Inversion Of Sedimentary Basins Research Articles

Review of tectonic inversion of sedimentary basins in NE and N Brazil: Analysis of mechanisms, timing and effects on structures and relief

Most intraplate areas worldwide are under compression characterized by thrust and strike-slip deformations. The sources of the stresses in these regions are a combination of far-field (regional) stresses (e.g., ridge push, slab pull, lithospheric drag) and near-field (local) stresses (e.g., topography, lateral and vertical anisotropy of strength or elastic properties, erosion, flexural bending, overloading, buoyancy of low-density regions). These intraplate regions are sites favorable for the tectonic inversion of sedimentary basins. Here, we review the tectonic inversions of the sedimentary basins in NE and N Brazil, which comprise a significant part of the South American intraplate (the South American Platform). These regions have been under compression since the Late Cretaceous. Reports of post-rift basin inversions derived from seismic profiles, fault-slip data, and topography have been described in the Sergipe-Alagoas, Paraíba, Potiguar, Ceará, Rio do Peixe, Araripe (NE Brazil), and Solimões (N Brazil) basins. Reports of inversions in the rift phase have also been described in the Araripe Basin. The present-day stress field indicates that inversions in NE Brazil can mainly be characterized as strike-slip and thrust fault regimes, whereas in N Brazil, inversions have occurred under reverse stress regimes. The most frequent inversion structures are reactivated faults, folds, and dome structures affecting the topography and the consequent uplift of rift and post-rift sedimentary units. Inversions have led to the reactivation of continental-scale structures, such as the strike-slip dextral shearing of the Transbrasiliano lineament, which affected rift and post-rift units in the Equatorial Margin of Brazil. The small crustal thickness of these areas favors inversion, as indicated by the most recent Moho depth map of South America. The interplay between far-field and near-field stresses explains the stress pattern in NE and N Brazil, where inversions have been observed.

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The article focuses on the formation mechanisms of fold’s diversity of sedimentary basin inversion. They are investigated on the example of structures of the Dnieper-Donets paleorift system. To achieve this aim we systematized structural and lithofacial data of the Dnieper-Donets basin and Donbas; used numerical modelling to establish the regularities of deformations within lithosphere and sedimentary cover in collisional compression setting. It is shown that the formation of main folding styles as discontinuous (intermittent), transitional and continuous (full) is accompanied by characteristic features of the cover. In this respect, we formulated the basic dependence principle of folding from lithofacial and lithogenic factors, which defined different mechanical properties of sedimentary cover complexes (the lithomechanics principle). Modelling results confirm prime significance of horizontal compressional conditions of basin’s folds development. Moreover, the sedimentary basin plays the role of independent deformation attractor in the lithosphere. The main conclusion is that the transitional fold paragenesis of Donbas with crest-like Main anticline may be the result of particular strength’s distribution, i.e. axial weak zone and competent layer of variable thickness with central minimum. Main anticline formation mechanism is complex. It includes vertical, axial-parallel viscous-plastical flow with distant bending. It is shown that intermittent folds (uplifts) of the Dnieper-Donets basin may be a result of sedimentary cover compression with a random combination of weakened and strengthened zones. On the contrary, full folding of East Donbas and the Karpinsky ridge corresponds to a bending mechanism of competent layer compression of constant thickness. For the first time we obtained the evidence for the folding inversion mechanisms within Dnieper-Donets aulagogen (including Main anticline), which was problematic for many years. Folding is directly related to peculiarities of sedimentary basin infilling within formulated principle of lithofacial mechanics. With necessary caution, the study offers the results of modelling and conclusions for explanations of fold development within intracontinental basins and marginal folded belts. Practical significance. Numerical modelling and elaborated principles of analysis may be used in reconstructions, numerical investigations of fold structures (uplift) within inverted basins, as well as in prognosis of ore, oil-and-gas deposits.

