Tectonic Inversion Research Articles

Stratigraphic and tectonic architecture of the Middle Jurassic-Upper Cretaceous at the southern front of the Central High Atlas (Morocco): a cartographic revision

ABSTRACT The Middle Jurassic (Bathonian)-Upper Cretaceous (Maastrichtian) deposits exposed at the southern front of the Central High Atlas (CHA, Southern Morocco) include thick fluvial successions largely undifferentiated in previous studies. These continental strata record a long period of relief formation due to crustal shortening and subsequent denudation that predated the Cenozoic, syn-collisional, tectonic inversion of the CHA. This study, carried out through mapping along more than 270 km between Ouarzazate and Errachidia towns, firstly proposes a rock-stratigraphic unified scheme based on a framework of unconformity-bounded stratigraphic units, including sub-units, differentiated for their specific depositional meaning. Secondly, the geological maps and related cross-sections illustrate the evidence of syn-depositional shortening with distinct deformation styles, outlining pre- and syn-collisional tectonic inversion.

Late Cretaceous geodynamics of the Palaeo‐Pacific plate inferred from basin inversion structures in the Songliao Basin (NE China)

AbstractReconstructing the process of plate subduction is challenging, but clues can be found in sedimentary basins and the nature of deformation of the overriding plate. Here we analyse a seismic‐reflection dataset that indicates tectonic inversion in the southwestern Songliao basin, NE China, to construct the geodynamics of Palaeo‐Pacific plate. The study area consists of Lower Cretaceous rift sediments that were cut by normal faults, folded, and subsequently overlain by undeformed Upper Cretaceous strata, revealing a process of basin inversion. The timing of inversion is constrained to the interval between deposition of the Lower and Upper Cretaceous sediments (i.e. 87–71 Ma). Mud volcanoes and similar structures associated with inversion are observed in basins throughout the region. The change from tectonic extension to shortening in the overriding plate is recorded by sedimentation and inversion of the basins, and was triggered by an increase in the rate of motion of the subducting Palaeo‐Pacific plate.

Origin and timing of spilitic alterations in volcanic rocks from Głuszyca Górna in the Intra-Sudetic Basin, Poland

The formation of spilitic assemblages (i.e. chlorite and albite) has been ubiquitously involved during the evolution of continental early-Permian volcanics from the Intra-Sudetic Basin (ISB). Based on the investigation of laccolith-type and variably-altered trachyandesite exposure in the vicinity of Głuszyca Górna (Lower Silesia, Poland), we have demonstrated that apatite fission-track dating (AFT), coupled with chlorite geothermometry, can be successfully applied to denote the timing of low-temperature alterations within volcanic rocks. The primary magmatic assemblages of the trachyandesites (i.e. augite and andesine-labradorite) have been affected by chloritization and alblitization respectively, followed by the formation of secondary titanite, celadonite, and calcite. The chlorite species have crystallized in the range of 106–170 °C, that exceeds Apatite Partial Annealing Zone (70–110 °C). The secondary, nearly pure albite (Ab ~ 99 mol.%) with weak to dark-brown cathodoluminescence replaces primary plagioclase (~ An37–50Ab47–58Or2–4) along the cleavage and/or twinning planes during Al3+–conservative reaction. The accessory apatite is marked by swallow-tail terminations indicative of rapid cooling formation conditions. It shows homogenous chemical composition, high F− content, and pink to yellow (REE3+ and Mn2+-activated, respectively) cathodoluminescence. Based on the AFT dating, the development of spilitic alterations within the early-Permian (ca 290 Ma) laccolith from Głuszyca could not only span the range of 182–161 Ma (Middle Jurassic), but also occurred prior to large-scale geological events in the ISB, such as burial under late-Mesozoic sediments, as well as tectonic inversion and exhumation. Whole-rock geochemistry of trachyandesites altered to various extent, indicates that original trace elements concentrations, except for i.e. Sr, Cs, and Ba, could be preserved during low-temperature alteration (spilitization). Meanwhile, geochemical fingerprint of the volcanics (i.e. humped-shaped mantle normalized trace element diagrams and positive Zr–Hf anomaly) points to the crustal contamination during magma evolution, combined with the mantle metasomatism in the source via subduction-derived components (i.e. fluids), as shown by i.e. low Nb/Th and Nb/LREE ratios.

