GPS PERFORMANCE IN YUKON'S ARCTIC COAST          下载免费PDF全文

DAVID SWANLUND  RAMONA MARAJ  NADINE SCHUURMAN  ROXANNE HOPE  KATE DONKERS  MATT AQUIN  GWEN RICKERBY 《Geografiska Annaler: Series A, Physical Geography》2016,98(4):361-368

This study analyses GPS performance in Yukon's Arctic coast to inform future research that uses this technology in the region. To test this, Telonics GPS collars were placed on stakes during the summers of 2009 and 2010 throughout the region for varying lengths of time. The fix records produced by these collars were then collected and cleaned, leaving 30 samples. Using these records combined with a digital elevation model, eight variables were extracted and analysed in an attempt to find relationships, such that a fix rate could be predicted throughout the landscape. The results indicated that very few strong relationships existed. Densiometer values proved to be the only relationship between an environmental variable and fix rate. Available sky and aspect data produced results that were contrary to those expected. Overall, Telonics Generation 3 collars had extremely high fix rates, high accuracy, and low positional dilution of precision. Moreover, there was little variation in these results. This means that future GPS studies in the region would likely require minimal correction for fix rate bias. However, if corrections were to be made, more data would have to be gathered to ensure the results were statistically sound. The analysis suffered from the limitations of small sample size and low sample variance, among several others. Therefore, future studies should increase the number and diversity of sites tested.  相似文献   

Tidal inlet sequence, Sundance Formation (Upper Jurassic), north-central Wyoming     

DAVID M. UHLIR  ARTHUR AKERS†  CARL F. VONDRA 《Sedimentology》1988,35(5):739-752

The sandstones and coquinas of the upper 20 m of the Sundance Formation are interpreted as a tidal inlet, back-barrier shoal and sandy tidal-flat sequence deposited at the close of marine Jurassic sedimentation in north-central Wyoming. The barrier strandline maintained a generally E-W trend as it prograded to the north. The lateral migration of inter-barrier tidal inlets along the regressive shoreline of the late Sundance sea caused the coquinas and sandstones of the uppermost Sundance Formation to be deposited as tabular, laterally-extensive units. Tidal bundles, sigmoidal reactivation surfaces, herringbone cross-lamination and abundant mud drapes within the sandstones are evidence of considerable tidal influence during the deposition of the uppermost Sundance Formation. Earlier models, which attach an offshore environment of deposition to the sequence, do not explain the tabular geometries of the sandstone and coquina units and their conformable stratigraphic relationship with the overlying non-marine sediments of the Morrison Formation.  相似文献   

P-T Conditions and the Influence of Graphite on Pelitic Phase Relations in the Ballachulish Aureole, Scotland     

PATTISON  DAVID R. M. 《Journal of Petrology》1989,30(5):1219-1244

Pressure-temperature conditions of pelites in the Ballachulishaureole, Scotland, have been determined from a calibrated petrogeneticgrid and from published geothermometers and geobarometers. Tocalibrate the mineral reactions in the grid, thermodynamic datafor appropriate end members of Ms, Chi, Qtz, And, Sil, Ky, Crn,Crd, Kfs, and Bt were derived from experimental data. This approachwas hampered by the unknown compositions of many of the mineralsused in the experiments, and by apparent inconsistency betweenthe experiments. A best compromise grid that satisfies mostof the data was obtained, which is applicable to the Ballachulishand other contact aureoles. In this grid, the first developmentof sillimanite is constrained to lie between the Richardsonet al. (1969) and Holdaway (1971) andalusite-sillimanite boundaries. A pressure estimate of 3.0 + 0.5 kb is obtained from the calibratedgrid, within 0.3 kb of estimates from geobarometry and fromtwo other independent petrological studies. Temperatures rangedfrom 560?20?C at the first development of cordierite in theassemblage Ms+Qtz+Chl+Crd+Bt to 750–800?C in Grt+Crd+Hyassemblages in pelitic screens within the igneous complex. In graphitic slates, in contrast to non-graphitic pelites, anentire andalusite-bearing subzone is developed, and initialcordierite development occurs further from the igneous contacts.The presence of graphite lowered a_H2o in the slaters, expandingthe stability field of the andalusite-bearing assemblage And+Qtz+Bt+Ms+Crdrelative to the assemblage Kfs+Qtz+Bt+Ms+Crd developed in non-graphiticunits. Initial development of cordierite in the assemblage Ms+Qtz+Chl+Crd+Btwas also promoted by reduced a_H2o in graphitic slates. The regular sequence and spacing of mineral zones in the aureolesuggests that gross equilibrium was attained during contactmetamorphism, even though the thermal metamorphic pulse is estimatedto have been less than 0.2 Ma (Buntebarth, in press). Thereis no evidence for reaction overstepping in cordierite-producingreactions.  相似文献   

