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The competition between the impact of inherited weaknesses and plate kinematics determines the location and style of deformation during rifting, yet the relative impacts of these “internal” and “external” factors remain poorly understood, especially in 3D. In this study we used brittle-viscous analogue models to assess how multiphase rifting, i.e., changes in plate divergence rate or direction, and the distribution of weaknesses in the competent mantle and crust influence rift evolution. We find that the combined reactivation of mantle and crustal weaknesses without kinematic changes creates complex rift structures. Divergence rates affects the strength of the weak lower crustal layer and hence the degree of mantle-crustal coupling. In this context slow rifting decreases coupling, so that crustal weaknesses can easily localize deformation and dominate surface structures, whereas fast rifting increases coupling so that deformation related to mantle weaknesses can have a dominant surface expression. Through a change from slow to fast rifting mantle-related deformation can overprint previous structures that formed along (differently oriented) crustal weaknesses. Conversely, a change from fast to slow rifting may shift deformation from mantle-controlled towards crust-controlled. When changing divergence directions, structures from the first rifting phase may control where subsequent deformation occurs, but only when they are well developed. Alternatively, they are ignored during subsequent rifting. We furthermore place our results in a larger framework of brittle-viscous rift modelling results from previous experimental studies, showing the importance of genral lithospheric layering, divergence rate, the type of deformation in the mantle, and finally upper crustal structural inheritance. The interaction between these parameters can lead to a large variety of deformation styles that may often lead to comparable end products. Therefore, detailed investigation of faulting and to an equal extent basin depocenter distribution over time is required to properly determine the evolution of complex rift systems. These insights provide a strong incentive to revisit various natural examples.

Premise Among the sophisticated trap types in carnivorous plants, the underground eel traps of corkskrew plants (Genlisea spp., Lentibulariaceae) are probably the least understood in terms of their functional principle. Here, we provide a detailed analysis of structural and hydraulic features of G. hispidula traps, contributing to the ongoing debate on whether these traps can actively generate water streams to promote prey capture. Methods Anatomical and hydraulic traits of detached traps, including inner trap diameters, chamber line element, hair length, glandular pattern, and hydraulic conductivity, were investigated quantitatively using light and electron microscopy, x‐ray microtomography, and hydraulic measurements. Results Hydraulic resistivity in the neck of the trap, from the trap mouth toward the vesicle (digestive chamber) was 10 times lower than in the opposite direction. The comparison of measured and theoretical flow rates suggests that the retrorse hairs inside trap necks also provide considerable resistance against movement of matter toward the vesicle. Hairs showed a gradient in length along the neck, with the shortest hairs near the vesicle. Co‐occurrence of quadrifid and bifid glands was limited to a small part of the neck, with quadrifids near the vesicle and bifids toward the trap mouth. Conclusions The combination of structural gradients with hydraulic anisotropy suggests the trap is a highly fine‐tuned system based on likely trade‐offs between efficient prey movement in the trap interior toward the vesicle, prey retention, and spatial digestion capacities and is not counter to the generation of water streams., publishedVersion

