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Deciphering the evolution of spatial geometry of carbonate platforms in deeply buried successions is still a challenge due to the low resolution of seismic data and the constraints of drilling wells. In this study, by combining a seismic forward model, we systematically delineated the external morphology and internal architecture of seismic reflection and established a depositional model of a carbonate platform. The Lower Paleozoic strata display the high-amplitude reflection in the Lower-Middle Cambrian interval and the low-amplitude reflection in the Upper Cambrian-Middle Ordovician interval. The high-amplitude reflection interval thins or wedges out towards the center of the present Southwest Depression section, and thickens to the north and south. Inside of the high-amplitude interval, the seismic reflection terminated at the top reflector. Seismic forward modeling was performed to examine the validity of possible hypothetical models in the studied area. The modeling results show that the simulated stratigraphic patterns are comparable to a ramp or depression geometry which is well fit to the characteristics of actual seismic reflections. Such a ramp or depression geometry is built upon the changes in sea level and climate during the Cambrian period. This study emphasizes the potential of the integration of sequence stratigraphic analyses and seismic forward modeling as a seismic workflow for retrieving the stratigraphic architecture and platform geometry.

Objective To reveal the structures and evolutionary patterns of faults in the central and northern parts of Tazhong Uplift, Tarim Basin, Methods this paper systematically discusses the types of fault structures, geometric characteristics, differential activity mechanisms, and tectonic evolution processes in this area by analysing detailed structural interpretations and coherent slices of combined large 3D seismic data along with the regional dynamic background. Results The results show that there are 4 types and 7 evolution stages of faults in the central and northern parts of Tazhong Uplift, among which thrust faults and strike-slip faults are particularly common. On the plane, NW arc thrust faults intersect with NE-, NW- and NS-striking strike-slip faults; vertically, the fault stratification and differential activity characteristics are obvious. In the Lower Ordovician and the belowing layers, faults developed in large numbers and were mainly linear in their trending directions. As for the Middle Ordovician-Middle and Lower Devonian layers, faults are mostly in the echelon type. In the Upper Devonian-Permian layers, a few faults developed in the Tazhong Ⅱ fault zone and the southwestern end of the Shunbei 5 fault zone. Conclusion The fault activity in the study area was controlled by stress sites exhibiting diverse properties across multiple phases and directions and experienced an extremely complex evolutionary history: In the Early Caledonian period, a small number of normal faults, such as the Tazhong Ⅱ fault zone, were mainly active; in the Middle Caledonian Ⅰ period, the fault activity was very strong and was characterized by coevolution and mutual coupling of thrust faults and strike-slip faults. The strike-slip faults obviously cut or restricted the thrust faults. The fault activity of the Middle Caledonian Ⅲ period basically inherited the tectonic framework of the Middle Caledonian Ⅰ period, but the characteristics of transtensional fault activity in the Shunbei 4 and 5 fault zones are significant. From the Late Caledonian to Early Hercynian, some of the faults inherited activities with obvious transtensional characteristics. Conversely, in the Indochina-Yanshan period, only a few faults inherited activity, and the development area of transtensinal fault is further expanded to the south. During the Himalayan period, the tectonic movement of this area was relatively stable, and the complex fault structures that formed in the early stage transitioned into the deep burial stage.

The intensifying exploration for deep-buried oil and gas reserves in the southwestern Tarim Basin accelerates the necessity to understand how the structure and evolution of the Precambrian basement affect the development and distribution of Precambrian strata. However, the lack of systematic and comprehensive understanding of the structural characteristics of the Precambrian basement in the southwestern Tarim Basin restricts further advancements in the exploration of ultra-deep oil and gas reserves in this area. Based on the previous research results, this study analyzed the lithology, age, structure, and evolution of the Precambrian basement in the southwestern Tarim Basin by utilizing integrated research methods of geology and geophysics and in combination with the U-Pb dating results of the Precambrian basement. The results reveal that the structure of the Precambrian basement in the Bachu uplift region is characterized by Paleozoic strata overlying directly on the Paleo-proterozoic metamorphic rocks/granites. In the Maigaiti slope and southwestern depression, it exhibits a typical three-tier structure: the Paleoproterozoic metamorphic rocks/granites at the bottom, overlain by sedimentary build-ups from the rifting to depression evolution of the Nanhua-Sinian system. Evolution of the Precambrian basement in the southwestern Tarim Basin was primarily transpired in five phases: continental rifting in the Columbia supercontinent (> 1.1 Ga), assembly of the southwestern Tarim block and the Australian plate (about 1.0 Ga), assemblage between the northern and southern Tarim blocks (900-800 Ma), Nanhua rifting period (760-640 Ma), and Sinian depression period (< 635 Ma). The uplift and downwarping structures during the Nanhua rifting period dictated the development of the Sinian-Lower Cambrian sedimentary strata. In-depth research into the structure and evolution of the Precambrian basement in the southwestern Tarim Basin, as presented in this study, provides important theoretical basis for deep oil and gas exploration in the region, and helps to promote further development of ultra-deep oil and gas exploration.

