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1.
《Applied Geochemistry》2001,16(9-10):1021-1031
A set of chlorinated hydrocarbons (TCE, PCE, DCM, 1,1,1-TCA, chloroform) provided by four manufacturers has been isotopically characterised for both C and Cl, using a new sensitive method. A very large range of δ13C (from −51.66 to −24.07‰/PDB) associated with a very large range of δ37Cl (from −2.7 to +3.4‰/SMOC) was obtained. This range of δ37Cl is much larger than that of inorganic Cl (±1‰ SMOC) and most individual solvents show a very distinct δ37Cl compared to inorganic Cl isotopic signatures. Moreover, δ37Cl/δ13C pairs are distinct from one solvent/manufacturer to another. In a δ13C versus δ37Cl diagram, δ37Cl / δ13C pairs show different trends for the products of a single manufacturer compared to another. This suggests that Cl isotopic compositions are probably highly fractionated during organic synthesis. The δ37Cl values can be interpreted in terms of the probable manufacturing processes. Unlike the data published previously, with one exception, all the new results for samples reported here have positive δ37Cl values which might differentiate natural Cl from that derived from degradation. This method has significant potential as a tool for investigating environmental pollution problems; in particular, it offers the possibility for validating models of transport and fate of pollutants. 相似文献
2.
《Applied Geochemistry》2000,15(7):937-952
The B isotopic composition, in combination with O and H isotopes and hydrochemical tracers, is utilized to constrain the evolution of basement-hosted groundwaters via water–rock interactions and fluid infiltration from external (sedimentary) reservoirs. Two distinct groundwater types have been identified in the Central European crystalline basement (N Switzerland–SW Germany): (1) fresh groundwaters characterized by low values of δ11B (−3.5 to −0.6‰), δ18O (−12.0 to −10.0‰), and δD (−86.8 to −71.9‰), and (2) brackish groundwaters with distinctly heavier B, O, and H isotopic compositions (δ11B=+6.4 to +17.6‰, δ18O=−9.4 to −5.6‰, δD=−67.6 to −60.8‰). Fresh groundwaters show a systematic decrease in δ11B, related to an increase in B concentrations (and degree of total mineralization), along the pathway of groundwater migration which can only be interpreted in terms of leaching of crystalline host rocks. A δ11B value of −3.3‰ is inferred for the crustal B source (mainly Hercynian granites) involved in the leaching process, in agreement with the known δ11B range of granitic rocks. The evolution of brackish groundwaters, derived from crystalline basement reservoirs with little water circulation, is more complex. As indicated by B–O–H stable isotope and hydrochemical (e.g. B/Cl, Na/Cl, and Br/Cl) constraints, brackish groundwaters from the study area are influenced by admixture of sediment-derived fluids which infiltrated from Late Paleozoic (Permo-Carboniferous) and Early Mesozoic (Lower Triassic) sedimentary strata. The data presented show that B isotopes are sensitive to mixing processes of fluids derived from different crustal reservoirs and, hence, may be utilized as a tracer for constraining the internal (autochthonous) vs external (allochthonous) origin of salinity in basement-hosted groundwaters. 相似文献
3.
《Applied Geochemistry》2003,18(7):997-1009
The δ18O and δD values in the deep confined aquifer beneath the North China Plain which is located at 112°30′E–119°30′E and 34°46′N–40°25′N, reflect differences in paleoclimatic conditions between the Holocene and the late Pleistocene. Groundwater samples whose 14C ages are between 12 and 25 ka B.P have ranges of −9.4 to −11.7‰ for δ18O and −76‰ to −85‰ for δD values. These very negative δ18O and δD values reflect the cold and arid climate in the last glacial period. The temperature estimated in this period is 6–9 °C cooler than that of the present. The entire ranges of δ18O and δD values for samples with 14C dating from 7 ka B.P to present are −7.7‰ to −10.2‰ and −63‰ to −73‰, respectively. The greater δ18O and δD enrichments of these samples indicate a period of relatively humid and warm climate in the Holocene. However, the wide ranges of δ18O (−9.0‰ to −11.1‰) and δD (−66‰ to −80‰) values for samples with 14C age ranging from 12 to 7 ka B.P. imply an unstable climatic condition of rapidly increasing temperature, which marks the transition from the Pleistocene to the Holocene. 相似文献
4.
