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1.
The results of isotope-geochemical studies of carbonates of different mineral types from manganese and host rocks of the Famennian manganiferous formation of Pai-Khoi are reported. Kutnahorite ores are characterized by δ13C values from–6.6 to 1.3‰ and δ18O from 20.0 to 27.4‰. Rhodonite–rhodochrosite rocks of the Silovayakha ore occurrence have δ13C from–5.2 to–2.9 and δ18O from 25.4 to 24.3‰. Mineralogically similar rocks of the Nadeiyakha ore occurrence show the lighter carbon and oxygen isotopic compositions: δ13C from–16.4 to–13.1 and δ18O from 24.8 to 22.5‰. Similar isotopic compositions were also obtained for rhodochrosite–kutnahorite rocks of this ore occurrence: δ13C from–13.0 to–10.4‰ and δ18O from 24.6 to 21.7‰. Siderorodochrosite ores differ in the lighter oxygen and carbon isotopic compositions: δ18O from 18.7 to 17.6‰ and δ13C from–10.2 to–9.3‰, respectively. In terms of the carbon and oxygen isotopic compositions, host rocks in general correspond to marine sedimentary carbonates. Geological-mineralogical and isotope data indicate that the formation of the manganese carbonates was related to the hydrothermal ore-bearing fluids with the light isotopic composition of oxygen and carbon dissolved in CO2. The isotopic features indicate an authigenic formation of manganese carbonates under different isotopegeochemical conditions.  相似文献   

2.
The Verkhnyaya Kardailovka section is one of the best candidates for the GSSP (Global Stratotype Section and Point) at the base of the Stage (Mississippian). For boundary definition, the first appearance of the conodont Lochriea ziegleri Nemirovskaya, Perret et Meischner, 1994 in the lineage Lochriea nodosa (Bischoff, 1957)?L. ziegleri is used. L. ziegleri appears in the Venevian Substage somewhat below the base of the Serpukhovian in the Moscow Basin. The position of the FAD of L. ziegleri within the Hypergoniatites?Ferganoceras Genozone is confirmed and lies between 19.53 and 19.63 m above the section’s base. Before 2010, deep-water stylonodular limestone containing the boundary in unnamed formation C at Kardailovka was well exposed but only 3 m of Viséan strata cropped out immediately below. Recent trenching exposed another 10 m of underlying Viséan carbonates in formation C and older Viséan siliciclastics and volcanics in unnamed formation B. The contact between formation B and underlying crinoidal limestones in unnamed formation A representing the middle Viséan Zhukovian (Tulian) regional Substage was excavated. The boundary succession, situated in the Magnitogorsk tectonic zone above the Devonian Magnitogorsk arc and Mississippian magmatic and sedimentary rift succession, was deposited west of the Kazakhstanian continent during closure of the Ural Ocean. In the lower part of the section, Viséan tuffaceous siliciclastics and volcanics of formation B record rapid deepening after deposition of neritic middle Viséan crinoid lime grainstone of formation A and subsequent subaerial exposure. The overlying condensed upper Viséan to Serpukhovian succession in formation C comprises deep-water limestone deposited in a sediment-starved basin recording minor turbidite influx and carbonate-mound development. The δ13Ccarb plot shows a positive shift of 1‰ V-PDB (from +2 to +3‰) between 17.0 and 17.75 m (3.05 and 1.97 m below FAD L. ziegleri). The δ18Oapatite graph displays a prominent upward shift from 19.9 to 21.1‰ V-SMOW (at 19.15 to 19.51 m) in the nodosa Zone below FAD of Lochriea ziegleri.  相似文献   

