Molecular implications of hydrophobic organic partitioning theory     

Russell F. Christman  Frederic K. Pfaender 《洁净——土壤、空气、水》2006,34(4):367-374

Recent normal phase silica followed by reverse phase XAD separation has led to the identification of several flavonoid and condensed tannin structures in Suwannee River Fulvic Acid (SFRA) (Leenheer, J. A., Rostad, C. (2004) Scientific Investigations Report 2004–5276, U.S. Geological Survey). We have used the molecular properties of one of these structures to define ideal behavior during partitioning of PAHs assuming that these structures function as an immiscible liquid solvent bound to finely dispersed mineral particles. Existing data for the partitioning of PAHs into NOM compared well to this ideal behavior under Raoult/Henry and Flory‐Huggins treatments, and activity coefficients of pyrene in the hypothetical NOM phase and the free energy of transfer were estimated. If experimental data on partitioning of PAHs into synthesized samples of these structures is similar to NOM uptake data, it will be attractive to assume that, a) much smaller components of the NOM complex than suggested by gross molecular weight may be important in environmental properties such as solubility enhancement, and b) the effective molar volumes within the NOM complex responsible for solubility enhancement may be solute, or solute class dependent.  相似文献   

Analysis of organic matter by flash pyrolysis-gas chromatography–mass spectrometry in the presence of Na-smectite: When clay minerals lead to identical molecular signature     

Pierre Faure  Laurent Jeanneau  Frederic Lannuzel 《Organic Geochemistry》2006,37(12):1900

Different studies have already pointed out the influence of clays during the analysis of pure organic compounds (especially alkanols, alkanoic acids) as well as macromolecules (humic acids) by flash pyrolysis-gas chromatography–mass spectrometry (PyGC–MS). Especially, the occurrence of clay minerals favors the generation of aromatic units such as alkylbenzenes and polycyclic aromatic hydrocarbons. So as to better identify the nature of the organic compounds which are sensitive to the presence of clays during flash pyrolysis, a humic acid mixed in variable proportions of a Na-homoionic clay was tested. The smectite/humic acid mixtures containing from 10% to 100% humic acid allowed us to identify the progressive disappearance or appearance of specific compounds after PyGC–MS.n-Alk-1-enes disappear when the clay proportion is higher than 67%. For higher contents of Na-smectite, n-alkanes become less and less abundant with a preferential consumption of high molecular weight n-alkanes, whereas the aromatic hydrocarbon proportion increases. Moreover, the distribution of each aromatic hydrocarbon family (alkylbenzenes and alkylnaphthalenes) has been investigated. The pyrogram of pure humic acid exhibits a specific distribution of alkylbenzenes and alkylnaphthalenes reflecting the structure of the organic macromolecule. With the increase in clay proportion, these distributions are modified and lead to other distributions with a preferential predominance of thermally stable isomers.Pyrograms of humic acid and undecanoic acid in the presence of 90% of Na-smectite are similar, especially concerning alkylbenzene and alkylnaphthalene distributions. Therefore, clays (Na-smectite in our experiments) in high proportion modify initial organic products by recombination reactions and lead to the generation of new compounds of very similar distribution, whatever the nature of the initial organic matter. Such results underline the very important catalytic properties of clay minerals on functionalized organic matter during flash pyrolysis.  相似文献   

Geomorphic evidence of active deformation and uplift in a modern continental wedge-top–foredeep transition: Example of the eastern Ecuadorian Andes   总被引：1，自引：0，他引：1  

