Heat flow in the Ozark Plateau, Arkansas and Missouri: relationship to groundwater flow     

Joseph G. Meert  Douglas L. Smith  Len Fishkin 《Journal of Volcanology and Geothermal Research》1991,47(3-4)

Heat flow values were calculated from direct measurements of temperature and thermal conductivity at thirteen sites in the Arkansas-Missouri Ozark Plateau region. These thirteen values are augmented by 101 estimates of heat flow, based on thermal conductivity measurements and temperature gradients extrapolated from bottom-hole temperatures. The regional heat flow profile ranges from 9 mW m⁻² to over 80 mW m⁻², but at least two distinct thermal regimes have been identified. Seven new heat flow determinations are combined with three previously published values for the St. Francois Mountains (SFM), a Precambrian exposure of granitic and rhyolitic basement rocks, average 47 mW m⁻². Radioactive heat production of 76 samples of the exposed rocks in the SFM averages 2.4 μW m⁻² and a typical continental basement contribution of 14 mW m⁻² is implied. Conversely, the sedimentary rock sequence of the plateau is characterized by an anomalously low heat flow, averaging approximately 27 mW m⁻². Groundwater transmissivity values that are based on data from 153 wells in deep regional aquifers demonstrate an inverse relationship to the observed heat flow patterns. The areas of high transmissivity that correspond to areas of low total heat flux suggest that the non-conservative vertical heat flow within the Ozark sedimentary sequence can be attributed to the effects of groundwater flow.  相似文献   

Case Histories of Shallow Time Domain Electromagnetics in Environmental Site Assessment     

Pieter Hoekstra  Raye Lahti  Jim Hild  C. Richard Bates  David Phillips 《Ground Water Monitoring & Remediation》1992,12(4):110-117

Time domain electromagnetic (TDEM) soundings were utilized in site assessment studies for the purpose of accomplishing two objectives: (1) measuring the migration of brines from oil and gas field evaporation pits, and (2) mapping the continuity of clay strata. Both case histories are representative of common objectives in site assessment. The data for both examples were analyzed by one-dimensional ridge regression inversions.
Both case histories illustrate that TDEM is an effective method for determining the lateral and vertical resistivity distribution (geoelectric section) of the subsurface in the depth range from about 5 m to 100 m, and it is known from other investigations that depths of investigations up to 2500 m can be achieved with TDEM.
Frequently, the lateral extent of contaminant plumes emanating from localized sources are of limited areal extent. The case history involving the use of TDEM to map a brine plume shows that a TDEM measurement has a relatively small zone of influence, so that meaningful information about the lateral and vertical extent of the plume can be obtained. Both case histories demonstrate the ability of TDEM to determine geoelectric sections below layers of low resistivity.  相似文献   

Eutrophication,water management,and the functioning of Dutch estuaries and coastal lagoons     

Pieter H. Nienhuis 《Estuaries and Coasts》1992,15(4):538-548

A number of major European rivers (especially the Rhine) have a prevailing influence on the nutrient cycling of most Dutch estuaries. Owing to the increased loading of the estuaries with nitrogen and phosphorus compounds, effects of eutrophication on the biological communities are most evident in the tidal Western Wadden Sea and in a nontidal brackish lagoon, Veerse Meer. Whether the relation between changed nutrient loadings and changed biomass and production of primary and secondary producers in the turbid tidal Dutch ecosystems should be considered as a causal relation is questionable. The very widespread practice of lagoon modification confuses the effects of nutrient loading.  相似文献   

α-Emitting mineral inclusions in apatite, their effect on (U-Th)/He ages, and how to reduce it     

Pieter Vermeesch  Diane Seward  Martin Wipf  Heinrich Baur 《Geochimica et cosmochimica acta》2007,71(7):1737-1746

