Big lake records preserved in a little lake’s sediment: an example from Silver Lake,Michigan, USA     

Timothy G. Fisher  Walter L. Loope  William Pierce  Harry M. Jol 《Journal of Paleolimnology》2007,37(3):365-382

We reconstruct postglacial lake-level history within the Lake Michigan basin using soil stratigraphy, ground-penetrating radar (GPR), sedimentology and ¹⁴C data from the Silver Lake basin, which lies adjacent to Lake Michigan. Stratigraphy in nine vibracores recovered from the floor of Silver Lake appears to reflect fluctuation of water levels in the Lake Michigan basin. Aeolian activity within the study area from 3,000 years (cal yr. B.P.) to the present was inferred from analysis of buried soils, an aerial photograph sequence, and GPR. Sediments in and around Silver Lake appear to contain a paleoenvironmental record that spans the entire post-glacial history of the Lake Michigan basin. We suggest that (1) a pre-Nipissing rather than a Nipissing barrier separated Silver Lake basin from the Lake Michigan basin, (2) that the Nipissing transgression elevated the water table in the Silver Lake basin about 6,500 cal yr. B.P., resulting in reestablishment of a lake within the basin, and (3) that recent dune migration into Silver Lake is associated with levels of Lake Michigan. This is the fourth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue.  相似文献   

Thoughts on Reconnection     

Harry E. Petschek 《Astrophysics and Space Science》1998,264(1-4):9-16

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Three-body dynamics: intermittent chaos with strange attractor     

Pekka Heinämäki  Harry J. Lehto  Mauri J. Valtonen  & Arthur D. Chernin 《Monthly notices of the Royal Astronomical Society》1998,298(3):790-796

We have studied the structure of chaos in three-body dynamics using the concept of intermittency, implying that violent states of a system alternate in time with quasi-regular states producing together a non-stationary and evolving pattern of unpredictable behaviour. Computer simulations are produced to demonstrate explicitly sporadic short violent bursts in quasi-regular hierarchical states of the systems. This is seen both in orbits and in the long time series generated by the system. The time series prove to be similar in shape to what is observed in various physical experiments with laboratory chaotic systems when they reveal the so-called type-III intermittency. The new effective methods of time series analysis enable us to discover a strange attractor with a fractal dimension slightly above 2. This shows that three-body dynamics has the same intrinsic qualitative structure and quantitative measure of chaos as the widely known chaotic system, the Lorenz attractor.  相似文献   

Heavy Metal Concentrations in European Mosses: 2000/2001 Survey   总被引：3，自引：0，他引：3  

Harry Harmens  Alan Buse  Patrick Büker  David Norris  Gina Mills  Bronwen Williams  Brian Reynolds  Trevor W. Ashenden  Åke Rühling  Eiliv Steinnes 《Journal of Atmospheric Chemistry》2004,49(1-3):425-436

The heavy metals in mosses survey was originally established in 1980 as a joint Danish–Swedish initiative under the leadership of Åke Rühling, Sweden and has, since then, been repeated at five-yearly intervals with an increasing number of countries and individuals participating. Twenty-eight European countries, almost 7000 sites and about 100 individuals have been involved in the most recent survey in 2000/2001. The survey provides data on concentrations of 10 heavy metals (arsenic, cadmium, chromium, copper, iron, lead, mercury, nickel, vanadium, zinc) in naturally growing mosses throughout Europe. The technique of moss analysis provides a surrogate measure of the spatial patterns of heavy metal deposition from the atmosphere to terrestrial systems, and is easier and cheaper than conventional precipitation analysis. The aims of the survey are to determine patterns of variation in the heavy metal concentration of mosses across Europe, identify the main polluted areas, produce regional maps and further develop the understanding of long-range transboundary pollution.As in previous surveys, there was an east/west decrease in heavy metal concentrations in mosses, related in particular to industrial emissions. Former industrial sites and historic mines accounted for the location of some high concentrations in areas without contemporary industries. Long-range transboundary transport appears to account for elevated concentrations of heavy metals in areas without emission sources, such as lead in southern Scandinavia (presumably from emission sources elsewhere in Europe).  相似文献   

Textural evidence bearing on the origin of isolated olivine crystals in C2 carbonaceous chondrites     

Steven M. Richardson  Harry Y. McSween 《Earth and Planetary Science Letters》1978,37(3):485-491

In some cases the mechanical competence of chondrules in carbonaceous chondrites has been reduced by alteration of their mesostasis glass to friable phyllosilicate, providing a mechanism by which euhedral olivines can be separated from chondrules. Morphological features of isolated olivine grains found in carbonaceous chondrites are similar to those of olivine phenocrysts in chondrules. These observations suggest that the isolated olivine grains formed in chondrules, by crystallization from a liquid, rather than by condensation from a vapor.  相似文献   

Naturally decorated dislocations in olivine from peridotite xenoliths     

David H. Zeuch  Harry W. Green II 《Contributions to Mineralogy and Petrology》1977,62(2):141-151

