Trending Faults Research Articles

Structural containment in the Port Campbell Embayment and on the Mussel Platform, Otway Basin, Victoria

As part of the Victorian Gas Program, new geological modelling of the Cretaceous to recent deposits in the Port Campbell Embayment and the Mussel Platform was carried out to investigate fault seal and trap integrity. Structural characterisation of the Late Cretaceous to present-day sedimentary sequence highlights cross-cutting fault trends defining potential structural traps containing Waarre Formation reservoirs. The fault trends are primarily controlled by Cretaceous-Paleogene extension and are reactivated during the Paleogene. Seismic facies in the top seal suggest an N-S environmental shift from open-marine to proximal nearshore marine. The quantification of fault membrane seals suggests that while reservoir-on-reservoir juxtapositions may enable some degree of lateral flow, efficient trapping relying on juxtaposition seal against the Belfast or Skull Creek mudstones is widespread. Fault geomechanics suggests that NW-SE and E-W faults accommodated most of the extensional strain and could have been associated with increased vertical structural permeability; however, there are no leakage indicators to support widespread vertical migration. These results do not support previous assumptions that fault seal integrity and top seal bypass represent a critical and widespread issue within the nearshore Otway Basin.

Geo-hazard assessment of the NEOM area, Northwest Saudi Arabia, using seismological and potential field data

The active tectonics of the Gulf of Aqaba (Red Sea) may affect the newly established NEOM megacity in northwestern Saudi Arabia. Using seismological and potential field data, this study aimed to evaluate the major tectonic trends around NEOM area and their hazard impacts on the NEOM area. In particular, aeromagnetic and gravity data were used to explore the major tectonic trends that may affect this area. The interpreted tectonic trends are directed mainly along the NNE and NNW, as well as NW and EW tectonic trends. A good correlation was found between the distribution of the earthquake epicenters (Mw ≥ 4) and the interpreted tectonic trends. Moreover, the distribution of epicenters was congruent with the fault trends obtained from the potential field data, implying that the observed fault trends can generate earthquakes. For the seismic hazard assessment, the source parameters and expected ground motions of two moderate earthquakes that occurred in the Gulf of Aqaba in 2015 and 2016 were analyzed. Assuming an omega-squared source model, a grid search method was applied to fit the amplitude spectra of the S-wave group over the model parameters that were used to compute Mo values of 4.06E + 23 and 2.14E + 23 Nm, corresponding to Mw of 5.0 and 4.8, fault radii of 831 m and 835 m, and stress drop (Δσ) values of 7.72 and 4.01 MPa for the 2015 and 2016 earthquakes, respectively. An empirical Green’s function summation technique was performed to simulate high-frequency ground motions expected for future large earthquakes, demonstrating the influence of such earthquakes on the study area. For a Δσ value of 10 Mpa (characteristic of past earthquakes in the Gulf of Aqaba), peak ground accelerations of ∼ 5.6 and 5.53 m/s2 are to be expected for future earthquakes with Mw 7.0 in the epicentral regions of the 2015 and 2016 earthquakes.

Shale fault zone structure and stress dependent anisotropic permeability and seismic velocity properties (Opalinus Clay, Switzerland)

Given shale's potential to serve as both a caprock for geological carbon sequestration and as the host for nuclear waste disposal, this study focuses on the structural characterization around a 1.5–3 m thick fault within the Opalinus Clay host rock and petrophysical characterization of both the host rock and fault core. Seven boreholes were drilled at the Mont Terri Rock laboratory in late 2018 to constrain the orientation of the so-called ‘Main Fault’ and several fracture families within the fault core using core and image logs. Contrary to typical fault models, matrix permeability and seismic velocity measurements show similarities in the host rock and within the Main Fault. In the clay-rich samples, measurements performed in laboratory at varying confining pressures indicate p-wave velocities range from 2.60 to 2.95 km/s perpendicular to foliation and 3.38–3.58 km/s parallel to foliation at near in-situ confining pressures, which increase with similar anisotropy at higher confining pressures (200 MPa). Since the permeability of the host rock and fault zone is very low (10−19–10−21 m2) flow is expected to prevail along fractures, where critical stress fault analysis suggests that potential hydraulically conductive fractures are actually conjugate to the Main Fault trend.

