Belemnopsis en el jurásico superior (tithoniano superior) de la cuenca neuquina

En esta contribución se da a conocer un nuevo registro para la cuenca Neuquina del género de belemnites Belemnopsis Bayle (O. Belemnopseidina, Familia Belemnopseidae). El ejemplar mejor preservado (MCNAM-PI 24881, colección Museo de Ciencias Naturales y Antropológicas “Juan Cornelio Moyano”, Mendoza) se trata de un rostro cilindro-cónico, elongado, de 98 mm de longitud máxima. Preserva la porción apical y parte de la región del tronco. Presenta un diámetro transversal máximo de 14 mm alcanzado a alrededor de 60 mm del ápice. El contorno es simétrico, no alabardiforme (no hastado), con márgenes que convergen en un ápice agudo levemente orientado hacia dorsal. El perfil es algo asimétrico, aplanado en la región dorsal pero levemente inflado en la región ventral y alrededor del ápice. La sección transversal del rostro es elíptica y deprimida pero este carácter puede estar acentuado por compresión sedimentaria. Un surco ventral estrecho, poco profundo y con márgenes angulares recorre la región media del tronco y se extiende posteriormente hasta la región apical. El surco presenta una forma de “v” en sección transversal y parece profundizarse hacia anterior. La línea apical es ligeramente ventral y no se observaron líneas laterales. La forma general del contorno, perfil y surco ventral permiten comparar el material estudiado con Belemnopsis patagoniensis (Favre), una especie bien documentada y frecuente en el Cretácico Inferior (Berriasiano–Hauteriviano) de la cuenca Austral-Magallánica. B. patagoniensis usualmente presenta un rostro mucho más robusto, casi dos veces más ancho y largo que el material aquí presentado, por lo que el mismo se designa como Belemnopsis cf. B. patagoniensis. El ejemplar MCNAM-PI 24881 fue colectado en afloramientos de la Formación Vaca Muerta en Las Alcantarillas, alrededor de 40 km al oeste del paraje Las Loicas, Mendoza. Su posición estratigráfica en niveles asignables a la base de la Biozona de Corongoceras alternans indican una edad tithoniana tardía para este registro. La cercanía morfológica de B. cf. B. patagoniensis con las formas de cuenca Austral-Magallánica y de estas últimas con especies del Jurásico Tardío–Cretácico Temprano de Madagascar y el este de África, suma un nuevo elemento de correlación para el Tithoniano tardío entre las cuencas andinas y las de la Subprovincia Etíope de la Provincia Indopacífica.Fil: Vennari, Verónica Vanesa. Universidad Tecnológica Nacional. Facultad Regional San Rafael. Instituto de Evolución, Ecología Histórica y Ambiente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Evolución, Ecología Histórica y Ambiente; ArgentinaFil: Aguirre Urreta, María Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Marin, Luciana Sabina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Pellenard, Pierre. Universite de Bourgogne; FranciaFil: Martinez, Mathieu. Universite de Rennes I; Francia12° Congreso de la Asociación Paleontológica ArgentinaBuenos AiresArgentinaAsociación Paleontológica Argentin

LIBS profiles of sedimentary sections: a new tool for paleoclimatic and paleoenvironmental reconstructions?

peer reviewedReconstructing climates and/or environments of the past requires analysis of sedimentary sections based on profiles of various geological data (geochemistry, sedimentology, mineralogy, paleontology, ...). LIBS analysis can be carried out with a fast acquisition rate on minimally-prepared samples, allowing measurement of large geological sample sets such as sedimentary sections. Here we show preliminary results obtained from a field and a core section to illustrate the potential of LIBS for paleoclimatic and paleoenvironmental studies. The studied field section consisted in 6 m thick Devonian siliciclastics with varying carbonate content used as a reference for cyclostratigraphy (New York State, USA [1]). 300 samples were analyzed manually in less than two days and the results showed very good match with the XRF measurements previously used for astrochronology, including productivity (Ca) and detrital (Ti, Al, etc.) proxies. Therefore, astronomically-forced climatic cycles could be analyzed based on LIBS data as it is reliably done with XRF. The studied core section, which consists of 150 m of Ypresian to Bartonian formations (Le Tillet borehole, France) was more challenging for LIBS measurement as it consists of both soft siliciclastic sediments and consolidated carbonate rocks [2]. Therefore, the 157 selected samples were powdered and fixed onto double-sided adhesive and automatically analyzed with the LIBS within about 1 hour. The obtained data, still under interpretation, showed that some elemental ratios such as Cs/k and Li/k exhibit interesting correlations with mineralogical and environmental data (Fig. 1)

Continental weathering as a driver of Late Cretaceous cooling : new insights from clay mineralogy of Campanian sediments from the southern Tethyan margin to the Boreal realm

21 pagesInternational audienceNew clay mineralogical analyses have been performed on Campanian sediments from the Tethyan and Boreal realms along a palaeolatitudinal transect from 45° to 20°N (Danish Basin, North Sea, Paris Basin, Mons Basin, Aquitaine Basin, Umbria-Marche Basin and Tunisian Atlas). Significant terrigenous inputs are evidenced by increasing proportions of detrital clay minerals such as illite, kaolinite and chlorite at various levels in the mid- to upper Campanian, while smectitic minerals predominate and represented the background of the Late Cretaceous clay sedimentation. Our new results highlight a distinct latitudinal distribution of clay minerals, with the occurrence of kaolinite in southern sections and an almost total absence of this mineral in northern areas. This latitudinal trend points to an at least partial climatic control on clay mineral sedimentation, with a humid zone developed between 20° and 35°N. The association and co-evolution of illite, chlorite and kaolinite in most sections suggest a reworking of these minerals from basement rocks weathered by hydrolysis, which we link to the formation of relief around the Tethys due to compression associated with incipient Tethyan closure. Diachronism in the occurrence of detrital minerals between sections, with detrital input starting earlier during the Santonian in the south than in the north, highlights the northward progression of the deformation related to the anticlockwise rotation of Africa. Increasing continental weathering and erosion, evidenced by our clay mineralogical data through the Campanian, may have resulted in enhanced CO2 consumption by silicate weathering, thereby contributing to Late Cretaceous climatic cooling

Workshop on the base of the Oxfordian Stage in the Subalpine Basin, France, 30th September to 2nd October 2013.

