Immediate and delayed signal of slab breakoff in Oligo/Miocene Molasse deposits from the European Alps

High-resolution 32-20 Ma-old stratigraphic records from the Molasse foreland basin situated north of the Alps, and Gonfolite Lombarda conglomerates deposited on the southern Alpine margin, document two consecutive sedimentary responses - an immediate and delayed response - to slab breakoff beneath the central Alps c. 32-30 Ma ago. The first signal, which occurred due to rebound and surface uplift in the Alps, was a regional and simultaneous switch from basin underfill to overfill at 30 Ma paired with shifts to coarse-grained depositional environments in the foreland basin. The second signal, however, arrived several million years after slab breakoff and was marked by larger contributions of crystalline clasts in the conglomerates, larger clast sizes, larger sediment fluxes and shifts to more proximal facies. We propose that this secondary pulse reflects a delayed whiplash-type erosional response to surface uplift, where erosion and sediment flux became amplified through positive feedbacks once larger erosional thresholds of crystalline bedrock were exceeded

Reply to comment by Yanni Gunnell and Marc Calvet on "Origin of the highly elevated Pyrenean peneplain"

4 p.International audienceGunnell and Calvet [2006] (hereinafter referred to asGC) challenge the recent model that we proposed for theorigin of the highly elevated Pyrenean peneplain by contest-ing our morphometric analysis of this chain and the relationwe made between the morphological evolution and thepiedmont sedimentation. Their reasoning is as follows: (1)According to Calvet [1996] (on which their comment islargely based) the high-elevation, low-relief surfaces in theEastern Pyrenees are remnants of a peneplain that devel-oped before the Pliocene from applanation near to sea level,and which was later uplifted by 2000 m during the Plio-Quaternary (in other words, GC belong to the ‘‘applanation’’school, whereas we woul d belong to the ‘‘altiplanation’’school); (2) high-elevation, low-relief surfaces do not existin the Central Pyrenees; (3) therefore the relationships wemade between the morphology of the Central Pyrenees andthe pattern of the detrital sedimentation in the adjacent Ebroforeland basin is meaningless; (4) contrary to the initialinterpretation of Calvet [1996], GC recognize that crustalthickening did not develop since the Pliocene in the EasternPyrenees, so they appeal to another geodynamical processsuch as extension or lithosphere delamination to explain thesupposed uplift

Deglaciation and glacial erosion: A joint control on magma productivity by continental unloading

Glacial-interglacial cycles affect the processes through which water and rocks are redistributed across the Earth's surface, thereby linking the solid Earth and climate dynamics. Regional and global scale studies suggest that continental lithospheric unloading due to ice melting during the transition to interglacials leads to increased continental magmatic, volcanic, and degassing activity. Such a climatic forcing on the melting of the Earth's interior, however, has always been evaluated regardless of continental unloading by glacial erosion, albeit the density of rock exceeds that of ice by approximately 3 times. Here we present and discuss numerical results involving synthetic but realistic topographies, ice caps, and glacial erosion rates suggesting that erosion may be as important as deglaciation in affecting continental unloading. Our study represents an additional step toward a more general understanding of the links between a changing climate, glacial processes, and the melting of the solid Earth

Fluvio-deltaic record of increased sediment transport during the Middle Eocene Climatic Optimum (MECO), Southern Pyrenees, Spain

