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51.
R. Eugene Turner 《Estuaries and Coasts》1978,1(1):65-68
Results from the reverse-flow concentration method used to determine community plankton respiration vary significantly because of metabolic inactivation or losses of a portion of the concentrated sample during the filtering process. These losses seem to be nearly constant at concentrations greater than 150X. The within sample coefficient of variation is 20–40% and is primarily a result of clumping and inadequate mixing before subsampling. A rapid processing of the samples is critical for best results. 相似文献
52.
Francis J. Turner 《Contributions to Mineralogy and Petrology》1975,53(4):241-252
Moderate to strong biaxiality (2V = 10 °–45 °) in experimentally deformed calcite (in single crystals and in marble) is attributed to overlap between one or two thin {01¯12} twin lamellae and the enclosing host. A perfectly centered conoscopic figure (section normal to [0001]) is perceptibly asymmetric about the trace of the optic axial plane. This asymmetry is pronouned in thick sections (> 0.04 mm) and completely distrupts the biaxial configuration of the figure if the overlapping lamella exceeds about 0.0025 mm in thickness. In sections somewhat oblique to [0001] and cut at 20 ° or less to the plane of twinning the conoscopic figure may appear to be perfectly biaxial-expecially in thin sections ( 0.02 mm) enclosing thin ( 0.001 mm) but still visible twins.Similar values of 2V recorded for natural calcite likewise are attributed to twinning on a visible scale. 相似文献
53.
Red beds in the Lower Old Red Sandstone Gamrie Outlier on the southern margin of the Orcadian Basin originated through the diagenetic breakdown of iron silicates. The magnetic evidence indicates that haematite pigment was produced over a long time period because both normal and reversed components of magnetisation are present in individual specimens. A part of the magnetisation in these rocks is carried by coarse particle specularite but there is no evidence that this is DRM or PDRM. The composite nature of the magnetisation and its acquisition over a relatively long time period is also indicated by the fact that all sample/site mean directions are of the same polarity (reversed) but originated over a period when normal and reversed polarities were common. There is evidence that the production of early diagenetic pigment was necessary for the preservation of Devonian magnetisations in these sandstones.Another group of sandstones acquired their magnetisation in Permo-Carboniferous times and these occur in intimate association with those which retain the original composite Devonian direction. The stable NRM of these rocks is carried by specularite and they are thought to have been remagnetised because they originally contained a greater proportion of magnetite than those sandstones which retain the original magnetisation and also an unstable pigment magnetisation. In-situ oxidation of magnetite in Permo-Carboniferous times is thus thought to be responsible for the remagnetisation of these rocks. 相似文献
54.
Professor Dr. Francis J. Turner 《Contributions to Mineralogy and Petrology》1965,11(4):393-397
Consideration of available thermodynamic data and the published results of direct experiments relating to (1) formation. of periclase from dolomite and (2) hydration of periclase to brucite, permits the following conclusions to be drawn: (1) At very low partial pressures of CO2 (perhaps of the order of 1 bar) and relatively high partial pressures of water (up to 2000 bars), dolomite can break down directly to brucite and calcite at temperatures above about 400° C, and below temperatures on the brucite dehydration curve. (2) The reaction dolomite calcite + periclase + CO2 in contact metamorphism near granitic bodies is likely to occur only at low partial pressures of CO2 (perhaps 10 or 20 bars); this can be achieved without direct formation of brucite, by maintaining a partial pressure of water of the order of 1000 bars or more. (3) At low CO2 pressures dolomite may re-form in the cooling stages of metamorphism by reaction between calcite, brucite, and CO2 at temperatures below about 400° C. 相似文献
55.
This paper deals with the incidence and geometry of lattice bending in calcite of naturally strained marble and possible relations in time to associated {01¯12} twinning, as revealed by microscopic examination with a universal stage. Microscopic technique and graphic treatment of data with a view to identifying the relation in time of bending to twinning, and possible glide mechanisms involved in the bending process are reviewed as a basis for present and subsequent investigation of this general topic.In most instances development of surviving thin e twins postdates bending of the host crystal (such twins everywhere are rationally oriented). Rarely (in contrast with experimental experience) some thin twins are slightly irrational (Le lamellae) and apparently developed in the final stages of bending. Thick twins (a few tens of microns wide) on the other hand rather commonly predate or are synchronous with bending.The geometry of bending (external rotation) — especially for rotation less than 25° —commonly is compatible with models (based on experimental experience) of simple translation in the strained domains. The commonest translation system so identified is on {10¯11}, with sense of shear, where recognizable, either negative or positive. Translation on {02¯21} is relatively rare. Unexpectedly there is rather strong but not conclusive evidence of translation on {0001} parallel to an a axis. This mechanism, hitherto never identified with certainty, is now here documented unequivocally in a crystal of calcite experimentally strained at 300° C, 5 kb. 相似文献
56.
