Wrench Fault Research Articles

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.

Subduction zone processes and crustal growth mechanisms at Pacific Rim convergent margins: modern and ancient analogues

AbstractContinents grow mainly through magmatism, relamination, accretionary prism development, sediment underplating, tectonic accretion of seamounts, oceanic plateaus and oceanic lithosphere, and collisions of island arcs at convergent margins. The modern Pacific–Rim subduction zone environments present a natural laboratory to examine the nature of these processes. The papers in this special issue focus on the: (1) modern and ancient accretionary margins of Japan; (2) arc–continent collision zone in the Taiwan orogenic belt; (3) accreting versus non-accreting convergent margins of the Americas; and (4) several examples of ancient convergent margins of East Asia. Subduction erosion and sediment underplating are important processes, affecting the melt evolution of arc magmas by giving them special crustal isotopic characteristics. Oblique arc–continent collisions cause strong deformation partitioning that results in orogen-parallel extension, crustal exhumation and wrench faulting in the hinterland, and thrust faulting–folding in the foreland. Trench-parallel widths of subducting slabs exert major control on slab geometries, the degree of coupling–decoupling between the lower and upper plates, and subduction velocity partitioning. An initially large width of the subducting Palaeo-Pacific Plate against East Asia caused flat subduction and resistance to slab rollback during the Triassic Period. These conditions resulted in shortening across SE China. Foundering and delamination of the flat slab during the Early Jurassic Epoch led to slab segmentation and reduced slab widths, followed by slab steepening and rollback. This pull-away tectonics induced lithospheric extension and magmatism in SE China during Late Jurassic – Cretaceous time. Melting of subducted carbonaceous sediments commonly produces networks of silicate veins in CLM that may subsequently undergo partial melting, producing ultrapotassic magmas.

UAS-Derived Surficial Deformation around the Epicenter of the 2016 Mw 5.8 Pawnee, Oklahoma, USA, Earthquake

ABSTRACT Unmanned aerial systems (UAS) provide a framework for recording perishable surficial data or information. Open fractures exhibiting regular en-echelon patterns were captured by a 12-megapixel, FL-9 mm camera attached to a Phantom IV UAS over the epicenter of the magnitude (Mw) 5.8 earthquake of September 3, 2016, 15 months later. The Digital Surface Models (DSMs) and orthoimagery offered a spatial resolution (∼1 cm) sufficient to identify small-scale plastic deformations that appear to be controlled by en-echelon joint sets developed in the underlying formation. The fissure boundaries and intersections are remarkably linear and sharp. They appeared to have been recently formed, presumably by seismic swarms believed to have been associated with wastewater injection. The DSMs revealed a series of conjugate patterns suggestive of regional systematic joints with apparent subsidence of infilling up to 50 cm. The earthquakes emanated from the Precambrian metamorphic basement, with epicentral clusters at ∼5- and 8-km depths. Low energy release from depths >1.5 km appears to be locally attenuated by an unconsolidated “soil cap,” which likely formed an impedance contrast. The maximum deformation direction from the cumulative energy of earthquakes correlates with a wrench fault tectonics model that could conceivably produce the observed en-echelon joint sets observed in the orthoimagery and DSMs. These features were observed within 275 m of the reported Mw 5.8 epicenter. The remarkably linear repeating pattern of deformation appears to express fissures that preserve the wrench fault fractures generated by the Mw 5.8 earthquake emanating from discontinuity suites within marine sandstone, shale, and limestone of Pennsylvanian to Permian age.

The deformation and mechanisms of the Zhangbaling tectonic belt during Indosinian to early Yanshanian: Implications for the relationship with the Tan-Lu Fault Zone

