首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到6条相似文献,搜索用时 4 毫秒
1.
N has a controlling effect on litter biodegradation in the forest floor, while stabilization of organic matter in the mineral soil may be influenced by physical parameters related to soil texture. In this study, in order to understand the processes involved in soil organic matter (SOM) formation, the chemical composition of SOM was followed and evaluated with regards to N contents and soil texture. Samples were taken on sites covered with Norway spruce and displaying contrasting values of C/N ratios in the forest floor. The chemical structure of OM was characterized using solid-state CPMAS 13C and 15N nuclear magnetic resonance (NMR) spectroscopy, along with Proton Spin Relaxation Editing (PSRE) sequences. Four groups of sampling sites were defined based on the NMR spectra of Oh and A horizons. In each group displaying similar NMR characteristics, N content and soil texture could be highly different among sites. Some Oh horizons with similar NMR spectra had very different N contents. Highly humified OM in Oh horizons were observed mainly on sites with low N contents. Some A horizons with different soil texture displayed similar OM chemical structure. High contents of O-alkyl C in some A horizons could originate from higher fresh root material input.  相似文献   

2.
Insoluble organic matter (IOM) isolated from 22 carbonaceous and ordinary chondrites spanning a wide range of groups and petrologic types were analyzed using Fourier transform infrared spectroscopy (FTIR). Based on common IR spectral features, it is observed that IOM falls into 4 molecularly distinct groups (designated here as A through D). Spectral group A includes type 1 and 2 chondrites and exhibits intense aliphatic C-H and carboxyl vibrational peaks. Spectral group B includes the least metamorphosed type 3 chondrites and Tagish Lake, and exhibits weaker aliphatic and carboxyl vibrational intensity. Spectral groups C and D include metamorphosed type ?3.1 chondrites and a heated CM chondrite. The carbonyl stretching features in spectral groups C and D differ from that in spectral groups A and B and from each other. In spectral group C, the carbonyl stretching is assigned to cyclic unsaturated lactones; in spectral group D carbonyl exists predominantly in the form of unsaturated ketone moieties. Both spectral groups C and D have a relatively narrow band structure around 1210 cm−1 (assigned to aromatic skeletal modes) as compared with spectral groups A and B, which is consistent with the formation of more condensed aromatics by extensive thermal metamorphism. The differences in carbonyl structures in spectral groups C and D are not the result of different effective metamorphic temperatures, rather these differences likely result from variation in the activity of water and oxygen at different stages of parent body metamorphism. Such environmental variations must be local phenomena in the parent bodies as there is no correlation between spectral grouping and chondrite class or group.  相似文献   

3.
探讨了渤中坳陷石臼陀凸起东段CO2来源及CO2充注对储层粘土矿物的影响.研究表明,CO2中δ13C组成较重,R/Ra值较大,CO2为幔源成因;控盆的深大断裂是CO2的主要运移通道;CO2热流体晚期充注对砂岩储集层粘土矿物产生了明显的影响:CO2热流体侵位后形成的热波动效应加快了储集层中伊蒙混层粘土的演化,含CO2储集层中伊蒙混层中蒙脱石含量要比同深度的泥岩低15% ~30%;CO2热流体晚期侵入加剧了长石的溶蚀作用,长石溶蚀促进了自生高岭石的大量形成;CO2热流体侵位后形成的偏酸性环境抑制伊利石生长,促进了其他粘土矿物向高岭石转化;含CO2储集层以少见的高自生高岭石、低伊利石为特征,这对储层物性改善起到了决定性的影响.  相似文献   

4.
Four lithotypes (vitrain, bright clarain, clarain, and fusain) of a high volatile bituminous Springfield Coal from the Illinois Basin were characterized using advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. The NMR techniques included quantitative direct polarization/magic angle spinning (DP/MAS), cross polarization/total sideband suppression (CP/TOSS), dipolar dephasing, CHn selection, and recoupled C-H long-range dipolar dephasing techniques. The lithotypes that experienced high-pressure CO2 adsorption isotherm analysis were also analyzed to determine possible changes in coal structure as a result of CO2 saturation at high pressure and subsequent evacuation. The main carbon functionalities present in original vitrain, bright clarain, clarain and fusain were aromatic carbons (65.9%-86.1%), nonpolar alkyl groups (9.0%-28.9%), and aromatic C-O carbons (4.1%-9.5%). Among these lithotypes, aromaticity increased in the order of clarain, bright clarain, vitrain, and fusain, whereas the fraction of alkyl carbons decreased in the same order. Fusain was distinct from other three lithotypes in respect to its highest aromatic composition (86.1%) and remarkably small fraction of alkyl carbons (11.0%). The aromatic cluster size in fusain was larger than that in bright clarain. The lithotypes studied responded differently to high pressure CO2 saturation. After exposure to high pressure CO2, vitrain and fusain showed a decrease in aromaticity but an increase in the fraction of alkyl carbons, whereas bright clarain and clarain displayed an increase in aromaticity but a decrease in the fraction of alkyl carbons. Aromatic fused-rings were larger for bright clarain but smaller for fusain in the post-CO2 adsorption samples compared to the original lithotypes. These observations suggested chemical CO2-coal interactions at high pressure and the selectivity of lithotypes in response to CO2 adsorption.  相似文献   

