Deep-seated Basement Faults Research Articles

Utilization of seismic attributes for structural pattern detection In Bualawn, Dor Mansour fields, Western Sirt Basin, Libya

An integrated approach to the study of fault patterns carried out in the complex geological structures of Bualawn, Dor Mansour fields by using multiple seismic attributes of 3-D seismic data. Each type of geological structure event usually generates a unique seismic signature that can be recognized and identified. This paper highlights the practical importance of analyze integrated attributes and interpret them within the context of an appropriate structural deformation. Many of discontinuity attributes such as variance, 3DEE (3D edge enhancement), ant tracking, chaos and structure smoothing have been selected to delineate fault styles and their displacement effectively, which cannot be fully delineated using seismic amplitude data. Conjugate growth faults in NW-SE and NE-SW direction, dipping toward SW with antithetic faults dipping in opposite direction to the growth faults and other minor faults. The faults were identified manually and then tested by discontinuity attributes. Fault system is represented by a fracture system comprising long en echelon seismic faults and several discontinuities. This system of en echelon faults was initiated by left-lateral wrenching movements. This wrenching system has been identified by negative and positive flower structure along the releasing and restraining bends. The current understanding that these faults are strike-slip faults despite the absence of extensive horizontal displacements along them as shown on different time slices. A periodic strike-slip movement along deep-seated basement faults have developed many structural features, such as horst-graben styles, which is the orientation of the transtensional movements linked to the Upper Cretaceous Succession.

Interpretation of aeromagnetic data to detect the deep-seated basement faults in fold thrust belts: NW part of the petroliferous Fars province, Zagros belt, Iran

Detection and delineation of basement faults are fundamental exercises in petroleum geology. This is because such structures can guide later deformation and the associated structures within the younger overlying sediments. This work presents aeromagnetic data interpretation and a comparison with the Digital Elevation Model (DEM) to detect basement structures covering the NW part of the petroliferous Fars province, Zagros belt. Anticlinal axes deflect in the NW-part of the province. The reason for this deflection is debated. We identified basement faults from the airborne geomagnetic data. Tilt filtering was applied on the magnetic data to enhance such faults. Two NE-trending cross-sections perpendicular to the anticlinal axes were prepared to show the effect of the basement faults in the sequence stratigraphy. The results of this research indicate a major NW and another NE trending deep-seated fault. Most of the extracted magnetic lineaments correspond to these faults. These faults were confirmed by the high displacement of the layers and changes of the thickness in the sequence stratigraphy. The result of this research suggests that the deep-seated basement faults are the main controlling factor of structural style in the NW part of Fars province in terms of a thick-skinned tectonics.

Tectonic evolution of the Zagros foreland basin since Early Cretaceous, SW Iran: Regional tectonic implications from subsidence analysis

• Basement palaeo-highs exert major impact on the basin's subsidence history. • Architecture of the Zagros foreland dramatically changed during the Cretaceous. • NE-SW deep-seated basement faults were intensively re-activated during the Turonian . • N-S deep seated basement faults were re-activated during the last 20 Ma. Subsidence analysis of 42 exploration wells in the Zagros foreland basin indicates the tectonic evolution of the basin since Early Cretaceous. The impact of inherited basement structures on the basin evolution is documented in this study. Subsidence maps show that the architecture of the basin dramatically changed during the Cretaceous. In the Central Zagros, the Hercynian palaeo-high (i.e. Wadi Al Batin palaeo-high), which affected sedimentation until the Early Cretaceous time gradually disappeared and the South Pars palaeo-high within the central Persian Gulf started to show more impact on sedimentation. The palaeo-highs in the Zagros basement have different geometrical characteristics and origin. The Hercynian and South Pars are wide-wavelength palaeo-highs with a regional-scale impact on subsidence. In contrast, the Hendijan, Kharg-Mish and Kazerun palaeo-highs with different orientations and quite smaller wavelengths show different impact on the subsidence pattern. These kinds of palaeo-highs could be related to re-activation of pre-existing basement faults. Whereas South Pars and Hercynian paleo highs are possibly related to thermal expansion or contraction of the crust. The Hendijan and Kharg-Mish palaeo-highs with the NE-SW orientation were intensively re-activated during Turonian time. On the contrary, the Kazerun Fault with the N-S orientation became more active and considerably influenced sedimentation during the last 20 Ma. Selective re-activation of deep-seated faults might have taken place as a result of changes in the orientation of the far-field stress in the region. Understanding the complexities of inherited structures and their impact on reservoir characteristics can support future exploration activities in the Zagros foreland basin.