The Zhangbaling tectonic belt is located in the middle segment of Dabie-Sulu Orogenic Belt and in the eastern part of the main segment of the Tan-Lu Fault Zone (TLFZ). Based on detailed field work and comprehensive analysis, this study discussed the tectonic evolution mechanics of the Zhangbaling tectonic belt and the Tan-Lu Fault Zone as well as the relationship between them during Indosinian to early Yanshanian period. Three stages of tectonic deformation have been determined in the period from Indosinian to early Yanshanian in Zhangbaling area, i.e., a series of WNW and nearly EW trending tight congruous nearly recumbent folds formed in the early stage; a flatly ductile shearing zone formed mainly between Beijiangjun lithofm. and Xileng lithofm. in the middle stage and the demonstrate NNE trending wide flat folds and strong thrusting or napping from NW to SE formed in the last stage. The superimposition of these three deformation stages formed the basic tectonic framework of this area. The folding and thrusting (sliding in the front margin) was developed in the mid-upper crust (include sedimentary cover) during the period of subduction and collision processes between South China Block and North China Block, shows a progress deformation of the three stages during the period of Indosinian and early Yanshannian due to the conversion of the Tethyan to the Circle Pacific Ocean tectonic regimes. The Tan-Lu Fault Zone can be divided into two big development phases since Hercynian. The first phase is a fault zone sensu lato, as a boundary of a rifted cratonic margin (or basin) that shows a wide arc-shaped along the northeastern margin of the South China Block during Indosinian. The TLFZ of this period is a collision suture between South China Block and North China Block during Indosinian period, a thrust-napping fault zone belong to the Tethyan regimes sensu lato, as well as the southeast margin of the Zhangbaling tectonic belt. This big phase corresponds to the three stages deformation activities in Zhangbaling area. The second phase is a wrench fault system usually mentioned by most researchers, which belongs to the Pacific Ocean Cycle Regime sensu stricto since early Yanshanian to Himalayan periods.

Avalonian arc-to-platform transition in southeastern New England: U-Pb geochronology and stratigraphy of Ediacaran Cambridge “argillite,” Boston Basin, Massachusetts, USA

High-precision CA-TIMS 206Pb/238U zircon dates clarify the age and tectonic significance of the Cambridge Formation which is poorly exposed in the Boston Basin, eastern Massachusetts, but transected by ∼50 km of tunnels beneath the mainland and Boston Harbor. The youngest detrital zircon in a sample from the northern Braintree Weymouth Tunnel establishes a maximum depositional age of 584.09 ± 1.98 Ma, consistent with sources in sills of that age in underlying Roxbury Conglomerate. A 551.22 ± 0.20 Ma ash bed from the Mystic Quarry in Somerville, Massachusetts lies near the top of an approximately 5350 m thick, dominantly argillaceous section measured in subsurface cross sections. These were constructed from attitudes reported in pre-1960 tunnels and from mapping logs obtained from tunnels completed decades later during the federally ordered clean-up of Boston Harbor. A 488.58 ± 0.16 Ma aplite sill intruding argillite ∼800 m above the ash bed sets the minimum depositional age on the north side of the Basin. A tighter constraint comes from trilobite-bearing strata of the lower Cambrian Weymouth Formation located south of Boston that overlies the Cambridge Formation without obvious break in the Braintree Weymouth Tunnel. If Cambridge deposition was continuous after 584 Ma, the depositional interval would exceed 40 million years. An estimated ∼20 Ma depositional hiatus seems more likely because the base of the Cambridge Formation appears to define a regional unconformity above which argillite rests variously on magmatic arc-related units of both the 595 to 584 Ma Roxbury Conglomerate and the 597 to 593 Ma Lynn-Mattapan Volcanic Complex. Cambridge deposition set in once arc activity in more northerly “West” Avalonian terranes extending through Atlantic Canada to the Avalon Peninsula, Newfoundland had given way to wrench faulting and bimodal magmatism. This regime is manifested structurally in Boston-area tunnels by later-reactivated normal faults in which hanging wall blocks of Cambridge argillite were originally downthrown relative to older footwall units. Pyroclastic volcanic textures and thin basaltic flows with soft sediment contacts are present in argillite of the City Tunnel Extension, and whole rock major element and REE compositions reveal mixed terrigenous and volcanic components deposited under marine conditions throughout the Basin. Proposed sources for the latter are voluminous eruptions recorded in the 560 to 550 Ma Coldbrook Group in New Brunswick9s Caledonia terrane.

