Mud volcanoes of the Orinoco Delta, Eastern Venezuela

Mud volcanoes along the northwest margin of the Orinoco Delta are part of a regional belt of soft sediment deformation and diapirism that formed in response to rapid foredeep sedimentation and subsequent tectonic compression along the Caribbean–South American plate boundary. Field studies of five mud volcanoes show that such structures consist of a central mound covered by active and inactive vents. Inactive vents and mud flows are densely vegetated, whereas active vents are sparsely vegetated. Four out of the five mud volcanoes studied are currently active. Orinoco mud flows consist of mud and clayey silt matrix surrounding lithic clasts of varying composition. Preliminary analysis suggests that the mud volcano sediment is derived from underlying Miocene and Pliocene strata. Hydrocarbon seeps are associated with several of the active mud volcanoes.Orinoco mud volcanoes overlie the crest of a mud-diapir-cored anticline located along the axis of the Eastern Venezuelan Basin. Faulting along the flank of the Pedernales mud volcano suggests that fluidized sediment and hydrocarbons migrate to the surface along faults produced by tensional stresses along the crest of the anticline. Orinoco mud volcanoes highlight the proximity of this major delta to an active plate margin and the importance of tectonic influences on its development. Evaluation of the Orinoco Delta mud volcanoes and those elsewhere indicates that these features are important indicators of compressional tectonism along deformation fronts of plate margins.     

Sedimentation and deformation in a Pliocene–Pleistocene transtensional supradetachment basin, Laguna Salada, north-west Mexico

This study examines a thick section of Pliocene–Pleistocene sedimentary rocks exposed in the footwall of an active normal fault (Cañon Rojo fault) near its intersection with the dextral-normal Laguna Salada fault in north-western Mexico. These rocks are situated in the upper plate of an inactive strand of the Cañada David detachment fault, which is cut on the north-east by the Laguna Salada fault. The stratigraphy is divided into three unconformity-bounded sequences: (1) marine mudstone of the Pliocene Imperial Formation; (2) nonmarine Pliocene–Pleistocene redbeds, consisting of sedimentary breccia, conglomerate, conglomeratic sandstone (all un-named) and fine-grained sandstone and mudstone of the Palm Spring Formation; and (3) uncemented Pleistocene boulder gravel. Coarse deposits of the redbeds sequence were deposited in fault-bounded, high- and low-gradient alluvial fans that passed laterally into a low-energy fluvial plain of the ancestral Colorado River (Palm Spring Formation) which occupied the present-day Laguna Salada. Detailed mapping reveals convergence and lap-out of bedding surfaces in the redbeds sequence onto the west limb of a large anticline cored by Imperial Formation. These geometries, combined with fanning dips and thickening of stratigraphy into the flanking syncline, indicate that the anticline grew during deposition of the redbeds. Fold axes of the growth anticline and smaller related folds trend N to NNE, parallel to the strike of associated normal faults and perpendicular to the extension direction. Based on its orientation, large size and relationship to neighbouring structures, the anticline is interpreted to be a fault-bend fold that grew in response to slip of the upper plate over a bend in the Cañada David detachment fault during deposition in a transtensional supradetachment basin. Localized subsidence in the flanking syncline resulted in deposition of >1000 m of alluvial sediments near its intersection with the Laguna Salada fault. Sedimentary detritus is derived exclusively from the north-east (footwall) side of the dextral-normal Laguna Salada fault, indicating that topographic relief was high in the Sierra Cucapa and was subdued or negligible in the footwall of the coeval Cañada David detachment. Following deposition of the redbeds and grey gravel units, the northern part of the detachment fault was abandoned and the modern Cañon Rojo fault was initiated, producing rapid footwall uplift and erosion of previously buried stratigraphy. Slip rate on the Cañon Rojo fault is estimated to be ≈2–4 mm yr^?1 since middle Pleistocene time, similar to the late Pleistocene to Holocene rate determined in previous studies.     

