Age of Sheep Creek Tephra (Pleistocene) in Central Alaska from Thermoluminescence Dating of Bracketing Loess     

Glenn W. Berger  Troy L. Péwé  John A. Westgate  Shari J. Preece 《Quaternary Research》1996,45(3):263-270

The age of the Sheep Creek tephra (SCt), a widespread marker ash bed in eastern Alaska and western Yukon Territory, has been ambiguous and controversial. We have obtained three reliable thermoluminescence age estimates from bracketing loess near Fairbanks that imply a deposition age of about 190,000 ± 20,000 yr for SCt. Three of six loess samples near and closely bracketing the SCt beds near Fairbanks yielded younger age estimates (∼117,000 and ∼135,000 yr), most likely (based on field aspects) because of reworking and contamination by translocated grains. The new, reliable age assignment of 190,000 yr confirms independent stratigraphic evidence of a pre-last interglaciation age, and stratigraphic evidence from one site (Upper Eva Creek) that SCt is older than the more-widespread 140,000-yr-old Old Crow tephra. The SCt age also has implications for regional correlations of glacial and nonglacial deposits. In particular, it supports the stratigraphic and geomorphic interpretation that the Delta Glaciation in the east-central Alaska Range and the Reid Glaciation in western Yukon Territory are older than the last interglaciation (isotope substage 5e).  相似文献   

A new extraction technique for in situ analyses of amino and carboxylic acids on Mars by gas chromatography mass spectrometry   总被引：1，自引：0，他引：1  

A. Buch  D.P. Glavin  R. Sternberg  C. Szopa  C. Rodier  R. Navarro-Gonzlez  F. Raulin  M. Cabane  P.R. Mahaffy 《Planetary and Space Science》2006,54(15):1592-1599

In order to target key organic compounds in the Martian regolith using gas chromatography mass spectrometry (GC-MS), we have developed a new extraction procedure coupled with chemical derivatization. This new technique was tested on a Mars analog soil sample collected from the Atacama Desert in Chile. We found that amino and carboxylic acids can be extracted from the Atacama soil in a 1:1 mixture of isopropanol and water after ultrasonic treatment for 30 min. The extracted organic compounds were then derivatized in a single-step reaction using N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA) as the silylating agent in order to transform these compounds into volatile species that can then be detected by GC-MS. We are currently developing a miniaturized reaction cell suited for spaceflight, where both organic extraction and chemical derivatization processes can take place in a single step.  相似文献   

Long-range transport of Asian emissions to the West Pacific tropical tropopause layer     

Treadaway  Victoria  Atlas  Elliot  Schauffler  Sue  Navarro  Maria  Ueyama  Rei  Pfister  Leonhard  Thornberry  Troy  Rollins  Andrew  Elkins  James  Moore  Fred  Rosenlof  Karen 《Journal of Atmospheric Chemistry》2022,79(2):81-100

Journal of Atmospheric Chemistry - Rapid transport by deep convection is an important mechanism for delivering surface emissions of reactive halocarbons and other trace species to the tropical...  相似文献   

Biogeochemical implications of the isotopic equilibrium fractionation factor between the oxygen atoms of acetone and water     

Leonel da Silveira Lobo O&#x;Reilly Sternberg  Michael Joseph DiGiacomo DeNiro 《Geochimica et cosmochimica acta》1983,47(12):2271-2274

Carbonyl oxygens of organic molecules undergo isotopic exchange with water during reversible hydration reactions. The equilibrium isotopic fractionation factors between the carbonyl oxygen of acetone and water at 15°, 25°, and 35°C are 1.028, 1.028, and 1.026 respectively. The differences between the δ¹⁸O values of the carbonyl oxygen of acetone and of the water with which it is in equilibrium are similar to the differences that have been observed between the δ¹⁸O values of cellulose and the water used in its synthesis by a variety of aquatic plants and animals. Additionally, the identity of the acetone-water fractionation factors at 15° and 25°C parallels the observation that the difference between the δ¹⁸O values of cellulose and water shows no temperature dependence for individual species of plants grown over the same temperature range. These results are discussed in relation to the proposal that the oxygen isotopic relationship between cellulose and water is established by isotopic exchange occurring during the hydration of carbonyl groups of the intermediates of cellulose synthesis.  相似文献   

