Interpretation Of Seismic Lines Research Articles

Late Miocene-Quaternary sedimentary environment evolution of the Kerch seep area, Black Sea

A set of 2D high resolution seismic lines was acquired near the Kerch Peninsula during R/V Meteor Cruise M72/3 in March/April 2007 to the Eastern Black Sea. The high resolution seismic data were used for analysis of seismic facies and seismic sequences to gain insight into the sedimentary evolution of the study area. Seven seismic facies types were identified and six seismic units could be mapped. Based on seismic line interpretation, isopach and seismic facies distribution maps, a chronostratigraphic framework could be established for the study area. The study reveals that the sediment deposits were influenced by syndepositional tectonic movements, sea level and climate. During the late Miocene and the early Pliocene, possible slope fan deposits developed. At the boundary between the Miocene and Pliocene, the Messinian erosional truncation surface was observed. After the Messinian sea level fall, accompanied by a major transgressional phase during the Pliocene, the Paleo-Don and Kuban Rivers delivered a large terrigenous input to the Black Sea from the uplifted Crimean Mountains. This formed thick submarine fan deposits near the mouth of Kerch Strait during the late Pliocene. Facies variations within the seismic units are related to the sea-level and climate curves, and are reflected by grain size variations in the sediments and the shift of the river mouth. During the Quaternary, hemipelagic sediments interbedded with coarse-grained fluvial sediments developed in the study area, along with slumps, river channels and fan deposits.

Late Quaternary Tectonics along the Peri-Adriatic Sector of the Apenninic Chain (Central-Southern Italy): Inspecting Active Shortening through Topographic Relief and Fluvial Network Analyses

Abstract Active compressional tectonics along the outer front of the Apenninic-Maghrebian chain (Italy) is well documented along the northern and central segments and in Sicily. On the other hand, the Southern Apenninic Outer Front (SAOF) orogenic activity is well established only until the Lower-Middle Pleistocene. We address the hypothesis of its subsequent late Quaternary activity in central-southern Italy (Abruzzo and Molise regions). We integrated topographic and fluvial network analyses along with morphotectonic investigation of fluvial terraces to identify evidence of differential rock uplift. We compared the results with the main geolithological units, known structural elements, and long-term deformation history from seismic line interpretation. We found variable evidence suggesting localized rock uplift in the Abruzzo region along the SAOF (Abruzzo Citeriore Basal Thrust segment) and inward structures on its hanging wall (Casoli-Bomba high), as well as along part of the Struttura Costiera thrust. Middle-to-Late Pleistocene deformation is constrained by terrace tilting and disruption along the Pescara river. Localized shortening along segments of the Apenninic Outer Front could explain the observed pattern of anomalies which is difficult to explain with long-wavelength regional uplift alone. Our reconstruction is consistent with the long-term deformation of the area and agrees with its seismotectonic setting. Despite the low deformation rate context and the peculiar geological setting which challenges the interpretation of the topographic and geomorphic signals, this study compels reconsideration, in terms of seismic hazard assessment, of the existence of late Quaternary active thrusting in central-southern Italy.

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.

Structural and Geophysical Characterization of the Western Termination of the South Pyrenean Triangle Zone

AbstractThe South Pyrenean triangle zone represents the southernmost front of the Pyrenees at its central portion deforming the Upper Eocene‐Miocene Ebro Basin deposits. Two main structures characterize its western termination, the Barbastro anticline and the San Román backthrust, which detached on the Barbastro Formation (and lateral equivalents), an Upper Eocene‐Lower Oligocene syntectonic evaporite‐rich formation that acted as a multidetachment unit. Northward, the south directed Pyrenean thrust unit (i.e., Gavarnie‐Sierras thrust sheet) detached along the Middle‐Upper Triassic evaporitic rocks to finally ramp up and glide along the same Upper Eocene‐Lower Oligocene multidetachment unit. A multidisciplinary approach allowed constructing a detailed structural and stratigraphic model of the study area. The workflow consisted of (1) constraining the geometry and structural architecture based on surface geology, interpretation of seismic lines (>900 km), and wells and (2) obtaining the 3‐D density distribution of the multidetachment unit using gravity stochastic inversion (more than 7,000 gravity stations and 1,500 density data). The geometry of the sole thrust of the Gavarnie‐Sierras thrust sheet was controlled by the distribution of the evaporite‐rich units of the Barbastro Fm. Weak detachments promoted thrust salient formation and thrust flat geometries. The western termination of the South Pyrenean triangle zone is defined as a westward transition from a ramp‐dominated and multiple triangle zone to a detachment‐dominated one. Its geometry, kinematics, and location were controlled by the heterogeneous lithology of the Barbastro Fm. and its basal, halite‐based detachment southern pinch‐out.

