Strong Deformation Research Articles

Deformation of the Crust and Upper Mantle beneath the North China Craton and Its Adjacent Areas Constrained by Rayleigh Wave Phase Velocity and Azimuthal Anisotropy

The North China Craton (NCC) has experienced strong tectonic deformation and lithospheric thinning since the Cenozoic. To better constrain the geodynamic processes and mechanisms of the lithospheric deformation, we used a linear damped least squares method to invert simultaneously Rayleigh wave phase velocity and azimuthal anisotropy at periods of 10–80 s with teleseismic data recorded by 388 permanent stations in the NCC and its adjacent areas. The results reveal that the anomalies of Rayleigh wave phase velocity and azimuthal anisotropy are in good agreement with the tectonic domains in the study area. Low-phase velocities appear in the rift grabens and sedimentary basins at short periods. A rotation pattern of the fast axis direction of the Rayleigh wave together with a distinct low-velocity anomaly occurs around the Datong volcano. A NW–SE trending azimuthal anisotropy and a low-velocity anomaly at periods of 60–80 s are observed subparallel to the Zhangbo fault zone. The whole lithosphere domain of the Ordos block shows a high-phase velocity and counterclockwise rotated fast axis. The northeastern margin of the Tibetan plateau is dominated by a low-velocity and coherent NW–SE fast axis direction. We infer that the subduction of the Paleo-Pacific plate and eastward material escape of the Tibetan plateau mainly contribute to the deformation of the crust and upper mantle in the NCC.

Grain refinement mechanism in 6082 Al alloy fabricated by cryo-multiaxial forging

In the present investigation, grain refinement mechanism in 6082 Al alloy fabricated by multi-axial forging at liquid nitrogen temperature (MCF) was proposed. The hardness and tensile properties were correlated to the microstructural characteristics of the processed alloy. The samples were subjected to open die MCF up to the 2 cycle (true strain = 1.26), 4 cycle (true strain = 2.52), and 6 cycle (true strain = 3.78), respectively. With the increased number of induced forging cycles, strength of the processed samples was significantly increased. The number density of dynamic recrystallized (DRXed) grains has significantly increased as the number of induced MCF cycles increases. The micro-texture analysis suggested the presence of the strong recrystallization (Rotated Cube ({001} <110>)) and strong deformation (Goss ({110}<001>) & Cu ({112}<111>)) texture components, after inducing the total true strain of 3.78. The supressed and broadened differential scanning calorimetry (DSC) exothermic peaks of β″&β′-phases of the MCF up to 6 cycles have revealed the high dislocation density in the processed samples. The MCF up to 6 cycles, followed by isochronal annealing treatment of Al alloy exhibit the highest strength in all investigated conditions. It was occurred due to the grain boundary strengthening owing to the development of nano-size sub-grains, as well as formation of needle shape β″-phases, which imparted the greater pinning effect during the interaction with the dislocations and grain boundaries.

Modeling of rubber-cord layers under quasi-static loading

Modeling a pneumatic tire with a strong change in shape causes the problem of choosing an adequate model for rubber-cord plies. Generally, the classical method of asymptotic homogenization is not suitable due to physical and geometrical nonlinearity for the strain up to 15 %. The known models used for simulation the entire tire as well as rubber-cord plies are analyzed. A choice is made in favor of modeling the plies using the stress anisotropic potential, which is an anisotropic function of the strain tensor invariants. The relationship of such a constitutive law with a quasi-linear constitutive equation in terms of stress and strain differentials is indicated. A convenience of these two types of constitutive equations in terms of numerical implementation is also given. A modification of the effective properties definition for an inhomogeneous layer is explained. The difference from the standard effective moduli definition is clarified. The arrangement of the cords is supposed to be approximately periodic and all cords to be equivalent to the effective fiber. Two models of a rubber-cord plies are described under such assumption. These are a model of an orthotropic material and a model of a transversely isotropic material. Computational experiments, which make it possible to determine the material parameters of anisotropic potentials, are pointed out. Real tests with a sample of rubber ply under slow quasi-static loading were conducted. Significant hysteresis was detected. It is shown that an additive model combining a hyper elastic material with Maxwell viscoelastic model provides good accuracy in stress dependence on the strain rate. The numerical procedure developed to calculate solution to the quasi-static problem of tire deformation is described. It is implemented in home-made computer code. A numerical example on the tire simulation is given. That is so-called breaking test, in which strong deformation is achieved and the developed model is applied to.