U-Th rich mineral inclusions in apatite are often held responsible for erroneously old (U-Th)/He ages, because they produce “parentless” He. Three aspects associated with this problem are discussed here. First, simple dimensional considerations indicate that for small mineral inclusions, the parentless helium problem might not be as serious as generally thought. For example, a mineral inclusion that is 10% the length, width and height of its host apatite needs to be a thousand times more concentrated in U and Th to produce an equal amount of He. Therefore, single isolated inclusions smaller than a few μm are unlikely to contribute significant helium. For larger or more abundant inclusions, the parentless helium problem can be solved by dissolution of the apatite and its inclusions in hot HF. Second, besides creating parentless helium, inclusions also complicate α-ejection corrections. Mathematical exploration of this latter problem for spherical geometries reveals that for randomly distributed inclusions, the probability distribution of single-grain ages is predicted to have a sharp mode at the mean age, with tails towards younger and older ages. Multiple-grain measurements will yield accurate and precise age estimates if 10 or more randomly distributed α-emitting mineral inclusions are present in a sample. Third, thermal modeling indicates that mineral inclusions have a non-trivial but minor (<5 °C) effect on the closure temperature. These predictions were tested on apatites from rapidly cooled migmatites of Naxos (Greece) which contain abundant U-rich zircon inclusions. Thirty-seven samples were subjected to two kinds of treatment. The “pooled” age (i.e., the synthetic multi-grain age computed from a number of single-grain analyses) of four inclusion-free samples (13 apatites), prepared in HNO₃ is 10.9 Ma, close to apatite and zircon fission-track ages from the same rock. (U-Th)/He ages of 14 inclusion-bearing samples dissolved in HNO₃ range between 9 and 45 Ma, with a pooled age of 22.6 Ma. The ages of 19 HF-treated samples range between 5 and 16 Ma, with 10 of 14 single-grain samples between 9 and 13 Ma and a pooled age of 10.9 Ma. These observations agree with the theoretical predictions and support the addition of HF-treated apatite (U-Th)/He dating to the thermochronological toolbox.  相似文献   

Preprocessing of gravity gradients at the GOCE high-level processing facility   总被引：3，自引：0，他引：3  

Johannes Bouman  Sietse Rispens  Thomas Gruber  Radboud Koop  Ernst Schrama  Pieter Visser  Carl Christian Tscherning  Martin Veicherts 《Journal of Geodesy》2009,83(7):659-678

One of the products derived from the gravity field and steady-state ocean circulation explorer (GOCE) observations are the gravity gradients. These gravity gradients are provided in the gradiometer reference frame (GRF) and are calibrated in-flight using satellite shaking and star sensor data. To use these gravity gradients for application in Earth scienes and gravity field analysis, additional preprocessing needs to be done, including corrections for temporal gravity field signals to isolate the static gravity field part, screening for outliers, calibration by comparison with existing external gravity field information and error assessment. The temporal gravity gradient corrections consist of tidal and nontidal corrections. These are all generally below the gravity gradient error level, which is predicted to show a 1/f behaviour for low frequencies. In the outlier detection, the 1/f error is compensated for by subtracting a local median from the data, while the data error is assessed using the median absolute deviation. The local median acts as a high-pass filter and it is robust as is the median absolute deviation. Three different methods have been implemented for the calibration of the gravity gradients. All three methods use a high-pass filter to compensate for the 1/f gravity gradient error. The baseline method uses state-of-the-art global gravity field models and the most accurate results are obtained if star sensor misalignments are estimated along with the calibration parameters. A second calibration method uses GOCE GPS data to estimate a low-degree gravity field model as well as gravity gradient scale factors. Both methods allow to estimate gravity gradient scale factors down to the 10⁻³ level. The third calibration method uses high accurate terrestrial gravity data in selected regions to validate the gravity gradient scale factors, focussing on the measurement band. Gravity gradient scale factors may be estimated down to the 10⁻² level with this method.  相似文献   

Effect of attachment configuration on the trapping efficiency of Vaseline-coated slide catchers for windblown particles     

Mustafa Basaran  Gunay Erpul  A. Ugur Ozcan  Pieter Bogman  Wim M. Cornelis  Donald Gabriels 《Environmental Earth Sciences》2010,61(7):1375-1384

There are various types of the windblown sediment traps developed for wind tunnel and field studies. One of the main supports expected from these traps is in measuring surface dust concentrations to appropriately derive flux equations. The measurement performance and accuracy of a trap is very important and depends strictly upon the physical characteristics and the behaviors of dust grains with air flows. This paper presents the measurement results of static pressure distribution (SPD) of wind flow around Vaseline-coated slide (VCS) catchers with an aim of finding out whether or not particle trapping efficiency (η) of the VCS is related to the SPD. The SPD was evaluated by a wind reduction coefficient (R _c) in a series of wind tunnel experiments with different VCS settings which have different attachment configurations on a pole. Three VCS configurations were considered: a configuration on a circular plastic pole (CPP) and two configurations on wooden square poles (WSP₁ and WSP₂, respectively). Thus, the primary contribution of this work was to experimentally analyze the effect of the different attachment configurations on the SPD, and the secondary objective was to determine the effect of the SPD on the η. It was shown that spatial correlation and spatial pattern of the R _c were different in the surrounding area of each configuration, and ANOVA and DUNCAN tests indicated that η(s) of WSP₁, WSP₂, and CPP were different at the significant level of P ≤ 0.05 with the mean of 0.94 ± 0.09, 0.63 ± 0.14, and 1.13 ± 0.07, respectively. Additionally, the amount of PM₂₀, PM₄₀, PM₆₀, PM₈₀, and PM₁₀₀ trapped by the configurations of WSP₁, WSP₂, and CPP considerably varied depending upon the particular aerodynamic circumstances associated with every configuration.  相似文献   

