Thermal structure and tectonic evolution of the Scandian orogenic wedge,Scottish Caledonides: integrating geothermometry,deformation temperatures and conceptual kinematic‐thermal models     

J.R. Thigpen  R.D. Law  C.L. Loehn  R. A. Strachan  R.J. Tracy  G.E. Lloyd  B.L. Roth  S.J. Brown 《Journal of Metamorphic Geology》2013,31(8):813-842

In the Caledonides of northwest Scotland, two independent geothermometers (Fe‐Mg exchange and quartz c‐axis fabric opening angle) are used to characterize the thermal structure of the lower part of the Scandian (435–420 Ma) orogenic wedge within the Moine, Ben Hope and Naver‐Sgurr Beag thrust sheets. Traced from west (foreland) to east (hinterland), Fe‐Mg exchange thermometry yields peak or near‐peak temperatures ranging from 484 ± 50 °C to 524 ± 50 °C in the immediate hangingwall of the Moine thrust to 601 ± 50 °C in the immediate hangingwall of the Ben Hope thrust, to 630 ± 50 °C in the Naver thrust sheet. Preserved metamorphic facies and textural relationships are consistent with thermometric estimates. Deformation temperatures calculated from quartz c‐axis fabric opening angles across two similar orogen‐perpendicular transects also yield systematic increases (Glen Golly – Ben Klibreck, 520–630 °C; Ullapool‐Contin, 465–632 °C) traced towards the Naver and Sgurr Beag thrusts. In addition, deformation temperatures show a pronounced increase along the leading edge of the Moine thrust sheet moving south towards the Assynt window, which is interpreted to reflect deeper exhumation of the thrust plane above the Assynt footwall imbricate stack. Because temperatures calculated from metamorphic assemblages are within error of the quartz fabric‐derived deformation temperatures that are of demonstrably Scandian age, the metamorphic sequence between the Moine and Naver‐Sgurr Beag thrusts is interpreted to have developed during the Scandian orogeny. Integration of our results with previous 2D thermal‐mechanical studies allows development of new conceptual thermal‐kinematic models of Scandian orogenesis that may be broadly applicable to other collisional systems. Furthermore, it highlights the critical nature of coupling between orogen kinematic and thermal evolution.  相似文献   

Doing community geography     

Fischer  Heather  Block  Daniel  Bosse  Amber  Hawthorne  Timothy L.  Jung  Jin-Kyu  Pearsall  Hamil  Rees  Amanda  Shannon  Jerry 《GeoJournal》2021,87(2):293-306

Community Geography offers researchers, community groups, and students opportunities to engage in action oriented applied geographical research. Creating and sustaining these research programs can be challenging, programs can involve many partners from both academic and the community, have different goals and purposes, and utilize a variety of methods to perform research. In this paper we offer a framework of three primary overarching principles for implementing CG projects; (1) Who, (2) Why, and (3) How. (1) “Who” describes who is involved in CG, including researchers, community partners, academic institutions, (2) “Why” describes the justifications and benefits of taking this approach. (3) “How” explains how CG borrows methodologies from many disciplines within geography and beyond. Our examples are not exhaustive; rather, they serve as starting points to inspire researchers interested in CG.

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Practicing community geography in times of crisis     

Shannon  Jerry  Torres  Hannah  Mariner  Kathryn A.  Hawthorne  Timothy L. 《GeoJournal》2021,87(2):151-157

Community geography emphasizes the centrality of community engagement to socially transformative research. This introduction to a special issue of GeoJournal on community geography outlines how this growing subfield provides a model for collaborative action with the crises of our time, from white supremacy through climate change. As the co-editors of this special issue, we summarize the contents of these 14 articles, grouping them by the shared themes of power, institutional partnerships, pedagogy, and methods.

