Sabina Bigi

Decollement depth versus accretionary prism dimension in the Apennines and the Barbados

(1) Along representative cross sections of the Apennines and the Northern Barbados accretionary prisms, we measured the area, the decollement depth, the angle a of the upper envelope and the angle b of the dip of the regional monocline. The continental sections of the Apennines accretionary prism have a deeper decollement than the oceanic sections of the Northern Barbados, 6-10 km depth and <1 km depth, respectively, because the sediment pile is thinner on the incoming Barbados plate and its denser oceanic structure is more easily subducted. Considering the frontal 50 km, the Apennines have an average cross- sectional area of 500 km 2 and the Northern Barbados Ridge of 100 km 2 . The total area is a function of the depth of the decollement plane. Therefore, at a given amount of subduction, the deeper the decollement depth is, the bigger the area of the wedge will result, assuming negligible compaction and erosion. As a consequence, the larger area/volume and higher elevation of the Apennines with respect to the Barbados is determined by the Apenninic deeper decollement. Despite these differences, the geometry of both decollements is, in some cases, comparable, in particular, close to the boundary between the crystalline crust and the sediment pile, where the main density and strength contrasts are concentrated. Variations in depth of the decollement occur moving along strike in both accretionary prisms. The geometry of the prisms is further controlled by the different values of a and b, their sum, and the distance of the accretionary prism relative to the subduction hinge. INDEX TERMS: 8099 Structural Geology: General or miscellaneous; 8150 Tectonophysics: Evolution of the Earth: Plate boundary—general (3040); 8122 Tectonophysics: Dynamics, gravity and tectonics; KEYWORDS: decollement depth, accretionary prism, Apennines, Barbados. Citation: Bigi, S., F. Lenci, C. Doglioni, J. C. Moore, E. Carminati, and D. Scrocca, Decollement depth versus

The tectonic puzzle of the Messina area (Southern Italy): Insights from new seismic reflection data

The Messina Strait, that separates peninsular Italy from Sicily, is one of the most seismically active areas of the Mediterranean. The structure and seismotectonic setting of the region are poorly understood, although the area is highly populated and important infrastructures are planned there. New seismic reflection data have identified a number of faults, as well as a crustal scale NE-trending anticline few km north of the strait. These features are interpreted as due to active right-lateral transpression along the north-eastern Sicilian offshore, coexisting with extensional and right-lateral transtensional tectonics in the southern Messina Strait. This complex tectonic network appears to be controlled by independent and overlapping tectonic settings, due to the presence of a diffuse transfer zone between the SE-ward retreating Calabria subduction zone relative to slab advance in the western Sicilian side.

Seismic interpretation of the Laga basin; constraints on the structural setting and kinematics of the Central Apennines

Abstract: The Messinian Laga basin is the largest foreland basin within the Central Apennines fold and thrust belt (Italy). This area, actively investigated in the 1980s and 1990s for hydrocarbon resources, is considered a valuable analogue for clastic reservoirs developed in confined structural settings. Furthermore, it represents a key area for understanding the evolution of the Apennines, as it links the internal, structurally uplifted Early Miocene fold and thrust belt of the western Central Apennines with the more external and recent belt to the east. Despite several papers published on this area, the only reconstruction of the substratum structure is an internal and classified industry report. During the present study, we had access to a seismic database comprising 200 km of seismic profiles that were collected between 1983 and 1990. These data allowed us to reconstruct the structural setting of the Laga basin substratum, define the lateral continuity of the main compressional structures within the basin, construct a balanced cross-section, and define the shortening values.

Soil gas distribution in the main coseismic surface rupture zone of the 1980, Ms = 6.9, Irpinia earthquake (southern Italy)

Soil gas measurements of different gas species with different geochemical behaviors were performed in the area of the Pecore Plain, a 200 m × 300 m sized, fault-bounded extensional basin located in the northern Mount Marzano massif, in the axial belt of the southern Apennine chain. The Pecore Plain area was affected by coseismic surface faulting during the Ms = 6.9, 1980 Irpinia earthquake, the strongest and most destructive seismic event of the last 30 years in southern Italy. The collected data and their geostatistical analysis provide new insights into the control exerted by active fault segments on deep-seated gas migration toward the surface. The results define anomalies that are aligned with the NW-SE trending coseismic rupture of the 1980 earthquake along the western border of the plain, as well as along the southern border of the plain where a hidden, E-W striking fault is inferred. Geospatial analysis highlights an anisotropic spatial behavior of 222Rn along the main NW-SE trend and of CO2 along the E-W trend. This feature suggests a correlation between the shape and orientation of the anomalies and the barrier/conduit behavior of fault zones in the area. Furthermore, our results show that gas migration through brittle deformation zones occurs by advective processes, as suggested by the relatively high migration rate needed to obtain anomalies of short-lived 222Rn in the soil pores.

Spatial and Temporal pCO2 Marine Monitoring Near Panarea Island (Italy) Using Multiple Low-Cost GasPro Sensors

The present paper describes the GasPro probe, a small, low-cost unit for in situ, continuous pCO2 monitoring. Laboratory tests defining its performance characteristics are reported, as are the results from a 60 h water-column deployment of 20 such units near a natural CO2 seep site off the coast of Panarea Island (Italy). The spatial-temporal evolution of dissolved CO2 movement is presented and possible origins and controlling mechanisms discussed. Results highlight the potential for this technology to be used for better understanding various dynamic physical and biochemical processes in marine environments, and for marine environmental monitoring of off-shore industrial sites. These experiments have allowed us to assess the advantages and disadvantages of the present GasPro prototype and to define areas for ongoing improvement.