3.
Stable isotope data of precipitation (δ18Op and deuterium excess), drip water (δ18Od), and modern calcite precipitates (δ18Oc and δ13Cc) from Yongxing Cave, central China, are presented, with monthly sampling intervals from June 2013 to September 2016. Moderate correlations between the monthly variation of δ18Op values (from ??11.5 to ??0.7‰) and precipitation amount (r = ??0.59, n?=?34, p?<?0.01) and deuterium excess (r?=?0.39, n?=?31, p?<?0.01) imply a combined effect of changes in precipitation amount and atmospheric circulation. At five drip sites, the δ18Od values have a much smaller variability (from ??9.1 to ??7.5‰), without seasonal signals, probably a consequence of the mixing in the karst reservoir with a deep aquifer. The mean δ18Od value (??8.4‰) for all drip waters is significantly more negative than the mean δ18Op value (??6.9‰) weighted by precipitation amount, but close to the wet season (May to September) mean value (??8.3‰), suggesting that a threshold of precipitation amount must be exceeded to provide recharge. Calculation based on the equilibrium fractionation factor indicates that the δ18Oc values are not in isotopic equilibrium with their corresponding drip waters, with a range of disequilibrium effects from 0.4 to 1.4‰. The δ18Oc and δ13Cc values generally increase progressively away from the locus of precipitation on glass plates. The disequilibrium effects in the cave are likely caused by progressive calcite precipitation and CO2 degassing related to a high gradient of CO2 concentration between drip waters and cave air. Our study provides an important reference to interpret δ18Oc records from the monsoon region of China.  相似文献   

4.
C and O isotope composition of Middle-Upper Miocene and Lower Pliocene carbonates from Kerch-Taman Region (Eastern Paratethys) have been studied in order to reconstruct palaeoenvironmental variability and post-sedimentation changes. The δ13C and δ18О values of the Upper Sarmatian to Lower Pliocene organogenic carbonates reflect the desalinization of paleobasins, global Late Miocene Cooling, and increase in seasonal temperature fluctuations. Isotopic composition of the Middle Sarmatian organogenic carbonates was strongly influenced by evaporation processes, high bioproductivity, and local submarine methane emissions. Warm climate and low bioproductivity together with unstable hydrological regime during the Late Chokrakian and the Karaganian times influenced the isotope composition of primary carbonates. Calcite shell of Spiratella sp. (δ13C =–0.4‰ and δ18О =–0.4‰) from Tarkhanian sediments was formed in warm marine environment. Dolomitization prevails over other secondary mineralization in the studied carbonate rocks. Two groups of secondary dolomites that are characterized by negative and positive δ13C values have been recognized. Lowe δ13C values (up to–31.4‰) in dolomites indicate the influence of both dissolved inorganic carbon (DIC) from oxidized organic matter (Сorg) and methane. Dolomites with positive δ13C values (7.0 and 7.8‰) associat with migration of CO2- and CH4-containing saline groundwater.  相似文献   

5.
The specific heat capacity (C p) of six variably hydrated (~3.5 wt% H2O) iron-bearing Etna trachybasaltic glasses and liquids has been measured using differential scanning calorimetry from room temperature across the glass transition region. These data are compared to heat capacity measurements on thirteen melt compositions in the iron-free anorthite (An)–diopside (Di) system over a similar range of H2O contents. These data extend considerably the published C p measurements for hydrous melts and glasses. The results for the Etna trachybasalts show nonlinear variations in, both, the heat capacity of the glass at the onset of the glass transition (i.e., C p g ) and the fully relaxed liquid (i.e., C p l ) with increasing H2O content. Similarly, the “configurational heat capacity” (i.e., C p c  = C p l  ? C p g ) varies nonlinearly with H2O content. The An–Di hydrous compositions investigated show similar trends, with C p values varying as a function of melt composition and H2O content. The results show that values in hydrous C p g , C p l and C p c in the depolymerized glasses and liquids are substantially different from those observed for more polymerized hydrous albitic, leucogranitic, trachytic and phonolitic multicomponent compositions previously investigated. Polymerized melts have lower C p l and C p c and higher C p g with respect to more depolymerized compositions. The covariation between C p values and the degree of polymerization in glasses and melts is well described in terms of SMhydrous and NBO/T hydrous. Values of C p c increase sharply with increasing depolymerization up to SMhydrous ~ 30–35 mol% (NBO/T hydrous ~ 0.5) and then stabilize to an almost constant value. The partial molar heat capacity of H2O for both glasses (\( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{g}} \)) and liquids (\( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \)) appears to be independent of composition and, assuming ideal mixing, we obtain a value for \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \) of 79 J mol?1 K?1. However, we note that a range of values for \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \) (i.e., ~78–87 J mol?1 K?1) proposed by previous workers will reproduce the extended data to within experimental uncertainty. Our analysis suggests that more data are required in order to ascribe a compositional dependence (i.e., nonideal mixing) to \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \).  相似文献   

