Abstract

A field project has been carried out in the Monti della Rossa area, between the Vernino Valley and Mt. Murano (Marche Apennines). Geological mapping coupled with biostratigraphy and sedimentology have led to the recognition of a rather complex pelagic carbonate platform/basin system in the Jurassic. Three facies associations have been recognized: a) condensed pelagic; b) "normal" and resedimented pelagic; c) composite pelagic. These characterize, respectively, the pelagic carbonate platform, basin and marginal scarp palaeoenvironments. Facies association (a) is seen to form bodies that spread from the platform in the lower Tithonian. Ammonite biostratigraphy provides constraints for recostructing the timing of the vertical and lateral changes in the depositional system throughout different palaeostructural compartments. Extensional tectonics created three submarine fault scarps in the Lias and were responsible for the overall Jurassic palaeogeography of the area. The Colle Foglia-Colle Tordina-Mt. Sassone area was a pelagic carbonate platform hosting condensed sedimentation; Mt. Murano was a tilted block which remained non-depositional for some 40 Myr and features a quasi-conformable Calcari diasprigni/Calcare Massiccio contact; Vernino Valley and Vallorana-Faedo Valley-Brecciara Valley were basins which became filled with the "normal" and resedimented pelagic facies association, which is seen to onlap the palaeoscarps. The composite pelagic facies association is found along the northern and western palaeoscarps. The present geology of the study area is also described and the impact of Liassic structures on later (Neogene) tectonics is discussed.

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