Fast dismantling of a mountain belt by mantle flow: Late-orogenic evolution of Pyrenees and Liguro-Provençal rifting

The Pyrenean Belt ends against the Gulf of Lion passive margin. The mechanism responsible for dismantling the mountain belt during Oligocene rifting has not yet found a proper explanation. The Late Eocene and Oligocene period is characterized by a first order change in subduction dynamics in the Mediterranean and the subduction zones started to retreat with back-arc basins forming at the expense of mountain belts build earlier. The slab subducting below Provence and Sardinia-Corsica started a fast south-eastward retreat, forming the Liguro-Provençal Basin. This syn-rift period in the Gulf of Lion margin is coeval with exhumation of the eastern Pyrenean basement, while underthrusting of Iberia continued until Early Miocene. Based on interpretation of seismic lines, we propose a tentative model in which the mantle flow related with Apennine slab retreat has (1) exhumed and thinned the continental mantle below the Gulf of Lion and the eastern Pyrenees and (2) exhumed the lower crust, leading to crustal thinning and subsidence of the Gulf of Lion margin. The wide distribution of syn-rift volcanism in the transition between the Gulf of Lion and Valencia Basin is in line with the geometry observed in the margin suggesting ductile deformation of a weak continental crust, typical of volcanic margins. The direction of SKS-waves seismic anisotropy below the Pyrenees and the observed migration of exhumation toward the west fit this simple model. The concentration of syn-rift magmatism and the ductile behaviour of the crust during rifting can be explained by the high heat flow above the slab tear that separates the future Apennines and Maghreb branches of the West Mediterranean subduction zone. Finally, removal of upper mantle, inducing uplift and an increase of potential energy, may explain why thrusting continued in the Pyrenees while rifting was still active nearby along strike.

The structure of the northern Agrio fold and thrust belt (37°30’ S), Neuquén Basin, Argentina

The Agrio fold and thrust belt is a thick-skinned orogenic belt developed since Late Cretaceous in response to the convergence between the Nazca and South American plates. The integration of new structural field data and seismic line interpretation allowed us to create two balanced cross-sections, which help to analyse the geometry of both thick and thin-skinned structures, to calculate the tectonic shortenings and finally to discuss the main mechanisms that produced this fold and thrust belt. The predominantly NNW-SSE structures show varying wavelengths, and can be classified into kilometer-scale first order basement involved structures and smaller second, third and fourth order fault-related folds in cover rocks with shallower detachments. Thick-skinned structures comprise fault-bend folds moving into the sedimentary cover, mainly along Late Jurassic evaporites, which form basement wedges that transfer the deformation to the foreland. Thus, shortenings in both basement and cover rocks must be similar and consequently, by measuring the contraction accounted for thin-skinned structures, is possible to propose a suitable model for the thick skinned deformation. The balanced cross-sections indicate shortenings of 11.2 km (18%) for the northern section and 10.9 km (17.3%) for the southern section. These values are different from the shortenings established by previous works in the region, reflecting differences in the assumed model to explain the basement-involved structures. According to our interpretation, the structural evolution of this fold and thrust belt was controlled by major basement-involved thrust systems with subordinate influence of inversion along pre-existing normal faults during the Andean compression.