Emplacement mechanics of sandstone intrusions: insights from the Panoche Giant Injection Complex,California

The Panoche Giant Injection Complex (PGIC; California) constitutes the most complete sandstone intrusion network yet described, and is an excellent analogue for subsurface hydrocarbon reservoirs modified by sand remobilisation. Sandstone dykes and sills were intruded during the Late Palaeocene into slope mudstones of the Great Valley forearc basin, and are exposed for more than 300 km². The PGIC consists of dykes and sills and represents upwards infilling of natural hydraulic fractures sourced from highly overpressured Cretaceous sand bodies. Over 1300 orientation measurements show that dykes are almost randomly oriented with only a slight orientation bias trending NE–SW, N–S or NW–SE, suggesting either a horizontally isotropic state of stress during intrusion or modification of stress by newly‐formed fractures that override the remote stress. Dykes are segmented in a pattern consistent with radial propagation with fingering towards tips similar to that observed for other mixed mode fractures. Kinematic indicators reveal there was no systematic sense of opening for the intrusions. This is interpreted as the result of short‐range mechanical interactions. Cross‐cutting relationships between injections imply a diachronous timing and a fluid pressure in the source units that was in excess of the lithostatic load. Finally we document a suite of minor structures within the host section that allowed the strain of the forcefully intruded sand to be accommodated.     

Listric extensional fault systems - results of analogue model experiments

Abstract Analogue models are a powerful tool for investigating progressive deformation in extensional fault systems. This paper presents exciting new insights into the progressive evolution of hanging wall structures in listric extensional terranes. Analogue models, scaled to simulate deformation in a sedimentary sequence, were constructed for simple listric and ramp/flat listric extensional detachments. For each detachment geometry homogeneous sand, sand/mica and sand/clay models were used to simulate respectively, deformation of isotropic sediments, of anisotropic sediments and of sedimentary sequences with competency contrasts. Roll-over anticlines with geometrically necessary crestal collapse graben structures are characteristic of the steepening-upwards segments of listric extensional fault systems in all of our models. With progressive deformation, crestal collapse grabens show hanging wall nucleation of new faults. Variations in graben size, amount of fault rotation and throw, are dependent on detachment curvature and amount of extension. Individual faults and associated fault blocks may significantly change shape during extension. Complex and apparently conjugate fault arrays are the result of superposition of successive crestal collapse grabens. Ramp/flat listric extensional fault systems are characterized by a roll-over anticline and a crestal collapse graben system associated with each steepening-upwards segment of the detachment and a ramp zone consisting of a hanging wall syncline and a complex deformation zone with local reverse faults. The roll-over anticlines and crestal collapse graben are similar in geometry to those formed in simple listric extensional systems. The models demonstrate that the geometry of the detachments exerts a fundamental control on the evolution of hanging wall structures. Analysis of particle displacement paths for these experiments provides new insights into the mechanical development of roll-over anticlines. Two general models for deformation above simple listric and ramp/flat listric extensional detachments have been erected.     

Tectonic and eustatic controls on Pliocene accommodation space along the front of the southern Apennine thrust‐belt (Basilicata,southern Italy)

The stratigraphical organization of the Pliocene thrust‐top deposits cropping out at the front of the Southern Apennine thrust‐belt has been debated for a long time taking a great importance in the context of the geodynamics of the Central Mediterranean area. During this time, spreading episodes in the Apennine backarc zone alternate with important phases of overthrusting in the thrust‐belt. As a consequence, the Pliocene succession appears to be arranged in a series of stacked units, recording the poliphase tectonic history that leads to the building of the front of the southern Apennine thrust‐belt. Although there is not yet an accordance on the nature and position of the main unconformities bounding the thrust‐top units, all authors agree that the creation of new accommodation space is mainly ruled by contractional tectonics consequent to the eastward nappe propagation according to the Apennine vergence polarity. A detailed geological survey, carried out along a large portion of southern Apennine thrust‐belt front, running south of the Vulture volcano, allowed the collecting of new data concerning the basinal‐formation mechanisms acting during the sedimentation of Pliocene deposits. From this analysis, it is clear that even if contractional tectonics is the predominant factor controlling the creation or destruction of accommodation space, other mechanisms, as well as wedge uplift‐related extensional tectonics and eustasy, could have also played a significant role in the basin accommodation. In order the considered sector of southern Apennines can provide an useful example about the complex phenomena occurring at mountain belt front where the accommodation space results from a concomitance of eustatic and tectonic factors mainly linked to the accretionary wedge activity.     