《Organic Geochemistry》2012,42(12):1269-1276
This study sought to characterize hydrogen isotopic fractionation during biosynthesis of leaf wax n-alkanes in succulent plants capable of crassulacean acid metabolism (CAM). The metabolic and physiological features of CAM represent crucial strategies for survival in hot and dry climates and have been hypothesized to impact hydrogen isotope fractionation. We measured the stable carbon and hydrogen isotopic compositions (δ13C and δD, respectively) of individual n-alkanes in 20 species of succulent plants from a global collection of the Huntington Botanical Gardens, San Marino, California. Greenhouse conditions and irrigation with water of constant δD value enabled determination of interspecies differences in net D/H fractionation between source water and leaf wax products. Carbon isotope ratios provide constraints on the extent of CAM vs. C3 photosynthesis and indicate a wide range of CAM use, with δ13C values ranging from −33.01‰ to −18.54‰ (C27–C33 n-alkanes) and −26.66‰ to −17.64‰ (bulk tissue). Despite the controlled growth environment, we observed ca. 90‰ interspecies range in δD values from −193‰ to −107‰. A positive correlation between δ13Cbulk and δDC31 values with R2 = 0.60 (δ13CC31 and δDC31 values with R2 = 0.41) implicates a metabolic isotope effect as the dominant cause of interspecies variation in the hydrogen isotopic composition of leaf wax n-alkanes in CAM-intermediate plants. 相似文献
5.
《Sedimentary Geology》2006,183(1-2):15-30
Carbonate concretions in the Miocene sedimentary rocks of the Yeonil Group in the Pohang Basin (Korea) were investigated in terms of stable oxygen and carbon isotope composition to delineate the origin and associated diagenetic environment for their formation. Carbonate concretions are widely distributed in all the sedimentary rocks in the Pohang Basin, showing that the calcitic concretions are preserved within the mass-flow deposits and the dolomitic ones mostly in the hemipelagic siliceous rocks (diatomites). Concretions can be classified into four different types, on the basis of the stable isotopic signatures, each of which represents its own geochemical range.Type I concretions are calcitic and are composed of micrite to microspar. They occur in the conglomerates and sandstones which were deposited by mass flows (debris flow to turbidity current). It shows relatively lower δ18O (− 14.0 to − 9.3‰) and δ13C (− 19.6 to − 8.4‰) values. These concretions grew in a sulfate reducing zone under the influence of residual ambient seawater which had been significantly modified by volcanogenic sediments. Type II concretions are also calcitic, composed mostly of micrite with minor microspar and found in the sandstones. These concretions are characterized by relatively high δ18O (+ 1.8 to + 2.4‰) and variable δ13C (− 17.3 to − 0.4‰) values. These isotopic signatures reflect that Type II concretions formed from just beneath the sediment/water interface down to the sulfate reducing zone through the early stage of methanogenesis. Type III concretions are also calcitic, and composed largely of micrite with a minor contribution of microspar. They are observed in hemipelagic mudrocks which were deposited under the influence of mass flows. They are characterized by intermediate to high δ18O (− 4.6 to + 1.6‰) and high δ13C (− 1.3 to + 8.8‰) values. These concretions grew in a methanogenic zone by residual ambient seawater and/or seawater slightly modified by reaction with volcanogenic sediments. Type IV concretions are dolomite with calcite inclusion, and occur in hemipelagic siliceous rocks. These concretions are mostly composed of micrite and characterized by variable δ18O (− 9.1 to + 0.7‰) and high δ13C (+ 3.1 to + 17.9‰) values, suggesting formation in the methanogenic zone, although the residual ambient seawater is slightly modified by volcanogenic sediments.The same type of the concretions is widely distributed throughout the basin and always shows its own distinctive stable isotopic signature. This means that the formation of the given type depends upon the lithology and composition of host sediments that are closely related to the depositional process of the fan-delta systems regardless of their localities. Further, the different types of concretions are also found at the different, but closely spaced stratigraphic levels in the same locality, displaying the distinctive diagenetic conditions for each type. Such preservation of the unique diagenetic signatures in individual type of concretion suggests that the concretions formed in a completely closed diagenetic system. Therefore, caution should be made to simplify and generalize the diagenetic condition for the formation of any concretions in a large sedimentary basin. 相似文献
6.
