Sicilian Fold Research Articles

Jurassic–Cretaceous intraplatform basins from NW Sicily fold and thrust belt: Implications for oblique rifting of the Southern Tethyan margin

Carbonate intraplatform basins are documented worldwide as peculiar synsedimentary tectonic features forming in rifted margins and especially in those cases where the direction of extension is oblique with respect to the rift axis. A detailed stratigraphy and facies analysis combined with subsidence history of the Upper Triassic-Cretaceous shallow-water carbonates outcropping in the Peninsula of Capo San Vito, representing the NW end of the Sicilian fold and thrust belt, has been performed. Three different sections, separated by faults and characterised by shallow-water and deep-water carbonate sedimentation, were distinguished. Their location and tectonic relationships highlight the occurrence of two structural highs (Monaco and Sparagio sections) separated by a structural low (Acci section).The Acci intraplatform basin, structured since the Pliensbachian, is characterised by mostly pelagic sedimentation with resedimentation of carbonate reef derived-elements from adjacent carbonate platform blocks. On the two structural highs, shallow-water sedimentation, since the Late Triassic, developed with progradational trends shedding out shallow-water elements towards the basin. The evolution of the narrow Acci intraplatform basin appears influenced by a transtensional regime creating a wedge-shaped basin. Backstripping analysis on the three measured sections was able to reconstruct subsidence curves, from which different evolutionary stages, marked by punctual synsedimentary tectonic activity, can be highlighted for the Late Triassic-Eocene time interval.Comparison with the adjacent basin system of Cala Rossa, located 30 km away eastward in the Palermo Mountains, allowed to recognise similar characteristics. The stratigraphic, sedimentologic and tectono-sedimentary common features, trend and kinematic of the paleofaults, and the same chronology of tectonic events, suggest that the two areas represent adjacent basins making part of a unique spindle-shaped basin system. Some variable evolutionary characteristics among the Acci and Cala Rossa basins, including the overall thicknesses, the thickness of the resedimented deposits, the occurrence of Upper Cretaceous shallow-water deposits only in the structural highs of the Acci Basin, are explained as features linked to the different location of the two basins with respect to the master fault. Many of the observed features are described from those rift systems where the direction of extension is not perpendicular to the rift axis, suggesting that this sector of the Southern Tethyan margin could be developed as an oblique rift system.

Active north-vergent thrusting in the northern Sicily continental margin in the frame of the quaternary evolution of the Sicilian collisional system

A three-stage evolution has characterized the Sicilian Fold and Thrust Belt (SFTB) during the last 15 My: two main thin-skinned shortening events involving mainly Meso-Cenozoic carbonate units, followed by thick-skinned thrusting involving Plio-Pleistocene deposits in the frontal area as well as the crystalline basement in the inner and deeper sector of the chain. We investigated the northern Sicily continental margin, by using differently-penetrative seismic reflection data and new field surveys, which revealed, both offshore and onshore, north-vergent compressional structures that affected the tectonic edifice during Quaternary time. These structures, correlated with the kinematic setting pointed out by seismicity and GPS measurements, could disclose an important change in distribution and orientation of deformation in the frame of the Africa-Europe convergence. Our hypothesis is that the most recent tectonic processes in the northern Sicily continental margin are representative of a jump of the deformation from the frontal area of the SFTB in the Sicily Channel to the inner sector in the Southern Tyrrhenian Sea. This study is in agreement with recent interpretations about a change in the subduction polarity in the central Mediterranean orogenic system, as a consequence of the ongoing collision of the African promontory with the thinned continental to oceanic sectors (Algerian and Tyrrhenian basins) of the European plate.The seismic activity associated with the north-vergent thrust could have implication for the assessment of the seismic risk in the Central Mediterranean and understanding of active structures in marine areas that could be responsible for tsunami hazard.

Synsedimentary tectonics vs paleoclimatic changes across the Aptian-Albian boundary along the Southern Tethyan margin: The panormide carbonate platform case history (NW Sicily)

