Basin Research - Volume 35, Issue 6, 2023

Salt structures can be used as an archive for tectonic and depositional processes as all salt structures respond distinctively. Few salt tectonic studies have investigated the evolution of multi‐stage salt structures, nevertheless, no previous study had systematically identified, mapped, nor classified, the evolution of multi‐stage salt structures in a regional study. Decades of hydrocarbon exploration and the heavily dense 3D seismic data available, make the Southern North Sea one of the best natural laboratories to investigate the evolution of salt structures. The Southern North Sea salt basin is a Late Permian Zechstein salt mega‐basin containing a myriad of salt structures. The complex tectonic evolution of the Southern North Sea created diverse Mesozoic structural sub‐basins with different tectonostratigraphic evolutions. We defined a nomenclature, linked to the mega‐stratigraphic sequences, for the classification of salt structures. We used a Two‐Way‐Travel‐Time 3D seismic reflection dataset and time‐thickness variations around salt structures to systematically analyse the evolution of salt structures across the diverse structural sub‐basins of the Southern North Sea. Multi‐stage salt diapirs were triggered halokinetically in the Early Triassic and are linked to regional palaeo‐depocentres controlled by the sub‐Zechstein structural configuration. Multi‐stage salt diapirs in the different sub‐basins evolved through three different regional phases and up to five distinctive local stages. The most complex salt diapirs developed in the Central Graben, Sole Pit High and Silver Pit Basin, where multi‐stage salt diapirs showed 4–5 local stages of salt diapirism. The multi‐stage evolution of salt structures should be thoroughly investigated to reduce risks and uncertainties in the energy sector and net zero projects, such as in carbon capturing and storage projects, and energy storage in man‐made salt caverns.

Visualization of the relationship between regional tectonic phases and local stages of salt diapirism with the chrono‐halokinetic stacks in the Southern North Sea salt basin.

The permeability of faults and their sedimentary host rocks is a critical input for models of fluid flow in sedimentary basins. Permeability of sedimentary rocks can vary by orders of magnitude over short distances due to variations in sedimentary facies, as well as being strongly anisotropic. Structural features also affect permeability, with faults acting as fluid conduits or barriers depending on the nature of the sedimentary host rock. Constraining these variations in permeability is challenging where outcrops are lacking and drillhole data are sparse. This study describes a workflow using stratigraphic forward modelling to estimate the permeability distribution (both magnitude and anisotropy) in sedimentary rocks and associated faults, which is then used in fluid flow simulations. Permeability is represented as a tensor in the global coordinate system, enabling the use of an unstructured mesh that is independent of stratigraphic layering. The workflow is demonstrated in a sub‐basin of the Proterozoic McArthur Basin of northern Australia. A range of fault permeability scenarios are explored, where fault permeability is a function of host rock properties. The simulation results demonstrate the importance of capturing the direction of permeability anisotropy in dipping strata, as well as highlighting the effect of different fault permeability scenarios. The workflow is particularly well‐suited to scenarios where there are sufficient boreholes to constrain a stratigraphic forward model, but insufficient to determine the permeability distribution by interpolation. Potential applications include mineral and hydrocarbon exploration, groundwater studies, contaminant dispersal modelling, and CO2 sequestration.

We describe a workflow for determining the permeability distribution in sedimentary basins. The workflow uses facies analysis, sequence stratigraphy and structural interpretation to build a stratigraphic forward model (SFM), from which the permeability of faults and host rocks is estimated. The resulting permeability distribution provides input for fluid flow simulations.

3D visualisation of the Upper Triassic, syn‐extension, top unit 1 showing the key inversion anticlines in the western Huincul High (Neuquen Basin).

