Apenninic Belt Research Articles

Drivers of vascular plant, bryophyte and lichen richness in grasslands along a precipitation gradient (central Apennines, Italy)

AbstractQuestionsSemi‐natural grasslands in Southern Europe are biodiversity hotspots, yet their patterns of plant species richness are less studied than in Central Europe. In the Central Apennines (Italy), there are large areas of dry calcareous grasslands, across a steep gradient of mean annual precipitation (from 650 to 1350 mm within c. 30 km). We asked: How do these grasslands compare to other Palaearctic grasslands in richness levels? How do the precipitation gradient and other environmental predictors influence species richness? Does this influence differ among taxonomic groups?LocationSubmontane and lower‐montane belt of the Central Apennines (Abruzzo and Lazio, Italy).MethodsWe recorded the species richness of vascular plants and (terricolous) bryophytes and lichens in 97 plots of 10 m2, aligning them with the precipitation gradient while maintaining geological substrate and elevation similar. Mean temperature and precipitation were estimated with a high‐resolution regional model. A wide array of environmental variables (including soil properties and grazing load) were measured for each plot. Multivariate relationships within and between response and predictor variables were studied with Canonical Correlation. The relative importance of predictors on response variables was modeled with Boosted Regression Trees.ResultsThe sampled grasslands were very species‐rich in the Palaearctic context. Vascular plant richness was negatively influenced by topographic heat load and soil sand content, but we did not detect a relationship with mean annual precipitation. Bryophyte richness was poorly modeled by the measured variables, although it was positively correlated with lichen richness. Lichen richness had a marked negative relationship with soil phosphorus and mean annual precipitation.ConclusionsIn Southern European semi‐natural mountain grasslands, vascular plant richness is driven more by fine‐scale edaphic factors than by precipitation gradients. In contrast, bryophyte and lichen species richness is predicted by a mixture of climatic and edaphic variables.

Interaction of accretion mechanisms and deep fluids in continental orogenesis

Mountain-building often involves the subduction of continental margins during the convergence of tectonic plates. Rheological heterogeneities and structural inheritance in the subducting lithosphere are main factors controlling the evolution of the process and deformation partitioning in orogenic wedges. Here, we present tomographic evidence of a main along-strike change in the structure of the Apennines belt, where frontal accretion diminishes laterally, as well as plate bending, and the contribution of underplating to crustal thickening becomes evident. We hypothesize that the diverse mechanisms of mountain formation can be attributed to rheological heterogeneity in the crust and interactions with fluids liberated during the subduction process. The development of shallow decollements versus underplating is favored by differing amounts and styles of deep fluid liberation from the subducting crust.

Deformation and pressure-temperature-time history of the External Tuscan Units in the Northern Apennines (Italy): The case of the Punta Bianca Unit

In this study we investigated through a multidisciplinary approach the still poorly known tectono-metamorphic evolution of the Punta Bianca Unit in the Northern Apennines. The Punta Bianca Unit is part of the Tuscan Metamorphic Units, a group of units derived from the Adria passive margin, metamorphosed at different conditions, and forming the backbone of the Northern Apennine belt. We combined meso- and microstructural analyses, 40Ar/39Ar white-mica geochronology and multi-equilibrium geothermobarometry from high-resolution X-ray chemical maps, to unravel the deformation and metamorphic history of this part of the belt. Meso- and microstructural data indicate that the Punta Bianca Unit recorded two main phases of ductile deformation (here referred to Dp-1 and Dp) associated with syn-kinematic growth of K-white mica, chlorite, calcite, quartz on the related tectonic foliations (Sp-1 and Sp), followed by a later ductile deformation phase (Dp+1) lacking of metamorphic blastesis. P-T estimates complemented by microstructural data suggest that peak metamorphic conditions reached ∼0.8 GPa and ∼350°C and occurred synchronously with the first deformation phase (Dp-1). Temperature values were also confirmed by Raman spectroscopy of carbonaceous material on selected samples. This stage was followed by the exhumation of the Punta Bianca Unit, as testified by decreasing pressure and temperature down to ∼0.4 GPa and ∼300°C respectively, together with the development of the main foliation (Sp). At the regional scale, the Tuscan Metamorphic Units have been mostly affected by HP-LT metamorphic gradients equilibrated under blueschist-facies conditions (up to ∼1.4 GPa). Results from the present work on the contrary, suggest that the Punta Bianca Unit never reached such HP-LT conditions, testifying that it was deformed at relatively upper structural levels, thus highlighting an important variation in the tectono-metamorphic evolution of the Tuscan Metamorphic Units along strike in the Northern Apennines. 40Ar/39Ar laserprobe data (using both the in-situ and step-heating techniques) indicate a minimum age for the onset of continental subduction of ∼20 Ma (Dp-1), which was followed in close succession by exhumation at ∼16 Ma. This approach, if applied to different tectonic units building up the nappe pile of the Northern Apennines, could be successful in better unravelling the tectonic history.