Plant and infaunal communities associated with a created marsh     

Martin H. Posey  Troy D. Alphin  Christopher M. Powell 《Estuaries and Coasts》1997,20(1):42-47

Destruction of tidal wetlands has led to a growing interest in the restoration and creation of new wetland habitat. However, while natural stands of vegetation have been successfully duplicated, less is understood about the establishment of faunal communities in created or restored tidal marshes. Infauna, which may form an important link between detrital production and commercially important finfish and decapods, have received limited attention in vegetated marsh habitats. We examined the infauna, changes in vegetation composition, and selected physical parameters in created marshes of different ages. Infauna were sampled using standard core sampling techniques. Vegetation composition and changes in relative abundance were observed using plot-point techniques. Vegetation plots indicated ongoing replacement ofSpartina alterniflora bySchoenoplectus robustus, a pattern supported by comparisons of vegetation at one of the sites to that reported in a previous study. Infauna exhibited significant differences between sites of different ages, with the intermediate-age site having intermediate densities for several taxa. These results suggest that both infauna and vegetation in created marshes undergo long-term change (ongoing after 10–20 yr), with both the plant and infaunal communities having qualitatively similar overall species composition to natural marsh areas.  相似文献   

Field measurements of fairweather bottom boundary layer processes and sediment suspension on the Louisiana inner continental shelf   总被引：1，自引：0，他引：1  

L. D. Wright  C. R. Sherwood  R. W. Sternberg 《Marine Geology》1997,140(3-4):329-345

Field measurements of bottom boundary layer and sediment-transport processes were made on the Louisiana inner continental shelf in spring 1992 at a depth of 15.5 m, and in spring and summer 1993 at a depth of 20.5 m. Two different wave–current boundary layer/sediment-transport models were applied to the measured near-bed flows. In addition, the log-profile method was applied to estimate hydraulic roughness and bed stress. Consistent with the results of others, our measurements show that near-bed flows were very weak under non-storm conditions. Bed stresses were typically too low to resuspend bed sediments. However, the advection of high-turbidity layers or plumes past the instrumentation apparently caused a sustained period of high suspended sediment concentration throughout the log layer in spring 1993. In the absence of wave activity or high suspended sediment concentrations, boundary layer profiles showed the bed to have been hydraulically very smooth with cm. However, wave agitation, combined with increased suspended sediment concentration caused hydraulically rough conditions with cm.  相似文献   

Separating soil and leaf water O isotopic signals in plant stem cellulose     

Leonel da Silveira Lobo Sternberg  William T. Anderson 《Geochimica et cosmochimica acta》2003,67(14):2561-2566

The oxygen-18 signal of soil and leaf water are both recorded in heterotrophically synthesized plant stem cellulose. Presently, these signals can only be teased apart with modeling and assumptions on the nature of the isotopic enrichment of leaf water. A method by which these two signals are chemically separated and analyzed is tested here. Heterotrophically synthesized cellulose from germinating seeds having a mixture of isotopic signals from the reserve carbohydrate (starch) and that of the water during cellulose synthesis was hydrolyzed and the resulting glucose converted to glucose phenylosazone. The analysis of the ¹⁸O/¹⁶O ratios of cellulose and of glucose phenylosazone were used to calculate the oxygen isotope ratio of the oxygen attached to the second carbon of the glucose moieties of the cellulose molecule. The calculated δ¹⁸O value of this oxygen was highly correlated with that of the water available for cellulose synthesis showing a nearly one-to-one relationship (slope = 1.027) and leading to the conclusion that it completely exchanges with water during heterotrophic cellulose synthesis. Once this method is refined so as to increase precision, it will be possible to derive the δ¹⁸O values of soil water available to plants from the oxygen isotope analysis of stem cellulose and its derivative.  相似文献   

