-
[show abstract]
[hide abstract]
ABSTRACT: The reconstruction of pCO2 in the tropic ocean is one of the most important issues to understand global climatic changes. In this study, the high-resolution
stratigraphic analysis of core 17962 was conducted, which is located in the southern South China Sea (SCS). The contents of
sedimentary organic matter, the stable carbon isotopic composition of sedimentary organic matter, and the δ13C values of black carbon and terrigenous n-alkanes were determined. And the δ13Cwc value of carbon derived from aquatic was calculated. On the basis of δ13Corg-pCO2 equation proposed by Popp et al. (1989), we estimated the pCO2 in the Nansha area, SCS, since the last glaciation using δ13Cwc instead of δ13Corg. The results show that the average pCO2 was estimated at 240 ppmV during the last glaciation, and at 320 ppmV in the Holocene. A comparison of surface sea pCO2 with the atmosphere CO2 recorded in the Vostok ice core, indicates that CO2 in surface water of the southern SCS could emit into atmosphere during the last 30 ka.
Chinese Science Bulletin 04/2012; 48(2):199-203. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Isotopic compositions of carbon-bound hydrogen in individual n-alkanes from several typical crude oil samples from Lunnan Oilfield, Tarim Basin, NW China, were firstly measured using newly
developed gas chromatography-thermal conversion-isotope ratio mass spectrometry. The similar range of δ D of individual n-alkanes of crude oils among reservoirs of different geological times reflects that hydrocarbons are all derived from the
same marine depositional environment. Compared to the theoretic value (-150‰) and the reported δ D values (nC13-nC27,-160‰-90‰) of individual n-alkanes for Ordovician-sourced crude oils in the Canadian Williston Basin, the hydrogen isotopic composition of individual
n-alkanes in crude oils from Lunnan Oilfield is characterized by heavy hydrogen isotopic values (nC12-nC27, -120‰-60‰). In terms of the factors that control the fractionation of hydrogen isotopes, relatively saline depositional
environment and higher thermal maturation were attributed to the heavy δ D values of individual n-alkanes in crude oils from Lunnan Oilfield.
Science in China Series D Earth Sciences 04/2012; 48(8):1220-1226. · 1.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Flash pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and in situ methylation-pyrolysis-gas chromatography-mass spectrometry (methylation-Py-GC-MS) have been employed for a study of molecular structure of kerogens from source rocks of the Tarim Basin. The main
products from Py-GC-MS of the Ordovician and Triassic kerogens from the Tarim Basin are n-alkanes and n-alk-1-enes which decrease in relative abundance with increased carbon number. The major products from methylation-Py-GC-MS are normal saturated fatty acid methyl esters which show maxima at C16 and C18. These aliphatic compounds are mainly
from lipids of planktonic algae. Moreover, there are more abundant long-chain fatty acids (C20-C26) and normal n-alkanes and n-alk-1-enes (C15-C25) in pyrolysates of Triassic kerogens than that of Ordovician kerogens, reflecting the discrepancies in
sources of the Triassic kerogens and the Ordovician kerogens. Besides these aliphatic compounds, methoxyl benzoic acid methyl
esters were detected only in products from methylation-Py-GC-MS of late Ordovician kerogen TAC1-1, which possibly was the first molecular evidence for the appearance of moss or
other terrestrial plants in the Tarim Basin. In addition, the relative intensity of 17β(H)-trisnorhopane, 17 β(H), 21 α(H)-30-normoretane
and 17 β(H)-moretane is lower, but 17α(H)-trisnorhopane and 17 α(H)-30-norhopane is higher in the pyrolysates of the Ordovician
kerogens in comparison with the pyrolysates of the Triassic kerogens. Moreover, Pr-1-ene has been detected in pyrolysates
of Triassic kerogens. These differences in pyrolysates consist with maturity of kerogens. In conclusion, combination of methylation-Py-GC-MS and Py-GC-MS are useful tools to investigate the molecular structure of geomacromolecules and can be subject to type
the organic matter, compare the maturity of kerogens and carry out the oil-source correlation.
