STATE PARKS AND JIM CROW IN THE DECADE BEFORE BROWN v. BOARD OF EDUCATION     

WILLIAM E. O'BRIEN 《Geographical review》2012,102(2):166-179

African Americans had access to only a small number of state parks in the Jim Crow South. Between the end of World War II and the U.S. Supreme Court's 1954 Brown v. Board of Education decision, however, state park officials oversaw a relative expansion in the construction of facilities available to southern blacks. Emphasizing developments leading up to that landmark court ruling, I note that this trend did not indicate waning support for segregation among whites. Rather, this relative expansion was part of a strategy to protect Jim Crow by demonstrating that the “separate‐but‐equal” principle was being successfully achieved by southern park agencies. This intensified construction was largely a reaction to increasingly successful legal action in federal courts by the naacp generally; and officials in the state agencies hoped—unsuccessfully—to avoid challenges to state park segregation. After the Brown decision, several border states integrated their park systems, but most agencies displayed the reactionary defiance that characterized most white Southerners as the civil rights movement grew.  相似文献   

Architecture of a coarse‐grained channel–levée system: the Rosario Formation,Baja California,Mexico     

IAN A. KANE  MASON L. DYKSTRA  BENJAMIN C. KNELLER  SACHA TREMBLAY  WILLIAM D. McCAFFREY 《Sedimentology》2009,56(7):2207-2234

Seafloor images of coarse‐grained submarine channel–levée systems commonly reveal complex braid‐plain patterns of low‐amplitude bedforms and zones of apparent bypass; however, mechanisms of channel evolution and the resultant channel‐fill architecture are poorly understood. At Playa Esqueleto the lateral relationships between various elements of a deep‐marine slope channel system are well‐exposed. Specifically, the transition from gravel‐dominated axial thalwegs to laterally persistent marginal sandstones and isolated gravel‐filled scours is revealed. Marginal sandstones pass into a monotonous thin‐bedded succession which built to form relatively low‐relief levées bounding the channel belt; in turn, the levées onlap the canyon walls. Three orders of confinement were important during the evolution of the channel system: (i) first‐order confinement was provided by the erosional canyon which confined the entire system; (ii) confined levées built of turbidite sandstones and mudstones formed the second‐order confinement, and it is demonstrated that these built from overspill at thalweg margins; and (iii) third‐order confinement describes the erosional confinement of coarse‐grained thalwegs and scours. Finer‐grained sediment was transported in suspension and largely was unaffected by topography at the scale of individual thalwegs. Facies and clast analyses of conglomerate overlying channel‐marginal scours reveal that they were deposited by composite gravity flows, which were non‐cohesive, grain‐dominant debris flows with more fluidal cores. These flows were capable of basal erosion but were strongly depositional; frictional freezing at flow margins built gravel levées, while the core maintained a more fluidal transport regime. The resultant architecture consists of matrix‐rich, poorly sorted levées bounding better‐sorted, traction‐dominated cores. The planform geometry is interpreted to have consisted of a low‐sinuosity gravel braid‐plain built by accretion around mid‐channel and bank‐attached bars. This part of the system may be analogous to fluvial systems; however, the finer‐grained sediment load formed thick suspension clouds, probably several orders of magnitude thicker than the relief of braid‐plain topography and therefore controlled by the levées and canyon wall confinement.  相似文献   

Fine-scale relief related to Late Holocene channel shifting within the floor of the upper Redondo Fan, offshore Southern California     

WILLIAM R. NORMARK†  CHARLES K. PAULL‡  DAVID W. CARESS‡  WILLIAM USSLER III‡  RAY SLITER 《Sedimentology》2009,56(6):1690-1704

Erosional and depositional bedforms have been imaged at outcrop scale in the upper Redondo Fan, in the San Pedro Basin of offshore Southern California in ≥600 m water depths, using an Autonomous Underwater Vehicle developed by the Monterey Bay Aquarium Research Institute. The Autonomous Underwater Vehicle is equipped with multibeam and chirp sub-bottom sonars. Sampling and photographic images using the Monterey Bay Aquarium Research Institute Remotely Operated Vehicle Tiburon provide groundtruth for the Autonomous Underwater Vehicle survey. The 0·3 m vertical and 1·5 m lateral bathymetric resolution and 0·1 m sub-bottom profile resolution provide unprecedented detail of bedform morphology and structure. Multiple channels within the Redondo Fan have been active at different times during the Late Holocene (0 to 3000 yr bp ). The currently active channel extending from Redondo Canyon makes an abrupt 90° turn at the canyon mouth before resuming a south-easterly course along the east side of the Redondo Fan. This channel is floored by sand and characterized by small steps generally <1 m in relief, spaced 10 to 80 m in the down-channel direction. A broader channel complex lies along the western side of the fan valley that was last active more than 850 years ago. Two distinct trains of large scours, with widths ranging from tens to a few hundred metres and depths of 20 m, occur on the floor of the western channel complex, which has a thin mud drape. If observed in cross-section only, these large scours would probably be misidentified as the thalweg of an active channel.  相似文献   

