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1.
Natural gases discovered up to now in Lishui Sag, the East China Sea Basin, differ greatly in gaseous compositions, of which hydrocarbon gases amount to 2%–94% while non-hydrocarbon gases are dominated by CO 2. Their hydrocarbon gases, without exception, contain less than 90% of methane and over 10% of C 2 + heavier hydrocarbons, indicating a wet gas. Carbon isotopic analyses on these hydrocarbon gases showed that δ 13C 1, δ 13C 2 and δ 13C 3 are basically lighter than ?44‰, ?29‰ and ?26‰, respectively. The difference in carbon isotopic values between methane and ethane is great, suggesting a biogenic oil-type gas produced by the mixed organic matter at peak generation. δ 13 \(C_{CO_2 } \) values of nonhydrocarbon gases are all heavier than ?10‰, indicating a typical abiogenic gas. The simulation experiment on hydrocarbon generation of organic matter in a closed gold-tube system showed that the proportion of methane in natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit is obviously higher than that in natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit, consequently the proportion of heavier hydrocarbons of the former is remarkably lower than that of the latter. Moreover, δ 13C 1 values of natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit are about 5‰ heavier than those of natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit while δ 13C 2 and δ 13C 3 values of the former are over 9‰ heavier than those of the latter. Currently the LS36-1 oil-gas pool is the only commercial oil-gas reservoir in Lishui Sag, where carbon isotopic compositions of various hydrocarbon components differ greatly from those of natural gases produced by the Lingfeng Formation organic matter but are very similar to those of natural gases derived from the Yueguifeng Formation organic matter, therefore, natural gases in the LS36-1 oil-gas pool are mainly derived from the Yueguifeng Formation lacustrine source rock rather than the Lingfeng Formation marine or Mingyuefeng Formation coal-measures source rocks. 相似文献
2.
Assessing natural vs. anthropogenic sources of methane in drinking water aquifers is a critical issue in areas of shale oil and gas production. The objective of this study was to determine controls on methane occurrences in aquifers in the Eagle Ford Shale play footprint. A total of 110 water wells were tested for dissolved light alkanes, isotopes of methane, and major ions, mostly in the eastern section of the play. Multiple aquifers were sampled with approximately 47 samples from the Carrizo‐Wilcox Aquifer (250‐1200 m depth range) and Queen City‐Sparta Aquifer (150‐900 m depth range) and 63 samples from other shallow aquifers but mostly from the Catahoula Formation (depth <150 m). Besides three shallow wells with unambiguously microbial methane, only deeper wells show significant dissolved methane (22 samples >1 mg/L, 10 samples >10 mg/L). No dissolved methane samples exhibit thermogenic characteristics that would link them unequivocally to oil and gas sourced from the Eagle Ford Shale. In particular, the well water samples contain very little or no ethane and propane (C1/C2+C3 molar ratio >453), unlike what would be expected in an oil province, but they also display relatively heavier δ 13C methane (>?55‰) and δD methane (>?180‰). Samples from the deeper Carrizo and Queen City aquifers are consistent with microbial methane sourced from syndepositional organic matter mixed with thermogenic methane input, most likely originating from deeper oil reservoirs and migrating through fault zones. Active oxidation of methane pushes δ 13C methane and δD methane toward heavier values, whereas the thermogenic gas component is enriched with methane owing to a long migration path resulting in a higher C1/C2+C3 ratio than in the local reservoirs. 相似文献
3.
The light hydrocarbon composition of 209 natural gas samples and individual light hydrocarbon carbon isotopes of 53 natural gas samples from typical humic-sourced gas and sapropelic-sourced gas in the four basins of China have been determined and analyzed. Some identification parameters for humic-sourced gas and sapropelic-sourced gas are proposed or corrected. The differences of compound-specific δ 13C value of individual light hydrocarbon between humic-sourced gas and sapropelic-sourced gas have been founded. The humic-sourced gas has the distribution of δ 13C benzene> ?24‰, δ 13C toluene >?23‰, δ 13C cyclohexane > ?24‰ and δ 13C methyl cyclohexane> ?24‰, while the sapropelic-sourced gas has the distribution of δ 13C benzene <?24‰, δ 13C toluene< ?24‰, δ 13C cyclohexane< ?24‰ and δ 13C methyl cyclohexane< ?24‰. Among the components of C 7 light hydrocarbon compound, such as normal heptane ( nC 7), methyl cyclohexane (MCH) and dimethyl cyclopentane (ΣDMCP), etc, relative contents of nC 7 and MCH are influenced mainly by the source organic matter type of natural gas. Therefore, it is suggested that the gas with relative content of nC 7 of more than 30% and relative content of MCH of less than 70% is sapropelic-sourced gas, while gas with relative content of nC 7 of less than 35% and relative content of MCH of more than 50% is humic-sourced gas. Among components of C 5–7 aliphatics, the gas with relative content of C 5–7 normal alkane of more than 30% is sapropelic-sourced gas, while the gas with relative content of C 5–7 normal alkane of less than 30% is humic-sourced gas. These paremeters have been suggested to identify humic-sourced gas and sapropelic-sourced gas. 相似文献
4.
