SEDIMENTOLOGIA E STRATIGRAFIA DELLE SUCCESSIONI RETICHE AL CONFINE FRA LOMBARDIA E TRENTINO

Abstract

This paper deals with Rhaetic facies at the Lombardy-Trentino border, in the Giudicarie Region. This area is characterized by important facies changes crossing strike slip faults. Two coeval sections, showing remarkable facies differences, are examined in detail, in order to describe the transition between the Rhaetic Lombardy Basin and the peritidal Trento Platform. The western section shows clear lombardian features and includes two marly formations: the Argillite di Riva di Solto and the Calcare di Zu. They are characterized by asymmetric marl-limestone cycles, developed on a metric scale, and show a shallowing upward evolution, from poorly oxygenated fairly deep environments to tidal flats. The upper portion of this section is referred as a new unit, the Tremalzo limestone, that is characterized commonly by a clear peritidal bathymetric cyclicity. The wholly carbonate eastern section is considered entirely Tremalzo limestone. It shows a similar evolution, but it was deposited in shallower environments on the western margin of the Trento Platform. Both sections are mud- dominated, but storm waves and tidal currents at times produced lenticular grainy beds. A detailed sedimentological analysis shows that these facies were deposited in a ramp system, the dynamics of which were mainly controlled by eustatic fluctuations and climatic cycles.