A STATISTICAL PROCEDURE TO EVALUATE CLEAN-UP STANDARDS     

ROBERT O''BRIEN BIMAL K.SINHA WILLIAM P.SMITH Statistical Policy Branch  Environmental Protection Agency  M St.  SW  Washington  DC  U.S.A. 《地理学报(英文版)》1991,(3)

The object of this paper is to develop a suitable statistical procedure to evaluate clean-up standards athazardous waste sites.Under the assumptions that contaminant masses at a site follow a gammadistribution and that the data from the pre-remediation baseline sample as well as from the interim orfinal sample taken after a certain period of operation are both distributed as gamma with the same shapeparameter but different scale parameters,we derive a uniformly most powerful unbiased test of thehypothesis that a specified percentage of contaminant mass has been reduced.A large-sampleapproximation of the exact test procedure and a comparison with the likelihood ratio test are provided.  相似文献   

Rock varnish in the Sonoran Desert: microbiologically mediated accumulation of manganiferous sediments   总被引：3，自引：0，他引：3  

BARTHOLOMEW NAGY  LOIS ANNE NAGY  MARK J. RIGALI  WILLIAM D. JONES  DAVID H. KRINSLEY  NORVAL A. SINCLAIR 《Sedimentology》1991,38(6):1153-1171

Rock varnish occurs in virtually all environments, most commonly in arid and semi-arid climates, including Antarctica. Rock varnish consists of thin layers of intimately mixed aeolian and chemical sediments often showing botryoidal and more rarely stromatolite-like morphologies. Typical rock varnish samples collected at Twin Peak Mountain Park, near Phoenix, Arizona, consist of abundant quartz, with plagioclase, illite and a mixed layer, Fe-clay mineral, probably corrensite. EDS, SEM (BSE) and TEM analyses revealed that the typical Mn, Fe minerals occur as minute particles; some of these particles and other mineral grains are attached to filaments. XRD and electron diffraction showed that the Mn.Fe-bearing particles are poorly crystalline. The filaments, based on morphological criteria, are virtually indistinguishable from fungal filaments. Most filaments are fragments, probably broken by scraping during sample collection. Coccoid and rod-shaped forms, resembling cyanobacteria and other bacteria, respectively, are also present. Unlike definitive minerals, these filaments disintegrated in the concentrated energy of the SEM electron beam at the instrumental and experimental conditions used. In addition, no filamentous, rod-shaped or coccoid forms were observed in samples hydrolysed with 6 N HCl for 24 h at 100°C. Bacteria and fungi in powdered rock varnish were cultured on four media, incubated aerobically in the dark at 25°C. The culture media yielded dense growths of spore-forming bacteria and filamentous fungi. One fungus and two Bacillus isolates oxidized and concentrated manganese. Control experiments revealed that fungi and bacteria are present on and below the surfaces of rock varnish. Free and hydrolysed, peptide/protein-bound amino acids were identified in the rock varnish. Amino acids showed virtually no racemization with the exception of D/L asp = 0.1. Relatively high molecular weight humic matter was also separated from the rock varnish. High-resolution mass spectrometry revealed non-hydrocarbon moieties, similar to a Suwannee River (FL) humic acid standard. Micro-organisms and their original biochemical compounds do not seem to be preserved for long in the accreting varnish layer. The studies showed that the filaments helped to trap mineral particles of rock varnish, and that bacteria and fungi abetted Mn concentration. Some structures in the layers of rock varnish resemble stromatolites and present definitions would allow them to be termed as such.  相似文献   

Distributary channels, sand lobes, and mesotopography of Navy Submarine Fan, California Borderland, with applications to ancient fan sediments     

WILLIAM R. NORMARK  D. J. W. PIPER  GORDON R. HESS 《Sedimentology》1979,26(6):749-774