The early Cenozoic marine sedimentary record is punctuated by several brief episodes (&lt;200 kyr) of abrupt global warming, called hyperthermals, that have disturbed ocean life and water physicochemistry. Moreover, recent studies of fluvial–deltaic systems, for instance at the Palaeocene–Eocene Thermal Maximum, revealed that these hyperthermals also impacted the hydrologic cycle, triggering an increase in erosion and sediment transport at the Earth's surface. Contrary to the early Cenozoic hyperthermals, the Middle Eocene Climatic Optimum (MECO), lasting from 40.5 to 40.0 Ma, constitutes an event of gradual warming that left a highly variable carbon isotope signature and for which little data exist about its impact on Earth surface systems. In the South Pyrenean foreland basin (SPFB), an episode of prominent deltaic progradation (Belsué–Atarés and Escanilla formations) in the middle Bartonian has been usually associated with increased Pyrenean tectonic activity, but recent magnetostratigraphic data suggest a possible coincidence between the progradation and the MECO warming period. To test this hypothesis, we measured the stable-isotope composition of carbonates (δ13Ccarb and δ18Ocarb) and organic matter (δ13Corg) of 257 samples in two sections of SPFB fluvial–deltaic successions covering the different phases of the MECO and already dated with magnetostratigraphy. We find a negative shift in δ18Ocarb and an unclear signal in δ13Ccarb around the transition from magnetic chron C18r to chron C17r (middle Bartonian). These results allow, by correlation with reference sections in the Atlantic and Tethys, the MECO to be identified and its coincident relationship with the Belsué–Atarès fluvial–deltaic progradation to be documented. Despite its long duration and a more gradual temperature rise, the MECO in the South Pyrenean foreland basin may have led, like lower Cenozoic hyperthermals, to an increase in erosion and sediment transport that is manifested in the sedimentary record. The new data support the hypothesis of a more important hydrological response to the MECO than previously thought in mid-latitude environments, including those around the Tethys.</p

Origin of the high elevated Pyrenean peneplain

Peneplanation of mountain ranges is generally considered the result of long-term erosional processes that smooth relief and lower elevation near sea level. Therefore peneplain remnants at high elevation in mountain ranges are used to infer posttectonic surface uplift. Such an interpretation has been proposed for the Pyrenees where high-elevation, low-relief erosional surfaces rose up to more than 2000 m. Because the Pyrenean foreland basins are filled with very thick continental deposits, which have buried the early jagged landscape, we challenge this hypothesis by pointing out that relief applanation does not necessarily require elevation lowering. We propose an alternative interpretation in which piedmont aggradation of detrital sediment that comes from erosion of the high chain induces the rise of the base level of the range, therefore reducing strongly the erosive efficiency of the drainage system and resulting in the progressive smoothing of the relief. Such a process allows a high-elevation, low-relief erosional surface to develop at the scale of the range. In the Pyrenees, occurrence of high-elevation, low-relief erosional surface remnants does not imply a posttectonic uplift, but is instead due to the dissection of the initial Miocene high-elevation, low-relief surface by the recent drainage system, the erosive activity of which has been enhanced by global climate change from the late Pliocene onward

Coupled surface to deep Earth processes: Perspectives from TOPO-EUROPE with an emphasis on climate- and energy-related societal challenges

Understanding the interactions between surface and deep Earth processes is important for research in many diverse scientific areas including climate, environment, energy, georesources and biosphere. The TOPO-EUROPE initiative of the International Lithosphere Program serves as a pan-European platform for integrated surface and deep Earth sciences, synergizing observational studies of the Earth structure and fluxes on all spatial and temporal scales with modelling of Earth processes. This review provides a survey of scientific developments in our quantitative understanding of coupled surface-deep Earth processes achieved through TOPO-EUROPE. The most notable innovations include (1) a process-based understanding of the connection of upper mantle dynamics and absolute plate motion frames; (2) integrated models for sediment source-to-sink dynamics, demonstrating the importance of mass transfer from mountains to basins and from basin to basin; (3) demonstration of the key role of polyphase evolution of sedimentary basins, the impact of pre-rift and pre-orogenic structures, and the evolution of subsequent lithosphere and landscape dynamics; (4) improved conceptual understanding of the temporal evolution from back-arc extension to tectonic inversion and onset of subduction; (5) models to explain the integrated strength of Europe's lithosphere; (6) concepts governing the interplay between thermal upper mantle processes and stress-induced intraplate deformation; (7) constraints on the record of vertical motions from high-resolution data sets obtained from geo-thermochronology for Europe's topographic evolution; (8) recognition and quantifications of the forcing by erosional and/or glacial-interglacial surface mass transfer on the regional magmatism, with major implications for our understanding of the carbon cycle on geological timescales and the emerging field of biogeodynamics; and (9) the transfer of insights obtained on the coupling of deep Earth and surface processes to the domain of geothermal energy exploration. Concerning the future research agenda of TOPO-EUROPE, we also discuss the rich potential for further advances, multidisciplinary research and community building across many scientific frontiers, including research on the biosphere, climate and energy. These will focus on obtaining a better insight into the initiation and evolution of subduction systems, the role of mantle plumes in continental rifting and (super)continent break-up, and the deformation and tectonic reactivation of cratons; the interaction between geodynamic, surface and climate processes, such as interactions between glaciation, sea level change and deep Earth processes; the sensitivity, tipping points, and spatio-temporal evolution of the interactions between climate and tectonics as well as the role of rock melting and outgassing in affecting such interactions; the emerging field of biogeodynamics, that is the impact of coupled deep Earth – surface processes on the evolution of life on Earth; and tightening the connection between societal challenges regarding renewable georesources, climate change, natural geohazards, and novel process-understanding of the Earth system