6.
δ13C and δ15N values of two generalists primary consumers, a strict deposit-feeder polychaete (Arenicola marina), and a strict suspension-feeder bivalve (Crassostrea gigas), were investigated to typify the trophic functioning of two contrasted marine coastal ecosystems (eutrophic and mesotrophic, east and west Cotentin peninsula, respectively, English Channel, Normandy, France). On average, δ13C and δ15N values of lugworms mirrored those of sediment organic matter (SOM), whereas δ13C and δ15N of oysters mirrored those of suspended particulate organic matter (SPOM). δ13C values of the two species displayed significant differences on the west coast (mesotrophic) contrary to the east coast (eutrophic; significant interactions). δ15N values differed only between sites and not between species. Diet of A. marina relied exclusively on microphytobenthos (MPB) and detritus of macroalgae (ULV) on the mesotrophic coast, whereas diet of C. gigas relied mainly on SPOM. Conversely, on the eutrophic ecosystem (the east coast), both species displayed the same diet, which was a mixture of pelagic sources (SPOM), benthic sources (MPB and ULV) and to a lesser extent riverine particulate organic matter (rPOM). These results were explained by the intensity of benthic vs. pelagic couplings (i.e. benthic-pelagic and pelagic-benthic) which differed in the two ecosystems. Low trophic coupling occurred on the mesotrophic (west) coast, whereas benthic-pelagic (SOM resuspension) and pelagic-benthic (settling of SPOM such as phytoplankton blooms) couplings were typified on the eutrophic (east) coast. This higher particulate organic matter (POM) pelagic-benthic coupling on the east coast was probably enhanced by nutrient enrichment caused by eutrophication. Comparison of δ13C ratios of both the strict deposit-feeder (e.g. A. marina) and the strict suspension-feeder (e.g. C. gigas) was then proposed as a bio-indicator of the trophic status and of POM benthic vs. pelagic couplings of soft-bottom coastal ecosystems.  相似文献   

7.
The Triassic–Jurassic boundary is characterized by strong perturbations of the global carbon cycle, triggered by massive volcanic eruptions related to the onset of the Central Atlantic Magmatic Province. These perturbations are recorded by negative carbon isotope excursions (CIEs) which have been reported worldwide. In this study, Triassic–Jurassic boundary sections from the southern margin of the Central European Basin (CEB) located in northern Switzerland are analyzed for organic carbon and nitrogen isotopes in combination with particulate organic matter (POM) analyses. We reconstruct the evolution of the depositional environment from Late Triassic to Early Jurassic in northern Switzerland and show that observed negative shifts in δ13C of the total organic carbon (δ13CTOC) in the sediment are only subordinately influenced by varying organic matter (OM) composition and primarily reflect global changes in the carbon cycle. Based on palynology and the stratigraphic positions of isotopic shifts, the δ13CTOC record of the studied sections is correlated with the GSSP section at Kuhjoch (Tethyan realm) in Austria and with the St. Audrie’s Bay section (CEB realm) in southwest England. We also show that in contrast to POM analyses the applicability of organic carbon/total nitrogen (OC/TN) atomic ratios and stable isotopes of total nitrogen (δ15NTN) for detecting changes in source of OM is limited in marginal depositional environments with frequent changes in lithology and OM contents.  相似文献   

