Northwestern Boundary Research Articles

Northward expansion of the West Kunlun orogenic belt during the Cenozoic and its implications for the evolution of the northwest Tibetan Plateau: Constraints from sediment dispersal patterns in the Buya Basin, China

The West Kunlun orogenic belt, which defines the northwestern margin of the Tibetan Plateau, holds important information on plateau growth. Despite its significance, views about its uplift history continues to be under debate, with two competing hypotheses involving episodic uplift or northward expansion, related to a fixed or movable plateau boundary, respectively. The Buya Basin, a small basin located between the North and South Kunlun terranes, is key to understanding the Cenozoic uplift history of the West Kunlun orogenic belt. In this study, we conducted sedimentary and detrital zircon UPb geochronological analyses on the Cenozoic sediments of the Buya Basin. According to the findings of the sedimentary investigation, the Cenozoic strata of the basin generally show gradual changes from low- to high-energy deposition interrupted by a reverse trend in the Anjuan Formation. Moreover, the detrital zircon UPb geochronological results indicate that the Buya Basin received sediments initially from the Songpan–Ganzi and South Kunlun terranes during the deposition of the Keziluoyi to Pakabulake formations and then from the South and North Kunlun terranes during the deposition of the Artux Formation. This change in sediment dispersal patterns demonstrates that the uplift of the West Kunlun orogenic belt has expanded northwards to the North Kunlun terrane, which suggests that the northwestern boundary of the Tibetan Plateau has been a northward-moving feature in the context of India–Eurasia convergence. Along with previous studies, we suggest that the northward expansion of the northwest Tibetan Plateau is accommodated by decoupling deformation along the southern Tarim Basin, with northward thrusting of the foreland fold-and-thrust belts in the upper crust and southward underthrusting in the lower plate.

Crustal architecture and tectonic development of western Queensland, Australia, based on deep seismic reflection profiling: Implications for Proterozoic continental assembly and dispersal

Interpretation of 2014–2015 deep crustal seismic reflection and magnetotelluric data has revised the architecture and geodynamic framework of western Queensland, with implications for the assembly and dispersal of the supercontinents Nuna, Rodinia and Gondwana. In the Mount Isa Province, crustal-scale boundaries of the Leichhardt River Domain, Kalkadoon-Leichhardt Domain and Eastern Subprovince are mapped in the third dimension. The Leichhardt River and Kalkadoon-Leichhardt domains have similar Nd isotopic T2DM model ages to provinces to the west, indicating they were part of ancestral North Australian Craton (NAC); the Eastern Subprovince is a separate terrane, with the Pilgrim Fault a collisional suture. The Gidyea Suture Zone separates the Mount Isa Province from the subsurface Numil Seismic Province. To the east, the west-dipping Yappar Fault separates east-dipping structures in the west from west-dipping structures in the east, forming a classic doubly vergent orogen within the upper plate of a convergent margin. The northwestern boundary of the Bernfels Seismic Province, the Kynuna Fault, truncates the Gidyea Suture Zone, implying this seismic province was welded to the NAC prior to initial deposition of the Etheridge Province. The Cork Fault truncates the north-south grain of the Mount Isa Province; the easternmost part of the NAC has been excised, presumably during breakup of Nuna. The subsurface Brighton Downs Seismic Province, formerly part of the northern Thomson Orogen, is a discrete seismic province, located between the NAC and the Thomson Orogen, and welded to the NAC during the accretion of Rodinia. Basement to the Thomson Orogen is a collage of microplates, accreted to the Brighton Downs Seismic Province during the assembly of Gondwana. By 530 Ma, eastern Australia faced an open Pacific Ocean, with the Thomson Orogen in a backarc setting. Thus, northeastern Australia contains a record of repeated continental accretion and breakup over at least three supercontinent cycles.

