Abstract

The Madonna del Sirino succession belongs to the Meso-Caenozoic Lagonegro basin (Southern Apennines). The aim of this study is to obtain more information about the evolution of this basin during the Late Triassic-Early Jurassic interval. The section of Madonna del Sirino begins with cherty limestones (upper part of the Calcari con Selce fm), passing upwards to radiolarites and shales (Scisti Silicei fm) through a "transitional interval". The Scisti Silicei fm is divided in four members: a) "Buccaglione" with red shales, radiolarites and two anoxic levels; b) "Nevera" with black shales and black cherty layers; c) "Serra" with red radiolarites and red shales; d) "Acqua Sulfurea" with green radiolarites and green chert. New biostratigraphic data provided elements for referring some events to specific ages. A conodont assemblage allows us to assert that the change from calcareous to siliceous deposition did not begin before the Sevatian. Various samples in the Buccaglione member provided radiolarian associations typical of the Rhaetian, never recorded in these sections by previous studies. Pyritized radiolarian assemblages in the calcarenites of the Nevera member display features typical of the Triassic and Jurassic forms. In the Serra member Early Jurassic radiolarians were found in the upper part. These observations allows us to confine the Triassic/Jurassic boundary in ten meters; it should be included in the last black shales interval (Nevera member). It is important to point out that in the Lagonegro Basin the Triassic/Jurassic boundary, which corresponds to a major mass extinction event, was preceded by a period of repeated environmental changes.

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