Natural gas in the Xujiahe Formation of the Sichuan Basin is dominated by hydrocarbon (HC) gas, with 78–79% methane and 2–19% C2+ HC. Its dryness coefficient (C1/C1–5) is mostly < 0.95. The gas in fluid inclusions, which has low contents of CH4 and heavy hydrocarbons (C2+) and higher contents of non-hydrocarbons (e.g. CO2), is a typical wet gas produced by thermal degradation of kerogen. Gas produced from the Upper Triassic Xujiahe Formation (here denoted field gas) has light carbon isotope values for methane (δ13C1: −45‰ to −36‰) and heavier values for ethane (δ13C2: −30‰ to −25‰). The case is similar for gas in fluid inclusions, but δ13C1 = −36‰ to −45‰ and δ13C2 = −24.8‰ to −28.1‰, suggesting that the gas experienced weak isotopic fractionation due to migration and water washing. The field gas has δ13CCO2 values of −15.6‰ to −5.6‰, while the gas in fluid inclusions has δ13CCO2 values of −16.6‰ to −9‰, indicating its organic origin. Geochemical comparison shows that CO2 captured in fluid inclusions mainly originated from source rock organic matter, with little contribution from abiogenic CO2. Fluid inclusions originate in a relatively closed system without fluid exchange with the outside following the gas capture process, so that there is no isotopic fractionation. They thus present the original state of gas generated from the source rocks. These research results can provide a theoretical basis for gas generation, evolution, migration and accumulation in the basin. 相似文献
7.
and ratios were measured for 114 petroleum samples and for several samples of related organic matter. δD of crude oil ranges from ?85 to ?181‰, except for one distillate (?250‰) from the Kenai gas field; δ13C of crude oil ranges from ?23.3 to ?32.5‰, Variation in δD and δ13C values of compound-grouped fractions of a crude oil is small, 3 and 1.1%., respectively, and the difference in δD and δ13C between oil and coeval wax is slight. Gas fractions are 53–70 and 22.6–23.2‰ depleted in D and 13C, respectively, relative to the coexisting oil fractions.The δD and δ13C values of the crude oils appear to be largely determined by the isotopic compositions of their organic precursors. The contribution of terrestrial organic debris to the organic precursors of most marine crude oils may be significant. 相似文献
8.
《Applied Geochemistry》2000,15(6):849-864
An extensive saline plume (>250 km2) within the regionally important unconfined aquifer in the Neogene Ogallala Formation overlies the Panhandle oil and gas field in the Southern High Plains, Texas, USA. Relative to upgradient Ogallala water, the plume waters have δ18O (−6.7 to −8.8‰) and δD (−42 to −88‰) values that tend to be depleted and have higher Cl (>150 mg/l) and SO4 (>75 mg/l) concentrations. Various end-member-mixing models suggest that the plume composition reflects the presence of paleowaters recharged during Middle to Late Wisconsinan time rather than salinization associated with petroleum production. Paleowaters probably mixed with salt-dissolution zone waters from the underlying Upper Permian formations before discharging upward into the Ogallala Formation. Cross-formational discharge is controlled primarily by the geometry of the underlying units, as influenced by the Amarillo uplift, pinch-out of the laterally adjoining confined aquifer in the Triassic Dockum Group, variations in the saturated thickness of the Ogallala aquifer and the presence of potential pathways related to salt dissolution. 相似文献
9.
