Search results for "uni"
showing 10 items of 37626 documents
Revised phosphate-water fractionation equation reassessing paleotemperatures derived from biogenic apatite.
2010
8 pages; International audience; Oxygen isotopes of biogenic apatite have been widely used to reassess anomalous temperatures inferred from oxygen isotope ratios of ancient biogenic calcite, more prone to diagenetic alteration. However, recent studies have highlighted that oxygen isotope ratios of biogenic apatite differ dependent on used analytical techniques. This questions the applicability of the phosphate–water fractionation equations established over 25 years ago using earlier analytical techniques to more recently acquired data. In this work we present a new phosphate–water oxygen isotope fractionation equation based on oxygen isotopes determined on fish raised in aquariums at contro…
The Mid-Cenomanian Event in southeastern France: evidence from palaeontological and clay mineralogical data.
2013
16 pages; International audience; Reconstruction of main palaeoenvironmental conditions across the Mid-Cenomanian Event (MCE I) in the hemipelagic Tethyan section of Blieux (Southeast France, Vocontian Basin) is proposed. Quantitative analyses of calcareous nannofossil, ammonoid and clay mineral assemblages have been made and compared with respect to sea level changes and the carbon cycle perturbations. The nannofossil primary productivity, as recorded by nannofossil fluxes and relative abundances of meso-eutrophic taxa, is low just below and during the MCE Ia, then slightly increases in the interval including the MCE Ib. The clay assemblages mainly consist of illite/smectite mixed-layers w…
Late Jurassic palaeoclimatic change from clay mineralogy and gamma-ray spectrometry of the Kimmeridge Clay, Dorset, UK
2009
Abstract: The Late Jurassic was a time of increasing aridity in NW Europe. Here, a new clay mineral dataset is presented from a 600 m thick composite core through the Kimmeridge Clay Formation, southern England. Clay mineral assemblages comprise mainly illite and kaolinite, with minor randomly interstratified illite–smectite mixed-layer clays. SEM observations indicate that clay minerals are mainly detrital, except in silty strata of late Tithonian age, which contain abundant pore-filling kaolinite aggregates. Th/K ratios determined from gamma-ray spectrometry mirror palaeoclimatically significant variations in kaolinite/illite ratios, with notable exception where diagenetic kaolinite occur…
Paleobiogeography of Early Cretaceous Ammonoids
2015
International audience
Facies variations in response to Holocene sea-level and climate change on Bora Bora, French Polynesia: Unravelling the role of synsedimentary siderit…
2017
International audience; Five mixed carbonate-siliciclastic sedimentary facies were identified in the barrier-reef lagoon of Bora Bora using microfacies and statistical analyses of 70 sediment samples taken at high resolution from two vibrocores. Fades and fades successions were interpreted with respect to Holocene sea-level and climate changes. The windward lagoon core is characterized by sideritic marly wackestones and foraminifera-sideritic wackestones, deposited around 7700 years BP (years before present) during the early-mid Holocene transgression. At that time, extensive weathering and erosion of iron-bearing minerals from the volcanic island, due to a wetter climate, were expressed in…
Les Gregoryceras (Ammonitina) de l'Oxfordien moyen terminal et supérieur téthysien : révision systématique, biostratigraphie et évolution.
2009
43 pages; Les Gregoryceras Spath, 1924 (Ammonitina, Peltoceratina) de la fin de l'Oxfordien moyen (sous-zone à Rotoides) et de la base de l'Oxfordien supérieur (zone à Bifurcatus) sont révisés. Les coupes ayant fourni la plupart des spécimens de ce travail (Espagne et Maghreb) sont décrites et datées sur la base de comparaisons fauniques entre les domaines téthysien et subtéthysien. Le meilleur outil pour ces corrélations est la présence du genre Gregoryceras. La succession des espèces de Gregoryceras est identique pour les deux domaines suscités, ce qui permet de compléter l'échelle biostratigraphique proposée antérieurement et parallèle à la zonation standard. Les espèces reconnues et red…
L’origine des Imerites Rouchadze, 1933 : résultat d’une innovation chez les Gassendiceratinae Bert, Delanoy et Bersac, 2006 (Ammonoidea, Ancylocerati…
2009
15 pages; La découverte récente de plusieurs spécimens remarquables d'Imerites dichotomum (Ammonoidea, Ancyloceratina) apporte de nouvelles précisions paléontologiques sur ce genre. L'étude du développement ontogénétique montre que les Imerites dérivent directement du genre Pseudoshasticrioceras. Leur origine se situe donc parmi les Gassendiceratinae et non chez les Heteroceratidae comme il était généralement admis. Par ailleurs, la cohabitation de formes macroconques et microconques au sein des espèces du genre Imerites confirme l'hypothèse du dimorphisme. Les nouvelles données paléontologiques obtenues montrent que le taxon « Crioceras » cristatus est un nomen dubium et qu'il doit être ab…
Climatic ups and downs in a disturbed Jurassic world.
2011
4 pages; International audience; The tropical, warm, and equable climate of the Jurassic world is regularly challenged by geoscientists, especially since oxygen isotopes ( 18O) of fossil hardparts have been used to reconstruct the paleotemperature history of seawater. By applying the innovative “SiZer” (significant zero crossings of the derivatives) statistical approach to a newly compiled 18O database for the Jurassic, we demonstrate the occurrence of major and multiscale 18O changes mainly related to climate disturbances. For the first time, two long-term anomalies in 18O are identified during the Toarcian and the Late Jurassic, in conjunction with intensive volcanism in large igneous pro…
Different parts of the same plants. Charcoals and seeds from Cova de les Cendres (Alicante, Spain)
2018
Abstract The analysis of archaeobotanical macroremains from Cova de les Cendres (Teulada-Moraira, Alicante, Spain) allows a better understanding of the dynamic of the vegetation during the Upper Palaeolithic in the region. The anthracological sequence shows that Pinus type nigra/sylvestris dominates in the area during the Upper Palaeolithic, while more open formations of Juniperus and Fabaceae spread in Upper Solutrean and Early-Middle Magdalenian. The carpological analysis that has been carried out in the Middle Magdalenian level has brought to light different species of Juniperus (J. sabina, J. communis and J. oxycedrus). This information indicates that during the period, Cova de les Cend…
Landscape and fuel management in the context of prehistoric and historical occupations of Cova des Moro (Manacor, Mallorca, Spain)
2021
Abstract In this paper, the first results of charcoal analyses carried out at Cova des Moro (Manacor, Mallorca, Spain) are presented. This cave is an archaeological but also palaeontological site that provides information on endemic fauna (the extinct caprine Myotragus balearicus) before the arrival of humans and, later, the relationship between the first farmers and the landscape. Several human occupations in the cave have been documented, from the Chalcolithic (end of the 3rd millennium cal BC), the Bronze Age (2nd millennium cal BC) and, finally, the Almohad period (13th century AD), during which the cave was used for different purposes. The first results of charcoal analyses at Cova des…