Age of the Fontainebleau sandstones: a tectonic point of view

Tectonophysics, 2011

Using field data, balanced cross-sections, gravity and reprocessed seismic reflection data, a detailed structural study has been realized on the Salon-Cavaillon fault (SCF) area, in Provence region (SE France). This fault separates two main ridges (the Alpilles to the west and the Luberon to the east). Field data and balanced cross-sections allow us to characterize the present-day structures and the post-Oligocene deformation that significantly differ on either sides of the SCF. Our structural study shows a post-Oligocene southward displacement of the structures on the two sides of the SCF. The Luberon ridge is a fault propagation-fold developed on a S-verging ramp. The anticline is bent as a drag fold in the vicinity of the dextral strike-slip SCF. The Alpilles ridge is a less developed fault propagation fold. Its eastern termination was affected by a counterclockwise rigid block rotation around a vertical axis. The differences between the two ridges in terms of structural architecture are explained by the deep geometry of their ramp, inherited from the Late Cretaceous to Middle Eocene Pyrenean tectonic phase. The décollement level is shallow to the western side of the SCF (2-3 km), probably in Lower Cretaceous or Upper Jurassic marls, than in the eastern side, the fault is rooted in Triassic layers at a depth > 5 km. The deep rooting favoured a large-scale fault propagation type of folding, whereas shallow-seated rooting favoured a small-scale fault propagation type of folding and block rotations. To image the sub-surface structures to the west of the SCF, we also included gravity data and reprocessed seismic reflection. It allows us to refine the regional tectonic framework and to detect several hidden E-trending S-verging folds. The main shortening episode in Provence occurred during the Pyrenean phase, with 65 % of the total shortening to the east of the SCF and 95 % to the west. From the Miocene to present, Alpine shortening decreases strongly to the West of the SCF (less than 400 m against 2 km to the East), providing evidence for the major role of the SCF in the transfer of the south-directed Alpine deformation.

Journal of Geophysical Research, 2007

Three-dimensional modelling tools are used with structural and palaeomagnetic analysis to constrain the tectonic history of part of the Dauphiné zone (external Western Alps). Four compressive events are identified, three of them being older than the latest Oligocene. Deformation D1 consists of W-SW directed folds in the Mesozoic cover of the study area. This event, better recorded in the central and southern Pelvoux massif, could be of Eocene age or older. Deformation D2 induced N-NW-oriented basement thrusting and affected the whole southern Dauphiné basement massifs south of the study area. The main compressional event in the study area (D3) was WNW oriented and occurred before 24 Ma under a thick tectonic load probably of Penninic nappes. The D2-D3 shift corresponds to a rapid transition from northward propagation of the Alpine collision directly driven by Africa-Europe convergence, to the onset of westward escape into the Western Alpine arc. This Oligocene change in the collisional regime is recorded in the whole Alpine realm, and led to the activation of the Insubric line. The last event (D4) is late Miocene in age and coeval with the final uplift of the Grandes Rousses and Belledonne external massifs. It produced strike-slip faulting and local rotations that significantly deformed earlier Alpine folds and thrusts, Tethyan fault blocks and Hercynian structures. 3D modelling of an initially horizontal surface, the interface between basement and Mesozoic cover, highlights large-scale basement involved asymmetric folding that is also detected using structural analysis. Both, Jurassic block faulting and basement fold-and-thrust shortening were strongly dependent on the orientation of Tethyan extension and Alpine shortening relative to the late Hercynian fabric. The latter's reactivation in response to oblique Jurassic extension produced an en-échelon syn-rift fault pattern, best developed in the western, strongly foliated basement units. Its Alpine reactivation occurred with maximum efficiency during the early stages of lateral escape, with tectonic transport in the overlying units being sub-perpendicular to it.

BSGF - Earth Sciences Bulletin, 2024

In this paper, and in previous works, quartzites within the Sable de Fontainebleau are clearly shown to occur only near outcrops in Plio-Pleistocene plateau landscapes and are related to groundwater flows. These arrangements, together with dating of encased calcites, led us to consider that silicification occurred during Plio-Pleistocene glacial stages. The precipitation of silica was most likely triggered by cooling of groundwaters as they approached cold zones in the regolith close to points of discharge. We describe the arrangement and morphologies of quartzites in Tertiary sand formations in the Paris Basin to demonstrate how cold climates could have influenced hydrologic regimes and promoted silicification. The coeval precipitation of calcite and silica in gypseous formations at the edges of plateaux-bordering valleys, along with the dissolution of gypsum, also points to interactions between silica-laden groundwater and carbonate host rocks during cold periods. In parallel, the distribution and micromorphology of silicifications in associated Tertiary limestone formations suggests that they formed during cold climates in the Quaternary. These are key pointers to the role of groundwater in regolith environments in controlling silicification processes. We detail a link to palaeosurfaces of the distinctive meulières facies in the Paris Basin. Geotropic structures and micromorphological organisations are the basis of new ideas about their origin in a combination of vadose and phreatic environments and proximity to impervious cold horizons. The active zone in a permafrost landscape is a good hydrological example. All silicifications in Tertiary formations in the Paris Basin can be linked to the hydrology of Quaternary periglacial environments in a single model. This could apply more widely to similar silicifications elsewhere and be tested using new analytical techniques that date silicifications and unravel the isotopic relationships between silicification, groundwater composition and the prevailing climate.

