Major Thrust Faults Research Articles

A Reappraisal of Nappe Structures and Strain Patterns in the Core of the Variscan Orogen (French Massif Central)

AbstractMajor influences on the architecture of orogens include the overall thermal conditions of orogeny (hot vs. cold) and the angle of collision (orthogonal vs. oblique). In the French Massif Central of the Variscan orogen, a cold‐orogen style crustal nappe architecture was interpreted in the Haut‐Allier, located in the core of the orogen. Based on this model, the Variscan orogenic crust is described as the superposition of three main allochthonous tectonic units juxtaposed along major thrust faults. However, based on a detailed structural analysis, we have found instead that the region is dominated by a network of anastomosing conjugate and coeval dextral and sinistral shear zones striking WNW‐ESE and ENE‐WSW, respectively. The dextral WNW‐trending shear zones are predominant, whereas the sinistral NE shear zones are mainly located in the eastern part of the massif. Between these sub‐vertical shear zones, a sub‐horizontal foliation is observed. Our results indicate that all planar fabrics were partially synchronous during suprasolidus low‐pressure‐high‐temperature conditions. Strain partitioning occurred from high‐temperature suprasolidus conditions to subsolidus retrogression and may represent orogen‐parallel flow, suggesting hot‐orogen style. These results call into question the validity of the crustal nappe model in the Haut‐Allier. Based on new structural data and related observations, we propose a new model in which metamorphic gaps between tectonic units are explained by the juxtaposition of different structural domains by displacement along strike‐slip shear zones.

Provenance and Diagenetic Features of Sandstones in the Surma -Tipam Transitional Sequence exposed in the Schuppen Belt, Naga Hills, NE India

The Schuppen Belt, a part of the Indo-Burma Ranges is basically comprised of molasses of Tertiary age. This tectono–stratigraphic belt is restricted by two major thrust faults, namely Disang and Naga. In the southern part of the Naga Hills a significant part is occupied by Surma–Tipam Transitional Sequences (STTS). This study deals with the petrography, provenance, and tectonic setting of the STTS sandstones. The sandstones are classified as arkose and arkosic wacke types. The major contribution of detritus has been observed from the recycled orogen, dissected arc, transitional continental and basement uplift. The geochemistry data reveals that the sandstones were derived from a collisional setting of an active continental margin. The low degree of chemical maturity indicates that the sandstones were deposited in an arid climatic condition. The diagenetic signatures observed in these sandstones such as, point, long and concavo-convex grain boundary, albitization, crushing and squashing of quartz grains, warping of mica around detrital grains, and bending of mica suggest early to a late stage deep burial diagenesis.

The Sendai river terraces monitored the co-seismic mega-thrusting

We conducted a detailed geological survey of the Sendai region, covering an area of 100 × 50 km. Our survey focused on accurately mapping river terraces, identifying the source volcanoes responsible for intercalated tephras, and locating the Nagamachi-Rifu fault and associated faults. The river terraces were observed and categorized based on their elevation relative to the present river channels. These terraces are predominantly found on the hanging wall of major reverse faults. Each terrace comprises fluvial gravels at the lower levels and eolian loam intercalated with local and regional tephras at higher levels, with the contact age corresponding to the time of emergence. To determine the ages of the terrace gravels, we employed a combination of zircon U–Pb dating, sedimentation rate calculations, and extrapolation techniques. This allowed us to establish the abandonment or emergent dates of the terraces. The formation of these terraces coincided with periods of fault activity, including hanging wall uplift, footwall subsidence, and fault vertical displacement, effectively monitoring the co-seismicity of the Nagamachi-Rifu fault. While we cannot predict the exact timing of future events, it is crucial to remain vigilant regarding the potential occurrence of a significant earthquake triggered by these fault activities.