Stable isotopic signatures (δ 13C and δ 15N) and C/N ratios of suspended particulate organic matter (POM) were investigated from the surface water of Daya Bay during summer and winter of 2015. The relatively high δ 13C POM values suggested the input of 13C-depleted terrigenous organic matter was low in Daya Bay. There were significant correlations between δ 13C POM values and chlorophyll a concentrations both during summer and winter, suggesting the δ 13C POM values were mainly controlled by the phytoplankton biomass in the surface water. The distribution of δ 15N POM values was more complicated than that of δ 13C POM and displayed low values in the outer bay and the Dan'ao River estuary. 15N-depleted ammonia originating from industrial wastewater might have strongly influenced the water quality and stable isotopic signatures of POM near the Dan'ao River estuary. The δ 13C POM and δ 15N POM values strongly reflect the influences of anthropogenic activity and eutrophication in Daya Bay. 相似文献
5.
CO 2-rich inclusions recovered from “popping” and related tholeiitic rocks from the Mid-Atlantic Ridge have δ 13C values of ?7.6 ± 0.5%. relative to PDB. δ 13C values of total carbon in the same rocks range from ?12 to ?13.7‰. These values are discussed in the light of the known δ 13C variations in rocks of deep-seated origin. The ?7.6‰ value is interpreted as a reasonable estimate of the primary value of δ 13C of deep-seated carbon in the ridge area. 相似文献
6.
According to gas compositional and carbon isotopic measurement of 114 gas samples from the Kuqa depression, accumulation of the natural gases in the depression is dominated by hydrocarbon gases, with high gas dryness (C 1/C 1–4) at the middle and northern parts of the depression and low one towards east and west sides and southern part. The carbon isotopes of methane and its homologues are relatively enriched in 13C, and the distributive range of δ 13C 1, δ 13C 2 and δ 13C 3 is ?32‰–?36‰, ?22‰–?24‰ and ?20‰–?22‰, respectively. In general, the carbon isotopes of gaseous alkanes become less negative with the increase of carbon numbers. The δ 13 \(C_{CO_2 } \) value is less than ?10‰ in the Kuqa depression, indicating its organogenic origin. The distributive range of 3He/ 4He ratio is within n × 10 ?8 and a decrease in 3He/ 4He ratio from north to south in the depression is observed. Based on the geochemical parameters of natural gas above, natural gas in the Kuqa depression is of characteristics of coal-type gas origin. The possible reasons for the partial reversal of stable carbon isotopes of gaseous alkanes involve the mixing of gases from one common source rock with different thermal maturity or from two separated source rock intervals of similar kerogen type, multistages accumulation of natural gas under high-temperature and over-pressure conditions, and sufficiency and diffusion of natural gas. 相似文献
7.
This paper focuses on the chemical and isotopic features of dissolved gases (CH 4 and CO 2) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH 4 and CO 2. The δ 13C-CH 4 and δD-CH 4 values of dissolved gas samples from the maximum depths of the investigated lakes (from ?66.8 to ?55.6?‰ V-PDB and from ?279 to ?195?‰ V-SMOW, respectively) suggest that CH 4 is mainly produced by microbial activity. The δ 13C-CO 2 values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from ?5.8 to ?0.4?‰ V-PDB) indicate a significant CO 2 contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO 2 source feeding the regional thermal and cold CO 2-rich fluid emissions. In contrast, the relatively low δ 13C-CO 2 values (from ?13.4 to ?8.2?‰ V-PDB) of Lake Averno indicate a prevalent organic CO 2. Chemical and isotopic compositions of dissolved CO 2 and CH 4 at different depths are mainly depending on (1) CO 2 inputs from external sources (hydrothermal and/or anthropogenic); (2) CO 2–CH 4 isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO 2 and CH 4 concentrations. In the hypolimnion, where the δ 13C-CO 2 values progressively increase with depth and the δ 13C-CH 4 values show an opposite trend, biogenic CO 2 production from CH 4 using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ 13C-CO 2 values, and measured δ 13C TDIC values are not consistent, indicating that CO 2 and the main carbon-bearing ion species (HCO 3 ?) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO 2 and CH 4. This study demonstrates that the vertical patterns of the CO 2/CH 4 ratio and of δ 13C-CO 2 and δ 13C-CH 4 are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO 2 input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes. 相似文献
8.