Science in China Series D Earth Sciences 04/2012; 48(3):313-325. · 1.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Binary solvent (CS2-NMP) has extreme high extraction ability to coals, and it can extract most bitumens out of coals and vitrinites. And large
amount of messages on side chains and their distribution character in vitrinites should be acquired through flash pyrolysis
before and after binary solvent (CS2-NMP) extraction. A few low maturated coals have been selected and vitrinites are handpicked from coals. Then vitrinites have
been extracted using different solvents in the order of polarity. Flash pyrolysis-Gas Chromatography/Mass spectrum has been
applied to samples. The result shows that CS2-NMP is efficient for the extraction of vitirnites, giving much higher extraction yield than common solvents. Production ratio
of liquid hydrocarbons in pyrolysates of vitrinites extracted with CS2-NMP is lower than that of raw vitrinites. And relative ratio of each component in pyrolysates has changed apparently. Production
ratio of aliphatic hydrocarbons, especially those long chain aliphatics have decreased much after mixed solvent extraction.
It shows that bitumens extracted with CS2-NMP have largely contributed to pyrolysates, especially those aliphatics in pyrolysates.
Chinese Science Bulletin 08/2006; 51(17):2103-2109. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The isotopic composition (d13C and d15N) and organic carbon (OC) and total nitrogen (TN, organic plus inorganic) content of
37 carbonate-free surficial sediments of the subtropical Pearl River estuary and the adjacent shelf of South China Sea (SCS) was
determined. The d13C values indicate that the sediment organic material is a mixture from two sources, terrestrial and marine.
Several of the sediments have extremely low (b4) OC/TN ratios, which could be due to low OC contents and/or to a significant
fraction of the TN present as inorganic nitrogen adsorbed on clays. In general, the spatial patterns of OC, TN, d13C and d15N are
similar. Values are low at the river mouth and on the western coast, suggesting proportionally greater accumulation of terrestrial
particulate organic matter relative to marine phytodetritus, which is limited by low productivity in the turbid plume of the Pearl
River. Algal-derived organic carbon (al-OC) content is estimated to be low (V0.06%) at the river mouth and higher (up to 0.57%)
on the adjacent inner shelf based on a mixing model of end members.
Marine Chemistry 01/2006; · 3.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Sulfur plays an important role in the generation and evolution of hydrocarbon from organic matter. Here, a pyrolysis experiment
in closed system was performed on Maoming oil shales kerogen (Type I), Maoming oil shales kerogen added with sulfur ether
and Maoming oil shales kerogen added with sulphur. The results suggest that the existence of sulfur can result in: (i) higher
yield of hydrocarbons generated from the kerogen; (ii) decrease of the temperature for the maximum generation of heavy hydrocarbons
(the C15+ fraction) by 20°C; (iii) decrease of the temperature for the maximum generation of the aromatics fraction by 40°C, and (iv)
acceleration of the aromatization process. The pyrolysates from kerogen added with sulfur are similar to the heating products
of the sulfur-rich kerogen as reported in the literatures. It seems that the sulfur catalysis is also an important factor
that can make the sulfur-rich kerogen generate low-mature oil at the earlier diagenesis stage, except for the weakness of
the C-S and S-S bonds.
Chinese Science Bulletin 11/2004; 49:10-18. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The molecular compositions and molecular carbon isotopic compositions of gas hydrocarbons produced in the hydrocarbon generation
of oil asphaltene from Lunnnan area were investigated by pyrolysis of asphaltene sealed in gold tube in a limited system.
The experimental results indicated that oil asphaltene from Lunnan area had relatively high generation potential of methane.
However, the molecular compositions and molecular carbon isotopic compositions of gas hydrocarbons in the hydrocarbon generation
of oil asphaltene exhibited different characteristics from that of gas hydrocarbons by primary cracking of kerogen and secondary
cracking of oil. Based on kinetic simulation with paleo-geothermal data of oil reservoir, the methane produced by cracking
of oil asphatene was characterized by relatively light carbon isotopic compositions. This result could not explain relatively
heavy carbon isotopic compositions of natural gas from Lunnan area. Pyrolysis of kerogen from source rocks under very high
temperature probably made remarkable contributions to natural gas from Lunnan area.