A Newly Discovered Late‐Cretaceous East Asian Flat Slab Explains Its Unique Lithospheric Structure and Tectonics

AbstractThe existence of historical flat slabs remains debated. We evaluate past subduction since 200 Ma using global models with data assimilation. By reproducing major Mesozoic slabs whose dip angles satisfy geological constraints, the model suggests a previously unrecognized continental‐scale flat slab during the Late Cretaceous beneath East Asia, a result independent of plate reconstructions, continental lithospheric thickness, convergence rate, and seafloor age. Tests show that the pre‐Cretaceous subduction history, both along the western Pacific and Tethyan trenches, is the most important reason for the formation of this prominent flat Izanagi slab. Physically, continuing subduction increases the gravitational torque, which, through balancing the suction torque, progressively reduces dynamic pressure above the slab and decreases the slab dip angle. The flat Izanagi slab explains the observed East Asian lithospheric thinning that led to the formation of the North‐South Gravity Lineament, tectonic inversion of sedimentary basins, uplift of the Greater Xing'an‐Taihang‐Xuefeng mountains and the abrupt termination of intraplate volcanism during the Late Cretaceous.

Upper plate proxies for flat-slab subduction processes in southern Alaska

The timing of initiation of flat-slab subduction beneath southern Alaska and the upper plate record of this process are not well understood. We explore the record of flat-slab subduction in southern Alaska by integrating stratigraphic, provenance, geochronologic, and thermochronologic data from the region directly above and around the perimeter of ongoing flat-slab subduction. These datasets document a change from regional Paleocene–Oligocene subduction-related magmatism and basin development to an absence of magmatism and initiation of rock exhumation that continues to today. We infer that initiation of flat-slab subduction prompted crustal shortening, exhumation, inversion of sedimentary basins, and cessation of magmatism above and around the area of ongoing flat-slab subduction. Surface uplift and erosion above the flat slab resulted in deposition of thick, clastic wedges in sedimentary basins located along the western and northern perimeters of the flat-slab region. Along the eastern perimeter, northwestward-propagating Oligocene–Quaternary slab-edge volcanism and transtensional basin development along dextral strike-slip faults record progressive northwestward insertion of a shallow slab against the curved continental margin of eastern Alaska. Collectively, these geologic data indicate that flat-slab subduction was shaping southern Alaska by late Eocene–early Oligocene time, much earlier than previous models infer. Upper plate processes related to subduction of a flat slab in Alaska are similar to those documented in other modern flat-slab regions. These processes include: 1) shortening and exhumation of the upper plate several hundred kilometers inboard from the plate margin, 2) cessation of subduction-related magmatism within ten million years of the onset of shallow subduction, 3) shoaling or inversion of sedimentary basins above the flat-slab region, 4) deformation and/or erosion of the accretionary prism during flat-slab subduction, and 5) in some settings, reestablishment of sedimentation in the accretionary prism after the shallow slab has migrated laterally. Unlike other flat-slab margins, strike-slip-related volcanism and basin development characterizes one edge of the flat-slab region in Alaska, a consequence of oblique insertion of the flat slab into the corner of a curved continental margin.

Cenozoic post-breakup compressional deformation and exhumation of the southern Australian margin

We present results from a margin-wide analysis of the history of post-breakup Cenozoic compressional deformation and related exhumation along the passive southern margin of Australia, based on a regional synthesis of seismic, stratigraphic and thermochronological data. The Cenozoic sedimentary record of the southern margin contains regional unconformities of intra-Lutetian and late Miocene–Pliocene age, which coincide with reconfigurations of the boundaries of the Indo-Australian Plate. Seismic data show that post-breakup compressional deformation and sedimentary basin inversion—characterised by reactivation of syn-rift faults and folding of post-rift sediments—is pervasive from the Gulf St Vincent to Gippsland basins, and occurred almost continually since the early- to mid-Eocene. Inversion structures are absent from the Bight Basin, which we interpret to be the result of both the unsuitable orientation of faults for reactivation with respect to post-breakup stress fields, and the colder, stronger lithosphere that underlies that part of the margin. Compressional deformation along the southeastern margin has mainly been accommodated by reactivation of syn-rift faults, resulting in folds with varying ages and amplitudes in the post-rift Cenozoic succession. Many hydrocarbon fields in the Otway and Gippsland basins are located in these folds, the largest of which are often associated with substantial localised exhumation. Our results emphasise the importance of constraining the timing of Cenozoic compression and exhumation in defining hydrocarbon prospectivity of the southern margin.

