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Fold-and-thrust belts are characterized by the occurrence of foreland-verging thrusts and antithetic backthrust, which develop in the hangingwall of thrust sheets. Both thrust and backthrust bound the so-called pop-up structure, which is a deformed zone characterized by thrust- and backthrust-related anticlines. Pop-up structures mainly develop in fold-and-thrust belts characterized by a multilayered sedimentary sequence, consisting of limestones, marls, and shales, deformed above a weak décollement, such as evaporites. However, in this work, we combine field mapping, stratigraphic constrains, and structural analysis with 2D kinematic forward modeling to document a pop-up structure developed within limestones/dolostones, deformed above a strong décollement consisting of dolostones, in the central Apennines, Italy. In particular, we describe a SW-verging anticline and a NE-verging anticline in the SW and NE margin of the Serra Lunga ridge, respectively. Such folds were generated by a NE-dipping backthrust and by SW-dipping forethrust, respectively. Therefore, we suggest that the Serra Lunga ridge represents a pop-up structure, showing geometries similar to other pop-up structures observed within fold-and-thrust belts characterized by a multilayered sedimentary sequence. In addition, backlimb tilting of backthrust-related anticlines generates the forelandward-dipping monoclines, observed within thrust sheets in the Central Apennines and in several fold-and-thrust belts worldwide. • Field mapping highlights the deep structure of an internal sector of the central Apennines fold-and-thrust belt. • Pop-up structure in the central Apennines was generated by a NE-dipping backthrust and by a SW-dipping forethrust. • Backthrust generated a forelandward-dipping monocline, which characterize carbonate ridges in the central Apennines. [ABSTRACT FROM AUTHOR]

The upper Miocene dominantly terrigenous succession cropping out at Monte San Fabrizio (Simbruini Mts.) shows peculiar, previously unreported bio‐sedimentological features, which bring fresh elements in a regional palaeogeographic/palaeotectonic key. Overlying the regional foredeep succession, an array of different lithofacies either form mappable outcrops or occur as clasts, remarkably not referable to any stratigraphic units already known in the Central Apennines. These lithologies, which include coral‐bearing siliciclastic sediments, mixed carbonate/siliciclastic deposits with benthic macrofaunas, rhodalgal facies, and conglomerates, essentially made of Mesozoic pelagic lithoclasts, are here grouped in a comprehensive informal unit, called Monte San Fabrizio Unit (MSFU). The most striking feature of the MSFU is a coralgal facies characterized by the occurrence of zooxanthellate (z) corals (Porites and Siderastrea crenulata). While the age of these deposits is not directly determinable due to the lack of biostratigraphic markers, their composition and field relationships clearly place their origin within a late‐orogenic setting: only the uplift, subaerial exposure, and erosion of large portions of the pre‐orogenic stratigraphy, also belonging to different geological domains, and subsequent sediment transport by rivers, can account for the heterogeneous composition of the conglomerates. Their sedimentological characters (i.e., shape and size of the clasts) suggest reworking of the pebbles in a shore environment. A shallow marine photic environment is confirmed by the presence of z‐corals, red algae, and abundant macrofauna. The occurrence of Porites and Siderastrea crenulata represents the first occurrence of corals subsequent to the drowning of the bryozoan limestone carbonate factory, being the youngest occurrence of corals in the Central Apennines and the first ever post‐Burdigalian z‐corals described in the region. This also constrains the age of the MSFU as early–middle (pre‐evaporitic) Messinian, due to the almost total demise of z‐corals known in the Mediterranean in response to the Messinian Salinity Crisis. In conclusion, sedimentology, palaeobiology, and field geology all point to a shallow‐water environment, close to a shoreline, for the MSFU. This unit can be interpreted as representing the vestiges of an ephemeral depositional environment, such as a small wedge‐top basin, an evidence that this portion of the Apennine chain was already structured in the early–middle Messinian. [ABSTRACT FROM AUTHOR]

In the Central Apennines, a Tertiary-Present eastward-vergent fold and thrust belt, thrusting mainly occurred in-sequence, cutting across a Mesozoic to Early Neogene succession, deposited in rifted (Early Jurassic) to passive continental margin, to foredeep (late Miocene) conditions. However, the Simbruini Mts were characterized by the occurrence of regional out-of-sequence thrusts (the Vallepietra-Filettino-Monte Ortara thrust fault) and ofTertiary prethrusting normal faults, associated with the deposition of thick breccia deposits (Brecce della Renga, Tortonian-early Messinian). A direct link between these two features is here proposed. Evidence for a prethrusting normal faulting origin for the Brecce della Renga is amply discussed. Although evidence for subduction-related normal faulting is growing in the Apennines literature, nowhere in the region are known extensional systems so vast and their syn-tectonic deposits so thick as in the Simbruini area. We propose that the Simbruini prethrusting normal faults were subduction related, i.e., they developed in the foreland due to anomalous bending of the lithosphere subducting in Late Tertiary time under the Apennines in the Simbruini Mts area. The associated breccia deposits were subsequently deformed during the development of the Simbruini Mts thrust front. We speculate that the prethrusting normal faults allowed the penetration of fluids within the subducting crust and possibly also in the mantle, weakening this part of the subducting plate. As a consequence, the weaker plate was anomalously down-bent, leading to a subcritical state of the Apennines wedge. The regional scale out-of-sequence thrust faults developed in order to bring the Apennines wedge back to the critical state. [ABSTRACT FROM AUTHOR]