The Gela Nappe of south central Sicily provides an example of a curved segment of an orogenic front that can be examined both onshore and offshore for deformational style and amount of shortening. Synorogenic sediments allow the deformation to be dated. Two distinct structural styles are observed in the Gela Nappe: The central salient part of the nappe (Caltanissetta basin) consists of a single thrust sheet containing a train of continuously tightening folds and the reentrant margins of the nappe (Sciacca and Monte Judica) consist of a stack of several thrust sheets. These different structural styles correspond to the pretectonic Mesozoic stratigraphy of the foreland plate. Carbonate platforms exist on the Adventure bank and Hyblean Plateau ahead of Sciacca and Monte Judica, respectively, while the Caltanissetta basin region appears to have accumulated basinal clay facies. Where the resistant carbonate stratigraphy provides a buttress to the propagation of the thrust front, deformation is taken up by imbrication on‐steep ramps through the carbonates generating a relatively thick orogenic wedge. In the basinal setting, where no strong rheology exists, the low angle of friction on the clay detachment levels requires the growing thrust wedge to be much thinner with a very low foreland dip. Hence the thrust front propagates much farther forward into the basin than it does in the adjacent platformal areas, producing a nonlinear thrust front. In the basinal region, accretion of foreland material to the nappe by imbrication was only prominent during the Messinian when subaerial exposure prevented low‐friction transport of the nappe across the highest levels of the stratigraphy. A steady thickening of the nappe by internal folding suggests an increase in friction along the basal detachment, possibly due to progressive compaction of the clays.

The Tertiary foreland basin of the southern Subalpine chains preserves a stratigraphic record of late Alpine deformation, both ahead of the thrust front in the Valensole basin, and in a series of thrust-sheet-top basin remnants. Stratigraphy and growth structures in these basin remnants have been used to identify the location and timing of deformation and hence to constrain the sequential restoration of a cross section through the region.The thrust belt developed as a single large thrust sheet riding on a weak Triassic evaporite layer. Minor breaching thrusts occur, in particular at Mesozoic normal faults. Kinematic studies of the Digne thrust sheet show a dominantly SW direction of tectonic transport. Where reactivated structures lie at a slightly oblique angle to the transport direction there has been a partitioning of deformation into SW-directed thrusting and a component of dextral strike-slip taken up on minor faults. The total shortening across the fold and thrust belt is 21.5 km, a much lower value than previously estimated but more in line with regional tectonics.The foreland basin stratigraphy demonstrates that deformation within the Digne sheet occurred in three stages. Firstly, during the late Eocene, Alpine collision in the hinterland caused flexure of the foreland plate to generate a simple broad marine foredeep. Slight detachment above the Triassic evaporites allowed gentle buckling of the floor of the foredeep. Secondly, in the Early to Mid-Oligocene overthrust shear associated with the SW emplacement of the internally derived Embrunais-Ubaye nappes into the foredeep caused substantial deformation in the underlying Digne sheet.

The arcuate form of the external western Alps was generated during Tertiary NW-directed collision between the Apulian indentor and the southward-subducting European passive margin. The evolution of peripheral syn-collisional depocentres around this arcuate orogen (in France and Switzerland) is reconstructed using a compilation of stratigraphic and tectonic data. This reveals fundamental changes in the flexural behaviour of the European lithosphere during collision. During early collision (Eocene), an increasingly arcuate, peripheral flexural basin migrated rapidly NW across the European plate. During peak collision (early Oligocene), frontal flexure, recorded in the North Alpine Foreland Basin (NAFB), steepened markedly, while lateral flexure of the European plate, affecting SE France, effectively ceased. Here, Oligocene sedimentation was confined to small thrust-sheet-top basins. Two rift systems initiating in the late Eocene, the West European rift system and the West Mediterranean oceanic basin (that created the Gulf of Lion passive margin), are superimposed in space and time on the outer margins of the alpine flexural depocentres. During waning collision (Mio-Pliocene) the NAFB became overfilled, then uplifted and abandoned while, in SE France, a local depocentre (Digne-Valensole) developed between uplifting blocks and continued to accumulate sediments until the late Pliocene.