Investigating Role of the Hormuz Salt Bodies in Initiation and Evolution of the Strike Slip Faults in the Fars Zone of the Zagros Fold and Thrust Belt: Insights from Seismic Data and Sandbox Modeling

The Zagros Belt has examples of strike-slip faults affected by precursor Hormuz Salt bodies. We attempted to examine the role of salt walls in localizing the strike-slip faults using field observations, seismic profiles and understandings from the sandbox modeling. Setting and performance of the pre-Hormuz features in connection to the salt tectonics are major questions. The inherited topography below the salt is an important parameter which controlled the structuration of the basin. The antecedent troughs provided accommodation for the thick Hormuz Salt. Differential loading above the salt helped generation of salt-related structures. The salt-walls caused formation of elongated highs. These highs were re-shaped in form of strike-slip faults during the Zagros Orogeny. The intersection of the salt walls and the Zagros-induced deformation fronts are location of potential diapirs needless of bending points along the tear faults. In contrast, the underlying deep-seated basement faults are hardly believed to be strike-slip.

Integrated 3D geomechanical modeling and its application for well planning in Bantumilli South area, Krishna-Godavari Basin, India

Complex geologic structure, a heterogeneous reservoir, and complications related to high pressure during drilling necessitate carrying out geomechanical modeling to understand the physical properties of rocks and fluids present within the Early Cretaceous synrift sequence in the Bantumilli South area of the Krishna-Godavari Basin in India. Reservoirs within the synrift sequence exhibit low permeability and high pore pressure. Identification of safe mud-weight window zones is critical for safe drilling of wells in this part of the basin. A detailed workflow for building a robust 3D geomechanical model and its applications to well planning and hydraulic fracturing are presented. Elastic properties of the reservoirs were estimated by prestack seismic inversion. Elastic properties and pore pressure volumes were used to simulate the 3D stress field. The maximum horizontal stress direction is observed to be 130°N ± 5°, i.e., northwest to southeast, and estimated fracture pressure (minimum horizontal stress) values range between 10,000 and 14,200 psi within the synrift sequence. The study has shown that the Cretaceous section of the reservoir has narrow mud-weight window zones. These zones are governed mainly by a high pore pressure regime in the reservoirs. Additionally, deep-seated basement faults have played an important role in the compartmentalization of the reservoir in terms of geomechanical properties.

Possible origin of inert gases in hydrocarbon reservoir pools of the Zindapir Anticlinorium and its surroundings in the Middle Indus Basin, Pakistan

The natural gas in several gas fields in Pakistan is associated with varying percentages of inert gases (e.g., CO2, N2, and H2S). The heating capacity of such natural gas is measured in British thermal units (BTU) in Pakistan and is based on the combustion of the natural gases. The study area of this work belongs to the Middle Indus Basin, which also covers some parts of the Sulaiman Foldbelt and the Punjab Platform. Petroleum wells drilled in the study area contain inert gases (mostly CO2 and N2) in varying percentages, which decreases the BTU value of sweet gases and the economic value of the gas reserves.Attempts were made to analyze the varying compositions of inert gases (mostly CO2 and N2) along the deep-seated basement faults in the Zindapir Anticlinorium, eastern Sulaiman Foldbelt, but no specific relation could be established. Similarly, geothermal gradient zones were identified and the distribution of inert gases in these zones was studied, but even so, no well-established relation could be tracked. However, variations in the amounts of inert gases in the Chiltan Limestone of the Rodho Structure and the Afiband Structure point to the generation of in situ inert gases because both wells were drilled on the same anticlinorium and share the same geology, and possibly, the same source rock. Post-accumulation changes probably play an important role in the generation of in situ inert gases in varying concentrations. H2S is also present in some parts of the Indus Basin. Therefore, a brief discussion about the possible origin of the H2S is also included in this paper.