Spatial-temporal evolution of the source-to-sink system in the northwestern South China Sea from the Eocene to the Miocene

The northwestern South China Sea (NW-SCS) presents a spatial-temporal evolution of its source-to-sink (S2S) system, that recorded the movement of the Indochina block and the collision between the Indian and Eurasian plates. However, complex tectonic movements and topographic evolution have led to controversial studies about the spatial-temporal distribution of allogenic materials and autogenic sediments. In this study, we integrated a number of multiscale data to review the S2S system evolution of the northwestern area of the South China Sea from the Eocene to the Miocene. The series include the initial synrift, postrift and thermal subsidence stages. First, we identified the major sediment pathways using seismic profile interpretation. We reconstructed the sediment distribution and lithofacies association within the dispersal sink area based on seismic data, core samples and grain-size analysis. We quantitatively studied the sediment flux and catchment area based on mass balance calculation modeling. Following this, we acquired rare-earth element (REE) data and zircon U–Pb age data from the bedrocks of the continental blocks and the South China Sea Cenozoic basement and rivers in the NW-SCS area to restore the provenance area and evaluate the migration distance by inspecting the heavy mineral assemblages. According to the above studies, three phases of S2S dynamics were identified. 1) The initial rifting stage occurred during the Eocene, and active rifting in the South China Sea induced a major topographic change. A large amount of autogenic slump sediments and a smaller amount of paleo-Red River sediments were injected into the Beibu Gulf Basin (BBGB) and the Yinggehai-Song Hong Basin (YGHB). 2) The postrift stage occurred during the Oligocene. Regional uplift and tectonic inversion probably linked to the clockwise rotation of the Indochina Block, broke the connection between the Beibu Gulf Basin and the Red River catchments. The paleo-Qin River and the paleo-Lian (Nanliu) River brought a large amount of clastic material into the Beibu Gulf Basin from the Cathaysia Block. 3) The thermal subsidence stage occurred during the Miocene: the eastward topographic tilt was enhanced, and the drainage basin entered postrift stage. The development of the Paleo-Red River and its branches, the Lam River and the Ma River, brought distal sediment into the YGHB, while the rivers in the west Cathaysia Block transported sediment into the BBGB. Statistical analysis of the S2S system parameters suggests that the average terrain altitude played a dominant role in determining the S2S system volume during the Eocene, while the dominant role transferred to the sediment supply during the Oligocene and Miocene. • Reconstructs the Source to sink system within NW-SCS from the Eocene to the Miocene. • Reveal the drainage evolution of basins in NW-SCS with multiple dates. • Put out the impact factors to the Source-to-Sink system developed during the rifting process.

Reply to the discussion of Moustafa (2021) on Sayed et al. (2020) (Marine and Petroleum Geology, 17, 2020-104401)

Moustafa (2021) addressed four main comments in his discussion “On the structures of Abu Roash area and inverted basins of northern Egypt - Comments on “Surface expression of the Syrian Arc Kattaniya inverted basin in the Abu Roash area, northeast Western Desert, Egypt: Structural style and tectonic history” by Sayed et al. (2020)”. Two of these comments criticized the new structural mapping of Abu Roash outcrops and the proposed model for El Ghigiga-El-Hassana Folds based on the early geologic mapping of the Abu Roash area by Moustafa (1988). His other comments were concerning the NE-orientation and end of tectonic inversion of the extensional Jurassic -Lower Cretaceous basins in North Egypt including the Kattaniya basin. Except for two constructive memos on drafting errors in the regional geologic map of Abu Roash, the registered comments were inaccurate and can be refuted with the results of the comprehensive regional and integrated subsurface geologic mapping on the North Western Desert basins, the previous works of Moustafa and his collaborators and the figures included in his discussion as we will present in this reply. It was documented that the inversion time, intensity, and type (orthogonal versus oblique or compressional versus transpressional/transtensional) differ from one basin to another in the northern part of Egypt. The geologic structures of Abu Roash helped to define a transpressional (oblique) inversion tectonic model that started at the Santonian and ended by the Latest Senonian. This tectonic model represents the northeastern segment of the Kattaniya basin and does not generalize to the whole basin or other basins in North Egypt.

