Lithological control on the elevation of shore platforms in a microtidal setting     

D. M. Kennedy  M. E. Dickson 《地球表面变化过程与地形》2006,31(12):1575-1584

The shore platforms on Shag Point, southern New Zealand, are quasi‐horizontal surfaces and are developed between supratidal and low water spring levels. A range of morphologies occur, with more exposed platforms having a distinct low‐tide cliff, in contrast to low‐tide surfaces where the seaward edge is buried beneath rubble and macro‐algal growth. The platforms range in width from 20 to 80 m and are eroded into Late Cretaceous/Early Tertiary fine marine sandstones and mudstones. Shore platforms have formed in two principal lithological units: a homogeneous unit that is characterized by few discontinuities, and a fractured unit with joints spaced about 0·5 m apart. Rock hardness is low in both units (L‐type Schmidt hammer rebound values of 31 ± 4), and there is little systematic variation in values between the two units in which platforms have developed. Case‐hardened concretions within the sandstone are significantly harder than surrounding rock and cause local relief of metre scale as the spherical diagenetic features are eroded from the bedrock. They do not, however, appear to affect broad‐scale platform geometry. Joints within the bedrock are a primary control on platform elevation. Platforms formed in jointed rock occur at the lower portion of the intertidal zone, in contrast to platforms formed in unjointed bedrock, in which horizontal surfaces occur at or above mean high water spring tide level. Rock structure, therefore, appears to be the primary determinant factor of platform geometry at Shag Point. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Radio H I and optical absorption-line spectra of an intermediate-velocity cloud in the general direction of the M15 globular cluster     

D. C. Kennedy  B. Bates  F. P. Keenan  S. N. Kemp  R. S. I. Ryans  R. D. Davies  & K. R. Sembach 《Monthly notices of the Royal Astronomical Society》1998,297(3):849-859

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Uncertainties in p-MODE POWER AND LINEWIDTH     

J. R. Kennedy 《Solar physics》1998,181(2):265-273

A statistical approach implies that the commonly accepted derivation for the stochastic variation in line power leads to a 67% underestimate. The 'lifetime of a mode should be defined in terms of the reciprocal of the linewidth, not the e-folding time of the mode. The ratio of positive to negative measurement uncertainties in observed linewidth data is essentially constant. Modeling the distribution of the linewidth measurement values as an exponential produces self-consistent estimates of the standard deviation, and can be useful in examining error propagation. The ratio of the line-power uncertainties is also nearly constant. However, the measurement distribution is more complex. It exhibits behavior similar to an exponential, but has more components.  相似文献   

Long-term biological data sets: Their role in research,monitoring, and management of estuarine and coastal marine systems     

D. A. Wolfe  M. A. Champ  D. A. Flemer  A. J. Mearns 《Estuaries and Coasts》1987,10(3):181-193

Long-term records of biological data are extremely valuable for documenting ecosystem changes, for differentiating natural changes from those caused by humans, and for generating and analyzing testable hypotheses. Long-term sampling, however, is generally discouraged by a variety of institutional disincentives, so that today such records are uncommon. We discuss approaches for overcoming these disincentives through improved research planning and design, including clearera priori definition of management and regulatory actions and information needs, more rigorous adherence to hypothesis formulation and testing, and proper spatial and temporal scaling in sampling. We distinguish between prospective study design, in which the foregoing elements are essential for coast-effectiveness, and retrospective analysis, which relies on reconstruction of long-term records from existing data sets. We demonstrate the great value of retrospective analysis of encountered data, and argue for renewed attention to archival of data sets with documented data quality, interacalibration and documentation of methodologies, and long-term storage of samples for future analysis. Such practices are essential to ensure the quality of long-term records that are reconstructed for retrospective examination of new hypotheses in the future.  相似文献   

Composite titanomagnetite-ferrian ilmenite grains and correlative magnetic components in a dacite with self-reversed TRM     

Lawrence P. Kennedy  Margery D.Osborne 《Earth and Planetary Science Letters》1987,84(4)

Electron microprobe and reflected light microscopic examinations confirm the presence of composite grains of ferrian ilmenite with X_ilm = 0.53 and titanomagnetite with X_usp = 0.13 in a dacite with self-reversed TRM. A parallel TRM component associated with titanomagnetite and a reversed component associated with self-reversing ferrian ilmenite are the principal NRM components. A subordinate, parallel component is associated with ferrian ilmenite which is not magnetically coupled to an “χ-phase”. The natural self-reversing properties are mainly a consequence of the dacite's high quenching temperature, calculated at 862–864°C using the Fe—Ti oxide geothermometer, and are most consistent with the self-reversal mechanism proposed by Lawson et al. [9].The conduction of thermal demagnetization and TRM induction tests in air had a much greater effect on the Fe—Ti oxides than did natural cooling, and resulted in significant oxidation with the consequent modification of some magnetic properties and the formation of another reversed TRM component. The subdivision of titanomagnetite grains by oxidation along fractures decreased its effective grain size and caused an apparent increase in its magnetic intensity, in addition to a slight increase in its resistance to alternating field demagnetization. The χ-phase associated with the reversed NRM component, with 0.42 > X_ilm 0.31, became Fe-enriched during the earlier stages of heat treatment. It is suggested that after heating at 600°C for two hours or more, this χ-phase exsolves as titanohematite with X_ilm < 0.33. The ferrian ilmenite host is consequently enriched in Ti, and another χ-phase much closer in composition to the host generates a reversed TRM component with T_b < 200°C.  相似文献   