New Probabilistic Seismic Hazard Model for Nepal Himalayas by Integrating Distributed Seismicity and Major Thrust Faults

Nepal is one of the most seismically active regions in the world, as highlighted by the recent devastating 2015, Mw~7.8 Gorkha earthquake, and a robust assessment of seismic hazard is paramount for the design of earthquake-resistant structures. In this study, we present a new probabilistic seismic hazard assessment (PSHA) for Nepal. We considered data and findings from recent scientific publications, which allowed us to develop a unified magnitude homogenized seismicity catalog and propose alternative seismic source characterization (SSC) models including up-to-date parameters of major thrust faults like main frontal thrust (MFT) and main boundary thrust (MBT), while also considering existing SSC models and various seismic hazard modeling strategies within a logic tree framework. The sensitivity analyses show the seismic hazard levels are generally higher for SSC models integrating the major thrust faults, followed by homogenous volume sources and smoothed seismicity approach. The seismic hazard maps covering the entirety of Nepal are presented as well as the uniform hazard spectra (UHS) for five selected locations (Kathmandu, Pokhara, Biratnagar, Nepalganj, and Dipayal) at return periods of 475- and 2475-years considering Vs,30 = 760 m/s. The results obtained are generally consistent with most recent studies. However, a notable variability in seismic hazard levels and several discrepancies with respect to the Nepal Building Building Code NBC105: 2020 and global hazard model, GEM are noted, and possible causes are discussed.

Application of bivariate statistical techniques for landslide susceptibility mapping: A case study in Kaghan Valley, NW Pakistan

Landslides are dangerous events that threaten both human life and property. This research presents a case study of Kaghan valley catchment, which is an area of frequent landslide activity. We aim to present a comparison between the bivariate Landslide Numerical Risk Factor (LNRF), Statistical Index (SI) and Information Value (InfV) statistical models to evaluate landslide susceptibility. A total of 1556 landslides were identified using earlier reports, field surveys, and GOOGLE Earth imagery. The abundance of landslides is primarily controlled by acute deformation caused by a major thrust fault system and proximity to Hazara Kashmir Syntaxis (HKS). A landslide inventory was randomly partitioned into two datasets. 70% (1106) of landslides were used as a training phase of the models, whereas 30% (450) as validation of the three models. A spatial database of 11 conditioning factors was produced consisting of slope, aspect, elevation, lithology, land use, Topographic Wetness Index (TWI), rainfall, Stream Power Index (SPI), distance to faults, rivers and streams. All the landslide susceptibility assessment parameters were obtained from different sources and different landslide susceptibility maps were prepared on the GIS software. Performance of the three models was validated through the Receiver operator Characteristics (ROC) through success and prediction rate curves. Results show that the area under the ROC curve (AUC) for InfV, LNRF and SI models are 70.95, 83.99 and 67.56 for success rate curves and 70.75, 83.99 and 67.85 for prediction rate curves, respectively. LNRF having the highest AUC value proved to be superior for generating regional scale landslide susceptibility maps.

The Geometry and Kinematics of the Latest Paleozoic Allatoona Fault, One of the Youngest Thrusts in the Southernmost Appalachian Hinterland, Alabama and Georgia, U.S.A.