Origine et modification des cycles stratigraphiques à haute-fréquence (10's à 100's ka). Rôle des déformations courte longueur et modélisation du comportement des systèmes fluviatiles

Thèse publiée dans la collection des Mémoires de Géosciences Rennes (ISSN 1240-1498) : Mémoire n° 104 (ISBN 2-914375-11-5)Detrital accummulations are always composed of stratigraphic cycles at a large range of time scales (0.01-100 Ma), linked to variations of the ratio between available space to sedimentation (accommodation) and sediment supply due to tectonics and climate. What are the respective contributions of each of these factors in the origin and expression of the cycles, in particular at high-frequency (10-100 ka) where they can all play a role? If regional and global accommodation variations (tectonics and climate) at these frequencies are largely admitted as a dominant origin, (1) the influence of intra-basin tectonic structures (folds and faults) on the expression of stratigraphic cycles, and (2) the controls on high-frequency sediment supply, are less well constrained. This work adresses both aspects through the sedimentological study of a growth anticline, and the numerical modelling of rivers and their control on sediment supply variations at the entrance of sedimentary basins.Dans les séries terrigènes, les cycles stratigraphiques sont présents sur une large gamme de périodes (0.01-100 Ma), et sont dus aux variations du rapport entre l'espace disponible à l'accummulation des sédiments et le flux sédimentaire. Quelle est la responsabilité de chacun de ces paramètres dans l'origine et l'expression des cycles stratigraphiques, en particulier à haute-fréquence (10-100 ka) où tous interviennent ? Si les variations d'espace disponible d'échelle régionale ou globale (tectonique et climat) existent à ces fréquences et sont une origine fréquement admise, on connaît mal (1) l'influence de la croissance des structures tectoniques intra-bassin (plis et failles) sur leur expression, et (2) les contrôles du flux sédimentaire à haute-fréquence. Ce travail examine ces deux aspects à travers l'étude sédimentologique d'un anticlinal de croissance, et la modélisation numérique de l'effet de la zone de transfert (rivières) des sédiments sur la variabilité du flux sédimentaire

Sébastien Castelltort, Professeur ordinaire, Section des sciences de la Terre et de l’environnement, Faculté des sciences, UNIGE. <p>--------</p> Sébastien Castelltort, Full Professor, Section of Earth and Environmental Sciences, Faculty of Science, UNIGE.

Sébastien Castelltort, Professeur ordinaire, Section des sciences de la Terre et de l’environnement, Faculté des sciences, UNIGE. -------- Sébastien Castelltort, Full Professor, Section of Earth and Environmental Sciences, Faculty of Science, UNIGE

Empirical relationship between river slope and the elongation of bars in braided rivers: A potential tool for paleoslope analysis from subsurface data

Paleoslope of ancient river systems is a fundamental parameter needed to reconstruct paleohydrology and paleoclimate from the fluvial sedimentary record. The shape of braid-bars in 22 modern rivers yields a relationship between average bar elongation (length/width) and river slope. Steep rivers display more elongated bars than gently dipping reaches. This relationship has potential application to ancient braided systems preserved in the subsurface and imaged by 3D seismic data. The average elongation of bars identified on a stratal-slice through the DaGang river deposits in North-East China yields a slope prediction which, combined with empirical data on grain-size and slope of alluvial rivers, predicts a median grain-size of between 0.1 and 1 mm for the considered river sediment, in agreement with grain-size data in an adjacent isochronous belt. This study provides an additional approach for paleohydraulics in sedimentary basins and grain-size prediction in exploration