8.
This study quantifies the influence of various intrinsic soil properties including particle roundness, R, sphericity, S, 50% size by weight, D 50, coefficient of uniformity, C u, and the state property of relative density, D r, on the compression and recompression indices, C c and C r, of sands of various geologic origins at pre-crushing stress levels. Twenty-four sands exhibiting a wide range of particle shapes, gradations, and geologic origins were collected for the study. The particle shapes were determined using a computational geometry algorithm which allows characterization of a statistically large number of particles in specimens. One dimensional oedometer tests were performed on the soils. The new data was augmented with many previously published results. Through statistical analyses, simple functional relationships are developed for C c and C r. In both cases, the models utilized only R and D r since other intrinsic properties proved to have lesser direct influence on the compression indices. However, previous studies showed that the contributions of S and C u are felt through their effects on index packing void ratios and thus on D r. The accuracy of the models was confirmed by comparison of predicted and observed C c and C r values.  相似文献   

9.
The paleohydrological and sedimentological characteristics of a playa lake in northern Kuwait (Arabian Gulf) are reconstructed using sedimentological, geochemical, and isotopic techniques. The sequence consists of up to 8 cycles of S-poor, alluvial sediments capped by a thin organic soil interbedded with gravity-fall calcrete sediments. The succession is locally derived from mainly Quaternary sediments and is regressive with upsection filling of the subsiding basin by cycles of sheetwash flow in response to climatic change. There is no natural, open-water lake water as indicated by low total organic carbon (TOC) data, but the presence of incised calcrete yardangs suggests that more extensive open-water conditions were operative in the past. Stable isotope (δ18O‰ and δ13C‰) values of the authigenic carbonates indicate the following three distinct processes: evaporation, meteoric fluid infiltration, and rapid per-descensum flow (rapid downward movement of water and playa sediment through pipes) through a porous, clastic sequence. Because evaporites are scarce, other factors besides evaporation action control chemical and isotopic compositions of the per-decensum lake fluids. Consequently, the isotopic composition cannot be interpreted exclusively as an indicator of salinity or evaporation ratio. The degassing of CO2 during groundwater discharge may explain the enriched carbon isotope values for the authigenic carbonates precipitated in the sediments. Hydrologically closed lake water bodies tend to show low negative carbonate oxygen and carbon isotopic signatures. Isotopically negative δ13C values imply a strong input of soil-zone carbon to the groundwater of the top 60 cm of the sediment. Lakes that are hydrologically closed and evaporate or equilibrate with atmospheric CO2 will tend to have low negative δ18O and δ13C values in the carbonates as reported by Talbot (Chem Geol: Isotope Geosci Sect 80(4):261–279, 1990). Biologically active lakes will tend toward lower δ13C of dissolved carbon due to the photosynthetic effects of 12C withdrawal as reported by Dunagan and Driese (J Sed Res 69:772–783, 1999). Increased biological activity during sedimentation may account for low carbon isotope values where plants were abundant, but in shrinkage-dominated systems (those of clay-rich soil subjecting to wet-dry conditions), carbon isotopes will be largely inherited from the calcretic limestones in the land extending landward of the coast and not influenced by coastal processes (known as hinterland), such as Umm Ar-Rimam depression. This basin does not fit the classic shallow playa-type basins of the Arabian Peninsula but rather the recharge playas of the southwestern USA.  相似文献   