The Allatoona thrust fault in the southernmost hinterland of the Appalachian Blue Ridge-Piedmont megathrust sheet is among the latest structures in the kinematic sequence of events along the west flank of the orogen. It is an out-of-sequence, craton-directed thrust fault that cuts metamorphic isograds and earlier thrusts, and it has a nearly linear trace of ≥280 km, making it one of the major thrust faults in the orogen. On the northwest, the fault cuts Pennsylvanian or younger(?) regional cross antiforms that cause significant orogenic curvature of older underlying thrust sheets and is likely Permian in age. To the southeast, however, units within the fault hanging wall maintain a nearly constant width resulting in a significant change in the regional structural architecture of the orogen. In the central segment of the fault, where it marks the western/eastern Blue Ridge domain boundary, a ~20 km-long eyelid window (Mulberry Rock window) framed by three amphibolite facies thrust sheets overlying the greenschist facies Talladega belt allochthon, allows a 3-D view into the structural architecture, kinematics, and trajectories of the regional thrusts. Two earlier thrusts within the window (Mulberry Rock and Burnt Hickory Ridge thrusts, with a combined minimum horizontal net slip component of 27 km) are cut by the Allatoona fault, which is a ~15 m-wide high strain zone with top-to-the-northwest displacement, and a >17.2 km horizontal net slip vector. Structural branch points between the Allatoona and Mulberry Rock thrusts indicate that the Mulberry Rock allochthon is a large north-trending horse beneath the Allatoona fault, centered on the Mulberry Rock window, which is likely the result of oblique ramp thrusting over the massive Mulberry Rock Gneiss. The Allatoona fault cuts down obliquely into the tectonostratigraphy progressively deeper both to the northeast and northwest, locally approaching underlying foreland thrust sheets, and cutting older regional structures. To the northeast, the Allatoona fault lies at the base of the Dahlonega gold belt, becoming an internal eastern Blue Ridge thrust at Dawsonville, Georgia. Although that sequence extends another 120 km into North Carolina, continuation of the Allatoona fault that additional distance is in debate. Regardless, the Allatoona is one of the kinematically latest and longest faults in the southern Appalachian orogen.

Integrated geophysical, petrophysical and petrographical characterization of the carbonate and clastic reservoirs of the Waihapa Field, Taranaki Basin, New Zealand

Despite the economic importance of the Waihapa Field in Taranaki Basin in New Zealand, the structural setting, petrographic and petrophysical properties of its Cenozoic reservoirs are still poorly understood. This research integrates a 3D seismic survey with core and well logs data, as well as petrographic description in order to discuss the structural setting and the reservoir characterization of the Cenozoic reservoirs along the Waihapa Field, Taranaki Basin, New Zealand. A major thrust fault was interpreted dissecting both the Kapuni (Paleocene- Eocene) and Ngatoro (Oligocene- Early Miocene) groups and another opposite thrust fault affecting the Ngatoro Group and the Waihapa anticline. These compressional structures were resulted from the regional compression which affected the Taranaki Basin during the Miocene. Wai-iti Group (Miocene) is dissected by a set of NE-SW normal faults. These normal faults remark the end of the compressional phase and the beginning of a new extensional phase along the Taranaki Basin.The petrographic data of the studied reservoirs indicate that the Late Miocene Mount Messenger Formation is composed of feldspathic wacke, micaceous feldspathic quartz arenite and mudstone microfacies, whereas the Oligocene Tikorangi Formation is composed of five microfacies (bioclastic grainstone, bioclastic packstone, sandy wackestone, highly fractured silty mudstone and sandy glauconitic packstone microfacies). Downward, the Upper Eocene Mangahewa Formation is composed of ferruginated quartz arenite, micaceous quartz arenite, and ferruginated calcareous quartz arenite microfacies. Cementation and compaction are mostly affected the Mangahewa Formation while fracturing and dissolution are primarily affected the Tikorangi and the Mount Messenger formations respectively. The studied core data was discriminated into four petrophysical static rock types (PSRTs). The PSRT1, representing the Mount Messenger reservoir, has the best reservoir quality (av. porosity = 23.3%, av. permeability = 45.0 md, and meso pores, 2.60 μm) while the PSRT4 of Tikorangi Formation has the lowest reservoir quality (av. porosity = 5.5%, av. permeability = 0.01 md, and nano pores, 0.07 μm). The PSRT2 (av. porosity = 4.17%, av. permeability = 0.26 md, and micro pores, 0.59 μm) and PSRT3 (av. porosity = 5.93%, av. permeability = 0.08 md, and micro pores, 0.22 μm) are petrophysically considered transitional rock types between the PSRT1 and the PSRT4.However, Tikorangi reservoir is already producing oil from the borehole scale fractures. This work represents the workflow applied during integrating seismic, petrographical and petrophysical data in order to characterize carbonate and clastic reservoirs for any further hydrocarbon development plans along the field.

