New biostratigraphic and petrographic data from the Poggio Carnaio Sandstone Fm (Val Marecchia Nappe): insights into the tectonic evolution of the Northern Apennines

Angelida Di Staso(*), Sonia Perrotta(**), Francesco Guerrera(**), Vincenzo Perrone(**) & Mario Tramontana(**)
(*) Dipartimento di Scienze della Terra, Università «Federico II», Largo San Marcellino, 10 - 80138 Napoli (Italy). (**) Dipartimento di Scienze Geologiche e Tecnologie Chimiche e Ambientali, Università «Carlo Bo», Campus Scientifico, Località Crocicchia - 61029 Urbino (Italy). Corresponding Author. Vincenzo Perrone, tel. 0722 304289; Fax 0722 304222; e-mail: vincenzo.perrone@uniurb.it.

In the Northern Apennines, the Poggio Carnaio Sandstone Formation consists of sandy-clayey turbidites, cropping out in the northernmost corner of the Val Marecchia Nappe. The formation has been considered Oligocene in age and is commonly interpreted as an Epiligurian unit, unconformably deposited above the Val Marecchia Nappe during its transport towards the Adriatic foreland. The Poggio Carnaio Sandstone Fm rests on the Argille Varicolori Fm of the Val Marecchia Nappe, but field data do not allow it to be recognized wherever it abruptly replaces the pelagic sediments of the Argille Varicolori Fm, thus testifying to the foredeep evolution of the basin, or where it unconformably overlies this latter formation. Nannofossil assemblages are characterized by abundant reworked Cretaceous and Paleogene taxa and by some taxa, whose first occurrence is reported in the upper part of the NN4 Zone = upper part of the CN3 Zone. Therefore the formation must be considered not older than Langhian. Detrital modes of arenites revealed a quartz-feldspathic composition and the lithic component includes mainly metamorphic fragments and minor plutonic, sedimentary, ophiolithic and volcanic clasts. The presence of clasts of garnet, sillimanite, hornblende and glaucophane is significant. Biostratigraphic as well as petrographic data agree with the interpretation of the Poggio Carnaio Sandstone Fm as an Epiligurian succession. Rock fragments indicate source areas characterized by Ligurian-, Pennidic- and Australpine-type units. Sedimentary facies and textural features of arenites, revealing a rapid erosion and deposition of clasts in a basin close to the source area of the clastic supply, indicate that the Alps cannot be considered as the source area of these arenites, as frequently argued for many North-Apennine clastic formations. Ligurian-, Pennidic- and Australpine-type units were located close to the Poggio Carnaio Sandstone basin, probably representing the geometrically highest units of the Palaeo-Apennine Chain.

Biostratigraphy, Langhian, Sedimentary petrography, Poggio Carnaio Sandstone, Val Marecchia Nappe, Northern Apennines.