Internal structure and eruptive history of a kilometre-scale mud volcano system, South Caspian Sea

We describe the internal structure of a multi‐kilometre scale mud volcano edifice from the South Caspian Sea using three‐dimensional (3D) seismic reflection data leading to a reconstruction of the volcano system's eruptive history. By adapting elements of classic seismic stratigraphy to the study of this volcano, we have found its edifice to consist of a series of stacked mud cones. This internal architecture is most likely to have formed as a result of repeated episodes of expulsion of a fluid‐mud mix. Underlying the stack of cones is an asymmetric fault‐bounded caldera measuring approximately 2 km in diameter. This caldera shows close structural similarity to the trapdoor type of magmatic caldera. Based on the geometrical relationships of individual mud cones to this caldera, we conclude that caldera‐like collapse of the edifice floor initiated following the deposition of the first mud cone (the pioneer cone). Growth of the caldera continued until the later stages of edifice evolution when it eventually abated. This eruptive history shows strong similarities to recent models for magmatic caldera eruption cycles. The study therefore highlights the potential analogue value of mud volcano systems to the study of igneous volcanism. Furthermore, it identifies 3D seismic data as a potentially useful tool in reconstructing the history of mud volcanic eruption and fluid and sediment expulsion from sedimentary basins.     

Spatial distribution of micrometre‐scale porosity and permeability across the damage zone of a reverse‐reactivated normal fault in a tight sandstone: Insights from the Otway Basin,SE Australia

Knowledge of the permeability structure of fault‐bearing reservoir rocks is fundamental for developing robust hydrocarbon exploration and fluid monitoring strategies. Studies often describe the permeability structure of low porosity host rocks that have experienced simple tectonic histories, while investigations of the influence of faults with multiple‐slip histories on the permeability structure of porous clastic rocks are limited. We present results from an integrated petrophysical, microstructural, and mineralogical investigation of the Eumeralla Formation (a tight volcanogenic sandstone) within the hanging wall of the Castle Cove Fault which strikes 30 km NE–SW in the Otway Basin, southeast Australia. This late Jurassic to Cenozoic‐age basin has experienced multiple phases of extension and compression. Core plugs and thin sections oriented relative to the fault plane were sampled from the hanging wall at distances of up to 225 m from the Castle Cove Fault plane. As the fault plane is approached, connected porosities increase by ca. 10% (17% at 225 m to 24% at 0.5 m) and permeabilities increase by two orders of magnitude (from 0.04 mD at 225 m to 1.26 mD at 0.5 m). Backscattered Scanning Electron Microscope analysis shows that microstructural changes due to faulting have enhanced the micrometre‐scale permeability structure of the Eumeralla Formation. These microstructural changes have been attributed to the formation of microfractures and destruction of original pore‐lining chlorite morphology as a result of fault deformation. Complex deformation, that is, formation of macrofractures, variably oriented microfractures, and a hanging wall anticline, associated with normal faulting and subsequent reverse faulting, has significantly influenced the off‐fault fluid flow properties of the protolith. However, despite enhancement of the host rock permeability structure, the Eumeralla Formation at Castle Cove is still considered a tight sandstone. Our study shows that high‐resolution integrated analyses of the host rock are critical for describing the micrometre‐scale permeability structure of reservoir rocks with high porosities, low permeabilities, and abundant clays that have experienced complex deformation.     

Growth‐faults from delta collapse – structural and sedimentological investigation of the Last Chance delta,Ferron Sandstone,Utah

Investigations of syn‐sedimentary growth faults in the Last Chance delta (Ferron Sandstone, Utah, USA) show that fault‐bounded half‐grabens arrested high amounts of sand in the mouth bar and/or distributary channel areas. Fault‐controlled morphology causes changes in routing of the delta top to delta front drainage towards the long axis of half‐grabens. Faulting was spatially and temporally non‐systematic, and polyphase, with 3D cusp/listric fault geometries instigated by linkage of variously oriented segments. Hanging wall rollover folds consisting of wedge‐shaped syn‐kinematic sand attest to rapid <1‐m slip increments on faults followed by mild erosion along crests of fault blocks and sedimentary infill of adjacent accommodation. Triangle‐zones in prodelta to delta front muds are located underneath steeper faults and interconnected rotated fault‐flats. Their geometry is that of antiformal stack duplexes, in an arrangement of low‐angle‐to‐bedding normal faults at the base, replaced by folded thrusts upwards. These faults show a brittle, frictional flow deformation mechanism ascribed to early compaction of mud. For syn‐kinematic sand, there is a change from general granular/hydroplastic flow in shear zones to later brittle failure and cataclasis, a transition instigated by precipitation of calcite cement. Extensional faulting in the Last Chance delta was likely controlled by gravity driven collapse towards the delta slope and prodelta, as is commonly observed in collapsing deltas. The trigger and driving mechanism is envisioned as localized loads from sand deposited within distributary channels/mouth bars and fault‐controlled basins along the delta top. A regional tilt and especially displacement of compacted mud below sand bodies towards less compacted muds also contributed to the faulting.     

