The "Flysch Rosso" Shales from the southern Apennines, Italy. 2. The origin of the colour

Mineralogical and geochemical studies were carried out on red and green shales from the «F lysch Rosso» sediments (southern Apennines, Italy) in order to investigate on the cause(s) of the colour variation. The two chromatic types show compositional analogies and few differences are relevant, the main consisting in Fe content. Although the statistical analyses evidenced a slightly significant difference in some chemical parameters indicative of the redox conditions at the water-sediment interface (U, Corg, FeO, V /Cr, U/Th), they, nevertheless, still indicate oxic environments both in red and in green shales. The difference in the organic carbon content is small and cannot be seen as the cause of the chromatic variation. The origin of the red colour is ascribed mainly to the presence of hematite, which is ubiquitous in the red shales but in a very little amount in a few of the green ones. D ifferent h ematite, feldspars, and kaolinite c o n te n ts of red and green shales as well as geochem ical considerations suggest a detrital hypothesis for Fe-hydroxides and a diagenetic one for the hematite.