116 research outputs found
Mass mortality or exceptional fossilization? The case of the early and middle Toarcian fossiliferous beds from the Digne-Les-Bains area (southeastern France)
La sĂ©rie sĂ©dimentaire dâĂąge domĂ©rien supĂ©rieur Ă toarcien supĂ©rieur (de â190 Ă â180 Ma) dans la RĂ©serve
GĂ©ologique de Haute-Provence (Sud-Est de la France) a lâintĂ©rĂȘt de prĂ©senter deux types de gisements fossilifĂšres remarquables.
Le premier type, dâĂąge toarcien infĂ©rieur, a la particularitĂ© de prĂ©senter des restes dâichtyosaures (dans au
moins six sites) en plus de trĂšs nombreux autres fossiles. Le deuxiĂšme type, dâĂąge toarcien moyen, est caractĂ©risĂ© par
lâabondance et la prĂ©sence presque exclusive dâammonites et de nautiles.
Des études lithostratigraphiques, biostratigraphiques, paléontologiques, sédimentologiques et géochimiques, ont
permis de savoir si ces accumulations rĂ©sultaient de mortalitĂ© en masse ou bien si elles nâĂ©taient dues quâĂ des fossilisations
exceptionnelles dâorganismes Ă taux de mortalitĂ© normal.
Les accumulations dâĂąge toarcien infĂ©rieur se sont effectuĂ©es, aprĂšs mortalitĂ© normale, par piĂ©geage avec des sĂ©diments
terrigĂšnes dans des hĂ©migrabens Ă la suite de jeu de blocs basculĂ©s et pendant une pĂ©riode dâanoxie ou
dâhypoxie. Les gisements dâĂąge toarcien moyen correspondent Ă des condensations et concentrations fauniques lors de
sédimentation carbonatée trÚs réduite en liaison avec une transgression marine de grande ampleur. Diverses conditions,
tectoniques locales de rifting, eustatiques rĂ©gionales liĂ©es Ă lâĂ©volution du domaine liguro-piĂ©montais, ocĂ©anographiques
globales dâanoxie et de crise de production carbonatĂ©e, ont toutes jouĂ© un rĂŽle dans la genĂšse des gisements fossilifĂšres.
Tout lien avec des extinctions massives, en rapport ou non avec des crises biologiques, est exclu
New perspective in steelmaking activity to increase competitiveness and reduce enviromental impact
The competitiveness of the European steel industry is strictly related to the introduction of high performanceproducts and to the increase in process efficiency and to the reduction in environmental impact. Thesechallenges can be faced to ensure a future to the areaâs important industrial assets and some actions need to beidentified. Several aspects about steelmaking plants, processes and steel products have been highlighted andnowadays, they may become the object of innovative action and efforts in order to achieve and maintain a highlevel of competitiveness and to solve this serious industrial crisis
Scaling of Star Polymers with one to 80 Arms
We present large statistics simulations of 3-dimensional star polymers with
up to arms, and with up to 4000 monomers per arm for small values of
. They were done for the Domb-Joyce model on the simple cubic lattice. This
is a model with soft core exclusion which allows multiple occupancy of sites
but punishes each same-site pair of monomers with a Boltzmann factor . We
use this to allow all arms to be attached at the central site, and we use the
`magic' value to minimize corrections to scaling. The simulations are
made with a very efficient chain growth algorithm with resampling, PERM,
modified to allow simultaneous growth of all arms. This allows us to measure
not only the swelling (as observed from the center-to-end distances), but also
the partition sum. The latter gives very precise estimates of the critical
exponents . For completeness we made also extensive simulations of
linear (unbranched) polymers which give the best estimates for the exponent
.Comment: 7 pages, 7 figure
The Impact of Global Warming and Anoxia on Marine Benthic Community Dynamics: an Example from the Toarcian (Early Jurassic)
The Pliensbachian-Toarcian (Early Jurassic) fossil record is an archive of natural data of benthic community response to global warming and marine long-term hypoxia and anoxia. In the early Toarcian mean temperatures increased by the same order of magnitude as that predicted for the near future; laminated, organic-rich, black shales were deposited in many shallow water epicontinental basins; and a biotic crisis occurred in the marine realm, with the extinction of approximately 5% of families and 26% of genera. High-resolution quantitative abundance data of benthic invertebrates were collected from the Cleveland Basin (North Yorkshire, UK), and analysed with multivariate statistical methods to detect how the fauna responded to environmental changes during the early Toarcian. Twelve biofacies were identified. Their changes through time closely resemble the pattern of faunal degradation and recovery observed in modern habitats affected by anoxia. All four successional stages of