An Australian geographical information and modelling system for natural area management     

STEPHEN R. KESSELL 《International journal of geographical information science》2013,27(3):333-362

A generic geographical information and modelling system (GIMS) has been developed and implemented for 6 million hectares of fire-prone rural land in eastern Australia. Viewed initially as a land management decision support system rather than as a geographical information system (GIS) per se, GIMS provides extensive capabilities for estimating and recording patterns of vegetation and fuel dynamics, analysing the behaviour of fire and its environmental effects, and reviewing strategies for fire control and related issues. The software operates on personal computers via linkage to an indexed, direct access, grid data base. The design, development, implementation, evolution and use of GIMS for land management decision support are described, and tests of the system's ability to predict real-time fire behaviour are provided. The relationship between commercial GIS packages and locally-developed dynamic modelling GIS programs is discussed.  相似文献   

Interplay between river discharge and topography of the basin floor in a hyperpycnal lacustrine delta     

CORNEL OLARIU  JANOK P. BHATTACHARYA  MATTHEW I. LEYBOURNE  STEPHEN K. BOSS  ROBERT J. STERN 《Sedimentology》2012,59(2):704-728

Basin‐floor topography influences the flow path of hyperpycnal plumes and delta morphology during progradation of the Red River delta in Lake Texoma, USA. The Red River discharge is typically a hyperpycnal plume due to elevated total dissolved solids. Because the river plume is a bottom‐hugging hyperpycnal flow, lake bathymetry and topography strongly influence deposition and subsequent delta morphology. In addition to elevated total dissolved solid concentrations compared with Lake Texoma water, the density contrast of the Red River outflow is increased by high suspended‐sediment concentrations during high‐discharge events. Steep lateral slopes in the Lake Texoma basin deflect hyperpycnal river plumes and, subsequently, change the delta progradation direction before the delta reaches the opposite bank of the lake. Analysis of multi‐temporal aerial and satellite images indicates that the hyperpycnal delta follows the steepest lake‐bottom gradients, corresponding to the pre‐impoundment river thalweg (i.e. bypassing shallow parts of the lake). An analytical model for the hyperpycnal‐plume trajectory indicates plume deflection during low‐discharge or high‐discharge events, towards the deepest part of the basin. The magnitude of plume deflection is a function of river discharge and basin‐margin gradients. Plume deflection can vary between 10° and 80° from the channel axis towards the old river thalweg. The high deflection appears in the case of maximum basin side gradients of 12·8° and in conditions of low river discharge. During low‐discharge periods, the Red River delta builds a lobate shape with multiple terminal distributary channels whereas, during high‐discharge periods the Red River delta builds an elongate shape with a single large distributary channel. The elongate morphology of the delta is formed through the development of a single distributary channel and abandonment of the other distributaries. Therefore, the lobate shaped delta is expected to be preserved in the rock record.  相似文献   

Apogean–perigean signals encoded in tidal flats at the fluvio–estuarine transition of Glacier Creek,Turnagain Arm,Alaska; implications for ancient tidal rhythmites     

STEPHEN F. GREB  ALLEN W. ARCHER  DARRON G. DEBOER 《Sedimentology》2011,58(6):1434-1452

Turnagain Arm is a macrotidal fjord‐style estuary. Glacier Creek is a small, glacially fed stream which enters the estuary tangentially near Girdwood, Alaska. Trenches and daily sedimentation measurements were made in a mudflat along the fluvio–estuarine transition of Glacier Creek during several summers since 2003. Each year, the flats appear to erode during the winter and then accrete vertically in the spring and summer. In each of the years studied, tidal laminae in vertically thickening and thinning laminae bundles were deposited by twice daily tides in neap–spring tidal cycles. In 2004, bundles of thickening and thinning laminae couplets were noted in trenches cut into the flats. Five laminae bundles alternated between thicker and thinner bundles, corresponding to the perigean (high spring) and apogean (low spring) tides. Well‐preserved apogean–perigean cycles have rarely been documented in modern tidal flat sediments. At this location, vertical accretion of tidal rhythmites with well‐developed neap–spring cyclicity is possible because of the near‐complete removal of the flat from the previous year, which creates accommodation space for vertical accretion without significant reworking. Macrotidal conditions, no reworking by infaunal invertebrates, protection from the main tidal channel by a gravel bar and protection from storm waves and fluvial erosion by a recess in the sedge marsh that surrounds the flats all aid in preservation of rhythmites during aggradation. The position of the flats relative to tidal range allows for accumulation of complete spring cycles and incomplete neap cycles. In the summer of 2004, apogee and perigee were closely aligned with the new and full moons, resulting in successive strong perigee and apogee tides which probably aided in the accumulation of successive thick–thin spring cycles encoding the apogean and perigean tidal cycle. The apogean–perigean signal was not observed in subsequent years.  相似文献   