River linear inversion to assess drainage base-level fall history in North-western Apennines and implications on the Alessandria Basin tectonic activity

Drainage network systems are responsive elements to recent active tectonics from among all the topographic features. In geodynamically active areas, fluvial landscapes can record different processes through the formation and current presence of features related to spatial-temporal variation in base-level fall and vertical incision of stream channels. This study focuses on the tectonic evolution of the Alessandria Basin, a synorogenic tectonic basin located at the junction between the Alps and the Apennines, that experienced progressive subsidence during the overthrusting of the Monferrato Thrust Front (the westernmost outer arc of the Apennine belt) onto the Po Foreland Basin. Even though several studies have assessed the Neogene tectonic evolution at a regional scale, rates and timing of the Quaternary activity are still poorly understood in terms of both Alps/Apennines uplift and activity of the compressive front of the Monferrato Arc. In this paper, we applied the method of the river profile linear inversions to reconstruct the base-level fall history of 6 catchments that drain into the Alessandria Basin. We used nine 10Be-derived basin-average denudation rates to constrain the erodibility parameter needed to infer base-level fall rates from χ-transformed river profiles. The results describe the tectonic history of the area in the last ∼5 Ma, documenting increases in base-level fall rate with an initial peak between 3 and 2.5 Ma, and a second between 2 and 1.5 Ma. While the first peak is coeval with the uplift phase that involved most of the northern-central Apennine, the second one suggests an acceleration in subsidence of the Alessandria Basin concurrently with the uplift of the Monferrato Thrust Front.

Subduction signature in the Internal Ligurian units (Northern Apennine, Italy): Evidence from P–T metamorphic peak estimate

AbstractThe Internal Ligurian units (Northern Apennine) represent deformed and metamorphosed fragments of the oceanic lithosphere of the Ligure–Piemontese oceanic basin. Different tectonic models have been proposed for the geodynamic setting in which the deformation and metamorphism have been acquired. However, the lack of updated, clear, thermo‐barometric data has made it hard to unambiguously discriminate between these different proposed models. In this article, we provide evidence for the deformation of the Palombini Shale, i.e., pelagic deposits belonging to the Internal Ligurian units, under P and T peak conditions of 230–300°C. and 0.6–0.9 GPa, respectively. These data indicate that the Internal Ligurian units were affected by a blueschist facies metamorphism achieved during the underplating within the accretionary wedge developed during the Late Cretaceous—Early Tertiary Alpine subduction. These data support the hypothesis of a unique, pre‐Oligocene orogenic system for the Alpine belt and the westernmost sector of the Northern Apennines belt.

Role of Inherited Tectonic Structures on Gravity-Induced Slope Deformations: Inference from Numerical Modeling on the Luco dei Marsi DSGSD (Central Apennines)

A pre-existing and inherited geostructural setting plays a fundamental role in preparing and developing large-scale slope deformational processes. These structures affect the kinematics of the process, the geometrical characteristics, and the geomorphological evolution. In the Apennine Belt, several deep-seated gravitational slope deformations (DSGSDs) that have evolved under a clear structural control have been recognized during the last decades, but none with a continuous and well-defined basal shear zone (BSZ). The structurally-controlled DSGSD of Luco dei Marsi represents the first case of a DSGSD in the Apennine Belt with a well-defined BSZ. Starting from a detailed study of the process and the reconstruction of a morpho-evolutionary model of the slope, a series of numerical modelings were performed for the study of the DSGSD. The analyses allowed us to reconstruct: (i) the mechanism of the process, (ii) the rheological behavior of the rock mass, and (iii) the main predisposing factors of the gravitational deformation. Numerical modeling has demonstrated the significant role played by the inherited structures on the DSGSD and, in particular, the importance of an intensely jointed stratigraphic level in the development of the BSZ.