Combined flow origin of edgewise intraclast conglomerates: Sellick Hill Formation (Lower Cambrian), South Australia   总被引：1，自引：0，他引：1  

JEFFREY F. MOUNT  DAVID KIDDER† 《Sedimentology》1993,40(2):315-329

Unusually thick, coarse grained edgewise intraclast conglomerates occur at eight or more horizons within subtidal nodular and ribbon bedded wackestones and packstones of the Lower Cambrian Sellick Hill Formation, South Australia. The intraclast beds are flat based and laterally discontinuous, forming bar-like structures that must have exhibited bathymetric relief of as much as 1 m. The internal fabrics of these beds are variable. Thinner beds are dominated by flat-lying intraclasts; thicker beds contain both chaotic, randomly oriented, steeply inclined intraclasts and clusters of fan-shaped, vertically stacked edgewise intraclasts. The Sellick Hill Formation intraclast conglomerates are inferred to have been formed by intense, storm-generated combined flows on a broad, subtidal carbonate ramp. Superimposition of wave-induced oscillatory motions on geostrophic bottom flows during large storms generates short-lived, but exceptionally high instantaneous shear stresses in the bottom boundary layer. Entrainment of the relatively large intraclasts occurs through sliding, rather than pivoting. Edgewise fabrics are a product of asymmetric acceleration and deceleration of intraclasts during passage of waves and the chaotic nature of collisions between intraclasts moving within the boundary layer. Collisions between intraclasts impart a rotating moment, causing intraclasts to tip up during maximum fluid shear stress. Lodgement or packing of clasts in vertical or steeply inclined positions occurs within scours, where intraclasts can wedge between other vertically inclined clasts, or where intraclasts are pinned in steep orientations by collisions with shallowly inclined intraclasts. Differential erosional resistance of the intraclast deposits probably led to the development of sharp lateral changes in thickness. The Sellick Hill Formation intraclast conglomerates record erosion and reworking of subtidal, subfairweather wave base environments by exceptionally intense and presumably rare storm flows. The intraclast horizons represent a substantial loss in stratigraphic resolution due to widespread erosion of the ramp.  相似文献   

Planned Shopping Centres     

DAVID L. PRESS 《New Zealand geographer》1994,50(2):14-18

Planned shopping centres affect the geographical direction of retailing and the nature of retailing in general. As major marketing outlets for national and international chains they are especially attractive to consumers. This paper examines shopping centres in New Zealand and their impact on stand alone retailers and includes a case study of the Queensgate shopping centre in Lower Hutt.  相似文献   

Transform-normal extension on the Northern Death Valley fault system, California-Nevada     

DAVID Applegate 《Basin Research》1995,7(3):269-280

The Northern Death Valley fault zone is a major right-lateral structure that has accommodated 70 km or more of regional transtensional deformation in Tertiary to Recent time. Extension parallel to its north-west transport direction in the Death Valley region of California has produced ‘pull-apart’ structures that are responsible for opening the central Death Valley rhombochasm. In several ranges along the length of the Northern Death Valley fault zone, there is also evidence for extension directed to the south-west, normal to strike-slip movement. Evidence from the Funeral, Grapevine and Cottonwood Mountains suggests that a significant amount of down-dip slip has occurred on the Northern Death Valley fault zone and parallel structures (together referred to as the Northern Death Valley fault system) coeval with the majority of right-lateral slip and transform-parallel extension. As a result of both these components of extension, a separate basin opened in northern Death Valley with an orientation and architecture very different from that of central Death Valley. In addition, the Northern Death Valley fault system may be responsible for the present topography of the Funeral and Grapevine Mountains. Transform-normal extension appears to be the result of a misorientation of the Northern Death Valley fault zone within the regional stress field over the past 6 Myr, as suggested by simple geometric calculations.  相似文献   

The non-linear influence of wind-speed variability on gas transfer in lakes   总被引：1，自引：0，他引：1  

DAVID M. LIVINGSTONE  DIETER M. IMBODEN 《Tellus. Series B, Chemical and physical meteorology》1993,45(3):275-295

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Rates of aerodynamic entrainment in a developing boundary layer   总被引：1，自引：0，他引：1  

JON J. WILLIAMS  GRAEME R. BUTTERFIELD†  DAVID G. CLARK‡ 《Sedimentology》1990,37(6):1039-1048

Despite its significance for inception of grain transport by wind, the initial dislodgement of grains from a static surface by aerodynamic forces of drag and lift in the absence of grain collision has received little attention. This paper describes a series of wind-tunnel experiments in which the erosion of narrow strips of loose grains from the roughened surface of a flat plate exposed to a range of wind speeds was examined. The progressive downwind development of the boundary layer over the plate provided a range of airflow conditions which permitted systematic evaluation of grain entrainment rates arising from purely aerodynamic forces. Use of closely graded size fractions in flat, single grain layers resting on identical, fixed grain support eliminated the effects of surface irregularities and impacts from saltation. Results show that erosion of strips of loose grains develops with time according to an inverse exponential function in which the entrainment rate time constant relates to Shields dimensionless shear stress function. An empirical expression defining aerodynamic entrainment rate in terms of rate of strip erosion is derived and comparisons are made between present and published data. The need for additional data to resolve several questions raised by the present investigation is stressed. In addition, a simple, objective technique for accurate determination of the aerodynamic entrainment threshold of any loose, granular sediment is proposed.  相似文献   

Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover   总被引：7，自引：0，他引：7  

STEVEN W. SQUYRES  DAVID W. ANDERSEN  SUSAN S. NEDELL  ROBERT A. WHARTON  JR 《Sedimentology》1991,38(2):363-379

Lake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross-sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 × 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice-covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach ～ 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization and stabilization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites.  相似文献   

The diagenesis of the late Dinantian Derbyshire-East Midland carbonate shelf, central England     

GORDON M. WALKDEN  DAVID O. WILLIAMS† 《Sedimentology》1991,38(4):643-670

Carbonate cements in late Dinantian (Asbian and Brigantian) limestones of the Derbyshire carbonate platform record a diagenetic history starting with early vadose meteoric cementation and finishing with burial and localized mineral and oil emplacement. The sequence is documented using cement petrography, cathodoluminescence, trace element geochemistry and C and O isotopes. The earliest cements (Pre-Zone 1) are locally developed non-luminescent brown sparry calcite below intrastratal palaeokarsts and calcretes. They contain negligible Fe, Mn and Sr but up to 1000 ppm Mg. Their isotopic compositions centre around δ¹⁸O =?8.5‰, δ¹³C=?5.0‰. Calcretes contain less ¹³C. Subsequent cements are widespread as inclusion-free, low-Mg, low-Fe crinoid overgrowths and are described as having a‘dead-bright-dull’cathodoluminescence. The‘dead’cements (Zone 1) are mostly non-luminescent but contain dissolution hiatuses overlain by finely detailed bright subzones that correlate over several kilometres. Across‘dead'/bright subzones there is a clear trend in Mg (500–900 ppm), Mn (100–450 ppm) and Fe (80-230 ppm). Zone 1 cements have isotopic compositions centred around δ¹⁸O =?8.0‰ and δ¹³C=?2.5‰. Zone 2 cement is bright, thin and complexly subzoned. It is geochemically similar to bright subzones of Zone 1 cements. Dull Zone 3 cement pre-dates pressure dissolution and fills 70% or more of the pore space. It generally contains little Mn, Fe and Sr but can have more than 1000 ppm Mg, increasing stratigraphically upwards. The δ¹⁸O compositions range from ?5.5 to ?15‰ and the δ¹³C range is ?1 to + 3.2^0/00. Zone 4 fills veins and stylolite seams in addition to pores. It is synchronous with Pb, Ba, F ore mineralization and oil migration. Zone 4 is ferroan with around 500 ppm Fe, up to 2500 ppm Mg and up to 1500 ppm Mn. Isotopic compositions range widely; δ¹⁵O =?2.7 to ?9‰ and δ¹³C=?3.8 to+2.50‰. Unaltered marine brachiopods suggest a Dinantian seawater composition around δ¹⁵O = 0‰ (SMOW), but vital isotopic effects probably mask the original δ¹³C (PDB) value. Pre-Zone 1 calcites are meteoric vadose cements with light soil-derived δ¹³C and light meteoric δ¹⁸O. An unusually fractionated‘pluvial’δ¹⁵O(SMOW) value of around — 6‰ is indicated for local Dinantian meteoric water. Calcrete δ¹⁸O values are heavier through evaporation. Zone 1 textures and geochemistry indicate a meteoric phreatic environment. Fe and Mn trends in the bright subzones indicate stagnation, and precipitation occurred in increments from widespread cyclically developed shallow meteoric water bodies. Meteoric alteration of the rock body was pervasive by the end of Zone 1 with a general resetting of isotopic values. Zone 3 is volumetrically important and external sources of water and carbonate are required. Emplacement was during the Namurian-early Westphalian by meteoric water sourced at a karst landscape on the uplifted eastern edge of the Derbyshire-East Midland shelf. The light δ¹⁸O values mainly reflect burial temperatures and an unusually high local heat flow, but an input of highly fractionated hinterland-derived meteoric water at the unconformity is also likely. Relatively heavy δ¹³C values reflect the less-altered state of the source carbonate and aquifer. Zone 4 is partly vein fed and spans burial down to 2000 m and the onset of tectonism. Light organic-matter-derived δ¹³C and heavy δ¹⁸O values suggest basin-derived formation water. Combined with textural evidence of geopressures, this relates to local high-temperature ore mineralization and oil migration. Low water-to-rock ratios with host-rock buffering probably affected the final isotopic compositions of Zone 4, masking extremes both of temperature and organic-matter-derived CO₂.  相似文献