Petrology and Geochemistry of Early Cretaceous Bimodal Continental Flood Volcanism of the NW Etendeka, Namibia. Part 2: Characteristics and Petrogenesis of the High-Ti Latite and High-Ti and Low-Ti Voluminous Quartz Latite Eruptives   总被引：1，自引：4，他引：1  

EWART  A.; MARSH  J. S.; MILNER  S. C.; DUNCAN  A. R.; KAMBER  B. S.  III; ARMSTRONG  R. A. 《Journal of Petrology》2004,45(1):107-138

As a result of their relative concentration towards the respectiveAtlantic margins, the silicic eruptives of the Paraná(Brazil)–Etendeka large igneous province are disproportionatelyabundant in the Etendeka of Namibia. The NW Etendeka silicicunits, dated at  相似文献   

Kinetics of the Reactions of Water, Hydroxide Ion and Sulfide Species with CO2, OCS and CS2: Frontier Molecular Orbital Considerations     

George W. Luther III 《Aquatic Geochemistry》2004,10(1-2):81-97

The kinetics of the reactions of water, hydroxide ion and sulfide species with CO₂, OCS and CS₂ are investigated using the molecular orbital approach and available kinetic data. Although these reactions are symmetry allowed, the lowest unoccupied molecular orbital (LUMO) for CO₂ is a poor electron accepting orbital as it has a positive potential energy. At low pH, hydration of CO₂ requires that the waters interact with CO₂ via hydrogen bonding for subsequent formation of H₂CO₃ in an effort to overcome the high energy of activation. These factors are significant for the slow kinetics of hydration and the persistence of CO₂ in water. The reaction of hydroxide ion with CO₂ has a much smaller energy of activation. For the isoelectronic species OCS and CS₂, their LUMO orbitals are good electron acceptor orbitals, and the energy of activation is less than that for the corresponding CO₂ reactions. The LUMO orbitals for OCS and CS₂ have less carbon character whereas the LUMO for CO₂ has more carbon character. The relative rates of these reactions (CO₂ > OCS > CS₂) reflect the increased carbon character of the π^* LUMO orbital for CO₂ over CS₂ and the fact that the LUMO for OCS is σ^*, which when filled can readily break the C—S bond leading to sulfide (even though the C character of the LUMO is less than those for CO₂ and CS₂). Also, the higher hydrogen bonding interactions with nearest water molecules is in the order CO₂ > OCS > CS₂ indicating that hydrolysis via water catalysis is retarded as the number of S atoms increases. Solid phase FeS has a highest occupied molecular orbital (HOMO) with a potential energy similar to that of CO₂ and can activate (or bond with) the carbon atom in CO₂ so that organic compounds can be produced under hydrothermal vent conditions.  相似文献   

Gas-Phase Ozone Oxidation of Monoterpenes: Gaseous and Particulate Products     

Jianzhen Yu  David R. Cocker III  Robert J. Griffin  Richard C. Flagan  John H. Seinfeld 《Journal of Atmospheric Chemistry》1999,34(2):207-258

Atmospheric oxidation of monoterpenes contributes to formation of tropospheric ozone and secondary organic aerosol, but their products are poorly characterized. In this work, we report a series of outdoor smog chamber experiments to investigate both gaseous and particulate products in the ozone oxidation of four monoterpenes: -pinene, -pinene, ³-carene, and sabinene. More than ten oxygenated products are detected and identified in each monoterpene/O₃ reaction by coupling derivatization techniques and GC/MS detection. A denuder/filter pack sampling system is used to separate and simultaneously collect gas and aerosol samples. The identified products, consisting of compounds containing carbonyl, hydroxyl, and carboxyl functional groups, are estimated to account for about 34–50%, 57%, 29–67%, and 24% of the reacted carbon mass for -pinene, sabinene, -pinene, and ³-carene, respectively. The identified individual products account for >83%, 100%, >90%, and 61% of the aerosol mass produced in the ozone reaction of -pinene, sabinene, -pinene, and ³-carene. The uncertainty in the yield data is estimated to be ±50%. Many of the products partition between gas and aerosol phases, and their gas-aerosol partitioning coefficients are determined and reported here. Reaction schemes are suggested to account for the products observed.  相似文献   

