STRATIGRAPHICAL AND PALEOENVIRONMENTAL ANALYSIS OF THE PERMIAN-TRIASSIC TRANSITION IN THE BADIA VALLEY (SOUTHERN ALPS, ITALY)

A sedimentological, palynological and microfaunal integrated analysis was carried out across the Permian-Triassic transition in a 35 m thick section near Seres (Badia Valley, northern Italy). This section inclu des the uppermost part of the Bellerophon Formation and the base of th e Werfen Formation (Tesero Horizon and the lowermost Mazzin Member). T he Bellerophon Formation ('badiota facies') displays a general shallow ing-upward trend. It has been subdivided into three intervals on the b asis of facies, microfacies, biofacies and palynofacies associations, The Bellerophon-Werfen Formation boundary was located at the boundary between a thin black organic-rich layer and a 50 cm thick limestone be d, containing in the upper part the first oolitic bads. The palynologi cal assemblages show throughout the Bellerophon Formation a gradual de crease of exclusive Permian palynomorphs and a concomitant increase of Triassic ranging forms. Triassic palynomorphs were found in the lower part of the Tesero Oolitic Horizon (TOH), where the Permian-Triassic transition can be recognized. Foraminifers with Triassic affinity appe ar just above the proposed Permian Triassic transition. This multidisc iplinary approach led to evidence the palaeoenvironmental evolution wh ich was characterized by variations in the water column oxygenation fr om dysoxic to oxic conditions related to climatic and/or physiographic changes influencing the water layering. Palynofacies studies show a s hift from relatively distal to more proximal conditions which reached the maximum during the deposition of the black organic-rich level at t he upper boundary of the Bellerophon Formation. The overlying shallowi ng upward cycle at the base of the TOH starts with an anoxic transgres sive layer and ends with the oolitic beds. (C) 1998 Elsevier Science B .V.