Anatomy and evolution of a Mediterranean-type fault bounded basin: the Lower Pliocene of the northern Crotone Basin (Southern Italy)

The complex development of the northern Crotone Basin, a forearc basin of the Calabrian Arc (Southern Italy), has been documented by sedimentological, stratigraphic and structural analyses. This Mediterranean‐type fault bounded basin consists of small depocentres commonly characterized by a mix of facies that grades from continental to shallow marine. The lower Pliocene infill of the Crotone Basin consists of offshore marls (Cavalieri Marl) that grade upwards into a shallow‐marine to continental succession up to 850 m thick (Zinga Formation). The succession is subdivided into three main stratal units: Zinga 1, Zinga 2, Zinga 3 bounded by major unconformities. The Zinga 1 stratal unit grades from the Cavalieri Marl to deltaic and shoreface deposits, the latter organized into several stacked progradational wedges that show spectacular thickness changes and progressive unconformities related to salt‐cored NE‐trending growth folds and listric normal faults. The Zinga 2 stratal unit records a progressive and moderate deepening of the area, marked by fluvial sedimentation at the base, followed by lagoonal deposits and by a stacking of mixed bioclastic and siliciclastic shoreface units, organized into metre‐scale high‐frequency cycles. Deposition was controlled by NE‐trending synsedimentary normal faults that dissected the basin into a series of half‐grabens. Hangingwall stratigraphic expansion was compensated by footwall condensed sedimentation. The extensional tectonic regime continued during sedimentation of the Zinga 3 stratal unit. Deposition confined within structural lows during a generalized transgressive phase led to local enhancement of tidal flows and development of sand‐wave trains. The tectonic setting testifies the generalized structural domain of a forearc region. The angular unconformity at the top of the Zinga 3 stratal unit is regional, and marks the activation of a large‐scale tectonic phase linked to strike‐slip movements.     

Salt tectonics in an intracontinental transform setting: Cumberland and Sackville basins,southern New Brunswick,Canada

Salt tectonics have markedly influenced the rapid evolution of the Upper Palaeozoic Cumberland Basin of Atlantic Canada, including the ca. 5 km‐thick Mississippian – Pennsylvanian stratigraphic succession exposed along the UNESCO World Heritage coastline at Joggins, Nova Scotia. A diapiric salt wall is exposed in the Minudie Anticline to the north of the Joggins section on the Maringouin Peninsula of New Brunswick, which corresponds to the fault‐bounded northern margin of the Cumberland Basin. The salt wall is of Visean evaporites of the Windsor Gp that originally were buried by red‐beds of the Mabou Gp in the Serpukhovian, and later by fluvial and floodplain strata (Boss Point Fm, Cumberland Gp) in the Yeadonian (mid‐Bashkirian, Early Pennsylvanian). Folds and faults in the Boss Point and overlying basal Little River formations are truncated by an angular unconformity at the base of overlying red‐beds of the Grande Anse Fm. Re‐evaluation of the palynological data delimits the Grande Anse Fm as Langsettian, providing a tight constraint of less than 2 myr on the timing of deformation. Diversion of palaeoflows by the rising salt structure, noted in previous work on the upper Boss Point Fm, occurs to the north of the diapiric anticline. This is interpreted to signify the development of a mini‐basin on commencement of diapirism once a ~1.5 km‐thick succession of clastic strata had buried the salt. Faults and folds in the succession below the unconformity indicate an initial phase of dextral transpressive strike‐slip motion, which may have promoted halokinesis. Reverse faults indicate shortening associated with northward development and overturn of the Minudie Anticline during transpression; subsequent normal faulting was associated with collapse of the sediment pile and underlying salt structure.     