Genesis and evolution of the Watukosek fault system in the Lusi area (East Java)

Detailed analysis of two-dimensional seismic lines acquired in the NE Java basin has been performed to unravel the subsurface geology of the region around the Lusi mud eruption. This work revealed the existence of a system consisting of a complex set of faults, here called the Watukosek fault system, forming triangular deformation zones converging at the top of the early Miocene Carbonates. This system continues downwards with vertical individual fault segments, often bordering the steep margins of the carbonate platforms. The analysis of data includes the interpretation of seismic lines, regional structural data inferred from basement gravity maps and present-day main direction of stress. Results suggest that a possible rotation of stress direction from N40E-S40W to N-S occurred during the post-Miocene history of the Java back arc tectonic evolution. The Watukosek fault system was first generated as a tensional lineament during the E-W sinistral transpressive strain, which involved the basement. In this phase, synthetic and antithetic Riedel faults formed, the former controlling the NW-SE orientation of the structural highs represented by Oligo-Miocene carbonate platforms. As a consequence of the rotation of the main principal stress direction to a N-S direction, the Watukosek fault and similar parallel lineaments became sinistral Riedel shears, developing intense triangular deformation zones. Based on the stratigraphic position of gentle anticlinal deformations with axis corresponding to the N40E-S40W oriented triangular deformation zones, the transpressive strain linked to the N-S main stress compression occurred likely in the Late Pliocene-Early Pleistocene.The detailed examination of a) stratigraphy at the wells BJP-1 and Porong-1 as well as b) the seismo-stratigraphic architecture of the entire succession in the study area, allowed a new subsurface interpretation and revision of the stratigraphic units below Lusi. The thick Early Miocene Tuban Formation is found sandwiched between the coheval Upper Kalibeng Formation and the Early Miocene Carbonate of the Kujung Formation, which in turn overlain the older Ngimbang Formation.

Multidisciplinary inferences on a newly recognized active east‐dipping extensional system in Central Italy

AbstractWe use a multidisciplinary approach to gather preliminary evidence for a Quaternary east‐dipping extensional detachment in Central Italy. This structure crops out in the Sabini‐Eastern Simbruini (SES) and would be hidden at mid‐crustal depths beneath the L'Aquila 2009 (Mw6.3) epicentral area. The SES geometry is reconstructed through geological mapping, structural analysis and seismic line interpretation. The geometry of the mid‐crustal segment, referred to as the Ocre Segment (OS), is interpreted through seismological analyses of the largest aftershock (Mw5.4) of the L'Aquila 2009 sequence. The kinematic compatibility between the SES and the OS under a common SW–NE tensional field is tested through stress inversion of both geological and seismological data. The reliability of OS activation is tested through slip tendency analysis. Like other Italian cases, the SES and the OS are preliminarily interpreted as expressions at different depths of the same unknown east‐dipping extensional detachment, characterized by a ramp–flat–ramp geometry.

Retro-wedge foreland basin evolution along the ECORS line, eastern Pyrenees, France

The eastern Aquitaine basin and North Pyrenean Zone show many characteristics of retro-wedge models. However, they differ significantly in that slow subsidence and low deformation continued throughout orogenesis so that growth and steady-state phases cannot be distinguished. We show that the eastern Pyrenees record two clear phases of convergence and probably never attained steady state. Analysis of the Aquitaine retro-foreland basin along the Ariege ECORS deep seismic line, eastern French Pyrenees, integrates a new litho- and chronostratigraphy, subsidence analysis, low-temperature thermochronology data, new interpretations of seismic lines and a balanced cross-section. Within an overall regression, two shallowing-up cycles (Latest Santonian–Danian, Thanetian–Oligocene) record slow tectonic subsidence of the eastern Aquitaine basin separated by a quiet period. Continuing thick-skinned shortening was low to moderate. The early marine basin, generated by loading of the weak, extended margin, was supplied axially from an unknown eastern edifice while the young Pyrenean orogeny to the south remained submerged. During the quiet period of ultra-slow subsidence, no basin migration and negligible sediment supply, continental conditions characterized the eastern orogen. The second marine transgression was quickly followed by continental conditions. The basin was supplied by the now emerging Pyrenean orogen and continued to subside until Miocene time.

Understanding the potential for tsunami generated by earthquakes on the southern Hikurangi subduction interface

ABSTRACTThe earthquake and tsunami potential of the southern Hikurangi subduction interface has been assessed by reviewing current research in paleoseismology, paleotsunami, geodesy and passive and active source seismology. In addition, new interpretations of seismic lines are presented demonstrating the location and influence of splay faults and a modelling study examines the sensitivity of tsunami in Cook Strait to the southern termination of Hikurangi earthquake ruptures. Key conclusions are: the southern portion of the Hikurangi interface, south of c. 40°S, is currently strongly coupled and experiences great megathrust earthquakes of Mw >8 (some of which may also rupture further north); the downdip limits of strong coupling at southern Hikurangi are outlined by slow slip events and non-volcanic tremor; and the behaviour at the updip limit and the southern termination will be strongly influenced by splay faults. The tsunami impact on Cook Strait is shown to be highly sensitive to how far ruptures extend across Cook Strait.

