Quelques problèmes de sedimentation géosynclinale dans les chaînes alpines de la Méditerranée moyenne

In the paleogeographic development of the alpine mountain belt in the central mediterranian a geosynclinal period may be differentiated from a late geosynclinal to postgeosynclinal period. Within the geosynclinal period one may recognize three stages: the stage of individualisation; the stage of geosynclinal development and the stage of orogeny. The stage of geosynclinal development includes a preflysch period and a flysch period. In the discussion of the preflysch period a number of sedimentational problems are dealt with: the distinction of swells of the Gavrovo typ with thick neritic sediments and those of the Briançonnais type with pelagic and condensed sedimentary sequences; the distribution of breccias on the flanks of troughs; the problem of the thickness of sediments on the swells and in the troughs. Two other problems treated are the nodular limestones of the ammonitico rosso and the radiolarites. The flysch period is characterised by relative temporal independence from the proceeding period. The terrigenous facies of the flysch period is viewed in space and time on the one hand as an expression of the trapping of terrigenous sediments and on the other as products of the orogenic polarity of the geosyncline system and of the orogeny moving from the interior to the exterior. In the flysch basins one can see all transitions between the conglomeratic flysch at the foot of the rising cordillera which furnished the terrigenous material, the arythmic pelites which were deposited at the external end of the flysch basin, through transitional sandy flysch over sandy pelites to pelites. From this viewpoint the scaglia appears as a cryptoflysch. From the temporal viewpoint the migration of flysch trough is emphasised, and an early internal flysch facies — mainly eugeosynclinal — and a later external flysch facies — mainly miogeosynclinal — are distinguished. The intensity of movements changes, decreasing gradually with the progressing orogeny. In overall view the sediments of the preflysch and flysch period may alternate, and are then succeeded by the sediments of the late geosynclinal and postgeosynclinal period. The flysch-molasse problem is viewed in this sense, and the development of the molasse is devided into a lategeosynclinal and a postgeosynclinal phase.