Experimental and numerical studies of the O exchange between CO₂ and water in the atmosphere-soil invasion flux     

Yaacov Kapiluto  Pieter Tans 《Geochimica et cosmochimica acta》2007,71(11):2657-2671

The ¹⁸O/¹⁶O ratio of CO₂ is a potentially powerful tracer of carbon dioxide fluxes from the soil to the atmosphere, which is influenced by complex interactions involving both biotic and abiotic soil processes. We use a simplified experimental approach and numerical simulations to examine in isolation the ¹⁸O exchange between CO₂ and soil water associated with the abiotic invasion of atmospheric CO₂ into soil. This allowed us to verify, in particular, whether the ¹⁸O of the retro-diffusion flux of CO₂ from the soil reflects ¹⁸O equilibration with water at the soil surface, or at some depth. Sterile soil samples with known water isotopic composition were placed in a closed box attached to a specially designed flow chamber and the changes in δ¹⁸O of CO₂ between the chamber inlet and outlet, due only to invasion effects, were determined. Numerical simulations constrained by the laboratory gas exchange measurements indicated that between the two commonly used diffusion models [Penman, H.L. (1940). Gas and vapor movements in soil, 1: the diffusion of vapors through porous solids. Int. J. Agric. Sci.30, 437-462; Moldrup, P., Olesen, T., Yamaguchi, T., Schjonning, P., Rolston, D.E. (1999). Modeling diffusion and reaction in soils, IX, the Backingham-Burdine-Campbell equation for gas diffusivity in undisturbed soil. Soil Sci.164, 542-551], only the former provided good agreement with the measurements over a wide range of soil water contents. Based on the model calculations constrained by experimental data, and on comparison of characteristic diffusion/reaction times, we conclude that the depth required for full CO₂-water ¹⁸O equilibration ranges between 2 and 8.5 cm. The depth depends, in order of importance, on (1) soil moisture content; (2) temperature, which dominates the rate of hydration isotopic exchange; (3) CO₂ residence time, which is determined by the time of replacement of the column air above the soil; and (4) soil structure, including porosity, tortuosity and grain size, with the later probably influencing the water surface area exposed to CO₂ exchange. Using field data from a semi-arid forest site in Israel, numerical simulations indicated that the ¹⁸O full equilibrium depth varied at this site between 4 cm (January) and 8 cm (November), being sensitive mostly to temperature and soil water content. Deepening of the equilibration depth as the soil dries should limit the effects of ¹⁸O evaporative enrichment at the surface on the isotopic composition of the soil-atmosphere CO₂ flux.  相似文献   

Molluscan assemblages of seagrass-covered and bare intertidal flats on the Banc d'Arguin, Mauritania, in relation to characteristics of sediment and organic matter     

Pieter J.C. Honkoop  Eilke M. Berghuis  Sander Holthuijsen  Marc S.S. Lavaleye  Theunis Piersma   《Journal of Sea Research》2008,60(4):255-263

The Banc d'Arguin, a non-estuarine area of shallows and intertidal flats off the tropical Saharan coast of Mauritania, is characterised by extensive intertidal and subtidal seagrass beds. We examined the characteristics of intertidal seagrass (Zostera noltii) meadows and bare areas in terms of the presence and abundance of molluscs (gastropods and bivalves). To explain observed differences between molluscan assemblages in seagrass and bare patches, some aspects of the feeding habitat (top-5 mm of the sediment) and of food (organic materials) of molluscs were examined. The novelty of this study is that phytopigments were measured and identified to assess source and level of decay (freshness) of organic material in the sediment and to study their importance as an explanatory variable for the distribution of molluscs. Over an area of 36 km² of intertidal flats, at 12 sites, paired comparisons were made between seagrass-covered and nearby bare patches. Within seagrass meadows, dry mass of living seagrass was large and amounted to 180 ±10 g AFDM m^− 2 (range 75–240). Containing twice the amount of silt per unit dry sediment mass, seagrass sediments were muddier than bare areas; the relative amount of organic material was also larger. The total number of species of bivalves and gastropods amounted to 27, 14 of which were found only in seagrass areas, 4 only in bare and 9 in both types of habitat. Among the three numerically most abundant species, the bivalves Anadara senilis, Dosinia hepatica and Loripes lacteus, the first was numerically most abundant in bare and the other two in seagrass-covered areas. Bare intertidal areas had greater mean total biomass of molluscs (80.5 g AFDM m^− 2) than seagrass meadows (30.0 g AFDM m^− 2). In both habitats, the bulk of the biomass was made up by A. senilis. Excluding this species, bare mudflats contained on average only 3.1 g AFDM m^− 2 and seagrass meadows 6.9 g AFDM m^− 2. As compared to previous surveys in 1980–1986, the biomass of A. senilis had increased almost 10-fold and D. hepatica, previously found in very small numbers, had become the most numerous species. However, the total biomass excluding that of A. senilis was similar. Concentrations of phytopigments were similar to those observed at temperate mudflats, indicating that the Banc d'Arguin might not be as oligotrophic as previously thought. Per unit of dry sediment mass, smaller amounts of phytopigments were found in bare than in seagrass areas. Per unit of dry organic material, bare sediments contained most (fresh) phytopigments. This suggests that in seagrass-covered meadows the organic material is more degraded than in bare sediments. Overall, the composition of phytopigments, quite surprisingly, indicated a benthic-diatom-dominated trophic system. Multivariate statistics revealed that patterns of zoobenthic assemblages were correlated with patterns of a combination of four environmental parameters: grain size of the sediment, amount of fresh phytopigments and amounts of leaves and roots of seagrass.  相似文献   