Frontal expansion of an accretionary wedge under highly oblique plate convergence: Southern Indo-Burman Ranges, Myanmar

The formation of accretionary wedges with oversteepened slopes and uplifted axial zones has been demonstrated to be potentially associated with highly oblique plate convergence by numerical and analog studies. The direct role of this mechanism, or other factor(s) in producing the described structural and morphological features in nature, however, has yet to be confirmed. We used seismic reflection sections, detrital zircon U-Pb ages, and detrital apatite fission-track thermochronological data to examine the effects of highly oblique convergence and sediment reworking on accretionary wedge growth in the Indo-Burma Subduction Zone. A detailed subsurface structural analysis of a two-dimensional seismic survey from the outer wedge of the southern Indo-Burman Ranges, Myanmar, yielded three primary characteristics. These are (1) a narrow, steep deformation front (average width 15.6 km) and a vast, low-relief shelf terrace (average width 49 km); (2) a comparatively long-lived growth thrust fault (FT1) with a convex-up geometry at the rear of the deformation front that controlled the vertical stack of the progradational sequences in the shelf terrace; and (3) a group of NE-striking transtensional faults that cut through entire outer-wedge successions and displays as a series of negative flower-like structures. These characteristic features are roughly consistent with the results of laboratory analog modeling of highly oblique plate convergence but significantly differ from those of natural accretionary wedges that formed under highly oblique convergence conditions, such as those in the Sumatra, Hikurangi, Chile, and Cascadia. We further analyzed the sediment provenance of the southern Indo-Burman Ranges and discovered that the outer-wedge rocks are a product of sediment reworking of the hinterland wedge that began to be uplifted and exhumed in the early Miocene (22−12 Ma) due to transpressional motion between the Indian plate and West Burma Terrane. Our analyses indicate that active sedimentation behind the major growth thrust fault (FT1) provided additional basal shear stress that strengthened the coupling of the interface between the wedge base and décollement and promoted the vertical expansion of the outer wedge of the southern Indo-Burman Ranges from the Neogene to the present day. In contrast, the outer wedge of the central Indo-Burman Ranges has experienced stronger forward accretion since the late Miocene, which could be explained by a smaller degree of obliquity and weaker sediment reworking. Our findings demonstrate that both highly oblique plate convergence and sediment reworking were the primary driving forces that triggered vertical development of accretionary wedges. The results of this research have significant implications for understanding the structures and kinematic evolution of wedge systems at other convergent plate margins, in which seamount passage or subduction erosion is often interpreted as the cause of the steeply tapered wedges.

Topographic development of a compressional mountain range, the western Transverse Ranges of California, USA, resulted from localized uplift along individual structures and regional uplift from deeper shortening

Abstract The western Transverse Ranges are a tectonically active mountain belt in southern California (USA) characterized by fast rates of shortening and rock uplift. Large drainages at the western end of this mountain belt, including the Santa Ynez River and its tributaries, transect regional west–northwest-striking reverse faults and folds. We used fluvial strath terraces within the Santa Ynez River watershed as geomorphic markers for measuring Quaternary rock uplift and deformation across these structures. Mapping, surveying, and numerical dating of these strath terraces in both hanging-wall and footwall blocks of the major reverse faults allow us to separate regional uplift from localized uplift along individual structures. Luminescence dates from 18 sites within the Santa Ynez River watershed show that the three prominent terrace levels present throughout the area formed between ca. 85 ka and 95 ka, 55 ka and 75 ka, and 30 ka and 45 ka. All three fluvial terrace straths grade into marine paleo-shore platforms along the coast that formed during sea-level highstands. The fluvial straths were formed as a result of lateral erosion during warm, dry climate intervals when vertical incision was temporarily arrested. Incision of the terraces followed during intervening periods of wet climate. Mapping and valley-long profiles of the terraces document deformation by faults and folds, and we infer minimum rock-uplift rates from the amount of incision below the terrace strath surfaces. Rock-uplift rates range from 0.3 mm/yr to 4.9 mm/yr, with faster rates in the hanging-wall blocks of the major reverse faults and slower rates in the footwall blocks. Rock-uplift rates calculated from strath terraces in the footwall blocks range from 0.3 mm/yr to 1.6 mm/yr, which indicates a regional component of uplift that results from deeper deformation. Higher rates of rock uplift in the hanging-wall blocks (0.5–4.9 mm/yr) are superposed on this regional component. Incremental rock-uplift rates calculated over three time intervals and differences in terrace deformation with age suggest that deformation rates across some structures have decreased over the past 85 k.y. We conclude that topographic growth of the western Transverse Ranges results from a combination of localized uplift along individual structures that varies both spatially and temporally and a more constant regional uplift that likely results from deeper ductile deformation or slip along detachment faults that have been inferred to underlie the area.