East Asian atmospheric rivers are most hazardous in summer

This study investigates the hazard of East Asian Atmospheric Rivers (ARs) by applying the AR scale to AR catalog. When AR scale is categorized into five ranks from Category 1 (Cat1) to Category 5 (Cat5) by considering the duration and intensity of each AR event, with Cat5 having the most hazardous hydrological impact, Cat5 ARs are most frequently found in East Asian summer, along the northwestern boundary of the western North Pacific subtropical high. More frequent Cat5 ARs than Cat1 to Cat4 ARs are robustly found in eastern China, Korea, and western Japan, due to the slowly-varying monsoonal flow during the East Asian summer monsoon, which transports a large amount of moisture to the region. Since Cat5 ARs often lead to large event-total rainfall, it explains a close relationship of East Asian summer ARs to heavy rainfall events. This finding helps to better understand the potential hydrological impacts of ARs in East Asia.

A refined search for high-velocity gas in the Cygnus Loop supernova remnant

ABSTRACT We present the results of a sensitive search for high-velocity gas in interstellar absorption lines associated with the Cygnus Loop supernova remnant (SNR). We examine high-resolution high signal-to-noise ratio optical spectra of six stars in the Cygnus Loop region with distances greater than ∼700 pc. All stars show low-velocity Na i and Ca ii absorption. However, only one star, HD 198301, exhibits high-velocity Ca ii absorption components, at velocities of +62, +82, and +96 km s−1. The distance to this star of ∼870 pc helps to constrain the distance to the receding edge of the Cygnus Loop’s expanding shock front. One of our targets, HD 335334, was previously thought to exhibit high positive and high negative velocity interstellar Na i and Ca ii absorption. This was one factor leading Fesen et al. to derive a distance to the Cygnus Loop of 725 ± 15 pc. However, we find that HD 335334 is in fact a double-line spectroscopic binary and shows no evidence of high-velocity interstellar absorption. As such, the distance to HD 335334 cannot be used to constrain the distance to the Cygnus Loop. Our detection of Ca ii absorption approaching 100 km s−1 toward HD 198301 is the first conclusive detection of high-velocity absorption from a low-ionization species associated with the Cygnus Loop SNR. A large jump in the Na i column density toward BD+31 4218, a star located beyond the northwestern boundary of the Cygnus Loop, helps to constrain the distance to a large molecular cloud complex with which the Cygnus Loop is evidently interacting.

Melt-enhanced strain localization and phase mixing in a large-scale mantle shear zone (Ronda peridotite, Spain)

Abstract. Strain localization in upper-mantle shear zones by grain size reduction and the activation of grain-size-sensitive deformation mechanisms is closely linked to phase mixing. With its mylonitic grain size (50–100 µm) and well-mixed phase assemblage, the kilometer-scale shear zone at the northwestern boundary of the Ronda peridotite is, in this respect, no exception. In transects across the high-strain mylonitic into the low-strain tectonitic part of this shear zone, the following four dominant microstructural domains were identified: (1) olivine-rich matrix, (2) mixed matrix, (3) neoblast tails of clinopyroxene porphyroclasts, and (4) neoblast tails of orthopyroxene porphyroclasts. In these domains, phase mixing and its impact on strain localization were investigated by a combination of microstructural (optical microscopy), textural (EBSD), and geochemical (EPMA) analysis. The dominant microstructural domain of all samples is the mixed matrix composed of olivine, orthopyroxene, and clinopyroxene. Its homogenous distribution of interstitial pyroxenes contradicts mechanical mixing. Instead, extensive phase mixing under near-steady-state conditions is documented by the constant grain size and by phase boundary percentages > 60 % for the entire mylonitic unit and all the microstructural domains. Lobate phase boundaries, homogenous phase mixing, and secondary-phase distribution, as well as continuous geochemical trends that are independent of the microstructural domain, point to a reaction-driven, metasomatic formation of the mixed matrix and pyroxene porphyroclast tails in the entire shear zone. An OH-bearing metasomatism by small fractions of evolved melts is indicated by amphibole abundance in pyroxene neoblast tails, olivine B-type-crystallographic-preferred orientations (CPOs), and the microstructural consistency of the garnet–spinel (grt–spl) mylonites from both major peridotite massifs of the Gibraltar arc, Ronda, and Beni Bousera (Morocco). The established syn-deformational temperature of 800–900 ∘C at 1.95–2.00 GPa suggests that the metasomatism did not reset the equilibrium temperatures. Consistent geochemistry and phase assemblage in mylonites and tectonites but a change from equiaxial (tectonites) to wedge-shaped pyroxenes aligned parallel to the foliation (mylonites) point to a pre- to syn-deformational metasomatism, with the potential annealing of the tectonites. For the mylonitic mixed matrix, wedge-shaped pyroxenes, and neoblast tail formation in pyroxene porphyroclast stress shadows point to the activity of incongruent dissolution–precipitation creep. Apart from the dissolution–precipitation creep, strong CPOs of all major phases (ol, opx, and cpx) suggest dislocation creep as being the major deformation mechanism in the entire shear zone.