5.
Pedogenic goethites in each of two Early Permian paleosols appear to record mixing of two isotopically distinct CO2 components—atmospheric CO2 and CO2 from in situ oxidation of organic matter. The δ13C values measured for the Fe(CO3)OH component in solid solution in these Permian goethites are −13.5‰ for the Lower Leonardian (∼283 Ma BP) paleosol (MCGoeth) and −13.9‰ for the Upper Leonardian (∼270 Ma BP) paleosol (SAP). These goethites contain the most 13C-rich Fe(CO3)OH measured to date for pedogenic goethites crystallized in soils exhibiting mixing of the two aforementioned CO2 components. δ13C measured for 43 organic matter samples in the Lower Leonardian (Waggoner Ranch Fm.) has an average value of −20.3 ± 1.1‰ (1s). The average value yields a calculated Early Permian atmospheric Pco2 value of about 1 × PAL, but the scatter in the measured δ13C values of organic matter permits a calculated maximum Pco2 of 11 × PAL (PAL = present atmospheric level). Measured values of the mole fraction of Fe(CO3)OH in MCGoeth and SAP correspond to soil CO2 concentrations in the Early Permian paleosol profiles of 54,000 and 50,000 ppmV, respectively. Such high soil CO2 concentrations are similar to modern soils in warm, wet environments.The average δ13C values of pedogenic calcite from 9 paleosol profiles stratigraphically associated with MCGoeth (Waggoner Ranch Fm.) range from −6.5‰ to −4.4‰, with a mean δ13C value for all profiles of −5.4‰. Thus, the value of Δ13C between the pedogenic calcite data set and MCGoeth is 8.1 (±0.9)‰, which is in reasonable accord with the value of 7.7‰ expected if atmospheric Pco2 and organic matter δ13C values were the same for both paleosol types. Furthermore, the atmospheric Pco2 calculated for the Early Permian from the average measured carbon isotopic compositions of the paleosol calcite and organic matter is also analytically indistinguishable from 1 × PAL, with a maximum calculated atmospheric Pco2 (permitted by one standard deviation of the organic matter δ13C value) of ∼5 × PAL.If, however, measured average δ13C values of the plant organic matter are more positive than the original soil organic matter as a result of diagenetic loss of 13C-depleted, labile organic compounds, calculated Permian atmospheric Pco2 using these 13C-enriched organic values would underestimate the actual atmospheric Pco2 using either goethite or calcite. This is the first stratigraphically constrained, intrabasinal study to compare ancient atmospheric CO2 concentrations calculated from pedogenic goethite and calcite. These results demonstrate that the two different proxies record the same information about atmospheric CO2.The Fe(CO3)OH component in pedogenic goethite from a Triassic paleosol in Utah is significantly enriched in 13C relative to Fe(CO3)OH in goethites from soils in which there are mixtures of two isotopic CO2 components. Field-relationships and the δ13C value (−1.9‰) of the Triassic goethite indicate that this ancient paleosol profile experienced mixing of three isotopically distinct CO2 components at the time of goethite crystallization. The three components were probably atmospheric CO2, CO2 from in situ oxidation of organic matter and CO2 from in situ dissolution of preexisting calcite. Although mixing of three isotopically distinct CO2 components, as recorded by Fe(CO3)OH in goethite, has been described in modern soil, this is the first example from a documented paleosol. Its preservation affirms the need for careful, case-by-case assessment of ancient paleosols to establish that goethite in any particular soil is likely to be a valid proxy of atmospheric Pco2.  相似文献   

6.
The combined results of 27Al-1H and 1H-29Si-1H cross polarization NMR experiments for hydrous glasses (containing 0.5-2 wt% water) along the SiO2-NaAlSiO4 join confirm that the dissolution mechanism of water in aluminosilicate glasses is fundamentally the same as for Al-free systems, i.e. the dissolved water ruptures oxygen bridges and creates Si-OH and Al-OH groups, in addition to forming molecular water (H2Omol). The fraction of Al-OH increases non-linearly as the Al content increases with up to half of the OH groups as Al-OH for compositions close to NaAlSiO4. The relative abundances of the different species are controlled by the degree of Al-avoidance and the relative tendency of hydrolysis of the different types of oxygen bridges, Si-O-Si, Si-O-Al and Al-O-Al. A set of homogeneous reactions is derived to model the measured Al-OH/Si-OH speciation, and the obtained equilibrium constants are in agreement with literature data on the degree of Al-avoidance. With these equilibrium constants, the abundance of the different oxygen species, i.e. Si-O-Si, Si-O-Al, Al-O-Al, Si-OH, Al-OH and H2Omol, can be predicted for the entire range of water and Al contents.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号