Dislocations decorated by hematite and magnetite have been observed optically in the olivine grains of undeformed or highly annealed peridotite xenoliths from Hawaii and Baja California ( 5 × 10⁵ cm^–2). The observed structures include loops, low-angle boundaries, and structures produced by multiple cross-glide of [100] screws. Loops are almost invariably parallel to (001). Simple arrays of parallel dislocations lie predominantly in (100), (010) and (001) with dislocation lines subparallel to low-index directions. [100] screws pinned to (100) boundaries are frequently seen to bow out on (001). Preliminary electron petrography has confirmed that all dislocations are decorated.  相似文献   

Correlation of the Rockland ash bed,a 400,000-year-old stratigraphic marker in northern California and western Nevada,and implications for middle Pleistocene paleogeography of central California     

Andrei M. Sarna-Wojcicki  Charles E. Meyer  Harry R. Bowman  N. Timothy Hall  Paul C. Russell  Marta J. Woodward  Janet L. Slate 《Quaternary Research》1985,23(2):236-257

Outcrops of an ash bed at several localities in northern California and western Nevada belong to a single air-fall ash layer, the informally named Rockland ash bed, dated at about 400,000 yr B.P. The informal Rockland pumice tuff breccia, a thick, coarse, compound tephra deposit southwest of Lassen Peak in northeastern California, is the near-source equivalent of the Rockland ash bed. Relations between initial thickness of the Rockland ash bed and distances to eruptive source suggest that the eruption was at least as great as that of the Mazama ash from Crater Lake, Oregon. Identification of the Rockland tephra allows temporal correlation of associated middle Pleistocene strata of diverse facies in separate depositional basins. Specifically, marine, littoral, estuarine, and fluvial strata of the Hookton and type Merced formations correlate with fluvial strata of the Santa Clara Formation and unnamed alluvium of Willits Valley and the Hollister area, in northwestern and west-central California, and with lacustrine beds of Mohawk Valley, fluvial deposits of the Red Bluff Formation of the eastern Sacramento Valley, and fluvial and glaciofluvial deposits of Fales Hot Spring, Carson City, and Washoe Valley areas in northeastern California and western Nevada. Stratigraphic relations of the Rockland ash bed and older tephra layers in the Great Valley and near San Francisco suggest that the southern Great Valley emerged above sea level about 2 my ago, that its southerly outlet to the ocean was closed sometime after about 2 my ago, and that drainage from the Great Valley to the ocean was established near the present, northerly outlet in the vicinity of San Francisco Bay about 0.6 my ago.  相似文献   

Possible ecological and environmental significance of the predominance of even-carbon number C₂₀-C₃₀n-alkanes     

Harry Dembicki  W.G Meinschein  Donald E Hattin 《Geochimica et cosmochimica acta》1976,40(2):203-208

Even-carbon number C₂₂-C₂₈n-alkanes, are present in higher concentrations than their C₂₁-C₂₉ odd-carbon number homologs in an organic-rich rock of Mississippian (ca. 310 × 10⁶-yr-old) age, which contains algae-like remnants. Environmental indicators associated with this organic-rich rock permitted environmental comparison with ancient and modern environments that contain n-alkanes which exhibit similar distributions. The results of these comparisons suggest that even-carbon number n-alkanes are preferentially produced in highly saline, carbonate environments where aerobic and anaerobic bacteria have subsisted on the remains of blue-green algae.  相似文献   

Use of oxygen isotope ratios in correlation of tuffs,East Rudolf Basin,northern Kenya     

Thure E. Cerling  Donald L. Biggs  Carl F. Vondra  Harry J. Svec 《Earth and Planetary Science Letters》1975,25(3):291-296

Oxygen isotope determinations were made using CoF₃ to extract oxygen from 27 volcanic glass samples from the East Rudolf Basin, northern Kenya. Results show that the older tuffs are progressively enriched in¹⁸O and that this index can be used in the correlation of volcanic ash units. This method could not distinguish individual samples from the youngest units studied because their ranges of δ¹⁸O overlap. The δ¹⁸O values for the shards in the Tulu Bor Tuff, the KBS Tuff, the Koobi Fora Tuff and the Chari Tuff range from 14.5 to 16.4, from 8.9 to 9.5, from 6.6 to 7.0 and from 7.0 to 7.2, respectively, in decreasing age. Determinations from pumice cobbles are consistently higher than the above values.  相似文献   

Consumer spatial choice strategies: A comparative study of some alternative behavioural spatial shopping models     

Harry Timmermans 《Geoforum》1980,11(2):123-131

The purpose of this paper is to outline a conceptual model of consumer spatial decision making and choice behaviour and to investigate the use of various combination rules of consumer's evaluations of attributes of shopping centres to predict spatial choice behaviour.The research findings indicate that the linear combination rules perform as well as the multiplicative rules and that both types of rules perform quite acceptably. The paper concludes by discussing some implications for future research on spatial decision making and choice.  相似文献