ORTHOPTERA OF AMURSKAYA OBLAST

An annotated list of 73 species from 50 genera and 7 families of orthopteran insects (Orthoptera) reliably noted for the Amurskaya oblast is given based on collection materials and literature data. Grasshoppers (Acrididae) and bush-crickets (Tettigoniidae) are best represented (38 and 19 species, respectively) while other families included of 1–7 species each. The Transpalaearctic (30%), Eastern-Palaearctic (30%) and Palaearchearctic (25%) species are dominated in the fauna of the Amurskaya oblast. Here lies the eastern boundary of the ranges of Transpalaearctic and Eastern-Palearctic species (Arcyptera fusca, Gomphocerippus rufus, Myrmeleotettix palpalis, and Psophus stridulus) and the northwestern boundary of 13 species known from the Pacific regions of East Asia (Atlanticus brunneri, Chizuella bonneti, Tettigonia uvarovi, Eobiana engelhardti, Ruspolia yezoensis, Shagniana ussuriana, Uvarovites inflatus, Oecanthus longicauda, Dianemobius csikii, Pteronemobius gorochovi, Xya japonica, Gryllotalpa orientalis, and Arcyptera orientalis).

Study of the Water Vole (Arvicola amphibius) at the Northwestern Boundary of Its Range

Study of the Water Vole (Arvicola amphibius) at the Northwestern Boundary of Its Range

Relationship between hydrogeochemical characteristics of hot springs and seismic activity in the Jinshajiang fault zone, Southeast Tibetan Plateau

Significant anomalous hydrogeochemical changes in hot spring water are detected during strong seismic cycles. It is now necessary to clarify the relationship between tectonic movements, earthquakes and the evolution of hot springs. In this paper, laboratory analyses of major, trace elements, δD, δ18O and 87Sr/86Sr values of 28 hot spring waters in the Jinshajiang fault zone (JSJFZ) in the northwestern boundary of the Sichuan-Yunnan block were conducted. The results showed that the primary source of water for JSJFZ hot springs was atmospheric precipitation. The geothermal reservoir temperature variation based on the silicon enthalpy mixing model ranged from 73 to 272°C. And the circulation depth range was 1.2–5.4 km. The segmentation characteristics of the 87Sr/86Sr values were related to the influence of source rocks on groundwater cycle processes. A conceptual model of the hydrologic cycle of hot springs explained the spatial distribution of earthquakes associated with tectonic movements. The Batang segment had the strongest water-rock reaction, the highest reservoir temperature and the deepest circulation depth; meanwhile, it was also an earthquake prone area. The fluid circulation of the JSJFZ corresponds well with the seismicity, which indicates that the hydrological characteristics of the hot spring water in a fracture zone play a crucial role in receiving information on seismic activity.

Tectonic affinity and significance of the Qilian Block: Evidence from river sediments in the Central Qilian Belt