Post Jurassic shortening in the western Surat Basin relative to underlying basement depth and faulting

The Hutton-Wallumbilla (HWF), Merivale (MF), Kia Ora, and Injune faults are the major structures in the western Surat Basin, deforming Palaeozoic to Jurassic rock units. The authors present results from the interpretation of gridded gravity data and open-file seismic reflection data, which provide constraints on the geometry and kinematics of these faults. The interpretation of gravity data indicates that the HWF and MF are expressed by sharp lineaments in moderate to high-amplitude anomalies, indicating a deep-seated nature of the faults. The interpretation of seismic lines shows that the HWF and MF are northeast-dipping and east-dipping reverse blind faults, respectively. Some other faults also displaced and folded the rock units of the Bowen and Surat basins, such as the Kia Ora and Injune faults. The MF, Kia Ora, and the northern part of the HWF acted as normal faults during the early Permian and then have been inverted during the Late Permian–Triassic Hunter-Bowen Orogeny phases, especially during the early Late Triassic. The largest fault throws in the Bowen Basin successions are observed along the southern part of the HWF and its central splay, which are around 350 m and 480 m, respectively. The stratigraphic units of the Surat Basin above it have gently been folded over the major blind faults. The largest amount of shortening in the Surat Basin has taken place over the southern part of the HWF by 0.5%. The basement depth played an important role in the amount of contractional deformation in the Bowen and Surat basins. Where the basement is shallow, the amount of deformation along the faults in both the Bowen and Surat basins is higher.

Miocene connectivity between the Central and Eastern Paratethys: Constraints from the western Dacian Basin

The Dacian Basin formed an important link between the central and eastern parts of the Paratethys, a chain of late Tertiary inland seas and lakes. This study presents constraints on Miocene sea and lake level fluctuations in the Dacian Basin and on the connectivity between it and other Paratethys basins, based on the interpretation of seismic lines, a micropalaeontological study and lithofacies analysis of a large number of outcrops. It is shown that relative sea level fluctuations in the western part of the Dacian Basin during the Middle Miocene were primarily driven by tectonic activity in the nearby Carpathian Mountains. From the Maeotian (Late Miocene) onwards, however, tectonic activity was minor and relative sea level fluctuations were primarily driven by changes in basin connectivity and climate. The connection between the Central and Eastern Paratethys was broken at the end of the Middle Miocene, leading to the development of an endemic fauna in the former, but new data presented here suggest that isolation was not sustained completely as Central Paratethys species appeared in the Dacian Basin during the Maeotian (Late Miocene). Besides the isolation two falls in water level occurred in the basin during the latest Miocene: Of these, the intra-Pontian sea-level drop is the best known. We show, however, that this drop was preceded by a larger sea or lake-level drop in the late Sarmatian/Maeotian. This latter event may have affected much larger parts of the Paratethys, and we recommend more study of the bordering basins. The hypothesis that the connection between the Dacian and Central Paratethys basins was located in the region where the Danube River presently crosses the Carpathians was tested, but no supporting evidence was found.

Lateral variations in tectonic style across cross-strike discontinuities: an example from the Central Apennines belt (Italy)

