Ladinian/Carnian ammonoids and conodonts from the classic Schilpario-PizzoCamino area (Lombardy): Revaluation of the biostratigraphic support to chronostratigraphy and paleogeography

The aim of this paper is to revise the ammonoid and conodont biostratigraph y of the Middle Triassic basinal formations in the classic area between the Scalve and Camonica Valleys (Southern Alps). This area played a key role in defining Middle Triassic stratigraphy. In th e nineteenth century the study of several ammonoids collected in the Wengen Formation served as a basis for the definition of the Longobardian substag e of the Ladinian. Moreover, during the 1960's the modern Triassic lithostr atigraphy of Lombardy was founded on sections from this area. The present study represents the first bed-by-bed sampling of this area and is focused mainly on the Wengen Formation and Pratotondo Limestone. In par ticular, conodonts were found in both units for the first time. The age of some Middle Triassic formations is revised: - the top of the Wengen Formation belongs definitively to the Lower Carnian i n a sizeable portion of the study area. The overlying carbonate platform, p reviously attributed to the Upper Ladinian Esino Limestone, is instead Carn ian and is coeval to the Breno Formation in the Southern Camonica Valley. - the Pratotondo Limestone is dared Late Ladinian/Early Carnian, while the overlying Lotio Shale is Carnian. These new data contradict the equivalence "Wengener Schichten" = Archelaus Zone = Longobardian so common in the literature. We demonstrate that the Re goledanus Zone represents a great part of the Wengen Formation. Moreover, a t the top of the Wengen Formation the ammonoid and conodont fauna represent s the Early Carnian Daxatina or Aon Zone. The biochronostratigraphic revision of the basinal formations requires modi fication of both the chronostratigraphic schemes and the paleogeographic hi story of the lombardian Southern Alps during Ladinian-Carnian time.