Electron pairing with gapless excitations in mixed double layers

We study the interlayer pairing states in layered systems of two different 2d electronic subsystems, one with relativistic linear and the other with non-relativistic parabolic spectrum. The complex order parameter of the paired state has a two component structure. We investigate the pairing state formation on the mean-field level, determine the critical interaction strength and evaluate the effective potential. The anisotropic three-band spectrum of quasiparticles depends explicitly on the phase difference of the order parameter components, rotates in momentum space as it changes. It is subject to the strong band deformation due to the pairing. It leads to the fusion and hybridization of initially decoupled bands. The quasiparticle spectrum has the shape of deformed Dirac cones in the vicinity of the two touching points between neighboring bands. The density of states exhibits a number of specific features due to band deformation, such as a van Hove singularity.

Оптичний контроль межі розподілу між поверхнею золота та зразками клітин крові

The optical properties of blood (spectra of the extinction coefficient, k, refractive index, n, etc.) carry important diagnostic information and are usually monitored using bulk samples. In this work, attention is drawn to the interface between the blood volume and the surface of glass or thin gold films on it, where the refractive index may differ from the bulk one. We draw attention to the relationship between two effects – SPR and TIR. It is shown that if the named effects are measured for two different external media 0 and 1 with different refractive indices, then the values of the angles SPR and TIR will be linearly related by the empirical formula SPR1=SPR0+TIR1- TIR0)*K, where the coefficient K depends on the thickness of the transition layer di between the surface and the volume of the liquid medium (suspension). Numerical calculation of K (di) for gold films shows that K = 1.6 at di = 0 and monotonically decreases to 0.01 with an increase in di to 300 nm (and further to 0). Measurement of the angular dependences of reflection, R(), on (1) 100% hematocrit blood samples, (2) hemolyzed samples and (3) washed erythrocytes with dilutions with a buffer solution. It was shown that all samples exhibit a minimum SPR, but the TIR angle can be measured only for blood samples with destroyed membranes (hemolyzed), buffer solution and plasma. The n-value for hemolyzed blood is 1.3505, which is indicative of a low hemoglobin content in the sample. At the same time, di for a sample of 100% hematocrit was 60-105 nm, which indicates a strong deformation of erythrocytes in the form of polyhedrocytes and their dense packing after centrifugation. Washing the cells with a buffer increases di to 280 nm and more and practically eliminates blood cells from the SPR sensitivity region. The reason for this may be that in the blood of 100% hematocrit, erythrocytes are in the form of polyhedrocytes tightly adhering to the gold surface, while as a result of washing and diluting with a buffer solution, the cells relax back into discocytes. As a result, the containing hemoglobin erythrocyte cytoplasm moves away from the surface at a distance di&gt; 300 nm into the suspension volume and leaves the area of the enhanced plasmon-polariton field.

Study on Deformation Evolution Characteristics of Reverse-Dip Rock Slope under the Influence of Rainfall

In Southwestern China, there exists deep river valleys and abundant rainfall, which leads to a large number of reverse-dip rock slopes. In order to investigate the evolution characteristics of toppling deformation of reverse-dip slope under the influence of rainfall, and a typical reverse-dip slope was taken as an engineering case. Firstly, the temporal and spatial evolution nephogram of toppling displacement under different rainfall was obtained based on the discrete surface displacement monitoring data of bank slope. Then, taking bank slope, gully buffer zone, and development degree of bank slope as development characteristics based on geological field survey, afterward, the evolution characteristics in different strong deformation zones were analyzed by superimposing the development characteristic partition and the spatial and temporal displacement nephogram. The results showed that the horizontal displacement mainly occurred on the right front and middle rear of the bank slope while large vertical displacement occurred on the middle of the bank slope under the influence of rainfall. As the rainfall increased to the maximum, the toppling deformation reached the peak, and vertical displacement was more sensitive to the rainfall than horizontal displacement. After the superposition, the largest strong deformation zone was located in the middle and rear part of the bank slope, which is characterized by medium and high slope and mature stage and 50 m gully buffer zone. This paper explores the deformation and failure process of reverse-dip rock slope considering the change of rainfall through real displacement monitoring data and focuses on the real deformation evolution law of each characteristic zone combined with different development characteristics partition.