Tectono‐sedimentary development of early syn‐rift deposits: the Abura Graben,Suez Rift,Egypt

The thickness and distribution of early syn‐rift deposits record the evolution of structures accommodating the earliest phases of continental extension. However, our understanding of the detailed tectono‐sedimentary evolution of these deposits is poor, because in the subsurface, they are often deeply buried and below seismic resolution and sparsely sampled by borehole data. Furthermore, early syn‐rift deposits are typically poorly exposed in the field, being buried beneath thick, late syn‐rift and post‐rift deposits. To improve our understanding of the tectono‐sedimentary development of early syn‐rift strata during the initial stages of rifting, we examined quasi‐3D exposures in the Abura Graben, Suez Rift, Egypt. During the earliest stage of extension, forced folding above blind normal fault segments, rather than half‐graben formation adjacent to surface‐breaking faults, controlled rift physiography, accommodation development and the stratigraphic architecture of non‐marine, early syn‐rift deposits. Fluvial systems incised into underlying pre‐rift deposits and were structurally focused in the axis of the embryonic depocentre, which, at this time, was characterized by a fold‐bound syncline rather than a fault‐bound half graben. During this earliest phase of extension, sediment was sourced from the rift shoulder some 3 km to the NE of the depocentre, rather than from the crests of the flanking, intra‐basin extensional forced folds. Fault‐driven subsidence, perhaps augmented by a eustatic sea‐level rise, resulted in basin deepening and the deposition of a series of fluvial‐dominated mouth bars, which, like the preceding fluvial systems, were structurally pinned within the axis of the growing depocentre, which was still bound by extensional forced folds rather than faults. The extensional forced folds were eventually locally breached by surface‐breaking faults, resulting in the establishment of a half graben, basin deepening and the deposition of shallow marine sandstone and fan‐delta conglomerates. Because growth folding and faulting were coeval along‐strike, syn‐rift stratal units deposited at this time show a highly variable along‐strike stratigraphic architecture, locally thinning towards the growth fold but, only a few kilometres along‐strike, thickening towards the surface‐breaking fault. Despite displaying the classic early syn‐rift stratigraphic motif recording net upward‐deepening, extensional forced folding rather than surface faulting played a key role in controlling basin physiography, accommodation development, and syn‐rift stratal architecture and facies development during the early stages of extension. This structural and stratigraphic observations required to make this interpretation are relatively subtle and may go unrecognized in low‐resolution subsurface data sets.     

The genesis of mud volcano conduits through thick evaporite sequences

This study documents the seismic expression of the conduits underlying over 350 mud volcanoes that were erupted in an area of the western Nile Cone in the past 5.3 Myr. The study is based on a c. 4300 km² 3D seismic survey. The conduits are interpreted to transect the >1000‐m‐thick Messinian Evaporite succession, demonstrating that the eruptive process is sufficiently dynamic to breach the formidable seal represented by the evaporites. The mud volcano conduits are remarkably similar in geometry and seismic characteristics to many previously described examples of fluid escape pipes. They are vertical to subvertical structures with a crudely cylindrical geometry, but that can either widen or narrow upwards towards their upper terminations in the mud volcano edifices. Imaging at depth within the Messinian Evaporites and pre‐evaporite successions is more uncertain, but direct sampling of mud from surface volcanoes suggests a pre‐Messinian source, confirming the seismic interpretation that they root within presalt stratigraphy. A conceptual model for the genesis of these mud volcano conduits through salt is proposed, for which hydraulic fracturing is driven by high overpressures that developed in the presalt source stratigraphy as a response to the Messinian Salinity Crisis. Dissolution and removal of evaporites resulting in fracturing and collapse via a stoping mechanism is a slow process by comparison to hydraulic fracturing but is argued to potentially contribute to conduit formation. The analysis presented here demonstrates the potential for bypassing a >1‐km‐thick unit of sealing evaporites via focused fluid and sediment mobilisation from deeper overpressured cells in other salt basins worldwide, and has significant implications for hydrocarbon exploration, CO₂ sequestration and nuclear waste disposal.     