Kinetic experiments of gas generation for typical samples of marine gas precursors including low-maturity kerogen, residual kerogen and oil as well as dispersed liquid hydrocarbon (DLH) in source rocks were performed by closed system, and the evolution trends of molecular and isotopic compositions of natural gases from different precursors against the maturity ( R 0%) at laboratory conditions were analyzed. Several diagrams of gas origin were calibrated by using the experimental data. A diagram based on the ratio of normal and isomerous butane and pentane ( i/nC 4 ? i/nC 5) was proposed and used to identify the origins of the typical marine natural gases in the Sichuan Basin and the Tarim Basin, China. And the maturities of natural gases were estimated by using the statistical relationships between the gaseous molecular carbon isotopic data and maturities (δ 13C- R 0%) with different origins. The results indicate that the molecular and isotopic compositions of simulated gases from different precursors are different from each other. For example, the dryness index of the oil-cracking gas is the lowest; the dryness indices of gases from DLH and kerogen in closed system are almost the same; and the dryness index of gases from residual kerogen is extremely high, indicating that the kerogen gases are very dry; the contents of non-hydrocarbon gases in kerogen-cracking gases are far higher than those in oil-cracking and DLH-cracking gases. The molecular carbon isotopes of oil-cracking gases are the lightest, those of kerogen in closed system and GLH-cracking gases are the second lightest, and those of cracking gases from residual kerogen are the heaviest. The calibration results indicate that the diagrams of In(C 1/C 2)-In(C 2/C 3) and δ 4 3C 2-δ 4 3C 3-In(C 2/C 3) can discriminate primary and secondary cracking gases, but cannot be used to identify gas origin sources, while the diagram of i/nC 4 ? i/nC 5 can differentiate the gases from different precursors. The application results of these diagrams show that gas mixtures extensively exist in China, which involved the gases from multiple precursors and those from different maturity stages. For example, marine gases in the Sichuan Basin involve the mixture of oil-cracking gases and high-over-maturated kerogen gases, while those in the Tarim Basin involve not only the mixture of gases from multiple precursors, but also those from different maturity gases and post-reservoir alternations such as oxidized degradation and gas intrusion processes. 相似文献
9.
Closely spaced samples (285 in number) of varved sediments from the Upper Permian in Delaware Basin, Texas, have been analyzed for δ 13C carb, δ 13C org, δ 18O carb, C org, C carb, and calcite/dolomite. δ 13C records a dramatic rise from ?2.8 to +5.7‰ in only 4400 years, detected in three sections across the basin, extrapolating smoothly through a 600-year interruption by a local (west side of the basin) fresh-water inflow evidenced by low δ 18O. This continuity and low C org within the basin, both indicate that the excess net deposition of C org, necessary to generate the rise in δ 13C, took place in the ocean external to the Delaware Basin. Correlation with similar records from the Zechstein Basin suggest that the event was world-wide, although this poses obvious difficulties for the carbon cycle. The rate of rise of δ 13C, and its sustained high level, must imply conversions of oxidized carbon to reduced carbon that are very large depending on which reservoirs were involved. 相似文献
10.