Submarine fan deposits are volumetrically the largest sediment accumulations on Earth and host significant hydrocarbon reserves. Extensive research has documented the bed-scale architecture of sandy, high net-to-gross (N:G), proximal and axial environments, which can have bed thicknesses of several meters; however less well-understood are thin-bedded turbidites, which are typically lower N:G and deposited in more distal environments. Conceptual models assume that lobe-fringe-to-basin plain environments consist of tabular, sheet-like beds that extend out continuously and predictably over long distances—sometimes as far as several kilometers. Extensive lateral continuity, however, is not necessarily reflected in ancient outcrop analogs. This study seeks to apply a quantitative approach to the characterization of thin-bedded turbidites to assess the impact of multi-scale heterogeneity on reservoir predictability. The sea-cliff outcrop exposures of the Upper Cretaceous Point Loma Formation in San Diego, California, exhibit a wide range of bed thicknesses and stratigraphic architecture, which have been used to interpret their relative position (e.g. axis-to-fringe, proximal-to-distal) in a submarine lobe. In this study, we characterize thin-bedded and interpret them to have been deposited in an off-axis-to-fringe environment. The study area spans 700 m of laterally continuous outcrop, across which 10 correlated stratigraphic sections are used to quantify lateral and vertical changes in metrics such as bed thickness, N:G, lithofacies proportions, etc. Results of this study demonstrate that thin sand beds experience both lateral facies changes (e.g. from turbidite to hybrid event bed) and rapid thickness changes (abrupt pinch-and-swell geometries) more frequently than conceptual models would predict. We find that a single measure of lateral heterogeneity (e.g. thinning rate away from the bed axis) does not reflect the true architecture of sandstone beds, and that significant information is lost when beds are correlated over tens-to-hundreds of meters. We also suggest that sands are deposited in irregular (e.g. “finger-like”) planform geometries, the effect of which compounds to the lobe-element scale and influences lateral lithofacies predictability. This study of the Point Loma Formation offers high-resolution bed-to-element scale data, which may be used as inputs for reservoir models and horizontal facies predictions (e.g., for geosteering) in both conventional and unconventional hydrocarbon reservoirs, such as those from the Wilcox (Gulf of Mexico) and the Wolfcamp (Permian Basin).

The interactions between old abandoned wellbores of suspect well integrity with hydraulic fracturing (HF), enhanced oil recovery (EOR), or salt water disposal (SWD) operations can result in upward leakage of deep aqueous liquids into overlying aquifers. This potential for upward fluid migration is largely unquantified as monitoring abandoned wells is rarely done, and leakage may go unnoticed especially when in deeper aquifers. This study performs a proximity analysis between old abandoned wells and HF, EOR, and SWD wells, and identifies commingled old abandoned wellbores, which are those wells where groundwater may flow from one aquifer to one or more other aquifers, to identify the locations with the greatest potential for upward aqueous fluid migration at three study sites in the Western Canadian Sedimentary Basin. Our analysis indicates that at all three study sites there are several locations where HF, EOR, or SWD operations are located in close proximity to a given old abandoned well. Much of this overlap occurs in formations above typically produced hydrocarbon reservoirs but below exploited potable aquifers, otherwise known as the intermediate zone, which is often connected between abandonment plugs in old abandoned wells. Information on the intermediate zone is often lacking, and this study suggests that unanticipated alterations to groundwater flow systems within the intermediate zone may be occurring. Results indicate the need for more field-based research on the intermediate zone.

High- and ultrahigh-pressure rocks occur in the Austroalpine Nappes in a ~400 km long belt from the Texel Complex in the west to the Sieggraben Unit in the east. Garnet growth during pressure increase was dated using Lu-Hf chronometry. The results range between c. 100 and 90 Ma, indicating a short-lived period of subduction. Combined with already published data, our estimates of metamorphic conditions indicate a field gradient with increasing pressure and temperature from the northwest to the southeast, where the rocks experienced ultrahigh-pressure metamorphism. The P-T conditions of the eclogites generally lie on the ‘warm’ side of the global range of subduction-zone metamorphic conditions. The oldest Cretaceous eclogites (c. 100 Ma) are found in the Saualpe-Koralpe area derived from widespread gabbros formed during Permian to Triassic rifting. In the Texel Complex garnets showing two growth phases yielded a Variscan-Eoalpine mixed age indicating re-subduction of Variscan eclogite-bearing continental crust during the Eoalpine orogeny. Jurassic blueschist-facies metamorphism at Meliata in the Western Carpathians and Cretaceous eclogite-facies metamorphism in the Austroalpine are separated by a time gap of c. 50 Ma and therefore do not represent a transition from oceanic to continental subduction but rather separate events. Thus, we propose that subduction initiation was intracontinental at the site of a Permian rift.