Investigation of the Luco dei Marsi DSGSD revealing the first evidence of a basal shear zone in the central Apennine belt (Italy)

Deep-seated gravitational slope deformations (DSGSDs) show a wide range of geomorphological characteristics and kinematic behaviours. In many cases, deforming rock masses move on a continuous surface or a thick basal shear zone (BSZ) overlying the stable bedrock. The nature of this boundary is a significant issue in scientific debates since examples of BSZs have been observed or inferred in some DSGSDs worldwide. In the central Apennines, although several cases of DSGSDs have been described in recent decades, no evidence of BSZs has been documented thus far.This work presents the first case of a BSZ found in the region at the bottom of a large-scale gravitational deformation that affects the Mesozoic-Cenozoic carbonate ridge overhanging the Luco dei Marsi village (Abruzzi region). The BSZ consists of several metres-thick, cataclastic breccia developed within middle-Upper Cretaceous biodetritic limestone. The breccia level is exposed for approximately 200 m with a subhorizontal geometry and shows severe rock damage and weathering.The DSGSD hosting the BSZ affects an NNW-SSE-oriented and wide Miocene anticline whose eastern limb is dismembered by Pliocene-Quaternary normal faults delimiting the edge of a large Quaternary intermontane basin (the Fucino Basin). Field survey, aerial photointerpretation, and remote sensing (DInSAR technique) analyses outline an active gravity-driven process. This is characterized by several kinds of geomorphological features, including downhill- and uphill-facing scarps, ridge-top depressions, gravitational grabens and trenches in the upper and middle parts of the ridge, and bulging at the toe of the slope. These features, which can be distinguished from tectonic elements due to their shape and extension, are an indication of a high degree of internal deformation and a compound sagging geometry for the Luco dei Marsi DSGSD.The short-term activity of the process was revealed by DInSAR time series covering almost thirty years of satellite datasets, including ERS1/2, ENVISAT, COSMO-SkyMed, and SENTINEL 1 constellations. Strain rates on the order of a few mm/yr were inferred, with a marked difference between different sectors of the DSGSD area. The long-term (y > 102) lifespan of the DSGSD was framed into a multiple-step conceptual model summarizing the Early Pleistocene-Holocene geological evolution of the area. The model results outline the control exercised by extensional tectonics on DSGSD development, as progressive displacements along normal faults in the latest Pleistocene were the cause of lateral unconfinement at the toe of the slope.This work further contributes to the increasing knowledge on DSGSDs in the central Apennines and the understanding of the relationship between deformation features induced by slope morphogenesis, such as the BSZ, and Quaternary tectonics within the mountain belt.

Alpine subduction zone metamorphism in the Palaeozoic successions of the Monti Romani (Northern Apennines, Italy)

AbstractThe hinterland of the Cenozoic Northern Apennines fold‐and‐thrust belt exposes the metamorphic roots of the chain, vestiges of the subduction‐related tectono‐metamorphic evolution that led to the buildup of the Alpine orogeny in the Mediterranean region. Like in other peri‐Mediterranean belts, the tectono‐metamorphic evolution of the Palaeozoic continental basement in the Apennines is still poorly constrained, hampering the full understanding of their Alpine orogenic evolution. We report the first comprehensive tectono‐metamorphic study of the low‐grade metasedimentary (metapsammite/metapelite) succession of the Monti Romani Complex (MRC) that formed after Palaeozoic protoliths and constitutes the southernmost exposure of the metamorphic domain of the Northern Apennines. By integrating fieldwork with microstructural studies, Raman spectroscopy on carbonaceous material and thermodynamic modelling, we show that the MRC preserves a D1/M1 Alpine tectono‐metamorphic evolution developed under HP–LT conditions (~1.0–1.1 GPa at T ~ 400°C) during a non‐coaxial, top‐to‐the‐NE, crustal shortening regime. Evidence for HP–LT metamorphism is generally cryptic within the MRC, dominated by graphite‐bearing assemblages with the infrequent blastesis of muscovite ± chlorite ± chloritoid ± paragonite parageneses, equilibrated under cold palaeo‐geothermal conditions (~10°C/km). Results of this study allow extending to the MRC the signature of subduction zone metamorphism already documented in the hinterland of the Apennine orogen, providing further evidence of the syn‐orogenic ductile exhumation of the HP units in the Apennine belt. Finally, we discuss the possible role of fluid‐mediated changes in the reactive bulk rock composition on mineral blastesis during progress of regional deformation and metamorphism at low‐grade conditions.