We present a time series of carbon and oxygen stable isotope records of the last 30?000 14C years throughout the last glacial-postglacial cycle from western Qinghai-Xizhang (Tibet) Plateau. A 20-m core drilled in the south basin of Zabuye Salt Lake was analyzed for inorganic and organic carbon and total sulfur contents, δ 13C and δ 18O values of carbonates. Our results indicate that climatic changes have led to a drastic negative shift of stable isotope ratios at the transition between the Last Full Glacial and the postglacial phase during Later Pleistocene times (∼16.2 kyr BP), and a rapid positive shift at the transition from Pleistocene to Holocene (∼10.6 kyr BP). The first shift is marked by the drop of δ 18O carb values of about 10‰ (from +2 to −8‰) and δ 13C carb values of about 3‰ (from 5 to 2‰). The second shift which occurred at the transition from Pleistocene to Holocene was of similar magnitude but in the opposite direction. Isotope data, combined with total organic and inorganic carbon contents and the lithological composition of the core, suggest this lake was an alluvial pre-lake environment prior to ca. 28 14C kyr BP. During ca. 28-16.2 14C kyr BP, Zabuye Lake was likely a moderately deep lake with limited outflow. The cool and arid glacial climate led the lake level to drop drastically. Extended residence time overwhelmed the lower temperature and caused a steady increase of δ 13C carb and δ 18O carb values and total inorganic carbon content in the sediments. During ca. 16.2-10.6 14C kyr BP, this lake probably overflowed and received abundant recharge from melting glaciers when the deglaciation was in its full speed. A spike of markedly enhanced δ 13C carb and δ 18O carb is seen at ∼11.5 kyr BP, probably due to the isotopic effects left behind by the short but severe Younger Dryas (YD) event. After ca. 10.6 14C kyr BP, Zabuye Lake probably closed its surface outflow, due to strong desiccation and drastic climate warming. The Early and Middle Holocene were characterized by unstable climatic conditions with alternating warmer/cooler episodes as indicated by the severe fluctuations of total organic carbon, δ 13C and δ 18O values. A hypersaline salt lake environment was finally formed at Zabuye after ∼5 14C kyr BP when the mirabilite and halite concentrations steadily increased and became the dominant minerals in the sediments. Severe imbalance of inflow/outflow resulted in the drastic increase of total sulfur, δ 13C carb and δ 18O carb values and dominance of halite in the lake since ca. 3.8 kyr BP to present. 相似文献
11.
The Xushen gas field, located in the north of Songliao Basin, is a potential giant gas area for China in the future. Its proved reserves have exceeded 1000×10 8 m 3 by the end of 2005. But, the origin of natural gases from the deep strata is still in debating. Epimetamorphic rocks as a potential gas source are widely spreading in the northern basement of Songliao Basin. According to pyrolysis experiments for these rocks in the semi-confined system, gas production and geochemistry of alkane gases are discussed in this paper. The Carboniferous-Permian epimetamorphic rocks were heated from 300°C to 550°C, with temperature interval of 50°C. The gas production was quantified and measured for chemical and carbon isotopic compositions. Results show that δ 13C 1 is less than ?20‰, carbon isotope trend of alkane gas is δ 13C 1< δ 13C 2< δ 13C 3 or δ 13C 1< δ 13C 2> δ 13C 3, these features suggest that the gas would be coal-type gas at high-over maturity, not be inorganic gas with reversal trend of gaseous alkanes ( δ 13C 1> δ 13C 2> δ 13C 3). These characteristics of carbon isotopes are similar with the natural gas from the basin basement, but disagree with gas from the Xingcheng reservoir. Thus, the mixing gases from the pyrolysis gas with coal-typed gases at high-over maturity or oil-typed gases do not cause the reversal trend of carbon isotopes. The gas generation intensity for epimetamorphic rocks is 3.0×10 8–23.8×10 8 m 3/km 2, corresponding to R o from 2.0% to 3.5% for organic matter. 相似文献
12.
Natural gases discovered up to now in Lishui Sag, the East China Sea Basin, differ greatly in gaseous compositions, of which hydrocarbon gases amount to 2%–94% while non-hydrocarbon gases are dominated by CO2. Their hydrocarbon gases, without exception, contain less than 90% of methane and over 10% of C2
+ heavier hydrocarbons, indicating a wet gas. Carbon isotopic analyses on these hydrocarbon gases showed that δ
13C1, δ
13C2 and δ
13C3 are basically lighter than −44‰, −29‰ and −26‰, respectively. The difference in carbon isotopic values between methane and ethane is great, suggesting a biogenic oil-type gas produced by the mixed organic matter at peak generation. δ
13
\( C_{CO_2 } \)
values of nonhydrocarbon gases are all heavier than −10‰, indicating a typical abiogenic gas. The simulation experiment on hydrocarbon generation of organic matter in a closed gold-tube system showed that the proportion of methane in natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit is obviously higher than that in natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit, consequently the proportion of heavier hydrocarbons of the former is remarkably lower than that of the latter. Moreover, δ
13C1 values of natural gases produced by terrigenous organic matter in the Lingfeng Formation marine deposit are about 5‰ heavier than those of natural gases derived from the aquatic and terrigenous mixed organic matter in the Yueguifeng Formation lacustrine deposit while δ
13C2 and δ
13C3 values of the former are over 9‰ heavier than those of the latter. Currently the LS36-1 oil-gas pool is the only commercial oil-gas reservoir in Lishui Sag, where carbon isotopic compositions of various hydrocarbon components differ greatly from those of natural gases produced by the Lingfeng Formation organic matter but are very similar to those of natural gases derived from the Yueguifeng Formation organic matter, therefore, natural gases in the LS36-1 oil-gas pool are mainly derived from the Yueguifeng Formation lacustrine source rock rather than the Lingfeng Formation marine or Mingyuefeng Formation coal-measures source rocks. 相似文献
13.