Fault Prediction of Electromagnetic Launch System Based on Knowledge Prediction Time Series

The fault prediction of the electromagnetic launch (EML) system is an important guarantee to improve the reliability of the system, but there is no mature method that can be directly applied. Combined with the engineering practice of large-scale EML system, a fault prediction method based on knowledge prediction time series is proposed. First, the high-frequency waveform collected in each launch is extended into a time series along the number of launches; second, an intelligent waveform features extraction expert system is constructed to realize feature extraction; third, multidimensional feature sequence prediction and waveform prediction are realized by using two neural networks, respectively; finally, fault prediction is realized by associating the fault diagnosis knowledge. The temperature rising test data of a railgun system for 15 consecutive launches and the recoil stroke test data of noncontinuous 78 launches are used as the input source of the proposed algorithm. The results show that the proposed algorithm can automatically extract the features with fault trend. The single step prediction error of features is less than 1.47%, and the mean square error of curve prediction is half of the results of SARIMA prediction algorithm. Through the temperature rise curves, the proposed algorithm can predict the fault free of the 14th and 15th launch. According to the recoil stroke curves, the fault of the launcher of the 75th launch is predicted. The actual analysis shows that the fault prediction accuracy is high, and the algorithm can significantly improve the system reliability after being applied to engineering.

Utilisation of GNSS and seismicity for monitoring crustal deformation of the Northern part of the Nile Delta, Egypt

ABSTRACT Nile Delta is one of the most significant regions in Egypt. The offshore Nile Delta is located in a complex structural area of Mediterranean Ridge, which is an important wrench fault separating the Arabian plate to the African Plate. This study aims at monitoring the recent crustal deformation and velocity of the Northern delta beside its connection to the seismicity and tectonic activities of the African plate using the permanent GNNS stations distributed at the Egyptian Delta and Europe. The available GNNS data (2009-2019) were analysed utilising the Bernese 5.2 software, to identify the velocity vectors, and the principal segments of crustal strains along the investigated region. The results show that the average absolute velocity ranges between 14 and 22 mm/yr with an accuracy of 3 mm/yr, and the residual velocity is estimated at 0.51 to 4.98 mm/yr with an accuracy of 2.5 mm/yr. Furthermore, the rate of the gathered strains in the northern Nile Delta was recently changed from low to moderate. The outcomes show that the area under investigation suffers from irregular seismic activity related to the crustal movements, which occurred along with the major fault trends in the region.

Seismicity in the Northern Rhine Area (1995\u20132018)

Since the mid-1990s, the local seismic network of the University of Cologne has produced digital seismograms. The data all underwent a daily routine processing. For this study, we re-processed data of almost a quarter century of seismicity in the Northern Rhine Area (NRA), including the Lower Rhine Embayment (LRE) and the Eifel Mountain region (EMR). This effort included refined discrimination between tectonic earthquakes, mine-induced events, and quarry blasts. While routine processing comprised the determination of local magnitude ML, in the course of this study, source spectra-based estimates for moment magnitude MW for 1332 earthquakes were calculated. The resulting relation between ML and MW agrees well with the theory of an ML ∝ 1.5 MW dependency at magnitudes below 3. By applying Gutenberg-Richter relation, the b-value for ML was less (0.82) than MW (1.03). Fault plane solutions for 66 earthquakes confirm the previously published N118° E direction of maximum horizontal stress in the NRA. Comparison of the seismicity with recently published Global Positioning System–based deformation data of the crust shows that the largest seismic activity during the observation period in the LRE occurred in the region with the highest dilatation rates. The stress directions agree well with the trend of major faults, and declining seismicity from south to north correlates with decreasing strain rates. In the EMR, earthquakes concentrate at the fringes of the area with corresponding the largest uplift.