Clues to inferred different thrust-related fold models and thin-thick skinned tectonics within a single folded structure in Iraqi Zagros, Kurdistan region

The Maqloub–BardaRash structure is situated at the Low Folded Zone within the NW of the Zagros fold-thrust belt in the Iraqi Kurdistan region. One of the main goals of this work is to reveal the variation in the fold architecture and fault shape with depth to build a plausible fold model, as well as to explain the kinematic evolution of the Maqloub–BardaRash structure. The middle part of the anticlinal hinge line of the studied structure shows deviation and anticlockwise rotation. This character is ascribed to the presence of a north-south trending left-lateral strike-slip fault. This fault is considered to be a deep-seated basement fault that likely caused segmentation of Maqloub–BardaRash structure into two parts: the northwestern Maqloub structure which exhibits a normal asymmetry and the southeastern BardaRash structure with a reverse asymmetry. The balanced cross sections based on the top of Middle Miocene Fatha Formation from the studied structures displays a maximum total horizontal shortening of 14% for the Maqloub structure and 9.89% for the BardaRash segment at the same stratigraphic level. Through the Maqloub section, the thrust-related shortening increases downsection, whereas the fold-related shortening increases upsection. Whereas along BardaRash section, the fold-related shortening smaller irregular variations at different stratigraphic levels are evidenced. The Maqloub segment is interpreted as a fault-propagation fold, but the BardaRash segment is interpreted as a faulted detachment fold based on the geometrical analysis of deformed models. Based on the resulting deformed geometries from the balanced cross sections, the propagation of the Maqloub segment is associated with the activation of an underlying basement fault, whereas the BardaRash segment is decoupled along the Triassic ductile sequence. The structural characterization of two different models of the fault-related deformation along the individual Maqloub–BardaRash folded structure will enhance accurate well position of the crestal reservoir.

Influence of inherited Indian basement faults on the evolution of the Himalayan Orogen

Abstract Indian basement faults, which bound three orogen-perpendicular palaeotopographic ridges of Precambrian Indian basement south of the Himalaya, extend to the base of the Indian lithosphere and to the northern extent of the Indian lithosphere underneath Tibet. In the eastern Himalaya, the active orogen-perpendicular Yadong–Gulu graben is aligned with an earthquake-generating strike-slip fault in the high Himalaya. We argue that the graben results from crustal necking during reactivation of the underplated basement fault. In the central Himalaya, along-strike diachronous deformation and metamorphism within the Himalayan metamorphic core, as well as lateral ramps in the foreland thrust belt, spatially correspond to the Lucknow and Pokhara lineaments that bound the subsurface Faizabad Ridge in the Indian basement. Analogue centrifuge modelling confirms that offset along such deep-seated basement faults can affect the location, orientation and type of structures developed at various stages of orogenesis and suggests that it is mechanically feasible for strain to propagate through a melt-weakened mid-crust. We suggest that inherited Indian basement faults affect the ramp-flat geometry of the basal Main Himalayan Thrust, partition the Himalayan range into distinct zones, localize east–west extension resulting in the Tibetan graben and, ultimately, contribute to lateral variability in tectonic evolution along the orogen's strike.

Evolution of the stress fields in the Zagros Foreland Folded Belt using focal mechanisms and kinematic analyses: the case of the Fars salient, Iran

The NW–SE trending Zagros orogenic belt was initiated during the convergence of the Afro–Arabian continent and the Iranian microcontinent in the Late Cretaceous. Ongoing convergence is confirmed by intense seismicity related to compressional stresses collision-related in the Zagros orogenic belt by reactivation of an early extensional faulting to latter compressional segmented strike–slip and dip–slip faulting. These activities are strongly related either to the deep-seated basement fault activities (deep-seated earthquakes) underlies the sedimentary cover or gently dipping shallow-seated decollement horizon of the rheological weak rocks of the infra-Cambrian Hormuz salt. The compressional stress regimes in the different units play an important role in controlling the stress conditions between the different units within the sedimentary cover and basement. A significant set of nearly N–S trending right-lateral strike–slip faults exists throughout the study area in the Fars area in the Zagros Foreland Folded Belt. Fault–slip and focal mechanism data were analyzed using the stress inversion method to reconstruct the paleo and recent stress conditions. The results suggest that the current direction of maximum principal stress averages N19°E, with N38°E that for the past from Cretaceous to Tertiary (although a few sites on the Kar-e-Bass fault yield a different direction). The results are consistent with the collision of the Afro–Arabian continent and the Iranian microcontinent. The difference between the current and paleo-stress directions indicates an anticlockwise rotation in the maximum principle stress direction over time. This difference resulted from changes in the continental convergence path, but was also influenced by the local structural evolution, including the lateral propagation of folds and the presence of several local decollement horizons that facilitated decoupling of the deformation between the basement and the sedimentary cover. The obliquity of the maximum compressional stress into the fault trends reveals a typical stress partitioning of thrust and strike–slip motion in the Kazerun, Kar-e-Bass, Sabz-Pushan, and Sarvestan fault zones that caused these fault zones behave as segmented strike–slip and dip–slip faults.