The Neuquén Basin is a major Mesozoic sedimentary depocentre located in the retroarc foreland of the Argentinian Andes. The basin hosts world renowned inversion systems that have been the target of georesource exploration for the last three decades. The Huincul High is a structurally and economically prominent ca. 270 km long, E–W trending feature that formed by the accretion of exotic Palaeozoic terranes, influencing subsequent Mesozoic deformation in the basin. Exploration in the Huincul High has been mainly focused on the shallow part of the inversion structures leaving a limited understanding of the deep structural architecture and early tectonic evolution, particularly in the western reaches of the high. This research reveals that Late Triassic extensional faulting was followed by widespread thermal subsidence in the Early Jurassic, as shown by the occurrence of an extensive ca. 60 km long, ca. 20 km wide, NE–SW‐trending, central depocentre. In the Early Jurassic, as contraction ensued across this regional sag basin, atypical inversion geometries were developed. These exhibited prominent thickening in the hanging‐wall and, strikingly, in the footwall of reactivated faults. The style of inversion was also markedly influenced by the mechanically weak stratigraphy of the thick, Lower Jurassic, Los Molles formation that promoted broad inversion folding, inhibited shortcut fault creation, and decoupled post inversion deformation from earlier faulting. Quantitative fault analysis suggests that the reactivated faults originated during the Late Triassic extensional phase as separate ca. 10 km long fault segments. The analysis also indicates that segmentation of extensional faults, as well as their orientation to the later contractional vector (SH), spatially dictated style and magnitude of inversion. This research highlights the critical role played by structural inheritance and mechanical stratigraphy in the development of inversion in the Neuquén Basin, which might be of relevance for characterising inversion systems elsewhere. This research also proposes an evolutionary model for the western reaches of the Huincul High that suggests crustal weakening and thermal sag in the Early Jurassic. Moreover, the model highlights a previously unknown late Early Cretaceous transtensional phase that overprints the main Early Jurassic–Early Cretaceous inversion.

We presented a detailed structural analysis of the fracture network exposed in the Lusitanian Basin based on field analysis and Virtual Outcrop Models to reconstruct the brittle deformation and related paleostress regimes. The brittle deformation evolution scenario and the stress field propoded in this work are associated with the main tectonic events established for W Iberian margin during the Mesozoic‐Cenozoic times.

A detailed structural analysis of the fracture network exposed in the Jurassic strata is used to reconstruct the Lusitanian Basin's brittle tectonic history related to the Meso‐Cenozoic paleostress trajectories of the Iberian plate. Structural analysis is made by high‐resolution virtual outcrop models and orthophoto mosaics, along with information obtained in the field. The paleostress regime is determined based on the fault‐slip inversion method. Structural features are predominantly NNE‐SSW, NE‐SW and NW‐SE‐trending extensional fractures, including joints, veins, normal faults, and ~E‐W‐oriented strike‐slip faults. These structures remained active in the early basin evolution and were repeatedly reactivated by shearing and contraction. The chronological succession and paleostress reconstruction revealed three tectonic regimes (i) NE‐oriented extension, (ii) NE‐oriented strike‐slip and (iii) NW‐shortening. The first stress regime was driven by the North Atlantic rift propagation in the Iberia's west and northwest margins in the Late Jurassic–Early Cretaceous. The younger stress states involve reactivation and inversion of pre‐existing fractures by Africa–Europe convergence since the Late Cretaceous. The findings are consistent with the regional stress field which the Iberian plate has experienced since the Meso‐Cenozoic.

