Discriminating between tectonic and sedimentary burial in a foredeep succession, Northern Apennines

Abstract

An extensive apatite fission-track survey has been carried out on the Marnoso-arenacea foredeep succession in the Northern Apennines. The data show a general decrease of the maximum paleotemperature undergone by the sediments toward the foreland areas. The maximum burial calculated by using a geothermal gradient of 20 C km 1 spans from more than 5 km to less than 2.5 km and indicates that the previously assessed total thickness of the Marnoso-arenacea succession is not enough to justify the determined values. It is concluded that a now eroded Ligurian wedge, up to 5 km thick, was present on top of the Marnoso-arenacea sediments.Apatite fission-track analysis is applied to sedimentary basins to unravel their low-temperature thermal history. The Middle to Upper Miocene foredeep succession of the Northern Apennines (Marnoso-arenacea Formation) has been studied for over 30 years and provides an ideal case study for apatite fission-track analysis, because of detailed knowledge of its stratigraphy, structures and petrography. Vitrinite determinations (Reutter et al. 1983) suggest that the outcropping sedimentary succession should encompass the whole apatite partial annealing zone (60-120 C) that is the range of temperature in which considerable information about the burial history can be obtained. The aim of this study is to assess the burial history in order to place new constraints on the geological evolution of a sector of the Northern Apennine fold-and-thrust belt and of the adjacent foredeep basins. In particular, our results are addressed to check the presence and the original extent of a now eroded 'far-travelled' thrust sheet, the so-called Ligurian nappe, whose existence on top of the thrust belt in the Romagna Apennines currently is a matter of debate. Based on the modelled total burial across the exposure of the Marnosoarenacea basin and on geological evidence (such as remnants of the Ligurian nappe), we suggest that the strata were originally covered by a tapered wedge of the Ligurian nappe which has since been removed by erosion and tectonic denudation.

The Romagna Apennines, Italy: an eroded duplex

“…The calculated palaeotemperatures and burial depths are consistent with the results of the apatite ®ssion-track analysis (Zattin et al 2000), which indicate that the palaeotemperatures reached by the MAF deposits range from < 70 to > 120 C and the corresponding maximum burial depths are between less than 2500 m and more than 5250 m, assuming a palaeogeothermal gradient of 20 C/km (Table 2). Further indications of post-depositional thermal conditions can also be derived from illite crystallinity (IC) measurements, which have been tentatively performed in our study, using the analytical methods outlined in the appendix.…”

“…In addition, recent apatite ®ssion-track analysis provides data about the thermal conditions that affected the MAF (Zattin et al 2000).…”

“…Apatite ®ssion-track > 120± < 70 > 5250± < 2500 (Zattin et al 2000) (20 C/km) Vitrinite re¯ectance 125±75 6250±3750 (from data in Reutter et al 1983) (20 C/km) 46 a. cerrina feroni et al…”

Using tracer tests and hydrological observations to evaluate effects of tunnel drainage on groundwater and surface waters in the Northern Apennines (Italy)

“…Drilling began in 1996 through four access windows (total length: 3,519 m) and was completed at the end of 2005. The tunnel is mostly drilled through silico-clastic turbidite units of the Miocene Marnoso Arenacea Formation (MAF), consisting of arenitic layers (sandstones) and pelitic layers (marls;Ricci Lucchi 1986;Zattin et al 2000). The MAF can be subdivided into lithostratigraphic members according to the ratio of arenitic to pelitic layers (A/P ratio) (Cibin et al 2004;Gargini et al 2006;Amy and Talling 2006).…”

Duplex architecture and late‐orogenic backthrusting in Foredeep Units of the Northern Apennines (Italy)

“…Moreover, the structural setting of the Northern Apennines is complicated by out-of-sequence thrusting, which locally inverts the primary relationships among the different tectonic units (Bendkik et al 1994;Cerrina Feroni et al 2004) (Figure 1). Deformation of the Foredeep Units occurred under non-metamorphic conditions, at temperatures less than 1308C and burial depths not greater than 6 km (Zattin et al 2000;Cerrina Feroni et al 2001;Botti et al 2003).…”