Selection of efficient degradation features for rolling element bearing prognosis using Gaussian Process Regression method

Rolling Element Bearings are one of the most ubiquitous machine elements used in various machineries in the manufacturing industry. Prognosis and estimation of residual life of rolling element bearing are very important for efficient implementation of health monitoring and condition-based maintenance. In this paper, a rolling element bearing fault or degradation trend prediction is modeled using Gaussian Process Regression (GPR) method. Various vibration features based on signal complexity, namely Shannon entropy, permutation entropy, and approximate entropy are estimated to obtain the bearing degradation trend. When fault or degradation occurs in rolling element bearing, there is a subtle change in the dynamics of the system and subsequently, there are changes in the features extracted from the vibration signal. In this paper, a comparative analysis of various kernel functions of the GPR model is carried out using accuracy-based metrics. In addition, the combination of goodness of metric (monotonicity (Mon), robustness (Rob), and prognosability (Pro)), namely hybrid metric, is proposed to select the efficient bearing degradation trend of features. Further, the GPR at ARD exponential kernel has been employed to make the prognosis of degradation trend in bearings with a 95% confidence interval (CI). The proposed methodology is validated through a mathematical model of the simulated vibration signal. Finally, from the simulated and experimental data, it is demonstrated that the entropy features have better performance than the statistical features.

Quantifying and modelling the effects of pre-existing basement faults on folding of overlying strata in the Surat Basin, Australia: Implications for fault seal potential

Ancient basement fault geometry has a systematic effect on the folding of overlying sedimentary successions. Using aeromagnetic, Bouguer gravity, as well as 2D and 3D seismic datasets, the characteristics of the basement structure underlying the Jurassic-Cretaceous Surat Basin were examined and used to contextualise the nature of its folded strata. Using Fault-Forward modelling software, the deformation of the basement structural layers was modelled and analysed for its influence on the reactivation of faulting. The results show that the major fault trends in the eastern Surat and Bowen basins consist of five key features with N- and NE-trending orientations: the Goondiwindi, Moonie, Undulla Transition Zone, Burunga-Leichhardt, and Cockatoo fault systems. Most of the major fault deformation ceased in the Late Triassic. However, some faults (i.e., the Moonie and Goondiwindi fault systems) were variably reactivated along their lengths during the Jurassic. Three models of pre-existing basement reactivation are proposed to explain the observed variability in folding style with application to different parts of the basin. Ancient fault systems with dip angles greater than 45° were readily reactivated and produced tight monocline structures with high strain (ε > 0.35) and fault throw (>60 m) (e.g. Moonie Fault System), while faults with small dip (<30°) or large apical angles generated folds with low strain and uplift of the hanging wall. This variability in fault reactivation according to differences in fault throw potentially influences across-fault juxtaposition of strata and sealing potential for CO2 storage. Modelling such as this should be undertaken elsewhere in situations where trishear structural domains are expected, to better understand and predict the deformation of overlying stratal successions.

Folding and faulting offshore Libya: Partly decoupled tectonics above evaporites

The Gabes-Tripoli Basin of western offshore Libya encompasses and neighbours several large hydrocarbon fields (e.g. the Bouri Field with 1000-3000 Million barrels oil), which are of major economic importance for Libya. Despite the relevance and value of the basin, there are today several unsolved geological questions concerning the basin's late Cretaceous to recent tectonic development; the role of a potential Triassic salt substratum influencing the development of hydrocarbon-bearing anticlines; and the interaction of tectonics and sedimentation controlling reservoir-rock deposition, reservoir fracturing, hydrocarbon migration and accumulation.This study presents detailed structural-stratigraphic interpretations of the Gabes-Tripoli Basin based on 3D-seismic-reflection data and borehole information. A workflow is used that is specifically designed to enhance the seismic interpretability of faults. The workflow integrates targeted 3D-seismic data pre-conditioning, volume-attribute analysis and isochore (TWT) interpretation. Detailed 3D subsurface attribute interpretations show that (i) different groups of faults with different structural orientation characterize the different stratigraphic intervals between the Late Cretaceous and today; (ii) major anticlines associated with the main hydrocarbon reservoirs trend WSW-ENE and SSE-NNW, which is oblique to the dominant NW-SE fault trend. The SSE-NNW-oriented anticlines present a newly documented fold orientation in the basin; (iii) large N-S oriented, gravity-driven, synsedimentary listric normal faults formed at the edges of major anticlines bounding kilometre-scale sedimentary depocentres; and (iv) Paleogene anticline growth and growth faulting at the anticline edges was decoupled from the dominant Late Cretaceous to recent NW-SE-oriented, deep-rooted crustal fault trend.Combined tectonic and stratigraphic interpretation documents partial decoupling of Eocene to Oligocene overburden faulting in the western and central study area from otherwise basement-rooted strike-slip tectonics. Lateral and vertical subsurface evaporite movement in the Paleogene is regarded as an important control for anticline growth and reservoir development in anticline crests, with contemporaneous and subsequent basement-involved strike-slip faulting contributing to a high variability in fault- and fracture-trends and types.