Shear zone fabrics and their significance in curved, inverted basin-derived thrust systems

In this study, we report how criteria inferred from structural and kinematic analysis of shear zone fabrics can be instrumental in deciphering events of positive or negative inversion tectonics. Mesoscopic structural and kinematic analyses are performed on well-exposed brittle-ductile thrust shear zones within curved thrust systems in the Central-Northern Apennines of Italy.The structural and kinematic features of thrust-related tectonites make it possible to outline a history of positive inversion. S/C- and S-tectonites/fabrics are distinctive of frontal or oblique thrust ramps, respectively. In particular, S-fabrics result from selective transpressional-reactivation of pre-thrusting normal faults. By contrast, more complex composite fabrics, characterized by folded cleavage, reveal a history of negative inversion tectonics. Mesocopic cleavage folding is ascribed to shear-sense reversal along the shear surfaces during extensional reactivation of pre-existing thrusts; or to synthetic reactivation by listric foreland-dipping normal faults, merging downwards on former thrust surfaces during protracted episodes of gravitational collapse.Shear zone fabrics identification criteria, here illustrated from thrusts of different size, if systematically used, may be diagnostic of different deformation paths, and hence provide useful tools to elucidate the tectonic history of curved thrust systems in orogens that have experienced multiple episodes of inversion.

Continental-scale structural heritage from rift extension to postrift inversion: Implications for the central Brazilian Equatorial Margin evolution

The link between major basement anisotropies and basin evolution is crucial for understanding the role of tectonic inheritance on continental margins. However, it is still a matter of debate how and why it happens, especially in the Equatorial Atlantic, where the interplay between Precambrian fabric and the shearing of major oceanic fractures has been studied. Here, we investigate the offshore Ceará Basin and its basement in the central part of the Brazilian Equatorial Margin to (1) map basement anisotropies underneath marginal basins and show how Precambrian crustal domains influenced basin evolution; (2) determine the deformation style of reactivated basement faults; and (3) assess the interplay between reactivated faults and the oceanic Romanche Fracture Zone. The combined geological and geophysical data show that reactivation of NE-SW to ENE-WSW continental-scale ductile shear zones that acted as crustal weakness zones started in the Early Cretaceous under a normal stress field. Stress field inversion occurred in the Barremian during the continental breakup when the South American plate started to became an independent intraplate area under a strike-slip stress regimes. The shear zones arrest at the E-W-striking Romanche Fracture Zone, which marks the continental-oceanic boundary. The major fault offsets occurred along the Transbrasiliano Shear Zone, which represented a collisional boundary between paleocontinents in the Neoproterozoic. Fault reactivation also occurred in the eastern boundary of the Ceará Terrace marginal ridge along the Transbrasiliano Shear Zone, uplifted during tectonic inversion. We conclude that fault reactivation mainly occurred between contrasting Precambrian terrains separated by ductile shear zones. Additionally, the folds associated with the Romanche Fracture Zone were mainly generated along reactivated faults that affected syn- to postrift units on the Equatorial Margin.

Tectono‐stratigraphic evolution of the rift and post‐rift systems in the Northern Campos Basin, offshore Brazil

AbstractThe Campos and Santos Basins have been a focus of subsurface studies since the discovery in 2006 of large accumulations of hydrocarbons in the Early Cretaceous rift and post‐rift strata below Aptian evaporites. In this study, regional 2D seismic lines, a 3D seismic survey and well data were interpreted to reconstruct the tectono‐stratigraphic evolution of the rift and post‐rift stages in the northern sector of the Campos Basin. Detailed 3D seismic interpretation and geological modelling were used to subdivide the pre‐salt sedimentary record. This revealed a diachronous strain distribution along the Guriri Fault System (GFS), a roughly NE‐SW striking fault‐bounded horst that was a focus of rift‐related deformation. The syn‐rift succession is interpreted to be the product of two episodes of rifting (RP1 and RP2) with contrasting fault activity patterns and lithostratigraphy. Volcaniclastics and coarse siliciclastics of RP1 were deposited under WNW‐ESE transtension that formed discontinuous half‐grabens followed by extensive erosion and tectonic inversion. Structurally controlled bioclastic rudstones and hybrid deposits characterize RP2 and were deposited in elongated half‐grabens that delimit the GFS horst, which developed under an NW‐SE extension. Deposition under increasingly less tectonically active transitional and post‐rift stages dominated by thermal subsidence gradually led to the healing of the rift‐related structural relief. Selective reactivation of rift faults testifies active tectonic inversion through compression from immediate post‐rift throughout evaporite deposition. These interpretations are put into the context of recent geochronological data of onshore dyke emplacement and the new age constraints for the end of deposition of the pre‐salt sequence. Therefore, we propose an earlier onset on rifting in the Campos Basin, at the Berriasian.

