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Géosciences Rennes
UMR 6118
Université de Rennes1
Campus de Beaulieu
35042 Rennes Cedex

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Accueil du site > Français > Les équipes > Paléoenvironnement, Paléomagnétisme, Dynamique des bassins

Paléoenvironnement, Paléomagnétisme, Dynamique des bassins

Membres de l’équipe

Permanents :

Bouffette Jacques (PRAG), Bourquin Sylvie (DR, CNRS - Responsable de l’équipe), Chauvin Annick (Pr), Cobbold Peter (DR, CNRS Emérite), Dabard Marie-Pierre (MC), Dauteuil Olivier (DR, CNRS), Dupont-Nivet Guillaume (CR, CNRS), Guillocheau François (Pr), Jolivet Marc (DR, CNRS), Lanos Philippe (DR, CNRS), Moreau Frédérique (MC), Nalpas Thierry (MC), Proust Jean-Noël (DR, CNRS), Robin Cécile (MC), Roperch Pierrick (DR, CNRS)

Personnels techniques et Ingénieurs impliqués dans les projets de l’équipe :

Cullerier Philippe (AI), Dufresne Philippe (IE), Le Carlier de Veslud Christian (IR, CNRS),

Doctorants :

Antoine Delaunay, Miguel Gonzalez Bonilla, Sage Kebi-Tsoumou, Chloe Le Gouche, Julien Morin, Carole Ortega, Alex Ortiz, Anne-Mouwenn Pastier, Jean-Pierre Ponte, Romain Rubi, Joseph Thompson Offei,

Post-Doctorants et ATER :

Guillaume Baby, Nicolas Bonnet, Celine Ducassou, Fernando Poblete, Hugo Pouderoux, Brendan Simon

L’équipe s’appuie sur les services spécialisés de Géosciences-Rennes :

1- Mesure de l’aimantation
2- Sédimentologie et Pétrophysique

L’équipe bénéficie d’un partenariat avec l’UMR IRAMAT (antenne de Bordeaux CRPAA) de l’Institut INSHS du CNRS.

L’équipe Paléoenvironnements, Paléomagnétisme et Dynamique des bassins est une équipe pluridisciplinaire dont l’objectif est de comprendre
- (1) les variations de préservation des environnements sédimentaires continentaux et de leurs marges (paléoenvironnements) et leurs facteurs de contrôle (climat, déformation…) dans l’espace (démarche source to sink) et à toutes les échelles de temps,
- (2) les variations séculaires du champs magnétique terrestre.

Notre démarche intégrée repose sur les acquisitions de terrain, l’interprétation de données de subsurface jusqu’à la quantification en intégrant la modélisation analogique.

Méthodes : Géodésie, Géomorphologique, Paléomagnétisme, Sédimentologique, Stratigraphie séquentielle, Tectonique, Thermochronologie basse température.

Principaux thème de recherche :

- 1 - Optimisation de la démarche source to sink et lois de transfert sédimentaire
- 2 - Surfaces continentales et déformations intraplaques
- 3 - Variations paléoclimatiques et eustatiques
- 4 - Variation séculaire du champ magnétique terrestre
- 5 - Datation par archéomagnétisme

1 - Source to sink : budget erosion-sedimentation

The understanding of the sedimentary system, i.e. the relationships between erosion in the upstream catchment, transfer and sedimentation in the downstream basins up to the deepest environments, is of primary importance for a better knowledge of (1) the erosion and sedimentation laws at the scale of geological times (10 Ka to 1 Ma) – sediment routing system, (2) the relative importance of deformation, climate and eustasy and (3) the prediction of the preservation of the sedimentary systems.
These approaches were successfully applied to the Atlantic Margin of southern Africa (South Africa and Namibia ; Guillocheau et al., 2012 ; Braun et al., 2014) and are still ongoing at the scale of Austral Africa, including the Orange, Limpopo and Zambezi sedimentary systems (PAMELA project – IFrEMer-Total). The main target is to understand the effect of mantle dynamics through the uplift of the southern African Plateau – in a well-known palaeoclimate (palaeo-precipitation) framework – on (1) the planation processes (chemical vs. physical erosion), (2) the stratigraphic architecture of the margin and (3) the sediment budget between plateau

Sedimentary fluxes around the Southern African Plateau since Cretaceous times. (a) Location of the main sediment feeders (deltas and deep-sea fans) and amount of deposited sediments (103 km3) for the Late Cretaceous and Cenozoic (numbers between parentheses). (b) Evolution of the deposited sediment volumes along the Orange Margin since Lower Cretaceous (Braun et al., 2014)

Another approach concerns the rift basins and especially the understanding of the early syn-rift sedimentation and their controlling factors, from the example of the Corinth rift (PhD in progress, R. Rubi, ENGIE-CNRS Project). Within its proximal part, this rift is well constraint in term of depositional model and stratigraphic architecture in relation with the geodynamic context (work initiated by PhD of S. Rohais, 2007 ; Rohais et al., 2007, 2008). The well-developed Gilbert-type delta with a short-length depositional profile from sediment source to deep basin, allow to constrain the transfer of sediment from the catchment area to the basin. The main target is to discuss the lateral and vertical variations of erosion and sedimentation along the depositional profile to better constrain the nature and architecture of the sediments, especially in the distal part of gravity deposits (in progress).

