SEDIMENTOLOGY AND ISOTOPE GEOCHEMISTRY OF CARNIAN DEEP-WATER MARL/LIMESTONE DEPOSITS FROM THE SICANI MOUNTAINS, SICILY - ENVIRONMENTAL IMPLICATIONS AND EVIDENCE FOR A PLANKTONIC SOURCE OF LIME MUD

The upper Triassic Halobia-bearing marl/limestone deposits from the Sicani Mountains (Sicily) record the sedimentary evolution of the Sicanian Basin through the middle and late Carnian time. Dark marls and interbedded grey calcilutites of Julian age are characterized by abundant pyrite, sparse bioturbation and negative carbonate carbon delta(13)C values. They accumulated in a basin with dominantly anoxic to dysaerobic bottom waters. Lower Tuvalian dark-grey pyritic marls and calcilutites, which contain carbonate minerals with relatively high Mn contents and widely fluctuating delta(13)C signatures, were deposited under dysaerobic conditions. Middle and upper Tuvalian cherty limestones show intense bioturbation and nearly invariable positive delta(13)C values (around 2% for calcite). They form a thick and monotonous succession accumulated in a deeper and more oxygenated basin. The Halobia-bearing deposits preserve some calcareous nannoplanktonic forms. The nannofossils, varying in size from 7 to 32 mu m, are significantly abundant in the cherty limestones pointing to a notable role of the calcareous nannoplankton as a source of carbonate mud in the deep-water basins of the southern Tethys during the late Triassic time.