The Role of a Detachment Fault in the Spatial Distribution of Ore-Bearing Paleofluid Flows in the Central Kolyma Region: A Nonconventional Approach to Predictive Metallogenic Modeling

—The Central Kolyma region is the main gold-bearing part of the Verkhoyansk–Kolyma fold-and-thrust belt. Analysis of the developed geodynamic models of fold and thrust belt formation mechanisms, the Verkhoyansk–Kolyma belt in particular, suggests the leading role of subhorizontal movements on the detachment zone (decollement) at the base of an orogen as the “sole,” on which nappes detached at an early stage and with which major reverse strike-slip listric faults were directly associated at the collisional stage. In our opinion, the role of a detachment fault, the most important regional structure, is obviously underestimated in predictive metallogenic models. The detachment fault zone is complicated by transverse NE-trending faults, where its thickness and the fluid permeability can occur. The paper proposes a variant that links previously discovered gold deposits and occurrences in five gold mineralization strips along the inferred paleofluid flow routes. Here, the paleofluid flow route is the horizontal projection of the most probable migration pathway of released fluids from their generation zone to the ore deposition zone, which is drawn across the largest ore accumulations.

Frequency-dependent quality factor of body waves in the Kathmandu region, Nepal

The Kathmandu region becomes situated in very close to the major thrust faults such as Main Boundary Thrust (MBT) and Main Central Thrust (MCT) has been significantly affected by a series of several major earthquakes in the past. The current study analyses the attenuation of body waves in the region using the coda normalization method based on the data of two stations (NA430 and NA060) essentially from a temporary seismic network deployed after the occurrence of the 25th April 2015 earthquake. The events considered for the study have a local magnitude of 4–5.5 ​at a depth range of 10–27 ​km. The estimated quality factor of primary and secondary waves are QP = (44 ​± ​12.896)f (0.82±0.173), QS = (62 ​± ​19.265)f (0.94±0.185) for NA430 station and QP = (35 ​± ​9.467)f (0.93±0.155), QS = (68 ​± ​22.510)f (0.91±0.198) for NA060 station. The QS/QP ratio more than one observed for the entire frequency range specifies the highly heterogeneous crust medium beneath the study region. The obtained quality factors could be used in the generation of target ground motion for engineering purposes and in the calculation of source parameters for seismic hazard assessment as risk reduction strategies in the study region.

Eocene to Quaternary Deformation of the Southern Puna Plateau: Thermochronology, Geochronology, and Structural Geology of an Andean Hinterland Basin (NW Argentina)

AbstractCordilleran orogens are complex tectonic systems, strongly influenced by lithospheric deformation and exhumation. However, in the type region of the Central Andes, the timing and mechanisms of deformation and mountain building remain poorly constrained, especially for the high‐elevation Puna Plateau of NW Argentina. We use geologic mapping, structural cross‐sections, low‐temperature thermochronology, and U‐Pb dating of ash and detrital zircons to elucidate the history and style of orogenic deformation in the Antofalla region of the Puna Plateau. Cooling ages of major reverse fault hanging walls and dated growth strata indicate that crustal shortening activated major reverse faults during the Eocene and continued out‐of‐sequence through the Early Miocene. This protracted period of shortening, which resulted in the filling of the Antofalla Basin, was followed by a transient episode of upper‐crustal E‐W extension on a major normal fault system during the Late Miocene. Pliocene to Quaternary time saw E‐W shortening return to the region. Our structural cross‐section permits only a low magnitude of shortening (∼15–25%), which stands in contrast to the 60‐km thick crust. Triassic to Cretaceous cooling ages from footwall rocks and minor structures indicate that the entire region experienced little exhumation or sedimentation during the Mesozoic, perhaps retaining a crust thickened during multiple episodes of Paleozoic orogenesis. The crust may also reflect lower‐crustal thickening due to the growth of a lithospheric drip during the Late Miocene.

