The Miocene turbidite deposits of the Marnoso-arenacea Formation (northern Apennines, Italy)

In the northern Apennines, thick and laterally extensive terrigenous turbidite successions were deposited during the late Oligocene and Miocene, as the fill of elongated, NW-stretched foredeeps formed in front of the growing Apennine orogenic wedge. These turbidites, which are the classic sandy flysch formations (Macigno, Cervarola,Marnoso-arenacea) upon which Migliorini (1943) elaborated his fundamental concept of resedimentation, were progressively incorporated into the frontal part of the orogen during its propagation towards the NE (see also Kuenen & Migliorini, 1950). Among these turbidite units, the Marnoso-arenacea Formation (Langhian to Tortonian in age) is the best exposed and less structurally deformed due to its relatively external position within the Apennine orogen. Thanks to the early works by Ricci Lucchi (1969, 1975, 1978, 1981, 1986),Mutti & Ricci Lucchi (1972), Ricci Lucchi & Pignone (1979) and Ricci Lucchi & Valmori (1980), the Langhian to Tortonian Marnoso-arenacea Formation (MAF) is probably the most famous among the clastic units, which record the structural evolution of the Apennine thrust belt. However, recent studies have shown that the MAF’s stratigraphy and depositional settings are more complex than previously thought, due to the accompanying structural deformation that exerted a control over basin geometry, facies distribution patterns and emplacement of mass-transport complexes (de Jager, 1979; Ricci Lucchi, 1986; Argnani & Ricci Lucchi, 2001; Mutti et al., 2002a, 2003; Roveri et al., 2002; Lucente & Pini, 2002, 2003; Lucente, 2004; Bonini, 2006).As a result, the vertical stacking pattern of the Marnoso-arenacea records a close interaction between thrust propagation towards the NE and deposition from turbidity currents flowing towards the SE, i.e. parallel to the thrust fronts. This view has prompted a re-examination of the MAF’s stratigraphy and facies starting with the Turbidite Workshop held in Parma in 2002 (Mutti et al., 2002a). The main intent of this field trip is to present the preliminary results of the continuation of this study, illustrating the sedimentary characteristics of the stratigraphic succession of MAF (about 4000m thick) that records the progressive closure of the foredeep due to the NE propagation of thrust fronts. In particular, this guide will present a detailed stratigraphic cross-section (with bed-by-bed correlations) of the upper Langhian to Serravallian stratigraphic succession of MAF outcropping in Romagna Apennines (Muzzi Magalhaes, 2009; see also Muzzi Magalhaes and Tinterri, 2009). This interval covers a thickness of about 2,500m and a distance of about 60km in a SE direction, i.e. parallel to the paleocurrents. It has well-exposed outcrops with good lateral continuity and numerous key beds - many of which are mapped on the geological maps of the Emilia-Romagna region (Cerrina Feroni et al., 2002; Martelli et al., 1994).These characteristics have proved fundamental for many MAF field studies attempting high-resolution stratal correlations over significant distances.The pioneering work in this sense was Ricci Lucchi & Valmori (1980), which took into account a stratigraphic interval of 200m around the Contessa key bed, for a horizontal distance of 120km. More recently, Amy et al. (2005), Amy and Talling (2006) presented correlations of a high number of stratigraphic logs covering an interval of about 25m comprised between the Contessa and Colombina 1 key beds.