Focused fluid flow systems of the Zhongjiannan Basin and Guangle Uplift,South China Sea

In this article, we document a large number of focused fluid escape structures using high quality 2D seismic reflection data and multibeam bathymetry data from a poorly known area at the intersection of the northern South China Sea (SCS) and the western SCS. Three types of focused fluid escape systems are identified and described: mud volcanoes, pipes and associated pockmarks. The mud volcanoes occur singly or as clustered groups. The overpressure driving the mud volcanism is argued herein to be related to the generation of thermogenic hydrocarbons. The clustered distributions are related to localized tectonic uplift in the basin. Pipes mainly occur within the Guangle Uplift or accompany the mud volcano clusters. The pipes located within the Guangle Uplift are attributed to carbonate dissolution caused by hydrothermal fluids. Fluids ascended through these structures and were expelled at the palaeo‐seabed or present seabed forming palaeo‐pockmarks and present‐day pockmarks. Some ‘mega‐pockmarks’ show evidence of enlargement due to bottom currents. The marginal basins of the SCS are petroliferous, with attention gradually shifting to the deep‐water area. Our results show that fluid migration must be taken into account when assessing seabed stability. This analysis also improves our understanding the petroleum geology in the study area, and is also useful for predicating where chemosynthetic ecosystems may be located.     

Tectonic and climatic control on the Late Messinian sedimentary evolution of the Nijar Basin (Betic Cordillera,Southern Spain)

The Late Messinian fill of the Nijar Basin (Betic Cordillera, southeastern Spain) mainly consists of clastic deposits of the Feos Formation that at basin margins rest unconformably above the primary evaporites of the Yesares Formation, the local equivalent of the Mediterranean Lower Gypsum. The Feos Fm. records the upward transition towards non‐marine environments before the abrupt return to fully marine conditions at the base of the Pliocene. The Feos Fm. is clearly two‐phase, with ‘lower’ and ‘upper’ members, which exhibit substantial differences in terms of facies, thickness, depositional trends and cyclical organization. These members record two distinct sedimentary and tectonic stages of Nijar Basin infilling. A high‐resolution, physical‐stratigraphic framework is proposed based on key beds and stratigraphic cyclicity and patterns that differ largely from those of most previously published studies. The predominant influence on stratigraphic cyclicity is interpreted to be precessionally driven climate changes, allowing their correlation to the Late Messinian astronomically calibrated chronostratigraphic framework. Detailed correlations suggest a phase of enhanced tectonic activity, possibly related to the Serrata‐Carboneras strike‐slip fault zone, during the first stage (‘lower’ member), resulting in a strongly articulated topography with structural lows and highs controlling sediment thickness and facies variation. Tectonic activity decreased during the second stage (‘upper’ member), which is characterized by (1) a progressively dampened and homogenized, (2) overall relative base‐level rise and (3) gradual establishment of hypohaline environments. Facies characteristics, overall stacking patterns and depositional trends of the Feos Fm. are analogous with uppermost Messinian successions of the Northern Apennines, Piedmont Basin and Calabria. Despite minor differences related to the local geodynamic setting, these basins experienced a common Late Messinian history that supports the development of a single, large Mediterranean water body characterized by high‐frequency, climatically‐driven changes in sediment flux and base‐level.     

Fluvial architecture in actively deforming salt basins: Chinle Formation,Paradox Basin,Utah

Determining the response of fluvial systems to syn‐sedimentary halokinesis is important for reconstructing the palaeogeography of salt basins, determining the history of salt movement and predicting development and architecture of sandstone bodies for subsurface fluid extraction. To assess both the influence of salt movement on fluvial system development and the use of lithostratigraphic correlation schemes in salt basins we have analysed the Triassic Chinle Formation in the Paradox Basin, Utah. Results indicate that sandstone body development proximal to salt bodies should be considered at two scales: intra‐ (local) and inter‐ (regional) mini‐basin scale. At the intra‐mini basin or local scale, conformable packages of up to 12 m deep meandering fluvial channel deposits and associated overbank deposits are developed, which may thin, pinch‐out or become truncated towards salt highs. When traced down the axis of a mini‐basin, individual stories extend for a few hundred metres, and form part of amalgamated channel‐belt packages up to 60 m thick that can be traced for at least 25 km parallel to palaeoflow. Where salt movement outpaces sediment accumulation, progressive low angle unconformities are developed along the flanks of salt highs. Significantly, in mini‐basins with high sand supply, sandstone bodies are present across salt highs where they show increased amalgamation, decrease in thickness due to truncation and no change in internal sandstone body character. At inter mini‐basin or regional scale, spatial and temporal variations in accommodation space generated by differential salt movement strongly influence facies distributions and facies correlation lengths. Broad lithostratigraphic packages (5–50 m thick) can be correlated within mini‐basins, but correlation of these units between adjacent mini‐basins is problematic. Knowledge of fluvial system development at a regional scale is critical as, fluvial sediment distribution is focussed by topography generated by growing salt bodies, such that adjacent mini‐basins can have significant differences in sandstone body thickness, distribution and lateral extent. The observations from the Chinle Formation indicate that lithostratigraphic‐based correlation schemes can only be applied within mini‐basins and cannot be used to correlate between adjacent mini‐basins or across a salt mini‐basin province. The key to predicting sandstone body development is an understanding of the timing of salt movement and reconstructing fluvial drainage system development.     

