Paleoshoreline geomorphology of Böön Tsagaan Nuur, Tsagaan Nuur and Orog Nuur: the Valley of Lakes, Mongolia     

Goro Komatsu  P. Jeffrey Brantingham  John W. Olsen  Victor R. Baker 《Geomorphology》2001,39(3-4)

We conducted a preliminary study of paleoshoreline features associated with Böön Tsagaan Nuur, Tsagaan Nuur, and Orog Nuur, lakes located in the Gobi–Altai transition zone of the Valley of Lakes (Dolina Ozor) which stretches from central to western Mongolia. The paleoshoreline features were first identified on RADARSAT satellite SAR imagery. We investigated the features during the 1998 field season of the Joint Mongolian–Russian–American Archaeological Expedition to the Gobi–Altai region. We identified paleoshorelines of multiple elevations in the field, which are considered to be relict beach ridges and wave-cut terraces. Other paleolake landforms include spits and Gilbert-type deltas. These landforms are complex, large and well established, implying that the paleolakes were stable for extended periods. The reconstructed paleolakes cover extensive areas of the valley floor, implying that hydrological and climatic conditions were very different in the past. Paleolake expansions may have occurred under a variety of circumstances. One hypothesis is that the high lake stands occurred during the wetter period corresponding to the Oxygen Isotope Stage 3 prior to the Last Glacial Maximum (LGM), during the warmest early Holocene and the late Holocene, or during all these periods. If low evaporation rates due to lower temperatures, glacier meltwater and possibly increased precipitation are important factors, then the expansions may have occurred during the terminal Late Glacial period after the Last Glacial Maximum. The greatly expanded lakes in the Gobi–Altai could have significantly affected the Quaternary human demography and migration in the region.  相似文献   

High-density CO2 inclusions in the Colorado Front Range   总被引：1，自引：0，他引：1  

Sakiko N. Olsen 《Contributions to Mineralogy and Petrology》1988,100(2):226-235

A fluid density in an inclusion is commonly observed to be too low for the P-T estimates for the postulated time of trapping, and is generally attributed to a fluid loss during the uplift process. It is more difficult to explain a fluid density which is too high. In the 1700 m.y. Front Range migmatites, such high densities occur in some of CO₂ inclusions which were deduced to have formed during the migmatization episode. The peak P-T estimates for migmatization in the Front Range are 4–6 kb and 650°–700° C (in sillimanite field) but pressures required to form the most dense inclusions are >7.6 kb (in kyanite field). The high density is not likely to be a relic of a higher pressure condition earlier than the main migmatization episode for the following reasons: (a) no kyanite (or any other relic high pressure phase) has been found in the Precambrian Front Range; (b) the high density inclusions are rare in zones with least signs of deformation and melting (paleosomes and quartz inclusions within feldspar grains) which instead contain relatively undisturbed early inclusions; (c) high density inclusions with Th <–30° C are associated with heavily altered plagioclase caused by hydrothermal activity which was a late event in leucosome formation. Further, there is evidence for post-entrapment change(s) in density: an intragranular trail in quartz contains CO₂ inclusions that exhibit almost the whole range in Th (–40 to +24° C) as displayed by the entire population of the early CO₂ inclusions (–66 to +30° C). The density of an inclusion in the trail is not related to inclusion size but to the position of the inclusion relative to apparent micro-shear zones crossing the CO₂ trail. A change to a higher density (=a smaller volume) could have resulted from an initially isobaric cooling path which intersects CO₂ isochores with increasingly higher densities. Additional excess pressure may have resulted from overthrusting. However, because high density inclusions occur selectively in the zones in which plagioclase shows alteration indicating a high and because there is a correlation between shear zones and high density inclusions, it is postulated that local hydrolytic weakening of quartz was necessary for the decrease of inclusion volume which occurred during deformation. The localized deformation may also result in an excess pressure. However, the introduction of a small amount of H₂O into these inclusions as a possible cause of high density inclusions cannot be ruled out.  相似文献   