community structure recorded in modern studies are recognised in the fossil data (i.e. Stage III: climax; II: transitional; I: pioneer; 0: highly disturbed). Two main faunal turnover events occurred: (i) at the onset of anoxia, with the extinction of most benthic species and the survival of a few adapted to thrive in low-oxygen conditions (Stages I to 0) and (ii) in the recovery, when newly evolved species colonized the re-oxygenated soft sediments and the path of recovery did not retrace of pattern of ecological degradation (Stages I to II). The ordination of samples coupled with sedimentological and palaeotemperature proxy data indicate that the onset of anoxia and the extinction horizon coincide with both a rise in temperature and sea level. Our study of how faunal associations co-vary with long and short term sea level and temperature changes has implications for predicting the long-term effects of âdead zonesâ in modern oceans
Evolution of the Toarcian (Early Jurassic) carbon-cycle and global climatic controls on local sedimentary processes (Cardigan Bay Basin, UK)
The late Early Jurassic Toarcian Stage represents the warmest interval of the Jurassic Period, with an abrupt rise in global temperatures of up to âŒ7â°C in mid-latitudes at the onset of the early Toarcian Oceanic Anoxic Event (T-OAE; âŒ183 Ma). The T-OAE, which has been extensively studied in marine and continental successions from both hemispheres, was marked by the widespread expansion of anoxic and euxinic waters, geographically extensive deposition of organic-rich black shales, and climatic and environmental perturbations. Climatic and environmental processes following the T-OAE are, however, poorly known, largely due to a lack of study of stratigraphically well-constrained and complete sedimentary archives. Here, we present integrated geochemical and physical proxy data (high-resolution carbon-isotope data (ÎŽ13C), bulk and molecular organic geochemistry, inorganic petrology, mineral characterisation, and major- and trace-element concentrations) from the biostratigraphically complete and expanded entire Toarcian succession in the Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, Wales, UK. With these data, we (1) construct the first high-resolution biostratigraphically calibrated chemostratigraphic reference record for nearly the complete Toarcian Stage, (2) establish palaeoceanographic and depositional conditions in the Cardigan Bay Basin, (3) show that the T-OAE in the hemipelagic Cardigan Bay Basin was marked by the occurrence of gravity-flow deposits that were likely linked to globally enhanced sediment fluxes to continental margins and deeper marine (shelf) basins, and (4) explore how early Toarcian (tenuicostatum and serpentinum zones) siderite formation in the Cardigan Bay Basin may have been linked to low global oceanic sulphate concentrations and elevated supply of iron (Fe) from the hinterland, in response to climatically induced changes in hydrological cycling, global weathering rates and large-scale sulphide and evaporite deposition
Paleoclimatic control of biogeographic and sedimentary events in Tethyan and peri-Tethyan areas during the Oxfordian (Late Jurassic)
A surge of late-occurring meiotic double-strand breaks rescues synapsis abnormalities in spermatocytes of mice with hypomorphic expression of SPO11
Anagenetic evolution of the Early Tithonian Ammonite genus Semiformiceras tested with cladistic analysis
International audienceThe Early Tithonian ammonite genus Semiformiceras represents a lineage that lasted almost 3 myr. Previously, a gradual, anagenetic evolutionary pattern has been proposed on the basis of both biostratigraphic data and the interpretation of morphological changes in successive species, subspecies or morphotypes. The existence of two almost homeomorphic species, S. birkenmajeri and S. gemmellaroi, at two separate stratigraphic intervals in the early Tithonian contrasts with the transformation of characters suggested by the stratigraphic distribution of others. New descriptions of 18 specimens of the poorly known species Semiformiceras gemmellaroi (Zittel) allow a more accurate analysis of its characters. Cladistic analysis of a taxon-character matrix is based on nine Semiformiceras phena (species, chronosubspecies and morphotypes) and two outgroup taxa (Taramelliceras and Streblites), using 14 morphological characters. The phyletic relationships inferred from these do not fit the anagenetic pattern and question the adequacy of the fossil record in reconstructing phyletic lineages
20 My hiatus in the Jurassic of Umbria-Marche Apennines (Italy): carbonate crisis due to eutrophication.
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