Reconstruction of the Provence Chain evolution, southeastern France

The Provence fold-and-thrust belt forms the eastern limit of the Pyrenean orogenic system in southeastern France. This belt developed during the Late Cretaceous-Eocene Pyrenean-Provence compression and was then deformed by Oligocene-Miocene Ligurian rifting events and Neogene to present-day Alpine compression. In this study, surface structural data, seismic profiles, and crustal-to-lithospheric-scale sequentially balanced cross sections contribute to the understanding of the dynamics of the Provence Chain and its long-term history of deformation. Balanced cross sections show that the thrust system is characterized by various structural styles, including deep-seated basement faults that affect the entire crust, tectonic inversions of Paleozoic-Mesozoic basins, shallower decollements within the sedimentary cover, accommodation zones, and salt tectonics. This study shows the prime control of the structural inheritance over a long period of time on the tectonic evolution of a geological system. This includes mechanical heterogeneities, such as Variscan shear zones, reactivated during Middle Cretaceous Pyrenean rifting between Eurasia and Sardinia. In domains where Mesozoic rifting is well marked, inherited basement normal faults and the thermally weak crust favored the formation of an inner thick-skinned thrust belt during Late Cretaceous-Eocene contraction. Here 155 km (similar to 35%) of shortening was accommodated by inversion of north verging crustal faults, north directed subduction of the Sardinia mantle lithosphere, and ductile thickening of the Provence mantle lithosphere. During the Oligocene, these domains were still predisposed for the localized faulting of the Ligurian basin rifting and the seafloor spreading.

Style of Atlassic tectonic deformation and geodynamic evolution of the southern Tethyan margin, Tunisia

The structure of the southern Atlas fold-and-thrust belt of Tunisia was investigated using new geologic mapping, seismic reflection data together with the construction of a balanced cross section. The structural architecture of the Tunisian foreland consists in a mixed tectonic style with deep-seated basement faults, shallower décollements within sedimentary cover and salt diapirism. The restoration of the cross section shows a surface shortening of 8.1 km (∼7.3%). Sequential restoration of the balanced cross section has been permitted to decipher the structure and evolution of the southern Tethyan margin of Tunisia. Structural geometry and orientation of the pre-existing Permian (?) to Cretaceous extensional structures controlled subsequent contractional deformation within the sedimentary cover. During the shortening, this inherited tectonic framework controlled the development of ENE-trending thrust-related anticlines such as the Orbata and Chemsi structures, NW-trending lateral ramp such as the Gafsa and Fejej faults and diapir structures as the Beidha anticline. The inversion of the margin can be correlated with the onset of the convergence between Africa and Eurasia. The first phase of the Orbata thrusting growth might occur in late Cretaceous. Continuous inversion of the margin occurred during the Eocene and mainly during the late Miocene to present day. This study underlines the predominant role of inherited basement structures acquired during the evolution of the southern Tethyan margin, and their influence on the geometry of the Atlassic thrust belt. This structural analysis provides new perspectives for future hydrocarbon exploration in this poorly explored region.

Noble gases (Ar, Kr, Xe) and halogens (Cl, Br, I) in fluid inclusions from the Athabasca Basin (Canada): Implications for unconformity-related U deposits