Pre-rift salt controls structural style variability within rifts by decoupling sub- and supra-salt faults. However, the way in which this variability controls sediment erosion and dispersal, and facies distributions within the coeval syn-rift stratigraphic succession, remains poorly known. We here use 3D seismic reflection and borehole data to study the tectono-stratigraphic development of the Halten Terrace, offshore Mid-Norway, a salt-influenced rifted margin formed during Middle to Late Jurassic extension. On the eastern basin margin the rift structural style passes southwards from an unbreached extensional growth fold dissected by numerous horst and graben (Bremstein Fault Complex), into a single, through-going normal fault (Vingleia Fault Complex). This southwards change in structural style is likely related to the pinch-out of or a change in the dominant lithology (and thus rheology) within a pre-rift (Triassic) evaporite layer, which was thick and/or mobile enough in the north to decouple basement- and cover-involved faulting, and to permit extensional forced folding. As a result, the salt-influenced Bremstein Fault Complex underwent limited footwall uplift, with minor erosion of relatively small horsts supplying only limited volumes of sediment to the main downdip depocentre. In contrast, the Vingleia Fault Complex, which was directly coupled to basement, experienced significant uplift and extensive footwall erosion. The footwall of this structure also locally underwent salt-detached gravity gliding and collapse as the pre-rift detachment was tilted. Our results show that where through-going normal faults develop along the rift flanks, the presence of a pre-rift salt layer will suppress the topographic expression of the footwall. The pre-rift salt layer may however facilitate footwall collapse and limit the volume of sediment supplied to downdip basins. Our results also show that variable topography along the rift flanks facilitated the development of relatively small, localised, intra-rift flank accommodation that trapped flank-derived sediment, and which meant basins nearer the rift axis were starved of sediment.

Class 1 hydrate reservoirs are regarded as the most promising targets for gas production. Previous investigations in the northern South China Sea have proven that the low‐permeability hydrate reservoir at site GMGS3‐W19 is a Class 1 hydrate deposit. However, the dynamic production behaviors of this type of reservoir are not yet fully understood. Here, we report gas recovery from hydrate reservoirs containing underlying free gas layers with different initial gas saturations and investigate the effects of absolute permeability and depressurization pressure on gas production performance. The results show that high initial gas saturation of the underlying free gas layer and low bottom‐hole pressure are advantageous for enhancing the gas production performance. The effects of absolute anisotropic permeability and isotropic permeability on gas recovery from Class 1 hydrate reservoirs are different. For long‐term gas production from this hydrate reservoir with any initial gas saturation, a higher horizontal permeability (permeability anisotropy more than 10) in the hydrate layer is remarkably beneficial to stimulate gas extraction and decrease the amount of produced water replenished by inflows from permeable overlying and underlying sediments. Moreover, the gas production rate is highly consistent with the hydrate dissociation ratio, one of the main factors affecting the gas production performance, in Class 1 hydrate reservoirs with different permeabilities. However, for this type of hydrate reservoir with permeability anisotropy larger than 5, the larger the horizontal permeability in the hydrate layer can form more secondary hydrates. The increment in secondary hydrate formation negatively influences the hydrate dissociation ratio and gas recovery. Thus, it is also significant to weigh the permeability anisotropy of the hydrate layer and the secondary hydrate formation amount during the production progress. These findings can contribute to estimating the gas recovery efficiency in Class 1 hydrate reservoirs and optimizing the production process in similar areas.