The deep-tow instrument package of Scripps Institution of Oceanography provides a unique opportunity to delineate small-scale features of a size comparable to those features usually described from ancient deep-sea fan deposits. On Navy Fan, the deep-tow side-scanning sonar readily detected steep channel walls and steps and terraces within channels. The most striking features observed in side-scan are large crescentic depressions commonly occurring in groups. These appear to be large scours or flutes carved by turbidity currents. Four distinct acoustic facies were mapped on the basis of qualitative assessment of reflectivity of 4 kHz reflection profiles. There is a distinct increase in depth of acoustic penetration, number of sub-bottom reflectors, and reflector continuity from the upper fan-valley to the lower fan. These changes are accompanied by a decrease in surface relief. Navy Fan is made up of three active sectors. The active upper fan is dominated by a single channel with prominent levees that decrease in height downstream. The active mid-fan region or suprafan is where sand is deposited. Well defined distributary channels with steps, terraces, and other mesotopography terminate in depositional lobes. Interchannel areas are rough, containing giant scours as well as other relief. The active lower fan accumulates mud and silt and is without resolvable surface morphology. The morphological features seen on Navy Fan other than levees, interchannel areas, and lobes are principally erosional. The distributary channels are up to 0.5 km wide and 5–15 m deep. Such features, because of their large size and low relief, are rarely completely exposed or easily detectable in ancient rock sequences. Some flute-shaped scours are larger than channels in cross section but many are 5-30 m across and 1-2 m deep. If observed in ancient rocks transverse to palaeo-current direction, they would perhaps be indistinguishable from channels. Surface sediment distribution combined with fan morphology can be used to relate modern sediments to facies models for ancient fan sediments. Gravel and sand occur in the upper valley, massive sand beds in the mid-fan distributary channels, classical complete Bouma sequences on depositional lobes, incomplete Bouma sequences (lacking division a) on the lower mid-fan, and Bouma sequence with lenticular shape or other limited extent on mid-fan interchannel areas and on levees.  相似文献   

Wolf Volcano, Galapagos Archipelago: Melting and Magmatic Evolution at the Margins of a Mantle Plume   总被引：1，自引：0，他引：1  

GEIST  DENNIS J.; NAUMANN  TERRY R.; STANDISH  JARED J.; KURZ  MARK D.; HARPP  KAREN S.; WHITE  WILLIAM M.; FORNARI  DANIEL J. 《Journal of Petrology》2005,46(11):2197-2224

Wolf volcano, an active shield volcano on northern Isabela Islandin the Galápagos Archipelago, has undergone two majorstages of caldera collapse, with a phase of partial calderarefilling between. Wolf is a typical Galápagos shieldvolcano, with circumferential vents on the steep upper carapaceand radial vents distributed in diffuse rift zones on the shallower-slopinglower flanks. The radial fissures continue into the submarineenvironment, where they form more tightly focused rift zones.Wolf's magmas are strikingly monotonous: estimated eruptivetemperatures of the majority of lavas span a total of only 22°C.This homogeneity is attributed to buffering of magmas as theyascend through a thick column of olivine gabbroic mush thathas been deposited from a thin, shallow (<2 km deep) subcalderasill that is in a thermochemical steady state. Wolf's lavashave the most depleted isotopic compositions of any historicallyactive intraplate ocean island volcano on the planet and haveisotopic compositions (except for ³He/⁴He) indistinguishablefrom mid-ocean ridge basalt erupted from the GalápagosSpreading Center (GSC) 250–410 km away from the peak ofinfluence of the Galápagos plume. Wolf's lavas are enrichedin incompatible trace elements and have systematic major elementdifferences relative to GSC lavas, however. Wolf's magmas resultfrom lower extents of melting, deeper melt extraction, and agreater influence of garnet compared with GSC magmas, but Wolfand the GSC share the same sources. These melt generation conditionsare attributed to melting in a thermal and mechanical boundarylayer of depleted asthenosphere at the margins of the Galápagosplume. The lower degrees of melting and extraction from deeperlevels result from a thicker lithospheric cap at Wolf than existsat the GSC. KEY WORDS: caldera; Galápagos; mush; partial melting; plume  相似文献   