The formation of unconformity-related uranium deposits in the Proterozoic Athabasca Basin (Canada) involved basin-scale circulation of U-bearing brines during high-grade diagenesis (150–200°C) at ∼1.6–1.5Ga. The UO2 ores occur both sides of the unconformity and are associated with extensive brecciation and illite–sudoite–dravite alteration. Quartz and dolomite cementing veins and breccias are associated with alteration and mineralisation and contain a fairly uniform population of fluid inclusions characterised by variable Na:Ca and salinities of 25–35wt.% salts and high U concentrations of up to 600ppm U. In order to further constrain the origin of these U-rich brines, we analysed the naturally occurring isotopes of Ar, Kr and Xe, together with halogens (Cl, Br and I), K, Ca and U in irradiated quartz and dolomite samples containing representative fluid inclusions. This was achieved by the noble gas method for halogen measurement (extended 40Ar–39Ar methodology) using a combination of noble gas extraction techniques.The fluid inclusions opened by crushing quartz and dolomite samples in vacuum have similar molar Br/Cl ratios of 5.8×10−3 to 10.4×10−3, and molar I/Cl ratios of 1.8×10−6 to 8.2×10−6. These compositions lie over the top half of the modern-day seawater evaporation trajectory, consistent with the fluids deriving the bulk of their salinity by subaerial evaporation of seawater, beyond the point of halite saturation. The I/Cl ratios are much lower than is typical of fluids that have interacted with I-rich organic matter present in many sedimentary basins or fluid inclusions found in Mississippi Valley type (MVT) Pb–Zn ore deposits. This is significant because provided the U-rich fluid inclusions are representative of the ore-stage fluids, the low I/Cl ratios of the fluid inclusions do not favour fluid interaction with organic matter (or hydrocarbons), as a major process for localising U mineralisation.The majority of samples contain fluid inclusions with age-corrected 40Ar/36Ar of between the modern atmospheric value of ∼300 and 450. These values are considered representative of the fluid's initial composition and are typical of upper crustal sedimentary formation waters. The fluid inclusions non-radiogenic 84Kr/36Ar and 129Xe/36Ar ratios are slightly enriched in 129Xe relative to air and the fluid inclusions are estimated to contain 0.5–17.3×10−10molg−136Ar which is up to twenty times the 36Ar concentration of air-saturated seawater. The data are interpreted to reflect acquisition of atmospheric noble gases from sedimentary rocks and suggest acquisition of radiogenic 40Ar within K-rich basement rocks, that would have been an important source of excess 40Ar, was limited by temperatures of less than 200°C.Taken together the halogen and noble gas composition of the U-bearing fluid inclusions are strongly controlled by subaerial evaporation and subsequent interaction with sedimentary rocks, showing that low temperature evaporitic brines dominated the mineralising system. Mineralisation is unlikely to have been triggered by fluid interaction with organic matter, or mixing with voluminous basement-derived fluids; however, the data do not completely preclude a role for volumetrically minor fluid or gas phases introduced by deep-seated basement faults preferentially located at the sites of mineralisation.

Structural style and fault kinematics of the Lower Eocene Rus Formation at Jabal Hafit area, Al Ain, United Arab Emirates (UAE)

The current contribution presents aspects of the structural style and fault kinematics of the Rus Formation that expose at Jabal Hafit, Al Ain, United Arab Emirates. Although the major structure of Jabal Hafit is an anticlinal fold, fractures (joints and faults) are the prominent structure of the study area. The fractures can be interpreted as the distributed effect of deep-seated basement fault reactivation or to be as reactivation of deep-seated basement faults. These fractures were created during two main tectonic stress regimes. The first is a WNW–ESE S Hmax strike-slip stress regime, responsible for producing E–W to ESE–WNW joints and E–W dextral strike-slip and NNE–SSW reverse faults. This stress is interpreted to be post-Early Eocene in age and related to the second phase of thrusting in the Oman Mountains in the Miocene. The second stress regime is a NNE–SSW S Hmax transtensional (strike-slip extensive) stress regime that was responsible for N–S to NNE–SSW striking joints and NE–SW sinistral strike-slip and N–S normal faults. This regime is interpreted to be post-Middle Eocene in age. This stress was the response to the collision of the Arabian–Eurasian Plates which began during the Late Eocene and continues to the present day.