Seismic Behavior of GFRP Tube Reactive Powder Concrete Composite Columns With Encased Steel

To obtain the seismic behavior of glass fiber–reinforced polymer (GFRP) tube reactive powder concrete composite columns with encased steel (GRS), a total of 17 full-scale GRS columns were designed in this study. The parametric studies were conducted to explore the influence of factors such as the diameter of GFRP tube (D), thickness of GFRP tube (t), number of fiber winding layers (n), fiber winding angle (θ), axial compression ratio (λ), compressive strength of reactive powder concrete (fc), the area of encased steel (As), and strength of encased steel (fsy) on the seismic behavior of the composite columns. The finite element models of this kind of columns were established by ABAQUS finite element software, and the seismic behavior analysis for GRS composite columns was carried out. The results show that all the specimens exhibit good ductility and strong deformation ability. The stiffness degradation of specimens significantly slows down with the increase of D, fsy, and λ. The energy dissipation capacity of specimens can be improved by increasing D and λ, while the increase of As and fsy leads to the decrease of the energy dissipation capacity. By observing the failure mode of such composite columns, local bulging occurs in the foot area of the columns. Based on the statistical analysis of the calculated results, the restoring force models for GRS composite columns are proposed, which agree well with the simulated results. The restoring force models can provide reference for the elastic-plastic seismic response analysis of this kind of composite columns.

New discoveries on the first petroleum scientific drilling (QK-1) of the Qiangtang Basin, Tibetan Plateau

<p indent=0mm>QK-1 is the first scientific drilling designed to solve the key problems in petroleum geology in the Qiangtang Basin on the northern Tibetan Plateau. Its altitude is <sc>5030 m,</sc> and the well depth is <sc>4696.2 m.</sc> It is also the highest-altitude scientific drilling on the globe, and is located in the Lake Bandaohu area in the northern Qiangtang Basin. By performing the QK-1 and its affiliated shallow drillings, a series of new discoveries has been made in regard to high-quality regional seals, source rocks, petroleum displays and the Jurassic strata succession. (1) Two sets of caprocks, which could be regional high-quality seals, were discovered through drilling, i.e., an anhydrite layer in the Quemoco Formation (J_1-2<italic>q</italic>) <sc>(354–365 m</sc> thick) and a gypsum-bearing mudstone in the Xiali Formation (J₂<italic>x</italic>) <sc>(230–252 m</sc> thick). Comprehensive analyses of drilling and seismic data show that the distribution of these caprocks is regionally continuous and stable. Moreover, petroleum displays and well logging data reveal that these two caprocks are characterized by low porosity, good permeability (the mean permeability is <sc>0.265×10⁻³ μm²,</sc> and the mean breakthrough capillary pressure is <sc>9.0 MPa),</sc> and good sealing. (2) The northern Qiangtang Basin contains high-quality hydrocarbon source rocks in Upper Triassic deltaic facies. The affiliated shallow drillings reveal a good Upper Triassic hydrocarbon source rock in a coastal swamp-deltaic plain facies on the northern Qiangtang Basin margin. The two mudstone source rock members have a thickness of <sc>36.0 m</sc> and total organic carbon (TOC) values of 2.0%–3.6%, and a thickness of <sc>61.0 m</sc> and TOC values of > 1.0%, respectively. The organic matter type is II₁-, II₂- and III-type kerogen with high to over-thermal maturation. Well logging, seismic data and facies analyses indicate that the pro-deltaic to shelf mudstones in the covered area in the central northern Qiangtang Basin are better source rocks than those in the deltaic plain on the basin margin. (3) Well logging petroleum displays provide important insights for petroleum reservoir formation and destruction. Based on petroleum displays and evidences of gas release in 250 outcrops, the QK-1 scientific drilling has also discovered 14 petroleum anomalies in the Eocene Suonahu Formation, Middle Jurassic Buqu Formation and the Upper Triassic Nadigangri Formation. One anomaly is oil-bearing, while thirteen anomalies are gas-bearing. The total hydrocarbon value of gas logging is 10%, and is mainly methane in composition. The petroleum displays of well logging occurred after drilling through the Xiali or Quemoco formations which are caprocks, while outcrop petroleum displays are mainly distributed on the basin margin or central uplift which are strong tectonic deformation zones. The widespread petroleum displays indicate good hydrocarbon-generation conditions and petroleum reservoir formation/destruction processes, while the distribution characteristics of petroleum displays indicate that the high-quality regional-seals-covered area in central basin could be favorable plays of petroleum reservoirs. (4) The QK-1 drilling cut through a sedimentary succession from the Upper Jurassic to Upper Triassic, i.e., from the upper to the bottom, the Upper Jurassic Suowa Formation (J₃<italic>s</italic>), Middle Jurassic Xiali (J₂<italic>x</italic>) and Buqu Formations (J₂<italic>b</italic>), Middle-Lower Jurassic Quemoco Formation (J_1-2<italic>q</italic>) and Upper Triassic Nadigangri Formation (T₃<italic>nd</italic>), in which the whole Jurassic strata is completely continuous. The Jurassic sedimentary succession shows a transition from alluvial facies to shore, shallow shelf and carbonate platform facies up section. This finding breaks the previous view that suggests a lack of Lower Jurassic strata, and provides new basics for Qiangtang Basin analysis. Overall, the discovery of two regional high-quality seals in the Jurassic Quemoco and Xiali formations in the Qiangtang Basin refutes the previous traditional perception, which suggests poor petroleum preservation conditions. The northern Qiangtang Basin contains high-quality source rocks with great hydrocarbon generation potential in the Upper Triassic deltaic facies. Petroleum display anomalies and distribution characteristics reveal that the Qiangtang Basin not only underwent large-scale hydrocarbon generation, reservoir formation/destruction processes, but also developed favorable display of petroleum preservation. The establishment of a continuous Jurassic strata succession provides a new evidence and valid framework for petroliferous basin analysis of the Qiangtang Basin.

