Climatic and tectonic controls on carbonate deposition in syn-rift siliciclastic fluvial systems: A case of microbialites and associated facies in the Late Jurassic

This work provides new insights to assess the factors controlling carbonate deposition in the siliciclastic fluvial systems of rift basins. Sedimentological and stable-isotope data of microbialites and associated carbonate facies, along with regional geological information, are shown to reveal the influence of climate and tectonics on the occurrence and attributes of carbonate deposits in these settings. The Vega Formation – a 150 m thick Lower Kimmeridgian siliciclastic fluvial sequence in Asturias Province (northern Spain) – constitutes a candidate for this approach. This unit includes varied facies (stromatolites; rudstones, packstones and wackestones containing oncoids, intraclasts, charophytes and shell bioclasts; marlstones and polygenic calcareous conglomerates) that formed in a low-gradient fluvial–lacustrine system consisting of shallow, low-sinuosity oncoid-bearing channels and pools within marshy areas, with sporadic coarse alluvial deposition. The sedimentological attributes indicate common erosion by channel overflow and rapid lateral changes of subenvironments caused by water-discharge variations. The carbonate fluvial–lacustrine system developed near uplifted marine Jurassic rocks. The occurrence of the system was conditioned by normal faults (active during the deposition of the unit) that favoured: (i) springs of HCO3–Ca-rich water from a Rhaetian–Sinemurian carbonate rock aquifer; and (ii) carbonate deposition in areas partially isolated from the adjacent siliciclastic fluvial system. The microbialite d13C and d18O values support deposition in a hydrologically open system, fed by ambient-temperature meteoric water, with riparian vegetation. Three types of lamination in the stromatolites and oncoids reflect distinct morphological types of cyanobacterial communities. The textural pattern of lamination parallels d13C and d18O changes, suggesting short-term cycles of precipitation and temperature. A moderately to strongly contrasted seasonal and/or pluriannual precipitation regime is inferred from the cyclic d13C pattern of the lamination and from the discontinuous and asymmetrical growth of oncoids. Thus, the isotopic and sedimentological attributes of the carbonate deposits were linked to short-term climate changes associated with semi-arid conditions, consistent with the studied climatic zone

First report of a Late Jurassic lizard-like footprint (Asturias, Spain)

This report describes an isolated footprint preserved as a natural cast (convex hyporelief) from the Lastres Fm. (Late Jurassic) of northern Spain. The track consists of a small isolated pentadactyl ectaxonic right manus footprint. It is very asymmetric, plantigrade, with digits and palm deeply marked on the substrate. Digit IV is the longest, digits II and I are nearly equal in length and only a little shorter than III and IV. The footprint morphology is typical of a lizard – like or “lacertoid” track .The general outline of the footprint, the width to length ratio approximately equal to 1, the marked plantigrady and the substantial similarity in length of digits IV-I are coherent with a Rhynchosauroidea manual print. The global record of Rhynchosauroides ichnogenus shows that this specimen represents the latest occurrence of the ichnogenus. The most probable trackmaker was possibly a rhyncocephalian reptile.Se describe una huella de mano aislada, preservada como contramolde natural (hiporrelieve convexo) de la Formacion Lastres (Jurasico Superior) del N de Espana. La icnita, aislada, pentadactila, ectaxonica y de pequeno tamano, es atribuida a una mano derecha. Es muy asimetrica y plantigrada, con los dedos y la palma profundamente impresos en el sustrato. El dedo IV es el mas largo, mientras que el II y el I son casi iguales en longitud y solamente un poco mas cortos que el III y el IV. La morfologia de la huella es tipica de un lagarto o “lacertoide”. El contorno de la huella, la relacion longitud/anchura en torno a 1, la longitud similar de los dedos I-IV y el hecho de que sea claramente plantigrada son rasgos coherentes con una huella de mano de un Rhynchosauroidea. El registro global de Rhynchosauroides indica que el ejemplar asturiano representa la evidencia mas reciente de este icnogenero. El autor de la huella fue probablemente un reptil rincocefalo

3Dpaleo.net, una plataforma web de fósiles en 3D hiperrealista para fomentar la difusión y el conocimiento del patrimonio paleontológico

3Dpaleo.net es una plataforma web en fase de desarrollo que muestra modelos tridimensionales hiperrealistas y en alta definición de algunos de fósiles más emblemáticos del Museo de Ciencias Naturales de la Universidad de Zaragoza y del Museo del Jurásico de Asturias (MUJA), colaboradores de la primera fase del proyecto. Se trata de una iniciativa promovida por la empresa Paleoymás con el fin de explorar y explotar las posibilidades de las nuevas tecnologías, aplicándolas a la divulgación de la paleontología y a la mejora de técnicas expositivas y de difusión del conocimiento. 3Dpaleo.net facilita, a través de internet, la visualización de los fósiles y de algunos de sus detalles más interesantes. 3Dpaleo.net is a website, under development, that shows high definition hyperrealistic 3D models of some emblematic fossils of the museums that have collaborated in this first stage of the project: The Natural Sciences Museum of the University of Zaragoza and the Jurassic Museum of Asturias (MUJA). It is promoted by Paleoymás with the aim of exploring and developing the possibilities of new technologies, applying them to the popularization of paleontology and the improvement of both; expositive technics and knowledge sharing. 3Dpaleo.net helps through the internet to display fossils and some of their most interesting details

The impact of the Pliensbachian–Toarcian crisis on belemnite assemblages and size distribution

The second-order Pliensbachian–Toarcian crisis affected major groups of marine organisms. While its impact has been intensively studied for ammonites, the response of belemnites is only currently emerging through quantitative studies. Novel overall and regional diversity analyses suggest that belemnite richness in the NW-Tethys drops at the Pliensbachian–Toarcian boundary, while overall diversity slightly increases in NW-Tethys assemblages during the Toarcian Oceanic Anoxic event (T-OAE), mostly driven by NW European assemblages (e.g., Yorkshire). The T-OAE coincides with marked taxonomic turnover within individual basins, which is associated with an increase in median rostrum size of specimens in taxa at most localities. The changes in median body size across the Pliensbachian–Toarcian boundary are less consistent and driven by changes in body size within individual lineages crossing the boundary. However, our analyses also illustrate differences in sampling across the Pliensbachian–Toarcian crisis, which needs to be considered in further studies. © 2021, The Author(s).Open Access funding enabled and organized by Projekt DEAL. KDB, PN and PR were supported by the DFG (Ba 5148/1-1, Ba 5148/1-2 to KDB). This research benefitted from a Synthesys Grant to Patricia Rita

Cliff Coast of Asturias

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