Centrifuge modelling of deformation of a multi-layered sequence over a ductile substrate: 1. Style and 4D geometry of active cover folds during layer-parallel shortening     

Chris Yakymchuk  Lyal B. Harris  Laurent Godin 《International Journal of Earth Sciences》2012,101(2):463-482

Centrifuge analogue modelling illustrates the progressive development of active folds in multilayers upon a ductile substrate during layer-parallel shortening. Models simulate folding of a mechanically stratified sedimentary sequence upon migmatitic gneisses in a large hot orogen, or upon a thick basal evaporite ± shale sequence in deeper levels of fold belts. The absence of a weak low-viscosity and low-density layer at the interface promotes infolding of the cover sequence and ductile substrate, whereas a planar upper surface to the basal ductile substrate is preserved when it is present. Whilst fold style, wavelength, and deformation of the interface with the ductile substrate differ depending on whether a low-viscosity and low-density layer is present at the base of the cover sequence, there is no marked systematic curvature of fold axes as seen in previous sandbox models for fault-bend or fault propagation folding during bulk shortening. Bulk shortening of a layered sequence with relatively thick individual layers above a ductile substrate promotes a regular and upright train of buckle folds, whereas thinner layers promote a more irregular distribution of buckle folds with variable vergence, style, and amplitude. Buckle folds above a ductile substrate progressively develop during bulk shortening from open and upright, to angular and tight, and may further develop into cuspate structures above relatively weak horizons. Relatively thick weak horizons within the layered sequence during bulk shortening interrupt regular fold patterns up structural section and allow out-of-phase folds to develop above and below the weak horizon.  相似文献   

Food Web Structure and Trophic Control in Central Puget Sound     

Chris J. Harvey  Gregory D. Williams  Phillip S. Levin 《Estuaries and Coasts》2012,35(3):821-838

We developed a food web model of central Puget Sound to provide science-based support for ecosystem-based management and to refine our understanding of bottom-up and top-down trophic forcing. Phytoplankton accounted for a large fraction of total biomass, total throughput, and caused considerable bottom-up effects in most functional groups in a dynamic simulation fit to time series data from 1981 to 2000. Top-down control was most apparent in the case of bald eagles (Haliaeetus leucocephalus), which exhibited keystone tendencies and appeared capable of causing trophic cascades. Increasing top-down control in several predator–prey relationships improved model fits to time series data from 1981 to 2000, but not as much as introducing non-equilibrium dynamics (biomass accumulation terms) to several key vertebrates. Fishing had little effect on system dynamics. Our model appears well-suited for addressing strategic, scenario-based questions of how the community as a whole will respond to management actions.  相似文献   

Observation of Conditions Preceding Peak Indoor Air Volatile Organic Compound Concentrations in Vapor Intrusion Studies     

Chris Lutes  Chase Holton  Brian Schumacher  John Zimmerman  Andrew Kondash  Robert Truesdale MS  AB. 《Ground Water Monitoring & Remediation》2021,41(2):99-111

Temporal and spatial variability of indoor air volatile organic compound (VOC) concentrations can complicate vapor intrusion (VI) assessment and decision-making. Indicators and tracers (I&T) of VI, such as differential temperature, differential pressure, and indoor radon concentration, are low-cost lines of evidence to support sampling scheduling and interpretation of indoor air VOC sampling results. This study compares peak indoor air chlorinated VOC concentrations and I&T conditions before and during those peak events at five VI sites. The sites differ geographically and in their VI conceptual site models (CSM). Relative to site-specific baseline values, the results show that cold or falling outdoor temperatures, rising cross slab differential pressures, and increasing indoor radon concentrations can predict peak VOC concentrations. However, cold outdoor air temperature was not useful at one site where elevated shallow soil temperature was a better predictor. Correlations of peak VOC concentrations to elevated or rising barometric pressure and low wind speed were also observed with some exceptions. This study shows how the independent variables that control or predict peak indoor air VOC concentrations are specific to building types, climates, and VI CSMs. More I&T measurements at VI sites are needed to identify scenario-specific baseline and peak related I&T conditions to improve decision-making.  相似文献   

Antecedent controls on the spatial organization of yardangs on the Puna Plateau,north-western Argentina     

Elena A. Favaro  Chris H. Hugenholtz  Thomas E. Barchyn 《地球表面变化过程与地形》2021,46(15):3063-3077

Yardangs are streamlined ridges that form in arid environments on Earth and Mars through wind-driven abrasion of consolidated substrates. Currently, there is limited consensus on the mechanisms that initiate and establish patterns of yardangs on the landscape. In this work, we examine the spatial organization of yardangs in the Campo de Piedra Pómez ignimbrite deposit of north-western Argentina and identify evidence of antecedent controls on yardang patterns and formation. We mapped 14,826 yardangs in the region using a high-resolution digital elevation model (DEM) and satellite imagery. We classified yardangs as points using a two-stage decision rule based on morphology and spectral characteristics. Point pattern analysis shows that yardangs in the study area are not randomly distributed and commonly exhibit directional anisotropy in point pattern. The anisotropic pattern manifests as bands of closely-spaced yardangs oriented transverse to the dominant northwesterly wind direction. We hypothesize that banding is controlled by pre-existing antecedent topography in the bedrock, such as fumaroles or ridges associated with pyroclastic flow deposits. We present evidence from other locations on Earth and Mars to illustrate that the transverse banding is a common pattern in yardang landscapes.  相似文献   