Kinematic evolution and strain simulation, based on cross-section restoration, of the Maiella Mountain: an analogue for oil fields in the Apennines (Italy)

Abstract Deformation predictive methods are useful for structural analysis from the scientific and industry point of view. We apply a strain simulation technique based on the inclusion of graphical strain markers in a cross-section, and subsequent cross-section restoration and numerical processing of strain markers, to the seismic-scale Maiella Mountain anticline (Central Apennines, Italy) considered a carbonate reservoir analogue for Apennines oil fields. The procedure followed involves field mapping and structural data collection, construction of cross-sections, sequential cross-section restoration, and application of the strain simulation technique. The cross-sections presented were constructed adopting one of the various structural interpretations proposed for this structure by different authors. According to this interpretation the Maiella Mountain structure resulted from Messinian–Early Pliocene extension and subsequent Late Pliocene shortening. According to our structural model the Maiella structure is a break-thrust fold and the comparison between the present-day and the restored cross-sections yields 1.3–4.6% of extension associated with two main normal faults and 21.5–22.1% and 2.5–3.4% of shortening due to a major thrust and folding respectively. The simulation of deformation distribution shows high deformation intensity in both limbs and low deformation in the anticline crest and part of the thrust footwall.

Discrete fracture network of the Latemar carbonate platform

The Latemar massif represents a good analogue of a carbonate fractured reservoir. Fractures are widely exposed all over the mountain and the stratigraphic relationships among carbonate platform units, such as the platform margin and slope, are very well preserved. Having escaped pervasive dolomitization, the Latemar is renowned for the study of Triassic stratigraphy and of the evolution of Triassic carbonate build-ups of Western Tethys. In this paper we present the results of fracture modelling performed at Latemar, by the construction of a discrete fracture network in the lower part of the stratigraphic sequence. The modelling methodology consists in using field data for generating fracture network models that can be used to represent the fracture density variability and to estimate permeability distribution on at a regional scale. These models can also be useful in the study of other petrophysical parameters, for instance generating synthetic seismic datasets for comparison with reservoirs in the subsurface.

Discussion on «Geological map of the partially dolomitized Jurassic succession exposed in the central sector of the Montagna dei Fiori Anticline, Central Apennines, Italy» by

In their paper on the Montagna dei Fiori area, [Storti et alii (2017][1]) present a new geological map and discuss the dolomitization pattern and the Jurassic extensional architecture of this sector of the Central Apennines. They conclude that their “field evidence does not support the gravity-

Discussion on «Geological map of the partially dolomitized Jurassic succession exposed in the central sector of the Montagna dei Fiori Anticline, Central Apennines, Italy» by G. Storti, F. Balsamo & A. Koopman (2017)

In their paper on the Montagna dei Fiori area, [Storti et alii (2017][1]) present a new geological map and discuss the dolomitization pattern and the Jurassic extensional architecture of this sector of the Central Apennines. They conclude that their “field evidence does not support the gravity-

The Laga Basin: stratigraphic and structural setting

Most of the ancient turbidite systems are known being deposited in foredeep basins at the front of active thrust belt. Differently from fluvio-deltaic systems generally lacated in the more internal portion of these basins, the turbidite systems occur at different depth in the more deeper portions of these basins (foredeep turbidite systems) or in the relatively shallower tectonically confined depressions occurring on top of the thrust belt (wedge-top turbidite systems) (see discussion in Mutti et al. 2002, 2003). Foredeep turbidite systems represent the classical sedimentation in a broad and flat basin plain, showing thick to thin parallel and continuous sandstone beds with the Bouma-type depositional division. Wedge-top turbidite systems are directly fed by fluvio-deltaic systems and more clearly record both climate changes affecting the source areas and tectonic activity of the orogenic wedge. Messinian turbidite deposits of the northern and central Apennines show many characters indicating sedimentation in confined basins, formed since the upper Tortonian in relation to the segmentation of the Langhian-lower Tortonian Marnoso- Arenacea foredeep basin (inner stage of the Marnoso-Arenacea, Ricci Lucchi, 1986). In these last years, detailed facies and physical stratigraphic analyses as a well as structural and thermal analyses, conducted on the Laga and Argilloso-Arenacea Fms (central Apennines), demonstrate as these basins were located at the hinge between foredeep and wedge-top depozones of the Messinian Apennine thrust belt (Milli and Moscatelli, 2000, 2001; Bigi et al., 2003; Moscatelli, 2003; Milli et al., 2004; Falcini et al., 2006; Stanzione et al., 2006; Casero and Bigi, 2006; Aldega et al., 2006; Critelli et al., 2007; Milli et al., 2007). Anisotropy of the subducted plate and thrust propagation rate deeply controlled the onset of complex basins at the top of the orogenic wedge (Casero and Bigi 2006; Bigi et al., 2006). The resulting topography of these basins and the concomitant climate changes exerted a strong control on turbidite sedimentation and on the stratigraphic organization of these deposits.