Geochemical and mineralogical approaches to assessing provenance and deposition of shales: a case study

Mineralogical and geochemical studies of Cretaceous segments of Argille Varicolori and Flysch Rosso successions from the southern Apennines allow their provenance and history to be evaluated. The occurrence of detrital kaolinite and fine-grained Fe-oxyhydroxides, the strong depletion of Na2O, K2O and CaO, and the enrichment in the transition elements document severe alteration in the source areas. Nevertheless, mineralogical and geochemical features able to discriminate the shale families are still preserved. The presence/absence of rock fragments derived from a 'crystalline' source, the significant chemical differences as well as the characteristics of clay minerals, discriminate the studied shales. The absence of indications suggestive of mixing of the detrital components favour the hypothesis that the two shales were deposited in distinct basins which probably received contributions from continent-ocean convergent areas (Argille Varicolori) and from more stable areas (Flysch Rosso).