Tertiary geodynamics of Sakhalin (NW Pacific) from anisotropy of magnetic susceptibility fabrics and paleomagnetic data   总被引：1，自引：0，他引：1  

Richard Weaver  Andrew P Roberts  Rachel Flecker  David I.M Macdonald   《Tectonophysics》2004,379(1-4):25-42

Sakhalin has been affected by several phases of Cretaceous and Tertiary deformation due to the complex interaction of plates in the northwest Pacific region. A detailed understanding of the strain is important because it will provide constraints on plate-scale processes that control the formation and deformation of marginal sedimentary basins. Anisotropy of magnetic susceptibility (AMS) data were obtained from fine-grained mudstones and siltstones from 22 localities in Sakhalin in order to provide information concerning tectonic strain. AMS data reliably record ancient strain tensor orientations before significant deformation of the sediments occurred. Paleomagnetically determined vertical-axis rotations of crustal rocks allow rotation of the fabrics back to their original orientation. Results from southwest Sakhalin indicate a N035°E-directed net tectonic transport from the mid-Paleocene to the early Miocene, which is consistent with the present-day relative motion between the Okhotsk Sea and Eurasian plates. Reconstruction of early–late Miocene AMS fabrics in east Sakhalin indicates a tectonic transport direction of N040°E. In west Sakhalin, the transport direction appears to have remained relatively consistent from the Oligocene to the late Miocene, but it has a different attitude of N080°E. This suggests local deflection of the stress and strain fields, which was probably associated with opening of the northern Tatar Strait. A northward-directed tectonic transport is observed in Miocene sediments in southeast Sakhalin, mid-Eocene sediments in east Sakhalin, and in Late Cretaceous rocks of west and northern Sakhalin, which may be associated with northwestward motion and subduction of the Pacific Plate in the Tertiary period. The boundaries of the separate regions defined by the AMS data are consistent with present-day plate models and, therefore, provide meaningful constraints on the tectonic evolution of Sakhalin.  相似文献   

Introduction: Doing cultural geography     

Chris Gibson  Lauren Costello  Rachel Hughes 《The Australian geographer》2004,35(2):123-130

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Seasonal Variability of Adsorption and Exchange Equilibria in Soil Waters   总被引：2，自引：0，他引：2  

Robert a. Berner  Ji-Long Rao  Soobum Chang  Rachel O'brien  C. Kent Keller 《Aquatic Geochemistry》1998,4(2):273-290

Chemical analyses for major ions have been conducted on waters,collected on an approximately weekly basis over the period April, 1993 toNovember, 1996, that drain three small experimental ecosystems(sandboxes) at Hubbard Brook, New Hampshire. One sandbox is planted withpine trees, another with grass, and the third is left bare (actually itis covered sporadically by bryophytes and lichens). Results show linearcorrelations, independent of discharge, between the concentrations ofdissolved Na⁺ and K⁺ on the one hand andCa⁺⁺ and Mg⁺⁺ on the other for all threesandboxes. No correlations between singly charged and doubly chargedcations were found. These correlations are interpreted to represent cationexchange equilibria between soil waters and clay minerals plus soil organicmatter. The correlation slope, representing the exchange constant, for Na vsK is different for the pine-covered sandbox than for the other two whereasfor Ca vs Mg the correlation is independent of the presence or absence oftrees. We interpret this as representing a shift of cation exchangeequilibria in the pine sandbox by the activities of growing trees.Concentrations of Na, K, Ca, Mg, and H₄SiO₄from the barren and grass-lined sandboxes were found to vary seasonally witha marked sinusoidal pattern which was independent of the discharge from eachsandbox. (The discernment of a similar pattern in the tree lined sandbox wasdifficult due to a lack of discharge over much of the year.) Concentrationmaxima occurred in August and minima in February, and there is a closeparallelism with soil temperature. We interpret this as representingtemperature induced variations in cation exchange equilibria and silicaadsorption. Independence from highly varying water discharge, e.g.,. thataccompanying severe rainstorms, indicates rapidly re-attained equilibrium.Variations in the concentrations of cations are likely due to exchange withunmeasured cations, probably H⁺ or dissolved Al species, as aresult of possible seasonal changes in internal acid production and externalinput of acid rain to the sandboxes. Internal production may represent aresponse to seasonal changes in respiration rate as it responds toseasonally varying temperature. Added to this is the effect of temperatureon exchange equilibrium. Seasonal variations in dissolved silica are mostlikely due to the dependence of adsorption/desorption equilibria ontemperature. The temperature dependence of a number of silica-consumingreactions are consistent with the measured values.  相似文献   

Weighing a galaxy bar in the lens Q2237 +=0305     

RobertSchmidt  Rachel L.Webster  Geraint F.Lewis 《Monthly notices of the Royal Astronomical Society》1998,295(2):488-496

