RICERCHE GEOLOGICHE SUL GRAN SASSO D'ITALIA (ABRUZZO). IV. EVOLUZIONE PALEOGEOGRAFICA, DURANTE IL GIURASSICO SUPERIORE ED IL CRETACEO INFERIORE, DEL MARGINE DELLA PIATTAFORMA CARBONATICA NELL'AREA TRA BARISCIANO E CASTEL DEL MONTE

Abstract

The paleogeographic evolution during the Upper Jurassic­Lower Cretaceous of the carbonate platform shelf-edge is described in the Barisciano-Castel del Monte area (Abruzzo, Italy). Three se­quences are examined; they are characterized by alternances of mudstones (similar to the internal carbonate platform mudstones) and grainstones, laminated at times. These are different from typical shelf-edge sequences autcropping in the same area in which the organogenic sedimentation is dominant. Rather these are sedi­. mented in a shelf-lagoon environment, just behind the shelf-edge ("retromargine" facies). The comparison with two shelf-edge sequences studied pre­viously reveals that, during Malm-Neocomian time, the shelf-edge facies of the area has been gradually replaced in places by a shelf­lagoon facies; the probable cause of this paleogeographic evolution is a progressive reduction of the high energy area, caused by the formation of more gentle slopes, during relative tectonic stability.