In foreland thrust belts, abrupt lateral changes in tectonic style, structural–stratigraphic features, and topography usually occur across cross-strike faults. The Central Apennines of Italy offer an exceptional scenario of lateral variations in tectonic setting. Here, the Sangro Volturno oblique thrust ramp (SVOTR) represents the outer thrust front of the Pliocene–Quaternary foreland thrust system, confining southward the axial culmination of the orogen that occurs in the Central Apennines. We present an interpretation of the Pliocene–Quaternary evolution of this cross-strike fault through an integrated dataset including structural-geological mapping and subsurface onshore seismic reflection profiles. The interpretation of the structural framework is augmented by the analysis of low-temperature thermochronometers from 32 new sites extending across the subsurface transverse structure. As evidenced by seismic line interpretation, the localization and development of the SVOTR have been influenced by inherited extensional faults within a positive inversion tectonics context. The regional distribution of the maximum paleotemperature values across the SVOTR constrains the original extent of the allochthonous thrust sheet over all its hanging-wall and footwall blocks. The Pliocene–Quaternary thrusting and inversion of SVOTR caused the strong hanging-wall uplift, which brought to the complete erosion of the allochthonous units and the exhumation of the Adria units. The integrated analysis of low-temperature thermochronometers and structural evidence as applied in the study case can define the role of major cross-strike discontinuities in foreland thrust belts, by constraining and verifying their tectonics inversion significance and the amount of related exhumation.

Neogene aquifer: geochemistry and structuring in the Sidi Saad basin, central Tunisia

The Sidi Saad basin is located in the NS axis in central Tunisia. This zone was affected by several distension and compression phases inducing the structuring and the distribution of Neogene deposits. The study area is known by the presence of important water reserves. The surface water needs for the demographic growth and for both the agricultural and industrial sector developments. So, the exploitation of deep aquifers reveals a vital issue in Tunisia whose water resources are limited. To satisfy these needs, exploration and characterization of deep aquifers is necessary. The present study, based on hydraulic and petroleum wells’ correlation, seismic line interpretation, and hydrochemistry, addresses the geometry, and the hydrogeological characterization of Miocene-Pliocene-Quaternary reservoirs is undertaken for the first time in Sidi Saad basin. The results highlight that the structural framework, based on major structures, controls the Mio-Pliocene siliciclastic deep reservoir deposits, the groundwater flow, and the sub-basin aquifer distribution. The water geochemistry study exhibits low salinities in the northern and the southeastern parts of the study area with different facies of Ca-HCO3 and Na-(Ca)-Cl-(SO4) and constitute an important source of drinkable and irrigation water.

Tectono-stratigraphic evolution of an inverted extensional basin: the Cameros Basin (north of Spain)

The Cameros Basin is a part of the Mesozoic Iberian Rift. It is an extensional basin formed during the late Jurassic and early Cretaceous, in the Mesozoic Iberian Rift context, and it was inverted in the Cenozoic as a result of the Alpine contraction. This work aims to reconstruct the tectono-stratigraphic evolution of the basin during the Mesozoic, using new and revised field, geophysical and subsurface data. The construction of a basin-wide balanced section with partial restorations herein offers new insights into the geometry of the syn-rift deposits. Field data, seismic lines and oil well data were used to identify the main structures of the basin and the basin-forming mechanisms. Mapping and cross-sectional data indicate the marked thickness variation of the depositional sequences across the basin, suggesting that the extension of the depositional area varied during the syn-rift stage and that the depocentres migrated towards the north. From field observation and seismic line interpretation, an onlap of the depositional sequences to the north, over the marine Jurassic substratum, can be deduced. In the last few decades, the structure and geometry of the basin have been strongly debated. The structure and geometry of the basin infill reconstructed herein strongly support the interpretation of the Cameros Basin as an extensional-ramp synclinal basin formed on a blind south-dipping extensional ramp. The gradual hanging-wall displacement to the south shifted the depocentres to the north over time, thus increasing the basin in size northwards, with onlap geometry on the pre-rift substratum. The basin was inverted by means of a main thrust located in a detachment located in the Upper Triassic beds (Keuper), which branched in depth with the Mesozoic extensional fault flat. The reconstruction of the tectono-stratigraphic evolution of the Cameros Basin proposed herein represents a synthesis and an integration of previous studies of the structure and geometry of the basin. This study can be used as the basis for future basin-scale research and for modelling the ancient petroleum system of the basin.