The tectonic affinity of the Qilian Block is crucial to reconstructing the ocean-continent configuration of Rodinia. This study integrates previous studies with new whole-sample Nd and zircon U-Pb-Hf isotopic data from modern river sediments to identify the origin of the Qilian Block and its tectonic role in the Rodinia supercontinent cycle. Zircon U-Pb-Hf data in combination with whole-sample/whole-rock Nd and Pb isotopic data indicate that the Central Qilian Belt (CQB) shows close tectonic affinity with the Hualong and North Wulan terranes and together constituted a coherent Qilian Block crustal domain, whereas the Quanji Block likely underwent an independent evolution prior to the early Paleozoic orogeny. A comprehensive assessment of geochronological and whole-rock geochemical-isotopic data reveal that the Precambrian basement of the Qilian and Alxa blocks experienced similar historical evolutions and possibly formed a coherent Qaidam-Altyn-Qilian-Alxa continent before the breakup of Rodinia. Moreover, the Qaidam-Altyn-Qilian-Alxa continent was probably once part of the Yangtze Block, laying along the periphery of the supercontinent Rodinia. Therefore, the northwestern boundary of the Yangtze-affinity block can extend to the Alxa Block and the Qilian Ocean is a branch of the proto-Tethys Ocean. A micro-block can serve as a window into reconstructing the ocean-continent configurations of supercontinents during certain periods.

“Cold and wet” and “warm and dry” climate transitions at the East Asian summer monsoon boundary during the last deglaciation

Studies on millennial‒centennial abrupt climate events during the last deglaciation have significant relevance to modern-day abrupt and extreme climate changes that are occurring more frequently in the context of global warming. The northwestern margin of the modern East Asian summer monsoon (EASM) region is particularly sensitive to such climatic changes. In this study, we employed the continuous sedimentary core sequence of Dali Lake, located on the north-western edge of the EASM region. Carbonate clumped isotope (Δ47) thermometry was applied to both fine-grained endogenic carbonates and ostracod (Limnocythere inopinata [Baird]) shells in the lake core sediments to quantitatively reconstruct lake water temperature and oxygen isotope (δ18OW [VSMOW]) changes during the period from approximately 15.6–10.5 cal kyr BP (calibrated years before the present; abbreviated to “kyr”). Fine-grained endogenic carbonate Δ47 temperatures suggest that the lake surface water temperature changes may have been mainly controlled by the northern high latitudes, reflected in the corresponding millennial‒centennial abrupt climate events (such as a 5–6 °C decrease of summer surface water temperature during approximately 12.9–11.8 kyr, indicative of Younger Dryas [YD] cooling). Ostracod shell Δ47 temperatures complement the endogenic carbonates but appear to be affected by changes in calcification season, likely linked to climatic changes. These data suggest a climatic shift at approximately 15.2 kyr, before the onset of the Bølling‒Allerød (BA) interstadial, which is interpreted as general warming.δ18OW from the endogenic carbonates is interpreted as changes in precipitation and conforms well with 18O isotope changes in Greenland ice cores, suggesting that the precipitation changes may have been influenced by the northern high latitudes. Regional rainfall increased during the Heinrich event 1 (H1) and YD stadials, whereas it appears to have decreased in the BA and during the early Holocene (EH). This study indicates that the primary climate pattern at the northwestern boundary of the EASM region during the last deglaciation was characterized by alterations of “cold and wet” and “warm and dry” climate, rather than the more typical “cold and dry” versus “warm and wet” pattern.

On the north equatorial current spatiotemporal modes and responses in the western boundary currents

The North Equatorial Current (NEC) and western boundary currents (WBCs) of the Kuroshio Current (KC) and the Mindanao Current (MC) characterize the circulation pattern and water mass transports in the tropical western North Pacific. We utilized the validated three-dimensional and time-dependent China Sea Multi-scale Ocean Modeling System to investigate the variability of the WBCs and the physical processes linked with the upstream NEC and associated with the circulation. The latitude-dependent KC and MC strengthen downstream from the NEC bifurcation (NB) and are maintained by the northern and southern parts of the NEC, respectively. By effectively isolating the NEC spatiotemporal modes representing its intensity, meridional migration, and bifurcation location, we investigate the responses of the WBCs to the characteristics in an integrated NEC-WBCs current system. The NEC intensity peaks in spring and summer, while its bifurcation location strongly correlates with its migration. The southward (northward) NEC migration during early spring (late autumn) feeds more NEC waters to the MC (KC). Yet, the simultaneous southward (northward) shifting NB distributes more NEC waters to the KC (MC) and offset the contribution of the migration. Thus, the intensity of the KC (MC) is primarily controlled by the NEC intensity, reaching the maximum during spring (summer). The specific water masses such as the North Pacific Tropical Water and the Equatorial Surface Water, are bounded by the time-dependent NB, distributing northward and southward respectively through the WBCs. By resolving spatiotemporal modes in NEC-KC-MC, the study provides a new understanding to the WBCs in the NEC-WBCs current system.

