Miocene fault-controlled sedimentation and thrust propagation in the previously faulted external zones of the Umbria-Marche Apennines, Italy

Abstract

Abstract. Thrust propagation through previously faulted continental margins may result in fold and thrust belts whose structure is strongly controlled by the inherited basin architecture. A detailed geological study has been carried out in the external zone of the Umbria-Marche Apennines, from Monte San Vicino to the north, to Montagna dei Fiori to the south. Stratigraphic and structural data, together with the construction of a series of balanced and restored geological sections, point out the fundamental role played by the preorogenic basin architecture in controlling the geometry and evolution of the fold and thrust belt. Pre-thrusting structures include not only those inherited from the Mesozoic rifted continental margin, but also synsedimentary faults associated with Miocene extension which occurred ahead of the advancing thrust front. The latter structures produced important facies and thickness variations in the units deposited during the late Burdigalian-early Messinian, pre-evaporitic stages of foredeep development. In the southern sector (Montagna dei Fiori), high values of Messinian regional subsidence, bathymetry and sedimentation rate overcome the effects of synsedimentary extensional tectonics, which is best recorded in pre-Messinian sequences. On the other hand, Messinian regional subsidence was significantly less in the northern sector (Monte San Vicino). Here, several minor sub-basins developed within the foredeep, generally reaching evaporitic conditions during the middle Messinian (marked by the deposition of the Gessoso-solfifera Fm). In this area, a major control by pre-thrusting normal faults on sedimentation is recorded in the foredeep siliciclastic sequences. Late Burdigalian-early Messinian extension, possibly associated with flexure of the foreland lithosphere, peripheral bulge uplift and/or foreland tectonic activity, was followed by a late Messinian (post-evaporitic) contractional episode of regional extent. During shortening, inversion of preexisting MioceneCorrespondence to: S. Mazzoli (s.mazzoli@geo.uniurb.it) extensional structures was quite limited. Hanging wall basin fills were retained and pre-thrusting faults show very limited or no reversal of slip. However, these faults and their hanging wall basin fills are generally deformed by buttressing phenomena, and fault planes are often tilted and/or locally reactivated in strike-slip. The present-day structure is dominated by newly-formed thrusts that cut across the preexisting extensional architecture, which is in general quite well preserved within different thrust sheets.

Contrasting styles of fault reactivation in curved orogenic belts: Examples from the Central Apennines (Italy)

“…The role of pre-thrusting normal faults in the evolution of the Apennine fold-and-thrust belt has been investigated by several authors (e.g., Tavarnelli, 1993;Bruni et al, 1996;Pierantoni, 1998;Mazzoli et al, 2002;Scisciani et al, 2002). Such faults, which can be differentiated as pre-orogenic (mainly Jurassic) or synorogenic (Neogene), were either truncated by thrusts with a shortcut trajectory, generating footwall shortcuts (sensu McClay, 1989;Coward, 1994) and related anticlines, or reactivated with reverse kine matic (Decandia, 1982;Butler, 1989;Argnani and Gamberi, 1995;Scisciani et al, 2002;Tozer et al, 2002;Tavarnelli et al, 2004;Calamita et al, 2009;Scisciani, 2009).…”

Contribution of different kinematic models and a complex Jurassic stratigraphy in the construction of a forward model for the Montagna dei Fiori fault‐related fold (Central Apennines, Italy)

“…(Figure 9). According to this view, the high structural elevation observed in the Montagna dei Fiori fault-related fold should be related only to the Miocene normal fault, as already proposed by Calamita et al, (1998), and to tectonic transport along the main deeper thrust (T1 thrust, Figure 4) (Mazzoli et al, 2002;Casero and Bigi, 2006;Tozer et al, 2006). Moreover, from a mechanical perspective, our interpretation implies that we are dealing with a large rigid object encased within a dominant layer-cake geometry (the pelagic succession), so that the competence contrast is mainly horizontal, due to the lateral contact of pluri-hectometric blocks of Calcare Massiccio Fm.…”

“…From the analysis of the 2D seismic lines crossing the structure (unavailable data), and according to several authors, the hanging-wall anticline related to the T1 thrust is cut by the Montagna dei Fiori-Montagnone Thrust (Figure 4). This geometric relationship indicates that the activity of the Montagna dei Fiori-Montagnone Thrust postdates the main propagation phase of the T1 thrust (Mazzoli et al, 2002;Casero, 2004;Casero and Bigi, 2006). Within the core of the Montagna dei Fiori Anticline, along the Salinello Valley, the Salinello Thrust is exposed (Mattei, 1987;Calamita et al, 1998 and references therein) ( Figure 5).…”

“…This normal fault has a maximum displacement of 1400 m (Centamore et al, , 1992, and it was active mainly before Neogene contractional deformation (Calamita et al, 1998;Mazzoli et al, 2002;Scisciani et al, 2002).…”

Geomorphological map of the Montelago area (North Marche Apennines, central Italy): constrains for two relict lakes

“…Thrust-faults affected a Meso-Cenozoic mainly carbonate and marly-carbonate multilayer and propagated upward and north-eastward into the overlying Mio-Plio-Pleistocene hemipelagic, turbiditic and evaporitic units (Mazzoli, Deiana, Galdenzi, & Cello, 2002) (Figure 1). Strike-slip faults, ranging from north-south (oblique) to east-west (transversal), dissect the overall northwest-southeast-oriented fold-and-thrust structural pattern (Di Bucci et al, 2003).…”