Geodinamica Acta, 2003

Combining fieldwork and surface data, we have reconstructed the Cenozoic structural and tectonic evolution of the Northern Bresse. Analysis of drainage network geometry allowed to detect three major fault zones trending NE-SW, E-W and NW-SE, and smooth folds with NNE trending axes, all corroborated with shallow well data in the graben and fieldwork on edges. Cenozoic paleostress succession was determined through fault slip and calcite twin inversions, taking into account data of relative chronology. A N-S major compression, attributed to the Pyrenean orogenesis, has activated strike-slip faults trending NNE along the western edge and NE-SW in the graben. After a transitional minor E-W trending extension, the Oligocene WNW extension has structured the graben by a collapse along NNE to NE-SW normal faults. A local NNW extension closes this phase. The Alpine collision has led to an ENE compression at Early Miocene. The following WNW trending major compression has generated shallow deformation in Bresse, but no deformation along the western edge. The calculation of potential reactivation of pre-existing faults enables to propose a structural sketch map for this event, with a NE-SW trending transfer fault zone, inactivity of the NNE edge faults, and possibly large wavelength folding, which could explain the deposit agency and repartition of Miocene to Quaternary deformation.

CATENA, 1996

The southern border of the Paris Basin has undergone successive weathering events during the Tertiary. Fluviatile and lacustrine deposits are scattered, being mainly confined to several North-South trending grabens. These are generally devoid of fossils which would allow them to 0341-8 163/96/S IS.00 G 1996 Ekevier Science B.V. All rights reserved .s.w/ 0341.R162(95)00044-5 M. Thiry. R. Simon-Coinpn / Cutenn 26 (1996) l-26 gypsum deposits in the center of the basin. No remnants from Oligocene-Miocene times are preserved in the region studied. During Late Miocene. the disruption of these landscapes took place because a very low sea lcvci led to the renewal of erosion. As a result residual landforms with siliceous crusts now cap IIIC higher elevations.

Swiss Journal of Geosciences, 2008

Three-dimensional modelling tools are used with structural and palaeomagnetic analysis to constrain the tectonic history of part of the Dauphiné zone (external Western Alps). Four compressive events are identified, three of them being older than the latest Oligocene. Deformation D1 consists of W-SW directed folds in the Mesozoic cover of the study area. This event, better recorded in the central and southern Pelvoux massif, could be of Eocene age or older. Deformation D2 induced N-NW-oriented basement thrusting and affected the whole southern Dauphiné basement massifs south of the study area. The main compressional event in the study area (D3) was WNW oriented and occurred before 24 Ma under a thick tectonic load probably of Penninic nappes. The D2-D3 shift corresponds to a rapid transition from northward propagation of the Alpine collision directly driven by Africa-Europe convergence, to the onset of westward escape into the Western Alpine arc. This Oligocene change in the collisional regime is recorded in the whole Alpine realm, and led to the activation of the Insubric line. The last event (D4) is late Miocene in age and coeval with the final uplift of the Grandes Rousses and Belledonne external massifs. It produced strike-slip faulting and local rotations that significantly deformed earlier Alpine folds and thrusts, Tethyan fault blocks and Hercynian structures. 3D modelling of an initially horizontal surface, the interface between basement and Mesozoic cover, highlights large-scale basement involved asymmetric folding that is also detected using structural analysis. Both, Jurassic block faulting and basement fold-and-thrust shortening were strongly dependent on the orientation of Tethyan extension and Alpine shortening relative to the late Hercynian fabric. The latter's reactivation in response to oblique Jurassic extension produced an en-échelon syn-rift fault pattern, best developed in the western, strongly foliated basement units. Its Alpine reactivation occurred with maximum efficiency during the early stages of lateral escape, with tectonic transport in the overlying units being sub-perpendicular to it. RESUME L'histoire des deformations dans un secteur du Dauphiné (zone externe des Alpes occidentales) est précisée en utilisant à la fois l'analyse structurale, le paléomagnétisme et la modélisation 3D. On y reconnait quatre évènements compressifs, dont trois antérieurs à l'Oligocène terminal. La deformation D1 se marque par des plis à vergence W à SW dans la couverture mésozoïque. Ce premier évènement, mieux connu dans la partie sud des massifs cristallins dauphinois, est antérieur à l'Eocène supérieur. La déformation D2 a produit des chevauchements de socle orientés vers le N et le NW dans les massifs dauphinois situés au Sud du secteur étudié. Mais ce dernier a été principalement marqué par le raccourcissement D3 orienté ESE-WNW, qui s'est produit avant 24 Ma sous une importante couverture tectonique de nappes penniques. Ce changement entre D2 et D3 marque une évolution importante de la collision alpine, d'abord dominée par la subduction continentale en conséquence directe de la convergence N-S entre Afrique et Europe, puis par l'échappement latéral vers l'ouest qui a généré l'arc des Alpes occidentales. Cette réorganisation oligocène a aussi provoqué l'activation du décrochement insubrien. La dernière déformation D4, d'âge Miocène supérieur, a accentué les bombements de socle des massifs des Grandes Rousses et de Belledonne, entre lesquels des mouvements décrochants et des rotations ont distordu à la fois les structures alpines antérieures, les failles et blocs téthysiens et la foliation hercynienne. L'interface socle hercynien/couverture mésozoïque, qui était initialement plan et horizontal, a été construit en 3D. Le réseau des blocs téthysiens y apparaît déformé par des failles et des plis de socle. Les observations de terrain montrent que l'orientation du grain hercynien a largement influencé la nature et la localisation des structures distensives et compressives. Les dépocentres jurassiques se seraient disposés en échelon à cause de l'obliquité de l'extension téthysienne par rapport à la foliation du socle. Durant la collision, cette dernière a été le plus intensément réactivée lorsque la contraction lui était subperpendiculaire, c'est à dire à partir de l'Oligocène quand le régime en échappement latéral vers l'Ouest a été établi.