[Petroleum system modelling showing present‐day maturity (%Ro) of the Vaca Muerta Formation from from the Agrio Fold and Thrust Belt (west) to the NE Platform (east). The increase in TOC0 values from east to west is associated with thickening of the unit, which suggests the potential larger volumes of generated hydrocarbons for the same thermal gradient. The E–W thermal maturity trend is consistent with the decrease in HI and increase in TR values to the west, indicating that in conjunction with increased TOC0, organic pores represent the main control on total porosity in organic‐rich intervals of the unit. , Abstract The Vaca Muerta Formation (Tithonian–early Valanginian) is the main source rock in the Neuquen Basin and the most important unconventional shale resource in South America. In the present study, organic geochemistry, electron microscopy and basin and petroleum system modelling (BPSM) were combined to evaluate source rock properties and related processes along a transect from the early oil (east) to the dry gas (west) window. The unit is characterized by high present‐day (1%–8% average) and original (2%–16% average) total organic carbon contents, which increase towards the base of the unit and basinal (west) settings. Scanning electron microscopy shows that organic pores derived from the transformation of type II kerogen. Isolated bubble pores are typical of the oil window, whereas bubble and densely distributed spongy pores occur in the gas stage, indicating that the maturity gradient exerts strong control on organic porosity. Organic geochemistry, pressure and porosity data were incorporated into a 2D basin petroleum system model that includes the sequential restoration of tectonic events and calculation of compaction trends, kerogen transformation, hydrocarbon generation and estimation of pore pressure through geologic time. The W–E regional model extends from the Agrio Fold and Thrust Belts to the basin border and allows us to evaluate the relationship between thermal maturity and timing of hydrocarbon generation from highly deformed (west) to undeformed (east) regions. Modelling results show a clear decrease in maturity and organic matter (OM) transformation towards the eastern basin margin. Maximum hydrocarbon generation occurred in the inner sectors of the belt, at ca. 120 Ma; long before the first Andean compression phase, which started during the Late Cretaceous (ca. 70 Ma). Miocene compression (15–7 Ma) promoted tectonic uplift of the inner and outer sectors of the belt associated with a reduction in thermal stress and kerogen cracking, as well as massive loss of retained fluids and a decrease in pore pressure. The OM transformation impacted (a) the magnitude of effective porosity associated with organic porosity development, and (b) the magnitude and distribution of pore pressure within the unit controlled by hydrocarbon generation and compaction disequilibrium. BPSM shows a progressive increase in effective porosity from the top to the base and towards the west region related to the original organic carbon content and maturity increasing along the same trend. Overpressure intervals with high organic carbon contents are the most prone to develop organic pores. The latter represent favourable sites for the storage of hydrocarbons in the Vaca Muerta Formation.]

Thrust faulting has been suggested as a viable mechanism of debris transport at many glaciers, often inferred from the presence of up-glacier dipping bands of debris that emerge at the ice surface to form ridges of basally derived material. However, modelling indicates that the development of thrust faults is mechanically inhibited because stresses are much lower than that required for shear failure, a prerequisite for thrust faulting, and field measurements fail to detect thrust-related displacement. The mechanism for the emplacement of these ridges that appear at the surface of many polythermal valley glacier termini remains open to question. This study re-examines the origin of debris ridges on the surface of Storglaciären, a polythermal valley glacier in northern Sweden, using field observations, ice microstructural analyses, sediment grain size analysis, stable isotope composition of the ice, and modelling. We find no evidence of discrete displacement across the debris bands that produce the ridges, nor do we find evidence that folding might be responsible. We propose that the bands originate at the base of the glacier by one of two mechanisms, perhaps in combination: (i) refreezing of meltwater near the thermal transition in basal ice, and (ii) injection into tensile fractures periodically opened at the base due to high fluid pressure and then freezing. In either case, separation from the base occurs due to high fluid pressure and freezing introduces ice below the debris bands, which are then transported forwards due to basal shear and upwards due to longitudinal compression, and revealed by surface ablation.