The Aptian-Albian boundary is a deeply investigated time interval on the basis of the deep oceanographic, environmental and climatic changes, globally recorded along the sedimentary rock successions.A regional latest Aptian extensional pulse in the Southern Tethyan margin is here envisaged as being responsible for different events of sedimentation and erosion in the Panormide carbonate platform as highlighted by the outcropping sections studied from the NW Sicilian fold and thrust belt.Integrating facies and stratal pattern analysis with backstripping methods has permitted to define the interaction between tectonics and sedimentary factors of the Lower Cretaceous shallow-water carbonates.Based on geometric configuration, lateral facies relationships, and thicknesses variations of the Lower Cretaceous Requienid limestone, is here envisaged a paleophysiography characterised by banks separated by deep channels. The margins of the isolated carbonate platform were oriented towards both the present-day west, where originally the Cala Rossa intraplatform basin developed driven by transtensional movements, and to the present-day east, where the continental slope was spreading.Including subsidence analysis and significance of the top-unconformity of the Requienid limestone a tectonic event at the end of the Aptian was detected as responsible for the fragmentation of the platform in various rotating fault-blocks and reworking of shallow-water carbonates towards the slope. The variable subsidence rates correspond to the different responses, both emersion and drowning, of the various platform-blocks to the extensional tectonics.Paleoceanographic changes, detected around the world during the Aptian-Albian, are well recorded also from the Sicilian sections, where continental clays – as the product of weathering of crystalline rocks – metallic crusts (hardgrounds) and condensed phosphatized pelagic deposits – as the product of sediment starvation, condensation and drowning – cover the Lower Cretaceous shallow-water carbonates respectively in the different faulted blocks of the segmented carbonate platform. Chemical and mineralogical analyses confirm for these deposits an influence in their formation caused by variations in oceanographic and environmental conditions, as increasing of metal ions in the surficial sea-water and high rates of groundwater precipitation. Paleoclimate evaluation reveals changes from the greenhouse arid conditions, developed during the lower Cretaceous and permitting the sedimentation of the shallow-water carbonates, to warm-humid climate condition during the latest Aptian-lower Albian boundary.

Mesozoic tectono-sedimentary evolution of the Trapanese SouthernTethyan margin (NW Sicily) integrating facies and stratigraphic analysis with subsidence history

Several Mesozoic successions of the Southern Tethyan margin were accumulated on a carbonate platform evolving to pelagic plateau depositional systems. Rifting paleotectonics was the main process conditioning their tectono-sedimentary evolution. The well-exposed outcrops in the NW Sicilian fold and thrust belt of the so-called Trapanese carbonate platform to pelagic succession highlight the occurrence of lateral facies and thickness changes, paleofaults, volcanics, and resedimented deposits. The integration of facies analysis, stratigraphic data, and subsidence history have permitted to decipher the polyphase tectono-sedimentary evolution and to distinguish different depositional settings. Structural lows, filled with up to 100m of pillow lavas and reworked deposits, appear as intraplatform basins bordered by structural highs, as horst ridges, characterised by condensed sedimentation, and isolated seamounts. These sectors were linked among them by stepped fault margins, scalloped margins and depositional slopes. The tectonic history, highlighted by the backstripped sections, reveals superimposed evolutionary stages reflecting rifting and rapid tectonic subsidence, leading to continental break-up (Late Triassic-Early Jurassic stage); the Middle Jurassic stage reflects slow thermal subsidence in the basin shoulders and higher rates in the intervening depressions; the Late Jurassic-Early Cretaceous regional uplift interrupts the thermal subsidence curve trend. The tract of the Late Cretaceous-Eocene curve suggests again slow thermal post-rift subsidence, also influenced by sediment load. The different subsidence curves, reconstructed from different positions in the sedimentary basin, demonstrate that its evolution could be driven by the identified syn-sedimentary faults that were formed and/or re-activated during several tectonic events encompassing the whole Jurassic-Cretaceous time period. The regional significance of this tectonics indicates that the Sicilian sector of the Southern Tethyan continental margin was tectonically active for the whole Mesozoic.The reconstructed paleophysiography of the Trapanese continental margin, during the Mesozoic, appears characterised by a segmented and drowned carbonate platform with morphostructural highs separated by deep channels. The comparison with the present-day morphostructural setting of some regions of the Atlantic continental margins (e.g. Caribbean, Brazilian equatorial margin), suggests also for the study region that the occurrence of transcurrent/transform faults and stretching of the continental lithosphere can have played an important role in determining the physiographic conformation.