Multiple Mantle Sources of High‐Magnesium Terranes on Mercury

AbstractThe composition and interior structure of Mercury's mantle are poorly known but critical to understanding its magma ocean differentiation, mantle dynamics, and crustal petrogenesis. Various crustal geochemical terranes are identified on Mercury based on their Mg/Si and Al/Si values, but element abundances exhibit a weak correlation with surface reflectances. The high‐magnesium region (HMR), which includes end‐members for both reflectance spectral units (high‐reflectance plains and low‐reflectance materials (HRP and LRM)) and geochemical terranes (Mg and Al contents), contains important information about Mercury's mantle composition and dynamics. We propose that the northwestern boundary of HMR can be extended to the Sobkou basin and its ejecta deposits. Within the resolution limit of element maps, we notice that mantle materials beneath the Sobkou basin have an elevated content of magnesium, and a large area of HRP‐like materials in HMR exhibit Mg/Si greater than 0.5. Our results suggest that HMR was formed by partial melting of heterogeneous mantle sources in terms of compositions, supporting the existence of stratified and/or lateral geochemical diversities in the mantle. While typical HRP on Mercury, including the Borealis Planitia and Caloris interior plains formed by effusive volcanism around 3.7 Ga, exhibit a lower Mg/Si than the global average, the Rachmaninoff interior plains emplaced by volcanism at 1.7 Ga exhibit a Mg/Si greater than 0.5. This observation indicates that local thermal anomalies may be prolonged in the mantle, inducing a higher degree of partial melting. We also report a weak correlation between the global LRM and magnesium content in the crust.

Holocene Millennial‐Scale Precipitation Variations in the Asian Summer Monsoon Margin of Northwest China and Their Relation to Migrations of Monsoon Northern Boundary via Oxygen Isotope Analysis of Calcareous Root Tubes in Deserts

AbstractThe Asian summer monsoon (ASM) margin of northwest China is a critical region for studying Asian monsoon variability during the Holocene. However, the pattern of precipitation variations and migration of the ASM northern boundary in arid regions during the Holocene remains unclear. In this study, we analyzed oxygen isotopes of 70 calcareous root tube (CRT) samples from the desert hinterlands in the ASM margin of northwest China, including the Badain Jaran, Tengger, Ulan Buh, and Kubuqi deserts. The CRT samples were analyzed to reconstruct millennial‐scale precipitation variation patterns during the Holocene and further explored the location of the ASM northwestern boundary during the middle Holocene. Our results demonstrated that the δ18O values of CRTs during the late Holocene (4.0–1.0 cal kyr BP) were all less negative than those during the middle Holocene (8.0–4.0 cal kyr BP), which revealed that the precipitation decreased from the middle Holocene to the late Holocene. Moreover, an increase in δ18O values from the southeast to northwest revealed that the precipitation decreased. We argued that the Holocene millennial‐scale precipitation changes in this region were influenced by the migrations in the ASM northern boundary. During the middle Holocene, due to the strong summer solar radiation and reduced ice sheets, the ASM northern boundary in the arid region advanced by at least 250 km to the northwest, which resulted in increased precipitation. During the late Holocene, the ASM northern boundary retreated southeastward, resulting in decreased precipitation.

Active faults, Paleoseismological trenching and seismic hazard assessment in the Northern Mygdonia Basin, Northern Greece: The Assiros-Krithia fault and the Drimos fault zone

