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131.
V. D. Mats 《Stratigraphy and Geological Correlation》2013,21(6):637-651
The data obtained from long-term field studies in the Baikal Rift area are summarized. A new stratigraphic scheme is developed on the basis of previous stratigraphic research of N.A. Logachev. The new elements of the scheme are (1) the use of regional correlation horizons; (2) recognition of pre-Tankhoi (pre-Late Oligocene) sediments correlated with the Maastrichtian-Early Oligocene deposits of the Baikal Fore-deep; (3) elimination from the scheme of the Khalagai and Anosovka formations and distinction on their basis of the Tagai, Sasa, Osinovka, and Shankhaikha formations; (4) recognition of several weathering crust beds and Neogene paleosols. The “lower Eopleistocene (Upper Pliocene)” red-rock formation of Logachev is subdivided into the following stratigraphic units: the Cretaceous-Paleogene unit characterized by a few finds of Early Oligocene fossils, the Upper Miocene-Lower Pliocene red clay bearing numerous fossil remains, and the Upper Pliocene reddish clay with abundant localities of fossils. The sections examined in the land portion of the Baikal Rift are correlated with bottom sediments of the Baikal depression and are subdivided into three instead of the two commonly accepted large tectonic-lithological-stratigraphic complexes. Stratigraphic studies provide a new insight into the history of the Baikal Rift and into some general questions of the continental rift formation. 相似文献
132.
133.
Tobias Nilsson Robert Heinkelmann Maria Karbon Virginia Raposo-Pulido Benedikt Soja Harald Schuh 《Journal of Geodesy》2014,88(5):491-502
In this paper we investigate the accuracy of the earth orientation parameters (EOP) estimated from the continuous VLBI campaign CONT11. We first estimated EOP with daily resolution and compared these to EOP estimated from GNSS data. We find that the WRMS differences are about 31 $\upmu $ as for polar motion and 7 $\upmu $ s for length of day. This is about the precision we could expect, based on Monte Carlo simulations and the results of the previous CONT campaigns. We also estimated EOP with hourly resolution to study the sub-diurnal variations. The results confirm the results of previous studies, showing that the current IERS model for high-frequency EOP variations does not explain all the sub-diurnal variations seen in the estimated time series. We then compared our results to various empirical high-frequency EOP models. However, we did not find that any of these gave any unambiguous improvement. Several simulations testing the impact of various aspects of, e.g. the observing network were also made. For example, we made simulations assuming that all CONT11 stations were equipped with fast VLBI2010 antennas. We found that the WRMS error decreased by about a factor five compared to the current VLBI system. Furthermore, the simulations showed that it is very important to have a homogenous global distribution of the stations for achieving the highest precision for the EOP. 相似文献
134.
Timo Christian Kessler Alessandro Comunian Fabio Oriani Philippe Renard Bertel Nilsson Knud Erik Klint Poul Løgstrup Bjerg 《Ground water》2013,51(5):692-705
Sand lenses at various spatial scales are recognized to add heterogeneity to glacial sediments. They have high hydraulic conductivities relative to the surrounding till matrix and may affect the advective transport of water and contaminants in clayey till settings. Sand lenses were investigated on till outcrops producing binary images of geological cross‐sections capturing the size, shape and distribution of individual features. Sand lenses occur as elongated, anisotropic geobodies that vary in size and extent. Besides, sand lenses show strong non‐stationary patterns on section images that hamper subsequent simulation. Transition probability (TP) and multiple‐point statistics (MPS) were employed to simulate sand lens heterogeneity. We used one cross‐section to parameterize the spatial correlation and a second, parallel section as a reference: it allowed testing the quality of the simulations as a function of the amount of conditioning data under realistic conditions. The performance of the simulations was evaluated on the faithful reproduction of the specific geological structure caused by sand lenses. Multiple‐point statistics offer a better reproduction of sand lens geometry. However, two‐dimensional training images acquired by outcrop mapping are of limited use to generate three‐dimensional realizations with MPS. One can use a technique that consists in splitting the 3D domain into a set of slices in various directions that are sequentially simulated and reassembled into a 3D block. The identification of flow paths through a network of elongated sand lenses and the impact on the equivalent permeability in tills are essential to perform solute transport modeling in the low‐permeability sediments. 相似文献
135.