Plutonium and radiocesium in the water column of the Hudson River estuary     

P. Linsalata  H. J. Simpson  C. R. Olsen  N. Cohen  R. M. Trier 《Environmental Geology》1985,7(4):193-204

Isotopes of plutonium (Pu), cesium (Cs), and cobalt (Co) introduced into the Hudson River Estuary from fallout deposition, the erosion of fallout-contaminated surface soils, and nuclear reactor effluent (isotopes of Cs and Co only) have been measured in water column samples collected from 1975 to 1980 Isotopic measurements conducted independently by two research groups utilizing different sampling and analytical techniques have been summarized. The major conclusions drawn from the work are that for water samples collected by the two laboratories over similar time periods, the mean concentrations of nonfilterable^239,240Pu (<0.45 μm) were identical at 0.13 fCi/l, mean concentrations of both¹³⁷Cs and^239,240Pu in suspended particulates were more divergent at 2,270±920 pCi/kg (±1 SD) and 1,430±430 pCi/kg for¹³⁷Cs, and 19±8 pCi/kg and 12±4 pCi/kg for^239,240Pu The behavior of^239,240Pu and¹³⁷Cs within the water column is shown to diverge within brackish waters Specifically, the magnitude of the¹³⁷Cs distribution coefficient (K _d ) can be expressed as an inverse power function of the chloride ion concentrations for chlorinities between 0.1 and 4 g Cl⁻/l No difference in the^239,240PuK _d has been observed between fresh and brackish waters Based on the expected inventories of^239,240Pu and¹³⁷Cs within watershed soils, the current downstream transport of these radionuclides represents fractional mobilization rates on the order of 1–4 (×10⁻⁴) per year  相似文献   

Modeling short-period crustal phases ($\text{P}$, Lg) for long-range refraction profiles     

K.H. Olsen  L.W. Braile  J.N. Stewart 《Physics of the Earth and Planetary Interiors》1983,31(4):334-347

The short-period seismic phases known as $\text{P}$ and Lg are often recorded at distances of 200–1000 km on long-range refraction profiles and are usually the largest-amplitude features on record sections for this distance range. $\text{P}$ and Lg propagate as multiply reflected compressional and shear waves in a crustal waveguide whose principal boundaries are the Moho and the free surface. Equivalently, they can be interpreted as the interference pattern produced by a superposition of higher-mode P, SV and SH waves propagating in a leaky waveguide. For compressional waves, the waveguide efficiency is a strong function of frequency and depends on the presence or absence of low-velocity layers within a few kilometers of the surface, such as deep sedimentary sections commonly found in active tectonic areas. Such low-velocity surface layers create constructive interference effects for upcoming P waves incident at near grazing angles at the free surface and lead to efficient $\text{P}$ propagation. Several good examples of strong $\text{P}$ phases can be found on long-range refraction profiles for the tectonically active western United States; the 550 km profile eastward from SHOAL to Delta, UT is analyzed here. We have used a modified reflectivity-method computer program to model crustal phases for the SHOAL-Delta profile. The reflectivity technique accounts for all body and surface waves contributing to the short-period seismograms. It is found that the synthetic waveforms realistically model the observed $\text{P}$ characteristics. In this case, the decay of $\text{P}$ amplitudes with distance appears to be dominated by surface-reflection leakage from the waveguide rather than by anelastic attenuation due to Q of crustal rocks.  相似文献   

Climate Change and Floodplain Management in the United States     

J. Rolf Olsen 《Climatic change》2006,76(3-4):407-426

Federal agencies use flood frequency estimates to delineate flood risk, manage the National Flood Insurance Program, and ensure that Federal programs are economically efficient. The assumption behind traditional flood risk analysis is that climate is stationary, but anthropogenic climate change and better knowledge of interdecadal climate variability challenge the validity of the assumption. This paper reviews several alternative statistical models for flood risk estimation that do not assume climate stationarity. Some models require subjective judgement or presuppose an understanding of the causes of the underlying non-stationarity, which is problematic given our current knowledge of the interaction of climate and floods. Although currently out of favor, hydrometeorological models have been used for engineering design as alternatives to statistical models and could be adapted to different climate conditions. Floodplain managers should recognize the potentially greater uncertainty in flood risk estimation due to climate change and variability and try to incorporate the uncertainties into floodplain management decision-making and regulation.  相似文献   