Strontium isotope composition of alpine-type ultramafic rocks in the Lake Chatuge District,Georgia—North Carolina     

Lois M. Jones  M. E. Hartley III  Raymond L. Walker 《Contributions to Mineralogy and Petrology》1973,38(4):321-327

The ⁸⁷Sr/⁸⁶Sr ratios for a series of ultramafic rocks from the Lake Chatuge region range from 0.7023 to 0.7047, suggesting a direct upper mantle source and precluding a multiple differentiation origin for these alpine-type rocks. Higher ⁸⁷Sr/⁸⁶Sr ratios (0.7058–0.7068) for serpentinized rocks from this suite apparently reflect the influx of radiogenic ⁸⁷Sr from the surrounding gneisses and schists during serpentinization.  相似文献   

DEGREE OF HYDRATION OF CLAYS     

GEORGE V. CHILINGAR  HERMAN H. RIEKE  III  JOHN O. ROBERTSON JR. 《Sedimentology》1963,2(4):341-342

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Paper 2. agricultural impacts of and responses to climate change in the Missouri-Iowa-Nebraska-Kansas (MINK) region     

William E. Easterling III  Pierre R. Crosson  Norman J. Rosenberg  Mary S. McKenney  Laura A. Katz  Kathleen M. Lemon 《Climatic change》1993,24(1-2):23-61

The climate of the 1930s was used as an analog of the climate that might occur in Missouri, Iowa, Nebraska and Kansas (the MINK region) as a consequence of global warming. The analog climate was imposed on the agriculture of the region under technological and economic conditions prevailing in 1984/87 and again under a scenario of conditions that might prevail in 2030. The EPIC model of Williamset al. (1984), modified to allow consideration of the yield enhancing effects of CO₂ enrichment, was used to evaluate the impacts of the analog climate on the productivity and water use of some 50 representative farm enterprises. Before farm level adjustments and adaptations to the changed climate, and absent CO₂ enrichment (from 350 to 450 ppm), production of corn, sorghum and soybeans was depressed by the analog climate in about the same percent under both current and 2030 conditions. Production of dryland wheat was unaffected. Irrigated wheat production actually increased. Farm level adjustments using low-cost currently available technologies, combined with CO₂ enrichment, eliminated about 80% of the negative impact of the analog climate on 1984/87 baseline crop production. The same farm level adjustments, plus new technologies developed in response to the analog climate, when combined with CO₂ enrichment, converted the negative impact on 2030 crop production to a small increase. The analog climate would have little direct effect on animal production in MINK. The effect, if any, would be by way of the impact on production of feed-grains and soybeans. Since this impact would be small after on-farm adjustments and CO₂ enrichment, animal production in MINK would be little affected by the analog climate.  相似文献   

Nitrate concentrations and nitrate reduction in acid groundwater/lake systems in southern Australia     

W. Berry Lyons  Mark E. Hines  David T. Long  John M. McArthur  Susan Welch 《International Journal of Salt Lake Research》1993,2(2):173-189

We have analyzed nitrate in saline groundwaters from the Lake Tyrrell region of north-western Victoria and the Norseman-Salmon Gums region of south-eastern Western Australia. These are regions where acid (pH<4) groundwater exists naturally. The nitrate concentrations of these groundwaters are ∼5–10 times lower than nitrate concentrations from other arid and semi-arid regions around the world and in Australia. The source of the nitrate to the groundwater is soil organic matter, not anthropogenic activity. The data from the Lake Tyrrell system suggest that the gain and loss of fixed nitrogen are probably important biogeochemical processes in the early evolution of these waters. Nitrate reduction also occurs in the shallow groundwaters of Western Australia. Nitrate reduction is very low due to the low concentrations of organic matter present. Groundwaters in both of these systems eventually discharge along the edges of playas. This process may concentrate nitrate in the surficial salts of the playa.  相似文献   