The traditional approximation of rotation for rapidly rotating stars and planets

Context. We examine the dynamics of low-frequency gravito-inertial waves (GIWs) in differentially rotating deformed radiation zones in stars and planets by generalising the traditional approximation of rotation (TAR). The TAR treatment was built on the assumptions that the star is spherical (i.e. its centrifugal deformation is neglected) and uniformly rotating. However, it has been generalised in our previous work by including the effects of the centrifugal deformation using a non-perturbative approach. In the meantime, TAR has been generalised in spherical geometry to take the differential rotation into account. Aims. We aim to carry out a new generalisation of the TAR treatment to account for the differential rotation and the strong centrifugal deformation simultaneously. Methods. We generalise our previous work by taking into account the differential rotation in the derivation of our complete analytical formalism that allows the study of the dynamics of GIWs in differentially and rapidly rotating stars. Results. We derived the complete set of equations that generalises the TAR, simultaneously taking the full centrifugal acceleration and the differential rotation into account. Within the validity domain of the TAR, we derived a generalised Laplace tidal equation for the horizontal eigenfunctions and asymptotic wave periods of the GIWs, which can be used to probe the structure and dynamics of differentially rotating deformed stars with asteroseismology. Conclusions. A new generalisation of the TAR, which simultaneously takes into account the differential rotation and the centrifugal acceleration in a non-perturbative way, was derived. This generalisation allowed us to study the detectability and the signature of the differential rotation on GIWs in rapidly rotating deformed stars and planets. We found that the effects of the differential rotation in early-type deformed stars on GIWs is theoretically largely detectable in modern space photometry using observations from Kepler and TESS.

Recent progress and future perspectives of flexible metal‐air batteries

AbstractWith the rapid development of wearable and intelligent flexible electronic devices (FEDs), the demand for flexible energy storage/conversion devices (ESCDs) has also increased. Rechargeable flexible metal‐air batteries (MABs) are expected to be one of the most ideal ESCDs due to their high theoretical energy density, cost advantage, and strong deformation adaptability. With the improvement of the device design, material assemblies, and manufacturing technology, the research on the electrochemical performance of flexible MABs has made significant progress. However, achieving the high mechanical flexibility, high safety, and wearable comfortability required by FEDs while maintaining the high performance of flexible MABs are still a daunting challenge. In this review, flexible Zn‐air and Li‐air batteries are mainly exemplified to describe the most recent progress and challenges of flexible MABs. We start with an overview of the structure and configuration of the flexible MABs and discuss their impact on battery performance and function. Then it focuses on the research progress of flexible metal anodes, gel polymer electrolytes, and air cathodes. Finally, the main challenges and future research perspectives involving flexible MABs for FEDs are proposed.

