Taking varves to bits: Scanning electron microscopy in the study of laminated sediments and varves   总被引：2，自引：0，他引：2  

Jean M. Dean  Alan E.S. Kemp  David Bull  Jennifer Pike  Gunilla Patterson  Bernd Zolitschka 《Journal of Paleolimnology》1999,22(2):121-136

Conventional high resolution studies of varved sediments are able to identify clastic and biogenic laminae, but are often unable to resolve the nature of fine-scale lamination contained therein. This intra-annual signal provides us with the highest potential resolution from the sedimentary record and can be resolved using scanning electron microscopy (SEM). Six case studies from lacustrine and marine settings are presented to illustrate the combination of clastic and biogenic fabric types typically found in laminated sediments. Clastic laminae fabrics include those which originate through grain settling and those which are event deposits. The correct identification of event deposits is essential if varves are to be used chronologically. SEM-based biogenic laminae fabric studies have identified seasonal faunal successions where individual laminae may be less than 100 thick and most recently, deep chlorophyll maxima (DCM) summer diatom floras, providing an insight into seasonal scale processes. High resolution lamina fabric studies can provide a basis for generating records of seasonal and inter-annual variability, thus contributing to our understanding of lacustrine and marine processes and palaeoenvironmental interpretation.  相似文献   

The role of chlorine in serpentinization     

J. C. Rucklidge  G. C. Patterson 《Contributions to Mineralogy and Petrology》1977,65(1):39-44

Chlorine present in altered ultramafic rocks resides in a compound which is readily soluble in neutral and acidic aqueous solution. Iron is also dissolved by the same solutions giving FeCl = 21. Statistical treatment of multiple microprobe analyses shows a positive correlation between Cl and Fe, and negative correlations between Cl and Mg, and Cl and Si. These, and other data, suggest that Cl is present in the form of submicroscopic grains of a compound for which a likely formula is Fe₂(OH)₃Cl, and which is dispersed through the regions of the rock suffering active alteration. Elsewhere, where alteration is complete the chloride phase is absent.A mechanism is proposed whereby initially acid chlorine bearing solutions become alkaline in bringing about the conversion of olivine to serpentine and at the same time transfer Fe into Fe₂(OH)₃Cl which precipitates in the reaction zone. Fresher, acid, solutions, following as the reaction front progresses, dissolve the Fe₂(OH)₃Cl phase, providing a possibility for long distance transport of Fe and recycling of Cl. pH gradients near the reaction zone may be matched by fO₂ gradients which may bring about the formation of magnetite in the centres of veins between the olivine crystals. All evidence of Cl will be removed when the process is complete, and the serpentine which forms will usually have Fe/Mg greater than the original olivine.  相似文献   

Chronological variations in concentrations and isotopic compositions of anthropogenic atmospheric lead in sediments of a remote subalpine pond     

H. Shirahata  R.W. Elias  C.C. Patterson  M. Koide 《Geochimica et cosmochimica acta》1980,44(2):149-162

Lead concentrations decrease 4-fold in going from the surface of sediments in a mountain pond to relatively small values in layers 130 yr old. There is a corresponding change in the $\text{Pb}{}^{206}\text{Pb}{}^{207}$ ratio in the sediments from industrial-like values of 1.18 near the surface to natural values of 1.24 at depth. Concentrations of Ca, Sr, and Ba remain relatively constant with depth. The excess Pb is shown to be of eolian anthropogenic origin, through isotopic, chemical, and mass balance relationships with metals in aerosols, dry deposition, and precipitation. This proves that inputs of contamination Pb were nearly absent centuries ago in a remote non-domesticated subalpine canyon, but are present today in that ecosystem in amounts more than 20 times the natural inputs and are irrefutably linked with industrial sources. As a consequence of these inputs, present Pb concentrations have been elevated 5-fold in plants and 50-fold in animals above natural levels. These Pb contamination effects are being caused by present-day atmospheric concentrations of ~10 ng Pb/m³. The ecosystem studied here characterizes the vast remote non-domesticated regions of North America, and these findings indicate that such regions are highly polluted by industrial Pb aerosols.  相似文献   

Simulation of the effect of methane bubble plumes on vertical mixing in Mono Lake     

José R. Romero  John C. Patterson  John M. Melack 《Aquatic Sciences - Research Across Boundaries》1996,58(3):210-223

A one-dimensional vertical mixing model modified for application to hypersaline Mono Lake reproduced mixed layer dynamics well but hypolimnetic heating was underestimated. One possible source of increased hypolimnetic heating is vertical mixing caused by bubble plumes of methane rising from the sediments. Estimates of vertical mixing from methane seepage in Mono Lake were made with the inclusion of a bubble plume algorithm. A methane ebullition rate three hundred times greater than the maximum estimate for Mono Lake was required to simulate the observed hypolimnetic heating.  相似文献   

Hilbert-semblance method for acoustic logging data processing     

R.D. Akhmetsafin  V. Dubinskii  D. Patterson 《Russian Geology and Geophysics》2008,49(9):692-697

We suggest a method of multi-element low-frequency acoustic logging data processing which combines advantages of the semblance and phase velocity processing (PVP) techniques, namely, the interference resistance in the former and better accuracy in the latter. The new method is based on point (windowless) semblance by the Hilbert transformation. The introduced concept of phase semblance makes it possible to estimate the signal distribution semblance and the phase. Also suggested are an algorithm for preliminary estimation of formation S-wave slowness from signal group power variations and improved forms of processed data imaging.  相似文献   

