Geochemistry of Oligocene-Miocene sandstones of the northern Apennines (Italy) and evolution of chemical features in relation to provenance changes

Integrated petrographic and geochemical criteria for provenance determination in elastic sedimentary rocks are applied to four flysch formations of Oligocene-Miocene age in the northern Apennines (Italy). Major and trace element geochemistry of 60 sandstones for the Macigno Formation, Monte Modino Formation, Monte Cervarola Formation, and Marnoso-arenacea Formation is presented. Geochemical criteria of discrimination based on element ratios (Y/Ni, Cr/V, Rb/Sr and Cu/Al2O3) allow distinction of the Macigno, Modino, Cervarola and Marnoso-arenacea. The differing geochemical features of the four flysch formations suggest a decrease of ultramafic and metamorphic supply and increase of carbonate and intrusive rock fragments from Macigno to Cervarola, and a sharp increase of carbonate/siliciclastic ratio at the transition to the Marnoso-arenacea Formation. All this provides significant insights and additional constraints about the chronostratigraphic evolution of sediment supply in the northern Apennines foredeep from Oligocene to Tortonian times: the decrease of detritus supply from the Adriatic Plate and the increase in felsic detritus from the Alps become apparent after the Oligocene-Miocene transition; the carbonate influx from E and SW starts from the Lower Miocene; the increasing importance of the Apennine Chain input, with the recycling of turbiditic successions and rocks from Ligurian units, is testified by the geochemical features of the Marnoso-arenacea Formation. On the whole, the applicability of the geochemical techniques to elastic sedimentary rocks is confirmed, but also the complementary character of petrographic and geochemical methods in provenance and evolution studies is emphasized. (C) 1999 Elsevier Science B.V. AU rights reserved.