2- Continental surfaces and intra-plate deformation

a - Geodynamic – topography – climate interaction in Central Asia

The Tertiary tectonic deformation and topographic evolution of Asia has been widely explored as it represents a key example of both continental tectonics and tectonic – erosion – sedimentation – climate interactions. A largely accepted idea among most studies is that the crustal and lithospheric heritage plays a large role in localizing Tertiary deformation within the entire Asian orogen. It also appears more and more clearly that some features of the Mesozoic topography of Central Asia are still preserved among the evolving Tertiary topography. Especially, remnants of widely distributed planation surfaces – possibly largely connected into a huge single surface – that reached from North Tibet to Siberia during the Late Jurassic – Cretaceous are preserved in the Tien Shan, Mongolia and Southern Siberia. Our recent researches have shown that the development of this surface is contemporaneous to a strong aridification of Central Asia, switching from a wet, vegetation-favouring climate to a arid to semi-arid climate that still pertains today. However, the exact impact of climate on the planation is still to be explored. Similarly, the geodynamic setting that prevailed during the formation of the planation surface and that who allowed its preservation during about 150 Ma across several major continent accretions and collisions remains to be assessed in details. These questions are investigated using an integrated approach based on basement geomorphology and low temperature thermal history, on sediment source tracking using detrital geochronology, on paleo-depositional environment analysis in the basins and on isotopic analysis of climate markers such as paleosols.

Mesozoic planation surface in the Kyrgyz Tien Shan overlain by Paleogene red clastic sédiments
(photo M. Jolivet).

Integrated approach developed to describe in details the topography – tectonic – climate interactions in Central Asia

b - Meso-Cenozoic planation surfaces and uplift of the Armorican studies – toward a characterization of the western European long wavelength deformation

The nature and age of the relief of the Armorican Massif are highly debated since the classical works of de Martonne (1905). An analysis of the planation surfaces (Bessin et al., 2015) and of the associated sediments provide (1) a mapping of the stepped planation surfaces of etchplain and pediment types ranging from at least Early Jurassic to Eocene and (2) a quantified model of surface uplift based on the intersection of dated marine sediments of known water depth (preserved on these planation surfaces) with a new compilation of sea level changes (eustasy) through time (Bessin et al., 2017). In the frame of the project Orogen-s2s (BRGM_Total), this type of approach will be extended to Western European basements (French Massif central, Ardennes-Rhine Massif, Cornwall…) and uplifted basins (Paris-Wessex Basin, Franconian Basin…) along regional transects in order to restore paleo-topographies using stepped planation surfaces and correlative sediments, for a better characterization and understanding of the lithospheric long wavelength (x100 km) deformations.

Synthetic map of the Armorican Massif planation surfaces and their ages (Bessin et al., 2015)

3- Palaeoclimatic and eustatic variations

a - Monsoons of Asia caused Greenhouse to Icehouse Cooling (ERC MAGIC).

Unraveling the cause for Cenozoic global climate cooling is one of the most important unresolved questions challenging the Earth and Environmental sciences community today (Raymo and Ruddiman, 1992). Increased erosion and weathering of the uplifted Tibetan Plateau and Himalayas, is advocated as the primary cause for the enigmatic pCO2 drawdown, that led to global cooling 50 to 34 Myrs ago from the warm ice‐free Greenhouse world to the bi‐polar Icehouse conditions still prevailing today (deConto and Pollard, 2003). Asian Monsoons are genetically linked to high orography associated with the India‐Asia collision starting ca. 50 Myrs ago (Molnar et al., 2010), however, the relation between Greenhouse to Icehouse cooling and Asian Monsoons remains to be explore as they were previously thought to intensify only much later ca. 25 Myrs ago (Guo et al., 2003). Our recent findings of monsoonal activity in Asia since at least 45 Myrs ago (Licht et al., 2014) raises the fascinating possibility that Asian Monsoons may have triggered global cooling from Greenhouse to Icehouse conditions. Testing this novel hypothesis and exploring its implications on feedback mechanisms between regional environments, Asian Monsoons and global climate, will constitute the stimulating objectives of MAGIC.