Molecular insights into the uptake of SiO2 nanoparticles on phospholipid membrane: Effect of surface properties and particle size

Silica (SiO2) nanoparticles (NPs) have attracted much attention due to the potential for a wide range of applications and they have been confirmed to be hazardous to humans. Partitioning to phospholipid bilayers is an important way for their bioaccumulation. However, the detailed mechanism of SiO2 NPs uptake by membrane phospholipids remains uncertain. In this work, molecular dynamics (MD) simulations were employed to study the uptake process of SiO2 NPs into DPPC bilayers. Results show that these SiO2 NPs uptake onto DPPC bilayer surface is favorable from the viewpoint of thermodynamics. During the uptake process, the SiO2 NP needed to adjust the angle of interaction with the DPPC surface until the most stable adsorption configuration was reached. After incorporating into DPPC bilayers, the interaction between PO4− group and SiO2 particle is stronger than -N+(CH3)3 group and SiO2. Small SiO2 NP was found to adsorb to the surface of DPPC bilayer without disturbing the morphology or membrane. In contract, bioaccumulation of large SiO2 NP to DPPC induced a strong local membrane deformation. In addition, the effect of SiO2 NP surface functionalization on its interaction with DPPC was also investigated. This molecular-level study reports a complete description of the interaction between SiO2 NPs and DPPC bilayer, aiming to provide some insights for the further work on the bioaccumulation and hemolytic activity of SiO2 NPs.

Chemical Structure Transformations in Kerogen from Longmaxi Shales in Response to Tectonic Stress as Investigated by HRTEM, FTIR, and 13C NMR

Kerogen molecular structure controls the micropore (<2 nm diameter) evolution in shale and exerts a significant impact on shale gas adsorption, desorption, and diffusion. However, the influence of tectonic deformation on kerogen structure and organic micropores needs intensive study. Our study mainly focuses on the transformations in the extracted kerogen structure and organic micropores of Longmaxi shale during tectonic deformation. Vitrinite reflectance measurement (VRM) and Raman spectroscopy (RS) were utilized to determine the maturity of organic matter. Organic pore network attributes of kerogen samples were estimated using CO2 adsorption experiments. High-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), and 13C nuclear magnetic resonance (13C NMR) were utilized to interpret the kerogen molecular structures of these samples. VRM and RS results show that Longmaxi shale has reached the wet gas window. Adsorption analyses of CO2 indicate that kerogen samples in shale with strong deformation have larger micropore volume and surface area (<2 nm). 13C NMR and FTIR results reveal that the tectonic stress may promote the shedding of aliphatic carbon. HRTEM images exhibit that aromatic rings with a size of 3 × 3 account for the largest proportion in all kerogen samples, which indicates that the kerogen samples have reached a high thermal evolution level, consistent with the Raman experiment. For weakly deformed shale samples, 66.5 and 88.8% of the total number of aromatic rings in LZ-1 and LZ-4 kerogen belong to the major direction (within a 45° range). In the most strongly deformed sample, LZ-2, distribution orientations of aromatic fringes are dispersed and primarily concentrated at 15–105°. Such disorientation of nanometer-sized polyaromatic layers in the strongly deformed sample creates a nanopore network in organic matter (OM) that increases the micropore volume and surface area. These findings from integrated approaches can provide a new perspective of adsorbed gas enrichment in the complex tectonic areas.