Basic Role of Extrusion Processes in the Late Cenozoic Evolution of the Western and Central Mediterranean Belts

Tectonic activity in the Mediterranean area (involving migrations of old orogenic belts, formation of basins and building of orogenic systems) has been determined by the convergence of the confining plates (Nubia, Arabia and Eurasia). Such convergence has been mainly accommodated by the consumption of oceanic and thinned continental domains, triggered by the lateral escapes of orogenic wedges. Here, we argue that the implications of the above basic concepts can allow plausible explanations for the very complex time-space distribution of tectonic processes in the study area, with particular regard to the development of Trench-Arc-Back Arc systems. In the late Oligocene and lower–middle Miocene, the consumption of the eastern Alpine Tethys oceanic domain was caused by the eastward to SE ward migration/bending of the Alpine–Iberian belt, driven by the Nubia–Eurasia convergence. The crustal stretching that developed in the wake of that migrating Arc led to formation of the Balearic basin, whereas accretionary activity along the trench zone formed the Apennine belt. Since the collision of the Anatolian–Aegean–Pelagonian system (extruding westward in response to the indentation of the Arabian promontory) with the Nubia-Adriatic continental domain, around the late Miocene–early Pliocene, the tectonic setting in the central Mediterranean area underwent a major reorganization, aimed at activating a less resisted shortening pattern, which led to the consumption of the remnant oceanic and thinned continental domains in the central Mediterranean area.

Segmentation of the Apenninic Margin of the Tyrrhenian Back‐Arc Basin Forced by the Subduction of an Inherited Transform System

AbstractThe Tyrrhenian back‐arc basin developed at the rear of the E‐ward migrating Apennine fold‐and‐thrust belt, with northward decreasing rollback of the subducting Adria slab leading to northward fading of back‐arc extension. The northern portion of the Tyrrhenian basin is made of thinned continental crust, whereas in the central/southern portion extension eventually evolved to oceanic crust production. In this framework, a long‐lasting debate concerns the existence of a >200 km long transform zone along the 41st parallel, which should separate the two portions of the Tyrrhenian basin. At its eastern termination, a branch of the presumed transform zone enters the Tyrrhenian margin of the Apennine belt and occurs as an accommodation zone made of a ribbon of extensional faults and related basins. This accommodation zone, which separates areas of mutually perpendicular extension directions, is here introduced, described, and named the Ponza‐Alife accommodation zone. Interpretation of seismic lines and new structural and stratigraphic data from this accommodation zone have been used to constrain the pre‐orogenic and syn‐orogenic architecture of the subducting plate and the Plio‐Quaternary back‐arc extensional stage. Our data indicate that the studied zone retraces a deep‐seated transform fault system located in the subducting plate and inherited from an Early Jurassic rifting episode, which caused the lateral juxtaposition of different rift domains in the subducting plate. We propose that during collision and trench retreat, this lateral juxtaposition has controlled differential retreat of the subducting plate across the studied zone, forcing the development of the Ponza‐Alife accommodation zone in the overlying back‐arc basin's margin.

Coseismic vertical ground deformations vs. intensity measures: Examples from the Apennines

DInSAR data provide a powerful tool to recognize the Earth's surface where permanent deformations are concentrated and undergo the strongest ground motion during an earthquake, i.e., defining the epicentral area. We analyzed three recent seismic events in the Apennines belt in Italy related to extensional and contractional earthquakes and documented that the largest macroseismic intensity is recorded where the ground underwent the largest vertical component of motion and the stronger vertical component of the peak ground acceleration. Besides site amplification effects that may occur everywhere even outside the epicentral area, we infer that the vertical oscillations in the so-called near-field allow the horizontal shaking to be more effective, hence producing larger damage above the active crustal volume. The active volume is the one moving vertically and is contemporaneously crossed by seismic waves nucleated by the shear on the fault. The surrounding passive volume in the far field is only crossed by seismic waves. The near field areas are elliptical and cover areas of 300–600 km2 for a range of Mw 6–6.9, and they should be the areas where the highest seismic hazard must be expected. Therefore, their area is too large to be neglected for seismic hazard assessment.

