Studio di minerali opachi in sabbie fluviali oloceniche e nelle corrispondenti rocce madri di zone sottoposte a climi diversi (Montagne Rocciose e Monti Appalachi in U.S.A.).

The distribution of the compositions and shapes of detrital zircons and that of the compositions and colors of detrital garnets in the Oligocene Renova Formation (RE), Miocene Six Mile Creek Formation (SX), and Holocene sands (HO) in southwestern Montana have been analyzed statistically to understand the evolution of their diversity through time. Field, stratigraphic, and provenance relations indicate that the cumulative maturity of the sediments increase in the order HO-RE-SX although Renova rocks had been buried most deeply. A multivariate analysis of chemical and petrographic data on detrital zircons and garnets from these sediments, all fluvial in origin, shows that the diversity of zircon properties decreases in the order HO-RE-SX but that of garnets does not show any systematic pattern. In general, however, diversity of garnet properties seems to be least in the Renova. We conclude that in these sediments: 1) the inherited diversity of physical and chemical properties of detrital zircons decreases with increasing maturity of sediments: 2) not all zircons are as durable as commonly believed; and 3) the inherited diversity of physical and chemical properties of detrital garnets is affected more by diagenesis than other sediment-maturing processes.