6 pagesInternational audienc

Isotropic 2D Quadrangle Meshing with Size and Orientation Control

18 pagesInternational audienceWe propose an approach for automatically generating isotropic 2D quadrangle meshes from arbitrary domains with a fine control over sizing and orientation of the elements. At the heart of our algorithm is an optimization procedure that, from a coarse initial tiling of the 2D domain, enforces each of the desirable mesh quality criteria (size, shape, orientation, degree, regularity) one at a time, in an order designed not to undo previous enhancements. Our experiments demonstrate how well our resulting quadrangle meshes conform to a wide range of input sizing and orientation fields

Découverte d’une flore autunienne et réinvestigation lithostratigraphique dans la bordure occidentale du bassin permien de Lodève (mont Sénégra, Hérault, France). Conséquences paléoenvironnementales

La ré-investigation de la bordure occidentale du bassin de Lodève a permis d’identifier une formation gréso-conglomératique de la base de l’Autunien à la place du « Stéphanien terminal », précédemment décrit. L’existence de deux mégaséquences, stéphanienne puis autunienne, discordantes et séparées par une lacune sédimentaire, est donc réaffirmée. Les auteurs ont aussi découvert, à environ 20 m au-dessus du conglomérat basal de cette formation gréso-conglomératique, une macroflore identique à celle du site des Tuilières, localisée à la base de l’Autunien gris, dans la partie orientale du bassin permien de Lodève. Outre le fait que cette macroflore confirme, au mont Sénégra, l’appartenance de cette nouvelle formation fossilifère à l’Autunien, ses différents taxa indiquent un changement important de la végétation par rapport à celle du Stéphanien productif sous-jacent. Les premières séquences autuniennes se sont d’abord déposées dans un environnement de cône alluvionnaire distal, passant verticalement à celui d’une plaine d’inondation évoluant dans un contexte volcanique actif.Re-investigation of the western edge of the Lodève basin allows reassignment of one sandstone-conglomerate formation previously identified as “terminal Stephanian” to Early Autunian. The existence of two unconformable (Stephanian and Autunian) megasequences, separated by a sedimentary gap, which had been rejected, is thus re-affirmed. The authors also found, less than 20 m above the basal Autunian conglomerate, a macroflora with taxa characteristic of the famous Tuilières flora from a site, located in the eastern part of the basin near Lodève, in the Grey Autunian group. This confirms that the new Mont Sénégra fossiliferous beds belong to the Lower Autunian. Moreover, the taxonomic differences between these plants and those from the underlying coal-bearing Stephanian beds indicate an important change in the vegetation between the Stephanian and the Autunian. The first Autunian sequences were initially deposited within a distal alluvial fan environment, which developed vertically into a floodplain, within an active volcanic context.</p

Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to middle Toarcian in the Paris Basin

Lower Toarcian strata (Lower Jurassic) have been extensively studied with a view to understanding the oceanographic, climatic and biological processes that drove the Earth’s system into an Oceanic Anoxic Event (OAE). For this time period, the evolution of the European marine seaways is now relatively well constrained owing to multiple geochemical studies, but investigations regarding climatic trends in the continental realm remain sparse. In the present study, we test the clay mineralogy as a continental climate-sensitive proxy in the well-documented Sancerre core (southern Paris Basin). We compare variations in the kaolinite content with pCO2 fluctuations (derived from paired carbon isotopes; Δ13C = δ13Ccarb – δ13Corg), taking advantage of the detailed chemostratigraphic, palaeoenvironmental and sequence stratigraphy frameworks established for this core material. The results indicate a substantial decrease in kaolinite abundance at the end of the Pliensbachian, which is compatible with a long-term diminution in continental weathering and an inferred temperature decrease. The early Toarcian, prior to the carbon cycle perturbation and deposition of black shale facies, remained relatively cold with minima in both the proportion of kaolinite and reconstructed pCO2. The mineralogical and geochemical responses across the prominent negative carbon isotope excursion (CIE) itself are not univocal. The first of four steps that compose the negative limb of the CIE at Sancerre is associated with decreased kaolinite and pCO2, and increased carbonate oxygen isotope ratios. Taken together, these trends are compatible with a transient cooling phase immediately preceding the onset of black shale deposition. Conversely, the subsequent steps are marked by substantial enrichment in kaolinite that matches increased osmium isotope ratios measured in Yorkshire, providing compelling evidence for rapid increases in continental weathering and riverine runoff forced by intensification of greenhouse conditions during the CIE. Relaxation in the intensity of continental weathering, as suggested by resumed low kaolinite abundance is seen immediately after the cessation of CO2 input (after the fourth step of the CIE). The interval spanning the upper portion of the early Toarcian and the middle Toarcian records a subsequent long-term increase in the proportion of kaolinite synchronous with significant clay enrichment of the sediment. Continued greenhouse conditions, even after the recovery from the carbon isotope perturbation and “regional” black shale deposition, are likely related to sustained CO2 emission by Karoo-Ferrar volcanism through the considered interval