeletal microstructure of A. millepora skeleton, together with a functional and biochemical characterization of its occluded SOM that focuses on the protein and saccharidic moieties. The skeletal matrix proteins show a large range of isoelectric points, compositional patterns and signatures. Besides secreted proteins, there are a significant number of proteins with membrane attachment sites such as transmembrane domains and GPI anchors as well as proteins with integrin binding sites. These features show that the skeletal proteins must have strong adhesion properties in order to function in the calcifying space. Moreover this data suggest a molecular connection between the calcifying epithelium and the skeletal tissue during biocalcification. In terms of sugar moieties, the enrichment of the SOM in arabinose is striking, and the monosaccharide composition exhibits the same signature as that of mucus of acroporid corals. Finally, we observe that the interaction of the acetic acid soluble SOM on the morphology of in vitro grown CaCO3 crystals is very pronounced when compared with the calcifying matrices of some mollusks. In light of these results, we wish to commend Acropora millepora as a model for biocalcification studies in scleractinians, from molecular and structural viewpoints

Les environnements de dépôt du Sinémurien de la région stratotypique (faciès et microfaciès).

16 pagesNational audienc

The Chupicuaro exploitation of hydrothermal resources, Mexico (600 B.C.- 300 A.D.): geochimical and mineralogical identification and archaeological inferences

International audienc

L’hydrosystème karstique du sanctuaire gallo-romain du lac d’Antre et des sources de l’Héria.

National audienc

Les interfaces à traces de pas de théropodes du Plateau des Causses (Sud de la France) : déterminations palichnologiques et interprétations paléoenvironnementales

International audienceDe nombreuses empreintes ont été découvertes depuis le début des années 2000 dans le Bathonien des Grands Causses, dans les vallées de la Jonte et de la Dourbie, autour de Meyrueis (48) et de Nant (12).Ces traces ont été identifiées par Sciau et al. (2006) comme étant des ichnites d’origine dinosaurienne. Les auteurs ont pu distinguer des traces tridactyles et d’autres de formes ovoïdes. Ils ont attribué la formation des premières à des théropodes et des autres à des sauropodes. Cependant, un doute subsistait quant à leur origine réelle, ainsi que leur détermination ichnologique qui restait à faire.Notre travail consiste en un relevé et des mesures des traces tridactyles et ovoïdes, supposées d’origine dinosaurienne. Ces traces se situent sur quatre sites (la Garène, le Capellan, Gayrand et Saint-Sulpice) dans les vallées de la Dourbie, de la Jonte et du Trévezel.Il apparaît que les traces tridactyles sont bel et bien des traces de dinosaures théropodes, apparentées à l’ichnotaxon Eubrontes giganteus, après comparaison statistique à une base de données des empreintes du Lias des Causses. Ces traces ont sans doute été faites alors que le dinosaure qui en est l’auteur marchait sur substrat couvert d’eau. Quant aux traces ovoïdes, nous pensons qu’il faut chercher leur origine ailleurs, et que des dinosaures ne seraient pas les auteurs de ces traces. Nous pouvons donc émettre plusieurs hypothèses au sujet de leur formation, que ce soit une origine biologique ou non.Ainsi, nous pouvons confirmer le passage de grands dinosaures théropodes dans cet environnement au cours du Bathonien