Study of Subsurface Structural Image and Model Using 2D Seismic Reflection Method of Injana Field Area, Northeastern Iraq

The Injana field area is located to the north of Baquba city within Diyala. which was studied and interpreted by using 2D seismic data from the Oil Exploration Company. The study was concerned with the Jeribe Formation which is located within the Injana field area and belongs to the Tertiary Age. Two reflectors were detected based on synthetic seismograms and well logs of the Khashim Al-Ahmer-2 well. The structural maps were derived from seismic reflection interpretations to determine the location and direction of the basin. The depth maps were conducted depending upon the structural interpretation of the picked reflectors to show several structural features. Structurally, seismic sections show that the Injana area is affected by two types of reverse fault systems trending in a NW-SE direction, the first represents thrust faults affected on the lower Fars (Red Beds & Seepage) and the layers above it, the salt bed within Lower Fars Formation being as a detachment surface of this fault, the second represents two reverse faults affected on the bottom part of the Lower Fars (Transition beds) and the layers beneath. In addition, the reverse faults become dense in the north part. The structural maps reveal an elongated asymmetrical narrow anticline affected by one major thrust fault at Lower Fars Formation, and an elongated asymmetrical narrow anticline surrounded by two major reverse faults and consisting of three domes separated, Injana, Khashim Al-Ahmer and Khashab domes at the Jeribe Formation.

<i>δ</i><sup>13</sup>C, CO<sub>2</sub> ∕ <sup>3</sup>He and <sup>3</sup>He ∕ <sup>4</sup>He ratios reveal the presence of mantle gas in the CO<sub>2</sub>-rich groundwaters of the Ardennes massif (Spa, Belgium)

Abstract. Although natural CO2-rich groundwaters of eastern Belgium have been known for centuries, the exact origin of their gas is still unclear. This paper presents the results of a sampling campaign in Belgium (Spa, Stoumont, Malmedy): 30 samples of both carbogaseous and non-carbogaseous groundwaters were analyzed for major elements, CO2 content and carbon isotopic composition. Among them, 13 samples were also analyzed for 3He/4He and 4He/20Ne ratios. The combination of δ13C (between ca. −9 ‰ VPDB1 and −2 ‰ VPDB), CO2/3He ratio (between 1.9×108 and 2.9×109) and 3He/4He (between 0.92 and 2.70 Ra) shows with a high level of confidence that the CO2 in the carbogaseous groundwater of Spa and Bru has a mantle origin. It can likely be attributed to the degassing of mantle from the neighboring Eifel volcanic fields, located at a distance of 100 km eastwards. The identity and nature of the deep-rooted fractures that act as CO2 transport pathways to the surface are still to be clarified, but several major thrust faults exist in the Rhenish Massif and could connect the Eifel volcanic fields with the studied area.

