Flysch facies and turbidite sedimentology

Abstract

The main facies of flysch in the Northern Apennines are listed, the importance of calcareous turbidites being noted. A summary is presented of Italian studies on selected sedimentologic features of the Apennines turbidites: 1. (1) Data on the occurrence of internal sedimentary structures in the turbidite rhythms, in function of thickness and grain size; the same in the flysch bands of thin or thick turbidites. 2. (2) Statistics on the occurrence and size of sole markings. 3. (3) Data on the relations between grain size and rhythm thickness. 4. (4) Types of graded bedding. 5. (5) Results of fabric studies. 6. (6) Data on the petrography of the turbidite sandstones. The sandstones are either feldspathic sandstones (up to arkoses and feldspathic litharenites) with a greywacke-like texture and secondary calcite, or very calcareous sandstones, either lithic or quartzose and fossiliferous. The micaceous matrix of the first group appears to be derived mainly from the diagenesis of clay and the fragmentation of metamorphic mica and micaceous rock fragments. The interstitial calcite of the second group is micrite and recrystallized sparry calcite; calcite as a primary cement is not common. Rock fragments are important in the classification of the sandstones. The main types are phyllite, quartzite, serpentinite, micritic limestones, dolostone and rhyolite to andesite lavas. The fact that various sandstones of the same age are different in composition and yet sandstones of different age can be grouped together, indicate the importance of separate sources repeatedly active through time. The Corsica-Sardinia Hercynian Massif was an important source, especially in the Upper Cretaceous, but in the Tertiary, internal sources in the Apennines-Western Alps geosynclinal belt became predominant. In general tectonics played an important role as a source factor in the genesis of the Apennines sandstones, but reworking appears to have been limited.