The Tsenkher structure in the Gobi-Altai, Mongolia: Geomorphological hints of an impact origin     

Goro Komatsu  John W. Olsen  Jens Orm  Gaetano Di Achille  David A. Kring  Takafumi Matsui 《Geomorphology》2006,74(1-4):164-180

The Tsenkher structure, in the Gobi-Altai region of Mongolia, was studied using a wide array of remote sensing data and field observations. The structure has a shallow, 3.6 km wide, central depression bordered by a near-circular ridge (putative crater rim) with breaches to the northwest. The central depression is obliterated partially by fluvial infill through these breaches. Outside the ridge, the western side is a rugged terrain, but the eastern half is characterized by a concentric outer ridge that occurs at about one radius distance from the inner ridge. Although intrusion, salt tectonics and maar crater hypotheses cannot be completely ruled out, its morphology strongly implies an impact origin for the Tsenkher structure. If of impact origin, it has a well-preserved morphology and its position in the basin fills indicates that the formation may have occurred relatively recently, sometime during the late Tertiary or Quaternary. The outer ridge morphology is similar to rampart craters on Mars, whose formation has been attributed to fluidization of a water-rich target layer and ejecta materials, or to atmospheric entrainment and deposition of ejected materials. However, other hypotheses including erosional remnant of ejecta blanket, erosional scarp of structural rim uplift, multi-ring or deeply eroded crater rim of a peak-ring crater are also possible at this stage. A complex fluvial and probable lacustrine history is envisaged within the Tsenkher structure. The structure is also associated with archaeology, including Paleolithic and Bronze Age remains.  相似文献   

CHAOS—a model of the Earth's magnetic field derived from CHAMP, Ørsted, and SAC-C magnetic satellite data     

Nils Olsen  Hermann Lühr  Terence J. Sabaka  Mioara Mandea  Martin Rother  Lars Tøffner-Clausen  Sungchan Choi 《Geophysical Journal International》2006,166(1):67-75

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Earth's lithospheric magnetic field determined to spherical harmonic degree 90 from CHAMP satellite measurements   总被引：3，自引：0，他引：3  

S. Maus †  M. Rother  K. Hemant  C. Stolle  H. Lühr  A. Kuvshinov  N. Olsen 《Geophysical Journal International》2006,164(2):319-330

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Treatment of a Chromate-Contaminated Soil Site by in situ Gaseous Reduction     

E.C. Thornton  T.J. Gilmore  K.B. Olsen  J.T. Giblin  J.M. Phelan 《Ground Water Monitoring & Remediation》2007,27(1):56-64

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Internal waves in the earth's core     

Peter Olsen 《Geophysical Journal International》1977,51(1):183-215

This paper investigates possible long-period oscillations of the earth's fluid outer core. Equations describing free oscillations in a stratified, self-gravitating, rotating fluid sphere are developed using a regular perturbation on the equations of hydrodynamics. The resulting system is reduced to a finite set of ordinary differential equations by ignoring the local horizontal component of the earth's angular velocity vector, Ω, and retaining only the vertical component. The angular dependence of the eigensolutions is described by Hough functions, which are solutions to Laplace's tidal equation.
The model considered here consists of a uniform solid elastic mantle and inner core surrounding a stratified, rotating, inviscid fluid outer core. The quantity which describes the core's stratification is the Brunt—Väisälä frequency N , and for particular distributions of this parameter, analytical solutions are presented. The interaction of buoyancy, and rotation results in two types of wave motion, the amplitudes of which are confined predominantly to the outer core: (1) internal gravity waves which exist when N ² > 0, and (2) inertial oscillations which exist when N ²<4Ω². For a model with a stable density stratification similar to that proposed by Higgins & Kennedy (1971), the resulting internal gravity wave eigenperiods are all at least 8 hr, and the fundamental modes have periods of at least 13 hr. A model with an unstable density stratification admits no internal gravity waves but does admit inertial oscillations whose eigenperiods have a lower bound of 12hr.  相似文献