Late syn‐rift evolution of the Vingleia Fault Complex,Halten Terrace,offshore Mid‐Norway; a test of rift basin tectono‐stratigraphic models

Rift basin tectono‐stratigraphic models indicate that normal fault growth controls the sedimentology and stratigraphic architecture of syn‐rift deposits. However, such models have rarely been tested by observations from natural examples and thus remain largely conceptual. In this study we integrate 3D seismic reflection, and biostratigraphically constrained core and wireline log data from the Vingleia Fault Complex, Halten Terrace, offshore Mid‐Norway to test rift basin tectono‐stratigraphic models. The geometry of the basin‐bounding fault and its hangingwall, and the syn‐rift stratal architecture, vary along strike. The fault is planar along a much of its length, bounding a half‐graben containing a faultward‐thickening syn‐rift wedge. Locally, however, the fault has a ramp‐flat‐ramp geometry, with the hangingwall defined by a fault‐parallel anticline‐syncline pair. Here, an unusual bipartite syn‐rift architecture is observed, comprising a lower faultward‐expanding and an upper faultward‐thinning wedge. Fine‐grained basinfloor deposits dominate the syn‐rift succession, although isolated coarse clastics occur. The spatial and temporal distribution of these coarse clastics is complex due to syn‐depositional movement on the Vingleia Fault Complex. High rates of accommodation generation in the fault hangingwall led to aggradational stacking of fan deltas that rapidly (<5 km) pinch out basinward into offshore mudstone. In the south of the basin, rapid strain localization meant that relay ramps were short‐lived and did not represent major, long‐lived sediment entry points. In contrast, in the north, strain localization occurred later in the rift event, thus progradational shorefaces developed and persisted for a relatively long time in relay ramps developed between unlinked fault segments. The footwall of the Vingleia Fault Complex was characterized by relatively low rates of accommodation generation, with relatively thin, progradational hangingwall shorelines developed downdip of the fault block apex, sometime after the onset of sediment supply to the hangingwall. We show that rift basin tectono‐stratigraphic models need modifying to take into account along‐strike variability in fault structure and basin physiography, and the timing and style of syn‐rift sediment dispersal and facies, in both hangingwall and footwall locations.     

Source‐to‐sink analysis of ancient sedimentary systems using a subsurface case study from the Møre‐Trøndelag area of southern Norway: Part 1 – depositional setting and fan evolution

In this study, we use seismic reflection, well and core data to investigate the role that basin physiography and sediment routing systems played on the distribution, geometry and stratigraphic architecture of Upper Cretaceous submarine fans (SF) offshore Norway. The Late Cretaceous Møre‐Trøndelag margin of western Norway was characterised by steep submarine slopes (gradient of ~0.3°–3°). Mudstones dominate the Upper Cretaceous slope succession, although a few regionally extensive, sandstone‐dominated units are developed. We focus on the most regionally extensive sandstone unit, which is of Late Turonian‐to‐Early Coniacian age. Mapping and visualisation of 2D and 3D seismic reflection data and analysis of well data indicates that the sandstone unit comprises a total of 11 SF, which were fed by sand‐rich sediment gravity flows routed through multiple upper slope canyons. Based on the internal organisation of seismic facies, four fan types have been identified: (i) Type Ia fans, which are characterised by <10 erosional channel complexes at their bases and aggradational to landward‐stepping lobes in their upper parts; (ii) Type Ib fans, which are characterised by >10 erosional channel complexes at their bases and aggradational to landward‐stepping lobe and mass‐transport deposits near the fan apex in their upper parts; (iii) Type II fans, which are dominated by aggradational lobe deposits; and (iv) Type III fans, which are dominated by a single channel complex that passes downdip into a small terminal lobe. The different fan types are interpreted to reflect variable stratigraphic responses to source proximity and basin physiography, which is principally related to the degree of local fault reactivation and differential compaction. This variability highlights the diversity of fan types that may occur over short distances along continental margins, and demonstrates the importance of local controls in understanding the internal stratigraphic variability that may be present in deep‐marine successions.     