Ongoing project :http://www.paleoenvironment.eu/Research/projects/Magic/

b – Late Permian to Jurassic co-evolution of tectonic, topographic, climatic, and paleobiological changes in SE Asia

The interactions between regional and global climate changes and the topographic evolution of major mountain ranges are not restricted to the Alpine system or the Cenozoic area. The Permian to Jurassic evolution of Asia was also characterized by major mountain building (late Permian-Triassic Indosinian orogeny in SE Asia) and profound changes in paleogeography (Jolivet, 2015). During this period of intense tectonic activity and mountain building, changes in climate, environment, and biology, including one of the major Phanerozoic mass extinction, punctuated Earth history. The capacity of sedimentary basins to concurrently record the evolution of orogenic domains (sediment dispersal patterns and fluxes), the climate signal, and the interactions between topography and climate is now well established. The main target is to understand the sedimentary basin evolution from late Permian to Jurassic, the results will offer a new perspective on topographic, climatic, and ecological changes during this critical period of geologic time in the region. The first results obtain, in South-East Asia, from Laos basin (Bercovici et al., 21012 ; Blanchard et al., 2015 ; Rossignol et al., 2016), Vietnam basins (Roger et al., 2014 ; Rossignol et al., in progress), allow to constrain geodynamic evolution for the Indochina and South China blocks.

Geodynamical model of SE Asia from basin studies : new constrain for palaeoenvironment and palaeoclimate reconstitutions

c - Sea-level change : New Jersey Passive Margin (IODP-ICDP 313)

Understanding the history, causes and impact of sea-level changes is a challenge for our societies facing global sea level rise. In such a context, the improvement of our knowledge of sea-level changes and shoreline divagation at geological time scale is critical. The simple and undeform, laterally correlative sedimentary record of passive margins is for a long time used to reconstruct past sea level. However, the detailed nature of their basic clinothem progradational pattern is still poorly known. This project aims at describing the sedimentary facies and interpreting the depositional environments and the architecture of the clinothems of the New Jersey shelf to depict their origin and controls of the distribution of geological reservoirs. We analyze 612 cores totaling 1311m in length collected at three sites c.60km offshore New York city, during the IODP-ICDP Expedition 313. The three sites sampled the early to mid-Miocene passive margin sediments of the New Jersey

Mid Miocene Transition of New Jersey passive margin (Proust et al., Geosphere, in prep)

4 – Secular Variation of the Earth’s magnetic field.

We study past directions and intensity of the geomagnetic field recorded by volcanic and archeomagnetic materials. Our study areas are Western Europe and Latin America. The aim of the work is to provide new constraints for the geodynamo’s models and efficient dating tools for archeological materials and young volcanic activity. We recently confirmed the exceptional geomagnetic secular variation in Chile over the last 3 centuries characterised by an almost linear 20° decrease in inclination and 25 T in intensity, making paleomagnetism the best tool for dating in this time interval for which uncertainties in calibrated 14C ages are often too large.

Comparison of the mean paleomagnetic results obtained on historical lava flows in Chile (dots) with predictions of geomagnetic models. (Roperch et al., Phys. Earth Planet. Int., 242, 65-78, 2015)

In Western Europe, during the first millennium BC, our data suggest an increase of the intensity of the geomagnetic field from the 9th century to 700 BC when a maximal value 90 μT is reached (Hervé et al., J. Archaelogical Sc. Reports, 7, 2016). During the same time period, the declination of the geomagnetic field decreased of about 30° (Hervé et al. Phys. Earth Planet. Int., 218, 1-13, 2013). As a consequence, archaeomagnetism promises to be a powerful dating tool to recover the historical processes at the transition between the Bronze and Iron Ages.

During the last two millenniums, the most significant geomagnetic field intensity feature is the maximum observed around 800 AD. We provide recently an improved description of the sharp abrupt intensity decay that took place during more recent periods. Our results confirm that several rapid intensity changes (with rates higher than 10 μT/century) took place in Western Europe during the recent history of the Earth (Gomez-Paccard et al., Earth Planetary Science Letters, 454, 55-64, 2016).

We pursue at the moment our work on some new sites of study in Argentina and in Mexico

5 – Dating by archeomagnetism

Development and application of archeomagnetism to the dating of archaeological baked clay (potters and tile kilns, fireplaces, and architectural baked clay : tiles and bricks) within the framework of archaeological problems covering the periods from protohistory to modern times In Western Europe.

This activity is supported by the UMR 5060 IRAMAT-CRPAA (INSHS) as part of a partnership with Géosciences-Rennes. The work deals with the dating of large antique or medieval pottery workshops in France, within the framework of rescue and programmed archeology. This work is carried out for dating purposes and also for the purpose of improving the accuracy of the curves of secular variation of the geomagnetic field. As an example, in 2016, we studied 62 structures in situ (kilns and hearths) of the Gallo-Roman and medieval periods in France.