Bias in estimating fractal dimension with the rescaled-range (R/S) technique     

Colin P. North  David I. Halliwell 《Mathematical Geosciences》1994,26(5):531-555

Fractal geostatistics are being applied to subsurface geological data as a way of predicting the spatial distribution of hydrocarbon reservoir properties. The fractal dimension is the controlling parameter in stochastic methods to produce random fields of porosity and permeability. Rescaled range (R/S)analysis has become a popular way of estimating the fractal dimension, via determination of the Hurst exponent (H). A systematic investigation has been undertaken of the bias to be expected due to a range of factors commonly inherent in borehole data, particularly downhole wireline logs. The results are integrated with a review of previous work in this area. Small datasets. overlapping samples, drift and nonstationariry of means can produce a very large bias, and convergence of estimates of H around 0.85–0.90 regardless of original fractal dimension. Nonstationarity can also account for H>1, which has been reported in the literature but which is theoretically impossible for fractal time series. These results call into question the validity of fractal stochastic models built using fractal dimensions estimated with the R/Smethod.  相似文献   

Comment on “Evidence for long residence times of rhyolitic magma in the Long Valley magmatic system: the isotopic record in precaldera lavas of Glass Mountain” by A.N. Halliday, G.A. Mahood, P. Holden, J.M. Metz, T.J. Dempster and J.P. Davidson     

R.Stephen J. Sparks  Herbert E. Huppert  Colin J.N. Wilson 《Earth and Planetary Science Letters》1990,99(4)

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On the kinetics of textural equilibration in forsterite marbles     

Marian B. Holness  M. J. Bickle  Colin M. Graham 《Contributions to Mineralogy and Petrology》1991,108(3):356-367

In the aureole of the Beinn an Dubhaich granite, Skye, the minimum observed median forsterite-calcite-calcite dihedral angle varies from 110° at the olivinein isograd to about 165° (the equilibrium value) at the granite-limestone contact. Laboratory experiments were performed to investigate the kinetics of this textural change. It was found that the rate of change of the forsterite-calcite-calcite dihedral angle followed approximately first-order kinetics with an activation energy of 48±4 kJ mol^-1 for fluid-present conditions, and 90 ±4 kJ mol^-1 for fluid-absent conditions. Scanning ion imaging demonstrated that, at least in the early stages of textural change, solution-reprecipitation of the calcite was the rate determining step in the fluid-present runs. The latter result and the value of the activation energy are both consistent with the activation energy found by previous authors for (albeit zeroth order) silicate-aqueous solution solution-reprecipitation reactions. The value of activation energy for the dry data does not correspond to those for either grain boundary or volume diffusion of oxygen or magnesium in forsterite. The mechanism for textural equilibration in the fluid-absent runs is uncertain. Application of the experimentally-derived rate equation to the Beinn an Dubhaich marbles gave activation energies higher than those obtained experimentally. It is concluded from consideration of grain growth effects that activation energies derived from the Beinn an Dubhaich marbles probably reflect textural equilibration under predominantly fluid-absent conditions.  相似文献   

Pollen representation,source area,and basin size: Toward a unified theory of pollen analysis     

I.Colin Prentice 《Quaternary Research》1985,23(1):76-86

The concepts of pollen source area and of production and dispersal biases in pollen representation are quantified by means of a simple theoretical model. Source areas and relative pollen representation are shown to depend on basin size according to functions that describe the amount of pollen remaining airborne at increasing distances from single pollen sources. The form of these functions is determined by physical processes. Standard formulas for elevated sources do not apply, but the integrated form of Sutton's equation for particle dispersal from a ground-level source gives useful approximations applicable to pollen transport over a forest canopy. Simulations using this equation yielded source areas that increased realistically with basin size, showed substantial differences between source areas for pollen grains with different deposition velocities, and predicted that lighter pollen grains should become better represented with increasing basin size. All of these predictions are qualitatively consistent with present knowledge of the characteristics of pollen assemblages in different depositional environments. The model further allows parameters that can be estimated by statistical calibration methods to be predicted from underlying physical quantities. This extension suggests procedures for testing the theory with quantitative data on surface pollen and forest composition. Preliminary results showed reasonable agreement between estimated and predicted values of dispersal indices for the most abundant taxa in pollen spectra from the northern midwestern United States.  相似文献   

Permo-Triassic tectonic evolution and metallogenesis of the Rockhampton—Maryborough area, Queensland — A photogeological investigation     