Deep Origin of the Dome‐Shaped Hyblean Plateau, Southeastern Sicily: A New Tectono‐Magmatic Model

AbstractSoutheastern Sicily is characterized by a prominent topography known as the Hyblean Plateau. It is commonly considered as a flexural bulge formed by the northwest plunging of the Hyblean‐Malta platform beneath the Sicilian Fold and Thrust Belt. However its noncylindrical shape and multiphase uplift history correlated to the Late Miocene and Plio‐Pleistocene volcanism outline a possible magmatic control on the Hyblean Plateau topographic expression. We argue, using 2‐D flexural models, that the flexural bending alone is unlikely to explain the high anomalous elevation of the Hyblean Plateau. Moreover, topographic analysis show that the Hyblean Plateau has a dome shape composed of radially tilted preserved surfaces defining individual blocks. The block edges seem to be related to deep‐seated inherited faults. Using an analogue modeling approach, we show that magmatic intrusions beneath the thick Meso‐Cenozoic sedimentary cover can reproduce the first‐order morphology of the Hyblean Plateau when a structural inheritance is imposed. Accordingly, we propose a tectono‐magmatic model that favors mafic sill intrusions as the major uplift source for the topographic anomaly. However, to explain the strong positive Bouguer anomaly, a deeper high‐density intracrustal body is needed. Moho uprising related to Mesozoic rifting or mafic lower crust underplating/intraplating since the Late Cretaceous can be evoked. The small wavelength of the topography and the deep intracrustal mass anomaly makes the lithospheric elastic stresses sufficiently high to maintain a nonisostatic state over the geological time scales.

Multi-temporal tectonic evolution of Capo Granitola and Sciacca foreland transcurrent faults (Sicily channel)

Joint analysis of high-penetration multi-channel and high-resolution single-channel seismic reflection profiles, calibrated by deep well boreholes, allowed a detailed reconstruction of the Late Miocene to Recent tectonic history of the Capo Granitola and Sciacca fault systems offshore southwestern Sicily. These two fault arrays are part of a regional system of transcurrent faults that dissect the foreland block in front of the Neogene Sicilian fold and thrust belt. The Capo Granitola and Sciacca faults are thought to reactivate inherited Mesozoic to Miocene normal faults developed on the northern continental margin of Africa. During Latest Miocene-Pliocene, the two ~NNE-SSW striking faults were active in left transpression, which inverted Late Miocene extensional half-grabens and created push-up ridges along both systems. Tectonic activity decreased during the Pleistocene, but transpressional folds deform Middle-Late Pleistocene sediments as well, suggesting that the two fault systems are active. The ~40 km long longitudinal amplitude profile of 1st order folds (Capo Granitola and Sciacca anticlines) shows ~15–20 km bell-shaped undulations that represents 2nd order folds. The length of these undulations together with the map pattern of faults allowed to divide the CGFS and SFS into two segments, northern and southern, respectively. Total uplift of the Sciacca Anticline is twice than the uplift of the Capo Granitola Anticline. Incremental fold growth rates decreased during time from 0.22 mm/yr (Capo Granitola Anticline) and 0.44 mm/yr (Sciacca Anticline) in the Pliocene, to 0.07 and 0.22 mm/yr, respectively, during the last ~1.8 Ma.

Integrating facies and structural analyses with subsidence history in a Jurassic–Cretaceous intraplatform basin: Outcome for paleogeography of the Panormide Southern Tethyan margin (NW Sicily, Italy)

We illustrate the tectono-sedimentary evolution of a Jurassic–Cretaceous intraplatform basin in a fold and thrust belt present setting (Cala Rossa basin). Detailed stratigraphy and facies analysis of Upper Triassic–Eocene successions outcropping in the Palermo Mts (NW Sicily), integrated with structural analysis, restoration and basin analysis, led to recognize and describe into the intraplatform basin the proximal and distal depositional areas respect to the bordered carbonate platform sectors. Carbonate platform was characterized by a rimmed reef growing with progradational trends towards the basin, as suggested by the several reworked shallow-water materials interlayered into the deep-water succession. More, the occurrence of thick resedimented breccia levels into the deep-water succession suggests the time and the characters of synsedimentary tectonics occurred during the Late Jurassic.The study sections, involved in the building processes of the Sicilian fold and thrust belt, were restored in order to obtain the original width of the Cala Rossa basin, useful to reconstruct the original geometries and opening mechanisms of the basin.Basin analysis allowed reconstructing the subsidence history of three sectors with different paleobathymetry, evidencing the role exerted by tectonics in the evolution of the narrow Cala Rossa basin. In our interpretation, a transtensional dextral Lower Jurassic fault system, WNW–ESE (present-day) oriented, has activated a wedge shaped pull-apart basin.In the frame of the geodynamic evolution of the Southern Tethyan rifted continental margin, the Cala Rossa basin could have been affected by Jurassic transtensional faults related to the lateral westward motion of Africa relative to Europe.