The Namche Barwa Syntaxis (NBS) is one of the most productive detrital factories on Earth. Previous studies have shown that the NBS supplies large amounts of sediment to the Brahmaputra River, although the sources and controlling factors of sediment production have not been ascertained in detail. This study presents petrographic and heavy‐mineral data for 43 sand samples collected in the Yarlung and Parlung river catchments covering the entire NBS and surrounding areas. Combined with U–Pb ages of detrital zircons, our data indicate that 89 ± 11% of Yarlung River sediments downstream of the NBS are produced in the Yarlung and Parlung gorges. The annual sediment flux of the Yarlung River increases by a factor of 20 within ca. 250 km from upstream of the NBS (ca. 10 Mt) to downstream (ca. 200 Mt/a). The Yarlung and Parlung gorges, representing only ca. 1% of the Yarlung‐Brahmaputra catchment area, contribute 74 ± 9% of the total Brahmaputra sediment flux. Average interannual erosion rates in the Yarlung and Parlung gorges corresponding to these fluxes are calculated to be 9.2 ± 1.2 mm/a and 6.5 ± 2.1 mm/a respectively. Focused erosion of the Namche Barwa Complex and Yarlung Suture Zone in the gorge, where high‐grade metamorphic rocks are exposed, is a consequence of high channel steepness (ksn values up to 800–1800), high stream power and extreme events including frequent earthquakes and landslides. The coupling between surface erosion and tectonic uplift in the Yarlung Gorge is in full agreement with the tectonic aneurism model of NBS evolution.

The erosion model of the Yarlung Tsangpo Gorge.

Comparison panel of key margin‐scale profiles along the West African salt‐bearing margin, between Gabon and Namibe, demonstrating the rifted margin, salt and post‐salt structural architecture and variability.

Salt‐bearing rifted margins comprise some of the most structurally complex and economically important sedimentary basin settings such as the South Atlantic and the Gulf of Mexico salt basins. They are also involved with some of the largest uncertainties regarding the crustal and syn‐rift basin architecture and supra‐salt tectonic evolution, as well as the link between rifted margin architecture with salt deposition and post‐rift gravity‐driven salt tectonics. We thus conduct a margin‐scale study along nearly the entire West African salt basin, from South Gabon to Namibe, combining a vast data set of 2D and 3D seismic and well data with gravimetric and magnetic data to analyse its along‐strike rift and salt tectonic structural variability. We construct regional structural and thickness maps of key salt and post‐salt intervals to depict the history of individual margin segments and to investigate (1) how rifting and rifted margin architecture influences post‐rift salt tectonics evolution, (2) how these vary through time and space and (3) what are the controls between their different salt tectonic styles. We show that rifting and rift structures controlled the salt basin geometry, thickness and base‐salt relief in different ways for the different margin segments, and drastically influenced their post‐rift salt tectonic evolution. Differences in post‐salt sediment supply and continental uplift also had a role in their salt tectonic evolution. The results also have general implications to understand the interplay between rifted margin architecture with post‐rift salt tectonics for salt‐bearing rifted margins.

Schematic Late Oligocene–present (a), the Early Oligocene (b) and the Eocene (c) reconstructions of the drainage system of the Pearl River, draining into the PRMB. The Eocene Pearl River was restricted in the eastern part of the Cathaysia Block. The river propagated to the Yangtze Block, west of the Shaoxing–Jiangshan–Pingxiang fault zone in the Early Oligocene (b). Further westward propagation formed the modern‐like drainage system at the Late Oligocene (a). The modern coastal line is plotted for showing the relative locations.

Drainage evolution of the Pearl River, one of the major rivers in the eastern margin of the Asian continent, has important implications for the tectonomorphic evolution of the northern margin of the South China Sea and the southeastern Tibetan Plateau. Previous reconstructions using different methods suggested discrepant timings for the formation of river, ranging from Early Oligocene to Middle Miocene. Here, we address this heavily debated topic using quantitative unmixing modelling of detrital zircon data from the Pearl River Mouth Basin in the northern margin of the South China Sea. In this study, we develop a novel approach for estimating the relative contributions of detrital zircon sources to their shared sink, and propose to use the correlation coefficients among zircon contribution models to evaluate the trade‐off among sources with similar age spectra, to avoid the potential overinterpretation of individual contributions. Our new method is applied to new (997) and published detrital zircon U–Pb data from offshore boreholes and modern Pearl River samples to quantitatively interpret and reconstruct the sediment provenance of the Pearl River Mouth Basin and the development of the Pearl River. Our findings reveal that the provenance change of the Pearl River Mouth Basin can be divided into three main stages. Eocene sediments were mainly sourced in the intra‐basinal highlands and the eastern coastal tributaries, indicating a local drainage system. Early Oligocene provenances extended westward, as shown by the increase in sediment contribution from the central and western parts of the Pearl River (28% in total). Since the Late Oligocene, the eastern, central and western parts of the modern Pearl River have contributed equal amounts of zircons to the Pearl River Mouth Basin, indicating the establishment and long‐term stability of the modern‐like drainage system, as highlighted by our new data acquired from the borehole Miocene strata. The Late Oligocene westward expansion of the Pearl River is consistent with the timing of the coeval breakup and spreading of the South China Sea and the intensified Asian monsoon precipitation, highlighting the importance of base level fall and climate in controlling the drainage evolution.

