Environmental evolution during the Late Jurassic at Lavarone (Trento Plateau, Italy)

Abstract

Abstract Four sections have been studied in the Monte Rust area (Lavarone, northern Italy) for the interpretation of depositional conditions. The biostratigraphic subdivision is based on more than 1400 stratigraphically controlled ammonite specimens, which enabled the recognition of five biozones in the Kimmeridgian and three in the Lower Tithonian. Three basic lithofacies are identified in the upper unit of the Rosso Ammonitico Veronese (nodular-marly, nodular-calcareous, and pseudonodular-calcareous-massive), which developed according to relative sea-level conditions. The depositional dynamics were closely related to increasing energy and winnowing during sea-level lows (nodular-calcareous ammonitico rosso), and the opposite during sea-level highs (nodular-marly ammonitico rosso). The highest energy conditions are assumed for the pseudonodular-calcareous-massive ammonitico rosso, revealing a probable interaction between tectonics and eustasy, and an increased mean rate of carbonate sedimentation. The cluster analysis of selected components of microfacies shows only minor fluctuations in a low-energy environment, and thus a rather variable relationship between micro- and macrofeatures in the ammonitico rosso facies studied. The correlation analysis between relative abundances of selected variables (components in the cluster analysis) has proven useful in interpreting fluctuations in energy conditions. For the Kimmeridgian, deposits formed during sea-level highs (Uhlandi and Beckeri Chrons) are especially well correlated in the area, as well as elsewhere in the Western Tethys. The progressive, long-term sea-level fall during the Early Tithonian does not diminish the possibility for correlation in the epioceanic area studied.