The Plio-Quaternary Mygdonia Basin in Northern Greece is bounded by active normal faults that can host significant earthquakes and produce considerable damage to the city of Thessaloniki (the second biggest city in Greece – 1 million population), located only 15–20 km away. In 1978, a damaging M = 6.5 earthquake occurred along a fault in the southern part of the basin, generating primary and secondary surface ruptures. This manuscript offers the results of the first detailed geomorphological and paleoseismological investigations in the northern part of the basin. As a result: i) a new active normal fault has been mapped, the Assiros-Krithia fault (AKF); and ii) another fault zone that has been assessed with probable activity in the literature, the Drimos fault zone (DFZ), has been confirmed active and mapped in detail. Paleoseismological trenching investigations supported by radiometric dating were carried out along both structures. The AKF and DFZ form the northern and northwestern boundaries of the Mygdonia Basin, respectively. The AKF deflects the local drainage network and is expressed as a single north dipping localised fault trace, gently uplifting the northern part of the Mygdonia Basin. The last event produced 48 cm of vertical displacement around 4540 cal. yrs BP, and the fault has an estimated slip rate of ∼0.1 mm/yr. The DFZ is an 8-10 km-long NW-SE trending normal fault that dips and downthrows to the NE (045o-050o). It is characterised by distributed deformation across eight major and secondary fault planes. Four of these planes have been activated over the last 9000 years, therefore the structure is Holocene active. The DFZ has an estimated slip rate of 0.1–0.3 mm/yr and may merged with the Liti-Gerakarou fault zone in multi-segment ruptures. The DFZ highlights that NW-SE trending faults are potentially active in Northern Greece. Their long recurrence intervals justify why they were not activated during the period covered by the historical record and emphasise, once again, the necessity of paleoseismological studies and the implementation of fault specific approaches in seismic hazard assessment.

The Castle Rock and Ironside Mountain calderas, eastern Oregon, USA: Adjacent venting sites of two Dinner Creek Tuff units—the most widespread tuffs associated with Columbia River flood basalt volcanism

Abstract The Dinner Creek Tuff is an important unit of mid-Miocene rhyolite volcanism contemporaneous to flood basalts of the Columbia River magmatic province. Field mapping along with analytical data of tuff samples identify two calderas, the Castle Rock and Ironside Mountain calderas, as the venting sites of two widespread ignimbrites of the Dinner Creek Tuff. Both calderas lie within the area of the proposed general storage sites of main-phase Columbia River Basalt magmas. The Castle Rock caldera formed during the eruption of the 16.16 Ma Dinner Creek Tuff unit 1. The northwestern boundary of the caldera is roughly defined by the juxtaposition of over 300 m of densely welded rheomorphic intra-caldera tuff and tuffaceous mega-breccia deposits against Mesozoic Weathersby Formation shale and pre-Miocene Ring Butte trachybasalt lavas. Following caldera collapse, fluvial and lacustrine volcaniclastic sediments were deposited on the caldera floor, and outflow tuffs of the Dinner Creek Tuff units 2 and 4 were deposited into the caldera. Aphyric basaltic andesite and icelandite (Fe-rich andesite), which correlate stratigraphically to upper Grande Ronde Basalt lavas, intrude the caldera floor deposits, and lavas are interbedded with sediments and Dinner Creek Tuff unit 4. The Ironside Mountain caldera formed during eruption of the 15.6 Ma Dinner Creek Tuff unit 2, which lies ~15 km north of the Castle Rock caldera. The caldera is an 11 × 6 km depression wherein over 900 m of intra-caldera, rheomorphic, and partially welded tuff are bound by Weathersby Formation shale and Tureman Ranch granodiorite. Post-caldera collapse, basaltic andesite and icelandite dikes and sills that are also stratigraphically correlative to upper Grande Ronde Basalt lavas intruded into the tuff, mostly along the margins of the caldera, which altered much of the tuff. Mafic lavas within the study area that closely pre- and post-date Dinner Creek Tuff units were correlated with regional units of the Columbia River Basalt Group. Porphyritic and aphyric mafic lava flows underlying Dinner Creek Tuff unit 1 at Castle Rock are correlated with Picture Gorge Basalt and Grande Ronde Basalt. Aphyric basaltic andesite and icelandite that intrude into and overlie the Dinner Creek Tuff units 1 and 2 are westward extensions of fractionated tholeiitic magmas as seen in late-stage Grande Ronde Basalt units such as the Hunter Creek Basalt. Finally, porphyritic basalt lava flows that overlie the Hunter Creek Basalt and volcaniclastic sediments at the Castle Rock caldera are correlative with the 13.5 Ma Tim's Peak Basalt. At Castle Rock, pre-caldera Columbia River Basalt Group lavas appear to lap onto a mid-Miocene topographic high that stretches northward and westward for tens of kilometers based on stratigraphic data, and it may be related to regional uplift at initial impingement of the mantle upwelling to produce the Columbia River Basalt Group. The Castle Rock and Ironside Mountain calderas exemplify bimodal volcanism of the Columbia River magmatic province. Eruption of rhyolites is closely pre- and post-dated by the eruption of local and regional tholeiitic lavas belonging to the Columbia River Basalt Group. The local eruption of evolved tholeiitic lavas likely concealed calderas, but these lavas also illustrate the close proximity of mafic and rhyolitic magmas at depth at these rhyolite centers. Consequently, the stratigraphy of both the Castle Rock and Ironside Mountain calderas somewhat differs from that of rhyolite calderas dominated by silicic and calc-alkaline intermediate pre- and post-caldera volcanism.