On Playfair's law of accordant junctions     

Barbara A. Kennedy 《地球表面变化过程与地形》1984,9(2):153-173

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Gold Content of Eleven French Geochemical Reference Samples     

T.J. Bornhorst  W.I. Rose  S.P. Wolfe  E.L. Hoffman 《Geostandards and Geoanalytical Research》1984,8(1):1-2

The gold content of eleven French geochemical reference samples has been determined by a combined neutron-activation and fire assay method. These data represent the first reported low-level and high quality gold analyses for these reference samples.  相似文献   

Influence of Mn oxides on the reduction of uranium(VI) by the metal-reducing bacterium Shewanella putrefaciens     

James K. FredricksonDavid W. Kennedy  Chongxuan LiuMartine C. Duff  Douglas B. Hunter  Alice Dohnalkova 《Geochimica et cosmochimica acta》2002,66(18):3247-3262

The potential for Mn oxides to modify the biogeochemical behavior of U during reduction by the subsurface bacterium Shewanella putrefaciens strain CN32 was investigated using synthetic Mn(III/IV) oxides (pyrolusite [β-MnO₂], bixbyite [Mn₂O₃] and K⁺-birnessite [K₄Mn₁₄O₂₇ · 8H₂O]). In the absence of bacteria, pyrolusite and bixbyite oxidized biogenic uraninite (UO₂[s]) to soluble U(VI) species, with bixbyite being the most rapid oxidant. The Mn(III/IV) oxides lowered the bioreduction rate of U(VI) relative to rates in their absence or in the presence of gibbsite (Al[OH]₃) added as a non-redox-reactive surface. Evolved Mn(II) increased with increasing initial U(VI) concentration in the biotic experiments, indicating that valence cycling of U facilitated the reduction of Mn(III/IV). Despite an excess of the Mn oxide, 43 to 100% of the initial U was bioreduced after extended incubation. Analysis of thin sections of bacterial Mn oxide suspensions revealed that the reduced U resided in the periplasmic space of the bacterial cells. However, in the absence of Mn(III/IV) oxides, UO₂(s) accumulated as copious fine-grained particles external to the cell. These results indicate that the presence of Mn(III/IV) oxides may impede the biological reduction of U(VI) in subsoils and sediments. However, the accumulation of U(IV) in the cell periplasm may physically protect reduced U from oxidation, promoting at least a temporal state of redox disequilibria.  相似文献   

Estuarine shore platforms in Whanganui Inlet, South Island, New Zealand   总被引：1，自引：0，他引：1  

D.M. Kennedy  R. Paulik   《Geomorphology》2007,88(3-4):214-225

Whanganui Inlet is a low mesotidal environment where wave energy at the shoreline is limited due to a small fetch, a narrow entrance and tidal flat accretion to intertidal elevations. Wave energy is therefore only an erosive force at high tide and under storm conditions. Despite this low-energy environment extensive shore platforms occur within the inlet. They are sub-horizontal and range in width from 4.1 to 185.2 m with an average of 44.9 m. All the platforms are formed in sandstone of low resistance (mean N-type Schmidt Hammer rebound value of 17 ± 8) and have their seaward edges buried by intertidal sediment flats. The majority of platforms occur at around MHWN level, corresponding to the elevation of those flats. Where wave energy is highest, opposite the inlet's entrance and at those sites with the largest fetch, platforms develop to 0.5–1.0 m below MSL. A higher platform level is also found at MHWS elevations, however it appears to be relict with active erosion of its seaward edge occurring and therefore is most likely related to a higher mid-Holocene sea level. Apart from the location of the lowest platforms little correspondence is found between platform morphology and wave energy. Platform evolution appears to be intrinsically linked to the intertidal sediment flats which determine the degree of surface saturation of the bedrock and, hence, the number of wetting and drying cycles the platforms may undergo. As the seaward edge is buried platform development is primarily through retreat of the landward cliff. This process can, however, be complicated by the migration of intertidal water channels onto the seaward edge of the platforms or relative sea level fall which may rejuvenate landward retreat of the low-tide cliff.  相似文献   

Do flexural stresses explain the mantle fault zone beneath Kilauea volcano?     

M. E. Pritchard  A. M. Rubin  C. J. Wolfe 《Geophysical Journal International》2007,168(1):419-430

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