The high-angle, structural genetic calcite veins of the Ordovician in the Shunnan-Gucheng area in the Tarim Basin provide a convenient study of fluid properties, hydrocarbon migration, and accumulation events in the fault zone of this area. Based on detailed core investigation, studies on fluid inclusions in calcite veins and comparison of geochemical characteristics of limestone matrix and calcite veins were carried out. Multiple types of hydrocarbons inclusion (e.g., dry asphalt inclusion,three-phase hydrocarbon inclusion, oil and water inclusion,gas-rich inclusion) were found in calcite veins. Furthermore, the coexisted aqueous inclusions with the gas–liquid phase had a high homogenization temperature (130–160 °C). The distribution characteristics of 18O-depleted (δ18O: −13.1‰ to −8.7‰), 87Sr-enriched (87Sr/86Sr: 0.708 879 to 0.710 432), relatively high total Rare Earth Elements (REEs), and positive Europium Anomalies indicated that the structural origin of calcite veins was mainly derived from the dissolution of surrounding rocks and diagenetic-hydrocarbon fluids. Participation signs of meteoric water were not proved. The rich hydrocarbon inclusions in the calcite veins indicated that the north-east strike-slip fault zone in the Shunnan-Gucheng area is an essential channel for hydrocarbon migration and accumulation.

Long-range surface plasmon resonance (LRSPR), generated from a coupled plasmon polariton in a thin metal slab sandwiched by two dielectrics, has attracted more and more attention due to its merits, such as longer propagation and deeper penetration than conventional single-interface surface plasmon resonance. Many useful applications related to light–medium interaction have been demonstrated based on the LRSPR effect, especially in the sensing area. Here, we propose and demonstrate an LRSPR-based refractive index sensor by using a SiO2-Au-TiO2 heterostructure, in which a D-shaped honeycomb-microstructure optical fiber (MOF) is designed as the silica substrate and then deposited with a gold film and thin-layer titanium dioxide (TiO2). By using the full-vector finite-element method (FEM), this heterostructure is numerically investigated and demonstrated to excite LRSPR without a buffer layer, which is usually necessary in previous LRSPR devices. Through comprehensive discussion about the influence of structural parameters on the resonant wavelength, the excitation of the LRSPR in the proposed heterostructure is revealed to be highly related to the effective refractive index of MOF’s fundamental core mode, which is mainly determined by the MOF’s pitch, the thicknesses of the silica web and the planar-layer silica. Moreover, the thin-layer TiO2 plays an important role in significantly enhancing the resonance and the sensitivity to analyte’s refractive index as well, when it is coated on the top of the Au film rather than between the metal and waveguide. Finally, the proposed LRSPR sensor based on SiO2-Au-TiO2 heterostructure shows an ultra-high wavelength sensitivity of 20,100 nm/RIU and the corresponding minimum resolution is as low as 4.98×10−7 RIU. Thus, the proposed LRSPR device offers considerable potential for sensing applications in biomedical and biochemical areas.

Polarization-maintaining fibers (PMFs) have always received great attention in fiber optic communication systems and components which are sensitive to polarization. Moreover, they are widely applied for high-accuracy detection and sensing devices, such as fiber gyroscope, electric/magnetic sensors, multi-parameter sensors, and so on. Here, we demonstrated the combination of a fiber Bragg grating (FBG) and Sagnac interference in the same section of a new type of PANDA-structure PMF for the simultaneous measurement of axial strain and temperature. This specialty PMF features two stress-applied parts made of lanthanum-aluminum co-doped silicate (SiO2-Al2O3-La2O3, SAL) glass, which has a higher thermal expansion coefficient than borosilicate glass used commonly in commercial PMFs. Furthermore, the FBG inscribed in this SAL PMF not only aids the device in discriminating strain and temperature, but also calibrates the phase birefringence of the SAL PMF more precisely thanks to the much narrower bandwidth of grating peaks. By analyzing the variation of wavelength interval between two FBG peaks, the underlying mechanism of the phase birefringence responding to temperature and strain is revealed. It explains exactly the sensing behavior of the SAL PMF based Sagnac interference dip. A numerical simulation on the SAL PMF’s internal stress and consequent modal effective refractive indices was performed to double confirm the calibration of fiber’s phase birefringence.

We theoretically propose an asymmetric plasmonic slot waveguide (APSW) with a thin silicon nanocrystal (Si-nc) layer and a thinner silicon layer that fills the bottom and the top of the metallic slot region to increase third-harmonic generation (THG) efficiency. The needed modal phase-matching condition is satisfied with properly mode dispersion engineering by exploiting the waveguide geometrical parameters. Combining the asymmetric waveguide structure and the high third-order susceptibility of the nonlinear materials, efficient phase-matched THG from mid-infrared (IR) to near-IR regions is realized. Then, the THG performance was further improved by increasing the silicon slot width wherein the THG nonlinear coefficient as large as 21452 $\hbox{m}^{-1} \cdot \hbox{W}^{-1}$ is achieved. The corresponding THG efficiency comes up to 0.5% at a waveguide length of 9.3 $\mu\hbox{m}$ with a pump power of 1 W.

We propose the asymmetrical plasmonic slot waveguide (APSW) design for third-harmonic generation (THG) from 2.25 μm. In this configuration, the phase-matching condition is fulfilled between the zeroth-order mode at fundamental frequency (FF) and the first-order mode at third-harmonic frequency (THF). Due to the asymmetrical geometry, the mode overlap between the two involved modes is significantly enhanced, leading to an efficient THG process. According to the numerical calculation, the conversion efficiency is predicted up to 1.4% with 1-W pump power. The proposed APSW has the potential to realize an integrated efficient THG device in nanometer scale.