The Alps-Apennines Interference Zone: A Perspective from the Maritime and Western Ligurian Alps

In SW Piemonte the Western Alps arc ends off in a narrow, E-W trending zone, where some geological domains of the Alps converged. Based on a critical review of available data, integrated with new field data, it is concluded that the southern termination of Western Alps recorded the Oligocene-Miocene activity of a regional transfer zone (southwestern Alps Transfer, SWAT) already postulated in the literature, which should have allowed, since early Oligocene, the westward indentation of Adria, while the regional shortening of SW Alps and tectonic transport toward the SSW (Dauphinois foreland) was continuing. This transfer zone corresponds to a system of deformation units and km-scale shear zones (Gardetta-Viozene Zone, GVZ). The GVZ/SWAT developed externally to the Penninic Front (PF), here corresponding to the Internal Briançonnais Front (IBF), which separates the Internal Briançonnais domain, affected by major tectono-metamorphic transformations, from the External Briançonnais, subjected only to anchizonal metamorphic conditions. The postcollisional evolution of the SW Alps axial belt units was recorded by the Oligocene to Miocene inner syn-orogenic basin (Tertiary Piemonte Basin, TPB), which rests also on the Ligurian units stacked within the adjoining Apennines belt in southern Piemonte. The TPB successions were controlled by transpressive faults propagating (to E and NE) from the previously formed Alpine belt, as well as by the Apennine thrusts that were progressively stacking the Ligurian units, resting on the subducting Adriatic continental margin, with the TPB units themselves. This allows correlation between Alps and Apennines kinematics, in terms of age of the main geologic events, interference between the main structural systems and tectonic control exerted by both tectonic belts on the same syn-orogenic basin.

Investigation of the Luco Dei Marsi DSGSD Revealing the First Evidence of a Basal Shear Zone in the Central Apennine Belt (Italy)

Investigation of the Luco Dei Marsi DSGSD Revealing the First Evidence of a Basal Shear Zone in the Central Apennine Belt (Italy)

Mantle upwelling beneath the Apennines identified by receiver function imaging

Magmatism, uplift and extension diffusely take place along collisional belts. Even though links between mantle dynamics and shallow deformation are becoming more evident, there is still poor understanding of how deep and surface processes are connected. In this work, we present new observations on the structure of the uppermost mantle beneath the Apennines belt. Receiver functions and seismic tomography consistently define a broad zone in the shallow mantle beneath the mountain belt where the shear wave velocities are lower than about 5% and the Vp/Vs ratio is higher than 3% than the reference values for these depths. We interpret these anomalies as a pronounced mantle upwelling with accumulation of melts at the crust-mantle interface, on top of which extensional seismicity responds to the crustal bending. The melted region extends from the Tyrrhenian side to the central part of the belt, with upraise of fluids within the crust favored by the current extension concentrated in the Apennines mountain range. More in general, mantle upwelling, following detachment of continental lithosphere, is a likely cause for elevated topography, magmatism and extension in post-collisional belts.

Constraints on the Structure of the Shallow Crust in Central Italy from Geophysical Log Data

To better define the seismic velocities of the shallow crust in central Italy, in the area affected by the 1997 Colfiorito, 2009 L’Aquila and 2016–2018 Amatrice–Norcia seismic sequences, we selected all deep wells with available sonic logs from the Apennine belt to the related Adriatic foredeep. Sonic logs are among the most important in situ measurements of rock properties and provide a reliable image of physical conditions at depth. By analysing the wave train transit times, we inferred the P-wave velocity within depth intervals displaying homogeneous sonic log properties, and estimated the rock density by applying an empirical relationship between the sonic velocity and density in sedimentary rocks. We compared these results with the main litho-stratigraphic units in stratigraphic profiles of the wells. From the density estimates, we inferred the trends of the vertical stress magnitude in the belt, eastern front and foredeep geodynamic domains. This work is a contribution to better interpretation of physical conditions at depth and provides data that can be applied to define more complete seismological, gravity and magnetic models. We provide data uncertainties that must be considered to ensure proper use of data and to evaluate the spatial resolution of the models derived from those data.