Deep controls on foreland basin system evolution along the Sicilian fold and thrust belt

Abstract Neogene-Quaternary wedge-top-basins arose during the Sicilian fold and thrust belt (FTB) build-up. The infilling sedimentary successions are: i) middle-upper Miocene silicoclastics succession, accommodated on top of the accreted Sicilide and Numidian flysch nappes; ii) upper Miocene-lower Pliocene deepening-upwards sediments unconformably overlying the inner Meso-Cenozoic deep-water, Imerese and Sicanian thrust units; iii) Upper Pliocene-Quaternary coastal-open shelf deposits unconformably covering (in the outer sector of the FTB) a tectonic stack (Gela thrust system). These successions are characterized by a basal unconformity on the deformed substrate believed to be the depositional interface common both to the coeval wedge-top and foredeep basins. The tectono-sedimentary evolution of the syn-tectonic basins was controlled by the progressive deepening of the structural levels, which were active during the growing of the FTB. The palinspastic restoration of a crustal geological transect in central Sicily points to: i) the occurrence of two subsequent, basal main thrusts (MT1 and MT2) active during the Neogene-middle Pleistocene tectonic evolution, as well as ii) a decrease in slip- and shortening-rate, estimated for the later MT2 as compared to earlier MT1 basal main thrust. The foreland-basin system evolution recorded during these two steps suggests: – the regional lithofacies distribution, during late Tortonian-early Pliocene, accounted for a wide depozone including the Iblean plateau and its offshore;– a crucial change was recorded by the late Pliocene-Pleistocene wedge-top depozone, when the deeper basal main thrust (MT2) involved and thickened (in the inner sector of the FTB) the crystalline basement (thin- to thick-skinned thrust tectonics); this change influenced the depozones, progressively narrowing up to the present-day setting. As regards this general evolutionary framework, thin-skinned and thick-skinned thrust tectonics can be recognized in the Sicilian FTB evolution. The late Tortonian-early Pliocene, thin-skinned thrust tectonics include two main tectonic events, a “shallow-seated” Event 1 and a “deep-seated” Event 2, with the Pliocene-Pleistocene thick-skinned thrust tectonics representing a third tectonic event (Event 3).

Geological – structural outlines of the southern Madonie Mts. (Central northern Sicily)

Geological and structural surveys were undertaken in central-northern Sicily along the southern slope of the Madonie Mts., a portion of the Sicilian Fold and Thrust Belt. Collected data have allowed the compilation of a new map of this region at 1:30,000 scale. The map is the result of a classic field survey supported by a combined analysis of 1:33,000 aerial photographs, 1:10,000 ortho-photos, and the use of a high-resolution Digital Elevation Model.The cartographic product displays the distribution of the distinct sedimentary successions and the geometric setting of the major tectonic lineaments, providing further constraints on the geology of the area. The mapped rocks mostly consist of Neogene syn-tectonic sedimentary successions deposited within basins developed in a SE-migrating piggy-back/foredeep system. Thrust-top deposits are floored by a clayey substratum pertaining to a former oceanic domain.The tectonic setting has been reconstructed through the mapping of structural lineaments and compared to available seismic sections. The geometries and orientation of the observed/measured faults and folds and the age of the sediments involved, suggest that since Miocene times the area experienced a multi-phased deformation with previously formed (middle Miocene) large flat thrusts and associated folds, re-deformed by a younger (Upper Miocene to Early Pliocene) and deep-seated thrust and folds system.Strike-slip deformation affected the area after the Early Pliocene with the nucleation of NW-SE-oriented right-lateral faults whose propagation produced vertical axis rotations with a general re-orientation of previously formed structures.

Vertical-axis rotations in the Sicilian fold and thrust belt: new structural constraints from the Madonie Mts. (Sicily, Italy)

A detailed geological and structural analysis was carried out in the Madonie Mts., along the central-northern sector of the Sicilian-Maghrebian Chain, in order to define the tectonic evolution of the area in relation to the rotation episodes occurred since the Middle Miocene. Upper Triassic-Middle Miocene successions are characterized by two fold systems with sub-perpendicular axes, the first one trending between NNW-SSE and SSW-NNE, characterized by 15-55° angle of plunging, the second one trending between WSW-ENE and WNW-ESE, characterized by sub-horizontal axes. The second system of folds is coaxial to major south-verging breaching thrust of the Madonie Mts. over the Upper Miocene-Lower Pliocene thrust-top deposits. Conversely, these latter show only one fold and thrust system, roughly coaxial to the second system recognized in the Upper Triassic-Middle Miocene successions. The structural analysis, compared with published paleomagnetic data, revealed that the Neogene thrusting was accompanied by vertical-axis clockwise rotations. In particular, Upper Triassic-Middle Miocene successions recorded both major 70° Langhian to Tortonian regional rotations and locally ~30° Pliocene rotations related to activity of strike-slip fault zone.So, the structures formed during the first deformation stage were totally rotated up to ~100°. Conversely, structures of the Upper Miocene-Lower Pliocene deposits were involved only in the Pliocene clockwise rotations, these latter related to activity of strike-slip faulting.