H2O Abundance in Depleted to Moderately Enriched Mid-ocean Ridge Magmas; Part I: Incompatible Behaviour, Implications for Mantle Storage, and Origin of Regional Variations   总被引：1，自引：0，他引：1  

DANYUSHEVSKY  LEONID V.; EGGINS  STEPHEN M.; FALLOON  TREVOR J.; CHRISTIE  DAVID M. 《Journal of Petrology》2000,41(8):1329-1364

The H₂O contents and trace-element abundances are presentedfor two well-studied suites of mid-ocean ridge basalt (MORB)glasses from the Northern East Pacific Rise (EPR, 9–11°N)and the South East Indian Ridge (SEIR, 127–129°E).Exactly the same region of the glass samples has been analysedfor these components using microbeam techniques. Our data allowexamination of the fine details of H₂O geochemical behaviourduring MORB genesis. We demonstrate that relative H₂O contents[i.e. H₂O/(another incompatible element)] vary systematicallywith increasing (La/Sm)_N in MORB glasses from both the EPR andSEIR. This indicates that H₂O behaves like other incompatible(in peridotite mineralogies) elements during MORB petrogenesis,and is primarily controlled by solid–melt partitioning.However, the relative H₂O contents of MORB glasses from theSEIR are higher than in glasses from the EPR at a given (La/Sm)_N,demonstrating global variations in the H₂O contents of MORB.Despite regional differences in relative H₂O contents, the incompatiblebehaviour of H₂O is similar in both studied regions. The relativeincompatibility of H₂O varies systematically with increasing(La/Sm)_N: in depleted MORB, H₂O is similar to La whereas inEMORB, H₂O is similar to Ce. Similar patterns of varying relativeincompatibility (to REE) are displayed by Zr, Hf, and P. Ourdata are best explained if H₂O is stored in the mantle in thesame phase with LREE (clinopyroxene?) at sub-solidus. Regionalvariations in relative H₂O contents in EMORB that have moreradiogenic Sr, Nd and Pb isotopes might be explained by differencesin the nature of enriched components recycled via subductionprocesses. However, when EMORB have the same radiogenic isotopecompositions as NMORB within a segment, relative H₂O contentsin EMORB probably reflect local processes that lead to enrichmentin incompatible elements. Regional differences in relative H₂Ocontents of NMORB may reflect either initial variations in theEarth’s mantle or inhomogeneities left after formationof the continental crust. KEY WORDS: glass; geochemistry; H₂O; MORB; petrology  相似文献   

Chromite in Komatiites, II. Modification during Greenschist to Mid-Amphibolite Facies Metamorphism   总被引：5，自引：2，他引：3  

BARNES  STEPHEN J. 《Journal of Petrology》2000,41(3):387-409

Chromite compositions in komatiites are influenced by metamorphicprocesses, particularly above 500°C. Metamorphosed chromiteis substantially more iron rich than igneous precursors, asa result of Mg–Fe exchange with silicates and carbonates.Chromite metamorphosed to amphibolite facies is enriched inZn and Fe, and depleted in Ni, relative to lower metamorphicgrades. Relative proportions of the trivalent ions Cr³⁺, Al³⁺and Fe³⁺ are not greatly modified by metamorphism up to loweramphibolite facies, although minor Fe³⁺ depletion occurs duringtalc–carbonate alteration at low temperature. SignificantAl is lost from chromite cores above 550°C, as a resultof equilibration with fluids in equilibrium with chlorite. ElevatedZn content in chromite is restricted to rocks with low (metamorphic)Mg/Fe ratios, and is the result of introduction of Zn duringlow-temperature alteration, with further concentration and homogenizationduring prograde metamorphism. Cobalt and Mn also behave similarly,except where carbonate minerals are predominant in the metamorphicassemblage. Chromite at amphibolite facies is typically extensivelyreplaced by magnetite. This is the result of incomplete metamorphicreaction between chromite and chlorite-bearing silicate assemblages.Magnetite compositions at the inner chromite–magnetiteboundary are indicators of metamorphic grade. KEY WORDS: chromite; komatiite; spinel; metamorphism; Zn  相似文献   