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A hierarchical approach measures the aerial extent and concentration levels of PAH-contaminated shoreline sediments at historic industrial sites in Prince William Sound, Alaska     

Page DS  Brown JS  Boehm PD  Bence AE  Neff JM 《Marine pollution bulletin》2006,52(4):367-379

A field study was conducted in 2003 to estimate the areal distribution and concentrations of polycyclic aromatic hydrocarbons (PAH) in intertidal sediments at sites of past human and industrial activity (HA sites) in Prince William Sound (PWS), Alaska, the site of the 1989 Exxon Valdez oil spill. More than 50 HA sites, primarily in western PWS, were identified through analysis of historic records and prior field studies, and nine sites were selected for detailed surveys. The areal assessment process consisted of seven steps: (1) identify site from historic records and field surveys; (2) locate visual evidence of surface oil/tar at a site; (3) prepare a site map and lay out a sampling grid over the entire site with 10-m grid spacing; (4) excavate pits to 50 cm depth on the grid; (5) perform a field colorimetric test to estimate total PAH (TPAH) in sediments from the wall of each pit and record the results in the ranges <1 ppm; 1-10 ppm; >10 ppm TPAH; (6) expand grid size if necessary if elevated PAH levels are detected colorimetrically; (7) select 20 samples from each site for same-day shipboard PAH analysis by immunoassay (SDI RaPID PAH) and, based on these results, select sediment samples from each site for full PAH analysis in the laboratory to identify PAH sources. A total of 416 pits were dug at the nine sites. Nine acres of sediments with TPAH >2500 ppb dry wt. were mapped at the nine sites. TPAH concentrations obtained by immunochemical analysis of 181 samples from the nine sites ranged from 20 to 1,320,000 ppb (wet wt.). The contaminants are mixtures of petroleum products (2-3 ring PAH) and combustion products (4-6 ring PAH) unrelated to the 1989 Exxon Valdez oil spill. Mussels and clams collected at these sites have elevated levels of PAH that are compositionally similar to the PAH in the sediments. These findings indicate that at least a portion of the sediment PAH is bioavailable. The PAH sources at these historic industrial sites are chronic. They include relict fuel oil tanks and works located above and within the intertidal zone, with contamination at some locations extending into nearshore sub-tidal sediments. This study shows how a hierarchical approach can be used to quickly and successfully map, quantify, and subsequently, identify sources of PAH in shoreline sediments.  相似文献   

Numerical evaluation of pumping well transmissivity estimates in laterally heterogeneous formations   总被引：1，自引：0，他引：1  

Leanne G. Tumlinson  James L. Osiensky  Jerry P. Fairley 《Hydrogeology Journal》2006,14(1-2):21-30

Transmissivity estimates derived from non-steady-state, single well, constant discharge, aquifer tests in laterally heterogeneous environments generally are questioned relative to their representativeness of aquifer conditions. Drawdown in pumping wells reflects the removal of water from storage in the aquifer and transient refraction of groundwater path-lines during the evolution of a non-symmetrical cone of depression. Simulations of single-well aquifer tests in aquifers with simple, arbitrary distributions of block heterogeneities suggest that transmissivity (T) values derived by the Cooper–Jacob (1946) method generally reflect volumetric, weighted mean T values of all of the heterogeneities contacted by the cone of depression at a particular time. This finding suggests that early-time drawdown data for single well aquifer tests reflect rapidly changing, volumetric, weighted mean T values proximal to the pumping well while late-time drawdown data reflect stabilized conditions and spatially averaged, volumetric weighted mean T out to a considerable distance from the pumping well.

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Resume Los estimados de transmisividad derivados de estados no estables, pozos individuales, descarga constante, pruebas de acuíferos en ambientes heterogéneos laterales generalmente se cuestionan en cuanto a su representatividad de las conidiones de los acuíferos. La extracción de agua en pozos de bombeo refleja la extracción de agua del depósito en el acuífero y la refracción transitoria de líneas de trayectoria del agua subterránea durante la evolución de un cono no simétrico de depresión. Las simulaciones de pozos individuales, pruebas de acuíferos en acuíferos con distribuciones simples, arbitrarias de heterogeneidades de bloque sugieren que los valores de transmisividad (T) derivados por el método Cooper–Jacob (1946) generalmente reflejan valores medios volumétricos potenciales (weighted) de todas las heterogeneidades en contaco con el cono de la depresión en un momento particular. Este descubrimiento sugiere que los datos de extracción tempranos de pruebas de pozos individuales reflejan valores medios potenciales volumétricos que cambian rápidamente en la proximidad del pozo de bombeo mientras que los valores de extracción tardíos reflejan condiciones estabilizadas y medias potenciales volumétricas a una distancia considerable del pozo de bombeo.

