The Grès d'Annot onlap on the outer basin margin has been extensively studied, but a number of important issues and critical outcrops remain controversial. A new geological map of the Annot syncline is here presented, supplemented with structural and sedimentological field observations. The mapped onlap traces in Annot reveal a curved, east-concave surface, with distinct westward shift of the successive onlap lines. The inferred onlap direction at Chalufy is to the SW, the only orientation compatible with the movement of the normal fault near Cabane des Abeurons. The similarity of the onlap relations between the areas of Annot and Chalufy, together with the structural features of the Annot syncline, support the concept of a common outer basin margin, rather than of a northern confinement of the Annot turbidites. The margin-onlap setting involved a specific style of syndepositional deformation. As a large, high-density turbidity current arrived on the basin-flank slope, it rapidly decelerated, thickened and dropped its coarse load, while being simultaneously deflected away from the slope. The associated normal stress and overpressure caused sub-horizontal injection and de-lamination of the soft substrate, with the tangential strain curling up the detached substrate slice into an overturned synclinal structure. The process provides an efficient way to incorporate fragments of mudstone and thin-bedded sandstone within the still moving highly-concentrated flow, eventually constituting the chaotic intervals within ‘tri-partite’ beds as the examples observed at the Braux section.
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Deep-Water Sedimentation in the Alpine Basin of SE France: New perspectives on the Grès d'Annot and related systems
The Grès d′Annot Formation of SE France constitutes a classic and outstanding example of a sand-rich turbidite system controlled by synsedimentary tectonics, and has often been used as an outcrop analogue for deep-water hydrocarbon reservoirs. Over the last 10 years, research efforts by different academic and industrial teams have led to important reappraisals of prevailing ideas on the Gres d′Annot, particularly on the nature and controlling factors of the depositional processes, the small-scale architecture and sequence organization of the deposits, the tectonic regime of the basin and its impact on palaeogeography, and the interaction between sediment gravity flows and basin-floor topography.
This volume offers a multidisciplinary overview and draws up the ′state-of-the-art′ of scientific knowledge on this influential turbidite system. Complementary aspects are covered, from structural geology, sedimentology and sequence stratigraphy, to modelling of sedimentary processes and architectures, geochemistry, reservoir characterization, seismic modelling and uses as analogues for deep-marine hydrocarbon fields.
This book will be of use to both academic researchers (geologists and geophysicists) and industry professionals dealing with the characterization and modelling of deep-water sediments.