Signature of cryptic sedimentary basin inversion revealed by shale compaction data in the Irish Sea, western British Isles

Inversion is one of the most common modes of intraplate deformation and a primary mechanism of sedimentary basin exhumation. The key criterion for identification of basin inversion is the contractional reactivation of extensional faults. Reverse displacement associated with inversion is focused along the upper segments of faults, so the evidence for inversion may be removed in deeply exhumed basins. We believe this is the case in the Irish Sea, western British Isles. Previous authors have attributed the severe exhumation of this basin to plume‐related uplift and have ruled out inversion as a cause of uplift. We present a method for identifying tectonic inversion in a basin where exhumation has removed evidence of reverse displacement on the upper segments of faults. We utilize compaction‐based mapping of erosion patterns recorded by anomalously high sonic velocities in Upper Triassic shales. We show that the amount of section removed during exhumation in the Irish Sea varies between 1.3 and 3.3 km and that exhumation patterns are markedly heterogeneous. Neither the heterogeneity of exhumation nor its focusing over hanging wall blocks of major faults is consistent with solely plume‐related uplift, and we believe that our results record cryptic basin inversion that is superimposed on epeirogenic exhumation (some of which may be plume related). The direct evidence for this inversion has been removed because erosion has proceeded beneath the null lines of reactivated faults, and we propose erosion of reactivated fault segments as one of the major reasons why shortening is frequently underestimated in inverted basins.

Temporal constraints on basin inversion provided by 3D seismic and well data: a case study from the South Viking Graben, offshore Norway

ABSTRACTThree‐dimensional (3D) seismic, well and biostratigraphic data are integrated to determine the timing of inversion on the hangingwall of the South Viking Graben, offshore Norway. Within the study area two, NW–SE to NE–SW trending normal faults are developed which were active during a Late Jurassic rift event. In the hangingwall of these faults asymmetric, 2–5 km wide anticlines are developed which trend parallel to the adjacent faults and are interpreted as growth folds formed in response to compressional shortening (inversion) of the syn‐rift basin‐fill. Marked thickness variations are observed in Late Jurassic and Early Cretaceous growth strata with respect to the inversion‐related folds, with seismic data indicating onlap and thinning of these units across the folds. In addition, well data suggests that not only are erosional surfaces only locally developed towards the crests of the folds, but these surfaces may also truncate underlying flooding surfaces towards the fold crests. Taken together, these observations indicate that inversion and growth of inversion‐related structures initiated in the late Early Volgian and continued until the Late Albian. Furthermore, it is demonstrated that individual folds amplified and propagated laterally through time, and that fold growth was not synchronous across the study area. This study demonstrates that the temporal evolution of structures associated with the inversion of sedimentary basins can be accurately determined through the integration of 3D seismic, well and biostratigraphic data. Furthermore, this study has local implications for constraining the timing of inversion within the South Viking Graben during the Late Mesozoic.

Unconformity-related uranium systems: Downunder and over the top

The essentials of the unconformity-related U (± precious and base metals, REE?) association are illustrated by the Mesoproterozoic systems of the Athabasca Basin (Canada) and the Alligator Rivers (Australia) regions, sites of major production and high grade resources of U. Significant elements of such systems include i) a regional redox interface corresponding broadly to the unconformity separating an oxidised sedimentary pile from C and/or Fe2+ rich reductants in or near the basement; ii) sources of oxidised (high SO42-/H2S, evaporite-interacted, moderate to high salinity) fluids in/above the sedimentary basin succession. Such fluids may transport numerous components and their progressive interaction with reductants may give rise to characteristic geochemical and mineralogical patterns at deposit and broader scales; iii) linked fault systems operative during sedimentary basin inversion or subsequent compression; iv) the mechanical contrasts of the basement with the sedimentary cover package; v) and probably, uranium-enriched rocks in the basement and/or in cover sediments and volcanics. Other well endowed uranium systems, for example the Proterozoic Westmoreland district (Queensland and the Northern Territory), exhibit the key elements of the unconformity-related association, but the main deposits are localised around redox interfaces the faults away from the basal unconformity. A clear picture of the Westmoreland regional mineralised system is provided by integrated airborne geophysical and geological information, providing a model for systems elsewhere. The prospectivity of the unconformity-related association is not restricted to the Mesoproterozoic. Examples of systems which display the essentials of the association include the late Palaeozoic-aged Ben Lomond and Maureen U-Mo deposits (Queensland) and others in Central Asia, plus Palaeoproterozoic U, precious and base metal deposits in Canada and elsewhere. More effective exploration and regional targeting models will result from the application of the model outlined above.

