ENVIRONMENTAL EVOLUTION DURING THE LATE JURASSIC AT LAVARONE (TRENTO PLATEAU, ITALY)

Four sections have been studied in the Monte Rust area (Lavarone, nort hern Italy) for the interpretation of depositional conditions. The bio stratigraphic 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 b asic lithofacies are identified in the upper unit of the Rosso Ammonit ico Veronese (nodular-marly, nodular-calcareous, and pseudonodular-cal careo us-massive), which developed according to relative sea-level con ditions. The depositional dynamics were closely related to increasing energy and winnowing during sea-level lows (nodular-calcareous ammonit ico rosso), and the opposite during sea-level highs (nodular-marly amm onitico rosso). The highest energy conditions are assumed for the pseu donodular-calcareous-massive ammonitico rosso, revealing a probable in teraction 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 environme nt, and thus a rather variable relationship between micro-and macrofea tures 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 en ergy conditions, For the Kimmeridgian, deposits formed during sea-leve l 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 diminis h the possibility for correlation in the epioceanic area studied. (C) 1997 Elsevier Science B.V.