Age of the Marwar Supergroup,NW India:A note on the U–Pb geochronology of Jodhpur Group felsic volcanics     

Huiru Xu  Joseph G.Meert  Manoj K.Pandit 《地学前缘(英文版)》2022,(1):244-254

The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the Marwar basin are still scarce.In this study,we report U–Pb zircon,LA-ICP-MS,and SIMS ages from the Chhoti Khatu felsic volcanic rocks,interlayered with the Jodhpur Group sandstones(Lower Marwar Supergroup).The cathodoluminescence images of the zircons indicate complex morphologies,and core-rim textures coupled with the wide range of ages indicate that they are likely inherited or in the case of thin poorly indurated ash-beds,detrital in origin.The age spectra of 68 zircon analyses from our sampling display a dominant 800–900 Ma age peak corresponding to the age of basement"Erinpura granite"rocks in the region.The youngest inherited zircon from a felsic ash layer yielded a U–Pb age of651 Ma±18 Ma that,together with previous studies and paleontological evidence,indicates a postCryogenian age for the initiation of Marwar sedimentation following a~125 Ma hiatus between the end of Malani magmatism and Marwar deposition.  相似文献   

The lacustrine microbial carbonate factory of the successive Lake Bonneville and Great Salt Lake,Utah, USA     

Emmanuelle Vennin  Anthony Bouton  Raphaël Bourillot  Aurlie Pace  Adeline Roche  Arnaud Brayard  Christophe Thomazo  Aurelien Virgone  Eric C. Gaucher  Guy Desaubliaux  Pieter T. Visscher 《Sedimentology》2019,66(1):165-204

The Bonneville Basin is a continental lacustrine system accommodating extensive microbial carbonate deposits corresponding to two distinct phases: the deep Lake Bonneville (30 000 to 11 500 ¹⁴C bp ) and the shallow Great Salt Lake (since 11 500 ¹⁴C bp ). A characterization of these microbial deposits and their associated sediments provides insights into their spatio‐temporal distribution patterns. The Bonneville phase preferentially displays vertical distribution of the microbial deposits resulting from high‐amplitude lake level variations. Due to the basin physiography, the microbial deposits were restricted to a narrow shoreline belt following Bonneville lake level variations. Carbonate production was more efficient during intervals of relative lake level stability as recorded by the formation of successive terraces. In contrast, the Great Salt Lake microbial deposits showed a great lateral distribution, linked to the modern flat bottom configuration. A low vertical distribution of the microbial deposits was the result of the shallow water depth combined with a low amplitude of lake level fluctuations. These younger microbial deposits display a higher diversity of fabrics and sizes. They are distributed along an extensive ‘shore to lake’ transect on a flat platform in relation to local and progressive accommodation space changes. Microbial deposits are temporally discontinuous throughout the lake history showing longer hiatuses during the Bonneville phase. The main parameters controlling the rate of carbonate production are related to the interaction between physical (kinetics of the mineral precipitation, lake water temperature and runoff), chemical (Ca²⁺, Mg²⁺ and HCO₃^? concentrations, Mg/Ca ratio, dilution and depletion) and/or biological (trophic) factors. The contrast in evolution of Lake Bonneville and Great Salt Lake microbial deposits during their lacustrine history leads to discussions on major chemical and climatic changes during this interval as well as the role of physiography. Furthermore, it provides novel insights into the composition, structure and formation of microbialite‐rich carbonate deposits under freshwater and hypersaline conditions.  相似文献