Sedimentary basin inversion and intra-plate shortening

Sedimentary basin inversion, the shortening of formerly extensional basins, is accommodated mainly by compressional reactivation of extant faults and fractures across a wide range of scales. As such, inversion is a large-scale manifestation of Byerlee friction, the dynamic criterion for fault reactivation governing the effective shear strength of the shallow crust. Basin inversion generates distinctive deformational architecture, and it is implicated strongly in sedimentary basin exhumation. As a principal source of horizontal stress, inversion drives significant sedimentary porosity reduction and resultant fluid flow. Upper crustal deformation is critically dependent on fluid overpressure (i.e., pore fluid pressures greater than would be calculated from a hydrostatic gradient), and, perhaps more than in any other tectonic setting, overpressures are potentially large during sedimentary basin inversion. This review therefore includes discussion of the role of fluid overpressure in inversion and the evidence for it. Collectively, inversion has profound implications—good and bad—for the prospectivity of many petroliferous sedimentary basins. Thus, recognizing the evidence for basin inversion, quantifying its magnitude and understanding the mechanisms that accommodate inversion and other phenomena affected by it, have become essential components of the basin analyst's remit.

Why rifts invert in compression

The common observation of sedimentary basin inversion in orogenic forelands implies that rifts constitute weak areas of the continental lithosphere. When compressed, the rifts respond with uplift of the deepest parts and erosion of sediments therein. Simultaneously, syn-compressional marginal troughs are formed flanking the inversion zone. Since rifting and subsequent post-rift thermal re-equilibration are processes expected to alter the long-term mechanical state of the lithosphere, the phenomenon of basin inversion is non-trivial from a rheological point of view. Stochastic modelling of the long-term thermal structure beneath sedimentary basins indicates that the crustal part of a rift is warmer, and hence weaker, than the surrounding crustal blocks. In contrast, the mantle part is cold and strong beneath the basin centre. In this paper, it is investigated whether the rifting-induced strength alterations constitute a sufficient condition for a thermally equilibrated rift to invert by compression. Numerical experiments with two-dimensional dynamic thermo-mechanical models are performed. In particular, the focus is on rifting-related mechanical instabilities that reduce the load bearing capacity of the lithosphere. In the experiments, strain-softening behaviour is introduced in the non-associated plasticity model representing brittle yielding. The result is self-consistent large-scale fault formation. The models predict that the rifting-related necking instability induces differential crustal thinning increasing the post-rift crustal weakness. Strain softening and the associated fault formation amplifies the necking instability and introduces zones of structural weakness exposed for compressional re-activation. Under these circumstances, basin inversion follows as a natural consequence of rift compression.

Review of the present-day geodynamics of the Pannonian basin: progress and problems