Sketches showing the geomorphic features expected after a river is dammed and diverted by a landslide. (a) Pre‐landslide geography. (b) Formation of a lake by landslide damming and eventual overflow. (c) Reconfiguration of the drainage network and catchment boundaries after erosion of the divide.

River‐blocking landslides exert a deep impact on mountain range landscapes and the organization of catchments. A blocked river diverted to another watershed modifies both original and transferred drainage networks both up‐ and downstream. Using western Pyrenees examples, a geological and geomorphic framework with diagnostic criteria to detect river diversion by landslides is presented, including the identification of elbows of diversion, eroded divides, beheaded underfit rivers, diverted overfit rivers, reversed river segments and the landslides at fault. Some landslides caused the formation of lakes that overflowed upstream at catchment divide segments with elevations lower than those of blocking landslide tops. Unravelling the presence of fan deltas at distinct sites/elevations of palaeolake shores contributed as well to identification of river damming and later diversion episodes. Reconstruction of the sedimentary organization of river palaeovalleys and of their associated fluvial terraces and palaeoriver channels (some currently submerged by the Cantabrian Sea), along with the reconstruction of river profiles, analysis of bedrock and morphology of watershed divides, identify seven river diversions caused by landslides and 14 additional slides that variably constrained river basin dynamics in the area studied. The diverting slides have current areas between 0.06 and 12.3 km² (thus including giant examples), thicknesses up to 300 m and translational–rotational rupture surfaces usually with low dip angles (3.5–12.3°). A combination of relative dating methods and published absolute ages suggests that diversion events occurred during the Quaternary. This study shows that river diversion by landslides can be significant in mountainous areas of moderate relief.

For the first time, this study presents interpretations of alluvial fans in spectral decomposition RGB Blends, analysed in seismic time slices from the Middle Triassic to Lower Jurassic stratigraphical interval of the Horda Platform (northern North Sea). The time slices record a shifting alluvial fan front, fluvial variability, uplift and erosion and reveals depositional elements that may set the common conception of the geological development of this area during the Early–Middle Mesozoic up for discussion. Results show that the Upper Triassic Lunde Formation in the eastern margin of the Horda Platform was characterized by the deposition of coalesced alluvial fans. A variable extent of the fan front through the Upper Triassic is linked to interplaying allogenic factors: uplifted source areas in the aftermath of Early–Middle Triassic rifting determined sediment availability; climate transitioning from arid to semi‐humid, with increasingly fluctuating precipitation, controlled sedimentation, and run‐off; provenance dictated bulk sedimentology and affected prevailing alluvial processes. An overall retreat of the fan system through the Late Triassic coincided with a significant change in landscape characteristics at the transition into the overlying Statfjord Group. Uplift and initial tilting of the Horda Platform caused landscape degradation and the formation of plateaus and incised valleys, contemporaneous with increased humidity and marine transgression, forming estuaries. The shift in depositional style has implications for reservoir properties, creating complexity and heterogeneity in terms of facies distribution and connectivity, which may benefit potential CO2 storage. Upper Triassic alluvial fan development in the Horda Platform (northern North Sea) depicted through spectral decomposition of seismic time slices Enhanced level of seismic stratigraphic interpretation with RGB blending Impact of allogenic factors on alluvial depositional development Implications of alluvial variability on reservoir properties