Influence of rift geometry over successive post-rift sedimentation: Tectonostratigraphy of the eastern Kopeh Dagh Belt (NE Iran)

Well, seismic (2D and 3D) and AHe age data, complemented by field surveys, were analyzed with the objective of investigating the tectono-stratigraphic evolution of syn- and post-rift sedimentary basins in the eastern Kopeh Dagh Belt (NE Iran), a region well known for its important oil and gas occurrences. The study was focused on evaluating how and when the geometry of syn-rift structures influenced the development of the post-rift sedimentation. Our results show that the Middle Jurassic rifting stage influenced the geometry of the post-rift basins. Carbonate buildup of the Upper Jurassic (Mozduran reservoir) was formed in the low relief accommodation zones between the Middle Jurassic opposing half-grabens in parallel to the sedimentation of argillaceous carbonates within the adjacent troughs. This geometry was also transmitted to the Lower Cretaceous, affecting the deposition of a relevant siliciclastic system (Shurijeh reservoir). The role of rifting was crucial in the distribution of reservoir facies and the generation of the structural-stratigraphic traps in the study area, which were also affected by late tectonic inversion. Uplift and denudation is likely to have occurred up to Late Miocene.

The Broken Hill Block, a new structure and mineral exploration target areas

The Broken Hill Block contains the Paleoproterozoic Willyama Supergroup, host to the world-renowned lead–zinc–silver deposits known as the Line of Lode. A new large-scale geological structural interpretation has been developed based on the construction of 11 regional-scale cross-sections and one longitudinal section. Over an extended period of major folding during the Olarian Orogeny, two distinct sets of regional folds were produced. The longitudinal folds are of similar-type and mostly trend northeast. The cross-folds are subtle, mostly trend at right angles to the longitudinal folds and are open-style. Longitudinal folds in or near the Line of Lode have been reinterpreted. A newly interpreted major slump fold, central to the Line of Lode, allows correlation of rock units from east to west. The well-known Western Anticline and Eastern Syncline, which host the main Line of Lode, are normal drag folds, formed during the initial folding with their axes folded by the later slump folding. The lead lodes are older than the zinc lodes. We interpret previously mapped longitudinal folds, as formed by successive pulses within the one tectonic event. This resulted in increased folding complexity on a local scale, but not a regional scale, and with no substantive impact on the regional structure. Pitch and plunge data were used to identify 23 cross-folds, some more than 50 km long. Away from the Line of Lode, the new structure is simpler than previous interpretations and with no tectonic inversion of the stratigraphy, other than gravity slumping, and no regional-scale nappe structures. The combination of cross-folds and longitudinal folds has produced regional-scale domes and troughs throughout the block. The intersection of longitudinal fold axes with cross-fold crests are proposed to be particularly prospective for metallic sulfides with 25 named and prioritised mineral exploration target areas identified. The cross-folding has caused the ore bodies to plunge steeply to great depths north of the Line of Lode. Further to the northeast, the plunge is reversed bringing strata, containing potential northern extensions of the Line of Lode, closer to the surface. The retrograde schist zones, which are regional-scale faults or shears that have undergone retrograde metamorphism, postdate the longitudinal and cross-folding and are not considered to be related to thrust structures. Displacement of strata and structures is evident across the zones and is generally well understood. KEY POINTS A new set of regional folds, termed cross-folds, has been identified. In the Line of Lode, large-sale longitudinal folds include a major slump fold. The stratigraphic sequence is not inverted; nappes are for the most part not present. Broken Hill-type lead–zinc–silver deposits are preferentially found close to the intersection of longitudinal and cross-fold axes.

Unraveling tectonic inversion and wrench deformation in the Eastern Cordillera (Northern Andes) with paleomagnetic and AMS data

Complex orogenic belts typically display internal variations in deformational style, as is the case of the northern Eastern Cordillera of Colombia, which changed abruptly into a regional strike-slip system in the NNW-striking Santander Massif. We report paleomagnetic data, anisotropy of magnetic susceptibility (AMS) data, and magnetic mineralogy from 47 sites distributed in the northern Eastern Cordillera and Santander Massif to investigate and compare: (1) variations in the intensity of the deformation, (2) magnitude and sense of vertical axes rotations, and (3) the character and effect of strike-slip displacements along the Bucaramanga fault and NE-striking transverse faults within the Santander Massif. Rock magnetic experiments show that hematite is the principal magnetization carrier in all these rocks. Rocks of the axial zone of the Eastern Cordillera show intermediate magnetic fabrics. Magnetic fabrics of rocks from the Santander Massif, and the western flank of the Eastern Cordillera, are uniformly oblate with preservation of sedimentary fabrics. Directions of the ChRM from sites in the Eastern Cordillera (30 accepted of 35 sites) are interpreted to indicate that the axial zone has not been rotated, whereas sites located along the western flank of the northern Eastern Cordillera yield data suggesting clockwise rotations, which increase in magnitude up to 90° in areas bounded by NE-striking transverse faults. In the Santander Massif (9 accepted of 12 sites) data suggest a mix of counterclockwise rotations (~30°) and clockwise rotations of ~40°. The inferred clockwise vertical-axis rotations in the northern Eastern Cordillera and Santander Massif of up to 45° are interpreted to be related to tectonic inversion of pre-existing Mesozoic age normal faults during the Neogene as right-lateral faults. Our corrected paleomagnetic inclination data are interpreted to support the hypothesis of northward translation of the studied tectonic elements during the Middle Jurassic to earliest Cretaceous time.