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Resumé Les estimés de transmissivité dérivés dessais de pompage en régime transitoire dans un seul puits contenu dans une formation latéralement hétérogène sont généralement questionable en ce qui concerne la représentativité des conditions de laquifère. Le rabattement dans les puits de pompage reflète lextraction deau provenant de lemmagasinement de laquifère et la réfraction en régime transitoire des lignes découlement durant lévolution dun cone de dépression non symétrique. Des simulations dessai de pompage dans un seul puits contenu dans un domaine avec des blocs hétérogènes distribués arbitrairement suggèrent que les valeurs de transmissivité obtenus avec la méthode dinterprétation de Cooper–Jacob (1946) sont généralement représentatifs du volume moyen pondéré de toutes les hétérogénéités en contact avec le cone de dépression à un temps particulier. Cette découverte suggère que les données de rabattement au début dun essai pour un seul puits reflètent un changement rapide des valeurs moyennes proximales pondérées tandis que le rabattement à un temps tardif reflète les conditions stabilisées et la moyenne spatiale jusquà une distance considérable du puits de pompage.

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Chilean and Southeast Pacific paleoclimate variations during the last glacial cycle: directly correlated pollen and δO records from ODP Site 1234     

Linda Heusser  Cal Heusser  Alan Mix  Jerry McManus 《Quaternary Science Reviews》2006,25(23-24):3404

Joint pollen and oxygen isotope data from Ocean Drilling Program Site 1234 in the southeast Pacific provide the first, continuous record of temperate South American vegetation and climate from the last 140 ka. Located at 36°S, 65 km offshore of Concepcion, Chile, Site 1234 monitors the climatic transition zone between northern semi-arid, summer dry-winter wet climate and southern year-round, rainy, cool temperate climate. Dominance of onshore winds suggests that pollen preserved here reflects transport to the ocean via rivers that drain the region and integrate conditions from the coastal mountains to the Andean foothills. Down-hole changes in diagnostic pollen assemblages from xeric lowland deciduous forest (characterized by grasses, herbs, ferns, and trees such as deciduous beech, Nothofagus obliqua), mesic Valdivian Evergreen Forest (including conifers such as the endangered Prumnopitys andina), and Subantarctic Evergreen Rainforest (comprised primarily of southern beech, N. dombeyi) reveal large rapid shifts that likely reflect latitudinal movements in atmospheric circulation and storm tracks associated with the southern westerly winds. During glacial intervals (MIS 2-4, and 6), rainforests and parkland dominated by Nothofagus moved northward into the region. At the MIS 6/5e transition, coeval with the rapid shift to lower isotopic values, rainforest vegetation was rapidly replaced by xeric plant communities associated with Mediterranean-type climate. An increased prominence of halophytic vegetation suggests that MIS 5e was more arid and possibly warmer than MIS 1. Although rainforest pollen rises again at the end of MIS 5e, lowland deciduous forest pollen persists through MIS 5d and 5c, into MIS 5b. Substantial millennial-scale variations occur in both interglacial and glacial regimes, attesting to the sensitivity of the southern westerly belt to climate change. Comparison of the cool, mesic N. dombeyi rainforest assemblage from Site 1234 with δ¹⁸O in the Byrd Ice core shows that on time scales longer than 10 ka, cool-moist conditions in central Chile were coherent with and occurred in phase with Antarctic cooling. This is also likely at millennial scales, although rainforest pollen lags Antarctic cooling with exponential response times of about 1000 years, which plausibly reflects the ecological response time to regional climate change.  相似文献   