OSL chronology of Quaternary terraced deposits outcropping between Mt. Etna volcano and the Catania Plain (Sicily, southern Italy)

In this paper we tested the applicability of the Optically Stimulated Luminescence (OSL) technique through Single-Aliquot Regenerative-dose (SAR) protocol, on single grain quartz extracted from alluvial–coastal sediments. Five samples were collected from deposits belonging to a flight of seven orders of coastal–alluvial terraces outcropping in the area between Mt. Etna volcano and the Catania Plain (Sicily, southern Italy), at the front of the Sicilian fold and thrust system. After various performance tests, we obtained OSL ages ranging between 240±12 and 80±4ka, consistent with the normal evolutionary model of a terraced sequence, moving from the highest to the lowest elevation. Obtained data allowed us to determine a mean uplift rate of 1.2mm/year during the last 240ka, mostly related to regional uplift processes coupled with sea-level changes. Moreover, terraces belonging to the two highest orders are folded, forming a large anticline. According to our results, the frontal thrust of the Sicilian chain was active between 236 and 197ka ago, even though seismological and geodetic data suggest current activity to the back.

Using high-resolution stratigraphy and structural analysis to constrain polyphase tectonics in wedge-top basins: Inferences from the late Tortonian Scillato Basin (central-northern Sicily)

The present paper aims to show, both from a stratigraphic and structural points of view, the main features of a wedge-top syntectonic basin which evolved recording polyphase and non-coaxial tectonics. The study area is the Scillato Basin (SB), a roughly N–S-oriented structural depression located in the central-northern sector of the Sicililian Maghrebides. There, an approximately 1300m-thick upper Serravallian to upper Tortonian succession of clastic units outcrops as a portion of the Neogene syntectonic covers of the Sicilian fold and thrust belt. Within the outcropping succession the upper Tortonian Terravecchia Fm represents the main topic of this paper. A multidisciplinary approach was carried out through an integration of sedimentology, facies, stratal pattern and structural analyses; this was applied to the formation enabling one to recognize in the Scillato Basin a fining to coarsening upward succession, deposited recording an early transgressive and a late regressive depositional stage. In our model these two main depositional stages developed and are directly relatable to a two-step structural evolution of the basin. During the first step, a NW–SE-oriented structural depression existed, enclosed between structural highs and accommodating the lower and middle portion of the upper Tortonian succession. Subsequently, during the second step, the NW–SE depression was non-coaxially deformed by superimposition of high-angle transpressive faults (many of which were SE-dipping), developed in response to the upward propagation of structures enucleated at deeper structural levels. This step was recorded in the basin by development of both depositional and structural interferences recognizable along the upper portion of the Scillato Basin succession. A comparison between field data and deep geophysical data interpreted at the preliminary stage, raises questions about the late Miocene geological evolution of this sector of the Sicilian chain, including: (i) the syn-tectonic deposition of the Terravecchia Fm. in the Scillato Basin clearly recorded the interference of two main and non-coaxial tectonic events; (ii) the younger of these two events has a clear tranpressional character and was active during the very late Tortonian; (iii) as also indicated by many authors in neighboring orogenic wedges, the main control on the location, geometry and depositional evolution of the Scillato wedge-top Basin was carried out by compressional and transpressional structures developed at a deeper structural level. Their deformation propagated upward both into the shallow structural level and sedimentary covers; therefore (iv) the late Miocene structural scenario here depicted is not consistent either with the back-arc-related extension or with the late orogenic gravitational collapse models previously invoked by other authors with regard to this sector of the Sicilian thrust belt.

