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61.
Maria D. Papanikolaou Maria V. Triantaphyllou Ellen S. Platzman Philip L. Gibbard Conall Mac Niocaill Martin J. Head 《第四纪科学杂志》2011,26(5):523-540
The chronostratigraphy of a long, onshore Early–Middle Pleistocene marine sedimentary sequence on the south‐east part of Zakynthos island, Greece, is presented. Correlation of the succession with the isotope record of Ocean Drilling Program Site 963 reveals the combined influence of tectonics and eustacy in this area. The sequence is divided into three formations by two main unconformities that apparently relate to sea‐level lowstands associated with two major northern hemisphere glaciations, those of marine isotope stages (MIS) 22 and 12. The Zakynthos sequence in many ways is comparable with the Italian Valle di Manche section. Magnetostratigraphic and rock magnetic analyses, supported by biostratigraphy, document the position of the Matuyama/Brunhes Chron boundary (0.77 Ma), the top and base of the Jaramillo Subchron (0.99–1.07 Ma), the Cobb Mountain Subchron (1.173–1.185 Ma) and the top of the Olduvai Subchron (1.78 Ma). The underlying strata are constrained exclusively by detailed nannofossil biostratigraphy extending at least to the lowermost Pleistocene at around 2.54 Ma and therefore certainly incorporating the base of the Olduvai Subchron (1.95 Ma) and possibly the Gauss/Matuyama Chron boundary (2.58 Ma). In addition, a remarkable increase in sedimentation rate (from 3.2 and 28 cm ka?1 to 167 cm ka?1) and hence resolution above the Matuyama/Brunhes boundary (Middle Pleistocene) reveals one short‐lived magnetic excursion, possibly 17a (0.66 Ma), within the normal polarity Brunhes Chron. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
62.
Measurements of sap flow, meteorological parameters, soil water content and tension were made for 4 months in a young cashew (Anacardium occidentale L.) plantation during the 2002 rainy season in Ejura, Ghana. This experiment was part of a sustainable water management project in West Africa. The Granier system was used to measure half‐hourly whole‐tree sap flow. Weather variables were observed with an automatic weather station, whereas soil moisture and tension were measured with a Delta‐T profile probe and tensiometers respectively. Clearness index (CI), a measure of the sky condition, was significantly correlated with tree transpiration (r2 = 0·73) and potential evaporation (r2 = 0·86). Both diurnal and daily stomata conductance were poorly correlated with the climatic variables. Estimated daily canopy conductance gc ranged from 4·0 to 21·2 mm s−1, with a mean value of 8·0 ± 3·3 mm s−1. Water flux variation was related to a range of environmental variables: soil water content, air temperature, solar radiation, relative humidity and vapour pressure deficit. Linear and non‐linear regression models, as well as a modified Priestley–Taylor formula, were fitted with transpiration, and the well‐correlated variables, using half‐hourly measurements. Measured and predicted transpiration using these regression models were in good agreement, with r2 ranging from 0·71 to 0·84. The computed measure of accuracy δ indicated that a non‐linear model is better than its corresponding linear one. Furthermore, solar radiation, CI, clouds and rain were found to influence tree water flux. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
63.
64.
William F. Bleam Philip E. Pfeffer James S. Frye 《Physics and Chemistry of Minerals》1989,16(5):455-464
This study examines the links between 31P solidstate NMR studies of aluminum phosphate minerals and their crystallographic structures. We found that 31P isotropic chemical shift values, iso, carry little information about mineral structures. There seems to be no relation between the chemical shift anisotropy, =33–11 (33>22> 11), and indicies of phosphate-tetrahedra distortion. 31P1H heteronuclear magnetic dipole interactions, on the other hand, carry important information about hydrous phosphate mineral structures, information that should prove to be quite valuable in studies of phosphate adsorbed on mineral surfaces. This interaction can be measured through a variety of qualitative and quantitative experiments. It appears that spin diffusion is so rapid that subtle differences in hydrogen-bonding environments cannot be resolved. 相似文献
65.
Bruce N. Bjornstad James P. McKinley Todd O. Stevens Shirley A. Rawson James K. Fredrickson Philip E. Long 《Ground Water Monitoring & Remediation》1994,14(4):140-147
Hydrogen gas was discovered within the steel casing above standing water in a percussion-drilled borehole on the Hanlord Site in south-central Washington state. In situ measurements of the borehole fluids indicated anoxic, low-Eh (<-400 mV) conditions. Ground water sampled from adjacent wells in the same formation indicated that the ground water was oxygenated. H2 was generated during percussion drilling, due to the decomposition of borehole waters as a result of aqueous reactions with drilled sediment and steel from the drilling tools or casing. The generation of H2 within percussion-drilled boreholes that extend below the water table may be more common than previously realized. The ambient concentration of H2 produced during drilling was limited by microbial activity within the casing-resident fluids. H2 was generated abiotically in the laboratory, whereby sterilized borehole slurry samples produced 100 times more H2 than unsterilizcd samples. It appears that H2 is metabolized by microorganisms and concentrations might be significantly greater if not for microbial metabolism. 相似文献
66.