Tectonic inversion of listric normal faults in the foreland of the Rinkian Orogen (Maarmorilik, central West Greenland)

Integration of field structural data and 3D-photogeology from the southern part of the Rinkian Orogen, in central West Greenland, indicates that Paleoproterozoic marbles of the Mârmorilik Formation were deformed by two compressional events in the foreland of the orogen, associated with tectonic inversion of normal faults. Tectonic transport and folding post-date the Rinkian metamorphism (c. 1830–1800 Ma) with the first event characterized by NNE-SSW oriented compression and tectonic stacking of folded calcitic marbles (Black Angel Tectonic Unit), above slightly deformed dolomitic marbles (South Lakes Tectonic Unit). The second event caused the inversion of NE-SW trending normal faults during NW-SE oriented compression. Field observations reveal that the normal faults have a listric geometry and were inverted after c. 20° tilting to the NE of the Maarmorilik carbonate platform. The style of tectonic inversion reflects the amount of extension accommodated along the listric faults showing rollover anticlines and extensional fault-bend-folds in the hanging wall, then inverted as thrust anticlines, back-thrusts antithetic to the normal fault or normal faults passively truncated by younger thrusts. This paper shows the power of 3D-photogeology that can provide observations of lithostratigraphic units and structural data to allow investigation of remote areas from otherwise inaccessible outcrops.

Characteristics, Main Controlling Factors and Prediction of Complex Fracture–Cavity Reservoirs of Buried Carbonate Hills in the Weixinan Depression, Western South China Sea

Buried hill oil reservoirs have become a key area for offshore oil and gas exploration. In this paper, a typical oil field in the western South China Sea is used as the research object, and a study on the characterization, cause of formation and prediction of the fracture–cavity reservoir distribution is carried out. The reservoir in the study area is a complex fracture–cavity reservoir that developed due to weathering and leaching, tectonic movement and dissolution reconstruction on the limestone skeleton. The reservoir spaces are composed of karst caves, fractures and pores. The main controlling factors include lithological changes, karst landforms, tectonic deformation and faulting. To address the controlling mechanisms of the lithological changes on the formation of fracture–cavity reservoirs, a new parameter, the lithology standard deviation, to evaluate lithological changes is proposed based on the characteristics of the lithological changes, and the distribution of these lithological changes is portrayed in combination with the seismic attributes. The tectonic deformation principal curvature inversion algorithm is used to simulate the distribution of the tectonic principal curvature at the top of the Carboniferous. The larger the tectonic principal curvature is, the stronger the deformation of the rock formation and the more favorable the conditions are for fracture formation. The karst geomorphology controls the overall reservoir distribution, and the karst highlands and karst slope areas are the zones with the most–developed secondary pore space (or fractures and karst caves). The faulting control area is the fracture and dissolution pore development area, major faults control the distribution of the karst cave reservoirs, and secondary faults influence the formation of fractures in the faulted area. The study predicts and evaluates the distribution of fracture–cavity reservoirs from the perspective of fracture–cavity genesis quantification, and by gridding and normalizing the four major genesis quantification evaluation parameters and fusing the geological factors that control the formation of fractures and karst caves by using Back–Propagation neural network deep learning algorithms, a method for predicting the distribution of fracture–cavity reservoirs constrained by geological genesis analysis is developed.

