Petrological features of a Numidian section in the Lucanian Apennine (southern Italy)

A continuous section of Numidian sandstones cropping out along the eastern margin of the Lucanian Apennine (southern Italy) has been studied in relati on to its petrographic and geochemical aspects. Owing to their simple miner alogy, both chemical and petrographic classifications indicate that the san dstones are subarkoses. They are characterized by high mineralogical maturi ty, poor sorting, abundant siliciclastic matrix and subangular quartz grain s. The principal composition is Q(80-94) F6-20 L0-1 corresponding to SiO2/A l2O3 and Fe2O3/K2O ratios ranging from 37.216 to 17.124 and from 1.182 to 0 .514 respectively. Two quartz grain types were distinguished: deformed and undeformed quartz grains, the former generally subangular in shape and the latter rounded. Two distinct origins of detritus can be suggested; (i) the undeformed and rounded quartz grains derive from arenaceous continental seq uences; (ii) the siliciclastic matrix, the deformed subangular quartz grain s, the heavy minerals and the large crystals of K-feldspar probably derive from a crystalline basement formed by low-medium-high grade metamorphic roc ks and granitoids. The Numidian subarkoses represent the mixing of these tw o components. Both kinds of detritus can be referred to the African Craton where crystalline basement is extensively overlain by Palaeozoic and Mesozo ic sandstones. The different proportions of the two components in the mixtu re account for the variability of the sandstone composition and might expla in the mixed Numidian successions cropping out in various sectors of the Me diterranean area. (C) 1998 John Wiley & Sons, Ltd.