3-D isotropic and anisotropic shallow crustal structure on Pingtan Island, Fujian, southeastern coast of China

Pingtan Island is located on the southeastern coast of China between the Changle-Zhao'an and Binhai fault zones. We use P- and S-wave traveltime data from marine large-volume airgun sources for 3-D velocity structure inversion, and the spatial resolution is high at depths of 1–3 km. The isotropic inversion results show that the velocity in the island is higher in the midwestern area, which consists of sedimentary plains. The velocity is lower in the southern and eastern areas, which consist of eroded hills. Then we perform azimuthally anisotropic inversion using the obtained isotropic model as the initial model. The fast directions in the island are predominantly NE-SW and NNE-SSW, consistent with the main fault structures along the southeastern coast of China. The magnitude of anisotropy gradually decreases from south to north, consistent with the decreasing intensity of fault activity from south to north. On the southeastern coast of China, the fast direction in the upper crust is nearly orthogonal to that in the upper mantle from previous studies, which is nearly parallel to the absolute plate motion in the lower crust and upper mantle. The faults along the Fujian coastal area and Taiwan formed at different time period. But the fast directions in these two areas are similar. Therefore, the fast direction is mainly dominated by the trends of faults and fractures in the upper crust. And it is dominated by aligned olivine crystals induced by plate motion in the lower crust and upper mantle.

Growth and geomorphic evolution of the Ustica volcanic complex at the Africa-Europe plate margin (Tyrrhenian Sea)

We present here for the first time a morpho-structural study of the submarine sector of the Ustica volcanic edifice, located in the south-western Tyrrhenian Sea, considered as an inactive volcanic system, middle Pleistocene in age. The main aim of this research study is to unravel the submarine dynamics along the slope sectors of the Ustica volcano, in order to provide new insights on one of the most tectonically active regions of the Central Mediterranean during the Quaternary. We analysed and interpreted an integrated seismo-acoustic data set consisting of multibeam swath-bathymetry, sub bottom profiles, single-channel seismic reflection records, all of them acquired during the last two decades. The seismostratigraphic analysis indicates that the Ustica volcano is composed by a sequence of lava flows and pyroclastic products, whose geometry can be interpreted as the consequence of combined upward growing and northward shifting of the volcanic centers. The mapped geomorphological elements distributed along the submerged slopes were classified based on their specific morphogenetic process. The achieved results reveal that volcanic, tectonic, oceanographic and gravity processes interacted in shaping the complex current physiography of the volcanic edifice, which is characterized by extremely uneven submarine flanks. The northern region is characterized by the widespread occurrence of well-preserved cones, probably linked to the last submarine volcanic activity of the area. Along the eastern sector, elongate gullies and linear furrows locally incise the shelf break and develop downward producing slope failures. Furrows and gullies represent the main conduits for flushing sediments through various types of flows and mass wasting, from the shallow sectors to the bathyal plain. Along the southern and eastern region slope failures processes carve almost totally of the shelf edge and mainly propagate through retrograding collapses. Further on, the southern region is mainly shaped by E-W and N-S trending fault escarpments that may have triggered the largest slope failures of the area. The main results of this study contribute to improve the understanding of the geological processes and geodynamic activity between the Northern Sicily Continental Margin and the Tyrrhenian Basin and represent a baseline for assessing the geo-hazard potential on the Ustica Island.

New Macroseismic and Morphotectonic Constraints to Infer a Fault Model for the 9 (Mw6.1) and 11 January (Mw7.3) 1693 Earthquakes (Southeastern Sicily)

