THE DISAPPEARANCE OF THE AMMONITICO ROSSO

Results of the research for the reconstruction of the Tethys paleoenvironments show that the Ammonitico Rosso disappeared in the late Berriasian. No typical analogues have been recorded so far in younger levels. The Ammonitico Rosso basically developed during the rifting of the continental margins pointing up the phases of the Tethys opening, It is found on tilted-block tops and slopes as well as in the related basins. The Ammonitico Rosso developed especially in areas characterized by a complex paleogeography such as Apulia or southern Iberia. Few occurrences are reported from the central Atlantic margins, although the information is scarce and only available by Deep Sea Drilling cores. The maps 1: 20,000,000 of middle Toarcian, early Kimmeridgian and late Tithonian paleoenvironments of the Tethys illustrate the gradual disappearance of this characteristic facies. This disappearance in the Berriasian is correlated with: (1) the increase of biogenic (e.g., the bloom of nannoplankton) and clastic sediment supply (development of flysch facies); (2) the establishment of an oceanic circulation, which was not suitable for the AR formation, from the Himalayan branch of the Tethys to the Caribbean; (3) the end of the rifting of the western Tethys continental margins, around Late Jurassic-Early Cretaceous times, which began to sink because of thermal subsidence; (4) the evolution of oceanic chemistry. However, these factors were controlled by the global paleogeographic evolution. The Tethys ocean occupied a triangle-shaped area bounded by huge continental masses situated in roughly tropical latitudes. The gradual fragmentation of Pangaea and Cretaceous-Tertiary continental collisions definitely modified the global paleogeography never again producing this kind of ocean.