We measured the concentrations of dissolved inorganic carbon (DIC) and major ions and the stable carbon isotope ratios of DIC (δ 13C DIC) in two creeks discharging from carbonate‐rich sulphide‐containing mine tailings piles. Our aim was to assess downstream carbon evolution of the tailings discharge as it interacted with the atmosphere. The discharge had pH of 6.5–8.1 and was saturated with respect to carbonates. Over the reach of one creek, the DIC concentrations decreased by 1.1 mmol C/l and δ 13C DIC increased by ~4.0‰ 200 m from the seep source. The decrease in the DIC concentrations was concomitant with decreases in the partial pressure of CO 2(aq) because of the loss of excess CO 2(aq) from the discharge. The corresponding enrichment in the δ 13C DIC is because of kinetic isotope fractionation accompanying the loss of CO 2(g). Over the reach of the other creek, there was no significant decrease in the DIC concentrations or notable changes in the δ 13C DIC. The insignificant change in the DIC concentrations and the δ 13C DIC is because the first water sample was collected 160 m away from the discharge seep, not accessible during this research. In this case, most of the excess CO 2(aq) was lost before our first sampling station. Our results indicate that neutral discharges from tailings piles quickly lose excess CO 2(aq) to the atmosphere and the DIC becomes enrich in 13C. We suggest that a significant amount of carbon cycling in neutral discharges from tailings piles occur close to the locations where the discharge seeps to the surface. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
14.
Abstract We review the carbon‐isotope data for finely disseminated carbonates from bioaltered, glassy pillow rims of basaltic lava flows from in situ slow‐ and intermediate‐spreading oceanic crust of the central Atlantic Ocean (CAO) and the Costa Rica Rift (CRR). The δ 13C values of the bioaltered glassy samples from the CAO show a large range, between ?17 and +3‰ (Vienna Peedee belemnite standard), whereas those from the CRR define a much narrower range, between ?17‰ and ?7‰. This variation can be interpreted as the product of different microbial metabolisms during microbial alteration of the glass. In the present study, the generally low δ 13C values (less than ?7‰) are attributed to carbonate precipitated from microbially produced CO 2 during oxidation of organic matter. Positive δ 13C values >0‰ likely result from lithotrophic utilization of CO 2 by methanogenic Archaea that produce CH 4 from H 2 and CO 2. High production of H 2 at the slow‐spreading CAO crust may be a consequence of fault‐bounded, high‐level serpentinized peridotites near or on the sea floor, in contrast to the CRR crust, which exhibits a layer‐cake pseudostratigraphy with much less faulting and supposedly less H 2 production. A comparison of the δ 13C data from glassy pillow margins in two ophiolites interpreted to have formed at different spreading rates supports this interpretation. The Jurassic Mirdita ophiolite complex in Albania shows a structural architecture similar to that of the slow‐spreading CAO crust, with a similar range in δ 13C values of biogenic carbonates. The Late Ordvician Solund–Stavfjord ophiolite complex in western Norway exhibits structural and geochemical evidence for evolution at an intermediate‐spreading mid‐ocean ridge and displays δ 13C signatures in biogenic carbonates similar to those of the CRR. Based on the results of this comparative study, it is tentatively concluded that the spreading rate‐dependent tectonic evolution of oceanic lithosphere has a significant control on the evolution of microbial life and hence on the δ 13C biosignatures preserved in disseminated biogenic carbonates in glassy, bioaltered lavas. 相似文献
15.