During the early development of the Rhodesian craton the regional metamorphism of some of the oldest rocks of Bulawayan and Shamvalan age, was apparently progressive and is expressed in terms of a clearly defined metamorphic zonation established under conditions of relatively high geothermal gradients in which very low grades typical of the central craton pass into extremely high grades that define the cratonic margin particularly within the Zambezi and the Limpopo belts. The distribution of the associated early granitic rocks relates to the metamorphic pattern, thus implying that both metamorphism and granite development were due to thermal highs centred on the Limpopo mobile belt and possibly the Zambezi belt. 相似文献
57.
Thermal demagnetization of red and drab sandstones from the St. Bees Sandstone shows a wide range of directional stability. After the removal of a metastable secondary magnetization at temperatures up to 300°C red sandstones may show stable or unstable magnetization. Experiments indicate that both the stable and unstable magnetization is carried by coarse haematite particles (specularite).Drab sandstones, which have been subject to reduction and dissolution of haematite are generally unstable but specimens with a stable NRM occur and this must be carried by specularite because the pigment has been removed from these specimens.The stable magnetization is believed to have developed during deposition and early diagenesis by the oxidation of detrital iron oxides. Pole positions correspond to known Triassic poles and there are abundant normal and reversed zones typical of the Lower Triassic.The unstable magnetization of the red sandstones is apparently due to the development of authigenic overgrowths of haematite on the detrital specularites. This phase of authigenesis may have taken place over a long time, and after significant changes in the ambient geomagnetic field resulting in complex magnetizations in individual grains and hence whole rocks. 相似文献
58.
David G. Turner 《Astrophysics and Space Science》2010,326(2):219-231
The rationale behind recent calibrations of the Cepheid PL relation using the Wesenheit formulation is reviewed and reanalyzed,
and it is shown that recent conclusions regarding a possible change in slope of the PL relation for short-period and long-period
Cepheids are tied to a pathological distribution of HST calibrators within the instability strip. A recalibration of the period-luminosity relation is obtained using Galactic Cepheids
in open clusters and groups, the resulting relationship, described by log L/L
⊙=2.415(±0.035)+1.148(±0.044)log P, exhibiting only the moderate scatter expected from color spread within the instability strip. The relationship is confirmed
by Cepheids with HST parallaxes, although without the need for Lutz-Kelker corrections, and in general by Cepheids with revised Hipparcos parallaxes, albeit with concerns about the cited precisions of the latter. A Wesenheit formulation of W
V
=−2.259(±0.083)−4.185(±0.103)log P for Galactic Cepheids is tested successfully using Cepheids in the inner regions of the galaxy NGC 4258, confirming the independent
geometrical distance established for the galaxy from OH masers. Differences between the extinction properties of interstellar
and extragalactic dust may yet play an important role in the further calibration of the Cepheid PL relation and its application
to the extragalactic distance scale. 相似文献
59.
Thallium(I) has been added to estuarine sediment suspended in various natural and artificial aqueous samples in order to examine its reactivity under simulated estuarine conditions. In river water and sea water, adsorption of Tl to sediment was so rapid that a period of desorption-relaxation succeeded instantaneous adsorption. Entire time-courses could not be fitted with a conventional kinetic model, but pseudo-first-order forward and reverse rate constants of 0.0044 and 0.30 h−1, respectively, were derived for river water by omitting measurements defining the adsorption “overshoot” observed at the onset of the experiment. The extent of adsorption after a 16 h equilibration period was considerably greater in river water than in sea water, and displayed a quasi-linear increase with increasing pH over the range 2-9 in the former but no clear dependence on pH in the latter. A logarithmic reduction in the sediment-water distribution coefficient, KD, was observed on estuarine mixing from river water to sea water. Experiments conducted in electrolyte solutions coupled with inorganic equilibrium speciation modeling revealed that the effect was the combined result of a reduction in the activity of Tl+, an increase in the proportion of TlCl0 and increasing competition for adsorption sites from K+ with an increase in salinity. Overall, there was little experimental evidence for either the oxidation of Tl+ or its complexation by dissolved organic matter. The findings of the investigation are discussed in terms of the likely behavior of Tl in estuaries. 相似文献
60.
Photographic plates of the Harvard Observatory stacks have been used to obtain 1261 brightness estimates for the low-amplitude Cepheid FF Aql (P = 4.47 days). Combined with published visual, photoelectric, and CCD observations, these data enable the construction of an O-C diagram spanning 122 years. The resulting O-C diagram is parabola-shaped, enabling the determination of quadratic brightness elements for the first time. The evolutionary rate of increase of the period, dP/dt = 0.072 ± 0.011 s/year, is in agreement with theoretical computations for the third crossing of the instability strip. The available data, reduced using the technique of by Eddington and Plakidis, reveal the presence of small, random period fluctuations, ? = 0.0061d ± 0.0044d, that do not distort the evolutionary trend of the O-C residuals. 相似文献