Diversity Study of Freshwater Fishes in Manimala River, Pathanamthitta, Kerala, India

The present study deals with the species diversity of fishes in Manimala River with reference to Eraviperoor region, Pathanamthitta, Kerala, India. The Manimala River forms the northern and north-western boundary and Varattar (a branch of river Pamba) forms the southern boundary of the study area. The wetlands (mainly paddy fields) consist of 18 small to medium-sized water bodies functioning as a water source for agriculture. A chain of canals connects many of them in the lower areas while the remaining ones get interconnected during monsoon floods during which the movement of fishes from rivers to other water bodies takes place. These small water bodies are extremely significant for the preservation and sustenance of the biodiversity of fishes. 24 species belonging to 12 families and 5 orders were collected and identified. This includes10 species from the family Cyprinidae, 3 species from the family Channidae, 2 species from family Cichlidae, and 1 species each from families Hemiramphidae, Belonidae, Anabantidae, Osphronemidae, Heteropneustidae, Claridae, Siluridae, Tetraodontidae, and Ambassidae.

Opposite Sense of Strike‐Slip Faulting and Crustal Rotation Accommodating Left‐Lateral Shear Between the Tianshan Mountains and Kazakh Platform

AbstractTectonic deformation of blocks neighboring fault zones has been thought to aid in accommodating regional displacements. In general, these block‐bounding faults possess continuous geometry and similar kinematics. However, the northwestern boundary of the Tianshan Mountains (NWBTS) involves two groups of faults that strike NW and NE. GPS velocities show that contemporary deformation takes place in a zone of 300 km wide in the NWBTS and is roughly dominated by left‐lateral shear. Left‐lateral shear motion of ∼5–6 mm/yr along the NWBTS is accommodated by right‐lateral slip and counterclockwise rotation of fault wallrocks on the NW‐striking faults and left‐lateral faulting on the NE‐striking faults. Present‐day deformation associated with the ongoing India‐Eurasia collision in the NWBTS is best described as the opposite sense of strike‐slip faulting and crustal rotation. The difference in lithospheric strengthening between the Kazakh Platform and Tianshan deflects strain toward the northeast and drives the dynamic process in this region.

Turbulent mixing and its contribution to the oxygen flux in the northwestern boundary current region of the Japan/East Sea, April–October 2015

The Japan/East Sea is well ventilated and is the most oxygen-rich region in the Pacific. However, quantitative estimates of the turbulent fluxes are missing due to a lack of observational data. To assess turbulent mixing, we employ data from the moored profiler Aqualog survey of April–October 2015 near the northwestern boundary of this region where the oxygen maximum is observed. The survey allowed observation of collocated depth profiles of conductivity, temperature, ocean current, and dissolved oxygen 8 times per day. The data were processed by using the Mixing (MX) Oceanographic Toolbox based on the fine-scale parameterization of turbulent dissipation. The dissipation rate, the eddy diffusivity and the diapycnal fluxes of heat, salt and oxygen are estimated in the depth range from 130 to 350 m throughout the profiler deployment period. The survey-averaged diffusivity increased with depth from 0.5 × 10 −5 to 4.0 × 10 −5 m 2 s −1 . The month-to-month variability in the mixing in the intermediate water is presented. Early in May 2015, a transition in mixing occurred from the winter regime with upward turbulent fluxes of both heat and salt to the summer regime with the downward mixing of heat. The turbulent mixing was elevated in June when large anticyclonic eddies passed the profiler mooring. The application of the eddy diffusivities to the profiler mooring oxygen data yields an average downward oxygen flux of roughly 8.6 mol m −2 month −1 . • 6-month survey using a moored profiler in the northern Japan/East Sea. • Collocated fine-structure data profiles in the westward coastal current. • Turbulent mixing induced by internal wave breaking was quantitatively assessed. • Turbulence was enhanced due to passage of eddies and after the atmospheric storms. • Turbulent oxygen flux was directed from the intermediate water downward in the summer.