Inversion tectonics in the Sorgenfrei–Tornquist Zone: insight from new marine seismic data at the Bornholm Gat, SW Baltic Sea

ABSTRACT New seismic profiles located within the Bornholm Gat in the SW Baltic Sea area image Late Cretaceous-Paleogene inversion and exhumation of a previously poorly characterized narrow crustal zone in the southern end of the Sorgenfrei–Tornquist Zone (STZ), a long pre-Alpine tectonic lineament in Europe. Thrusts and pop-up structures developed along the inversion axis accompanied by subsidence troughs on its sides. Stratigraphic analysis of chalk deposits indicates that structural shortening and inversion resulted from compressional deformation. Marginal troughs formed synchronously to inversion and adjacent to the tectonically active slope, where sediment redeposition was focused. Deposition of chalk units, composed predominantly of contourites and gravity-driven sedimentation were largely controlled by inversion tectonics and influenced by intensification of bottom currents. We find that allochthonous chalk has been buried in horizontally deposited autochthonous (pelagic) chalk. An erosional unconformity represents the base of the Maastrichtian and marks the onset of along slope deposition due to a more hydrodynamic environment. The revealed asymmetric inversion across the STZ with fold tightening and superposition of NE-NW folds attest to more than one pulse during the Late Cretaceous-Cenozoic inversion. The STZ may belong to the end-member mode of intraplate foreland basins resulting from a far-field NE-SW compression transmitted from the Africa-Iberia-Europe convergence. The intraplate stress associated with the following Maastrichtian enhanced collisional coupling between the Alpine-Carpathian orogen and its foreland, which is widely recognized (e.g., the Mid-Polish Trough, the Bohemian Massif and the Central Graben), may also have had its maximum extent to the northeast in southern Sweden.

Deep vs. shallow – two contrasting theories? A tectonically activated Late Cretaceous deltaic system in the axial part of the Mid-Polish Trough: a case study from southeast Poland

Abstract. The Polish Basin is a part of a trans-European sedimentary basin comprising the Central European Basin System and stretching from Denmark through Germany to southeastern Poland, and even further to the south into Ukraine. It experienced uplift during the Late Cretaceous, which consequently resulted in the inversion of its axial part (i.e., the Mid-Polish Trough) and development into the Mid-Polish Anticlinorium. In many existing paleotectonic interpretations, southeast Poland – i.e., the subsurface San Anticlinorium and the present-day Roztocze Hills – was included in the Mid-Polish Trough during the Late Cretaceous, representing its axial, most subsiding part. This paleotectonic model was the basis for facies and bathymetric interpretations that assumed Upper Cretaceous sediments, deposited close to the axial part of the Mid-Polish Trough (e.g., in the Roztocze Hills), constituted the deepest facies. In recent years, several studies have contradicted this notion. A growing body of data suggests that this area (southeast Poland) was already a landmass by the Coniacian and Santonian – and certainly in the Campanian and Maastrichtian – rather than forming the deepest part of the Polish Basin. The shallow marginal marine, cyclic middle Campanian, marly to sandy deposits, recently discovered in the Roztocze Hills, were interpreted to be of deltaic origin. This has led to the adoption of new facies and bathymetric models, which – notably – are in stark opposition to most previous interpretations. Notably, the new interpretation implies the presence of a landmass in the place where, in prior frameworks, the deepest and most subsiding part of the Polish Basin (i.e., Mid-Polish Trough) was located during the Cretaceous. Here, we document this Late Cretaceous depositional system – the Szozdy delta developed in the axial part of the Mid-Polish Trough. These middle Campanian deposits crop out extensively in the Roztocze Hills region, close to the village of Szozdy, and exhibit coarsening-upward tripartite cyclothems. Three facies associations have been distinguished: (1) dark grey calcareous mudstones, (2) a yellow calcareous sandstone, and (3) calcareous gaize lithofacies. The sequence, as a whole, was accumulated via the repeated progradation and abandonment of deltaic complexes on the delta front platform setting, with the primary transport direction originating from the axis of the inverting Mid-Polish Trough (thus from the subsurface San Anticlinorium) toward the northeast. This interpretation is supported by a suite of sedimentological, palynofacies, and heavy mineral data. The development of the Szozdy delta system is framed in the context of the dynamic tectonic processes operating contemporaneously in southeast Poland: that is, tectonic inversion (uplift) on one hand, and the generation of new accommodation space via enhanced subsidence on the other. This discovery sheds new light on our understanding of Late Cretaceous facies distribution, bathymetry, and paleogeography and might potentially suggest a different burial history than assumed so far.