This study deals with the earthquakes which occurred in southeastern Sicily in 1693 (January 9 and 11, Mw ≈ 6.1 and 7.3, respectively). Although they have been largely studied, robust and commonly accepted seismic sources are still missing. We performed a revision of the 1693 macroseismic data and, for the fore and main-shocks, modeled new NNE-SSW trending seismic sources. In the Hyblean Plateau area, we carried out an analysis of DEM and aerial photos to map tectonic features. Then, we performed field surveys on the main faults, and a morphotectonic study with the aim of characterizing the activity of mapped faults. The study revealed the presence of three main fault systems. The first is the Palazzolo-Villasmundo Fault System, composed of NNE-SSW and NE-SW trending north-west-dipping normal faults. Some of these faults could be reactivated as reverse faults. The second is the Augusta-Floridia Fault System, made of NNW-SSE and NW-SE normal faults. The third is composed of faults which have never been mapped before: the Canicattini-Villasmundo Fault System that shows both a segmented and stepping pattern, almost N-S trending and west-dipping normal faults; some of these faults show a left-lateral movement. The morphotectonic study demonstrated that the fault systems are active. Furthermore, both strike and kinematics of the studied faults well match with the regional stress field characterized by a NW-SE σ1, which in the study area is probably both affecting some pre-existing faults, the Palazzolo-Villasmundo and the Augusta-Floridia Fault Systems, and causing the formation of new faults, the Canicattini-Villasmundo Fault System. The latter system lies across the Hyblean Plateau with a total length of 35 km and, due to its aligned segmented pattern, it can be the surface expression of a master fault that seems dividing the Hyblean Plateau in two blocks. Moreover, the Canicattini-Villasmundo Fault System well fits the southern part of the 1693 revaluated seismic sources and matches with a current alignment of shocks mainly characterized by left-lateral focal mechanisms on almost N-S fault planes. Considering the possible rupture length in depth, it could manage to release Mw ≈ 7.1 earthquakes, representing a valuable candidate source for the 1693 earthquakes.

Fault diagnosis analysis and health management of thermal performance of multi-source data fusion equipment based on fog computing model

Waste heat boiler will be restricted by the exhaust parameters of gas turbine, at the same time, it will affect the thermal characteristics of steam side, and its flue gas resistance will directly affect the power and efficiency of gas turbine cycle, which will have an important impact on the efficiency of combined cycle system. Therefore, it is necessary to monitor the running status of the equipment in time, identify the early signs of faults, and make accurate judgments on fault location, fault degree and development trend, so as to improve the reliability and availability of the unit. The thermal system is the main part of thermal power plant production, so the fault diagnosis of this part is particularly important. In this paper, a method of thermal performance fault diagnosis and health management for multi-source data fusion equipment based on fog computing model is proposed. Using the theory of multi-source data fusion analysis, the qualitative values of the parameters of the fog computing model are marked, and the causes of the failure of the failure variables are obtained. Complete the fault subspace identification, and comprehensively evaluate the equipment status according to multi-attribute decision. This method is conducive to the accurate identification of early faults and the accurate judgment of fault degree and fault trend

Structural overprinting criteria determined from regional aeromagnetic data: An example from the Hill End Trough, East Gondwana

Determining overprinting relationships in the geological record has underpinned our understanding of the evolution of the Earth and has provided the context in which to interpret geoscientific datasets. Geological overprinting relationships are generally determined from outcrop relationships. When outcrop is absent or limited, overprinting relationships using geological observations is often ineffective or ambiguous. We show how aeromagnetic data can be used to inform superposition of geological structures using a combination of folded stratigraphy, faults (both high angle and low angle), and plutons from the well-exposed Hill End Trough, in the Phanerozoic eastern Lachlan Orogen. Overprinting relationships reveal episodic inversion of the Late Silurian to Early Devonian back arc basin succession, preserved within the Hill End Trough, occurred during superimposed shortening events. The first event resulted in the development of regional folds associated with the Tabberabberan Orogeny and the second event resulted in the development of overprinting north-south and north-northwest trending faults during the Early Carboniferous Kanimblan Orogeny. Inversion structures are overprinted by a Carboniferous granite, which is overprinted by previously unrecognised northeast- and northwest conjugate faults, which we interpret to be related to the Permo-Triassic Hunter Bowen Orogeny.

Unraveling the complex structure of popocatepetl volcano (Central Mexico): New evidence for collapse features and active faulting inferred from geophysical data