Mechanical and Wear Behavior of Steel Wires in Typical Contact Area Under Tension-tension Fatigue

In this study, the issues of the complex mechanical behavior inside steel wire rope and wear evolution of internal wire at typical contact areas where the fracture of the wire is more likely to occur is particularly considered. First, the fretting parameters of steel wires at typical contact areas were calculated. Then the wear evolution process under tensile loads with different stress ratios was simulated by using the finite element method (FEM) based on the calculated parameters. Finally, the micro-morphology and element concentration and distribution of wear scars at typical contact areas were observed. The results demonstrate that: (1) The relative displacement value and normal contact stress between the outer layer steel wires of core strand and outer strands are maximum, which cause the most severe wear in this area. As the stress ratio decreases from 0.5 to 0.25, the fretting parameters of steel wires increase. (2) The wear evolution process is divided into running-in stage and stable wear stage, which are characterized by the rapid decline and stabilization of wear rate, respectively. (3) Compared with other contact areas, the concentration of iron, carbon and chlorine in the contact area between strands is obviously higher. Meanwhile, there exist strong plastic deformation, severe delamination and primary and secondary cracks in this region, resulting in stress concentration and thus the fatigue life decrease of steel wire.

Robust and Scalable Flat‐Optics on Flexible Substrates via Evolutionary Neural Networks

Flexible Flat-Optics This work, presented in article 2100105 by Andrea Fratalocchi and co-workers, implements an artificial intelligent, end-to-end pipeline for the experimental realization of flexible, broadband ultra-flat optics for vectorial light control. The system takes advantage of “physical” neural networks, engineered into suitably designed optical nanoresonators. The design framework also considers fabrication robustness, furnishing devices that maintain their optical response even under strong stress perturbations and deformations.

Experiment and Research on Calculation Methods on Flexural Mechanical Behaviors of Non-Metallic Reinforced ECC Beams

Engineered cementitious composites (ECC) has high tenacity and the characteristics of strain hardening. In the bending test, ECC beams equipped with carbon fiber reinforced polymer (CFRP) in the tensile region show good deformation ability and bending ability. In this paper, the constitutive models of ECC and CFRP materials are established by uniaxial tensile compression test. Based on the plane section supposition, the analysis theory of bending capacity of cross section for ECC beams with non-metallic reinforcement is proposed. The calculation results are compared with the four-point bending test results. The results show that: (1) ECC beams with non-metallic reinforcement reflect the advantages of the two materials, and have strong deformation capacity before bending failure. (2) The calculation results based on the theory of flexural capacity of normal section are in good agreement with the experimental results, and the maximum error is less than 4%. The research results can provide the basis and reference for the calculation analysis and practical application of non-metallic reinforced high toughness material structure.

Application of Slope Radar (S-SAR) in Emergency Monitoring of the “11.03” Baige Landslide

On October 11 and November 3, 2018, the disaster chain of landslide-barrier lake occurred twice in Baige Village, Xizang Province. After the second sliding of the landslide, the danger of the landslide dam was eliminated by the manual excavation of the drain grooves. During this period, a ground-based interferometric synthetic aperture radar (GB-InSAR) called “S-SAR” was utilized for real-time monitoring and analyzing 48 selected target pixels on the residual deformation bodies of landslides (divided into K1, K2, and K3 deformation zones) for 8 days. Through the real-time deformation map of pixels in the monitoring area obtained by S-SAR, the ranges of five strong deformation regions were identified and delineated. Based on the apparent cumulative deformation-time curve of each target pixel, the overall deformation law of K1, K2, and K3 deformation zones could be monitored and analyzed in real time. Based on a curve graph of the deformation rate, acceleration, and time of each target pixel, the K1, K2, and K3 deformation zones were within a uniform deformation stage. Taking the target pixel point and the corresponding time in which the deformation rate and deformation acceleration had a large, abrupt jump at the same time as the position and time of the near-slip failure, the 11 positions and moments of the near-slip failure were counted. The results presented here may represent a workable reference for emergency monitoring and early warning of similar sudden geological disasters.

Molecular motion in mixtures of polymer melts in a capillary flow

The evolution of the morphology of two incompatible polymer melts in a capillary flow was studied using analytical electron microscopy. The spatial distribution of polysulfone and the liquid–crystal (LC) polymer was evaluated by measuring the concentration of sulfur (which is contained exclusively in polysulfone) and oxygen (contained in a much larger proportion in the LC polymer). The distributions of both polymers in the cross-sections of the strands do not change regardless of the specified shear rate, which varies by a factor of 25. However, a thin boundary layer with a width of about 10 μm formed by a low-viscosity LC polymer was detected. Nevertheless, there is a strong deformation and orientation of both polymers. This indicates that the movement of the mixture through the capillary occurs not due to sliding along the boundary layer but also due to shear in the entire volume of the material.