S. Bs de Berc  J.C. Soula  P. Baby  M. Souris  F. Christophoul  J. Rosero 《Tectonophysics》2005,399(1-4):351

The eastern Ecuadorian Andes appear as a fold-and-thrust belt adjacent to a continental foredeep represented by one of the world's largest tropical alluvial megafans, the Pastaza megafan, debouching into the Amazonian lowland. The apex of the Pliocene–Pleistocene megafan situated in the present-day wedge top (Subandean Zone) has been cut by an erosion surface, the western part of which has been uplifted of 500 m along the frontal thrust, forming a poorly dissected plateau, the Mera plateau. This erosion surface erased most of the previous fluvial landscape but preserved a large thrust-related anticlinal hinge deforming less erodible underlying strata, the Mirador fold and smaller-sized anticlines. This surface has been then incised by two antecedent major rivers, the Pastaza and the Napo, and few tributaries. The plateau edge is marked by a series of large scale gently sloping landslides clustered along a 70 km long concave eastward line associated with the frontal thrust fault. The newly formed immature rivers issued from the landslides or sourced within east-dipping remnants of the erosion surface downstream of the landslide line constitute the greatest part of the streams feeding the Ecuadorian Amazonian basin. At 70 to 100 km from the landslide line, the drainage abruptly changes from highly immature to mature with a well-defined hinge line representing the outer limit of landslide and tectonic control. The diversions of the Pastaza River indicate ongoing fold growth since at least the late Pleistocene in the Eastern Cordillera, and the early Holocene in the Mera plateau. The preserved terraces of the Pastaza valley are all degradational and are ascribed to periods of tectonic (seismic) activity alternating with periods of tectonic quiescence or decreased seismic activity rather than to climatic events. ¹⁴C dating of the plateau erosion surface and of the upper Pastaza terraces indicates that the minimum average incision rate since 18,000 years BP varies locally in the upper Pastaza valley from 0.5 to 0.67 cm year⁻¹ , increasing from 18,000 years BP to now. A comparison of these incision rates with fold-and-thrust fault uplift rates indicates that incision in the upper Pastaza valley was a result of rapid uplift (up to 1 cm year⁻¹) along the Mirador fold-and-thrust which caused a restoration of the local equilibrium profile of the upper reach, combined with smaller local fault uplift along the westernmost thrust faults. The uplift of the whole Mera plateau with respect to the upper Amazonian basin gives a minimum average uplift rate of 2.8 cm year⁻¹ since 18,000 years BP. The overall uplift of the Mera plateau and the Eastern Cordillera is likely to have been caused by a regional-scale low angle thrust ramp emerging as the frontal thrust fault.  相似文献   

Factors influencing subaqueous dunes in the Scheldt Estuary     

Frederic?FranckenEmail author  Stanislas?Wartel  Reg?Parker  Eric?Taverniers 《Geo-Marine Letters》2004,24(1):14-21

The size (wavelength and height) and the factors influencing the characteristics of subaqueous dunes in the river Scheldt between Antwerp and the Belgian-Dutch border were studied. More than 60 dune clusters (each cluster represented by a mean height and wavelength of mostly 10 to 20 or more observations) were analysed. A very good exponential correlation between dune height and wavelength was observed (r=0.90) which can be described by H _mean=0.0321L ^0.918. Length/depth ratios vary between 0.2 and 9, height/depth ratios between 0.25 and 0.01. There was no clear relationship between current velocity and dune size, as dunes of various sizes co-exist at the same current velocities. Twenty-two dunes were sampled and show grain sizes (d50) ranging between 0.1 and 0.7 mm. Seven out of eight large scale dune fields were found in sandy and/or hard bottom (gravel, coarse sand and shell fragments) environments, whereas small and medium dunes were found in muddy sand and sandy mud environments.  相似文献   

In-ground environmental radioactivity monitoring in the Culpeper Basin,Virginia, using LiF thermoluminescence dosimeters     

Frederic R. Siegel  Roy C. Lindholm  J. Eduardo Vaz 《Environmental Geology》1982,4(2):67-74