《Chemie der Erde / Geochemistry》2015,75(1):65-72
This study was conducted on recent desert samples—including (1) soils, (2) plants, (3) the shell, and (4) organic matter from modern specimens of the land snail Eremina desertorum—which were collected at several altitudes (316–360 m above sea level) from a site in the New Cairo Petrified Forest. The soils and shellE. desertorum were analyzed for carbonate composition and isotopic composition (δ18O, δ13C). The plants and organic matterE. desertorum were analyzed for organic carbon content and δ13C. The soil carbonate, consisting of calcite plus minor dolomite, has δ18O values from −3.19 to −1.78‰ and δ13C values −1.79 to −0.27‰; covariance between the two values accords with arid climatic conditions. The local plants include C3 and C4 types, with the latter being dominant. Each type has distinctive bulk organic carbon δ13C values: −26.51 to −25.36‰ for C3-type, and −13.74 to −12.43‰ for C4-type plants.The carbonate of the shellE. desertorum is composed of aragonite plus minor calcite, with relatively homogenous isotopic compositions (δ18Omean = −0.28 ± 0.22‰; δ13Cmean = −4.46 ± 0.58‰). Most of the δ18O values (based on a model for oxygen isotope fractionation in an aragonite-water system) are consistent with evaporated water signatures. The organic matterE. desertorum varies only slightly in bulk organic carbon δ13C values (−21.78 ± 1.20‰) and these values suggest that the snail consumed more of C3-type than C4-type plants. The overall offset in δ13C values (−17.32‰) observed between shellE. desertorum carbonate and organic matterE. desertorum exceeds the value expected for vegetation input, and implies that 30% of carbon in the shellE. desertorum carbonate comes from the consumption of limestone material. 相似文献
10.
《Applied Geochemistry》1994,9(6):609-626
The Saint-Salvy vein-hosted Zn (+Ge) deposit occurs in an E–W fault system which flanks the southern margin of the late Variscan Sidobre granite, and cross-cuts Cambrian black shales of the Palaeozoic basement. Comprehensive mineralogical and geochemical studies of vein samples have revealed four mineralizing events (M1–M4) related to late and post-Variscan tectonic events. A further late-stage event may be related to weathering.M1 (=skarn deposits) and M2 (=patchily mineralized quartz veinlets) are associated with granite emplacement. Quartz contains low salinity, H2OCO2(NaCl)-dominated fluids(⩽6wt% NaCl equiv.) of relatively high temperature (300–580°C), trapped under moderate to high pressure. Estimated M1 fluid δD and calculated fluidδ18O plot within the metamorphic water field. There appears to be no involvement of magmatic fluids.By contrast, M3 (= barren quartz) and M4 (= zinciferous economic mineralization) stages have H2OCO2NaClCaCl2 fluid inclusions with high salinities (23–25 wt% NaCl equiv.) and low temperatures(∼ 80–140°C), which were trapped under low-pressure conditions. The high salinity and NaCl + CaCl2 content of both M3 and M4 indicates that their parent fluids leached evaporitic salts. M3 fluids are meteoric water dominated, falling close to the meteoric water line (δD andδ18O averaging −64 and −8‰, respectively). M4 fluids have highly distinctive δD averaging −101‰, and calculated fluidδ18O varying from−1.2to+7.1‰. The unusually low δD composition of M4 suggests the involvement of “organic” fluids, in which H is derived directly or indirectly from organic matter. The relatively highδ18O of M4 fluids indicates that considerable isotopic exchange with sedimentary material took place, displacing theδ18O from the meteoric water line. The data imply interaction of meteoric waters with evaporite and hydrocarbon-bearing sedimentary sequences, most probably the adjacent Aquitain Basin.The main economic mineralization (M4 stage) took place during a tensional event, probably coincident with the Lias-Dogger transition.Calculatedδ34SH2S of M4 sulphide(+5.4to+8.2‰) is almost identical toδ34S of local Cambrian sulphides(+4.7to+9.4‰) suggesting a genetic link. Abundant siderite associated with M4 sphalerite hasδ13C ranging from−2.6to−4.4‰ indicating that carbon was sourced from sedimentary carbonate mobilized by, or equilibrated with the hydrothermal fluid.Late-stage sulphides exhibit extraordinary and highly distinctiveδ34S. Sphalerite has extremely low δ34S(−42.5to−50.5‰), whereas pyrite has an extraordinary large range from−33.2‰to+74.3‰. Closed system sulphate reduction is held to be responsible for the extremely highδ34S: whereas more open system reduction produces the very low values. The coincidence of isotopically lowδ13C(−7.6to−11.9‰) for co-genetic calcite suggests the involvement of organic matter in the reduction process. 相似文献
11.