Restraining stepover deformation superimposed on a previous fold-and-thrust-belt: A case study from the Mt. Kumeta–Rocca Busambra ridges (western Sicily, Italy)

The western segment of the Sicilian Apennines (southern Italy) is affected by poly phase deformation characterized by non-coaxial structural associations. In particular, this study is focused on two narrow ∼E–W oriented structural and topographic culminations of the fold and thrust belt (Mt. Kumeta and Rocca Busambra ridges), resulting from the exhumation of a deep-seated tectonic unit. A detailed field mapping and meso-structural analysis reveals that since Pliocene time the region was tectonically controlled by the propagation of two major NW–SE oriented right-lateral shear zones and associated structures that often propagated along inherited discontinuities. In particular, the left-stepping geometry and the sense of motion of these regional strike-slip fault systems produced in the overlapping area a wide rhomboidal-shaped contractional region characterized by the occurrence of double-verging ∼E–W striking compressive structures. These bound the Mt. Kumeta and Rocca Busambra carbonate ridges, forming a pair of pop-up structures which link the coeval transcurrent boundary faults. Field data show that contractional structures are affected by significant bending along strike that increases close to the major shear zones. Structural rotations around the vertical axis allowed the carbonate ridges to develop a typical sigmoidal shape.The topographic expression and the internal structural architecture, compared with experimental models describing deformations associated with segmented strike-slip faults, suggest that the analyzed segment of Sicilian fold and thrust belt can be interpreted as a restraining stepover in which crustal shortening, exhumation and vertical axis rotation occurred.Moreover, field data, compared to the subsurface setting imaged by the analysis of available geophysical data (e.g. gravimetric maps and available/interpreted seismic profiles), reveal that, since Pliocene times, the restraining stepover deformation was transversally superimposed on a pre-existing NE–SW oriented thrust and fold system related to the Miocene Africa–Europe collision.

Fluid flow compartmentalization in the Sicilian fold and thrust belt: Implications for the regional aqueous fluid flow and oil migration history

The fluid flow history in the frontal part of the Sicilian fold and thrust belt (FTB) has been reconstructed using an integrated structural, petrographic, geochemical and microthermometric approach. The study focused on comparing fluid flow during progressive deformation along major thrust horizons and in pelagic sediments occurring in the associated thrust sheets (foot- and hanging wall). A fluid flow model is constructed for the frontal part of the Sicilian FTB.Syn-deformational quartz and calcite have been precipitated along décollement horizons in the Iudica–Scalpello study area. The microthermometric analysis of fluid inclusions in the quartz and calcite indicated migration of low saline high temperature aqueous fluids (−1.5<Tm<−0.2°C and 80<Th<200°C) and hydrocarbons along the main thrusts. Geochemical and petrographic analysis showed the presence of high manganese (2500–25,000ppm) and iron (300–7000ppm) contents in certain calcite phases, suggesting that the migrating fluids originate from clay dewatering and clay–water interactions.The fluid flow history in the thrust sheets can be subdivided into two stages. Calcite of types 1 and 2 has identical light orange cathodoluminescence as the surrounding mudstone. Furthermore, its isotope signature (2<δ13C<3‰ and −6<δ18O<−2‰) and minor element content are also in line with closed, host rock buffered fluid flow during the initial stages of the fluid flow history. Type 3 calcite is volumetrically by far the most important calcite phase. It occurs in (hydro-)fractures that are limited to the hanging wall of major thrusts and within major strike-slip faults that are interpreted as transfer faults as a result of thrust development. The presence of associated fluorite suggests more open fluid flow conditions during the final stages of the fluid flow history. Fluorite is characterized by low salinity fluid inclusions (−2.6<Tm<−1.6°C) with Th between 80 and 140°C. Type 3 calcite has less depleted δ18O values compared to calcite of types 1 and 2 and the δ18O from calcite in faults is even positive. During the final stages of fluid flow with precipitation of calcite type 3, the fluid flow model invokes infiltration of overpressured fluids that migrated along the décollement zone. These fluids only infiltrate the thrust sheet in the hanging wall of the thrust, leading to a compartmentalized fluid flow pattern.An identical fluid flow pattern with migration of low and hot saline fluids, associated with hydrocarbons, was observed in other parts of the Sicilian fold and thrust belt. With identical structural deformation and fluid flow patterns, the study confirms the suitability of the frontal part of the Sicilian fold and thrust belt as an outcrop analog for deeply submerged accretionary prisms. The study thus offers unique insights in expected fluid flow patterns in thrust sheets of deeply submerged accretionary complexes.