A new environmental in-ground radioactivity monitoring technique using LiF thermoluminescence dosimeters was tested in the Culpeper Basin, Northern Virginia. The dosimeters were buried at a depth of 0.45 m (∼ 18 in.) for approximately four months. There was a significant positive correlation (at the 99.9% confidence level) between the total accumulated radioactivity signal from the dosimeters and the on-site 100 second gamma-ray spectrometer measurements. The minimum-maximum dose rate from the buried thermoluminescence dosimeter measurements was 0.06 to 1.08 mR per day (or 2.5 to 44.5μR per hour). There are two factors which permit better background levels of radioactivity to be established by thermoluminescence dosimeters compared with other methods for environmental monitoring programs. First is the great sensitivity of thermoluminescence dosimeters in terms of minimum dose rate that can be registered (mR per month orμR per hour). Second is the fact that accumulation of radioactivity signal over a long period of time tends to eliminate short-term environmental changes that affect measurements with gamma-ray spectrometers and scintillation counters.  相似文献   

Exploration for Mississippi-Valley type stratabound Zn ores with stream suspensates and stream sediments, Virginia, U.S.A.     

Frederic R. Siegel 《Journal of Geochemical Exploration》1990,38(3)

Suspended and equivalent active sediments were collected from streams at 84 sites at the eastern and western sides of a ridge with stratabound Zn mineralization, Rockingham County, Virginia (USA). The purpose was to evaluate the relative effectiveness of suspended and bottom sediment in the geochemical exploration for Mississippi-Valley type Zn ores. The orebody is composed of sphalerite and minor amounts of galena with some chalcopyrite, strikes parallel to the enclosing dolomite beds at N34°E, and cuts vertically across the 30°SE dip. Oxidation of the ore extends to about 100 m in depth.Zinc was effective in detecting the mineralized zone. Zinc in the suspensates provided a denser anomaly system (7 strong and 2 moderate samples) than Zn in the <150 μm size of the bottom sediment, either totally dissolved (4 strong and 1 moderate anomalies) or extracted with cold 3% HCl (5 strong and 3 moderate anomalies). The magnitude of the high values for suspensate Zn was considerably higher than those for the other sample types studied. Suspensate Zn was complemented by 3 strong suspensate Cu anomalies. The suspensate Zn anomaly dispersion was about 850 m, 400 m of which was upstream from the mineralization. Lead was detected only in the cold acid extraction and in combination with Cu and Zn gave an extensive overlapping multielement anomaly string that targeted the ore zone and had a dispersion downstream from the mineralization of more than 1000 m. The Pb anomalies extended about 900 m upstream and 400 m downstream from the ore zone. Together with suspensate Zn, the Pb anomalies suggest a continuation of mineralization upstrike from the known orebody.The major anomaly systems are along the eastern side of the ridge with comparatively few anomalies present in the drainage along the western side. The concentration of anomalies in the eastern drainage and anomaly disposition with respect to known mineralization result from structural control on the hydromorphic dispersion of metals from the orebody.  相似文献   

Increased concentrations of potassium in heartwood of trees in response to groundwater contamination     

Don A. Vroblesky  Thomas M. Yanosky  Frederic R. Siegel 《Environmental Geology》1992,19(2):71-74

The wood of tuliptrees (Liriodendron tulipifera L.) growing above groundwater contamination from a hazardous-waste landfill in Maryland contained elevated concentrations of potassium (K). The groundwater contamination also contained elevated concentrations of dissolved K, as well as arsenic (As), cadmium (Cd), chloride (Cl), iron (Fe), manganese (Mn), zinc (Zn), and organic solvents. The dissolved K is derived from disposed smoke munitions. The excess K in the tuliptrees is concentrated in the heartwood, the part of the xylem most depleted in K in trees growing outside of the contamination. These data show that the uptake and translocation of K by tuliptrees can be strongly influenced by the availability of K in groundwater contamination and suggest the utility of this species as an areal indicator of groundwater contamination.  相似文献   

Identifying geochemical reactions on wellbore cement/caprock interface under sequestration conditions     

