Integrated stratigraphic-petrographic and biostratigraphic analysis of Modino Unit turbiditic system (Northern Apennines, Italy)

The study of the relationships between the Oligo-Miocene foredeep sequences represented by Modino Unit the Tuscan Nappe, can be considered as a classic topic of the Northern Appenines geologists. This topic was widely debated starting from the 60’s by several authors (eg. Abbate & Bortolotti, 1961; Reutter, 1969; Plesi et al., 2000 and many Others). It is a problem more articulated that sees deal two positions radically different: For many authors, including Abbate & Bortolotti (1961), the contact between the Macigno Fm. (upper formation of the Tuscan Nappe) and Monte Modino Sandstone Fm. is a stratigraphic contact, and the sediments interposed between this formations are the so called "olistostroma di Monte Modino". This term is referred to submarine landslides derived from the front of an advancing nappe and sedimented within the foredeep deposits. Other authors as Reutter (1969) and successively Plesi et al., (2000) have supported the tectonic origin of the complexes deposits between Macigno Fm. and Monte Modino Sandstone. This sediments was considered as remanents of the Cretaceous-Eocene Ligurian and Subligurian units. The tectonic surfaces are resolved as a frontal thrust by Plesi, (2000) or as a back thrust from Reutter (1969) but both consider the direction of tectonic transport normal to the main axis of the belt. In more recent papers (Cerrina Ferroni et al., 2004), interpreted this tectonic surface as a splay of a regional flower structure with sense of transport parallel to the belt (right transpression).