Upper Devonian to Lower Mississippian conodont biostratigraphy of uppermost Wabamun Group and Palliser Formation to lowermost Banff and Lodgepole formations, southern Alberta and southeastern British Columbia, Canada: Implications for correlations and sequence stratigraphy

Research Article| December 01, 2010 Upper Devonian to Lower Mississippian conodont biostratigraphy of uppermost Wabamun Group and Palliser Formation to lowermost Banff and Lodgepole formations, southern Alberta and southeastern British Columbia, Canada: Implications for correlations and sequence stratigraphy David I. Johnston; David I. Johnston 103 - 3017 Blakiston Drive NW, Calgary, AB T2L 1L7, johnstda@shaw.ca Search for other works by this author on: GSW Google Scholar Charles M. Henderson; Charles M. Henderson Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, charles.henderson@ucalgary.ca Search for other works by this author on: GSW Google Scholar Michael J. Schmidt Michael J. Schmidt ConocoPhillips Canada, 401 9th Avenue SW, Calgary, AB T2P 2H7, Mike.J.Schmidt@conocophillips.com Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2010) 58 (4): 295–341. https://doi.org/10.2113/gscpgbull.58.4.295 Article history received: 23 Sep 2009 accepted: 02 Nov 2010 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David I. Johnston, Charles M. Henderson, Michael J. Schmidt; Upper Devonian to Lower Mississippian conodont biostratigraphy of uppermost Wabamun Group and Palliser Formation to lowermost Banff and Lodgepole formations, southern Alberta and southeastern British Columbia, Canada: Implications for correlations and sequence stratigraphy. Bulletin of Canadian Petroleum Geology 2010;; 58 (4): 295–341. doi: https://doi.org/10.2113/gscpgbull.58.4.295 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract Biostratigraphic analysis of conodont faunas from the Upper Devonian Wabamun Group, the Upper Devonian to Lower Mississippian Exshaw Formation and the Lower Mississippian Banff Formation in southern Alberta has shown that significant hiatuses may exist within the Late Devonian Big Valley and equivalent upper Costigan Member of the Palliser Formation and within the Early Mississippian lower Banff and Lodgepole formations. Minor hiatuses occur in the Late Devonian to Early Mississippian Exshaw Formation between the lower and upper members and between the equivalent lower black shale and middle sandstone members of the Bakken Formation. All of these hiatuses are interpreted to have been the result of forced regression due to uplifts. Biostratigraphic data and stratigraphic evidence derived from mapping suggest an erosional high existed at about the position of the Fifth Meridian in southwestern Alberta, as indicated by the repeated removal of Upper Devonian to Lower Mississippian strata in this area. The only other tectonic elements that may have influenced sedimentation and distribution patterns of these strata are possible deep-seated basement faults beneath the position of the Early Cretaceous Cutbank channel and the Sweetgrass Arch.The lower part of the Big Valley Formation and upper Costigan Member may represent one major episode of deposition, whereas the upper part of these units, the Exshaw Formation and the lower and middle members of the Bakken Formation appear to represent another depositional event. At least two depositional events may be represented in the lower Banff and Lodgepole formations in the study area. The depositional events and hiatuses documented in the study area generally correlate with similar events in western North America and globally. However, discordance between events in our study area and elsewhere probably reflect the masking effect of local tectonism. Correspondingly, one transgressive-regressive sequence may be recognized in the lower part of the Big Valley and upper Costigan Member. The upper part of these units, the Exshaw Formation and the lower and middle members of the Bakken Formation are interpreted as a single transgressive-regressive sequence, contrary to previous interpretations. One complete sequence and a portion of another are recognized in the lower Banff and Lodgepole formations.Many of the unconformities may be linked to Antler orogenesis, which also would have affected subsidence rates. Changes in subsidence rates interacting with eustatic sea level changes produced the stratigraphic framework and distribution of units observed in the study area. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Integrated gravity and seismic investigations over the Jebel Es Souda-Hmaeima structure: implication for basement configuration of the eastern frontal fold-and-thrust belt of Tunisian Atlasic Mountains

A gravity and seismic analysis was conducted over and around Jebel Es Souda-Hmaeima, located on the eastern border of the Tunisian Mountains between the Atlasic block to the west and the Pelagian Block to the east, as part of a study to investigate the subsurface structures. These data, together with outcrop geology, well data, and measurements of physical properties of rock samples, were integrated with a new interpretation of the tectonic model of Jebel Es Souda-Hmaeima anticline. This structure represents a backfolded anticline associated with a steep east-vergent thrust above a blind thrust fault along the base of Triassic formations. The proposed model emphasizes the role of transpressional deformation along deep-seated basement faults and has implications for petroleum generation, migration, and entrapment in central Tunisia.