Baseline characterization of concentrations and isotopic values of dissolved natural gases is needed to identify contamination caused by the leakage of fugitive gases from oil and gas activities. Methods to collect and analyze baseline concentration‐depth profiles of dissolved CH 4 and C 2H 6 and δ 13C‐CH 4 in shales and Quaternary clayey tills were assessed at two sites in the Williston Basin, Canada. Core and cuttings samples were stored in Isojars ® in a low O 2 headspace prior to analysis. Measurements and multiphase diffusion modeling show that the gas concentrations in core samples yield well‐defined and reproducible depth profiles after 31‐d equilibration. No measurable oxidative loss or production during core sample storage was observed. Concentrations from cuttings and mud gas logging (including IsoTubes ®) were much lower than from cores, but correlated well. Simulations suggest the lower concentrations from cuttings can be attributed to drilling time, and therefore their use to define gas concentration profiles may have inherent limitations. Calculations based on mud gas logging show the method can provide estimates of core concentrations if operational parameters for the mud gas capture cylinder are quantified. The δ 13C‐CH 4 measured from mud gas, IsoTubes ®, cuttings, and core samples are consistent, exhibiting slight variations that should not alter the implications of the results in identifying the sources of the gases. This study shows core and mud gas techniques and, to a lesser extent, cuttings, can generate high‐resolution depth profiles of dissolved hydrocarbon gas concentrations and their isotopes. 相似文献
16.
ABSTRACTThis study aims to differentiate the potential recharge areas and flow mechanisms in the North-eastern Basin, Palestine. The results differentiate the recharge into three main groups. The first is related to springs and some of the deep wells close to the Anabta Anticline, through the Upper Aquifer (Turonian) formation, with depleted δ 18O and δ 2H. The second is through the Upper Cenomanian formation surrounding the Rujeib Monocline in the southeast, where the lineament of the Faria Fault plays an important role, with relatively enriched δ 13C DIC values of about ?4‰ (VPDB). The third is the Jenin Sub-series, which shows higher δ 13C DIC values, with enriched δ 18O and δ 2H and more saline content. The deep wells from the Nablus area in the south of the basin indicate low δ 13C DIC values due to their proximity to freshwater infiltrating faults. The deep wells located to the northwest of the basin have δ 13C DIC values from ?8 to ?9‰ (VPDB), with enriched δ 18O signatures, indicating slow recharge through thick soil. 相似文献
17.
Abstract Carbon isotope fluctuations of sedimentary organic matter along the two geological traverses in the Yezo Group, Hokkaido, northern Japan, elucidate a detailed chemostratigraphy for the Cenomanian Stage on the northwestern Pacific margin. Visual characterization of the kerogen from mudstone samples shows that the major constituents of sedimentary organic matter originated as terrestrial higher plants. The atomic hydrogen/carbon ratios of the kerogen suggest that the original δ 13C values of terrestrial organic matter (TOM) have not been affected significantly by thermal diagenesis. The patterns in two δ 13C TOM curves are similar and independent of changes in lithology and total organic carbon contents, which suggests that TOM was mixed sufficiently before the deposition in the Yezo forearc basin for the δ 13C composition having been homogenized. In addition, this implies that the Hokkaido δ 13C TOM profiles represent the averaged temporal δ 13C variations of terrestrial higher‐plant vegetation in the hinterlands of northeast Asia during Cenomanian time. Three shorter‐term ( ca. 0.1 my duration) positive‐and‐negative δ 13C TOM fluctuations of ∼1‰ are present in the Lower to Middle Cenomanian interval in the Yezo Group. On the basis of the age‐diagnostic taxa (ammonoids, inoceramids and planktic foraminifers), these discrete δ 13C TOM events are interpreted to be correlated with those in the δ 13C curves of pelagic carbonates from European basins. The correlation of δ 13C events between the European and Yezo Group sections suggests that the shorter‐term δ 13C fluctuations in Cenomanian ocean‐atmosphere carbon reservoirs are useful for global chemostratigraphic correlation of marine strata. In particular, the correlation of δ 13C fluctuations of the so‐called ‘Mid‐Cenomanian event’ (MCE) implies: (i) the δ 13C variations of global carbon reservoir during the MCE are precisely recorded in the δ 13C TOM records; and (ii) the MCE δ 13C TOM event is an efficient chronostratigraphic index for the Lower/Middle Cenomanian boundary of the Mid‐Cretaceous sequences. 相似文献
18.