Seismic identification of geothermal prospecting in Harrat Rahat, Northern Arabian Shield

Harrat Rahat volcanic field lies along the Makkah-Madinah-Nafud active volcanic line. It has extensive linear weak zones of wrench faults that could provide ideal conduits for upwelling magma and hydrothermal fluids as well. Passive seismic data recorded by seismic stations installed within and around Harrat Rahat has been processed for the detection of microseismic events. Moreover, ambient noise was also gathered and analyzed to construct a subsurface velocity model. This model indicates low velocity zone in Harrat Rahat, and two areas with coincident basement faults and possibly with enhanced subsurface temperatures were identified. It is concluded that Harrat Rahat has high geothermal potential and promising for geothermal renewable power.

Acadian detachment and wrench faults in central Pennsylvania: Implications for the Marcellus Shale reservoir integrity and gas productivity in the hinge of the Pennsylvania salient

High-quality 3D seismic data in Clearfield County, central Pennsylvania, reveal subsurface structural details of regional flat-top, box-shaped folds, convergent reverse faults, and cross-regional lineaments in the hinge of the Pennsylvanian salient. Cross-stratal variations in structural relief, bed curvature, and seismic facies indicate that the deformational intensity increases from below the Salina (Upper Silurian) to the Onondaga (Middle Devonian) and then decreases from the Onondaga to the Elk (Upper Devonian). The pre-Onondaga isochron thickness sees an increasing trend but the post-Onondaga isochron thickness sees a decreasing trend on the anticlinal axes. The seismically imaged subsurface structures are consistent with outcrop and topographic observations, wireline and formation microimager (FMI) logs, and gravity and magnetic intensity measurements. The Marcellus Shale (Middle Devonian) gas exploration and production data indicate that the operational activity and gas productivity drop significantly in Clearfield County and other counties in the hinge of the Pennsylvanian salient. We interpret that the regional folds and faults and cross-regional lineaments are detachment and wrench faults that were most likely caused by gravitational sliding above the Salina (salt) during the Acadian (Middle Devonian-Early Mississippian). We infer that the co-occurrence of the regional and the cross-regional faults, particularly the cross-regional wrench faults, might have had a significant impact on the Marcellus Shale reservoir integrity and gas productivity in the hinge of the Pennsylvania salient. These observations and interpretations demonstrate the dynamic interplay among tectonic deformation, syntectonic deposition, and shale gas retention, thus entailing significant geologic, economic, and environmental implications in the Appalachian Basin.

Mineralogy, geochemistry and ore genesis of Kanawa uranium mineralization, Hawal Massif, eastern Nigeria terrane: Implications for uranium prospecting in Nigeria and Cameroon

The Kanawa area, Eastern Nigeria Terrane (ENT), located proximal to Pan-African shear zone, has U prospects with an average U concentration of ~0.1 wt%. Samples taken from the fault breccia, mylonite, cataclasite and ore zone show increasing U contents of 2.2–6.7 ppm, 4–7 ppm, 36–253 ppm, and 165–>1000 ppm, respectively. U-Pb dating of magmatic zircons from the granite hosting the U prospect yield 206Pb/238U concordia age of 603 ± 5.9 Ma suggesting Pan-African (Ediacaran) age for the host granite. In contrast, zircon grains from the U-ore zone yield 206Pb/238U concordia age of 228 ± 2 Ma, considered here as the estimated age of U mineralization, an interpretation that need to be supported by additional data. The Pan-African granite hosting Kanawa U mineralization has very low U content (U = 1.0–6.7 ppm) and therefore could not have been the main source of the U mineralization. Considering that the Kanawa U ore zone shows broadly similar geochemical signature and yield roughly similar age with its spatially associated Mesozoic rocks in area, we suggest that the U mineralization was probably sourced from the Mesozoic volcanics rocks. Uranium, Zr, V may have been leached out from the Mesozoic volcanic by hydrothermal fluid circulating along the channel ways provided by Pan-African wrench fault. Taken together, our combined major and trace element data in conjunction with previously reported data of U mineralization from western Cameroon allow us re-evaluate the geochemical signatures of Pan-African granite hosting U mineralization in these regions and reassess their U potential in relation to some well-known U deposits elsewhere in the world. It is noteworthy that the Kanawa U mineralization shows broadly similar geochemical features with the volcanic-related Streltsovskoye-Antei U deposit, Transbaikalia, Russia. The highly evolved Ekomédion granites in Cameroon have high U and F content and exhibit geochemical features typical of U-fertile granite suggesting that U mineralization Ekomédion area was probably sourced from the granites. In contrast, Pan-African granites from Kitongo have low U and F content and may not have been the primary source of the Kitongo U mineralization. As suggested for Kanawa U mineralization, the Kitongo U mineralization was probably sourced from the Mesozoic rocks in the area. These chains of Mesozoic volcanic and plutonic suites, largely emplaced within Pan-African mega- shear zones, extend from Nigeria into Cameroon and Niger, and could be linked to other mega shear zones in Egypt and Saudi Arabia where similar U mineralization have been reported. This study, therefore, allows for an initial correlation of U occurrences and provides a framework for further regional investigation.