10.
A high-pressure single-crystal X-ray diffraction study has been carried out on a P21/c natural Mg-rich pigeonite sample with composition ca. Wo6En76Fs18 using a diamond anvil-cell. The unit-cell parameters were determined at 14 different pressures to 7.14 GPa. The sudden disappearance of the b-type reflections (h + k = odd) and a strong discontinuity (about 2.8%) in the unit-cell volume indicated a first-order P21/c–C2/c phase transition between 4.66 and 4.88 GPa. The P(V) data of the P21/c phase were fitted to 4.66 GPa by a third-order Birch–Murnaghan equation of state (BM3 EoS), whereas the limited number of experimental data collected within the C2/c phase between 4.88 and 7.14 GPa were fitted using the same equation of state but with K′ constrained to the value obtained for the P21/c fitting. The equation of state coefficients are V 0 = 424.66(6) Å3, K T0 = 104(2) GPa and K′ = 8(1) for the P21/c phase, and V 0 = 423.6(1) Å3, K T0 = 112.4(8) GPa, and K′ fixed to 8(1) for the C2/c phase. The axial moduli for a, b, and c for the P21/c phase were obtained using also a BM3-EoS, while for the C2/c phase only a linear calculation could be performed, and therefore the same approach was applied for comparison also to the P21/c phase. In general the C2/c phase exhibits axial compressibilities (β c > β a >> β b) lower than those of the P21/c phase (β b > β c ≈ β a; similar to those found in previous studies in clinopyroxenes and orthopyroxenes). The lower compressibility of the C2/c phase compared with that of the P21/c could be ascribed to the greater stiffness along the b direction. A previously published relationship between P c and M2 average cation radius (i.r.) has been updated using all the literature data on P21/c clinopyroxene containing large cations at M2 site and our new data. The following weighted regression was obtained: P c (GPa) = 26(4) ? 28(5) ×  i.r (Å), R 2 = 0.97. This improved equation can be used to predict the critical pressure of natural P21/c clinopyroxene samples just knowing the composition at M2 site.  相似文献   

11.
SDO/HMI and SDO/AIA data for the 24th solar-activity cycle are analyzed using a quicker and more accurate method for resolving π ambiguities in the transverse component of the photospheric magnetic field, yielding new results and confirming some earlier results on the magnetic properties of leading and following magnetically connected spots and single spots. The minimum inclination of the field lines to the positive normal to the solar surface α min within umbrae is smaller in leading than in following spots in 78% of the spot pairs considered; the same trend is found for the mean angle 〈α〉 in 83% of the spot pairs. Positive correlations between the α min values and the 〈α〉 values in leading and following spots are also found. On average, in umbrae, the mean values of 〈B〉, the umbra area S, and the angles α min and 〈α〉 decrease with growth in the maximum magnetic field B max in both leading and following spots. The presence of a positive correlation between B max and S is confirmed, and a positive correlation between 〈B〉 and S in leading and following spots has been found. Themagnetic properties of the umbrae of magnetically connected pairs of spots are compared with the contrast of the He II 304 emission above the umbrae, C 304. Spots satisfying certain conditions display a positive correlation between C 304?L and 〈α L 〉 for the leading (L) spots, and between C 304?L /C 304?F and l L /l F , where l L (l F ) are the lengths of the field lines connecting leading (L) or following (F) spots from the corresponding spot umbrae to the apex of the field line.  相似文献   

12.
Crystals of lead oxychloride Pb13O10Cl6 have been synthesized on the basis of high-temperature solid-state reactions. The Pb13O10Cl6 structure was studied using X-ray single-crystal diffraction analysis. The compound is monoclinic, and the space group is C2/c; the unit-cell dimensions are a = 16.1699(14), b = 7.0086(6), c = 23.578(2) Å, β = 97.75°, and V = 2647.6(4) Å3. The structure has been solved by direct methods and refined to R 1 = 0.0505 for 2671 observed unique reflections. The structure is a 3D framework consisting of OPb4 tetrahedrons. Chlorine atoms are located in the framework channels. The structure contains seven symmetrically independent Pb atoms, which are coordinated by 2 to 4 O2? and 2 to 4 Cl? anions. The synthesized compound is compared with other natural and synthetic lead oxyhalides.  相似文献   