Together but separate: decoupled Variscan (late Carboniferous) and Alpine (Late Cretaceous–Paleogene) inversion tectonics in NW Poland

Abstract. In Europe, formation of the Palaeozoic Variscan orogenic belt, and the Mesozoic–Cenozoic Alpine–Carpathian orogenic belt led to a widespread inversion events within forelands of both orogenic domains. We used legacy 2-D seismic data together with the newly acquired 3-D seismic data that, for the first time, precisely imaged sub-Zechstein (i.e. sub-evaporitic) upper Palaeozoic successions in NW Poland in order to develop a quantitative, balanced 2-D model of the late Palaeozoic–recent evolution of this area, characterised by a complex pattern of repeated extension and inversion. Four main tectonic phases have been determined: (1) Late Devonian–early Carboniferous extension and subsidence possibly related to extensional reactivation of Caledonian thrusts, (2) late Carboniferous inversion caused by the Variscan orogeny, (3) Permo-Mesozoic subsidence related to the development of the Polish Basin and (4) its Late Cretaceous–Paleogene inversion. Variscan and Alpine structures form a superimposed multilayer inversion system, mechanically decoupled by the Zechstein evaporites.

Virtual outcrop models: Digital techniques and an inventory of structural models from North-Northwest Iberia (Cantabrian Zone and Asturian Basin)

The first steps to study natural structures are data collection, their representation and their geological interpretation. There is no doubt that the development of digital techniques in recent times has facilitated these tasks. Here we present an inventory of virtual outcrop models from the Cantabrian Zone and Asturian Basin, North-Northwest Iberian Peninsula, and the procedure employed to obtain the data, construct the models and interpret them geologically. These models correspond to contractional folds and faults of Palaeozoic age, and to Mesozoic extensional structures affected by Cenozoic tectonic inversion in the form of folds and thrusts. The digital techniques and data employed are fieldwork, as well as Google Earth images, orthophotographs, stereoscopical pairs of photographs and virtual outcrop models, constructed using Structure from Motion photogrammetry based on images extracted from Google Earth or from photographs taken in the field using a tripod or unmanned aerial vehicles. The analysis of these models has provided us with geological information that would have been difficult to obtain using traditional techniques. Apart from their scientific interest, the examples shown may be helpful for structural geologists who wish to obtain 3D geological models, maps and sections, and additional structural information from field examples, as well as elements to prepare a virtual fieldtrip and/or for educational purposes.

Hyperextension and polyphase rifting: Impact on inversion tectonics and stratigraphic architecture of the North West Shelf, Australia

Restoration of interpreted 2D deep seismic lines across Australia's North West Shelf indicates that rifting style changed significantly during multiple phases of extension and continental breakup. Early phase rifting during the Neo-Proterozoic and Early Paleozoic, characterised by low-angle detachment faults, crustal-scale necking and hyperextension of the crust (Metamorphic Core Complex Mode), was localised over pre-existing Proterozoic orogenic belts formed adjacent to major cratonic blocks. Subsequent extensional events in the Late Paleozoic and Mesozoic reactivated these low-angle rift fault systems. However, a series of narrow rift basins (Narrow Rift Mode), bound by high-angle normal faults that cut into the upper mantle, also began forming due to changes in the rheological architecture of the lithosphere following previous extension, crustal thinning and post-rift cooling. Wide rift mode extension, wherein extensional deformation was distributed over broad areas, may have occurred prior to, or in conjunction with, the development of more localised narrow rifts (dual mode rifting) in areas such as the Northern Carnarvon and Browse basins. Extensional deformation progressively localised into the narrow rift basins, which in some cases, matured into seafloor spreading centres during breakup, typically outboard of the major low-angle detachment fault systems. The resulting general structural architecture evolution is consistent with several other hyperextended margins from around the world.The rift events were punctuated by periods of thermal sag, often in conjunction with pulses of compressional deformation associated with plate-scale tectonic events. Structural restoration of 2D regional seismic lines shows a marked difference in the way the different polyphase rift basin elements responded to shortening. Low-angle detachment faults were relatively well oriented for reactivation under compression, leading to the development of inversion anticlines and associated convergent unconformities towards the inboard basin margin. In contrast, high-angle normal fault systems associated with the pre-existing narrow rift basins were poorly oriented for reactivation during compression and tend to be characterised by minor wrench/flower structures, generally with relatively limited uplift and erosion on the basin margins. Regional in-plane compressional stresses also worked in combination with vertical loading due to thermal decay to downwarp the lithosphere, forming broad rapidly subsiding synclinal basins above axes of the pre-existing rift basins. The evolving structural architecture developed during the compressional events had significant impacts on the associated sequence stratigraphic architecture.