Quaternary reactivation of a basement structure in the Barreirinhas Basin, Brazilian Equatorial Margin

The Pirapemas Lineament is a remarkable 200-km-long, NE–SW trending structure in the Barreirinhas Basin, one of the several Brazilian coastal basins. This lineament splits the study area in two sectors of distinctive morphology, drainage patterns, and sedimentary covers. Terrain northward of the lineament presents a smooth topography with sub-parallel to sub-dendritic drainage patterns, whereas a dissected plateau characterized by incised valleys and rectangular drainage pattern occurs southward, suggesting a structural control by joints and faults. Geological field data, crossed with thermal luminescence (TL) and optically stimulated luminescence (OSL) dating, revealed that the surface southward of the lineament consists mostly of Miocene and late Pleistocene sedimentary deposits, represented by the Barreiras Formation and the Post-Barreiras sediments, respectively. In contrast, relatively younger sands mantle most of the northward terrain, as indicated by well-preserved paleodune deposits that grade into active aeolian dunes of the Lençóis Maranhenses National Park. Geomorphological and geological data analysis suggests that the northern sector is under the effect of subsidence, proving that the Pirapemas Lineament is an active agent modeling the landscape in the region. Geophysical data (gravity and seismic) confirm that such a structural feature is the surface expression of an active deep-seated basement fault.

Petroleum geology of the Puguang sour gas field in the Sichuan Basin, SW China

The Puguang sour gas field in northeastern Sichuan Basin is the largest gas discovery in the Paleozoic marine strata in China, with at least 9 trillion cubic feet (tcf) of proven gas reserves. It is one of the many anticlinal structures formed during the Indo-Sinian orogeny, with gas being trapped in a composite structure–lithology pool. The presence of the Upper Permian coal measures, Lower Silurian and Lower Cambrian marine shales provided excellent hydrocarbon source rocks. The Lower Triassic and Upper Permian oolitic dolomites serve as high quality reservoir rocks, with 10–25% porosity and 1–1000 mD permeability, largely due to diagenetically produced secondary porosity. The Lower and Middle Triassic evaporate beds have acted as the direct top seal for the large Lower Triassic–Upper Permian gas accumulation. The thick Upper Triassic and Jurassic mudstone beds regionally cap the underlying marine carbonate strata. The deep-seated basement faults acted as vertical hydrocarbon migration conduits during faulting, and became effective flow barriers when the faulting ceased. The deep burial of a paleo-oil accumulation in reservoirs rich in sulfate resulted in extensive thermochemical sulfate reduction (TSR). This, together with the new gas injection and structural reconfiguration, transformed a paleo-oil pool to a large sour gas pool.

The initiation and linkage of surface fractures above a buried strike-slip fault: An experimental approach

Surface fractures in the overburdened sedimentary rocks, formed above a deep-seated basement fault, often provide important information about the kinematics of the underlying master fault. It has already been established that these surface fractures dynamically evolve and link one another with progressive displacement on the master fault below. In the present study, two different series of riedel-type experiments were carried out with clay analogue models under different boundary conditions viz., (i) heterogeneous simple shear of the cover rocks above a buried strike slip fault (wrench system) and (ii) heterogeneous simple shear with a component of shear-normal compression of the overburden package above a basement fault (transpressional system), to observe the initiation and linkage of surface fractures with varying T′ (where T′ = thickness of the overburden normalized with respect to the width of the master fault). In the wrench system, Riedel (R) shears were linked by principal displacement (Y) shears at early stages (shear strain of 0.8 to 1) in thin (2 18) clay models at a minimum shear strain of 0.7. With increasing deformation (at a minimum shear strain of 1.2) two R′ shears were joined by an R shear and finally opened up to make a sigmoidal vein with an asymmetry antithetic to the major fault-movement sense. Under transpression, the results were similar to that of heterogeneous simple shear for layers 2 25) models (at minimum shear strain of 0.7 and shortening of 0.1), with marked angularity of secondary fault zone with the master fault at depth.