Karin Högdahl Jaroslaw Majka Håkan Sjöström Katarina Persson Nilsson Stefan Claesson Patrik Konečný 《Contributions to Mineralogy and Petrology》2012,163(1):167-188
Monazite in melt-producing, poly-metamorphic terranes can grow, dissolve or reprecipitate at different stages during orogenic
evolution particularly in hot, slowly cooling orogens such as the Svecofennian. Owing to the high heat flow in such orogens,
small variations in pressure, temperature or deformation intensity may promote a mineral reaction. Monazite in diatexites
and leucogranites from two Svecofennian domains yields older, coeval and younger U–Pb SIMS and EMP ages than zircon from the
same rock. As zircon precipitated during the melt-bearing stage, its U–Pb ages reflect the timing of peak metamorphism, which
is associated with partial melting and leucogranite formation. In one of the domains, the Granite and Diatexite Belt, zircon
ages range between 1.87 and 1.86 Ga, whereas monazite yields two distinct double peaks at 1.87–1.86 and 1.82–1.80 Ga. The
younger double peak is related to monazite growth or reprecipitation during subsolidus conditions associated with deformation
along late-orogenic shear zones. Magmatic monazite in leucogranite records systematic variations in composition and age during
growth that can be directly linked to Th/U ratios and preferential growth sites of zircon, reflecting the transition from
melt to melt crystallisation of the magma. In the adjacent Ljusdal Domain, peak metamorphism in amphibolite facies occurred
at 1.83–1.82 Ga as given by both zircon and monazite chronology. Pre-partial melting, 1.85 Ga contact metamorphic monazite
is preserved, in spite of the high-grade overprint. By combining structural analysis, petrography and monazite and zircon
geochronology, a metamorphic terrane boundary has been identified. It is concluded that the boundary formed by crustal shortening
accommodated by major thrusting. 相似文献
136.
Geostatistics provides a suite of methods, summarized as kriging, to analyze a finite data set to describe a continuous property of the Earth. Kriging methods consist of moving window optimum estimation techniques, which are based on a least-squares principle and use a spatial structure function, usually the variogram. Applications of kriging techniques have become increasingly wide-spread, with ordinary kriging and universal kriging being the most popular ones. The dependence of the final map or model on the input, however, is not generally understood. Herein we demonstrate how changes in the kriging parameters and the neighborhood search affect the cartographic result. Principles are illustrated through a glaciological study. The objective is to map ice thickness and subglacial topography of Storglaciären, Kebnekaise Massif, northern Sweden, from several sets of radio-echo soundings and hot water drillings. New maps are presented. 相似文献
137.
138.
Stable carbon isotope analysis of terrestrial plant leaves preserved in Quaternary lake sediments has the potential to provide high‐resolution reconstructions of past climatic conditions. Preferably, δ13C measurements should be made on a single leaf component, e.g. cellulose, but this approach is often precluded by limited leaf availability. Previous work suggests that reliable palaeoclimatic information also may be derived from δ13C measurements on whole‐leaf tissue, given a similar degree of leaf decomposition between samples. Leaf δ13C data for 12 Scandinavian species of dwarf‐shrubs, shrubs and trees, and a comparison of δ13C data on recent and late Holocene Salix herbacea leaves, revealed that the δ13C signal registered by holocellulose is largely reflected by measurements on whole‐leaf tissue. Holocellulose was found to be consistently enriched in 13C, although this δ13C offset was smaller for subfossil leaves. This supports the use of δ13C measurements on whole‐leaf tissue for climate reconstruction, at least for leaves preserved in soft, late Holocene sediments with minimal diagenetic effects. Leaf carbon and nitrogen data on fresh leaves of the same 12 Scandinavian species, and corresponding data on late Holocene Salix herbacea leaves, suggest that the leaf C:N ratio is a suitable indicator of the degree of leaf decomposition. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
139.
140.
Wolfgang Lutz Mahendra Shah Richard E. Bilsborrow John Bon-gaarts Partha DasGupta Barbara Entwisle Günther Fischer Brigida Garcia Daniel J. Hogan Arne Jernelöv Zhenghua Jiang Robert W. Kates Sanjaya Lall F. Landis MacKellar P.K. Makinwa-Adebusoye Anthony J. McMichael Vinod Mishra Norman Myers Nebojsa Nakicenovic Sten Nilsson Brian C. O'Neill Xizhe Peng Harriet B. Presser Nafis Sadik Warren C. Sanderson Gita Sen Barbara Torrey Dirk van de Kaa Hans J.A. van Ginkel Brenda Yeoh Huda Zurayk 《Global Change & Human Health》2002,3(1):33-35
The forthcoming World Summit on Sustainable Development (WSSD) in Johannesburg (August 26-September 4, 2002) has been set
by the United Nations to consider strategies toward sustainable development in all its dimensions. Hence, its mandate is broader
than that of the Rio 1992 United Nations Conference on Environment and Development (UNCED). Population issues have so far
been discussed in a separate series of World Population Conferences (Bucharest 1974, Mexico City 1984, Cairo 1994). With no
new World Population Conference scheduled for 2004 and Johannesburg having a mandate that is stated to explicitly include
social and economic aspects, population as a key component of sustainable development should figure prominently on the Johannesburg
agenda. Yet, after the third of four preparatory meetings for Johannesburg (which ended in New York on April 5th), consideration
of population is completely absent. The reasons for this are not entirely clear. We assume that they have to do with the fear
of entering into political controversies over abortion. We are concerned that, despite its broader mandate, in most countries
inputs to Johannesburg are being prepared mainly by environment ministries who have little experience in dealing with population
questions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献