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Abstract Digital elevation data spaced on a regular 30 m grid were generated over a region of moderate topography in south-east Australia. Six algorithms for calculating gradient and aspect from these data were compared. General linear regression models and the third-order finite difference methods were the most accurate. 相似文献
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ANDREW BOULTON 《Geographical review》2011,101(2):224-242
This article encapsulates my thoughts about how to look, through landscape aesthetics, at an ordinary residential landscape in order to understand the ways in which people make sense of, draw on, and attempt to secure particular landscape visions and dispositions. More precisely, it deals with the articulation of a specific bungalow landscape aesthetic and a specific proprietary sense of property ownership in the Kenwick neighborhood of Lexington, Kentucky. The framework adopted calls for a broadening of the purview of landscape aesthetics beyond the domains of “high culture,” elites, and the visual in order to interrogate the workings of ordinary landscapes at the interface of landscape epistemology (a way of seeing) and the tangible, visible scene. 相似文献
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The effect of species on lacustrine δ18Odiatom and its implications for palaeoenvironmental reconstructions
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HANNAH L. BAILEY ANDREW C. G. HENDERSON HILARY J. SLOANE ANDREA SNELLING MELANIE J. LENG DARRELL S. KAUFMAN 《第四纪科学杂志》2014,29(4):393-400
The oxygen isotope composition of diatom silica (δ18Odiatom) is increasingly being used to reconstruct climate from marine and lacustrine sedimentary archives. Although diatoms are assumed to precipitate their frustule in isotopic equilibrium with their surrounding water, it is unclear whether internal processes of a given species affect the fractionation of oxygen between the water and the diatom. We present δ18Odiatom data from two diatom size fractions (3–38 and >38 µm) characterized by different species in a sediment core from Heart Lake, Alaska. Differences in δ18Odiatom between the two size fractions varies from 0 to 1.2‰, with a mean offset of 0.01‰ (n = 20). Fourier transform infrared spectroscopy confirms our samples consist of pure biogenic silica (SiO2) and δ18Odiatom trends are not driven by contamination. The maximum offset is outside the range of error, but the mean is within analytical error of the technique (± 1.06‰), demonstrating no discernible species‐dependent fractionation in δ18Odiatom. We conclude that lacustrine δ18Odiatom measurements offer a reliable and valuable method for reconstructing δ18Owater. Considering the presence of small offsets in our two records, we advise interpreting shifts in δ18Odiatom only where the magnitude of change is greater than the combined analytical error. 相似文献
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ANDREW H. RANKIN 《Geology Today》1989,5(1):21-24
Fluid inclusions in crystals provide a valuable insight into the nature and origin of ancient mineral-forming fluids. Fluid inclusions are established geothermometers and geobarometers, but their use as chemical indicators has in the past been hampered by their extremely small size. With the rapid development of a range of modern instrumental microanalytical techniques it is becoming increasingly possible to determine in detail the compositions of various phases present within minute inclusions down to the parts-per-million level 相似文献
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Forests of Carboniferous age, first described in detail in the nineteenth century, are often illustrated in textbooks, but their ecological and evolutionary significance has been largely overlooked or, worse, misrepresented. It has often been thought that the standing fossil forests found rooted in coals represent relicts of the peat-forming vegetation. Recent research has suggested that this is not always the case and that many of the standing trees represent an essentially non-peat-forming wetland ('clastic swamp') vegetation comprising a distinctive set of genera and species of plants. Recent investigation of several famous examples - Weaklaw, Arran and Joggins as well as new examples such as Mary Lee and Table Head - is throwing new light on the ecological and evolutionary significance of these fossil forests. 相似文献
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A Detailed Geochemical Study of Island Arc Crust: the Talkeetna Arc Section, South-Central Alaska 总被引:13,自引:0,他引:13
GREENE ANDREW R.; DEBARI SUSAN M.; KELEMEN PETER B.; BLUSZTAJN JUREK; CLIFT PETER D. 《Journal of Petrology》2006,47(6):1051-1093
The Early to Middle Jurassic Talkeetna Arc section exposed inthe Chugach Mountains of southcentral Alaska is 518km wide and extends for over 150 km. This accreted island arcincludes exposures of upper mantle to volcanic upper crust.The section comprises six lithological units, in order of decreasingdepth: (1) residual upper mantle harzburgite (with lesser proportionsof dunite); (2) pyroxenite; (3) basal gabbronorite; (4) lowercrustal gabbronorite; (5) mid-crustal plutonic rocks; (6) volcanicrocks. The pyroxenites overlie residual mantle peridotite, withsome interfingering of the two along the contact. The basalgabbronorite overlies pyroxenite, again with some interfingeringof the two units along their contact. Lower crustal gabbronorite(10 km thick) includes abundant rocks with well-developed modallayering. The mid-crustal plutonic rocks include a heterogeneousassemblage of gabbroic rocks, dioritic to tonalitic rocks (3040%area), and concentrations of mafic dikes and chilled mafic inclusions.The volcanic rocks (7 km thick) range from basalt to rhyolite.Many of the evolved volcanic compositions are a result of fractionalcrystallization processes whose cumulate products are directlyobservable in the lower crustal gabbronorites. For example,Ti and Eu enrichments in lower crustal gabbronorites are mirroredby Ti and Eu depletions in evolved volcanic rocks. In addition,calculated parental liquids from ion microprobe analyses ofclinopyroxene in lower crustal gabbronorites indicate that theclinopyroxenes crystallized in equilibrium with liquids whosecompositions were the same as those of the volcanic rocks. Thecompositional variation of the main series of volcanic and chilledmafic rocks can be modeled through fractionation of observedphase compositions and phase proportions in lower crustal gabbronorite(i.e. cumulates). Primary, mantle-derived melts in the TalkeetnaArc underwent fractionation of pyroxenite at the base of thecrust. Our calculations suggest that more than 25 wt % of theprimary melts crystallized as pyroxenites at the base of thecrust. The discrepancy between the observed proportion of pyroxenites(less than 5% of the arc section) and the proportion requiredby crystal fractionation modeling (more than 25%) may be bestunderstood as the result of gravitational instability, withdense ultramafic cumulates, probably together with dense garnetgranulites, foundering into the underlying mantle during thetime when the Talkeetna Arc was magmatically active, or in theinitial phases of slow cooling (and sub-solidus garnet growth)immediately after the cessation of arc activity. KEY WORDS: island arc crust; layered gabbro; Alaska geology; island arc magmatism; lower crust 相似文献