《Applied Geochemistry》2005,20(11):2017-2037
The Tertiary Thrace Basin located in NW Turkey comprises 9 km of clastic-sedimentary column ranging in age from Early Eocene to Recent in age. Fifteen natural gas and 10 associated condensate samples collected from the 11 different gas fields along the NW–SE extending zone of the northern portion of the basin were evaluated on the basis of their chemical and individual C isotopic compositions. For the purpose of the study, the genesis of CH4, thermogenic C2+ gases, and associated condensates were evaluated separately.Methane appears to have 3 origins: Group-1 CH4 is bacteriogenic (Calculated δ13CC1–C = −61.48‰; Silivri Field) and found in Oligocene reservoirs and mixed with the thermogenic Group-2 CH4. They probably formed in the Upper Oligocene coal and shales deposited in a marshy-swamp environment of fluvio-deltaic settings. Group-2 (δ13CC1–C = −35.80‰; Hamitabat Field) and Group-3 (δ13C1–C = −49.10‰; Değirmenköy Field) methanes are thermogenic and share the same origin with the Group-2 and Group-3 C2+ gases. The Group-2 C2+ gases include 63% of the gas fields. They are produced from both Eocene (overwhelmingly) and Oligocene reservoirs. These gases were almost certainly generated from isotopically heavy terrestrial kerogen (δ13C = −21‰) present in the Eocene deltaic Hamitabat shales. The Group-3 C2+ gases, produced from one field, were generated from isotopically light marine kerogen (δ13C = −29‰). Lower Oligoce ne Mezardere shales deposited in pro-deltaic settings are believed to be the source of these gases.The bulk and individual n-alkane isotopic relationships between the rock extracts, gases, condensates and oils from the basin differentiated two Groups of condensates, which can be genetically linked to the Group-2 and -3 thermogenic C2+ gases. However, it is crucial to note that condensates do not necessarily correlate to their associated gases.Maturity assessments on the Group-1 and -2 thermogenic gases based on their estimated initial kerogen isotope values (δ13C = −21‰; −29‰) and on the biomarkers present in the associated condensates reveal that all the hydrocarbons including gases, condensates and oils are the products of primary cracking at the early mature st age (Req = 0.55–0.81%). It is demonstrated that the open-system source conditions required for such an early-mature hydrocarbon expulsion exist and are supported by fault systems of the basin. 相似文献
12.
Wenxin Cao Dangpeng Xi Mihaela C.Melinte-Dobrinescu Tian Jiang Sherwood W.Wise Jr. Xiaoqiao Wan 《地学前缘(英文版)》2018,9(5):1465-1478
The Paleocene-Eocene Thermal Maximum(PETM) event was a dramatic global warming w55.93 Ma ago that resulted in biological extinction events, lithological changes, and major deviations in σ13 C and σ18 O.The southwestern Tarim Basin of China exposes successive Paleogene strata as a result of Tethys evolution and is considered an ideal region for PETM research.Based on calcareous nannoplankton biostratigraphy, we also used stable isotopes and XRD to analyse the Paleocene-Eocene transition in the Tarim Basin. At the Bashibulake Section, the PETM interval is characterized by(1) an abrupt negative shifts in σ13 C_(org), σ13 C_(carb) and σ18 O(-3%, -4.5% and -3%respectively);(2) an obvious negative correlation between the K-mode(Discoaster, Fasciculithus, Ericsonia, Sphenolithus and Rhomboaster) and r-mode(Biscutum, Chiasmolithus, Toweius) nannofossil taxa coincident with a robust Rhomboaster-Discoaster assemblage; and(3) a significant increase in the percentage of detrital input along with an increase in gypsum content. In the upper part of the Qimugen Formation Micrantholithus and Braarudosphaera are commonly found right up to the top where most of the nannofloras suffer a sharp decrease. In the overlying Gaijitage Formation, calcareous nannofossils disappear completely. These events indicate that the southwestern Tarim Basin was a warm shallow continental shelf during the deposition of the Qimugen Formation. From the early Eocene, the environment changed conspicuously. Evaporation increased and sea level fell, which led to an acid climate.This climate mode continued within the youngest unit studied, the Gaijitage Formation, characterized by the deposition of thick evaporates. Consequently, most of the marine plankton, i.e. calcareous nannoplankton, became disappear, because of the significant climate shift. 相似文献
13.