Historical changes in sediments of Pyramid Lake,Nevada, USA: consequences of changes in the water balance of a terminal desert lake 总被引:1,自引:0,他引:1
Sediment cores from the shallow and deep basins of Pyramid Lake, Nevada, revealed variations in composition with depth reflecting changes in lake level, river inflow, and lake productivity. Recent sediments from the period of historical record indicate: (1) CaCO3 and organic content of sediment in the shallow basin decrease at lower lake level, (2) CaCO3 content of deep basin sediments increases when lake level decreases rapidly, and (3) the inorganic P content of sediments increases with decreasing lake volume. Variations in sediment composition also indicate several periods for which productivity in Pyramid Lake may have been elevated over the past 1000 years. Our data provide strong evidence for increased productivity during the first half of the 20th Century, although the typical pattern for cultural eutrophication was not observed. The organic content of sediments also suggests periods of increased productivity in the lake prior to the discovery and development of the region by white settlers. Indeed, a broad peak in organic fractions during the 1800's originates as an increase starting around 1600. However, periods of changing organic content of sediments also correspond to periods when inflow to the lake was probably at extremes (e.g. drought or flood) indicating that fluctuations in river inflow may be an important factor affecting sediment composition in Pyramid Lake. 相似文献
67.
A. G. Taher S. Abdel Wahab G. Philip W. E. Krumbein A. M. Wali 《International Journal of Salt Lake Research》1995,4(2):95-116
A salina system along the Mediterranean coast of Egypt was investigated. Five sedimentary facies are described. For each facies, the evaporitic sedimentation and the biological conditions are considered. Comparisons of evaporite precipitates in the salina with ancient deposits are made. 相似文献
68.
Beginning in 1986, the U.S. Geological Survey began an effort to develop a National Water-Quality Assessment Program. The basic premise underlying this initiative is that a better understanding of the quality of water resources across the country, both surface- and groundwater, is needed to develop effective programs and policies to meet the nation's water-quality concerns. The program will focus on water-quality conditions that are prevalent or large in scale, such as occur from nonpoint sources of pollution or from a high density of point sources.The design of the program is substantially different from the traditional approach of a diffuse national monitoring network.The major activities of the assessment program will be clustered within a set of hydrologic systems (river basins and aquifer systems), referred to as study units. In aggregate, the study units will account for a large part of the nation's water use and represent a wide range of settings across the country.Unique attributes of the program include: (1) the use of consistent study approaches, field and laboratory methods, water-quality measurements, and ancillary data measurements for all study units; (2) the development of a progressive understanding of water-quality conditions and trends in each study unit through long-term studies that rotate periods of intensive data collection and analysis with periods during which the assessment activities are less intensive; and (3) the focus of considerable effort on synthesizing results from among the study units to provide information on regional and national water-quality issues.Paper presented at 28th International Geological Congress, Washington, D.C., July 10, 1989. 相似文献
69.
A. G. Taher S. Abd el Wahab G. Philip A. M. Wali W. E. Krumbein 《Mineralium Deposita》1994,29(5):427-429
Heavy metal concentrations of a recent salina on the shore of the Mediterranean Sea near Port Said (Egypt) were investigated. Samples for the heavy metal study were taken in different ponds of the salina. It was found that microbial mat dominated brine sediments concentrated and enriched heavy metal 2–3 times more than sediments lacking microbial mat developments, suggesting that cyanobacteria play a major role in this enrichment. Heavy metal enrichment by cyanobacteria was therefore also studied in the laboratory environment. This study is compared with a recent study of Solar Lake and Sabkha Gavish sediments (Sinai, Egypt). Our conclusion is that recent hypersaline environments with ambient microbial mat (potential stromatolite) developments are ideal examples of present-day environments of metal accumulations. 相似文献
70.
A sequence of satellite images of near-surface phytoplankton pigment concentrations and sea surface temperature together with concurrent surface measurements are used to study an upwelling event during the Coastal Ocean Dynamics Experiment off northern California. These data sets show a high degree of temporal and spatial variability during this episode. Recurrent patterns in this variability give insight into the dynamics of coastal upwelling and its effects on biological distributions. Simple models of coastal upwelling cannot explain the observed phenomena in the CODE region. Satellite estimates of phytoplankton growth rates were about 0.8 day−1 near persistent upwelling centers. 相似文献