Coupling between surface processes and crustal deformation: Insights from the late Cenozoic development of the Qaidam Basin, China

A central issue when studying landscape evolution is to quantify the effect of surface processes on tectonic deformation. To address this question, we systematically examine the relationship between the late Cenozoic pattern of sedimentary dispersal system in the endorheic Qaidam Basin in the northern Tibetan Plateau and its spatiotemporal variation in hydrological conditions. At present, the depocenter of the Qaidam Basin is located in the southern Qaidam Basin, which correlates with the largest stream runoff, whereas smaller depressions are located in the northern Qaidam Basin owing to lower stream runoffs. The northwestern boundary without obvious runoff corresponds to large-scale modern erosion regions in the northwestern Qaidam Basin. Based on these findings, good spatiotemporal couplings between sedimentary depressions and hydrological conditions have been proved in the Qaidam Basin, indicating that the changing hydrological pattern in the basin-bounding ranges has played as a first-order role in controlling the Quaternary landscape evolution of the Qaidam Basin. • Spatiotemporal coupling of hydrological condition and basin infilling in Qaidam Basin. • Widespread Quaternary overlapping at all the three margins of Qaidam Basin. • Hydrological pattern changes Quaternary sedimentary distribution in Qaidam Basin.

Spatio-Temporal Characteristics of Dry-Wet Conditions and Boundaries in Five Provinces of Northwest China from 1960 to 2020

The study of dry-wet climate boundaries in the context of climate warming is of great practical significance for improving the environment of ecologically fragile zones and promoting economic and natural sustainable development. In this study, based on the daily meteorological data of 110 stations, using the wetness index, empirical orthogonal function decomposition, regime shift detection test, Fourier power spectrum, and Kriging interpolation, the researchers analyzed the spatiotemporal characteristics of dry-wet conditions and boundaries in five provinces of Northwest China from 1960 to 2020. The results showed that the overall wetness index increased in the past 61 years, but with significant internal differences, among which the western and central climate tended to be warm and wet, and the eastern tended to be warm and dry. The annual wetness index changed abruptly in 1986 with cycles of 3.61 a, 7.11 a and 8.83 a. The mutations occurred correspondingly in spring, summer, autumn, and winter in 1972, 1976, 1983, and 1988, with periods of 3.88 a and 4.92 a, 2.18 a and 2.81 a, 2.15 a, and 2.10 a, respectively. The dry-wet climate boundary has fluctuated markedly since 1960. The extreme arid and arid regions boundary shifted southward and shrank in size until the extreme arid region disappeared in the 2010s. The arid along with semi-arid regions and semi-arid in addition to semi-humid regions boundaries both have two boundary lines, and show the shift of the northwestern boundary to the southeast and the southeastern boundary to the northwest, with the area of the arid together with semi-arid regions shrinking significantly by 5.64%, simultaneously, the area of the semi-humid region area expanding significantly by 84.11%. The boundary of semi-humid and relatively humid regions, and the boundary of relatively humid and humid regions all shifted to the southeast, moreover, the area of the relatively humid region and humid region shrank significantly by 12.08%. The expansion of semi-humid region and the contraction of other climate regions are characteristics of the dry-wet climate variability in five provinces of Northwest China. The area of the three arid climate zones dwindled by 9.61%, and the area of the three humid zones extended by 39.01%. Obviously, the climate inclined to be warm and humid in general.