The “Camporeale wedge-top Basin” (NW Sicily; Italy) in the frame of the Late Miocene Sicilian Foreland Basin System; Inferences from the Upper Tortonian–Lower Messinian Terravecchia Formation

Since the latest Oligocene–earliest Miocene the building of the Sicilian fold and thrust belt has been accompanied by development of a “peripheral” foreland basin system which migrated toward the foreland. In north-western Sicily, the sedimentary record of the foreland basin system migration is represented by a stratigraphic succession made up of several lithostratigraphic units, bounded by regional unconformity surfaces, deposited recording at least four main sedimentary phases, each characterized by the development of different types of syntectonic basins. In particular, during the Late Miocene (Late Tortonian to Early Messinian) a wide wedge-top depozone developed in the innermost sectors of the Sicilian foreland basin system, above the moving thrust sheets. There, wide to quite narrow “syn-kinematic” sedimentary basins developed in response to the tectonic deformation of the deeper carbonate units (Cu). These basins were filled by a thick wedge of silico- and carbonate-clastic deposits pertaining to the Terravecchia Formation (Upper Tortonian–Lower Messinian) which unconformably overlaid the already deformed substrate. Among these basins, the “Camporeale wedge-top Basin” (NW Sicily) was located between an uplifting subaerial chain (northward) acting as source area for coarse clastics and a major depositional area (foredeep depozone) mainly characterized by fine-grained marine sedimentation. Integrated stratigraphic and sedimentologic analyses performed on the Terravecchia Fm. in the Camporeale Basin allowed us to identify a coarsening to fining upward “outer wedge-top sequence” characterized by three main facies associations (i) sandy-to-gravelly unconfined braidplain, (ii) sandywave and storm-dominated delta front, (iii) clayey offshore, settled in several adjacent sedimentary environments. Sedimentation has been driven by several interplaying control factors among which the tectonics played a predominant role. Moreover, the structural analysis performed on the Camporeale Basin fill allows us to recognize major E-W, NE-SW, N-S-, NW-SE-trending structures (faults and folds) interpreted as the superficial expression of deep-seated thrusts with both S-ward and predominantly N-ward vergence, developed under a roughly N170°-oriented stress field. The comparison of the Camporeale Basin with other coeval basins of Sicily allows us to image the Late Miocene Sicilian foreland basin system, as being characterized by a wide continental to shallow-marine wedge-top depozone characterized, in turn, by an inner and outer sector passing basinward, through a foredeep transition zone, into a foredeep depozone characterized by open marine deposition.

Interference between shallow and deep-seated structures in the Sicilian fold and thrust belt, Italy

Abstract: The fold and thrust belt in western Sicily is characterized by the presence and interference of shallow and deep-seated compressional structures, which were generated and developed at different structural levels. The shallow structures consist of imbricated thrusts and asymmetric folds, with a typical wavelength of 2 km, involving relatively thin deep-water units. These units are superimposed on thick platform carbonate units, along a wide and originally almost flat floor thrust. The axial trend of the folds is variable, as multi-phase folding often occurred, producing a characteristic interference pattern, reflecting continuous variations of the apparent transport direction during the emplacement (i.e. rotation of the allochthonous thrust sheets). The deep-seated structures consist of large, double-verging pop-up structures, with a typical wavelength of 5–10 km, involving thicker platform carbonate successions. The deep-seated structures are characterized by large folds, with vertical to overturned limbs, caused by high-angle, transpressive ramps that reactivated previous (i.e. Mesozoic) synsedimentary normal or transtensional faults. The floor thrust of the shallow structures was passively deformed by the subsequent growth of the underlying, younger deep-seated structures. Large clockwise rotations of the tectonic units occurred during the compressional deformation, and the amount of rotation is apparently related to the timing and amount of the tectonic transport.

Fluid flow reconstruction in karstified Panormide platform limestones (north-central Sicily): Implications for hydrocarbon prospectivity in the Sicilian fold and thrust belt

Diagenetic analysis based on field and petrographic observations, isotope and microthermometric data was used to reconstruct the fluid flow history of the Cretaceous shallow water limestones from the Panormide platform exposed in north-central Sicily. Analysis focused on diagenetic products in cavities and dissolution enlarged fractures of the karstified limestones that occur just below a regional unconformity. The fluid flow history could be broken down into five stages that were linked to the kinematic and burial history of the region. (1) Petrography (zoned cathodoluminescence and speleothem textures) and stable isotopes (6.5 < δ 18O V-PDB < −3.5‰ and 0 < δ 13C V-PDB < −14‰) indicate that the earliest calcite phase was associated with karstification during emergence of the platform. Limestone dissolution at this stage is important with regard to possible reservoir creation in the Panormide palaeogeographic domain. (2) Fine-grained micrite sedimentation, dated as latest Cretaceous by nannopalaeontology and its 87Sr/ 86Sr isotope ratio (0.7078), marks replacement by marine fluids during subsequent submergence of the karstified platform. (3) The following calcite cement was still precipitated by marine-derived fluids (−7.0 < δ 18O V-PDB < −5.0‰ and −3.0 < δ 13C V-PDB < 0.5‰/ T m = −2 to −5 °C), but at increasingly higher temperatures ( T h = 60–120 °C). This has been interpreted as precipitation during Oligocene foredeep burial. (4) Hot ( T h = 130–180 °C), low saline ( T m < −2.5 °C) fluids with increasingly higher calculated δ 18O SMOW signatures (+6 to +14‰) subsequently invaded the karst system. These fluids most likely migrated during fold and thrust belt development. The low salinity and relatively high δ 18O SMOW signatures of the fluids are interpreted to be the result of clay dewatering reactions. The presence of bitumen and associated fluorite with hydrocarbon inclusions at this stage in the paragenesis constrains the timing of oil migration in the region. (5) Finally, high saline fluids with elevated 87Sr/ 86Sr (0.7095–0.7105) signatures invaded the karst system. This last fluid flow event was possibly coeval with localized dolomitization and calcite cementation along high-angle faults of Pliocene age, as suggested by identical radiogenic signatures of these diagenetic products.