In the gravitational lens system Q2237+0305 the cruciform quasar image geometry is twisted by 10c by the lens effect of a bar in the lensing galaxy. This effect can be used to measure the mass of the bar. We construct a new lensing model for this system with a power-law elliptical bulge and a Ferrers bar. The observed ellipticity of the optical isophotes of the galaxy leads to a nearly isothermal elliptical profile for the bulge, with a total quasar magnification of 16⁺⁵₋₄. We measure a bar mass of (7.5 ∼ 1.5) −10⁸ h ⁻¹₇₅ M⊙ in the region inside the quasar images.  相似文献   

Cold dark matter variant cosmological models — I. Simulations and preliminary comparisons     

Michael A. K. Gross  Rachel S. Somerville  Joel R. Primack  Jon Holtzman  & Anatoly Klypin 《Monthly notices of the Royal Astronomical Society》1998,301(1):81-94

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Fluoride-Selective Electrode as a Tool to Evaluate the Degradation of PFAS in Groundwater: A Bench-Scale Investigation     

Janice Stonebridge  Rachel Baldwin  Neil R. Thomson  Carol Ptacek 《Ground Water Monitoring & Remediation》2020,40(2):73-80

Fluoride (F⁻) concentration in groundwater can be used as an independent measure of the degradation of per- and polyfluoroalkyl substances (PFAS) at contaminated sites. This study assessed the impact of the groundwater matrix, oxidizing reagents, quenching agent, and sample handling procedures (filtration) on determinations of F⁻. F⁻ was quantified using a fluoride-selective electrode (FSE) using matrix spike recovery (acceptable range 75 to 125%) and electrode slope performance (ideal range −54 to −60 mV). For the unaltered aqueous matrices considered (ultrapure water, ultrapure water with sodium chloride, and simulated groundwater), matrix spike recoveries were greater than 93% and acceptable electrode slopes (−59.5 ± 0.2 mV) were obtained. Matrix spike recoveries and electrode slopes when persulfate or permanganate was added were 87 and 93%, and −58.4 ± 1.3 and −47.3 ± 2.2 mV, respectively. Therefore, quantifying F⁻ in matrices containing permanganate should involve use of either a matrix-matched calibration curve or the method of standard additions due to the low electrode slope. The addition of ascorbic acid as a quenching agent resulted in a decrease in matrix spike recoveries to <74% and suggests alternate quenching procedures should be used if an FSE is employed to measure F⁻. Removal of sediments by filtration prior to the addition of the fluoride spike led to improved matrix spike recoveries (>96%), which were otherwise underestimated using the FSE in the presence of sediments. While the FSE may be a quick and portable tool, its significant limitations need to be fully understood before it can be used to quantify the production of F⁻ resulting from the potential degradation of PFAS at field sites.  相似文献   

Order of diagenetic events controls evolution of porosity and permeability in carbonates     

Aleksandra Hosa  Rachel Wood 《Sedimentology》2020,67(6):3042-3054

The properties of carbonate rocks are often the result of multiple, diagenetic events that involve phases of cementation (porosity occlusion) and dissolution (porosity enhancement). This study tests the hypothesis that the order of these events is a major control on final porosity and permeability. A three-dimensional synthetic model of grainstone is used to quantify trends that show the effect of early cementation, non-fabric selective dissolution, and then a second-generation of (post-dissolution) cement. Models are 3 mm³ with a resolution of 10 μm. Six simple paragenetic sequences are modelled from an identical starting sediment (without accounting for compaction) where the same diagenetic events are placed in different sequences, allowing for quantification of relative changes in the resultant porosity and permeability for each diagenetic event, the trajectory through time, as well as for each final rock. All modelled paragenetic sequences result in reductions in porosity and permeability, but the order of diagenetic events controls the trajectory and final rock properties. Differences in the order of early cement precipitation alone produce variable final values, but all follow the porosity–permeability relationship as expressed by the Kozeny-Carman equation. However, final values for the sequences which include a phase of dissolution fall on a new curve, which departs from that predicted by the Kozeny-Carman relationship. This allows an alternative form of porosity–permeability relationship to be proposed: κ = 2280ϕ–30,400, where ϕ is porosity (%) and κ is permeability (mD). Hence while the Kozeny-Carman relationship predicts porosity–permeability changes that occur with cementation, it is unable to capture accurately changes within the pore network as a result of dissolution. Although the results may be dependent on the properties of the initial carbonate sediment and simplified diagenetic scenarios, it is suggested that this new porosity–permeability relationship may capture some generalized behaviour, which can be tested by modelling further sediment types and diagenetic scenarios.  相似文献   

The deglaciation of the western sector of the Irish Ice Sheet from the inner continental shelf to its terrestrial margin     