13.
The lower part of Shayi Member (Es1x Sub-Member) composed mainly of dark mudstones and shales is the dominant source rocks for the Lixian Slope. Based on organic petrology, organic and inorganic geochemistry analyses of several mudstone and shale samples selected from Es1x Sub-Member, this research provides an overview on type, origin and thermal maturity of organic matters, as well as depositional environment of Es1x Sub-Member. Kerogen microscopy observation shows that the macerals are dominated by sapropelinite with a significant mixture of vitrinite and inertinite, indicating that aquatic algal-bacterial organic matter inputs are dominate with a significant contribution of terrigenous organic matter inputs. This statement is supported by n-alkane patterns distribution characteristics, high (n-C21 + n-C22)/(n-C28 + n-C29) values (average = 1.77), the plot of high Ph/n-C18 values (average = 4.15) versus low Pr/n-C17 values (average = 1.13), and high proportion of C27 sterane and C29 sterane (average = 37.7 and 42.0%, respectively). In addition, the rather low Pr/Ph values (average = 0.38), high gammacerane index values (average = 0.30), high V/Ni and V/(V + Ni) values (average = 11.84 and 0.89, respectively), high Sr/Ba and Sr/Cu values (average = 8.54 and 108, respectively), indicative of a saline water condition and a anoxic depositional environment. The low C29 sterane ααα 20S/(20S + 20R), C29 sterane αββ/(αββ + ααα), C31 homohopane 22S/(22S + 22R), C32 homohopane 22S/(22S + 22R), Ts/(Ts + Tm) values and relatively high moretane/hopane values show that the level of thermal maturity of organic matters in Es1x Sub-Member are low.  相似文献   

14.
Peralkaline syenite and granite dykes cut the Straumsvola nepheline syenite pluton in Western Dronning Maud Land, Antarctica. The average peralkalinity index (PI?=?molecular Al/[Na?+?K]) of the dykes is 1.20 (n?=?29) and manifests itself in the presence of the Zr silicates eudialyte, dalyite and vlasovite, and the Na–Ti silicate, narsarsukite. The dykes appear to have intruded during slow cooling of the nepheline syenite pluton, and the petrogenetic relationship of the dykes and the pluton cannot be related to closed-system processes at low pressure, given the thermal divide that exists between silica-undersaturated and oversaturated magmas. Major and trace element variations in the dykes are consistent with a combination of fractional crystallization of parental peralkaline magma of quartz trachyte composition, and internal mineral segregation prior to final solidification. The distribution of accessory minerals is consistent with late-stage crystallization of isolated melt pockets. The dykes give an Rb–Sr isochron age of 171?±?4.4 Ma, with variable initial 87Sr/86Sr ratio (0.7075?±?0.0032), and have an average ε Nd of ? 12.0. Quartz phenocrysts have δ18O values of 8.4–9.2‰, which are generally in O-isotope equilibrium with bulk rock. Differences in the δ18O values of quartz and aegirine (average Δquartz?aegirine = 3.5‰) suggest aegirine formation temperatures around 500 °C, lower than expected for a felsic magma, but consistent with poikilitic aegirine that indicates subsolidus growth. The negative ε Nd (< ? 10) and magma δ18O values averaging 8.6‰ (assuming Δquartz?magma = 0.6‰) are inconsistent with a magma produced by closed-system fractional crystallization of a mantle-derived magma. By contrast, the nepheline syenite magma had mantle-like δ18O values and much less negative ε Nd (average ??3.1, n?=?3). The country rock has similar δ18O values to the granite dykes (average 8.0‰, n?=?108); this means that models for the petrogenesis of the granites by assimilation are unfeasible, unless an unexposed high-δ18O contaminant is invoked. Instead, it is proposed that the peralkaline syenite and granite dykes formed by partial melting of alkali-metasomatised gneiss that surrounds the nepheline syenite, followed by fractional crystallization.  相似文献   

