Articles

Séminaire de Bruno Dhuime (Géosciences Montpellier)

Séminaire de Judith Masters (APIES, South Africa)

Living non-human primates inhabit the forests and woodlands of South and Central America, Africa, Madagascar, India and Sri Lanka, and south-east Asia as far north as Japan. Their current ranges are often separated by vast tracts of ocean or hostile environment. The date estimated by molecular data for the origin of the primate order is latest Cretaceous, approximately 75 Ma, although the oldest recognisably primate fossils have been found in theHigh Atlas Mountains of Morocco, and date to 60 Ma. How primates came to occupy their current distributions has been an issue of great interest and debate among primate evolutionary biologists. The strepsirrhine (or tooth-combed) primates in particular occupy a range that borders on much of the Indian Ocean, and it is difficult to believe that the formation of the ocean was unrelated to the evolution of these primates. In this talk I discuss the timing of important events in early primate evolution, and the fossils that testify to these events. Primates appear to have evolved long after major sundering events in the break-up of the continents occurred, particularly those involving the Indian Ocean margins. This has led to a general belief that primates rafted across oceans, both from Africa to South America, and from Africa to Madagascar, in order to generate their current biogeographic pattern. I shall investigate the likelihood of these scenarios, and seek alternative explanations for these patterns.

8 avril 2019

Séminaire de Elena Spagnuolo (INGV, Rome, Italy)

Reliable estimations of the seismic hazard in a region requires the prediction of the size, location and magnitude of future earthquake events. However, such prediction is hindered by limited constraints on the real earthquakes physics, which is governed by the interplay of friction, healing, stress perturbations and strain events on faults operating at different spatial and temporal scales. Not all these evolving variables are directly accessible from either seismological, geodetic observations or filed survey so that laboratory investigations are becoming increasingly relevant to provide a ready access to the experimental seismic source.
At INGV (Rome, IT) we avail of SHIVA (Slow to HIgh Velocity Apparatus), the most powerful rotary shear apparatus installed worldwide able to apply close to natural earthquake deformation conditions (slip velocities of up to 10 m/s, accelerations of 65 m/s2, a nominally infinite slip and normal stresses larger than 30 MPa) on fault rock samples (50 mm of diameter) under a variety of environmental setup (e.g. room humidity, vacuum, fluid pressure). We simulate the entire seismic cycle on fault materials either form outcrops, cores exhumed from deep drilling projects (e.g. IODP JRSO expedition 362 Sumatra seismogenic zone) or selected lithologies ( e.g. Carrara marble, 99% calcite).
Our investigations spans from the nanoscale to the large scale of megathrusts availing of integrated geological, experimental and numerical approaches. Our aim is twofold in discussing the micro-physics of laboratory earthquakes – that intimately govern natural fault rocks behavior – and in deepening our previous knowledge of fault stability heavily challenged by the unexpected behaviour of recent tsuamigenic events like the 2004 Sumatra and 2011 Tohoku earthquakes.

22 mars 2019

Séminaire de Marion Peral (Paris Saclay, Lab Sci Climat & Environment)

Quantifier les variations de température océanique du passé est nécessaire pour comprendre les mécanismes qui régissent l’évolution climatique. Les méthodes de paléothermométrie classiques peuvent souffrir de limitation inhérents à l’écologie des organismes et/ou à cause de l’influence d’effets physico- chimiques (salinité, acidité de l’eau de mer…). Durant les 10 dernières années, la technique de paléothermométrie ∆47, qui repose sur la mesure du « clumping isotopique » dans les carbonates a été développé. Afin d’appliquer cette méthode aux foraminifères, un travail méthodologique était nécessaire avec la mise en place d’une calibration. Notre calibration, couvrant une gamme de température de -2 à 25 °C, montre une excellente corrélation avec la température et l’absence d’effets qui limitent généralement les autres méthodes de paléothermométrie. Nous avons ensuite validé cette calibration pour l’étude des variations climatiques au cours de la transition du Pléistocène moyen (MPT) en mer Méditerranée. Nos résultats montrent des reconstructions de températures robustes comparées à celles reconstruites en utilisant d’autres paléothermomètres. Ils nous permettent aussi d’observer les grandes tendances climatiques au cours de la MPT.

8 mars 2019

Séminaire de Mélanie Wary (Universitat Autònoma de Barcelona)

Dynamique de la cryosphère dans l’Atlantique boréal lors de la dernière période glaciaire : l’apport des biomarqueurs 

12 février 2019