The 2013–2018 Matese and Beneventano Seismic Sequences (Central–Southern Apennines): New Constraints on the Hypocentral Depth Determination

The Matese and Beneventano areas coincide with the transition from the central to the southern Apennines and are characterized by both SW- and NE-dipping normal faulting seismogenic structures, responsible for the large historical earthquakes. We studied the Matese and Beneventano seismicity by means of high-precision locations of earthquakes spanning from 29 December 2013 to 4 September 2018. Events were located by using all of the available data from temporary and permanent stations in the area and a 1D computed velocity model, inverting the dataset with the Velest code. For events M > 2.8 we used P- and S-waves arrival times of the strong motion stations located in the study area. A constant value of 1.83 for Vp/Vs was computed with a modified Wadati method. The dataset consists of 2378 earthquakes, 18,715 P- and 12,295 S-wave arrival times. We computed 55 new fault plane solutions. The mechanisms show predominantly normal fault movements, with T-axis trends oriented NE–SW. Only relatively small E–W trending clusters in the eastern peripheral zones of the Apenninic belt show right-lateral strike-slip kinematics similar to that observed in the Potenza (1990–1991) and Molise (2002 and 2018) sequences. These belong to transfer zones associated with differential slab retreat of the Adriatic plate subduction beneath the Apennines. The Matese sequence (December 2013–February 2014; main shock Mw 5.0) is the most relevant part of our dataset. Hypocentral depths along the axis of the Apenninic belt are in agreement with previous seismological studies that place most of the earthquakes in the brittle upper crust. We confirm a general deepening of seismicity moving from west to the east along the Apennines. Seismicity depth is controlled by heat-flow, which is lower in the eastern side, thus causing a deeper brittle–ductile transition.

Travertine deposits constraining transfer zone neotectonics in geothermal areas: An example from the inner Northern Apennines (Bagno Vignoni-Val d’Orcia area, Italy)

Studying travertine deposits and the network of banded calcite veins that form their roots in the substratum can place important constraints on neotectonic activity and the seismotectonic settings of geothermal areas. In this paper, we present the results of integrated studies of a geothermal area located in the inner Northern Apennines (Bagno Vignoni area, Italy), where low magnitude (M < 4) seismicity suggests the occurrence of active faults, but information on their location, time-span of activity and seismotectonic setting is lacking. The study area is characterised by thermal springs (T<50 °C) and travertine deposits well exposed in saw-cut walls of abandoned quarries. We investigate the relationships between faults and the travertine deposits, in order to reconstruct the syn-sedimentary tectonic activity and the age of faulting, by combining analyses of: i) geological setting and structural/kinematic analyses of faults; ii) travertine morpho-structural and architectural setting; iii) travertine facies; iv) U-Th radiometric, stable- and clumped isotopes of travertine and banded calcite veins. The results highlight the occurrence of a wide brittle shear zone (>3 km) formed by two orthogonal faults systems, NE- and NW-striking, characterised by oblique-slip to normal kinematics, respectively; these faults belong to a tract of the so-named “Grosseto-Pienza” transfer zone, crossing the southern Tuscany from the sea-cost to the outer Apennines belt. The Grosseto-Pienza transfer zone formed with extensional tectonics that have been affecting the inner Northern Apennines since the middle Miocene. U-Th dating of travertine and banded calcite veins indicates that faulting enhanced the hydrothermal fluid circulation since the middle Pleistocene, in an unvaried tectonic setting, as indicated by the δ18O signature and temperature of the hydrothermal fluids, which remained stable through time. The activity of the faults continued until the Holocene and still produces seismicity. Finally, our findings permit to define the seismo-tectonic setting of this sector of the inner Northern Apennines, demonstrating more broadly the utility of travertine deposits in reconstructing the neotectonics in geothermal areas.