Chinese Science Bulletin 11/2004; 49:83-88. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Kinetics study of gaseous hydrocarbons generated from vitrinites based on pyrolysis of gold tube closed system shows that
the activation energies of methane generated from telocollinite are higher than that from desmocollinite due to structure
differences. But carbon isotope ratios of generated methane in pyrolysates of vitrinites at the same temperature points are
similar. Carbon isotope ratio of methane may decrease in the early stage of gas generation and then increase in the later
stage. But at higher temperature, δ13C1 decreases slightly or almost keeps stable with increasing temperature. Since it is known that carbon isotope distillation
is controlled by time, temperature and carbon isotope ratio of bulk organic matter, the character of side chains connected
to macromolecule of vitrinite and distribution of activation energies have no obvious effect on carbon isotope fraction. Decreasing
trend of δ13C1 in the early stage may be caused by contagious structure of vitrinite or differences of activation energies between12C-12C and12C-13C are not strictly constant at different ranges of activation energy area.
Chinese Science Bulletin 01/2004; 49:72-78. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Nanosized coupled ZnO/SnO 2 photocatalysts with different Sn contents were prepared using the coprecipitation method, and char-acterized by X-ray diffraction, specific surface area and UV-Vis diffuse reflectance spectroscopy. The phases, mean grain sizes and band gap energy of the coupled ZnO/SnO 2 photocatalysts varied with the Sn contents and the calcination temperatures. The photo-catalytic activities of the coupled ZnO/SnO 2 photocatalysts, evaluated using the photodegradation of methyl orange as a probe re-action, were also found to be related to the calcination temperatures and the Sn contents. The photocatalytic activities of the cou-pled ZnO/SnO 2 photocatalysts decreased with the increasing calcination temperatures. The maximum photocatalytic activity of the coupled ZnO/SnO 2 photocatalyst, which is about 1.3 times the photocatalytic activity of ZnO and 21.3 times that of SnO 2 , was ob-served with a Sn content of 33.3 mol% under calcination at 500 • C for 10 h. The enhancement of the photocatalytic activity might arise from the hetero-junctions ZnO/SnO 2 in the coupled oxides. The photo-stability of the ZnO/SnO 2 photocatalyst was also studied.
Journal of Photochemistry and Photobiology A: Chemistry. 01/2004; 168:47-52.
-
[show abstract]
[hide abstract]
ABSTRACT: Core 17962 taken from the sea area of the Nansha Islands recorded a sedimentary history of more than 30 000 years. The black
carbon data from the core, which can inform us of the history of vegetation fires, show that during the last glaciation, especially
during the last glacial maximum at about 18 kaBP, the fluctuation of the concentration and accumulation rate of the black
carbon was relatively great, whereas it was small during the Holocene. The isotope composition of the black carbon indicates
that the precursors of black carbon were mainly grasses from the last glaciation to the Holocene. The sub-alpine and alpine
vegetation zones covered mainly with grass and bush on the lands around the southern South China Sea were probably the sources
of black carbon. The altitudinal vegetation changes from the last glaciation to the Holocene gave rise to the changes of the
sedimentary characteristics of black carbon.
Chinese Science Bulletin 08/2000; 45(17):1594-1598. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The peculiarities of lipids in lacustrine core sediments from Fildes Peninsula, King George Island, Antarctica, are reported.
The origin of high-molecular-weight n-alkanes, alkenes, fatty acids, alcohols Is supposed to be related to the abundant moss
occurring in the sediments. Abundantiso- andanteiso-fatty acids that occur in the sediments indicate a relatively strong bacterial activity in non-ice-cover zone than in other
regions in Antarctica. The C18:2 unsaturated fatty acids mainly originate from autochthonous algae in the sediment pool, and the C18:2C18:0 ratios in the profile are controlled more by paleotemperatures than source assemblies. Long-chain alkenones were identified
in freshwater lacustrine sediment in Antarctica for the first time, of whichPrymnesiophyceae is assumed to be the source organism. High relative abundance of C37:4 homologue in long-chain alkenone well correlates to the severely cold climate in Antarctica.