Stable chlorine isotopes are useful geochemical tracers in processes involving the formation and evolution of evaporitic halite. Halite and dissolved chloride in groundwater that has interacted with halite in arid non-marine basins has a δ37Cl range of 0 ± 3‰, far greater than the range for marine evaporites. Basins characterized by high positive (+1 to +3‰), near-0‰, and negative (−0.3 to −2.6‰) are documented. Halite in weathered crusts of sedimentary rocks has δ37Cl values as high as +5.6‰. Salt-excluding halophyte plants excrete salt with a δ37Cl range of −2.1 to −0.8‰. Differentiated rock chloride sources exist, e.g. in granitoid micas, but cannot provide sufficient chloride to account for the observed data. Single-pass application of known fractionating mechanisms, equilibrium salt-crystal interaction and disequilibrium diffusive transport, cannot account for the large ranges of δ37Cl. Cumulative fractionation as a result of multiple wetting-drying cycles in vadose playas that produce halite crusts can produce observed positive δ37Cl values in hundreds to thousands of cycles. Diffusive isotope fractionation as a result of multiple wetting-drying cycles operating at a spatial scale of 1–10 cm can produce high δ37Cl values in residual halite. Chloride in rainwater is subject to complex fractionation, but develops negative δ37Cl values in certain situations; such may explain halite deposits with bulk negative δ37Cl values. Future field studies will benefit from a better understanding of hydrology and rainwater chemistry, and systematic collection of data for both Cl and Br. 相似文献
14.
《Journal of Asian Earth Sciences》2008,31(5-6):591-598
1-Alkyl-2,3,6-trimethylbenzenes and a high relative amount of 1,2,3,4-tetramethylbenzene (TTMB) have been previously detected in the marine oils and asphaltenes in the oils from the Tarim Basin. In the present study, the stable carbon isotopic compositions of TTMB and n-alkanes in the pyrolysates of asphaltenes in the marine oils from the northern Tarim Basin and Silurian tar sands from the Tarim Basin were determined. TTMB has stable carbon isotopic compositions in the range from −23‰ to −24‰ and are about 12‰ more enriched in 13C than concomitant n-alkanes (−35‰ to −37‰) in the pyrolysates. The results indicate a contribution from green sulfur bacteria (Chlorobiaceae) to TTMB. Thus, the depositional environments of the source rocks for the marine oils and the bitumen in tar sands from the Tarim Basin are characterized by periods of euxinic conditions within the photic zone. 相似文献
15.
The most widely accepted origin of n-alkan-2-ones in peats is the microbial oxidation of the related n-alkanes and/or oxidative decarboxylation of fatty acids derived from plant input. The distributions of n-alkanes and n-alkan-2-ones in 48 samples from the Roñanzas 6000 cal. yr BP peat bog profile (N Spain) do not justify a single source. The n-alkan-2-ones typically dominate the n-alkanes, maximizing at C19 or C25/C27, whereas the n-alkanes maximized either at C23 or at C31/C33. The averaged δ13C values of the n-alkanes ranged from −32.3‰ to −33.1‰, but those of the n-alkan-2-ones were consistently higher (−29.2‰ to −29.9‰), suggesting a different, probably bacterial, source for the ketones. 相似文献
16.