Journal of Structural Geology, 1994

The palaeo-seismicity and history of strain accumulation within the Rencurel Thrust Zone, French Sub-Alpine Chains, has been investigated by examining fracture-filling cements. Two generations of fracture-13 18 filling cement with distinct petrographic characteristics, cation geochemistries and C and O stable isotopic compositions have been distinguished within the Rencurel Thrust Zone. The hanging-wall rocks contain fracture-filling calcite cements, whereas ferroan calcite fills fractures within the Central Gouge Zone. Calcitecemented faults include frontal, oblique and lateral ramps, as well as faults dipping in the movement direction, whereas, ferroan calcite-cemented faults include only frontal ramps and faults dipping in the movement direction. Fragments of calcite cement occur as clasts within the Central Gouge Zone, indicating that the calcite cements formed prior to precipitation of ferroan calcite in the Central Gouge Zone. Lineation data indicate that precipitation of both generations of cement occurred during a single phase of thrusting. The lack of ferroan calcite cements in the hanging-wall rocks suggests that the hanging-wall of the Rencurel Thrust was not fractured during displacements within the Central Gouge Zone. This contrasts with seismogenic faults where rocks surrounding major faults are fractured during fault slip, and it is inferred that the exposed portion of the Rencurel Thrust may have experienced aseismic fault displacements. The aseismic fault slip may have been the consequence of the shallow burial depths (<3 km) experienced by the exposed portion of the Rencurel Thrust during faulting.

Quaternary International, 2012

A B S T R A C T Much of France remained unglaciated during the Late Quaternary and was subjected to repeated phases of periglacial activity. Numerous periglacial features have been reported but disentangling the environmental and climatic conditions they formed under, the timing and extent of permafrost and the role of seasonal frost has remained elusive. The primary sandy infillings of relict sand-wedges and composite-wedge pseudomorphs record periglacial activity. As they contain well-bleached quartz-rich aeolian material they are suitable for optically stimulated luminescence dating (OSL). This study aims to reconstruct when wedge activity took place in two regions of France; Northern Aquitaine and in the Loire valley. Results from single-grain OSL measurements identify multiple phases of activity within sand wedges which suggest that wedge activity in France occurred at least 11 times over the last 100 ka. The most widespread events of thermal contraction cracking occurred between ca. 30 and 24 ka (Last Permafrost Maximum) which are concomitant with periods of high sand availability (MIS 2). Although most phases of sand-wedge growth correlate well with known Pleistocene cold periods, the identification of wedge activity during late MIS 5 and the Younger Dryas strongly suggests that these features do not only indicate permafrost but also deep seasonal ground freezing in the context of low winter insolation. These data also suggest that the overall young ages yielded by North-European sand-wedges likely result from poor record of periglacial periods concomitant with low sand availability and/or age averaging inherent with standard luminescence methods.