Chinese Science Bulletin 02/2000; 45:67-70. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In terms of the individual carbon isotope data of biomarkers present in the typical freshwater lake sediment (Maoming oil
shale) and saline lake sediment lake (Jianghan oil shale) of China, this paper discusses their precursors and depositional
environments of biomarkers in both sediment samples. Our studies showed that phytane and pristane of the Maoming oil shale
were derived from the phytol side chain of chlorophyll a. By comparing the isotopic composition of 4-methyl sterane with that
of sterane and hopane, it is suggested that 4-methyl sterane which has a higher abundance in the Maoming oil shale come from
bacteria. The isotopic composition of biomarkers from the Jianghan rock sample (saline lake sediment) is significantly different
from that of the Maoming oil shale (freshwater lake sediment). Gammacerane was derived from haloprotozoan, with δ13C being about −25.8‰, just in consistency with the value reported in previous studies. The isotopic composition of phytane
and pristane in the Jianghan rock is similar to that of sterane and 4-methyl sterane derived from phytoplanktons, illustrating
their common precursors were algae. This paper reported for the first time the carbon isotope data of porphyrin obtained by
GC-IRMS techniques. The approximate δ13C of C32DPEP and C31DPEP porphyrin from the Jianghan Basin indicated that the porphyrin was derived from chlorophyll. In the Maoming oil shale
C32DPEP was enriched in13C relative to C32etio and C31DPEP, implying that C32DPEP came from chlorophyll, and C32etio and C31DPEP are of other origins.
Chinese Science Bulletin 02/2000; 45:90-96. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The late progress of the research on Precambrian organic matter in biomarkers, isotopes and relative analytical techniques
is reviewed. The key problems in the research of Precambrian organic matter, such as indigenous test of soluble organic matter,
are also discussed. At the end, the further work upon Precambrian organic matter is suggested.
Chinese Science Bulletin 01/2000; 45(4):295-304. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The present paper studies the mineralogy and geochemistry of a geological section in Jianghan basin. Widely distributed immature
oils in this basin have been shown to relate to the carbonate depositional stage of salt lake sedimentation cycle. It is concluded
that only when the content of organic carbon in the rocks is taken into account, is it meaningful to calculate the immature
oil in the source rocks.
Chinese Science Bulletin 01/2000; 45:1-6. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: High performance liquid chromatography (HPLC) has the advantages of rapid analysis and high sensitivity. In the present study
a suitable analytical condition has been established for HPLC, and the LAS in modem sediments from core Zhu-9 at the Pearl
River mouth has been determined by HPLC. The concentrations of C12-LAS homologues are the highest. The sedimentation flux of C12-LAS was correlated with the average flow of the Xijiang and Beijiang rivers: the higher the flow rate, the larger the C12-LAS sedimentation flux. This shows that the more rapidly the river flows, the shorter the LAS will stay in freshwater, the
less the extent of biodegradation, the larger the C12-LAS sedimentation flux in the core Zhu-9.
Chinese Science Bulletin 01/2000; 45:80-85. · 1.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In an attempt to assess the paleoenvironments of terrestrial sediments, some twenty-two representative Chinese non-marine
sediment samples were studied using the molecular organic geochemistry method. The sediment samples studied include oilshale,
shale, mudstone and glauber salt from Tertiary to Cretaceous in age. Judging from geological /geochemical data and paleosalinity
data, the samples studied are of lacustrine sedimentary origin and can be divided into three different types: fresh water,
brackish and saline /hypersaline lake sediments. The aliphatic fractions were separated from the extracts of the samples and
analysed by means of GC and GC /MS instruments, giving a number of parameters such as relative abundances of alkanes and cycloalkanes
as shown in the mass chromatograms.
Chinese Journal of Geochemistry 12/1991; 11(1):1-12.
-
[show abstract]
[hide abstract]
ABSTRACT: Natural gas is dominated by low-molecular weight gaseous hydrocarbons (C1–C5) whose genetic and diagenetic information is mainly obtained from stable carbon isotope compositions. Ordos Basin is one of the largest natural gas provinces in China. By means of examining the carbon isotope compositions of the Ordos basin gases, altered patterns of the isotope-type curves due to secondary cracking, thermochemical sulphate reduction (TSR) and mixing of gases generated from different sources are recognized and discussed. A typical carbon isotope-type curve is nearly linear on the natural gas plot [Chung, H.M., Gormly, J.R., Squires, R.M., 1988. Origin of gaseous hydrocarbons in subsurface environments: theoretical considerations of carbon isotope distribution. Chemical Geology 71, 97–103]. Our results show that the isotope-type curve pattern of TSR and gas secondary cracking in coal is convex due to catalysis, while the isotope-type curve of gas secondary cracking in reservoirs is concave. The natural gas of Yulin, Suligemiao and Wushenqi gas fields is coal-derived gas; both coal-derived gas and mixed gas from oil- and gas-prone sources exist in the Ordovician reservoirs of the Jingbian gas field, depending on the borehole locations. In the Ordovician carbonate reservoirs TSR is recorded but uncommon, whereas secondary cracking in reservoirs is often observed.
