RICERCHE GEOLOGICHE SUL GRAN SASSO D'ITALIA (ABRUZZO). 7) LA ZONATRA VALLE FREDDA E VALLE DELL'INFERNO (PROVV. DI L'AQUILA E TERAMO)

Abstract

In the centrai section of the Gran Sasso d'Italia group, two zones with distinct tectonic-sedimentary evolution can be recogniz­ed. The northern one {Valle dell'Inferno) shows, from the Lower Cretaceous upwa.rd, the same stratigraphic characteristics found in the outer Umbrian-Marchean basin. However, the carbonatic clastic component is much higher in the former than in the latter. The south-central zone (Monte Aquila and Albergo Campo Imperatore) show Jurassic sequences which may be complete in some areas but may also contain stratigraphic gaps in others, as in the "structural highs" of the Umbrian-Marchean basin, and be characterized by a pelagic-clastic Cretaceous sedimentation. During all the Paleogene, a very important stratigraphic gap developed in the south-central zone, similar to that observed in the adjacent Latium-Abruzzo carbonate platform. Thus, the south-central zone of the Gran Sasso appears to be a "transitional zone" with pelagic sediments on the one band, and with a structural evolution influenced by that of the adjacent car­bonate platform on the other band. The orogenesis developed through several stages. In this zone the first stage, which occurred during the Upper Miocene-Lower Pliocene, represents the main one. lt produced the prevailing struc­tural characteristics of the area as a result of a northward compres­sional thrust. Neitherthe Middle Pliocene and Upper Pliocenestages nor t'he latest one (Quaternary in age and showing tensional effects along the apenninic strike) appear to be as important as the first one.