Popocatepetl volcano located in central Mexico has been erupting since December 1994 and since then many studies have been carried out in order to understand its eruptive behavior and assess the volcanic hazard since more than 25 million people are at risk. Nevertheless, few geophysical studies have been conducted in order to image the structure of the volcano. For this reason, we carried out magnetotelluric and gravity surveys on the northern flank of the volcano and also modeled magnetic data for the area. In this paper we provide new insight into the structure of the northern part of this complex volcanic structure, which is made up of several volcanoes that had been camouflaged by later pyroclastic deposits from recent eruptions. Results show major northwest-and northeast trending faults in the area that displaced blocks toward the south. These scarps are related to sector collapses. The oldest part of the complex, the Tlamacas volcano was identified by the discontinuities inferred from gravity, magnetic and magnetotelluric data. Electrical resistivity distribution also shows the existence of a lack of continuity in a conductive horizon on the eastern side of the prospected area, which coincides with the location of the hypocenter of the May 6, 2013 earthquake. This feature also corresponds to the position of Tlamacas Volcano and its late dome, that is also faulted, confirming that the NE-SW trending fault is still active. Faulting inferred from geophysical data and confirmed by the occurrence of earthquakes and vent alignment suggests the structural control on magma ascent and the weakness of the southeastern flank of the volcano.

Structural style of buried Ediacaran basins in Saudi Arabia on seismic reflection data

Several isolated Ediacaran basins subcrop Phanerozoic strata in Saudi Arabia. The structural styles of these subcropping basins are reviewed here based on interpretation of 2D and 3D seismic reflection data and comparison with Arabian Shield outcrops. The basins are distinguished by layered seismic reflectors that are interpreted as sedimentary and volcanic strata. Due to limited well penetrations these packages cannot be directly dated but a relative chronology is established, anchored by constraints from the Arabian Shield and regional studies. Most of the basins are bound by extensional faults and the basin fills show growth architectures and angular unconformities. The bounding faults trend broadly north–south and are interpreted to be late to post-orogenic reactivations of oceanic terrane margins. Based on their structural characteristics in comparison with sub-basins exposed on the shield, the basin fills are correlated with the Ediacaran Jibalah Group, an equivalent of the Omani Nafun Group. These sub-basins experienced inversion and exhumation prior to ongoing volcanism and unconformable deposition of late Ediacaran to earliest Cambrian Kurayshah Group sediments. The Kurayshah Group is disconformably overlain by the widespread Tayma Group siliciclastics. This disconformity correlates to the Angudan Unconformity in Oman. The Kurayshah Group includes a late Ediacaran stratovolcano over 40 km in diameter. In the eastern basins, evaporitic structural styles indicate the presence of Hormuz / Ara evaporites, with local igneous intrusions, that correlate at least in part to the Kurayshah Group. The Tayma Group infills significant accommodation space variations and was affected by ongoing but declining differential subsidence and reactivation of the underlying basin-bounding faults.

Creep Along the Central San Andreas Fault From Surface Fractures, Topographic Differencing, and InSAR

AbstractImaging tectonic creep along active faults is critical for measuring strain accumulation and ultimately understanding the physical processes that guide creep and the potential for seismicity. We image tectonic deformation along the central creeping section of the San Andreas Fault at the Dry Lake Valley paleoseismic site (36.468°N, 121.055°W) using three data sets with varying spatial and temporal scales: (1) an Interferometric Synthetic Aperture Radar (InSAR) velocity field with an ~100‐km footprint produced from Sentinel‐1 satellite imagery, (2) light detection and ranging (lidar) and structure‐from‐motion 3‐D topographic differencing that resolves a decade of deformation over a 1‐km aperture, and (3) surface fractures that formed over the 3‐ to 4‐m wide fault zone during a drought from late 2012 to 2014. The InSAR velocity map shows that shallow deformation is localized to the San Andreas Fault. We demonstrate a novel approach for differencing airborne lidar and structure‐from‐motion topography that facilitates resolving deformation along and adjacent to the San Andreas Fault. The 40‐m resolution topographic differencing resolves a 2.5 ± 0.2 cm/yr slip rate localized to the fault. The opening‐mode fractures accommodate cm/yr of fault slip. A 90% ± 30% of the 1‐km aperture deformation is accommodated over the several meter‐wide surface trace of the San Andreas Fault. The extension direction inferred from the opening‐mode fractures and topographic differencing is 40°–48° from the local trend of the San Andreas Fault. The localization of deformation likely reflects the well‐oriented and mature fault.