The development of the Horda Platform during the Middle Triassic to Lower Jurassic depicted through spectral decomposition of seismic time slices. The interpretation level has been significantly enhanced with RGB blending, which reveal the buildout and retreats of an alluvial fan complex, fluvial variability in the alluvial plain, and the eventual uplift and transgression of the area leading to the establishment of a coastline and formation of incised valleys and estuaries. Changing climate concurrent to hinterland degradation resulted in the alluvial variability and changing landscape morphology, which have a significant impact on reservoir properties.

Updated Early Cretaceous configuration of south‐western Gondwana (base plate model after Müller et al., 2019) including the distribution of crustal types in the Falkland Plateau Basin (FPB). Black lines—faults; red lines—dykes; double red line and double arrows—oceanic ridge and spreading direction; grey lines—extent of Chon Aike and Karoo—Dronning Maud Land—Ferrar volcanics. Question marks in the FPB oceanic domain mark its uncertain southern extent and relation to the Weddell Sea oceanic crust. Brown shades mark the interpreted intruded and underplated continental crust in the FPB. EANT, East Antarctica; FB, Fitzroy sub‐basin; FPB, Falkland Plateau Basin; MB, Malvinas Basin; MEB, Maurice Ewing Bank; NFB, North Falkland Basin; NSR, North Scotia Ridge; NWMP, Northern Weddell Magnetic Province; OB, Outeniqua Basin; oc. c., oceanic crust; SDR, seaward dipping reflectors; SJB, San Julian Basin; SJoB, San Jorge Basin; VB, Volunteer sub‐basin. NWMP from Jordan et al. (2017); East Antarctica dykes after Curtis et al. (2008); Patagonia dykes after Rapalini and Lopez de Luchi (2000); Falkland Islands onshore dykes after Stone et al. (2009); SNFB and NFB faults after Lohr and Underhill (2015) and Stanca et al. (2019); FB and VB dykes and faults after Stanca et al. (2021); South America fault network after Lovecchio et al. (2019); Karoo lavas extent after Jourdan et al. (2007); Chon Aike lavas extent after Bouhier et al. (2017); DML‐Ferrar lavas extent after Elliot (1992) and Elliot et al. (1999); Outeniqua Basin fault network after Paton et al. (2006) and Parsiegla et al. (2009).

Continental break‐up can be oftentimes associated with intracontinental wrenching that can lead to the generation of transform margins and transform marginal plateaus. The wrenching phase can be accompanied by complicated processes, which result in heterogeneous structural and crustal architectures. This makes understanding the evolution of such tectonic settings challenging. The Falkland Plateau is an example of a transform marginal plateau where regional wrenching accompanied the incipient stages of Gondwanan continental break‐up to result in a mosaic of crustal types underlying its largest basin: the Falkland Plateau Basin (FPB). The uncertainties in crustal boundaries have led to several models for the evolution of the plateau, which hinder the development of a reliable plate reconstruction of Southern Gondwana. We integrate seismic reflection, gravity and magnetic data to propose an updated crustal architecture of the FPB. The results show that extended continental crust underlies the basin in the west and north. The eastern and central parts consist of a juxtaposition of intruded and underplated continental crust which transitions southwards to a thick oceanic domain. The basin is crosscut by three main NE–SW trending shear zones which facilitated the development of the contrasting crustal and structural domains interpreted across the plateau. This integrated reassessment of the FPB provides new insights into the tectonic evolution of the plateau, the deformation associated with wrenching and transform margin formation and our understanding of the tectono‐stratigraphic evolution of such areas.

