Regional and local controls on the spatial distribution of bedrock reaches in the Upper Guadalupe River, Texas     

Amanda Keen-Zebert  Joanna C. Curran 《Geomorphology》2009,112(3-4):295-305

While studies on gravel mantled and mixed alluvial bedrock rivers have increased in recent decades, few field studies have focused on spatial distributions of bedrock and alluvial reaches and differences between reach types. The objective of this work is to identify the spatial distribution of alluvial and bedrock reaches in the Upper Guadalupe River. We compare reach length, channel and floodplain width, sinuosity, bar length and spacing, bar surface grain size, and slope in alluvial and bedrock reaches to identify whether major differences exist between channel reach types. We find that local disturbances, interaction of the channel and valley sides, variation in lithology, and regional structural control contribute to the distribution of bedrock reaches in the largely alluvial channel. Alluvial and bedrock channel reaches in the Upper Guadalupe River are similar, particularly with respect to the distribution of gravel bars, surface grain size distributions of bars, and channel slope and width. Our observations suggest that the fluvial system has adjusted to changes in base level associated with the Balcones Escarpment Fault Zone by phased incision into alluvial sediment and the underlying bedrock, essentially shifting from a fully alluvial river to a mixed alluvial bedrock river.  相似文献   

Assessment of metals and a metalloid in sediments from Hawaiian coral reef ecosystems     

Laetitia Hdouin  Amanda J. Reichelt-Brushett  Ruth D. Gates 《Marine pollution bulletin》2009,58(11):1759-1765

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Anisotropic photocatalytic properties of hematite     

Carrick M. Eggleston  Angela J. A. Shankle  Amanda J. Moyer  Ilkay Cesar  Michael Grätzel 《Aquatic Sciences - Research Across Boundaries》2009,71(2):151-159

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Diatomaceous sedimentation in late Neogene lacustrine basins of western Macedonia, Greece     

R. B. Owen  R. W. Renaut  M. G Stamatakis 《Journal of Paleolimnology》2010,44(1):343-359

Several lacustrine basins were formed by late Miocene tectonic processes in western Macedonia, Greece. These were occupied by a series of lakes and wetland swamps during the late Miocene and early Pliocene giving rise to diatomaceous claystones, siltstones and diatom-bearing tufa deposits. Diatoms are rare or fragmentary in sandstones and chemical sediments, and are absent in conglomerates. The Fe²⁺-rich phosphate minerals anapaite and vivianite are present in parts of the diatomaceous siltstones. Six major diatom groups were identified using cluster and correspondence analyses, each of which tends to be associated with a particular lithofacies. The floras are indicative of mildly acidic to alkaline water of varying depths. The dominant taxa include Aulacoseira ambigua, A. distans, Cyclotella iris and several of its varieties, C. aegeae, C. castracanei, C. elymaea, C. ocellata, and two unidentified Cyclotella. Fragilariaceae are common, consisting mainly of Fragilaria bituminosa, Pseudostaurosira brevistriata, P. zeilleri, Staurosira construens, Staurosirella leptostauron, and S. pinnata. Locally, chysophycean stomatocysts are common, suggesting more oligotrophic conditions. Nine diatom stages are recognized in the Lower Neogene Series at Kariditsa (Kozani basin), reflecting shallow swamps, small alkaline lakes, and terrestrial settings. The Upper Neogene Series rocks are characterized by Mg-rich carbonates such as hydromagnesite, huntite and magnesite. A detailed stratigraphy was developed for Mio-Pliocene deposits in the Florina basin at Klidi. Parts of this sequence show clear cyclicity in both the sediments and the diatom floras, with shallow-water diatoms repeatedly giving way to taxa indicative of deeper conditions. Larger-scale, shallow-deep cycles are also present and may be related to precession- and eccentricity-forced climate change.  相似文献   

Composition and origin of the atmosphere of Jupiter—an update, and implications for the extrasolar giant planets     

S.K Atreya  P.R MahaffyH.B Niemann  M.H WongT.C Owen 《Planetary and Space Science》2003,51(2):105-112

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Evolution of CO on Titan     

Ah-San WongChristopher G. Morgan  Yuk L. YungTobias Owen 《Icarus》2002,155(2):382-392

The early evolution of Titan's atmosphere is expected to produce enrichment in the heavy isotopomers of CO, ¹³CO and C¹⁸O, relative to ¹²C¹⁶O. However, the original isotopic signatures may be altered by photochemical reactions. This paper explains why there is no isotopic enrichment in C in Titan's atmosphere, despite significant enrichment of heavy H, N, and O isotopes. We show that there is a rapid exchange of C atoms between the CH₄ and CO reservoirs, mediated by the reaction ¹CH₂+*CO→¹*CH₂+CO, where *C is ¹³C. Based on recent laboratory measurements, we estimate the rate coefficient for this reaction to be 3.2×10⁻¹² cm³ s⁻¹ at the temperature appropriate for the upper atmosphere of Titan. We investigate the isotopic dilution of CO using the Caltech/JPL one-dimensional photochemical model of Titan. Our model suggests that the time constant for isotopic exchange through the above reaction is about 800 Myr, which is significantly shorter than the age of Titan, and therefore any original isotopic enhancement of ¹³C in CO may have been diluted by the exchange process. In addition, a plausible model for the evolution history of CO on Titan after the initial escape is proposed.  相似文献   

Origin of the major planet atmospheres: Clues from trace species     

S. K. Atreya  S. G. Edgington  D. Gautier  T. C. Owen 《Earth, Moon, and Planets》1994,67(1-3):71-75

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INFLUENCES ON COUNTY FARMLAND PROTECTION EFFORTS IN CALIFORNIA: A DISCRIMINANT ANALYSIS*     

Owen J. Furuseth 《The Professional geographer》1985,37(4):443-451

County-level policies and programs to conserve farmland in California are examined through discriminant analysis. Based on 1981 state planning data, four degrees of farmland protection effort are established. A two-function discriminant analysis using 17 agricultural, socioeconomic, and political-ideological variables correctly predicts the fourfold classification of 88 percent of the counties. The propensity to enact protective actions is associated with the intensity of agricultural development, local government spending and taxing practices, demographic characteristics, ideological and political party voting traditions.  相似文献   

Effects of line blanketing on the solar windows     

Duane Carbon  Owen Gingerich  Robert Kurucz 《Solar physics》1968,3(1):55-63

The increasingly high flux predicted to the violet of 4500 Å by many model solar atmospheres stands in contradiction to the observations. Since one possible cause of the disagreement is that the solar windows by which the observed continuum is established might be obscured by line wings, we have made detailed calculations of these narrow spectral regions. With the exception of a few windows affected by the wings of Balmer lines, those redward of the Balmer discontinuity appear free of line blanketing. Even the assumption that the ultraviolet continuum is depressed 5% by unseen lines not included in our calculations leaves substantial disagreements between the models and observations. The discrepancies could perhaps be explained by a veil of weak lines across the ultraviolet spectrum.Our calculations indicate that the windows become narrower at shorter wavelengths. Many of the ambiguities to the violet of 3600 Å would be resolved if spectrophotometric tracings with a band pass of 10 mÅ were available.  相似文献   

Metric capabilities of low-cost digital cameras for close range surface measurement   总被引：1，自引：1，他引：1  

Jim H.  Chandler  John G.  Fryer  Amanda  Jack 《The Photogrammetric Record》2005,20(109):12-26

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