Tectonic evolution and controls on natural gas generation and accumulation in the Ordovician system of the Ordos Basin, North China

The Ordovician system of the Ordos Basin is rich in oil and gas resources, but the tectonic evolution of Ordovician strata and controls on natural gas generation and accumulation are poorly understood. In this study, we integrate field observations, seismic and drill core interpretation, and geochemical data analysis [total organic carbon (TOC) and vitrinite reflectance (Ro)] to address this issue. Results show a clear depositional axis, with thick (>2500 m) Ordovician sediments in the southern half of the basin, and thinner strata in the central and northern parts. Ro values range from 2.04% to 3.45%, and 55 of 73 samples have TOC > 0.23 wt%. Our novel findings made as below: (i) Ordovician strata have high contents of organic matter and that thermal evolution reached the dry gas stage, favorable for natural gas generation. (ii) Ordovician strata have recorded multiple tectonic events and experienced erosion that resulted in the formation of a karst type residuum in the central and northeastern parts of the basin. (iii) An Early Cretaceous tectono-thermal event controlled the generation and accumulation of natural gas, and this was the peak period of gas generation of Ordovician strata. (iv) Natural gas accumulation and adjustment occurred during the Cretaceous and Cenozoic, respectively. The Ordos Basin has experienced strong deformation and denudation since the Late Cretaceous. Collectively, the deformation was more intense in the south and weaker in the north, preventing hydrocarbon preservation in the southern part of the basin. These findings provide new insights to guide oil and gas exploration of the Ordos Basin.

Displacement evolution of reverse-dip rock slope considering the change of the reservoir level

The fluctuation and periodic change of reservoir level are the important incentives that affect the stability of the reverse-dip rock slope. Based on the field monitoring data, this paper investigates the topping deformation evolution characteristics of a typical reverse-dip slope containing different geological partitions considering the fluctuation of reservoir level. A typical reverse-dip rock slope was taken as an engineering case, whose geological factors including elevation, slope angle, and aspect were first obtained by a field survey. Subsequently, the factors were superimposed through ArcGIS to obtain the geological partitions. Afterwards, a spatiotemporal evolution nephogram of the topping displacement was obtained by discrete monitoring data of surface displacement of the slope. Finally, the deformation characteristic of the prone zone was analyzed by superposing the nephogram of the displacement and the geometrical partition, considering the change of the reservoir level. The results show that the largest geological and geometric characteristic zone is at the bottom elevation, medium slope, and north aspect. The zone with significant horizontal displacement is distributed in the front and middle edges of the slope, which increases with the increase of the reservoir level and vice versa. The vertical displacement mainly occurs in the trailing of the slope. The area of superimposed displacement in strong deformation zones increases as either the reservoir level rises or falls. After the superposition, zones with strong deformation increase with the variation of the reservoir level, and the area with the largest displacement is distributed at the medium gradient, low elevation, and north aspect zones.

Crustal Anisotropy Beneath the Trans-North China Orogen and its Adjacent Areas From Receiver Functions

As an important segment of the North China Craton, the Trans-North China Orogen (TNCO) has experienced strong tectonic deformation and magmatic activities since the Cenozoic and is characterized by significant seismicity. To understand the mechanism of the crustal deformation and seismic hazards, we determined the crustal thickness (H), Vp/Vs ratio (κ) and crustal anisotropy (the fast polarization direction φ and splitting time τ) beneath the TNCO and its adjacent areas by analyzing receiver function data recorded by a dense seismic array. The (H, κ) and (φ, τ) at a total of 309 stations were measured, respectively. The Moho depth varies from ∼30 km beneath the western margin of the Bohai bay basin to the maximum value of ∼48 km beneath the northern Lüliang Mountain, which shows the positive and negative correlations with the elevation and the Bouguer anomaly. The average φ is roughly parallel to the strikes of the faults, grabens and Mountains in this study area, whereas a rotating distribution is shown around the Datong-Hannuoba volcanic regions. Based on the φ measured from the Moho Ps and SKS/SKKS phases, we propose that the crustal deformation and seismic hazards beneath the TNCO could be due to the counterclockwise rotation of the Ordos block driven by the far-field effects of the India-Eurasian collision.