SOME ASPECTS OF THE INTERACTION OF BLOWING SNOW WITH THE ATMOSPHERIC BOUNDARY LAYER     

STEPHEN J. DRY  PETER A. TAYLOR 《水文研究》1996,10(10):1345-1358

Several possible effects of blowing snow on the atmospheric boundary layer are investigated, mostly within the general framework of the Prairie Blowing Snow Model (PBSM). The processes of snow saltation and suspension are first described. Variations to the drift density profile are tested and the effects of stratification and density variation calculations are evaluated. Despite high density gradients of blowing snow, stratification effects on turbulence and the velocity profiles can generally be neglected. However, with saltating or suspended snow in a constant shear stress layer, part of the shear stress is carried by the particles. A highly simplified, single-phase approach, based on the density variation of the air–snow mixture coupled to a simple turbulent stress–strain relationship, is used to illustrate this. Sublimation rates in a column of blowing snow are calculated using the PBSM and results are compared with those obtained with a modified formulation which incorporates a spectrum of sublimating particles of varying sizes at each height in a steady-state surface boundary layer and different specifications of the ventilation velocity.  相似文献   

Comparison of accelerator and radiometric radiocarbon measurements obtained from Late Devesian Lateglacial lake sediments from Llyn Gwernan, North Wales, UK     

J. JOHN LOWE  STEPHEN LOWE  ALISON J. FOWLER  ROBERT E. M. HEDGES  TIM J. F. AUSTIN 《Boreas: An International Journal of Quaternary Research》1988,17(3):355-369

Accelerator mass spectrometry measures of the radiocarbon activity of various chemical fractions prepared from Late Devensian Lateglacial lake sediments from the site of Llyn Gwernan, near Cader Idris, North Wales are presented and assessed. These are compared with radiocarbon measurements obtained by radiometric (decay) counting which were reported earlier from the same site and are considered in the light of pollen-stratigraphic information. The potential advantages of accelerator radiocarbon measurements to the assessment of the chronology and correlation of Lateglacial lake sediments are evaluated.  相似文献   

Formation of Anorthosite-Gabbro Rhythmic Phase Layering: An Example at North Arm Mountain, Bay of Islands Ophiolite     

KOMOR  STEPHEN. C.; ELTHON  DON 《Journal of Petrology》1990,31(1):1-50

Rhythmically layered anorthosite and gabbro are exposed in a4–10-m thick interval at the base of the layered gabbrounit on North Arm Mountain, one of four massifs that composethe Bay of Islands ophiolite, Newfoundland. Within the rhythmicallylayered interval, up to 37 anorthosite layers 1–2 cm thickalternate with gabbroic layers 7–10 cm thick. Anorthositesare adcumulates (most contain <6ppm Zr) with 98–99%plagioclase (Plag) and 1–2% intergranular clinopyroxene(Cpx), whereas gabbros are adcumulates to mesocumulates (<6–20ppmZr) with 35–55% Plag, and the balance olivine (Ol) + Cpx? orthopyroxene (Opx). Average mineral compositions are: Olmg-number [100 ?Mg/(Mg + Fe)]=84?9, NiO=0?13wt. % Plag An =87?9; Cpx mg-number = 88?3, TiO₂=0?20 wt %; and Opx mg-number= 85?7. Rare earth element (REE) concentrations in clinopyroxeneand plagioclase are low throughout the rhythmically layeredinterval (<5 times chondrites). The rhythmically layeredinterval is sandwiched between thick layers of adcumulate toorthocumulate uniform gabbro with average modal proportionsof 54% Plag-39% Cpx-3% Ol-4% Opx. Average mineral compositionsare: Ol mg-number = 75?5, NiO = 0?08 wt. %; Plag An=69%6; Cpxmg-number = 81?2, TiO₂ =0?53 wt. %, and Opx mg-number = 77?5.Clinopyroxene and plagioclase REE abundances are systematicallyhigher in the uniform gabbro interval than in the rhythmicallylayered interval. Calculated fractional crystallization pathsand correlated cryptic variation patterns suggest that uniformand rhythmically layered gabbros represent 20–30% in situcrystallization of two distinct magma batches, one more evolvedand the other more primitive. When the more primitive magmaentered the crystallization site of the NA300–301 gabbros,it is estimated to have been 40?C hotter than the resident evolvedmagma, and may have been chilled by contact with a magma chambermargin composed of uniform gabbro. In this model, chilling causedthe liquid to become supercooled with respect to plagioclasenucleation temperatures, resulting in crystallization of gabbrodeficient in plagioclase relative to equilibrium cotectic proportions.Subtraction of a plagioclase-poor melagabbro enriched the liquidin normative plagioclase, which in turn led to crystallizationof an anorthosite layer. Alternating anorthosite and gabbrolayers in the rhythmically layered interval built up by coupledand sustained variations in crystal nucleation and growth rates,and associated variations in liquid compositions at the crystallizationfront. Relatively stagnant magma-flow conditions may be requiredto accumulate substantial thicknesses of rhythmically layeredcumulates by sustained oscillatory crystallization. The rarityof anorthosite-gabbro rhythmic phase layering on North Arm Mountainmay indicate that convective magma currents in the Bay of Islandsmagma chamber were too vigorous for oscillatory crystallizationto commonly occur.  相似文献   