Structural styles, hydrocarbon prospects, and potential of Miano and Kadanwari fields, Central Indus Basin, Pakistan

The main purpose of this paper is to evaluate the structural styles of Miano and Kadanwari Fields, located in the Central Indus Basin, Sindh province, Pakistan. Discovered in 1989 and 1993, Kadanwari and Miano Fields are located on the Pano Aqil graben and Kadanwari High, in between two extensive NW-SE-oriented regional highs, i.e., Jacobabad-Khairpur and Mari-Kandhkot High. The Central Indus Basin is an extensional basin exhibiting normal faulting. Fourteen seismic lines were interpreted to understand the presence, trend, and development of the fault system in the Central Indus Basin along with the assessment of the Petroleum system based on the analysis of seismic reflection data and well logs across the Cretaceous clastic reservoirs. The tectonics of Miano and Kadanwari Fields has been interpreted with the presence of normal faults, strike-slip faults, and inverted structures leading to ambiguities about the structural framework of the area. However, with this detailed study, an extensional fault system has been interpreted in the Cretaceous and lower Tertiary sections over a detachment in the incompetent Sembar Formation. In Miano Field, the faults are dominantly recognized to have NNW-SSE trend due to NW-SE-oriented extension related to northward drift of Indian Plate from Madagascar. Resultantly tilted fault blocks of half grabens geometry have developed in the area depicting bookshelf geometry of an extensional system Wrench fault system is found to be absent with exception of a probable strike-slip fault in the Kadanwari Field. The fields are interpreted to have significant recoverable reserves of 1662 (bcf) equivalents to 280 (mmboe) in tilted fault blocks having an average displacement of about 50 m.

Cryptic regional magmatism in the southern Saharan Metacraton at 580 Ma

The Saharan Metacraton is largely covered by the Sahel and Sahara with only sparse bedrock exposure making it one of the most poorly studied cratons in the World. Consequently, detrital zircon geochronology is invaluable to discern the lithotectonic development of the Saharan Metacraton in the absence of outcrop. Detrital zircons from the northern Chari River, the largest river system of North-Central Africa, have ages between ~700 Ma and ~500 Ma with a small Cambrian to Ordovician (486 ± 11 Ma and 422 ± 11) population, a few Devonian to Middle Jurassic zircons (394 ± 9 Ma–159 ± 4) and a single Mesoproterozoic (959 ± 19 Ma) zircon. The absence of ancient detrital zircons suggests that the crust in the vicinity of Lake Chad is primarily juvenile. A significant (~17%) proportion of zircons yielded ages of ~580 Ma that are broadly coeval with nappe and wrench faulting, and granulite exhumation in the Central African and Trans-Saharan orogenic belts. Moreover, we identified a gabbro from the Guéra Massif of south-central Chad that yielded an in situ zircon weighted-mean 238U/206Pb age of 580 ± 6 Ma. The age of the gabbro is similar to the Kekem gabbro-norite complex (576 ± 4 Ma) in west Cameroon, inherited zircons from silicic rocks near Lake Fitri and Lake Chad, and the detrital zircons from the Chari River. Our results unequivocally demonstrate that there was magmatism at ~580 Ma and that it was contemporaneous with deformation along the Tcholliré-Banyo and Central Cameroon shear zones indicating there was a major regional tectonomagmatic episode at that time. We suggest the mafic magmatism was related to post-orogenic mantle upwelling that may have been responsible for or contributed to lithospheric delamination of the southern Saharan Metacraton.

