ABSTRACT The Sibillini Mountains, which make up the southern part of the Umbria-Marche Apennines, were struck by a series of earthquakes in 2016, including five with magnitudes greater than 5. The largest event, M w 6.5, occurred on 30 October 2016. A M w 5.9 earthquake on 26 October ruptured several faults in the northern third of the Vettore–Bove fault system, and the M w 6.5 event produced surface ruptures along the entire 30-km length. Ground surveys conducted shortly after these earthquakes showed that many, but not all, of the surface ruptures corresponded to previously mapped faults. Also, some faults that had been mapped as Quaternary did not produce surface ruptures during the earthquakes. In this study, we present the results of detailed field mapping that was conducted prior to the 2016 earthquakes and provide evidence that all of the surface ruptures in the northern part of the Vettore–Bove fault system occurred along preexisting faults. Paleostress analysis shows that the reactivated faults had been active prior to 2016 in stress fields with similar orientations to the modern-day stress field. In addition, we show that one fault segment, which is the southern continuation of a major fault that slipped during the 2016 earthquakes, was not reactivated because it was unfavorably oriented.

ABSTRACT The formation of the “expansion breccia” observed in the Lower Cretaceous Maiolica limestone in the Umbria-Marches region of Italy is attributable to a fluid-assisted brecciation process that occurred during the late Miocene exhumation of the Northern Apennines. The hydrothermal fluids probably originated as brine solutions trapped in the Burano anhydrite while it was in a plastic state. The migration of the Burano from the plastic to the brittle domain during unroofing resulted in liberation and injection of over-pressured hydrothermal fluids into the overlying limestone, causing hydraulic fracturing. Mapping of breccia morphology along a 400-m transect showed structures produced by different flow regimes, with chaotic and mosaic breccia characterizing the core parts of the section and mineral-filled fractures and veins in the margins. Based on the clast size in the chaotic breccia, the estimated velocities for fluidizing the aggregates of clasts and sustaining the clasts in suspension are, respectively, 15 cm/s and 65 cm/s. Crack growth was probably the main mechanism for the fragmentation of the limestone. Explosion fracturing patterns were only sporadically observed in the breccia, indicating substantial heat loss of the over-pressured fluids during their ascent to the Earth’s surface.

ABSTRACT The reduced Jurassic sedimentary sequences deposited on a structural high in the Umbria-Marche Apennines, as well their relationships with adjacent expanded basinal sequences, have been reconstructed through detailed, interdisciplinary study of the Sasso di Pale and Monte Serrone areas near Foligno, Italy. The physiographic features of the basin originated in the Early Jurassic (latest early Pliensbachian), when extensional tectonic activity broke up a shallow water platform where the Calcare Massiccio had been deposited, and the area evolved from an edge-stepped structural high to a distally steepened ramp. The biostratigraphic framework of this paper is mainly based on calcareous nannofossils, which are a useful tool for dating condensed Jurassic successions. Although the sections studied have limited thickness and much lateral facies variation, the sedimentary evolution can be traced and interpreted within a wider Jurassic environmental perspective. In the upper Pliensbachian–lower Bajocian interval, local sea-level variations are compatible with the global sea-level curve. Furthermore, some of the characteristic events—such as the Pliensbachian–Toarcian crisis, the Early Toarcian Jenkyns Event, and the Middle Jurassic carbonate crisis—can be recognized. The present study shows how the reconstruction of local paleogeography can fit into a more general framework and how regional and global signals can be recognized even in a small structural high such as the one we have investigated.

ABSTRACT At present, the Global Stratotype Section and Point (GSSP) for the base of the Bartonian remains the only GSSP of the Paleogene System to be defined by the International Subcommission on Paleogene Stratigraphy (ISPS) and the International Commission on Stratigraphy (ICS). Here, we present the results of an integrated, high-resolution study of calcareous plankton and benthic foraminifera biostratigraphy and a detailed magneto-, chemo-, and cyclostratigraphic analyses carried out through the upper Lutetian to the upper Priabonian pelagic sediments of the Bottaccione Gorge section near Gubbio, central Italy, to check its stratigraphic completeness and constrain in time the optimal interval for defining and positioning the GSSP for the base of the Bartonian Stage. The high-resolution and solid integrated stratigraphic framework established at Bottaccione confirmed the completeness of the section, which meets the ICS recommendations for a potential designation as a GSSP for the base of the Bartonian Stage. Thus, the Bottaccione section was compared with the parastratotype section of the Bartonian in its type area, Alum Bay, UK. On this basis, two reliable criteria for defining and positioning the Bartonian GSSP at Bottaccione are provided: (1) the base of magnetic polarity chronozone C18r as the primary correlation criterion and (2) the base of the calcareous nannofossil Dictyococcites bisectus , which defines the CNE14/CNE15 zonal boundary as a secondary correlation criterion.

ABSTRACT The Bottaccione Gorge at Gubbio, in central Italy, has been an important source of information about Cretaceous and Paleogene Earth history. At the much younger end of the historical continuum, it is also important for understanding the early history of Gubbio itself, for which the only written, although somewhat ambiguous, evidence comes from the Tavole eugubine, the unique bronze tablets which are a kind of Rosetta Stone for the Umbrian language. The role of the Bottaccione Gorge is debated in the history of Gubbio. The road through the gorge, crossing the Monti di Gubbio, is an important element for explaining the location of the city. One of the first settlements (late Bronze Age) is recognized from archaeological evidence at the top of a morphological fault scarp on the slope of Monte Ingino. In the Iron Age, the city described in the Tavole eugubine developed, in which Okri (fortress), Tota (city), and three sacred gates are mentioned. The locations of Okri , Tota , and the gates are still under study. According to the most likely hypothesis, Tota would have developed in the plain, on the right bank of the Torrente Camignano, while the initial settlement would have been transformed into Okri , to which the sacred gates would belong. Another gate may have been placed at the entrance to the Bottaccione Gorge. When the Eugubini (the people of Gubbio) built the new, post-Roman Gubbio in the twelfth century, they still identified, as the most suitable place for a fortified city, the location above the scarp on the slope of Monte Ingino, and they built two new gates at its lateral ends. The city was likely equipped with a third gate that faced the Bottaccione Gorge. In the thirteenth century, the Bottaccione Aqueduct was built to bring water to the highest point of Gubbio. Thus, two waterways—one natural (Torrente Camignano) and the other artificial—still branch off from Bottaccione to reach Gubbio at two different points that determine the lowest and highest levels of the city.

ABSTRACT The structural style at depth of the Umbria-Marche fold-and-thrust belt, which occupies the outer province of the Northern Apennines of peninsular Italy, has long been debated and interpreted in terms of thin-skinned or thick-skinned deformation models, respectively. Thin-skinned models predict that the Mesozoic–Tertiary sedimentary cover was detached along Upper Triassic evaporites and translated northeastward along stepped thrust faults above a relatively undeformed basement. On the other hand, thick-skinned models predict the direct involvement of conspicuous basement slices within thrust-related folds. A description of selected examples in the southeastern part of the Umbria-Marche belt reveals that some compressional structures are indeed thin-skinned, their style being controlled by rheological properties of a mechanically heterogeneous stratigraphy containing multiple décollements, whereas other structures are genuinely thick-skinned, their style being dominated by the reverse-reactivation of pre-orogenic normal faults deeply rooted within the basement. Therefore, the contrast of thin- versus thick-skinned structural styles, an issue that has generated a long-lasting debate, is only apparent, since both styles are documented to coexist and to have concurred in controlling the final compressional geometry of the fold-and-thrust belt.