The Middle-Upper Jurassic succession of the Marguareis-Mongioie area (Ligurian Briançonnais Domain), developed in a protected shelf environment evolving into a pelagic plateau, bears clear evidence of synsedimentary tectonics such as: growth fault-related structures; neptunian dykes; marked lateral variations in stratigraphic thicknesses testifying to the juxtaposition of sectors characterized by different sedimentation and subsidence rates; discordant, anomalous stratigraphic contacts corresponding to paleoescarpments; nodular beds showing evidence of fluidification interpreted as seismites; and the occurrence of sand-sized quartz grains pointing to denudation of Permo-Triassic quartz-rich rocks. Such evidence documents an important Middle-Late Jurassic post-breakup tectonic activity, which was more effective in controlling the basin topography than the Early Jurassic syn-rift tectonic phase. Two main tectonosedimentary stages, one occurring during the Bathonian, the other falling within the Callovian-Kimmeridgian interval, were reconstructed. The first stage can be referred to a faultrelated activity occurring shortly after the initial stages of oceanic spreading of the Ligurian Tethys; the second can be genetically related to the far effects of the first rifting stage of the Bay of Biscay and the Valais basin.

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succession. Submarine ridges were generated and favoured rock fall phenomena that involved both small, mm-to dm-sized, clasts and huge slabs detached from the main rock masses. These morphostructural highs were flanked by oversteepened slopes affected by failures that gave rise to debris flows, involving hemipelagic muds and turbidite sands and lithified fragments of older formations, which resulted in strongly polygenic paraconglomerates. The studied mélange is thus fully due to sedimentary processes that were, however, completely controlled by early Alpine tectonics.

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Dolomite crystals, occurring in Middle Jurassic dolostones and dolomitic limestones of theLigurian Briançonnais Domain (French-Italian Ligurian Alps), show irregular, complex zoning evidenced by cathodoluminescence (CL) and backscattered electron imaging. Comparable zoning patterns from other study areas have been attributed alternatively to recrystallization or dissolutionprecipitation processes. However, none of these mechanisms can account for the range of observations from the Ligurian Briançonnais Domain, which include: 1) the presence of multiple core types, each with different CL characteristics; 2) marked compositional differences between cores and surrounding rims (ferroan vs. nonferroan, Mg/Ca ratio); 3) a marked shape difference between cores, with irregular outlines, and rims which progressively approach a well-developed rhombohedral habit. These features are most reasonably interpreted as dolomitic rims that formed as syntaxial overgrowths around detrital dolomite nuclei, which in turn originated from erosion of underlying Triassic rocks and triggered selective replacement of fine-grained calcareous sediment.Failure to recognize the exact nature of this type of dolomite crystal may lead to overestimating the degree of dolomitization and to overlooking possible detrital inputs in a basin otherwise supplied with pure allochemical sediments, with consequent loss of information on the tectonosedimentary evolution.

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