Slope destabilization during the Messinian Salinity Crisis

During the Messinian Salinity Crisis, ~6Myr ago, deep canyons were incised when a huge sea-level drawdown of ~1.5km affected the Mediterranean Sea. Nearly contemporaneously, more than 2km of evaporites accumulated in the basin. This event was the consequence of a complex interaction of tectonic movements and global sea-level variation associated with climatic evolution. This unusual event ended with the reflooding of the Mediterranean area. In this paper, using seismic line interpretation, we show that several landslides occurred in various parts of the Mediterranean Basin during this crisis. Three of these landslides are well preserved, and their dynamics were analyzed. Modeling of the slope stability demonstrates that these landslides may have been due to (i) the relief created by the deep erosion, and/or (ii) the reflooding, which triggered a pore pressure increase. The relatively small run-out distances of the three landslides suggest propagation in a submarine environment and triggering by sea-level rise.

3D structural modelling of the southern Zagros fold-and-thrust belt diapiric province

Abstract3D modelling of geological structures is a key method to improve the understanding of the geological history of an area, and to serve as a drive for exploration. Geomodelling has been performed on a large 60000 km2area of the Zagros fold-and-thrust belt of Iran, to reconcile a vast but heterogeneous dataset. Topography, geological surface data and dips, outcrop surveys, and well and seismic data were integrated into the model. The method was to construct a key surface maximizing the hard data constraints. The Oligo-Miocene Top Asmari layer was chosen, as this formation was regionally deposited before the main Zagros collision phase and because the numerous outcrops allow proper control of the bed geometry in the fold cores. Interpreted seismic data have been integrated to interpolate the surfaces at depth within the synclines. Several conceptual models of fold geometry have been applied to estimate the best way to convert seismic time signal to depth. Several deeper horizons down to Palaeozoic strata were deduced from this key horizon by applying palaeo-thickness maps. During the construction, the 3D interpolated surfaces could be reconverted to time, using a velocity model, and compared with previous seismic interpretations. This exercise obliged us to revise some early interpretations of seismic lines that were badly tied to wells. The 3D modelling therefore clearly improves regional interpretation. In addition, the 3D model is the only tool that allows drawing consistent cross-sections in areas where there are no seismic lines. Emerging Hormuz salt diapirs were added to the model. Dimensions and shapes of the individual diapirs were modelled using a statistical survey on the cropping out Hormuz structures. Modelling reliably demonstrated that the diapirs, when piercing, show a constant mushroom shape whose diameter depends on the stratigraphic depth of observation. This observation allowed us to exemplify relations between the pre-existing diapirs and the anticlines of the area, and to highlight the morphological changes from the inner onshore areas to the coastal and offshore areas. In addition, one of the surprising results of this study was the observation of the increasing diameter of the diapirs at the time of the Zagros collision and folding event, with growth strata and overhangs on the flanks of the diapirs.

Contrasting styles of fault reactivation in curved orogenic belts: Examples from the Central Apennines (Italy)

The geometry of the Apennine fold-and-thrust belt has been strongly influenced by the original architecture of the Adria paleomargin. In the Central Apennines, pre-thrusting normal faults (pre-orogenic Permian(?)/Triassic–Jurassic and synorogenic Neogene) were reactivated with compressional kinematics during the Neogene–Quaternary orogenesis. We present a study of the control of preexisting extensional faults on thrust tectonics in the Central Apennines. We describe positive inversion geometries of some salient fold-and-thrust structures from the Central Apennines (Setteporte, the Sabini Mountains, the Sibillini Mountains, Montagna dei Fiori, the Gran Sasso range, Maiella Mountain, and Casoli-Bomba) by integrating surface geological data and seismic-line interpretation. In these structures, different styles of fault reactivation depend on their orientation with respect to the subsequent compressional NE-SW-trending stress field. The NW-SE– and WNW-ESE–trending pre-thrusting normal faults in the backlimbs of the anticlines were displaced and passively translated in the hanging-wall blocks of the thrust planes, thus exhibiting a classical shortcut geometry (shortcut anticlines). Differently, pre-orogenic normal faults in the N-S–trending anticlines were reactivated in a transpressive deformational context, as documented by the mainly dip-slip and strike-slip kinematics along the thrusts and back thrusts, respectively (reactivation anticlines). The cases studied document differences in geometry in fold-and-thrust structures related to the trend of preexisting extensional faults, showing that different reactivation geometries linked to the same inversion event can coexist at regional scale in curved fold-and-thrust belts. The proposed inversion tectonic model and the resulting geometry of the fold-and-thrust belt could possibly be applied to analogous orogenic belts.