《Organic Geochemistry》1999,30(8):881-889
The 13C/12C isotopic ratios for coal-derived polycyclic aromatic hydrocarbons (PAHs) from a number of processes encompassing low and high temperature carbonisation, gasification and combustion have been determined using gas chromatography–isotope ratio mass spectrometry (δ13C GC–IRMS). The results, in conjunction with those for PAHs released under controlled laboratory pyrolysis conditions, indicate that the primary control on the isotopic values of coal-derived PAHs is likely to be the extent of ring growth required to form PAHs during processing. Thus, for relatively mild conversion processes such as low temperature carbonisation where the major aromatics are alkyl substituted 2–3 ring PAHs, the isotopic signatures are similar to those of the parent coals (−24 to −25‰ for UK bituminous coals). However, the δ13C values for the PAHs become lighter in going to high temperature carbonisation (−25 to −27‰), gasification (−27 to −29‰ for old Town gas plants in the UK) and combustion (−29 to −31‰) as the extent of ring condensation increases and confirming that the PAHs are not released as primary volatiles. To demonstrate the potential of applying these differences to source apportion environmental PAHs where major inputs from coals can be expected, soil and vegetation samples taken close to a low temperature carbonisation plant (Bolsover, North Derbyshire) have been analysed. In addition to low temperature coal tar, significant inputs of PAHs from transport fuels, high temperature carbonisation and possibly combustion (coal/biomass) have been inferred from the isotopic ratios, taken in conjunction with the differences in alkyl substitution patterns. 相似文献
17.
《Applied Geochemistry》1993,8(4):403-407
The Cl isotope ratio, mass37Cl/35Cl, was measured on 22 formation waters from Mississippian, Devonian, Silurian, Ordovician and Cambrian strata in the Michigan Basin. Because of its resistance to fractionation, the ratio was used to find evidence of mixing of formation waters within the Michigan Basin and between the Canadian Shield and the basin. The δ37Cl composition of waters decreased from +0.05 to −0.55 (per mil difference from SMOC, precision of 0.16) with age of the strata among Devonian, Silurian, Ordovician and Cambrian samples from the basin margin. Mississippian samples from the middle of the basin were isotopically heaviest at +0.1. Ordovician samples, also from mid-basin, were isotopically lightest at −1.2. On plots of δ37 Cl vs Cl/Br and δ37 Cl vs87Sr/86Sr samples at the basin margin trend toward enrichment in35Cl and87Sr and increasing Cl/Br suggesting interformational mixing of the waters. On a δ37 ClCl/Br plot, three samples not on this trend and tending toward high Cl/Br may reflect evaporite dissolution. Canadian Shield Waters were plotted with Michigan Basin waters on the graphs of δ37 Cl vs Ca/Cl and δ37 Cl vs K/Cl. On both plots data fall along linear trends of35Cl depletion with Ca/Cl increase and with K/Cl decrease. Ordovician waters from the middle of the basin and shield waters are end members on the plots. The results suggest that despite water-rock interactions, δ37 Cl data may be useful in studies of mixing relations in formation waters. 相似文献
18.
《Applied Geochemistry》2004,19(6):937-946
Analysis of stable isotopes and major ions in groundwater and surface waters in Belize, Central America was carried out to identify processes that may affect drinking water quality. Belize has a subtropical rainforest/savannah climate with a varied landscape composed predominantly of carbonate rocks and clastic sediments. Stable oxygen (δ18O) and hydrogen (δD) isotope ratios for surface and groundwater have a similar range and show high d-excess (10–40.8‰). The high d-excess in water samples suggest secondary continental vapor flux mixing with incoming vapor from the Caribbean Sea. Model calculations indicate that moisture derived from continental evaporation contributes 13% to overhead vapor load. In surface and groundwater, concentrations of dissolved inorganic carbon (DIC) ranged from 5.4 to 112.9 mg C/l and δ13CDIC ranged from −7.4 to −17.4‰. SO42, Ca2+ and Mg2+ in the water samples ranged from 2–163, 2–6593 and 2–90 mg/l, respectively. The DIC and δ13CDIC indicate both open and closed system carbonate evolution. Combined δ13CDIC and Ca2+, Mg2+, and SO42− suggest additional groundwater evolution by gypsum dissolution and calcite precipitation. The high SO42−content of some water samples indicates regional geologic control on water quality. Similarity in the range of δ18O, δD and δ13CDIC for surface waters and groundwater used for drinking water supply is probably due to high hydraulic conductivities of the karstic aquifers. The results of this study indicate rapid recharge of groundwater aquifers, groundwater influence on surface water chemistry and the potential of surface water to impact groundwater quality and vise versa. 相似文献
19.
