Sedimentology, Petrografy and Provenance of the triassic Verrucano Group, Monte Argentario (Tuscany Italy)

Deposition of the Verrucano Group (max. thickness 700 m) took place in a series of N-Strending grabens after rifting of the Hercynian basement. The presence of violet-gray mudrocks, caliche nodules and crusts, and the abundance of iron oxides in the sandstones and siltstones suggest that the Verrucano was deposited when the climate was semiarid.The scarcity of conglomerates and presence of upward-fining cycles suggest that the upper part was deposited by low-sinuosity mcandcring streams. T'he abundance ofconglomerate andabsenceo f sequencest ypic:rl of point bars indicate that the rest of the Verrucano was deposited chiefly by high-gradient braidcd streams. Low-grade metamorphism, which occurred duringthe Alpine orogcny, resulted in the recrystallization of argillaceous rock fragments and clay rip-up clasts, but did not clestroy primary sedimentary structures or recrystallize detrital quartz. Based on modal analyses, the sandstone composition in percents is quartz, ; microcrystalline quartz in rock fragments, quartz-mica rock fragments, mica rock fragments, iron oxides, Feldspars:The conglomerates are composed chiefly of quartz, showing various degrees of strain,and metachert .metasandstones, micas chist.