15.
While multiple species of macroalgae and seagrass can benefit from elevated CO2 concentrations, competition between such organisms may influence their ultimate responses. This study reports on experiments performed with a Northwest Atlantic species of the macroalgae, Ulva, and the seagrass, Zostera marina, grown under ambient and elevated levels of pCO2, and subjected to competition with each other. When grown individually, elevated pCO2 significantly increased growth rates and productivity of Ulva and Zostera, respectively, beyond control treatments (by threefold and 27%, respectively). For both primary producers, significant declines in tissue δ13C signatures suggested that increased growth and productivity were associated with a shift from use of HCO3? toward CO2 use. When grown under higher pCO2, Zostera experienced significant increases in leaf and rhizome carbon content as well as significant increases in leaf carbon-to-nitrogen ratios, while sediments within which high CO2 Zostera were grown had a significantly higher organic carbon content. When grown in the presence of Ulva; however, above- and below-ground productivity and tissue nitrogen content of Zostera were significantly lower, revealing an antagonistic interaction between elevated CO2 and the presence of Ulva. The presence of Zostera had no significant effect on the growth of Ulva. Collectively, this study demonstrates that while Ulva and Zostera can each individually benefit from elevated pCO2 levels, the ability of Ulva to grow more rapidly and inhibit seagrass productivity under elevated pCO2, coupled with accumulation of organic C in sediments, may offset the potential benefits for Zostera within high CO2 environments.  相似文献   

16.
In this study, the effects of salinity of infiltrating solutions on the swelling strain, compressibility, and hydraulic conductivity of compacted GMZ01 Bentonite were investigated. After swelling under vertical load using either distilled water or NaCl solutions with concentrations of 0.1, 0.5 M, and 1 M, laboratory oedometer tests were conducted on the compacted GMZ01 Bentonite. Based on the oedometer test results, hydraulic conductivity was determined using the Casagrande’s method. Results show that the swelling strain of highly compacted GMZ01 Bentonite decreases as the concentration of NaCl solution increases. The compression index C c * increases and then turns to decrease with an increase in the vertical stress or a decrease in the void ratio for different solutions, and the C c * decreases as the concentration of NaCl solution increases. The secondary consolidation coefficient C α increases linearly with the increase of the compression index C c * . Furthermore, a bi-linear relationship between the swelling index C s * and the secondary consolidation coefficient C α can be characterized clearly. The hydraulic conductivity increases as the concentration of NaCl solution increases, however, this increase can be prevented if a high confining stress is applied.  相似文献   

17.
Nutrient sources of San Quintin Bay, a coastal lagoon affected by coastal upwelling off Baja California (Mexico), were traced using generalized additive (mixed) models (GAMM) to the stable nitrogen isotopic composition, C:N and N content of two co-occurring macrophytes (the macroalgae Ulva spp. and the seagrass Zostera marina). The geochemical tracers followed a spatial trend that partly responded to the long-term nutrient gradient from the ocean towards the interior of the bay. N content in Z. marina and Ulva spp. decreased linearly (while C:N increased) towards the middle section of the bay to concentration levels that indicate potential N limitation for growth. Concurrently midway into the bay (6–9 km), the δ15N of both macrophytes showed a gradual enrichment in 15N reflecting progressive denitrification. The spatial pattern of δ15N and the decrease in C:N of the macrophytes towards the innermost section of the bay indicated an additional nonoceanic source of dissolved nitrogen in this zone. The similarity of the δ15N pattern of Z. marina and Ulva spp. implies that their δ15N composition is mainly controlled by the availability of N, in spite of the physiological differences between taxa. A better fit of GAMM to N content and C:N was obtained for Z. marina than for Ulva spp. indicating that the former delineate more steadily and smoothly the influence of upwelling along the spatial gradient. Nonetheless, Ulva spp. may be analyzed in combination with Z. marina to characterize the environmental conditions at the time of sampling.  相似文献   

