Géodynamique andine : résumés étendus = Andean geodynamics : extended abstracts = Geodinamica andina : resumenes expandidos

Le Bassin Oriente d'Equateur est un bassin d'avant-pays qui s'est développé depuis le Crétacé supérieur. Il a été déformé par 3 événements tectoniques (Turonien-Maastrichtien ; Eocène ; Pliocène-Quaternaire) qui se sont traduits par le fonctionnement transpressif dextre de 3 zones de décrochements NNE-SSW, qui d'est en ouest sont : 1) le Système Subandin toujours très actif ; 2) le Couloir Sacha-Shushufindi qui correspond à l'inversion d'un rift jurassique ; 3) le Système Inversé de Capiron-Tiputini hérité d'un bassin extensif permo-triasique. (Résumé d'auteur

Géodynamique andine : résumés étendus = Andean geodynamics : extended abstracts = Geodinamica andina : resumenes expandidos

Dans le Bassin Oriente équatorien, les cycles sédimentaires de l'Aptien au Turonien montrent une influence eustatique. A partir du début du Maastrichtien, le bassin s'inverse et la dynamique est directement liée à l'évolution d'un bassin d'avant-pays. Durant l'Eocène supérieur et l'Oligocène, les formations sédimentaires sont apparemment post-tectoniques, mais on montre qu'elles sont tout de même sous l'influence des Andes en surrection. (Résumé d'auteur

The role of salt tectonics in the evolution of the northeastern Pyrenees

Résumés dela 24eRéunion des Sciences de la Terre, 27-31 octubre, 2014 ,Université de Pau et des Pays de l’AdourEvaporites can play a major role in controllmg the architecture or exter­ nal orogenic belts, both during extensional and subsequent compressio­ nal phases. However, salt can also 'hide' deformation due to its ability to flow and dissolve. The challenge is to recognise the imprint of its past presence and influence. In the NE Pyrenees multiple deformation phases have been identified based on locally anomalous stratigraphic and structural relationsh ips. This has resulted in complex, sometimes in­ coherent and often conflictual models of orogenic history. For example, a pre-Cenomanian deformation phase has been interpreted as either ex­ tensional or compressional. As part of the ANR-PYRAMID project, we re-examine a series of key localities around the eastern Mouthoumet massif, in the Corbieres foreland and along the Corbieres thrust front to reconstruct a coherent deformation history involving salt tectonics. Keuper (Carnian - Rhetian) evaporitic deposits gave rise to diapirs and detachments that were particularly active during Early to Late Creta­ ceous extension and later during Late Cretaceous to Eocene compres­ sion. Growth unconforrnities and rapid thickness changes in the Aptian Quillan basin indicate that it developed as a salt controlled minibasin. Olistoliths, gypsum breccias and presence of bipyramidal quartz in Al­ bian strata preserved as footwall imbricates along the North Pyrenean thrust front (e.g. around Cucugnan) attest to the proximity of a large dia­ piric body. Below the Cenomanian un confor mity, rotated fault blocks of Liassic to Albian strata lie above a Keuper detachment. These extensio­ nal fault blocks have already been recognised at the Serre de Bouchard. They are also preserved north of Cucugnan, and in the Montagne de Tauch with little or no alpine inversion. In the Corbieres foreland area salt influenced extensional and compres­ sional deformation generated growth folds, with completely overturned li mb s (flaps), welds, growth unconformities and pinched salt-cored an­ ticlines. Several of these structures have generated considerable contro­ versy in the past (Pinede de Durban, Boutenac anticline, Ripaud syn­ cline). In the light on new advances in understanding salt related strata! and fault geometries we propose a new interpretation integrating halo­ kinesis of these foreland structures

Stabilization of large drainage basins over geological time scales : Cenozoic West Africa, hot spot swell growth, and the Niger River

Reconstructing the evolving geometry of large river catchments over geological time scales is crucial to constraining yields to sedimentary basins. In the case of Africa, it should further help deciphering the response of large cratonic sediment routing systems to Cenozoic growth of the basin-and-swell topography of the continent. Mapping of dated and regionally correlated lateritic paleolandscape remnants complemented by onshore sedimentological archives allows the reconstruction of two physiographic configurations of West Africa in the Paleogene. Those reconstructions show that the geometry of the drainage is stabilized by the late early Oligocene (29 Ma) and probably by the end of the Eocene (34 Ma), allowing to effectively link the inland morphoclimatic record to offshore sedimentation since that time, particularly in the case of the Niger catchment—delta system. Mid-Eocene paleogeography reveals the antiquity of the Senegambia catchment back to at least 45 Ma and suggests that a marginal upwarp forming a continental divide preexisted early Oligocene connection of the Niger and Volta catchments to the Equatorial Atlantic Ocean. Such a drainage rearrangement was primarily enhanced by the topographic growth of the Hoggar hot spot swell and caused a stratigraphic turnover along the Equatorial margin of West Africa

Rift inversion to full collision: intrinsic threshold and characteristics

Defining the history of shortening distribution in an orogeny, integrating both the pro- and retro-wedges, can help identify the transition from rift inversion to full collision. The Pyrenees are a Late Cretaceous to Miocene orogen that inverted a hyperextended rift system with exhumed mantle between Europe and Iberia. We performed a detailed study of the Eastern Pyrenees and its forelands to constrain shortening and timing for individual structures. These data were then used to reconstruct a shortening history across both wedges, revealing a change in the distribution of shortening through time. During early inversion (Late Cretaceous) shortening was distributed roughly equally between the European and Iberian rifted margins. A quiescent period (Paleocene) was apparently limited to the retro-wedge. During full collision (Eocene) around 80% of the overall shortening was accommodated in the pro-wedge, and the retro-wedge was reactivated slowly. A similar change in the shortening distribution is reproduced by numerical models, coinciding with the onset of continental subduction. The change in shortening distribution is thus the result of reaching a threshold that is intrinsic to inverted rift systems, implying other inverted rifts should behave similarly. Based on these results, we propose a generic evolutionary model for inverted rift systems. The transition from rift inversion to full collision is caused by the onset of continental subduction. This transition can be recognised by a change to a pro-wedge dominant shortening distribution, and may be accompanied by a temporary abandonment of the retro-wedge. This model cannot be applied to orogens with inherited asymmetry (e.g., precursor oceanic subduction). The High Atlas (Morocco) and Pyrenees can be regarded as examples of initial symmetric rift inversion and later asymmetric full collision phases, respectively.Peer Reviewe