Carboniferous\u2013Permian magmatism and Mo\u2013Cu (W) mineralization in the contact zone between the Ma\u0142opolska and Upper Silesia Blocks (south Poland): an echo of the Baltica\u2013Gondwana collision

The Kraków–Lubliniec tectonic zone (KLFZ) in southern Poland, which divides the Małopolska Block (MB) from the Upper Silesia Block (USB), is a portion of the SW margin of the Trans-European Suture Zone. Zircon U–Pb dating of a variety of igneous rocks (granodiorites, dacites, lamprophyre and diabase) from the subsurface Kraków–Lubliniec igneous belt along the KLFZ shows that magmatism spanned within a narrow time period (ca. 10 Ma) between 303.8 ± 2.2 and 292.7 ± 4.9 Ma. The earlier magmatism (303.8 ± 2.2–294.7 ± 2.3 Ma) was felsic calc-alkaline, and the contemporaneous or/and slightly later alkaline volcanism (294.4 ± 4.9–292.7 ± 4.9 Ma) was of mafic–intermediate composition. The felsic rocks (granitoids and dacitoids) are weakly peraluminous, medium to high K, moderate Mg# (0.39–0.46), weakly evolved and I-type rocks. Due to the intensive development of hydrothermal alteration, these rocks are commonly strongly altered and locally mineralized by porphyry and other types of Mo–Cu (W) ores that are closely related to the felsic magmatism in space and time. The zircon U–Pb dating yielded ages which are similar to the previously measured Re–Os ages of molybdenites from the KLFZ. Felsic magmatism at the Myszków Mo–Cu–W deposit yielded ages in the range 301.0 ± 2.1–295.9 ± 2.9 Ma. The youngest rocks dated are from the Mysłów area in the USB—volcanic alkaline rocks (lamprophyre and diabase) of shoshonitic character, with low Mg# (0.49 and 0.69, respectively) and Ni contents (< 62 ppm), indicative of a relatively juvenile magma composition. Inherited zircon cores, remnant detrital zircon from a sediment component in the source rocks, were dated to be ranging from ca. 2775 to 575 Ma. Inheritance of ca. 600 Ma (Cadomian basement) and ca. 1.40 Ga (Mesoproterozoic) is common in the rocks from both blocks, but those from the MB contain additional inheritance with dates of 2.78–2.67 and 2.05–1.92 Ga, both ages characteristic of zircon from the Svecofennian of northern Europe (Baltica). The inherited zircon from the youngest alkaline rocks provided evidence for Mesoproterozoic (ca. 1.55–1.44 and 1.09 Ga) and Palaeoproterozoic (1.96 Ga) thermal events in the USB, and its possible affinity to Avalonian cratonic crust as a source for its igneous protolith. U–Pb isotopic studies of zircons from KL igneous belt indicate its inherited signatures from the crustal sources and magma emplacements during the KLFZ wrenching which allowed channels and room for magma emplacement along the MB and USB in upper Carboniferous–lower Permian on SW margin of the East-European Craton. Mo–Cu (W) ore mineralization, associated with the ~ 300 Ma felsic magmatism, represents rather the product of decompression melting induced in the areas of decreased pressure, undergone in the regional wrench fault zones than the classic Mo–Cu porphyry-style mineralization.

A Model of Hydrothermal Dolomite Reservoir Facies in Precambrian Dolomite, Central Sichuan Basin, SW China and its Geochemical Characteristics