18.
The improvement in the capabilities of Landsat-8 imagery to retrieve bathymetric information in shallow coastal waters was examined. Landsat-8 images have an additional band named coastal/aerosol, Band 1: 435–451 nm in comparison with former generation of Landsat imagery. The selected Landsat-8 operational land image (OLI) was of Chabahar Bay, located in the southern part of Iran (acquired on February 22, 2014 in calm weather and relatively low turbidity). Accurate and high resolution bathymetric data from the study area, produced by field surveys using a single beam echo-sounder, were selected for calibrating the models and validating the results. Three methods, including traditional linear and ratio transform techniques, as well as a novel proposed integrated method, were used to determine depth values. All possible combinations of the three bands [coastal/aerosol (CB), blue (B), and green (G)] have been considered (11 options) using the traditional linear and ratio transform techniques, together with five model options for the integrated method. The accuracy of each model was assessed by comparing the determined bathymetric information with field measured values. The standard error of the estimates, correlation coefficients (R 2 ) for both calibration and validation points, and root mean square errors (RMSE) were calculated for all cases. When compared with the ratio transform method, the method employing linear transformation with a combination of CB, B, and G bands yielded more accurate results (standard error = 1.712 m, R 2 calibration = 0.594, R 2 validation = 0.551, and RMSE =1.80 m). Adding the CB band to the ratio transform methodology also dramatically increased the accuracy of the estimated depths, whereas this increment was not statistically significant when using the linear transform methodology. The integrated transform method in form of Depth = b 0  + b 1 X CB  + b 2 X B  + b 5 ln(R CB )/ln(R G ) + b 6 ln(R B )/ln(R G ) yielded the highest accuracy (standard error = 1.634 m, R 2 calibration = 0.634, R 2 validation = 0.595, and RMSE = 1.71 m), where R i (i = CB, B, or G) refers to atmospherically corrected reflectance values in the i th band [X i  = ln(R i -R deep water)].  相似文献   

19.
Carbon (POC, DOC) and carbon isotopes (δ13C) within two headwater tributaries to the Xi River Basin, southwest China were analyzed to document the geochemical characteristics and sources of organic carbon (C) within basins characterized by a monsoonal climate and karst landforms. δ13 C POC value and C/N ratio data indicate that suspended soil organic carbon (SOC) was an important source of POC in both the Nanpan and Beipan rivers (i.e., the studied tributaries). However, differences in C sources exist between the Nanpan and Beipan River Basins. Higher terrestrial plants supplied a portion of the POC within the Beipan River. In contrast, the Nanpan River was characterized by an inverse correlation between POC and DOC, and a positive relationship between the δ13C values. These trends indicate that DOC within the Nanpan River was partly derived from the degradation of soil C within the water column. In addition, the interception of C by hydrological projects (e.g., dams) positioned along the Nanpan River led to higher DOC/POC ratios. In contrast, within the Beipan River δ13C DOC values range from ?20 to ?25.2 ‰ and are consistent with ratios associated with soil C, suggesting that leaching of C from catchment soil was the dominant source of DOC. Organic C in tributaries to the Beipan River may also have been derived from intense upland soil erosion, a process that resulted in the lowest DOC/POC ratios. The collected data indicate that land-use changes have potentially influenced regional- to local-scale organic C budgets within subtropical basins subjected to karstification.  相似文献   

20.
The purpose of the investigation is to reveal the dependences of P p = f(C p) on reservoir conditions and the lithological composition of rocks. The samples were studied using a set of lithological-petrographic investigations. To obtain the dependences on thermobaric conditions, 90 samples of different porosities (C p) of 15, 20, and 25% were collected. As a result, the general pattern of the change in the rock resistivity during the transition from atmospheric conditions of measuring to reservoir conditions was established. Dependences of porosity parameter P p on porosity coefficient C p were obtained for three values of formation water salinity and three reservoir conditions. The measurement errors of the porosity parameter P p were calculated using dependences obtained under atmospheric conditions.  相似文献   

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