Organic Geochemistry.
-
[show abstract]
[hide abstract]
ABSTRACT: An unusual series of C22–C27 monounsaturated sterenes and C24–C30 tetracyclic terpanes (17,21-secohopanes) were detected in relatively high concentrations in an immature evaporitic marl sediment of the Jinxian Sag, Bohai Bay Basin, North China. The site of unsaturation in these novel sterenes is assigned tentatively to the D ring on the basis of mass spectral interpretation, which also distinguishes them from reported unsaturated sterenes. Other hydrocarbon biomarker or stable isotope characteristics are indicative of microbial (e.g. methyl hopanes), phytoplankton or higher plant (depleted δ13C values of isoprenoids and hopanes) inputs and an anoxic carbonate depositional environment (hexacyclic hopanes; tetracyclic terpanes). The hydrocarbon composition showed no obvious biodegradation and the relatively high concentration of unsaturated terpenoids (e.g. gammacerene) and low values of other established maturity parameters (Ts/Tm = 0.23; Ro = 0.44%; Tmax = 417 °C), are consistent with sediments of low maturity. The novel, low molecular weight sterenes and the tetracyclic terpanes may be early diagenetic products of microbial sources in a carbonate environment.
Organic Geochemistry.
-
[show abstract]
[hide abstract]
ABSTRACT: Polycyclic aromatic hydrocarbons (PAHs) are becoming a major component of atmospheric toxic pollutants (ATPs) in Guangzhou city, China. Studies showed that ATPs may have adverse health effect in urban area. An investigation on particulate- and vapor-phase distribution of n-alkanes and PAHs in urban atmosphere has been conducted. In LiWan district, 24 h sampling for three consecutive days was performed in April and July 2001 at ground level. For comparison, samples were also collected on a nine-story building, ca. 25 m above ground level. The ambient concentrations of ∑n-alkanes and ∑PAHs, compositional variations including molecular diagnostic ratios, natural biogenic and anthropogenic sources, as well as phase distributions of n-alkanes and PAHs are discussed. In addition, there are discernible differences with height, in terms of concentration and, to a lesser extent, in profiles of the compounds investigated.
Atmospheric Environment.
-
[show abstract]
[hide abstract]
ABSTRACT: The altitude effect on the isotopic composition of precipitation and its application to paleoelevation reconstruction using authigenic or pedogenic minerals have been intensively studied. However, there are still no studies on variations in biomarker δD along altitude transects to investigate its potential as a paleoelevation indicator, although it has been observed that δD of higher plant lipid may record changes in precipitation δD (δDp). Here, we present δD values of higher plant-derived C27, C29, and C31n-alkanes from surface soil along the eastern slope of Mount Gongga, China with great changes in physical variables and vegetation over a range from 1000 to 4000 m above sea level. The weighted-mean δD values of these n-alkanes (δDwax) show significant linear correlations with predicted δDp values (R2 = 0.76) with an apparent isotopic enrichment (εwax–p) of −137 ± 9‰, indicating that soil δDwax values track overall δDp variation along the entire altitudinal transect. Leaf δDwax is also highly correlated with mountain altitude by a significant quadratic relationship (R2 = 0.80). Evapotranspiration is found declining with altitude, potentially lowering δDwax values at higher elevations. However, this evapotranspiration effect is believed to be largely compensated by the opposing effect of vegetation changes, resulting in less varied εwax–p values over the slope transect. This study therefore confirms the potential of using leaf δDwax to infer paleoelevations, and more generally, to infer the δD of precipitation.
Geochimica et Cosmochimica Acta.