The Cenozoic evolution of the Intrarif (Rif, Morocco)

AbstractThis paper provides an understanding of the sedimentary-tectonic evolution of the Cenozoic strata of the El Habt and Ouezzane Tectonic Units (Intrarif, External Rif) in Morocco. New data provide information about the depositional architecture and enable a correlation of the evolution of the External Rif in Morocco with that of the Betic Cordillera in Spain and the Tunisian Tell, which provides new insights for hydrocarbon exploration in the region regarding possible source, reservoir, and seal rocks. The reconstructed Cenozoic succession was bio-chronologically defined, and the major unconformities and stratigraphic gaps were identified. The presence of these unconformities allowed three main stratigraphic sequences to be defined by age: Danian p.p., early Ypresian–early Bartonian p.p., and the early Rupelian–early Serravallian p.p. Three secondary stratigraphic sequences in the former upper main sequence were also defined by age: early Rupelian–late Chattian p.p., Burdigalianp.p., and the Langhian–Serravallian p.p. The depositional setting evolved from deep basin during the Late Cretaceous–Paleocene to external platform-slope during the Eocene–Miocene. The Cenozoic sandstones contain metamorphic and sedimentary rock fragments derived from a recycled orogen source area. The clay mineralogy in the Cenozoic strata consists of associations of Ill+(I–S) ± Sme, Ill+(I–S) ± Sme+Kln and Ill+(I–S) ± Sme+Kln+Chl. These associations indicate an initial unroofing in the Paleogene period, then in the Cretaceous period, and finally in the Late Jurassic period during the Eocene–Oligocene. This detritus was followed by variable amounts of a sedimentary mix of Paleogene to Late Jurassic terrains due to several phases of erosion and deposition partly related to syn-sedimentary tectonics during the Miocene. Equivalent features (similar types of sediments, tectofacies, gaps, and unroofing) were also recognized along the Betic Cordillera in Spain and Maghrebian Chain (Morocco and Tunisia) and interpreted as related to a pre-nappe tectonic activity of soft basement folding, which occurred during the Paleogene after the generalized tectonic inversion (from extension to compression) occurred in the Late Cretaceous. The Upper Cretaceous is considered to be the hydrocarbon source rock, while the fractured Eocene and the porous Oligo-Miocene suites are proposed as possible hydrocarbon reservoirs. The Cenozoic stratigraphic architecture and the nappe structure of the region could provide the necessary trap structures.

Fore-to-retroarc crustal structure of the north Patagonian margin: How is shortening distributed in Andean-type orogens?

Orogenic belts like the Andes experience several changes during long-term evolution of the subduction margin; however, the degree to which their different components (the fore-to-retroarc domains) are jointly or separately deformed is not well understood. To investigate this problem, we provide new field and seismic data of the Chilean forearc at the Chiloé island latitude (~41-44°S) integrated with the retroarc structure, in order to obtain a clear visualization of the crustal architecture in the north Patagonian margin. Field work in the western Andean flank and Coastal Cordillera along with 2D multichannel lines, basement isobaths and borehole data in the forearc basins are used to build a structural framework and stratigraphic correlations between the offshore and onshore areas. Forearc syntectonic strata associated with basement faults show a change in the tectonic regime from late Oligocene-early Miocene extension to middle-late Miocene contraction, coincidently to the previously determined deformational stages in the main cordillera and retroarc regions. This coupled fore-to-retroarc behavior ceased during the Pliocene when glaciations covered the North Patagonian Andes, providing abundant sedimentary supply to the forearc and promoting the growth of the accretionary wedge. During this period the retroarc fold-thrust belt growth stagnated and a strike-slip regime was activated in the western Andean flank. Different mechanisms controlled the forearc basins during these late Cenozoic changing tectonic conditions; whilst the external depocenter at the oceanic platform is part of a west-vergent wedge affected by a major splay-like thrust beneath the Coastal Cordillera, the internal depocenter next to the main orogen is overthrusted by the steep western Andean slope through a major west-directed fault. We refer to this latter structural system as the “Western Patagonian Thrust” and find that positive tectonic inversion is the main deformation mechanism. These west-directed crustal faults are part of the orogenic prowedge that is associated with considerably less crustal shortening (~4.2 km) than the retroarc fold-thrust belt (~18 km), part of the retrowedge. By placing these values in a global context through a comparison with other segments of the Andes and with type-examples of collisional orogens, we find that shortening along the Andes is preferentially accommodated in the retrowedge, while shortening in collisional orogens is mainly absorbed in the prowedge. These results have implications for models of subduction orogeny and the crustal architecture of the Andes.