AbstractHydrothermal mineral assemblages and related hydrothermally enhanced fracturing are common in the Precambrian Dengying Formation of Central Sichuan Basin. Petrographic and geochemical analyses of core samples show that the hydrothermal dolomite reservoirs of Dengying Formation consist of four main types of pores in the reservoir facies. These include: 1) hydrothermal dissolution vug (or pore), 2) intercrystalline pore, 3) residual inter‐breccia vug (or pore), and 4) enlarged dissolved‐fracture. There are three different fabrics dolomite in hydrothermal dolomite reservoirs, namely, saddle dolomite, fine‐medium dolomite and micritic dolomite. Micritic dolomite is the original lithology of host rock. Saddle dolomite with curved or irregular crystal faces was directly crystallized from hydrothermal fluids (average temperature 192°C). Fine‐medium dolomites are the products of recrystallization of micritic dolomite, resulting in abnormal geochemical characteristics, such as slight depletion of δ18O, significant enrichment of Mn‐Fe and 87Sr/86Sr, and positive Eu anomaly. A model for the distribution of various hydrothermal dolomite reservoir facies is proposed here, which incorporates three fundamental geological controls: 1) extensional tectonics and tectono‐hydrothermal events (i.e., the Xingkai Taphrogenesis of Late Sinian‐Early Cambrian, and Emei Taphrogenesis of Late Permian), 2) hydrothermal fluid storage in clastic rocks with large thickness (e.g., Nanhua System of Chengjiang Formation and part of Doushantuo Formation), and 3) confining bed for hydrothermal fluids (such as, the shale in Qiongzhusi Formation). The supply of hydrothermal fluid is critical. Large basement‐rooted faults and associated grid‐like fracture system may function as the channels for upward migration of hydrothermal fluid flow. The intersection of the above‐mentioned faults (including the conversion fault), especially transtensional sags above negative flower structures on wrench faults can serve as a key target for future hydrocarbon exploration.

Fracture patterns associated with the evolution of the Teton anticline, Sawtooth Range, Montana, USA

Abstract The Teton anticline and adjacent structures, in the Sawtooth Range, Montana, USA, are fractured in such a way that may be taken as a model for fractures propagating during buckle folding. However, advances in understanding both the process of folding in forelands and the evolution of fracture patterns found within these folds suggest that it is time to reinterpret the nexus between fracturing and folding within these classic structures. With the benefit of seismic lines, the Teton anticline is best described as a fault-propagation fold. Joint propagation initiated with the formation of two major sets whose orientation is controlled by pre-folding, regional stresses. Two more joint sets propagated in local stress fields, developed in response to anticline growth. Some early joints were reactivated as wrench faults during amplification and tightening of the anticlines. The fracture sets identified are consistent with: (a) propagation in a regional stress field, which may be related to stretching in the Sawtooth Range orocline; and (b) tangential longitudinal strain of the backlimb and forcing or trishear of the forelimb during anticline development. Thus, we suggest that fracture networks across folded structures should be interpreted and characterized in the light of the geological history of the entire system.

The role of structural inheritance in continental break-up and exhumation of Alpine Tethyan mantle (Canavese Zone, Western Alps)

The Canavese Zone (CZ) in the Western Alps represents the remnant of the distal passive margin of the Adria microplate, which was stretched and thinned during the Jurassic opening of the Alpine Tethys. Through detailed geological mapping, stratigraphic and structural analyses, we document that the continental break-up of Pangea and tectonic dismemberment of the Adria distal margin, up to mantle rocks exhumation and oceanization, did not simply result from the syn-rift Jurassic extension but was strongly favored by older structural inheritances (the Proto-Canavese Shear Zone), which controlled earlier lithospheric weakness. Our findings allowed to redefine in detail (i) the tectono-stratigraphic setting of the Variscan metamorphic basement and the Late Carboniferous to Early Cretaceous CZ succession, (ii) the role played by inherited Late Carboniferous to Early Triassic structures and (iii) the significance of the CZ in the geodynamic evolution of the Alpine Tethys. The large amount of extensional displacement and crustal thinning occurred during different pulses of Late Carboniferous–Early Triassic strike-slip tectonics is well-consistent with the role played by long-lived regional-scale wrench faults (e.g., the East-Variscan Shear Zone), suggesting a re-discussion of models of mantle exhumation driven by low-angle detachment faults as unique efficient mechanism in stretching and thinning continental crust.