Fluid flow reconstruction in the Sicilian Fold and Thrust Belt

Fluid flow reconstruction in the Sicilian Fold and Thrust Belt

Structural evidence for Neogene rotations in the eastern Sicilian fold and thrust belt

A geological and structural analysis carried out on a sector of the eastern Sicilian fold and thrust belt pointed out the occurrence of two systems of structural associations, typical of collisional fronts. In particular, the Mesozoic–Serravallian succession of the Mt. Judica unit, outcropping in three W–E- to WNW–ESE-striking distinct ridges, is characterized by two fold systems with sub-perpendicular axes, the first plunging towards 010–040 at angles of 30–55°, the second one with sub-horizontal axes trending 090–115. The different angular values of plunging suggest that the folds of the first system underwent the effects of severe tectonic deformation following their formation. Moreover, the distinct ridges were uplifted by south-verging thrusts and relative back-thrusts coaxial to the second system of folds. Conversely, the Upper Tortonian–Lower Pliocene deposits of Mt. Pulicara show only one fold and thrust system, WNW–ESE-trending, roughly coaxial to the second system recognized in the Mt. Judica unit succession. The structural analysis carried out in the two areas, compared with published eastern-central Sicily palaeomagnetic data, suggest that the Mesozoic–Serravallian succession of the Mt. Judica Unit recorded both major 70° Langhian–Late Tortonian clockwise rotations and locally 30° Pliocene clockwise rotations. So, the structures formed during the first deformation stage were totally rotated up to 100°. Conversely, structures of the Mt. Pulicara Upper Tortonian–Lower Pliocene deposits were involved only in the Pliocene clockwise rotation. From a geodynamic point of view, the Neogene clockwise rotation in the eastern Sicily fold and thrust belt is related to the regional framework of the Africa–Europe convergence.

Tectonic analysis of a flexed foreland: the Ragusa Platform

Detailed field studies of fracture patterns and paleostress reconstructions based on analyses of fault-slip data sets allow the identification of the Late Cenozoic stress pattern evolution of the Ragusa Platform. During the Late Miocene to Early Pleistocene period, a complex extensional pattern developed. It was dominated in almost the entire Hyblean Plateau by NW-SE to NNW-SSE extensions related to the flexure of the foreland under the load of the allochthonous units of the Sicilian Fold and Thrust Belt. These extensional tectonics were characterized by NE-SW to ENE-WSW trending normal faults and grabens. In eastern Hyblea, NE-SW to ENE-WSW extension have prevailed at least since the Late Cretaceous. They are linked to the effects of the Malta Escarpment. In the western Ragusa Platform, a third, minor, WNW-ESE extension associated with sets of NNE-SSW trending normal faults, may be correlated with the development of the Gela basin. In addition, these major extensions induced complex patterns of perpendicular normal fault systems through permutations between the principal stress axes σ2 and σ3. The Pliocene-Pleistocene extensional paleostress field evolution is marked in almost the entire platform by the alternation of two or three main extensional stress patterns (NE-SW to NNW-SSE, WNW-ESE and NE-SW to ENE-WSW extensions), each of them controlled by particular boundary conditions. Three minor compressional paleostress orientations have been identified. They correspond to three minor compressional events dominated by 020°–030°, 070°–080° and 100°–110° compressional directions. These events occurred in within the general Pliocene-Pleistocene extensive context. The 100°–110° event is of Early-Middle Pliocene age. Its large regional distribution suggests that this event may have resulted from interactions between the major blocks constituting the Africa-Eurasian boundary. The relative chronology shows that the 020°–030° compression predates the 070°–080° one. The origins of these compressional events are still uncertain due to poor regional control.