Classic models of gravity-driven salt tectonics commonly depict kinematically-linked zones of overburden deformation, characterised by updip extension and downdip contraction, separated by a weakly deformed zone associated with downdip translation above a relatively smooth base-salt surface. We use 2D and 3D seismic reflection and borehole data from the south-central Campos Basin to show that these models fail to adequately capture the complex range of structural styles forming during salt-detached gravity-driven deformation above a rugose base-salt surface. In the Campos Basin the base-salt is defined by broadly NE-trending, margin-parallel, generally seaward-dipping ramps that have up to 2 km of structural relief. We define three domains of overburden deformation: an updip extensional domain, an intermediate multiphase domain, and a downdip contractional domain. The multiphase domain is defined by large, partly fault-bounded, ramp-syncline basins, the stratigraphic record of which suggest c. 28 km of seaward gravity-driven translation of salt and its overburden since the end of the Albian. We also identify three main types of salt structures in the multiphase domain: (i) contractional anticlines that were subjected to later extension and normal faulting; (ii) passive-to-active diapirs that were later extended and widened, and which are bound on their landward margins by landward-dipping, salt-detached normal faults; and (iii) reactive (extensional) diapirs that were subsequently squeezed. We argue that this multiphase deformation occurs because of basinward translation of salt and its overburden over complex base-salt relief, consistent with the predictions of physical models and several other seismic reflection data-based studies. Critically, these complex local strains overprint margin-scale patterns of deformation.

Despite high pressure being ubiquitous in the Yanan Sag of the Qiongdongnan Basin, South China Sea, its potential effect on gas migration-accumulation remains unclear. In this study, a series of geochemical indicators combined with the origin of high pressure were used to elucidate the cause of gas accumulation failure in the overpressured YC19-1 structure. Drill-stem tests, mud weights, and well-loggings reveal two vertical overpressure systems. Pore pressure in the deep Lingshui and Yacheng formations almost reaches a lithostatic magnitude, which was interpreted as a result of gas generation and disequilibrium compaction triggered by the Pliocene-Quaternary rapid subsidence. A thermal anomaly above the high-pressure system was evidenced by high homogenization temperature (Th) of fluid inclusion, abnormally high vitrinite reflectance, and a rapid transformation from kaolinite to illite. The high thermal field likely resulted from a cross-stratal fluid migration from the deep high-pressure system. Both methane-bearing inclusions in sandstones and abnormal Rock-Eval data of mudstones above the high-pressure surface suggest an influx of external hydrocarbons. Based on primary aqueous inclusion Th and salinity, carbon and oxygen isotope compositions, and petrographic observations, widespread silica and carbonate cements near the overpressure surface were interpreted to be derived from extraformational materials carried by deep-seated basinal fluids. Fluid inclusion Th coupled with burial model suggests that the gas leakage took place at circa 1.6 Ma, coinciding well with the stages of both gas generation and overpressure. These observations suggest an upward leakage of gas-bearing fluids induced by pressure release, thus leading to the existence of only non-commercial gas-bearing aquifers in the overpressured YC19-1 structure.

Subsurface salt flow can deform overlying strata and influence contemporaneous sedimentary processes. Studying salt-sediment interactions is challenging in the subsurface due to poor imaging adjacent to salt, and in the field due to the dissolution of halite. Discrete Element Modelling provides an efficient and inexpensive tool to model stratigraphy and deformation around salt structures, which is advantageous over other modelling techniques as it realistically recreates brittle processes such as faulting. Six 2D experiments were run representing 4.6 Myr (46,000 timesteps) to determine the effect of salt growth on syn-kinematic stratigraphy. Halokinetic deformation of stratigraphic architecture was assessed by varying sediment input rates (slow, intermediate, and fast), and increasing and decreasing them through time. Results show the realistic formation and evolution of salt-related faults which define a zone of halokinetic influence, ~3 times the width of the initial diapir. Outside of this, pre- and syn-kinematic stratigraphy are undeformed. Within this zone, syn-kinematic strata are initially isolated into primary salt withdrawal basins, onlapping and thinning towards the salt-cored high. In most models, syn-kinematic strata eventually thin across and cover the diapir roof. Thinning rates are up to six times greater within 350 metres of the diapir, compared to further afield, and typically decrease upwards (with time) and laterally (with distance) from the diapir. Outputs are compared to a subsurface example from the Pierce field, UK North Sea, which highlights the importance of considering local fluctuations in diapir rise rate. These can create stratigraphic architectures that may erroneously be interpreted to represent ‘apparent’ increases/decreases in sedimentation rate. Exposed examples, such as the Bakio diapir, northern Spain, can be used to make inferences of the expected depositional facies, below model resolution. Our models aid prediction of sedimentary unit thickness and thinning rates, and can be used to test interpretations arising from incomplete or low-resolution subsurface and outcrop data when building geological models for subsurface energy.