We present a comprehensive review on what we have learned during the last decade and what we need to know in the future about the present-day crustal deformation and geodynamics of the Pannonian basin and its surroundings. The recent tectonic activity of the region is controlled primarily by the counterclockwise rotation of the Adriatic microplate relative to Europe around a pole in the Western Alps. Due to the indentation of this crustal block against the Southern Alpine–Dinaric fold and thrust belt, intense shortening is effecting these orogens as evidenced by the general seismicity pattern and crustal deformation. The present-day kinematics of the Pannonian basin shows that the area is pushed from the south-southwest. As a result, strike-slip to compressive faulting is observed well inside the Pannonian basin and, furthermore, the nearly complete absence of normal faulting in the whole study area suggests that extension in the Pannonian basin has been finished and structural inversion is in progress. Due to an increase of intraplate compressional stress the Pannonian lithosphere exhibits large-scale bending manifested by the Quaternary subsidence and uplift history. The orientation of the modern tectonic stress field in and around the Pannonian basin shows a remarkable radial pattern of maximum horizontal stress around the Adriatic microplate. N–S directed compression observed at its northern tip in the Southern Alps gradually becomes NE–SW oriented along the Dinaric belt. This pattern is further traceable well inside the Pannonian basin, while in the Vrancea zone of the southeastern Carpathians E–W to ESE–WNW directed compression can be determined. Finite element stress modelling suggests that the stress regime in the Pannonian basin is governed by distinct tectonic factors in the overall convergent setting associated with the Africa–Europe collision. The most important stress source appears to be the active push of the Adriatic microplate. Additional boundary conditions, such as the deformation of crustal blocks with different geometry and rigidity at the margin of the Pannonian–Carpathian area and the effect of active compression in the Vrancea zone, significantly influence the stress regime and pattern. Finally, with a brief overview about the principal aims of the Central Europe Regional Geodynamic Project (CERGOP), we argue for the need of further investigations applying the latest techniques of space geodesy (GPS). This international cooperation can provide an excellent opportunity to further develop our understanding of the recent crustal deformation in Central Europe and to refine concepts and models about the tectonic inversion of sedimentary basins with back-arc origin.

The link between sedimentary basin inversion and igneous underplating

Abstract There is now general agreement that many sedimentary basins on the northwest continental shelf of Europe underwent permanent exhumation during the Tertiary. The most dramatic indicator of this process is the present-day absence of up to 3 km of anticipated post-rift subsidence in the midlands of Britain and in the East Irish Sea. Any explanation must take into account the fact that the entire shelf has very small, long wavelength, free-air gravity anomalies. This constraint is of fundamental importance and implies either that the crust has been thickened, that phase changes have occurred within the lithosphere, or that low density material has been added to the lithosphere. Tertiary epeirogenic uplift and exhumation is often attributed to horizontal shortening which is assumed to be related in a general sense to Alpine mountain building. However, the removal of 3 km of sediment from a basin, which was originally 100 km wide, requires 20–30 km of shortening. Whilst minor Tertiary shortening is observed all over the continental shelf, nowhere is it sufficient to account for the inferred amount of denudation. More significantly, exhumation is thought to have commenced in the Early Tertiary and dramatically increases from south to north. Shortening is generally younger (mid-Tertiary) and decreases in intensity from south to north. Here we argue that Tertiary uplift and denudation are a consequence of regional igneous underplating. At the beginning of the Tertiary, rifting associated with the initiation of the Iceland plume generated substantial volumes of melt. Petrological arguments and the results from inversion of rare earth element concentrations of MgO-rich igneous rocks suggest that a minimum of 2–5 km of melt were produced beneath a substantial part of the continental shelf. We infer that much of this melt was trapped within the lithosphere, presumably close to the Moho, which would have acted as a density filter. Such underplating will have caused rapid surface uplift whilst maintaining isostatic equilibrium. Simple calculations based on deep seismic reflection data and the high P-wave velocities observed beneath Scotland are consistent with the petrological arguments.

Sedimentary basin inversion caused by igneous underplating: Northwest European continental shelf