Gravitational deformation and inherited structural control on slope morphology in the subduction zone of north‐central Chile (ca. 29–33°S)

Subduction zones provide direct insight into plate boundary deformation and by studying these areas we better understand tectonic processes and variability over time. We studied the structure of the offshore subduction zone system of the Pampean flat‐slab segment (ca. 29–33°S) of the Chilean margin using seismic and bathymetric constraints. Here, we related and analysed the structural styles of the offshore and onshore western fore‐arc. Overlying the acoustic top of the continental basement, two syn‐extensional seismic sequences were recognised and correlated with onshore geological units and the Valparaíso Forearc Basin seismic sequences: (SII) Pliocene‐Pleistocene and (SI) Miocene‐Pliocene (Late Cretaceous (?) to Miocene‐Pliocene) syn‐extensional sequences. These sequences are separated by an unconformity (i.e. Valparaíso Unconformity). Seismic reflection data reveal that the eastward dipping extensional system (EI) recognised at the upper slope can be extended to the middle slope and controlled the accumulation of the older seismic package (SI). The westward dipping extensional system (EII) is essentially restricted to the middle slope. Here, EII cuts the eastward dipping extensional system (EI), preferentially parallel to the inclination of the older sequences (SI), and controlled a series of middle slope basins which are filled by the Pliocene‐Pleistocene seismic sequence (SII). At the upper slope and in the western Coastal Cordillera, the SII sequence is controlled by eastward dipping faults (EII) which are the local reactivation of older extensional faults (EI). The tectonic boundary between the middle (eastern outermost forearc block) and upper continental slope (western coastal block) is a prominent system of trenchward dipping normal fault scarps (ca. 1 km offset) that resemble a major trenchward dipping extensional fault system. This prominent structural feature can be readily detected along the Chilean erosive margin as well as the two extensional sets (EI and EII). Evidence of slumping, thrusting, reactivated faults and mass transport deposits, were recognised in the slope domain and locally restricted to some eastern dipping faults. These features could be related to gravitational effects or slope deformation due to coseismic deformation. The regional inclination of the pre‐Pliocene sequences favoured the gravitational collapse of the outermost forearc block. We propose that the structural configuration of the study area is dominantly controlled by tectonic erosion as well as the uplift of the Coastal Cordillera, which is partially controlled by pre‐Pliocene architecture.     

Architecture of growth basins in a tidally influenced,prodelta to delta-front setting: The Triassic succession of Kvalpynten,East Svalbard

World-class examples of fault-controlled growth basins with associated syn-kinematic sedimentary fill are developed in Upper Triassic prodelta to delta-front deposits exposed at Kvalpynten, SW Edgeøya in East Svalbard. They are interpreted to have interacted with north-westerly progradation of a regional delta system. The syn-kinematic successions consist of 4 to 5 coarsening-upward units spanning from offshore mudstones to subtidal heterolithic bars and compound tidal dunes, which were blanketed by regional, post-kinematic sandstone sheets deposited as laterally continuous, subaqueous tidal dune fields. The rate of growth faulting is reflected in the distribution of accommodation, which governs sedimentary architecture and stacking patterns within the coarsening-upward units. Fully compartmentalized basins (12, 200–800 m wide and c. 150 m high grabens and half grabens) are characterized by syn-kinematic sedimentary infill. These grabens and half-grabens are separated by 60–150 m high horsts composed of pro-delta to distal delta-front mudstones. Grabens host tabular tidal dunes (sandwaves), whereas half-grabens bound by listric faults (mainly south-dipping) consist of wedge-shaped, rotated strata with erosive boundaries proximal to the uplifted fault block crests. Heterolithic tidal bars (sand ridges) occur in narrow half-grabens, showing migration oblique to the faults, up the dipslope. Structureless sandstone wedges and localized subaqueous slumps that formed in response to collapse of the block crests were only documented in half-grabens. Late-kinematic deposition during the final stages of faulting occurred in partly compartmentalized basins, filled with variably thick sets of continuous sandstone belts (compound tidal dunes).