A Methodology for the Assessment of Unconventional (Continuous) Resources with an Application to the Greater Natural Buttes Gas Field,Utah   总被引：1，自引：0，他引：1  

Ricardo A. Olea  Troy A. Cook  James L. Coleman 《Natural Resources Research》2010,19(4):237-251

The Greater Natural Buttes tight natural gas field is an unconventional (continuous) accumulation in the Uinta Basin, Utah, that began production in the early 1950s from the Upper Cretaceous Mesaverde Group. Three years later, production was extended to the Eocene Wasatch Formation. With the exclusion of 1100 non-productive (“dry”) wells, we estimate that the final recovery from the 2500 producing wells existing in 2007 will be about 1.7 trillion standard cubic feet (TSCF) (48.2 billion cubic meters (BCM)). The use of estimated ultimate recovery (EUR) per well is common in assessments of unconventional resources, and it is one of the main sources of information to forecast undiscovered resources. Each calculated recovery value has an associated drainage area that generally varies from well to well and that can be mathematically subdivided into elemental subareas of constant size and shape called cells. Recovery per 5-acre cells at Greater Natural Buttes shows spatial correlation; hence, statistical approaches that ignore this correlation when inferring EUR values for untested cells do not take full advantage of all the information contained in the data. More critically, resulting models do not match the style of spatial EUR fluctuations observed in nature. This study takes a new approach by applying spatial statistics to model geographical variation of cell EUR taking into account spatial correlation and the influence of fractures. We applied sequential indicator simulation to model non-productive cells, while spatial mapping of cell EUR was obtained by applying sequential Gaussian simulation to provide multiple versions of reality (realizations) having equal chances of being the correct model. For each realization, summation of EUR in cells not drained by the existing wells allowed preparation of a stochastic prediction of undiscovered resources, which range between 2.6 and 3.4 TSCF (73.6 and 96.3 BCM) with a mean of 2.9 TSCF (82.1 BCM) for Greater Natural Buttes. A second approach illustrates the application of multiple-point simulation to assess a hypothetical frontier area for which there is no production information but which is regarded as being similar to Greater Natural Buttes.  相似文献   

The soft-bottom macrobenthos of North Carolina estuaries     

Jeffrey L. Hyland  W. Leonard Balthis  Martin Posey  Courtney T. Hackney  Troy Alphin 《Estuaries and Coasts》2006,29(4):709-710

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The effects of thin layer sand renourishment on tidal marsh processes: Masonboro Island, North Carolina     

Alex L. Croft  Lynn A. Leonard  Troy D. Alphin  Lawrence B. Cahoon  Martin H. Posey 《Estuaries and Coasts》2006,29(5):737-750

The objective of this study was to determine if the placement of dredged material on sediment-starved back barrier marshes in southeastern North Carolina could offset submergence without negatively affecting function. Clean sediment was placed in thickness from 0 to 10 cm, on deteriorated and non-deteriorated marsh plots. Original stem densities were greater, in non-deteriorated plots (256 stems m⁻²) compared to deteriorated sites (149 stems m⁻²). By the second growing season (after sediment additions), stem densities in the deteriorated plots (308 stems m⁻²) approached levels in the non-deteriorated plots (336 stems m⁻²). Sediment additions to, both nos-deteriorated and deteriorated plots resulted in a higher redox potential with plots receiving the most sediment exhibiting the highest E_h values. In deteriorated plots, placement of dredged material had the greatest effect on plant density, but also affected soil oxidation-reduction potential and sediment deposition (or mobility). Following sediment placement, substrate texture and composition incrementally returned to prefill conditions due to a combination of bioturbation and sedimentation. Where infaunal differences occurred, they were generally less abundant in deteriorated plots, but responses to sediment addition were variable. Sediment addition had little effect on the non-deteriorated plots, suggesting that the disposal of certain types of dredged material in marshes may be useful to mitigate the effects of marsh degradation without adversely affecting non-deteriorating marsh.  相似文献