David H. Roberts  Colm Ó Cofaigh  Colin K. Ballantyne  Matthew Burke  Richard C. Chiverrell  David J. A. Evans  Chris D. Clark  Geoff A. T. Duller  Jeremy Ely  Derek Fabel  David Small  Rachel K. Smedley  S. Louise Callard 《Boreas: An International Journal of Quaternary Research》2020,49(3):438-460

This paper provides a new deglacial chronology for retreat of the Irish Ice Sheet from the continental shelf of western Ireland to the adjoining coastline, a region where the timing and drivers of ice recession have never been fully constrained. Previous work suggests maximum ice-sheet extent on the outer western continental shelf occurred at ~26–24 cal. ka BP with the initial retreat of the ice marked by the production of grounding-zone wedges between 23–21.1 cal. ka BP. However, the timing and rate of ice-sheet retreat from the inner continental shelf to the present coast are largely unknown. This paper reports 31 new terrestrial cosmogenic nuclide (TCN) ages from erratics and ice-moulded bedrock and three new optically stimulated luminescence (OSL) ages on deglacial outwash. The TCN data constrain deglaciation of the near coast (Aran Islands) to ~19.5–18.5 ka. This infers ice retreated rapidly from the mid-shelf after 21 ka, but the combined effects of bathymetric shallowing and pinning acted to stabilize the ice at the Aran Islands. However, marginal stability was short-lived, with multiple coastal sites along the Connemara/Galway coasts demonstrating ice recession under terrestrial conditions by 18.2–17. ka. This pattern of retreat continued as ice retreated eastward through inner Galway Bay by 16.5 ka. South of Galway, the Kilkee–Kilrush Moraine Complex and Scattery Island moraines point to late stage re-advances of the ice sheet into southern County Clare ~14.1–13.3 ka, but the large errors associated with the OSL ages make correlation with other regional re-advances difficult. It seems more likely that these moraines are the product of regional ice lobes adjusting to internal ice-sheet dynamics during deglaciation in the time window 17–16 ka.  相似文献   

The trophic ecology of key megafaunal species at the Pakistan Margin: Evidence from stable isotopes and lipid biomarkers     

Rachel M. Jeffreys  George A. Wolff  Sarah J. Murty 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1816-1833

The Arabian Sea is subject to intense seasonality resulting from biannual monsoons, which lead to associated large particulate fluxes and an abundance of organic carbon, a potential food source at the seafloor for benthic detritivores. We used the stable isotopes of carbon and nitrogen alongside lipid analyses to examine potential food sources (particulate and sedimentary organic matter, POM and SOM respectively) in order to determine trophic linkages for the twelve most abundant megafaunal species (Pontocaris sp., Solenocera sp., Munidopsis aff. scobina, Actinoscyphia sp., Actinauge sp., Echinoptilum sp., Pennatula aff. grandis, Astropecten sp. Amphiura sp. Ophiura euryplax, Phormosoma placenta and Hyalinoecia sp.) at the Pakistan Margin between 140 and 1400 m water depth. This transect spans a steep gradient in oxygen concentrations and POM flux. Ranges of δ¹³C and δ¹⁵N values were narrow in POM and SOM (4‰ and 2‰ for δ¹³C and δ¹⁵N, respectively) with little evidence of temporal variability. Labile lipid compounds in SOM originating from phytoplankton did exhibit seasonal change in their concentrations at the shallowest sites, 140 and 300 m. Benthic megafauna had broad ranges in δ¹³C and δ¹⁵N (>10‰ and >8‰ for δ¹³C and δ¹⁵N, respectively) suggesting they occupy several trophic levels and utilize a variety of food sources. There is evidence for feeding niche separation between and within trophic groups. Lipid biomarkers in animal tissues indicate a mixture of food sources originating from both phytoplankton (C_20:5(n-3) and C_22:6(n-3)) and invertebrate prey (C_20:1 and C_22:1). Biomarkers originating from phytodetritus are conserved through trophic transfer to the predator/scavengers. Six species (Pontocaris sp., Solenocera sp., Actinoscyphia sp., Echinoptilum sp., Amphiura sp. and Hyalinoecia sp.) showed a significant biochemical response to the seasonal supply of food and probably adapt their trophic strategy to low food availability. Biotransformation of assimilated lipids by megafauna is evident from polyunsaturated fatty acid distributions, for example, Echinoptilum sp. converts C_20:5(n-3) to C_24:6(n-3).  相似文献   

Results from the Wide Angle Search for Planets Prototype (WASP0) – III. Planet hunting in the Draco field     

Stephen R. Kane †  rew Collier Cameron  Keith Horne  David James  T. A. Lister  Don L. Pollacco  Rachel A. Street  Yiannis Tsapras 《Monthly notices of the Royal Astronomical Society》2005,364(3):1091-1103

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