The Abiotic Nitrite Oxidation by Ligand-Bound Manganese (III): The Chemical Mechanism     

Luther III  George W.  Karolewski  Jennifer S.  Sutherland  Kevin M.  Hansel  Colleen M.  Wankel  Scott D. 《Aquatic Geochemistry》2021,27(3):207-220

Aquatic Geochemistry - Given their environmental abundances, it has been long hypothesized that geochemical interactions between reactive forms of manganese and nitrogen may play important roles in...  相似文献   

Late Pleistocene dune construction in the Central Sand Plain of Wisconsin, USA     

J.E. Rawling III  P.R. Hanson  A.R. Young  J.W. Attig   《Geomorphology》2008,100(3-4):494-505

Wisconsin's Central Sand Plain east of the Wisconsin River is composed of eolian sand forming high-relief dunes surrounded by sand sheets and scattered low-relief dunes. To establish a maximum age for dune formation, three samples for optical dating were taken from glacial Lake Wisconsin lacustrine sediment that underlies eolian sand. These age estimates range from 19.3 to 13.6ka. Age estimates taken from within or at the base of the dunes range from 14.0 to 10.6ka. Samples taken from < 2m of the ground surface were slightly younger, indicating dunes were stabilized between 11.8 and 5.5ka. The younger ages near the surface of some dunes were most likely the result of pedoturbation or localized problems with applying the optical dating method. The majority of the optical age estimates from dunes (18 of 21) indicated that most of the dunes were active between 14 and 10ka and that most dune activity ended by 10ka. These ages suggest that localized activity on dune crests may have occurred in the Holocene but would have been limited to < 1m of sand accumulation. The timing of dune activity and the lack of any significant Holocene reactivation suggest that dune activation in this setting cannot be attributed solely to changes in aridity. Instead, we attribute dune formation to changes in sediment availability from either sand inputs from the Wisconsin River or the melting of permafrost.  相似文献   

Linking the Abundance of Estuarine Fish and Crustaceans in Nearshore Waters to Shoreline Hardening and Land Cover     

Matthew S. Kornis  Denise Breitburg  Richard Balouskus  Donna M. Bilkovic  Lori A. Davias  Steve Giordano  Keira Heggie  Anson H. Hines  John M. Jacobs  Thomas E. Jordan  Ryan S. King  Christopher J. Patrick  Rochelle D. Seitz  Heather Soulen  Timothy E. Targett  Donald E. Weller  Dennis F. Whigham  Jim UphoffJr 《Estuaries and Coasts》2017,40(5):1464-1486

Human alteration of land cover (e.g., urban and agricultural land use) and shoreline hardening (e.g., bulkheading and rip rap revetment) are intensifying due to increasing human populations and sea level rise. Fishes and crustaceans that are ecologically and economically valuable to coastal systems may be affected by these changes, but direct links between these stressors and faunal populations have been elusive at large spatial scales. We examined nearshore abundance patterns of 15 common taxa across gradients of urban and agricultural land cover as well as wetland and hardened shoreline in tributary subestuaries of the Chesapeake Bay and Delaware Coastal Bays. We used a comprehensive landscape-scale study design that included 587 sites in 39 subestuaries. Our analyses indicate shoreline hardening has predominantly negative effects on estuarine fauna in water directly adjacent to the hardened shoreline and at the larger system-scale as cumulative hardened shoreline increased in the subestuary. In contrast, abundances of 12 of 15 species increased with the proportion of shoreline comprised of wetlands. Abundances of several species were also significantly related to watershed cropland cover, submerged aquatic vegetation, and total nitrogen, suggesting land-use-mediated effects on prey and refuge habitat. Specifically, abundances of four bottom-oriented species were negatively related to cropland cover, which is correlated with elevated nitrogen and reduced submerged and wetland vegetation in the receiving subestuary. These empirical relationships raise important considerations for conservation and management strategies in coastal environments.  相似文献