A Review of the Geology and the Petroleum Potential of the Cretaceous Tano Basin of Ghana

This is a review of the geology and the petroleum potential of the Cretaceous Tano Basin of Ghana, one of the coastal sedimentary basins in Ghana. It is located on the West African Transform Margin. It initially evolved as a pull-apart basin and later became modified by wrench faulting in the Cretaceous period. It has been known to have potentials for hydrocarbons, as indicated by oils seeps observed in the late 19th century. The presence of active source rocks deposited in the Albian to Cenomanian as well as the Turonian charges the Upper Cretaceous reservoirs sealed by widespread marine shales, as well as faulted traps and pinch-outs, has spurred exploration efforts. Thus, as expected, commercial discoveries of oil and gas have been made in the Tano Basin which evidently has become a ‘hot cake’ in deepwater exploration, even though the ultradeep water could show even more exciting hydrocarbon plays.

Acadian hinterland-vergent detachment structures in the southwestern Appalachian Plateau: Implications for the Marcellus Shale gas exploration and production

Three-dimensional seismic data in southwestern Pennsylvania in the Appalachian Plateau demonstrate that the structural style in the Devonian section is dominated by east-vergent folds and reverse faults, which contrasts with that in the Valley and Ridge Province where west-vergent folds and thrusts dominate. Vertical (cross-stratal) variations in fold curvature and fault throw indicate that the intensity of shortening increases from the Salina (Upper Silurian) to the Onondaga (Middle Devonian) and then decreases from the Onondaga to the Elk (Upper Devonian). Lateral (along-stratal) variations in fold curvature and fault throw indicate that the folds and faults tend to propagate in the cross-strike and along-strike directions. Isochron thickness below the Onondaga increases on the anticlinal, up-thrown side of the faults, whereas isochron thickness above the Onondaga increases to the synclinal, down-thrown side of the faults. In concert with seismic structure and isochron thickness, seismic facies see vertical and lateral variations that are spatially and temporally related to folds and faults. Four years of gas production data from the Middle Devonian Marcellus Shale show that the gas productivity drops near the regional reverse faults, whereas regional drilling patterns from a broader perspective of the Plateau reveal operational gaps near major cross-regional wrench faults. These observations are indicative of the dynamic interplay among hinterland-vergent detachment deformation, syntectonic sedimentation, and shale gas preservation during the Acadian (Middle Devonian–Early Mississippian).

UNALTERED NACRE FROM THE PENNSYLVANIAN BUCKHORN ASPHALT, AND IMPLICATIONS FOR THE ARMS RACE BETWEEN MOLLUSKS AND THEIR PREDATORS

Nanoscale details of original aragonite crystals and organic inclusions are preserved in shells from the Pennsylvanian Buckhorn Asphalt of Oklahoma, USA. Exceptional preservation occurred because, either during or shortly after deposition, oil migrated along wrench faults generated during the simultaneous Ouachita Orogeny. The early sealing by oil (later converted into asphalt) prevented diagenetic alteration of shell material. Field Emission Scanning Electron Microscopy (FE-SEM), Electron Backscatter Detection (EBSD), and Atomic Force Microscopy (AFM) reveal a striking high fidelity of preservation, including the oldest known unaltered nacre tablets in gastropods, bivalves, and cephalopods. These nacre tablets are indistinguishable from modern representatives in nanoscale morphology and crystallographic orientations. Fossils from the Buckhorn Asphalt show that by the Pennsylvanian Period, nacre and crossed lamellar were the dominant microstructures in the inner shell layer of the Mollusca. Calcitic microstructures and loosely organized horizontal bundles of aragonite fibers were common among Cambrian mollusks and problematic lophotrochozoans (e.g., hyoliths). Through the early to middle Paleozoic the dominance changed to more fracture-resistant textures nacre and crossed lamellar. This transition reflects the importance of these two types of shell microstructure in deterring predation, and it is clear that the ability to produce crossed lamellar and nacreous microstructures contributed to molluscan success during the Mesozoic and Cenozoic eras.