《Applied Geochemistry》1997,12(3):333-343
Deep formation waters were sampled from boreholes on the S-E slopes of the Bohemian Massif. They are NaClHCO3 waters with TDS in the range 6–52 g L−1. Some of them are associated with gas and oil deposits. The waters are rich in Br and I and their δDandδ180 isotope compositions vary from −12 to −77‰ and + 4.6 to −10‰ respectively.The processes of concentration and dilution have been discussed based on deuterium and conservative element contents of the waters. Three regional groups can be identified in the plots Br vs I and Cl vs I: the Vienna Basin samples (VB), southern (S) and northern (N) flanks of the Bohemian Massif (BM). The VB samples have as an end member brackish water with about 7 g L−1 Cl (about 40% marine component) enriched in Br and I. This water has been later diluted by meteoric water of recent isotopic composition. Only 3 VB samples can be considered as derived from the dissolution of evaporites. The salt content of the S and N end members is very close to or higher than sea water with an isotopic composition similar to the brackish water. Subaerial evaporation of diluted sea water is suggested as the process increasing salt content. The evaporative enrichment of primary brackish solution can be estimated from extrapolation of Cl vs I and Br vs I plots to zero I (about 25 mg L−1 Br and 6 g L−1 Cl for the southern flanks of the BM). Evaporated solutions were later diluted by meteoric waters with δD in the range from −50 to −80‰ (southern flanks) and about −80‰ (northern flanks). 相似文献
20.
《Sedimentary Geology》2006,183(1-2):51-69
The Chicxulub Sedimentary Basin of the northwestern Yucatan Peninsula, Mexico, which was formed because of the largest identified Phanerozoic bolide impact on Earth, became a site of deposition of dominantly marine carbonate sediments during most of the Cenozoic Era. This is a study of the filling and diagenetic history of this basin and surrounding areas. The study makes use of lithologic, biostratigraphic, petrographic, and geochemical data obtained on core samples from boreholes drilled throughout the northwestern Yucatan Peninsula.The core sample data indicate that: 1) The Chicxulub Sedimentary Basin concentrated the deposition of pelagic and outer-platform sediments during the Paleocene and Eocene, and, in places, during the Early Oligocene, as well, and filled during the Middle Miocene, 2) deeper-water limestone also is present within the Paleocene and Lower Eocene of the proposed Santa Elena Depression, which is located immediately south of the Basin, 3) shallow-water deposits are relatively more abundant outside the Basin and Depression than inside, 4) the autigenic and allogenic silicates from the Paleogene formations are the most abundant inside the Depression, 5) sediment deposition and diagenesis within the Basin also were controlled by impact crater topography, 6) the abundance of the possible features of subaerial exposure increases upward and outward from the center of the Basin, and 7) the formation of replacive low-magnesium calcite and dolomite, dedolomitization, dissolution, and precipitation of vug-filling calcite and dolomite cement have been more common outside the Basin than inside.δ18O in whole-rock (excluding vug-filling) calcite from core samples ranges from − 7.14‰ to + 0.85‰ PDB. δ13C varies from − 6.92‰ to + 3.30‰ PDB. Both stable isotopes correlate inversely with the abundance of subaerial exposure features indicating that freshwater diagenesis has been extensive especially outside and at the edge of the Chicxulub Sedimentary Basin.δ18O and δ13C in whole-rock (excluding vug-filling) dolomite ranges from − 5.54‰ to + 0.87‰ PDB and − 4.63‰ to + 3.38‰ PDB, respectively. Most dolomite samples have negative δ18O and positive δ13C suggesting that replacive dolomitization involved the presence of a fluid dominated by freshwater and/or an anomalously high geothermal gradient.Most dolomite XRD-determined mole percent CaCO3 varies between 51 and 56. Replacive dolomite is larger, more euhedral, and less stoichiometric inside the Chicxulub Sedimentary Basin than outside. 相似文献