Foreland Basin Geometry and Disposition of Major Thrust Faults as Proxies for Identification of Segmentation along the Himalayan Arc

Abstract Along-arc variation in the geometry of the décollement surface at a convergent margin is one of the significant parameters to assess the likely magnitude of a major/great earthquake. It is linked to the crustal/lithospheric structure and pre-existing tectonic fabric of the underthrusting plate. For the Himalayan collision belt, segmentation of the Indian lithosphere along the arc has been suggested based on seismological and GPS studies, and by analysis of topography and Bouguer gravity anomaly data. These studies, confined to the Himalaya-Tibet region, linked major segmentation boundaries to three transverse ridges in the Ganga basin. Since the formation of the Indo-Gangetic foreland basin is also controlled by the thermomechanical properties of the underthrusting Indian plate, in the present work, we study the Himalaya-foreland basin system for possible segmentation of the Indian lithosphere. We analyse the foreland basin width vis-à-vis the disposition of major thrust faults along several profiles cutting across the Himalayan arc to test a possible correlation between these two parameters. The results suggest a major segmentation boundary along the Indo-Nepal border in addition to other previously discussed segmentations coinciding with major transverse ridges in the Ganga basin. This segmentation boundary coincides with the Great Boundary fault separating the Aravalli Delhi fold belt (ADFB) from the Vindhyan basin further south. We infer a possible role of this boundary in limiting westward propagation of the rupture front of the 1505 paleo-seismic event and seismicity of the ADFB through coupling between the Himalayan collision belt and the intraplate Indian shield region.

Solid Bitumen Occurrences in the Pyrenean Basin (Southern France): A Case Study across the Pliensbachian–Toarcian Boundary

The study across the Pliensbachian–Toarcian boundary sedimentary record in the Bizanet section of the Pyrenean Basin (southern France) revealed the presence of solid bitumen. This secondary organic matter was characterized using petrographic (transmitted and reflected white lights, incident blue light, and scanning electron microscopy) and geochemical (total organic carbon, total sulfur, and insoluble residue) techniques. The spore coloration index (SCI) was also determined. With the characterization of the optical properties and reflectance of the solid bitumen, it was possible to distinguish four different families (A–D) that display a wide range of reflectance values, from 0.21% to 2.64% BRr, i.e., from glance pitch to meso-impsonite. SCI values were higher than 9–9.5 (%Req > 1.50%). The comparison between the equivalent vitrinite reflectance values of the solid bitumen and SCI showed that this index and the solid bitumen D values are concordant, indicating that solid bitumen D can be considered an indigenous bitumen. The other three families of solid bitumen (A–C) are considered as having migrated. The laterally equivalent Pont de Suert section (South Pyrenean Zone) displays no trace of solid bitumen which points to the important role of the morphotectonic context of the Bizanet section in the migration of these hydrocarbons, namely, the presence of a major thrust fault in the eastern Corbières close to the section’s location.

Geology of Bajalia Anticline of the Low Folded Zone of Iraq

Bajalia Anticline is located about 60km northeast of central Amarah city in Al-Teeb area near Iraq-Iran border. Field and laboratory works were conducted to study topography, geomorphology, stratigraphy, and structural geology of Bajalia Anticline. The Anticline has a longitudinal shape with about 29km in length and 5-7km in width. Injana, Mukdadiya, and Bai Hassan formations are the three formations that were recognized in the study area. The geometrical structural analysis depicts that the Anticline is non-cylindrical, asymmetrical, close, sub-horizontal, steeply inclined, and linear fold. Most of the fractures in the Anticline are joints. These joints were classified based on the tectonics axes, which are a, b, and c, into ac, bc, and hol. A major reverse fault is located at the margin of the southwestern limb parallel to the fold axis with about 25km length. This fault is responsible on the vergence of the Anticline and overturned part of the southwestern limb. The Anticline was formed as a result of the collision between the Arabian and Iranian plates during the Late Tertiary. The maximum stress axis, which is caused by collision, is perpendicular to the hinge line. The geometrical and genetic classification indicates that the Anticline was formed by the high folding intensity and with a role of evaporites layers.