The active Kalabsha Fault Zone in Southern Egypt: detecting faulting activity using field-structural data and EMR-technique, and implications for seismic hazard assessment

Since November 14, 1981 earthquake (ML 5.6), about 60 km southwest of Aswan High Dam, the seismic hazard raised and the Aswan Local Seismic Network (ALSN) has recorded and precisely monitored the seismic activity in the vicinity of the High Dam. The major source of seismic activity in this region is the active Kalabsha Fault Zone (KFZ). The focal mechanism solutions indicate that two nodal planes strike E to ENE, with subordinate right-lateral strike-slip component and N to NNW, with left-lateral movement. The directions of tectonic extension (T) and compression (P) are NNE-SSW and NNW-SSE, respectively. Structural investigations and application of the Electromagnetic Radiation (EMR) technique reveal ongoing activity on the KFZ. Kinematic evolution of the KFZ implies faulting events with a strong movement intervened with periods of severe crushing, grinding, and even pulverization. Such tectonic processes have resulted in fault-breccia and fault-gouge. Results obtained from the present study indicate that the KFZ is not a single transcurrent wrench fault with dextral sense of movement but, instead, it represents a major dextral transtensional shear or fault zone deforming southern Egypt and plays a significant role in the structural shaping of the area to the west of Nasser Lake. Furthermore, the activity on the KFZ is most probably controlling the seismic cycle in the area. Topographic expression of KFZ is evidently realized at Sinn El-Kaddab scarp, as well as at Gebel Marawa. Frequent surface rupturing and newly recorded strong seismic activity advocate faulting reactivation supported by the EMR data, which suggest an active fault system oriented ENE-WSW and NNW-SSE affecting the KFZ, with a maximum horizontal stress (σ1) perturbing between ENE and NNW directions.

Structure and Tectonic Reconstruction of Bayah Complex Area, Banten

The research aimed to reconstruct the geological structures and tectonics of the Bayah complex area. The structures found that grouped into regional structural patterns used to determine the ages and the events that responsible to its formation. The methods used in this research include field and studio method. Field method carried out to map the outcrops and record geological structures data using geological compass, GPS, tape measurement, and geological hammer, while studio method performed to process and analyze data using software such as Win Tensor, Dips, MapInfo Professional 10.5 and CorelDraw X4. The geological structure of the Bayah has varying patterns and ages. The fracture patterns show N-S and E-W direction which is belong to Sundanese and Java Pattern formed in range of the Early Eocene to Pliocene. While the faults that have direction of SW-NE and E-W are classified into Meratus and Java Pattern. However, metamorphic rock foliations show NW-SE and N-S direction that belonging to the Pre-Tertiary Sumatra Pattern. The three faults of this research are estimated to be formed by the effect of orogenesis that occurring in different events and ages. JSA-014 fault is predicted to form due to orogeny I or orogeny II in the Early Oligocene - Middle Miocene, this fault classified as the 2nd order right lateral wrench fault. JSA-034 fault is formed by orogeny I in Early Oligocene - Middle Miocene, this fault is also classified as the 2nd order right lateral wrench fault. While JSA-080 fault has relatively young age that formed due to orogeny III in the Middle Miocene - Pliocene and belonging to the 3rd order left lateral wrench fault.

Three Types of Flower Structures in a Divergent‐Wrench Fault Zone

AbstractFlower structures are typical features of wrench fault zones. In conventional studies, two distinct kinds of flower structures have been identified based on differences in their internal structural architecture: (1) negative flower structures characterized by synforms and normal separations and (2) positive flower structures characterized by antiforms and reverse separations. In addition to negative and positive flower structures, in this study, a third kind of flower structure was identified in a divergent‐wrench fault zone, a hybrid characterized by both antiforms and normal separations. Negative flower structures widely occur in divergent‐wrench fault zones, and their presence indicates the combined effects of extensional and strike‐slip motion. In contrast, positive and hybrid flower structures occur only in fault restraining bends and step overs. A hybrid flower structure can be considered as product of a kind of structural deformation typical of divergent‐wrench zones; it is the result of the combined effects of extensional, compressional, and strike‐slip strains under a locally appropriate compressional environment. The strain situation in it represents the transition stage that in between positive and negative flower structures. Kinematic and dynamic characteristics of the hybrid flower structures indicate the salient features of structural deformation in restraining bends and step overs along divergent‐wrench faults, including the coexistence of three kinds of strains (i.e., compression, extension, and strike‐slip) and synchronous presence of compressional (i.e., typical fault‐bend fold) and extensional (normal faults) deformation in the same place. Hybrid flower structures are also favorable for the accumulation of hydrocarbons because of their special structural configuration in divergent‐wrench fault zones.