Deep‐water foreland basin deposits of the Cerro Toro Formation,Magallanes basin,Chile: architectural elements of a sinuous basin axial channel belt     

STEPHEN M. HUBBARD  BRIAN W. ROMANS  STEPHAN A. GRAHAM 《Sedimentology》2008,55(5):1333-1359

Coarse‐grained deep‐water strata of the Cerro Toro Formation in the Cordillera Manuel Señoret, southern Chile, represent the deposits of a major channel belt (4 to 8 km wide by >100 km long) that occupied the foredeep of the Magallanes basin during the Late Cretaceous. Channel belt deposits comprise a ca 400 m thick conglomeratic interval (informally named the ‘Lago Sofia Member’) encased in bathyal fine‐grained units. Facies of the Lago Sofia Member include sandy matrix conglomerate (that show evidence of traction‐dominated deposition and sedimentation from turbulent gravity flows), muddy matrix conglomerate (graded units interpreted as coarse‐grained slurry‐flow deposits) and massive sandstone beds (high‐density turbidity current deposits). Interbedded sandstone and mudstone intervals are present locally, interpreted as inner levée deposits. The channel belt was characterized by a low sinuousity planform architecture, as inferred from outcrop mapping and extensive palaeocurrent measurements. Laterally adjacent to the Lago Sofia Member are interbedded mudstone and sandstone facies derived from gravity flows that spilled over the channel belt margin. A levée interpretation for these fine‐grained units is based on several observations, which include: (i) palaeocurrent measurements that indicate flows diverged (50° to 100°) once they spilled over the confining channel margin; (ii) sandstone beds progressively thin, away from the channel belt margin; (iii) evidence that the eroded channel base was not very well indurated, including a stepped margin and injection of coarse‐grained channel material into surrounding fine‐grained units; and (iv) the presence of sedimentary features common to levées, including slumped units inferring depositional slopes dipping away from the channel margin, lenticular sandstone beds thinning distally from the channel margin, soft sediment deformation and climbing ripples. The tectonic setting and foredeep architecture influenced deposition in the axial channel belt. A significant downstream constriction of the channel belt is reflected by a transition from more tabular units to an internal architecture dominated by lenticular beds associated with a substantially increased degree of scour. Differential propagation of the fold‐thrust belt from the west is speculated to have had a major control on basin, and subsequently channel, width. The confining influence of the basin slopes that paralleled the channel belt, as well as the likelihood that numerous conduits fed into the basin along the length of the active fold‐thrust belt to the west, suggest that proximal–distal relationships observed from large channels in passive margin settings are not necessarily applicable to axial channels in elongate basins.  相似文献   

Mid-cycle condensed shellbeds from mid-Pleistocene cyclothems, New Zealand: implications for sequence architecture     

STEPHEN T. ABBOTT 《Sedimentology》1997,44(5):805-824

Richly fossiliferous and disconformity-bounded facies successions, termed Mid-Cycle Condensed Shellbeds (MCS), occupy a mid-cycle position within depositional sequences in the Castlecliff section (mid-Pleistocene, Wanganui Basin, New Zealand). These shell-rich intervals (0.1–4.5 m thick) comprise the upper of two loci of shell accumulation in Castlecliff sequences. The lower disconformable contacts are sharp and variably burrowed, and are interpreted as submarine transgressive surfaces formed by storm or tidal current erosion at the feather-edge of contemporary transgressive systems tracts. Above (i.e. seaward) of this erosion surface, macrofossil remains (mainly bivalves and gastropods) accumulated, with little reworking, on the inner-shelf under conditions of reduced terrigenous sediment supply. The upper contacts are sharp transitions from shell-rich to relatively shell-poor lithofacies; parautochthonous shell accumulation was ‘quenched’by downlapping highstand systems tract shelf siltstones and muddy fine sandstones. Castlecliff MCS, together with the basal shell-rich part of overlying highstand systems tracts, occupy a stratigraphic position which corresponds to the condensed section that forms at the transgressive/highstand systems tract boundary in the sequence model of Haq et al. (1987). Palaeoenvironmental analysis indicates that Castlecliff MCS are substantially, if not entirely, transgressive deposits. This study therefore shows that the ‘condensation maximum’within a depositional sequence does not necessarily bracket the transgressive systems tract/highstand systems tract boundary.  相似文献