Geochemical Assessment and Lateral Reservoir Continuity of Asmari Reservoir Oils in the Cheshmeh‐Khush Oilfield, SW Iran

AbstractA total of 6 oil samples were systematically selected from six Asmari Reservoir wells in the Cheshmeh‐Khush Oilfield for geochemical evaluation of the hydrocarbon system, based on reservoir geochemistry and oil fingerprints. An investigation of the distribution patterns of normal alkanes and tricyclic and tetracyclic terpanes along with characteristic biomarkers of the depositional environment and sedimentary facies, indicated that the source rock of the studied hydrocarbons was deposited in a reducing aquatic environment with a low input of terrigenous material and predominantly carbonate lithology derived from organic algal matter. The studied oil samples exhibited moderate maturity, as was further confirmed by the parameters extracted from the light hydrocarbons. Statistical clustering based on different biomarker parameters indicated the presence of two oil families. Additionally, the application of branched and cyclic compounds in the light hydrocarbons (C5–C11) to evaluate lateral continuity of the Asmari reservoir further supported the presence of the two oil families. Other evidence proved the presence of a NE–SW trending fault separating wells X5 and X6 from the other wells in the field. In other wells across the field, good lateral reservoir continuity was observed, despite the presence of faults on the northern and southern plunges of the structure.

A revised synthesis of the rift and drift history of the Gulf of Mexico and surrounding regions in the light of improved age dating of the Middle Jurassic salt

Abstract We present an updated, internally consistent synthesis of the Permo-Triassic assembly and Mesozoic evolution of the Gulf of Mexico, Mexico, Florida–Bahamas and northern South America (Guiana margin and northern Andes), incorporating advances at regional, field and geochronological levels. The recently determined Bajocian age for salt deposition (using 87 Sr/ 86 Sr isotopes) is integrated by modifying the plate kinematic framework with a new Equatorial Atlantic reconstruction that expands the gap between the Americas by 180 km over many kinematic frameworks. NW–SE synrift lithospheric extension along western Florida–Bahamas is estimated at 40%, implying thinned continental crust beneath Great Bank, Bahamas, the conjugate for the Guianas Basin margin. In cordilleran Mexico (excluding the Yucatán Block), we propose two new means by which continental crust migrated into the ‘Colombian overlap position’ of Pangaean reconstructions. The first involved Jurassic–earliest Cretaceous sinistral displacement of the Oaxaca Block along a NW–SE ‘North Oaxaca Transfer’ through or adjacent to the Cuicateco Belt. The second applies to the continental crust in eastern Mexico to the north of Cuicateco, a region we refer to as ‘peninsular Mexico’. There, most Mesozoic basement faults trend NW–SE, and the common occurrence of Permian mid-crustal anatectic basement directly beneath Mesozoic red beds, salt and marine strata suggests extreme extension prior to the onset of sedimentation. Because these Mesozoic sedimentary sections typically sum to 3–8 km in thickness, the post-rift crust of peninsular Mexico probably averaged about 25 km in thickness before later orogenesis. Our reconstructions suggest that this Triassic–Middle Jurassic extension approached 100%, beginning with overthickened Alleghanian (Permian) crust about 50 km in thickness in palaeo-northern Mexico, and was accompanied by a significant sinistral component broadly distributed across the rift array. The updated model provides an exploration and kinematic framework for the entire region.

Evolution of a Normal Fault System Along Eastern Gondwana, New Zealand

AbstractThe Great South Basin (GSB) developed in the Cretaceous from continental rifting at the southeastern margin of Gondwana. The basin contains a thick Cretaceous succession that is largely unaffected by Neogene compressional tectonics, with rift faults and associated growth strata imaged by good‐quality 2‐D and 3‐D seismic data tied to wells. These data show three distinct stages of normal faulting here referred to as fault system initiation (Stage 1), fault system growth (Stage 2), and fault system death (Stage 3). The different stages of fault system evolution comprise dominant NE trending faults (NW‐SE extension), and minor NW trending faults (NE‐SW extension). Fault initiation at ~105–101 Ma mainly occurred in the central GSB with rift depocenters mostly on, or close to, NW trending basement terrane boundaries. These preexisting basement boundaries represent zones of weakness that locally promoted early localization of NW faults and retarded the propagation of NE faults. With increasing regional extension and fault system growth from ~101 to 90 Ma the influence of the basement fabric gradually decreased, while NE trending faults increased in length, number, displacements, and spatial distribution. Finally, during the fault system death stage from ~90 to 83 Ma the length, number and displacements of faults decreased. Fault death coincided in time with Gondwana breakup and reflects the localization of extension along spreading centers distal to the GSB.