Lithospheric Evolution of Gondwana East from Interdisciplinary Deep Surveys (LEGENDS)     

Larry D. Brown  Alfred Krner  Chris McA Powell  Brian F. Windley  Masaki Kanao 《Gondwana Research》2001,4(4):582-583

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A note on a property of pulasting stars     

Chris Koen 《Astrophysics and Space Science》1987,132(1):53-56

An explanation for the observed correlation between the ratio (relative amplitude of flux variation)/(relative amplitude of radius variation) and the period of radial pulsation in cepheids is proposed. If the explanation is correct, correlations may be expected for other classes of pulsating stars with the general functional form determined by physical conditions in the atmosphere.  相似文献   

The Oxford–Dartmouth Thirty Degree Survey – I. Observations and calibration of a wide-field multiband survey     

Emily C. MacDonald  Paul Allen  Gavin Dalton  Leonidas A. Moustakas  Catherine Heymans  Edward Edmondson  Chris Blake  Lee Clewley  Molly C. Hammell  Ed Olding  Lance Miller  Steve Rawlings  Jasper Wall  Gary Wegner  Christian Wolf 《Monthly notices of the Royal Astronomical Society》2004,352(4):1255-1272

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Increased risk of non-seasonal and body immersion recreational marine bathers contacting indicator microorganisms of sewage pollution     

Bradley G  Hancock C 《Marine pollution bulletin》2003,46(6):791-794

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A modular injection system, multilevel sampler, and manifold for tracer tests   总被引：1，自引：0，他引：1  

Mailloux BJ  Fuller ME  Rose GF  Onstott TC  DeFlaun MF  Alvarez E  Hemingway C  Hallet RB  Phelps TJ  Griffin T 《Ground water》2003,41(6):816-827

Ground water injection and sampling systems were developed for bacterial transport experiments in both homogenous and heterogeneous unconsolidated, surficial aquifers. Two types of injection systems, a large single tank and a dynamic mixing tank, were designed to deliver more than 800 L of amended ground water to the aquifer over 12 hours, without altering the ground water temperature, pH, Eh, or dissolved gas composition. Two types of multilevel samplers (MLSs) were designed and installed. Permanent MLSs performed well for the homogenous surficial aquifer, but their installation procedure promoted vertical mixing, which could obfuscate experimental data obtained from vertically stratified, heterogeneous aquifers. A novel, removable MLS was designed to fit in 2- and 4-inch wells. Expandable O-rings between each sampling port hydraulically isolated each port for sample collection when a nut was tightened at the land surface. A low-cost vacuum manifold system designed to work with both MLS designs used 50 mL centrifuge tubes to efficiently sample 12 MLS ports with one peristaltic pump head. The integrated system was developed and used during four field campaigns over a period of three years. During each campaign, more than 3000 ground water samples were collected in less than one week. This system should prove particularly useful for ground water tracer, injection, and push-pull experiments that require high-frequency and/or high-density sampling.  相似文献   

Herbicides implicated as the cause of severe mangrove dieback in the Mackay region, NE Australia: consequences for marine plant habitats of the GBR World Heritage Area     

Duke NC  Bell AM  Pederson DK  Roelfsema CM  Bengtson Nash S 《Marine pollution bulletin》2005,51(1-4):308-324

Herbicides, particularly diuron, were correlated with severe and widespread dieback of the dominant mangrove, Avicennia marina (Forsk.) Vierh. var. eucalyptifolia (Val.) N.C. Duke (Avicenniaceae), its reduced canopy condition, and declines in seedling health within three neighbouring estuaries in the Mackay region of NE Australia. This unusual species-specific dieback, first observed in the early 1990s, had gotten notably worse by 2002 to affect >30 km(2) of mangroves in at least five adjacent estuaries in the region. Over the past century, agricultural production has responded well to the demands of increasing population with improvements in farm efficiency assisted by significant increases in the use of agricultural chemicals. However, with regular and episodic river flow events, these chemicals have sometimes found their way into estuarine and nearshore water and sediments where their effects on marine habitats have been largely unquantified. Investigations over the last three years in the Mackay region provide compelling evidence of diuron, and possibly other agricultural herbicides, as the most likely cause of the severe and widespread mangrove dieback. The likely consequences of such dieback included declines in coastal water quality with increased turbidity, nutrients and sediment deposition, as well as further dispersal of the toxic chemicals. The implications of such findings are immense since they describe not only the serious deterioration of protected and beneficial mangrove habitat but also the potential for significant direct and indirect effects on other highly-valued estuarine and marine habitats in the region, including seagrass beds and coral reefs of the Great Barrier Reef lagoon. This article reviews all key findings and observations to date and describes the essential correlative and causative evidence.  相似文献