Erosion of Tortonian phosphatic intervals in upwelling zones: The role of internal waves

During the Miocene, the upwelling is assumed to be important in the formation of many Mediterranean phosphate deposits in carbonate platform successions.There are different types of upwelling mechanisms such as equatorial upwellings, ice-edge upwellings and coastal upwellings. The carbonate platforms are mainly affected by wind-driven coastal upwelling systems. During upwelling season, the seawater in coastal areas is strongly density stratified and the permanent pycnocline rises inshore forming an inclined frontal layer. The liaison between upwellings and internal waves is widely documented in the literature. Internal waves result from perturbations of the hydrostatic equilibrium, where balance is sustained between the force of gravity and buoyant restoring force. Many perturbations of the pycnocline can propagate as an internal wave. In a coastal upwelling, a key role for wave propagation is played by permanent pycnocline. The run-up swash currents develop during the break of internal waves and produce erosional processes. In particular, the backwash return flow may induce the erosion of seafloor sediments and transport these sediments downslope as bedload.Erosion of phosphate-rich intervals has been extensively documented. The deposition of gravity-flow sediments is followed by intervals of non-deposition, incipient lithification, phosphogenesis and erosion. In this work, we evaluate the role of internal waves in the formation of the resedimented phosphate-rich intervals characterising the basal portion of the hemipelagic Orbulina marls. These marls are deposited on the low-angle Latium-Abruzzi carbonate ramp and represent deposition in a foreland basin during the initial stages of evolution of the Central Apennine Belt during the early Tortonian age.

Aftershock Patterns in Recent Central Apennines Sequences

AbstractDuring the last 20 years, three seismic sequences affected the Apenninic belt (central Italy): Colfiorito (1997–1998), L'Aquila (2009), and Amatrice Visso‐Norcia Campotosto (2016–2017). They lasted for a long time, with a series of moderate‐to‐large earthquakes distributed over 40‐ to 60‐km‐long Apenninic‐trending segments. Their closeness in space and time suggested to study their aftershock sequences to highlight similarities and differences. Aftershock space migration and the distribution of aftershock interarrival times were studied. Mathematical Morphology and nonparametric statistics were applied to reduce the effect of spatial noise. Parametric analysis in time domain and spectral analysis were performed. Two different types of aftershock sequences were found. The L'Aquila sequence presented a continuous and periodic temporal variation (period ≃120 days) of aftershock activity center along the sequence axis, while the other two sequences showed a piecewise continuous pattern and a shorter duration. We also found two different types of temporal evolution of the mean radial distance between the aftershock hypocenters and the one of a reference event corresponding to the start of a large and fast increase of daily energy release. One type was well described by a simple exponential model, while a power law model was more appropriate for the other one. Furthermore, in the first case, the aftershock interarrival time was very well fitted by an exponential model, while noticeable deviations were present in the other case. A possible explanation was provided in terms of the local geological and hydrogeological properties, which depend on the region location with respect to the Ancona‐Anzio tectonic lineament.

How and why the present tectonic setting in the Apennine belt has developed

The building of the Apennine belt slowed down or ceased around the Early Pleistocene. Since then, the belt has undergone strong uplift and considerable distortion. This change, from belt-normal to belt-parallel shortening, has been determined by the fact that the continental Adriatic domain (Adria) was almost completely surrounded by buoyant orogenic structures. In that context, the mobility of Adria underwent a considerable reduction, whereas uplift and deformation of its southern part was strongly emphasized as an effect of the convergence of the confining plates. Around the middle Pleistocene, the deformation pattern in the peri-Adriatic zones changed again, in response to acceleration of Adria. The outer (Adriatic) sector of the Apennine belt underwent belt-parallel shortening, accommodated by uplift and outward escape of upper crustal wedges. The separation between the extruding wedges and the almost stable inner belt has generated a series of extensional or transtensional fault systems along the axial part of the Apennines, which now correspond to the main seismogenic sources. The spatio-temporal distribution of major tectonic events in the study area can plausibly be explained as an effect of the least-action principle. Thematic collection: This article is part of the ‘Apennines and Tyrrhenian system’ collection available at: https://www.lyellcollection.org/cc/the-apennines-tyrrhenian-system