Coupled Rapid Erosion and Foreland Sedimentation Control Orogenic Wedge Kinematics in the Himalayan Thrust Belt of Central Nepal

AbstractSpatial and temporal coincidence among rapid Pliocene‐Holocene bedrock exhumation, development of a topographic bight, abundant monsoonal precipitation, accumulation of anomalously thick proximal foreland basin deposits, and development of an opposite‐polarity salient‐reentrant couple on the two most frontal major thrust faults in the Himalayan orogenic wedge of central Nepal provide a basis for a model that links these diverse phenomena and could be operating in other parts of the frontal Himalaya. Rapid bedrock erosion is documented by a concentration of young (<5 Ma) low‐temperature thermochronologic ages in the Narayani River catchment basin. Where the river exits the Lesser Himalayan Zone, the Main Boundary thrust has a 15‐km‐amplitude reentrant. Directly south of the reentrant lies the ∼50 km wide Chitwan wedge‐top basin, which is confined by a large salient on the Main Frontal thrust. Rapid erosion and sediment flux out of the Narayani catchment basin, possibly due to anomalously intense monsoonal precipitation in this topographically depressed region of central Nepal, causes greater flexural subsidence and surface aggradation in the foreland, both of which increase initial wedge taper and render this region more susceptible to anomalous forward propagation of the thrust front. Analysis of the modern and post‐early Miocene taper history of the thrust belt suggests that rapid erosion hindered forward propagation of the contemporaneous Main Boundary thrust, but simultaneously produced conditions in the foreland that eventually elevated initial taper to a critical/supercritical value promoting forelandward propagation of the Main Frontal thrust. This analysis has implications for large damaging earthquakes in the Himalaya.

Subsurface Structural Interpretation of Missa Keswal Area, Eastern Potwar, Pakistan

Potwar Basin is although a hydrocarbon prolific basin but shows mixed scenarios regarding the success ratio of the wells. Several wells are producing good but a significant number of wells ended up with a great loss. Missa Keswal area is also a part of the Potwar Basin which was discovered in 1991. The main objective of this research is to find the subsurface structure of the Missa Keswal area with the help of seven seismic lines, 3-D modeling, and the correlation of five wells. Kingdom suite 8.8 is the main software used to delineate the subsurface structure along with some other software. Results indicate that the tectonic framework of the study area is mainly controlled by the Jhelum strike-slip fault and decollement layer i.e., Pre-Cambrian salt. Structural analysis shows that the study area bears NE-SW trending salt cored pop-up anticlinal structure bounded by major thrust fault and back thrust. Patala Formation acts as a source, Lockhart Limestone, Sakesar Limestone, and Chorgali Formation acts as a reservoir while fault surface (often acts a good conduit) and Neogene clays providing a potential sealing mechanism for entrapment.

Tectonic Controls on Surface Erosion Rates in the Longmen Shan, Eastern Tibet

AbstractThe Longmen Shan range, located on the eastern margin of the Tibetan Plateau, is characterized by steep topography and a shortening rate of <3 mm/yr. This peculiar configuration is a source of controversy and questions about the topographic evolution and dynamics of this orogenic plateau margin. Investigating the variations in surface denudation over different spatial and temporal scales is important for a better understanding of topographic evolution, but there is still a lack of erosion‐rate data averaged over millennial timescales along the frontal range of the Longmen Shan, especially in its southern part. We present 25 new catchment‐wide denudation rates derived from 10Be concentrations in river sediments across the southern Longmen Shan. Our results show that average denudation rates increase from <0.15 mm/yr near Ya'an, located in the Sichuan Basin, northwestward to >0.50 mm/yr inside the southern Longmen Shan. The denudation rates correlate with slope gradient, relief, channel steepness, and specific stream power but exhibit a fair degree of scattering at high values. In combination with previous 10Be and low‐temperature thermochronology analyses, we found the denudation rates over kyr‐ to Myr‐timescales to be roughly consistent across the southern Longmen Shan, suggesting this part of the range is close to an exhumational steady state. In terms of spatial distribution, high rates of exhumation and denudation are localized in the hanging walls of major thrust faults, highlighting the role of tectonic structures in regulating the pattern of denudation and topography across the Longmen Shan. Our results favor the “brittle crustal shortening” model in which rock uplift pattern across the Longmen Shan is largely controlled by upper crustal shortening. Along‐strike variations in the distribution of denudation rates and topography can probably be attributed to segmentation of subsurface fault structures.