Distribution of total Al,Cd, Co,Cu, Ni and Zn in the tongue of the ocean and the northwestern Atlantic Ocean     

James J. Alberts  Donald E. Leyden  Thomas A. Patterson 《Marine Chemistry》1976,4(1):51-56

The elements Al, Cd, Co, Cu, Ni and Zn were concentrated from seawater using tetraethylenepentamine resin and analysed by atomic absorption spectrophotometry. The spatial distribution of these elements in the northwest Atlantic Ocean is discussed with respect to possible riverine inputs to the area from Puerto Rico.  相似文献   

Calendar of events     

C. Patterson 《Applied Ocean Research》1984,6(2):123-124

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Experience on offshore cathodic protection retrofitting in the northern South China Sea     

Guo Jinwen  L. Patterson  A. Amorelli  D. Condanni  B. Bazzoni 《海洋学报(英文版)》2003,22(4):679-688

Platforms Ⅰ and Ⅱ are steel structures located in offshore areas southeast of the Zhujiang(Pearl) River Delta, the northern South China Sea, in about 110 m water depth. The jackets, with aluminum sacrificial anodes for cathodic protection (CP) of the immersed zone, were launched in March 1995. In May 1996 a CP survey showed that, after almost one year of service, a low polarization level had been achieved and some extended unprotected zones existed, mainly in the deepest part of the Platform Ⅱ. Further to this, a joint activity was decided in order to assess the need of a possible retrofitting of the CP systems. The results of the activity carried out are dealt with, including technical and economical comparisons amongst several retrofitting options, both with sacrificial anodes and with impressed current systems. The adopted solution is illustrated and data are reported on the level of protection presently achieved.  相似文献   

Measurement of persistent organic pollutants (POPs) in plastic resin pellets from remote islands: toward establishment of background concentrations for International Pellet Watch   总被引：1，自引：0，他引：1  

Heskett M  Takada H  Yamashita R  Yuyama M  Ito M  Geok YB  Ogata Y  Kwan C  Heckhausen A  Taylor H  Powell T  Morishige C  Young D  Patterson H  Robertson B  Bailey E  Mermoz J 《Marine pollution bulletin》2012,64(2):445-448

Plastic resin pellets collected from remote islands in the Pacific, Atlantic, and Indian Oceans and the Caribbean Sea were analyzed for polychlorinated biphenyls (PCBs), dichloro-diphenyltrichloroethane and its degradation products (DDTs), and hexachlorocyclohexanes (HCHs). Concentrations of PCBs (sum of 13 congeners) in the pellets were 0.1-9.9 ng/g-pellet. These were 1-3 orders of magnitude smaller than those observed in pellets from industrialized coastal shores. Concentrations of DDTs in the pellets were 0.8-4.1 ng/g-pellet. HCH concentrations were 0.6-1.7 ng/g-pellet, except for 19.3 ng/g-pellet on St. Helena, where current use of lindane is likely influence. This study provides background levels of POPs (PCBs<10 ng/g-pellet, DDTs <4 ng/g-pellet, HCHs <2 ng/g-pellet) for International Pellet Watch. Sporadic large concentrations of POPs were found in some pellet samples from remote islands and should be considered in future assessments of pollutants on plastic debris.  相似文献   

A Holocene record of Pacific Decadal Oscillation (PDO)-related hydrologic variability in Southern California (Lake Elsinore,CA)     

M. E. Kirby  S. P. Lund  W. P. Patterson  M. A. Anderson  B. W. Bird  L. Ivanovici  P. Monarrez  S. Nielsen 《Journal of Paleolimnology》2010,44(3):819-839

High-resolution terrestrial records of Holocene climate from Southern California are scarce. Moreover, there are no records of Pacific Decadal Oscillation (PDO) variability, a major driver of decadal to multi-decadal climate variability for the region, older than 1,000 years. Recent research on Lake Elsinore, however, has shown that the lake’s sediments hold excellent potential for paleoenvironmental analysis and reconstruction. New 1-cm contiguous grain size data reveal a more complex Holocene climate history for Southern California than previously recognized at the site. A modern comparison between the twentieth century PDO index, lake level change, San Jacinto River discharge, and percent sand suggests that sand content is a reasonable, qualitative proxy for PDO-related, hydrologic variability at both multi-decadal-to-centennial as well as event (i.e. storm) timescales. A depositional model is proposed to explain the sand-hydrologic proxy. The sand-hydrologic proxy data reveal nine centennial-scale intervals of wet and dry climate throughout the Holocene. Percent total sand values >1.5 standard deviation above the 150–9,700 cal year BP average are frequent between 9,700 and 3,200 cal year BP (n = 41), but they are rare from 3,200 to 150 cal year BP (n = 6). This disparity is interpreted as a change in the frequency of exceptionally wet (high discharge) years and/or changes in large storm activity. A comparison to other regional hydrologic proxies (10 sites) shows more then occasional similarities across the region (i.e. 6 of 9 Elsinore wet intervals are present at >50% of the comparison sites). Only the early Holocene and the Little Ice Age intervals, however, are interpreted consistently across the region as uniformly wet (≥80% of the comparison sites). A comparison to two ENSO reconstructions indicates little, if any, correlation to the Elsinore data, suggesting that ENSO variability is not the predominant forcing of Holocene climate in Southern California.  相似文献