The interactions between salt diapirs, thrust welds and thrusts in contractional belts are poorly understood due to, first, the inability of seismic data to distinguish between thrusts and welds or resolve associated sub-resolution deformation, and second, the paucity of good field examples. The Warraweena area in the Northern Flinders Ranges of South Australia contains examples of Neoproterozoic to Early Cambrian squeezed diapirs linked by steep reverse faults formed during the Delamerian Orogeny. Benefiting from good field exposures, we use geological mapping, cross-section construction and conceptual structural models to assess the three-dimensional geometry and evolution of the structures, the lateral transition from diapirs to linking faults and the variability of associated meso- and small-scale deformation. Three discrete diapirs consist of narrow outcrops of Callanna Group megabreccia (Willouran in age) up to 5-km long. Their diapiric origin is confirmed by local development of caprock, steepening of flanking strata in composite halokinetic sequences and reworked diapir and roof debris in adjacent strata. The surrounding rocks display only background levels of small-scale deformation. In contrast, the linking faults show no evidence of precursor diapirism, have fault-related anticlines up to 100s of m in wavelength in their hanging walls, and an associated increase in small-scale deformation (i.e. millimetre to metre scale folds, fractures and shear fabrics). The transitions from diapirs to faults occur within less than 200 m as short thrust welds at the diapir terminations. The exposed structures are analogous to those found on the subsurface of other salt basins such as the Gulf of Mexico and the South Atlantic conjugate margins. The results of this work can aid geoscientists evaluating three-way traps against squeezed diapirs, welds or faults, and can help them to predict the style and abundance of both halokinetic and small-scale structures that are below seismic resolution.

This contribution reviews the effects of source heterogeneities, melt-rock reactions and intracrustal differentiation on magma chemistry across mid-ocean ridges, intraplate settings and subduction zones using experimental studies and natural data. We compare melting behaviors of pyroxenites and peridotites and their relative contributions to magmas as functions of composition, mantle potential temperatures and lithospheric thickness. We also discuss the fate of chemically distinct melts derived from heterogeneities as they travel through a peridotitic mantle. Using nearly 60,000 natural major element compositions of volcanic rocks, melt inclusions, and crystalline cumulates, we assess broad petrogenetic trends in as large of a global dataset as possible. Consistent with previous studies, major element chemistry of mid-ocean ridge basalts (MORBs) and their cumulates favor a first-order control of intracrustal crystal-liquid segregation, while trace element studies emphasize the role of melt-rock reactions, highlighting the decoupling between the two. Ocean island basalts (OIB) show a larger compositional variability than MORB, partly attributed to large variations of pyroxenite proportions in the mantle source. However, the estimated proportions vary considerably with heterogeneity composition, melting model and thermal structure of the mantle. For arcs, we highlight current views on the role of the downgoing slab into the source of primary arc magmas, and the role of the overriding lithosphere as a magmatic chemical filter and as the repository of voluminous arc cumulates. Our approach of simultaneously looking at a large database of volcanic + deep crustal rocks across diverse tectonic settings underscores the challenge of deciphering the source signal versus intracrustal/lithospheric processes., Comment: 42 pages, 9 figures, Accepted chapter to appear in "Mantle Convection and Surface Expressions", H. Marquardt, M. Ballmer, S. Cottar, K. Jasper (eds.), AGU Monograph Series