The impact of landfill contaminated groundwater along a reach of a small stream adjacent to a municipal landfill was investigated using stable carbon isotopes as a tracer. Groundwater below the stream channel, groundwater seeping into the stream, groundwater from the stream banks and stream water were sampled and analysed for dissolved inorganic carbon (DIC) and the isotope ratio of DIC (δ 13C DIC). Representative samples of groundwater seeping into the stream were collected using a device (a ‘seepage well’) specifically designed for collecting samples of groundwater seeping into shallow streams with soft sediments. The DIC and δ 13C DIC of water samples ranged from 52 to 205 mg C/L and ?16·9 to +5·7‰ relative to VPDB standard, respectively. Groundwater from the stream bank adjacent to the landfill and some samples of groundwater below the stream channel and seepage into the stream showed evidence of δ 13C enriched DIC (δ 13C DIC = ?2·3 to +5·7‰), which we attribute to landfill impact. Stream water and groundwater from the stream bank opposite the landfill did not show evidence of landfill carbon (δ 13C DIC = ?10·0 to ?16·9‰). A simple mixing model using DIC and δ 13C DIC showed that groundwater below the stream and groundwater seeping into the stream could be described as a mixture of groundwater with a landfill carbon signature and uncontaminated groundwater. This study suggests that the hyporheic zone at the stream–groundwater interface probably was impacted by landfill contaminated groundwater and may have significant ecological implications for this ecotone. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
19.
The chemical and isotopic compositions (δD H2O, δ 18O H2O, δ 18O CO2, δ 13C CO2, δ 34S, and He/N 2 and He/Ar ratios) of fumarolic gases from Nisyros, Greece, indicate that both arc-type magmatic water and local seawater feed the hydrothermal system. Isotopic composition of the deep fluid is estimated to be +4.9±0.5‰ for δ 18O and ?11±5‰ for δD corresponding to a magmatic water fraction of 0.7. Interpretation of the stable water isotopes was based on liquid–vapor separation conditions obtained through gas geothermometry. The H 2–Ar, H 2–N 2, and H 2–H 2O geothermometers suggest reservoir temperatures of 345±15 °C, in agreement with temperatures measured in deep geothermal wells, whereas a vapor/liquid separation temperature of 260±30 °C is indicated by gas equilibria in the H 2O–H 2–CO 2–CO–CH 4 system. The largest magmatic inputs seem to occur below the Stephanos–Polybotes Micros crater, whereas the marginal fumarolic areas of Phlegeton–Polybotes Megalos craters receive a smaller contribution of magmatic gases. 相似文献
20.
The Ordos Basin, the second largest sedimentary basin in China, contains the broad distribution of natural gas types. So far, several giant gas fields have been discovered in the Upper and Lower Paleozoic in this basin, each having over 1000×10 8m 3 of proven gas reserves, and several gas pools have also been discovered in the Mesozoic. This paper collected the data of natural gases and elucidated the geochemical characteristics of gases from different reservoirs, and then discussed their origin. For hydrocarbons preserved in the Upper Paleozoic, the elevated δ 13C values of methane, ethane and propane indicate that the gases would be mainly coal-formed gases; the singular reversal in the stable carbon isotopes of gaseous alkanes suggests the mixed gases from humic sources with different maturity. In the Lower Paleozoic, the δ 13C 1 values are mostly similar with those in the Upper Paleozoic, but the δ 13C 2 and δ 13C 3 values are slightly lighter, suggesting that the gases would be mixing of coal-type gases as a main member and oil-type gases. There are multiple reversals in carbon isotopes for gaseous alkanes, especially abnormal reversal for methane and ethane (i.e. δ 13C 1> δ 13C 2), inferring that gases would be mixed between high-mature coal-formed gases and oil-type gases. In the Mesozoic, the δ 13C values for gaseous alkanes are enriched in 12C, indicating that the gases are mainly derived from sapropelic sources; the carbon isotopic reversal for propane and butane in the Mesozoic is caused by microbial oxidation and mixing of gases from sapropelic sources with different maturity. In contrast to the Upper Paleozoic gases, the Mesozoic gases are characterized by heavier carbon isotopes of iso-butane than normal butane, which may be caused by gases generated from different kerogen types. Finally, according to δ 13C 1- R 0 relationship and extremely low total organic carbon contents, the Low Paleozoic gases would not be generated from the Ordovician source as a main gas source, bycontrast, the Upper Paleozoic source as a main gas source is contributed to the Lower Paleozoic gases. 相似文献
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