Abstract:The integration of structural and stratigraphic data is fundamental for determining rates of deformation in the uppermost continental crust. The high temporal resolution provided by Neogene marine sediments is used here to examine deformation rates in part of a thrust belt chosen from the Maghrebian orogen of Sicily. Conventional biozonal stratigraphy, calibrated against the geomagnetic polarity time scale, shows that individual thrust-fold structures grew steadily over many millions of years. Structures across the thrust belt were active at the same time and accommodated bulk shortening rates of c. 0.5 mm a 1 . In contrast the basal detachment operated about ten times faster. These results are in broad agreement with some theoretical models for orogenic wedge kinematics. Shore-line carbonate successions, calibrated with precession cycles of sea-level change, provide a very high-resolution, temporal scale with which to chart tilt rates on fold limbs (1 /27.6 ka=0.036 ka 1 ). These show that fold amplification was continuous although the rates may have varied with time. Incremental tilting of limbs during fold amplification is not predicted by popular models of fault-bend and 'fault-propagation' folding. Geometric modelling suggests that folding occurred by limb rotation, with minor hinge migration during buckling above buried thrusts. Thus stratigraphic data may be used to examine the kinematic evolution of thrust-fold systems along regional cross-sections, and of local structures. However, the types of structural models that can be tested using estimates of deformation rates depend upon the chrono-stratigraphic resolution available for the syn-tectonic sediments.

The Lower Cambrian McNaughton Formation of the Gog Group occupies a stratigraphic position transitional between the rift-related rocks of the underlying Upper Proterozoic Miette Group, and the overlying Paleozoic passive margin succession. A major regional unconformity, overlain by a distinctive orthoquartzite marker, has been traced within the McNaughton Formation. This unconformity has been shown to truncate normal faults active during the deposition of the lower McNaughton Formation. The lower McNaughton Formation consists of mature, coarse-grained fluvial sediments accumulated in hanging-wall half-grabens of active normal faults. These faults represent the final stage of rifting on the continental margin. The unconformity on the footwall blocks of these faults can be traced into the hanging wall, and is overlain by the shoreface sediments of the transgressive upper McNaughton Formation. Formal subdivision of the McNaughton Formation into four lithostratigraphic members is proposed, in order to describe this geometry.

The Eocene to Oligocene deposits of the Alpine Foreland Basin of Southeast France include a series of partially preserved, originally interconnected turbidite-filled subbasins. Within these remnants, well-constrained interpretations of sediment architectures have been developed by many geologists of the last five decades which are used to resolve both intrabasinal and interbasinal filling histories (e.g., the Annot, Grand Coyer, Col de la Cayolle, and Trois É vêchés subbasins). However, little is known about the depositional system in more distal areas. The Eastern Grès du Champsaur (Champsaur Sandstones), which has not been subject to detailed evaluation, is thought to represent the down-dip continuation of the Grès d'Annot Turbidite System. Presented here is an outcrop case study from the Eastern Champsaur Basin that describes how intrabasinal bathymetry affected gravity-current behavior, in turn driving quantifiable variations in sediment distribution patterns.The initial paleobathymetric template of the Eastern Champsaur Basin prior to turbidite deposition is reconstructed here through the generation of isopach maps constructed from field studies of the basin fill. The extent to which successive onlapping turbidity-current deposits were controlled by this bathymetry is determined through the analysis of paleocurrent, facies proportion, and isopach data from measured sections. Quantifiable variations in both facies (particularly the occurrence of clast-rich intervals) and sand/shale ratio are observed in association with an intrabasinal high, which is interpreted to have contained flows within this depositional system, allowing only a relatively finer fraction of the flow to move down dip in the distal parts of the basin. This study has direct application in aiding the understanding of sand emplacement processes at the fringes of turbidite basins, in defining the genesis of stratigraphic trap geometries in confined deep-water settings, and in better understanding connectivity issues within deep-water reservoirs.

In the external Western Alps, two regional structural arcs were generated during Tertiary northwest-directed collision between the Apulian indenter and the European passive margin. These arcs, distinguished by their geographic position and their age, are examined by using a new compilation of structural data and comparing these to the results of sandbox-analogue experiments. The principal Western Alpine arc comprises two orthogonal, synchronous thrust systems. In the late Eocene–early Miocene, major shortening (105 km) was toward the northwest to west-northwest, and minor shortening (11 km) was toward the southwest. Shortening in each branch decreased toward the core of the arc. During the late Miocene and Pliocene, the Jura arc accommodated 35 km of northwest- directed shortening, while 10.5 km of southwest- to south-southwest–directed shortening was accommodated on the Digne thrust system. Sandbox experiments were used to investigate the role of the motion vector of a rigid rectangular indenter (orthogonal, diagonal, curved, or rotational paths) and the mechanical stratigraphy of the foreland in the evolution of upper-crustal arcuate systems (e.g., presence of a basal easy-slip [silicone] horizon). Comparison of experimental results with the external Alpine arc suggests that the indenter followed a slightly diagonal path with respect to the European margin from the Eocene to the early Miocene and curved counterclockwise by 10°–15° in the middle Miocene. Mechanical stratigraphy experiments support the hypothesis that thick Triassic evaporites played a primary role in the evolution of the Jura arc. The influence of mechanical stratigraphy was most prominent during weak deformation at the external boundaries of the Alpine orogen (Jura fold-and-thrust belt, Digne thrust).

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