Małgorzata Labus  Frederic Wertz 《Environmental Earth Sciences》2017,76(12):443

The integrity of wells, which are key components for CO₂ sequestration, depends mainly on the seal between the wellbore cement and the geologic formation. To identify the reaction products that may alter the cement/caprock interface, batch experiments and computer modelling were conducted and analysed. Over time, the dissolution and precipitation of minerals alters the physical properties of the interface, including its tightness. One main objective of the simulation was thus to analyse the evolution of the porosity of cement and caprock over time. The alteration of the cement/caprock interface was identified as a complex problem and differentiated depending on rock type. The characteristic feature of a cement/shale contact zone is the occurrence of a highly carbonated, compacted layer within the shale, which in turn causes cement/shale detachment. In the case of a cement/anhydrite interface, the most important reaction is severe anhydrite dissolution. Secondary calcite precipitation takes place in deeper parts of the rock. The cement/rock contact zone is prone to rapid mineral dissolution, which contributes to increased porosity and may alter the well integrity. Comparison of computer simulations with autoclave experiments enabled the adjustment of unknown parameters. This enhances the knowledge of these particular assemblages. Overall, a good match was obtained between experiments and simulations, which enhances confidence in using models to predict longer-term evolution.  相似文献   

Erratum to “26Al–26Mg and 207Pb–206Pb systematics of Allende CAIs: Canonical solar initial 26Al/27Al ratio reinstated” [Earth Planet Sci. Lett. 272 (2008) 353–364]     

Benjamin Jacobsen  Qing-Zhu Yin  Frederic Moynier  Yuri Amelin  Alexander N. Krot  Kazuhide Nagashima  Ian D. Hutcheon  Herbert Palme 《Earth and Planetary Science Letters》2009,277(3-4):549

  相似文献   

Isotopic fractionation of zinc in tektites     

Frederic Moynier  Pierre Beck  Fred Jourdan  Qing-Zhu Yin  Uwe Reimold  Christian Koeberl 《Earth and Planetary Science Letters》2009,277(3-4):482-489

Tektites are terrestrial natural glasses produced during a hypervelocity impact of an extraterrestrial projectile onto the Earth's surface. The similarity between the chemical and isotopic compositions of tektites and terrestrial upper continental crust implies that the tektites formed by fusion of such target rock. Tektites are among the driest rocks on Earth. Although volatilization at high temperature may have caused this extreme dryness, the exact mechanism of the water loss and the behavior of other volatile species during tektite formation are still debated. Volatilization can fractionate isotopes, therefore, comparing the isotope composition of volatile elements in tektites with that of their source rocks may help to understand the physical conditions during tektite formation.For this study, we have measured the Zn isotopic composition of 20 tektites from four different strewn fields. Almost all samples are enriched in heavy isotopes of Zn compared to the upper continental crust. On average, the different groups of tektites are isotopically distinct (listed from the isotopically lightest to the heaviest): Muong-Nong type indochinites (δ^66/64Zn = 0.61 ± 0.30‰); North American bediasites (δ^66/64Zn = 1.61 ± 0.49‰); Ivory Coast tektites (δ^66/64Zn = 1.66 ± 0.18‰); the Australasian tektites (others than the Muong Nong-type indochinites) (δ^66/64Zn = 1.84 ± 0.42‰); and Central European moldavites (δ^66/64Zn = 2.04 ± 0.19‰). These results are contrasted with a narrow range of δ^66/64Zn = 0–0.7‰ for a diverse spectrum of upper continental crust materials.The elemental abundance of Zn is negatively correlated with δ^66/64Zn, which may reflect that isotopic fractionation occurred by evaporation during the heating event upon tektite formation. Simple Rayleigh distillation predicts isotopic fractionations much larger than what is actually observed, therefore, such a model cannot account for the observed Zn isotope fractionation in tektites. We have developed a more realistic model of evaporation of Zn from a molten sphere: during its hypervelocity trajectory, the molten surface of the tektite will be entrained by viscous coupling with air that will then induce a velocity field inside the molten sphere. This velocity field induces significant radial chemical mixing within the tektite that accelerates the evaporation process. Our model, albeit parameter dependent, shows that both the isotopic composition and the chemical abundances measured in tektites can be produced by evaporation in a diffusion-limited regime.  相似文献