Colin R. Nash 《Ore Geology Reviews》1986,1(2-4)

Structural analysis of remotely sensed data provides a method of assessing the tectonic significance of regional metallogenic lineaments in the New England Orogen of southeastern Queensland. Photogeological analysis of Landsat imagery and small-scale aerial photography reveals a pattern of WNW—NNW-oriented structures, which were apparently generated in response to Mesozoic crustal extension and reactivated during Early Tertiary block faulting. These structures tend to overprint arcuate late Palaeozoic to early Mesozoic trends and batholith belts, and exert a control over Middle to Late Triassic rifting and epizonal plutonism. The distribution of epigenetic base and precious metal deposits in the Rockhampton—Maryborough area is locally but not regionally related to identifiable structural lineaments.  相似文献   

Ground-Water Flow Simulation for Management of a Regulated Aquifer System: A Case Study in the North Carolina Coastal Plain     

Jeffrey W. Reynolds  Richard K. Spruill 《Ground water》1995,33(5):741-748

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Estimation of meiobenthic nematode diversity by non-specialists     

Colin G. Moore  Scot Mathieson  David J. L. Mills  Brian J. Bett 《Marine pollution bulletin》1987,18(12):646-649

A methodology is presented for the estimation of nematode diversity using Cairns' technique of sequential comparisons. The accuracy and precision of the method are examined and a test presented for the comparison of diversity estimates.  相似文献   

The age and nature of Mesozoic-Tertiary magmatism across the Indus Suture Zone in Kashmir and Ladakh (N. W. India and Pakistan)     

P. H. Reynolds  M. E. Brookfield  R. H. McNutt 《International Journal of Earth Sciences》1983,72(3):981-1003

We report the following new⁴⁰Ar/³⁹Ar ages: 130–150 and 90–100 Ma from monzodiorite and tremolite-actinolite schist of the Kohistan Complex; 44±0.5, 39.7±0.2 Ma from dikes cutting the Ladakh-Deosai Batholith Complex; 130–145 Ma from a diorite in the Shyok melange; and 7.8±0.1 Ma from a late stage monzogranite of the Kärakorum Batholith. A 261±13 Ma age from gneiss of the Karakorum Batholith is of uncertain significance. These dates, previously published ones which we summarize here, and some Sr isotope data suggest the following, (due to subduction switching between the Indian and Asian margins during closing of the Tethys ocean): Late Cretaceous emplacement of the Dras-Kohistan Cretaceous Island arc, followed by rapid cooling between abut 85 and 45 Ma. A quiet phase tectonically on the northern Indian plate during the Palaeocene to early Eocene, when subduction was occurring on the Asian margin. Further southward thrusting of the Indian continental margin associated with the development of an Andean-type arc (the Ladakh-Desosai Batholiths) on the northern Indian margin during the Eocene. An Oligocene Andean arc (the Karakorum Batholiths) on the Asian margin, followed by Miocene collision of the two continents and intrusion of ‘true’ granites derived from partial melting of continental crust.  相似文献   

Reply     

T. Grant Caldwell  Hugh M. Bibby  Colin Brown 《Geophysical Journal International》2007,171(2):567-567

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Asymmetry in the time-lapse seismic response to injection and depletion     

Colin M. Sayers 《Geophysical Prospecting》2007,55(5):699-705

Large changes in seismic reflection amplitude have been observed around injectors, and result from the decrease in elastic‐wave velocity due to the increase in pore pressure in the reservoir. In contrast, the velocity change resulting from the decrease in pore pressure in depleting reservoirs is observed to be smaller in magnitude. Elastic‐wave velocities in sandstones vary with stress due to the presence of stress‐sensitive grain boundaries within the rock. Grain‐boundary stiffness increases non‐linearly with increasing compressive stress, due to increased contact between opposing faces of the boundary. This results in a change in velocity due to a decrease in pore pressure that is smaller than the change in velocity caused by an increase in pore pressure, in agreement with time‐lapse seismic observations. The decrease in porosity resulting from depletion is not fully recovered upon re‐pressurization, and this leads to an additional steepening of the velocity vs. effective stress curve for injection relative to depletion. This difference is enhanced by any breakage of cement or weakening of grain contacts that may occur during depletion and by the reopening or formation of fractures or joints and dilation of grain boundaries that may occur during injection.  相似文献