A considerable body of evidence indicates that many of the extensional sedimentary basins in the vicinity of the British Isles underwent permanent exhumation during the Tertiary. The most dramatic indicator of this process is the present-day absence of as much as 4 km of anticipated postrift thermal subsidence in basins just north and west of Scotland. Any explanation of this observation must take into account the fact that the entire region has very small,-long-wavelength, free-air gravity anomalies. This important constraint implies either that the crust has been thickened or that low-density material has been added to or formed from the lithosphere and rules out models that invoke flexural effects arising from the opening of the North Atlantic. Tertiary epeirogeny is often attributed to compression that is assumed to be related in a general sense to Alpine mountain building. However, to remove ∼3 km of sedi- mentary rock from a basin ∼100 km wide requires >15 km of shortening. Minor Tertiary compression is observed all over the continental shelf, but nowhere is it sufficient to account for the required amount of uplift and erosion. In addition, exhumation dramatically increases from south to north, whereas the observed compression decreases markedly in the same direction. At the beginning of the Tertiary, rifting associated with the initiation of the Iceland plume generated substantial volumes of melt. Inversion of rare-earth- element concentrations of MgOrich igneous rocks suggests that a minimum of ∼5 km of melt was produced beneath at least part of the continental shelf. We infer that much of this melt remains trapped within the lithosphere, presumably close to the Moho, which acted as a density filter. Such underplating will generate rapid uplift.

Inversion tectonics along the Western margin of the Bohemian Massif

The block-faulted southwestern margin of the Bohemian Massif is superimposed on a Permo-Carboniferous graben, major faults of which became repeatedly reactivated during the Mesozoic and Cenozoic. Inversion of sedimentary basins associated with this fault system occurred during the Early Cretaceous and again during the latest Cretaceous-Early Cenozoic.

Small inversion structures on seismic sections from the southern North Sea

Fig. 1. Structural elements of the southern North Sea, after Glennie and Bougner (1981) and Dunning (1985). Fig. 2 at about 0.9 to 1.0 sees TWT. The corresponding depths are about 800 to 900 metres, and there is virtually no structuring at or above this level. The Chalk extends to rather more than 1.4 sees TWT at the left hand side of Fig. 2. Seismic energy travels through carbonates at much higher velocities than through Tertiary shales, and the Chalk thickness at this point is about 600 metres. The strong reflection from its base is, however, severely distorted by geometrical effects and particularly by diffraction hyperbolae generated by discontinuities at the edges of fault blocks. The way in which these features are produced on seismic sections is well understood but where several intersect it is extremely difficult to 'see through' to the true geological structure. Fortunately the processing technique known as migration can be used to correct for such distortions (Fig. 3). A single seismic section can be successfully migrated only if the seismic line crosses the geological structures at right angles to their strike. This condition The inversion of sedimentary basins to form structural highs has long been recognised as a feature of the geology of southern England. The classic example is the Weald Basin of Sussex and Kent, which suffered inversion early in the Tertiary. More recently, inversion structures have been mapped in the course of exploration for oil and gas in the North Sea. In the southern North Sea the major inverted feature is the Sole Pit Basin, which occupies much of the subsea region between the UK and the Netherlands (Fig. 1; cf Glennie & Boegner, 1981). The Sole Pit inversion extends almost to the southern limit of North Sea basinal structures. This limit is marked by the northern flank of the London-Brabant Platform, which was a positive and intermittently emergent structural feature from Early Palaeozoic times until the Cretaceous. Numerous seismic surveys have covered the region between the Platform and the Sole Pit, many of the most recent having been shot in anticipation of the UK Ninth Round allocations in late 1984. The Sole Pit Basin formed in the Permian as a large half-graben, subsiding along the Dowsing Fault Zone which formed its southwest margin. Rotation took place about a horizontal axis along the Swart Bank Hinge to the NE (Fig. 1). The hinge converges with the Dowsing Fault near the UK-Netherlands median line off the coast of East Anglia . Associated faulting produced numerous small basins which are shown by seismic reflection surveys to have also suffered Cretaceous inversion. The small inverted basins are preserved beneath a thick pile of younger sediments. Late Cretaceous seas which transgressed across the London-Brabant platform deposited a rather uniform layer of Chalk in the region close to the present-day Norfolk coast . Further to the northeast, and crossing the Swart Bank Hinge , the West Netherlands Basin developed late in the Cretaceous and continued to subside and receive sediments throughout the Tertiary. The Tertiary and youngest Cretaceous rocks have suffered little or no deformation and are clearly imaged on 'Final Stack' seismic sections (cf Fig. 2). The strongest reflectors are the top of the Chalk and a thin high-velocity Eocene bed. Together these give rise to the complex of high-amplitude events , seen on o ! km 50 [ [ I r