Structures that facilitate fluid migration are common in sedimentary basins. We document several possible hydrothermal and/or volcanic vents located above a >157 km², late Cretaceous volcanic field in the Great South Basin, offshore New Zealand. Three of the four vents are vertically stacked, suggesting episodic re‐use of the same fluid pathway between ca. 75 and 56 Ma. A palaeo‐pockmark dated to ca. 49 Ma and free gas occurring within strata ca. 21 Myr old are located directly above these stacked vents. The spatial association of the vents, pockmark and free gas further suggests re‐use of the fluid migration pathway(s) extended for over 54 Myr. Our results imply that reutilization of fluid flow pathways can affect the distribution of fluids within basins over prolonged periods, potentially impacting hydrocarbon/geothermal exploration and geohazard assessment.

Stacked vents, pockmark and free gas indicate long‐lived reutilization of fluid migration pathway over 54 Myr.

Continental rifted margins can be associated with widespread and thick salt deposits, which are often formed during the final stages of rifting, prior to breakup. These salt‐bearing margins are typically characterized by pronounced post‐rift salt tectonics with variable and complex structural styles and evolution. We use a lithosphere‐scale geodynamic numerical model to investigate the role of varying post‐rift sediment fluxes and progradation rates on rifted margin salt tectonics. We focus on a single, intermediate, rifted margin type and salt basin geometry to explore scenarios with different: (i) constant and (ii) time‐varying post‐salt sediment fluxes. We demonstrate that these promote significant contrasts in the style and magnitude of salt tectonics in the proximal, transitional and distal margin domains. The differences are primarily controlled by the relationship between the rates of sediment progradation (Vprog) and salt flow (Vs). When Vprog > Vs, the salt is rapidly buried and both vertical and lateral salt flow are suppressed across the entire margin. When Vprog < Vs, the salt flows vertically and seaward faster than sediments prograde producing major diapirism in the proximal domain and major distal nappe advance, but only moderate overburden extension and distal diapirism. When Vprog ~ Vs, there is moderate proximal diapirism and distal nappe advance, but major updip extension and downdip shortening, which produces major distal diapirism. Modelling results are comparable to various natural systems and help improve our understanding of the controls and dynamics of salt tectonics along salt‐bearing rifted margins.

Summary diagram illustrating the contrasts in the styles and magnitude of salt tectonic processes across different structural domains for different post‐salt sediment fluxes and progradation rates: (a) high flux, (b) medium flux and (c) low flux. The differences are primarily controlled by the relationship between the rates of sediment progradation rate (Vprog) and salt flow (Vs).

The first record of the upper Eocene contractional pulse (Incaic phase) as far south as 32 ° LS. Clastic continental deposits in a foreland basin.

The Eocene compressional phase is well known to have contributed to the construction of the Andes orogen at latitudes north of 30° S, but its extension to the south has not been fully studied. Moreover, synorogenic deposits of Eocene age across the foreland are scarce. The Cenozoic Manantiales Basin records the unroofing sequence of the Andes at 32° S. This study focuses on the basal infill of the Manantiales Basin, informally called the Areniscas Chocolate, which has received less attention than the upper infill until now. Sedimentological, geochronological and provenance studies were carried out on this unit. Here, we present the first ages for the Areniscas Chocolate sequence, of ca. 35–39 Ma (maximum depositional age, MDA). This MDA is interpreted as close to its depositional age, which together with their stratigraphic characteristics, allow us both to separate it from the overlying Miocene Chinches Formation and to propose it as an independent lithostratigraphic unit called Río de los Patos Formation (nov. den.). The provenance analysis of the Río delos Patos Formation indicates a sediment input from western sources located in the Coastal Cordillera and Western Principal Cordillera. Facies associations suggest that the Río de los Patos Formation represents the distal synorogenic deposits during the construction of an Eocene relief to the west. Therefore, the Manantiales Basin started during the late Eocene as a distal foreland basin, indicating that Eocene compression reached latitudes as far south as 32° S. Our results shed light into the characterization of the earliest infill of the Manantiales Basin, as well as into the tectonic evolution of the basin.