High-speed knots in the hourglass-shaped planetary nebula Hubble 12     

N. M. H. Vaytet  A. P. Rushton  M. Lloyd  J. A. López  J. Meaburn  T. J. O'Brien  D. L. Mitchell  D. Pollacco 《Monthly notices of the Royal Astronomical Society》2009,398(1):385-393

We present a detailed kinematical analysis of the young compact hourglass-shaped planetary nebula Hb 12. We performed optical imaging and long-slit spectroscopy of Hb 12 using the Manchester echelle spectrometer with the 2.1-m San Pedro Mártir telescope. We reveal, for the first time, the presence of end caps (or knots) aligned with the bipolar lobes of the planetary nebula shell in a deep [N  ii ]λ6584 image of Hb 12. We measured from our spectroscopy radial velocities of  ∼120 km s⁻¹  for these knots.
We have derived the inclination angle of the hourglass-shaped nebular shell to be ∼65° to the line of sight. It has been suggested that Hb 12's central star system is an eclipsing binary which would imply a binary inclination of at least 80°. However, if the central binary has been the major shaping influence on the nebula, then both nebula and binary would be expected to share a common inclination angle.
Finally, we report the discovery of high-velocity knots with Hubble-type velocities, close to the core of Hb 12, observed in Hα and oriented in the same direction as the end caps. Very different velocities and kinematical ages were calculated for the outer and inner knots showing that they may originate from different outburst events.  相似文献   

Linearly Organized Turbulence Structures Observed Over a Suburban Area by Dual-Doppler Lidar   总被引：1，自引：1，他引：0  

Rob Newsom  Ron Calhoun  David Ligon  Jerry Allwine 《Boundary-Layer Meteorology》2008,127(1):111-130

Dual-Doppler lidar observations are used to investigate the structure and evolution of surface-layer flow over a suburban area. The observations were made during the Joint Urban 2003 (JU2003) field experiment in Oklahoma City, U.S.A. in the summer of 2003. This study focuses specifically on a 10-h sequence of scan data beginning shortly after noon local time on 7 July 2003. During this period two coherent Doppler lidars performed overlapping low elevation angle sector scans upwind and south of Oklahoma City’s central business district. Radial velocity data from the two lidars are processed to reveal the structure and evolution of the horizontal velocity field in the surface layer throughout the afternoon and during the evening transition period. The retrieved velocity fields clearly show a tendency for turbulence structures to be elongated in the direction of the mean flow throughout the entire 10-h study period. In order to quantify the observed anisotropy and its dependence on stability, integral length scales are estimated directly from the spatially resolved velocity retrievals. As the flow became more stably stratified the characteristic cross-stream dimension of the linear structures decreased. The streamwise component was consistently more anisotropic than the cross-stream component, and both velocity components exhibited maximum anisotropy under neutral conditions. The ratio of the streamwise to cross-stream length scale was estimated to be about eight for the streamwise component, and four for the cross-stream component under neutral conditions.  相似文献   

Hurricane Katrina storm surge delineation: implications for future storm surge forecasts and warnings   总被引：1，自引：1，他引：0  

Ginni Melton  Melanie Gall  Jerry T. Mitchell  Susan L. Cutter 《Natural Hazards》2010,54(2):519-536

The storm surge in coastal Mississippi caused by Hurricane Katrina was unprecedented in the region. The height and geographic extent of the storm surge came as a surprise to many and exceeded pre-impact surge scenarios based on SLOSH models that were the basis for emergency preparedness and local land use decision-making. This paper explores the spatial accuracy of three interpolated storm surge surfaces derived from post-event reconnaissance data by comparing the interpolation results to a specific SLOSH run. The findings are used to suggest improvements in the calibration of existing pre-event storm surge models such as SLOSH. Finally, the paper provides some suggestions on an optimal surge forecast map that could enhance the communication of storm surge risks to the public.  相似文献   

Erratum to: A diverse rodent fauna from the middle Bartonian (Eocene) of Les Alleveys, Switzerland: snapshot of the early theridomyid radiation     

Jerry J. Hooker  Marc Weidmann 《Swiss Journal of Geoscience》2010,103(1):137-137

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