Sustainable Development: The Economic and Environmental Case for Policy Reform     

WILLIAM SMITH 《New Zealand geographer》1993,49(2):69-74

Abstract. Acceptance of the concept of sustainable development as a long term goal has shifted the nature of the debate about the environment and its relation to development. Previously, emphasis was on the adverse effects of economic development on the environment. It is now argued that a degraded and deteriorating environment is a threat to economic development. However, if the promise of sustainability is to be fully explored some fundamental changes must be made. The most important changes concern: first, the way ecological factors are integrated into economic decision making; second, the design of domestic policies; third, the emergence of environmental change as a force in international relations; and, fourth, the need to restructure the international economy and global political arrangements. Canada and New Zealand provide examples of efforts to tackle these issues, to halt environmental destruction and resource depletion, and to meet global development needs.  相似文献   

The variability of critical shear stress, friction angle, and grain protrusion in water-worked sediments   总被引：3，自引：0，他引：3  

JAMES W. KIRCHNER  WILLIAM E. DIETRICH†  FUJIKO ISEYA‡  HIROSHI IKEDA‡ 《Sedimentology》1990,37(4):647-672

The erodibility of a grain on a rough bed is controlled by, among other factors, its relative projection above the mean bed, its exposure relative to upstream grains, and its friction angle. Here we report direct measurements of friction angles, grain projection and exposure, and small-scale topographic structure on a variety of water-worked mixed-grain sediment surfaces. Using a simple analytical model of the force balance on individual grains, we calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography. The friction angle, projection, and exposure of single grain sizes vary widely from point to point within a given bed surface; the variability within a single surface often exceeds the difference between the mean values of disparate surfaces. As a result, the critical shear stress for a given grain size on a sediment surface is characterized by a probability distribution, rather than a single value. On a given bed, the crtitical shear stress distributions of different grain sizes have similar lower bounds, but above their lower tails they diverge rapidly, with smaller grains having substantially higher median critical shear stresses. Large numbers of fines, trapp.ed within pockets on the bed or shielded by upstream grains, are effectively lost to the flow. Our calculations suggest that critical shear stress, as conventionally measured, is defined by the most erodible grains, entrained during transient shear stress excursions associated with the turbulent flow; this implies a physical basis for the indeterminacy of initial motion. These observations suggest that transport rate/shear stress relationships may be controlled, in part, by the increasing numbers of grains that become available for entrainment as mean shear stress increases. They also suggest that bed textures and grain size distributions may be controlled, within the constraints of an imposed shear stress and sediment supply regime, by the influence of each size fraction on the erodibility of other grain sizes present on the bed.  相似文献   

Anorthosites and Related Megacrystic Units in the Evolution of Archean Crust   总被引：1，自引：0，他引：1  

PHINNEY  WILLIAM C.; MORRISON  DONALD A.; MACZUGA  DAVID E. 《Journal of Petrology》1988,29(6):1283-1323

Archean anorthositic complexes occur in essentially all Archeancratons and contain large equidimensional plagioclase crystals(up to 30 cm. diam.) with highly calcic compositions (An₈₀ toAn₉₀) but are not readily amenable to determination of theirparent melt compositions. However, insight into petrogenesisof the complexes is provided by megacrysts of plagioclase thatare identical to those in the complexes and occur in many Archeanflows, sills, and dikes whose matrices display REE and fractionationpatterns that indicate tholeiitic trends and are compatiblewith prior subtraction of plagioclase during earlier evolutionof the melts. Included blocks of anorthosite and megacrystswith very thin rims that approach the more sodic compositionof lathy plagioclase in the matrices indicate an earlier stageof cryst formation under different conditions of crystallizationthan the matrices. The megacrystic units occur both in greenstonebelts that have oceanic affinities and stable cratonic dikeswarms that have continental affinities. Both major and traceelement contents of the matrices of the megacrystic units differbetween greenstone and cratonic dike environments; the dikesbeing higher in Si0₂, TiO₂ FeO, Na₂, K₂O, and light REEs butlower in Al₂O₃ and CaO. The matrices of both environments followseparate but parallel tholeiitic fractionation with high Fe-enrichmenttrends similar to Skaergaard liquids suggesting relatively lowvolatiles and fo₂. Experimental data and projections in CMAFspace suggest a multistage petrogenesis involving a relativelyhigh-pressure fractionation of olivine and/or orthopyroxenefrom a primitive mafic melt followed by ascension of the fractionated,less-dense melt, probably in several pulses, to a low-pressurechamber, probably at 1 to 2 kb. The depressurization accompaniedby cooling could easily place the melt composition in the plagioclasefield and significantly below the liquidus resulting in severalcrystallization cycles of plagioclase in the low pressure chamber.The melts would crystallize as anorthositic complexes and periodicallyexpel pulses that would form the observed megacrystic flows,sills, and dikes.  相似文献