Structural inheritance of pre- and syn-orogenic normal faultson the arcuate geometry of Pliocene-Quaternary thrusts:Examples from the Central and Southern Apennine Chain

n the frontal sector of the Central-Southern Apennines, surface geological data integrated with seismic line interpretation provide new constraints into the reconstruction of the structural inheritance of Mesozoic pre-orogenic and Messinian-Pliocene syn-orogenic normal faults on the salient geometry of the Pliocene-Quaternary thrust system.In the Umbria-Marche-Abruzzi area, pre-orogenic normal faults commonly juxtapose the complete Jurassic succession (about 900 metres in thickness) onto coeval condensed successions (about 50 metres in thickness) deposited over structural highs. In the Sibillini Mts and Gran Sasso area, pre-orogenic normal faults are truncated and rotated into Pliocene thrust-sheets according to simple short-cut trajectories. In particular the foreland-dipping Jurassic normal faults in the Sibillini Mts area have been rotated and reactivated during the thrust propagation forming high-angle blind-thrusts in the east verging overturned folds.The Maiella anticline, which involves the Mesozoic-Miocene Apulian carbonate succession and the related slope deposits, joins the Central Apennine fold-and-thrust system to the Apulian Chain buried below the allochthonous Units of the Southern Apennines. Seismic line interpretation allowed us to reconstruct the three-dimensional pattern of the Apulian thrusts, oriented N-S, NNW-SSE and E-W, that are parallel to normal faults related to the Pliocene-Quaternary flexural extension in the foreland. Detailed reconstruction of the Setteporte and Monte Taburno structures shows main N-S/NNE-SSW trending thrusts, branching into NW-SE/E-W trending minor thrusts and back-thrusts, characterized by push-up geometry, typically referable to a transpressive deformation and/or to the positive reactivation of normal faults. Moreover, the sharp westward deepening of the base of the Apulian sedimentary succession (from 4.5 to 6.0 sec in TWT), based on the interpretation of the CROP 11 seismic reflection profile, and the concomitant increase in thickness of the Triassic sequence along the Maiella-Casoli transect, suggest the existence of west-dipping (?)Permian-Triassic normal faults that strongly controlled the distribution and thickness variation of syn-rifting sediments. An inversion of the deepest low angle portions of the pre- and syn-orogenic normal faults is in agreement with surface data (i.e., the structural elevation of the carbonate succession in the Casoli-Bomba anticline) and seismic line interpretation (i.e., deep seated location of the base of Apulian sedimentary succession below the same anticline).In the reconstructed inversion tectonics model, the N-S trending pre-thrusting normal faults are fully inverted as N-S transpressive segments of the salient structures of the chain, whereas, the NW-SE trending thrusts inverted the low angle portion of pre-thrusting normal faults in the middle-lower crust and displaced with a short-cut the normal faults in the upper portion of the crust. As a result, the pattern of the pre-existing normal faults is inherited on the salient structures of the Central and Southern Apennine Chain.

Structural evolution of the Rides Prerifaines (Morocco): structural and seismic interpretation and analogue modelling experiments

The Rides Prerifaines (RP) of Morocco constitute the leading edge of the Rif chain. They involve a Triassic–Palaeocene succession deposited on a peneplained Palaeozoic fold belt and accumulated in basins delimited by NE–SW-trending normal fault systems. A significant hiatus separates an overlying Middle Miocene–Upper Miocene foredeep sequence. The reconstruction of the complex structural evolution of the RP during the later compressive phases that affected the Rif chain since Middle Miocene time has been the aim of this paper. We integrated field structural analyses, seismic line interpretation, and analogue modelling in order to evaluate the control exerted by the Late Triassic–Jurassic normal fault systems onto the later compressive tectonics. The maximum compression direction associated with the first compressive phase is roughly NE–SW to ENE–WSW oriented. During this phase the Mesozoic basin fill was scooped-out from the graben and the main decollement level were the Triassic evaporites. Since Pliocene times the maximum compression direction was oriented roughly N–S. During this phase the RP assumed their present structural setting. The earlier normal faults delimiting the Mesozoic graben were reactivated in a strike–slip mode also involving the Palaeozoic basement. The analogue modelling experiments demonstrated that the basement reactivation promoted salt tectonics and favoured fluid circulation.