Neogene tectonic, stratigraphic, and play framework of the southern Laguna Madre–Tuxpan continental shelf, Gulf of Mexico

Neogene shelf, slope, canyon, and slope-to-basin-floor transition plays in the southern Laguna Madre–Tuxpan (LM-T) continental shelf reflect a variety of structural and stratigraphic controls, including gravity sliding and extension, compression, salt evacuation, and lowstand canyon and fan systems. The Neogene in the LM-T area was deposited along narrow shelves associated with a tectonically active coast affected by significant uplift and erosion of carbonate and volcanic terrains. This study characterizes 4 structurally defined trends and 32 Neogene plays in a more than 50,000-km2 (19,300-mi2) area linking the Veracruz and Burgos basins. The Caonero trend in the southern part of the LM-T area contains deep-seated basement faults caused by Laramide compression. Many of these faults are directly linked to the interpreted Mesozoic source rocks, providing potential pathways for vertically migrating hydrocarbons. In contrast, the Lankahuasa trend, north of the Caonero trend, contains listric faults, which detach into a shallow horizon. This trend is associated with thick Pliocene shelf depocenters. The dominant plays in the Faja de Oro–Nyade trend in the central part of the LM-T area contain thick lower and middle Miocene successions of steeply dipping slope deposits, reflecting significant uplift and erosion of the carbonate Tuxpan platform. These slope plays consist of narrow channel-fill and levee sandstones encased in siltstones and mudstones. Plays in the north end of the LM-T area, in the southern part of the Burgos basin, contain intensely deformed strata linked to salt and shale diapirism. Outer-shelf, slope, and proximal basin-floor plays in the Lamprea trend are internally complex and contain muddy debris-flow and slump deposits. Risk factors and the relative importance of play elements vary greatly among LM-T plays. Reservoir quality is a critical limiting play element in many plays, especially those in the Caonero trend directly downdip from the trans-Mexican volcanic belt, as well as carbonate-rich slope plays adjacent to the Tuxpan platform. In contrast, trap and source are low-risk play elements in the LM-T area because of the abundance of large three-way and four-way closures and the widespread distribution of organic-rich Upper Jurassic Tithonian-age source rock. The potential for hydrocarbon migration in LM-T plays is a function of the distribution of deep-seated faults inferred to intersect the primary Mesozoic source. Their distribution is problematic for the Lankahuasa trend, where listric faults sole out into the Paleocene. Seal is poorly documented for LM-T plays, although the presence of overpressured zones and thick bathyal shales is favorable for seal development in middle and lower Miocene basin and slope plays.

Palaeozoic structural development along the Tornquist Zone, Kattegat area, Denmark

The interpretation of newly released commercial 2D reflection seismic data in the Kattegat area, Denmark, has provided us with a better understanding of the Palaeozoic tectonic processes along the Tornquist Fault Zone. A Base Palaeozoic time structure map, a Lower Palaeozoic TWT isopach map, a “true” Lower Palaeozoic TWT isopach map, an Upper Carboniferous/Lower Permian syn-rift TWT isopach map, a Top pre-Zechstein time structure map and a Zechstein combined TWT isopach and Palaeogeography map have been generated. The uniform Lower Palaeozoic sequence thickness in the Kattegat, both inside and outside the Tornquist Zone indicates only minor lateral movements if any, whereas the extensive Upper Silurian sequence, increasing in thickness to the north, indicates a relatively fast regional subsidence. The Base Palaeozoic time structure map and the Late Palaeozoic syn-rift isopach map show a clear Late Palaeozoic extension in the area. The syn-rift isopach map, in combination with the time-equivalent opening of the Skagerrak graben at right angles to the Tornquist Zone in the Kattegat, indicates that this extensional tectonic event had a dextral slip component. Measurements on internal extensional faults in the Tornquist Zone, give a minimum right-lateral displacement of 10.4 km. The footwall blocks were deeply eroded during the Early Permian rifting, and at Zechstein times the area became a peneplane. The Tornquist Zone was later exposed to several tectonic phases, where dextral slip played a role, indicated by the “push up” and “pull down” structures caused by restraining and releasing bends of the Børglum Fault. The dextral displacement along the Børglum Fault since the beginning of the Permian is in the order of 5–7 km based on the displacement of a Lower Palaeozoic local depocentre. Early Permian depocentres and faults, which gives a total amount of right-lateral displacement since the Early Palaeozoic in the order of 15–20 km. The continuously repeated tectonic episodes along the Tornquist Zone throughout most of the Phanerozoic, show that the zone was easily reactivated, implying deep-seated basement faults. The Tornquist Zone can be seen as a “buffer zone”, between continental blocks, whenever changes in the regional stress field are induced.