An approach to noble-gas isotopic compositions in natural gases and gas-source tracing in the Ordos Basin,China

Isotopic compositions of noble gases, i.e. He Ar Kr and Xe, are measured in natural gases from the Zhongbu gasfield in the Ordos Basin. And heavy noble-gas isotopes (Kr, Xe) are here first used in geochemically studying natural gases and gas-source correlation. Isotopic compositions of heavy noble gases in natural gases, especially Xe, show two-source mixing in the Zhongbu gasfield. Gas sources are somewhat different in the northeast and the southwest of the gasfield. Generally, the gas source of the Lower Paleozoic makes a greater contribution in the southwest than in the northeast in the field. Two kinds of gases can be differentiated from isotopic compositions of heavy noble gases and from their relation with the Ar isotopic composition. Therefore, the comprehensive study on isotopic compositions of light and heavy noble gases can supply more useful information on gas-source correlation and tracing.

Noble gas isotopic compositions of deep carbonate rocks from the Tarim Basin

Abundances and isotopic compositions of noble gases (He, Ne, Ar, Kr) with various existence states in carbonate rocks from the Tacanl Well have been investigated by means of the stepwise heating technique. The elemental abundance patterns of noble gases in the samples show the enrichment of heavy noble gases and depletion of 20Ne relative to the atmosphere, which are designated as type-I and are similar to that observed in water, natural gases and sedimentary rocks. The 3He/4He ratios of deep carbonate samples at lower and medium temperature (300-700°C) and a majority of samples at higher temperature (1100-1500°C) steps are very similar to those of natural gases in the same strata in this area, this feature of radiogenic crustal helium shows that the Tazhong Uplift is relatively stable. However, significant helium and argon isotopic anomalies are found at the 1100°C step in the Middle-Upper Ordovi-cian carbonate rock, suggesting the incorporation of mantle-derived volatiles, this may be due to minor

Carboniferous biogenic sedimentary structures on the northwestern margin of Jungar Basin

Volcanic clastic rocks of 2 300 m thick are developed in the Carboniferous of the Halaalate Mountains in the northwestern margin of the Jungar Basin. The research of sedimentology indicates that they were formed by the sedimentation of deep-water enviroment. They could be divided into three ichnofacies from the lower part to the upper part, i.e. deep-sea ichnofacies, Nereites ichnofacies, and Zoophycos ichnofacies. From the vertical evolution of biogenic structures and ichnofacies it could be considered that during the Carboniferious a batheyl basin was gradually changed into a semideep sea basin where progradational sediments in the sea regression were deposited. The Carboniferous represents the sedimentary characteristics during a sea-level falling cycle.

On abiogenic natural gas

NATURAL gases usually refer to the inflammable gases dominated by methane from the angle of research on energy gases. Three genetic types of natural gases can be recognized according to the process of methane generation: (ⅰ) biogenic (bacterial) gas, mainly the gas formed by the decomposition of organic matter in sediments under the action of anaerobic bacteria; (ⅱ) thermogenic gas, mainly the gas formed by the degradation of organic matter in sediments under the action of certain temperature and pressure; (ⅲ) abiogenic gas, mainly the

Natural gas geochemistry of low evolutionary stage of mediumand small-sized basins in Yunnan Province, southwestern China

The biogenic gas and premature-low mature associated gases in some medium and small-sized basins of Yannan Province, such as Luliang, Yanglin, Baoshan and Jinggu basins, have beed researched. The results show that the biogenic-gas consists mainly of methane which is more than 99% in gasous hydrocarbons and of lighter carbon isotopic composition with δ13C1 values from -60.0‰ to - 75.4‰. The methane carbon isotopic compositions in the Baoshan Basin is relatively heavy (δ13C1, - 60‰-- 65‰), but those in Luliang and

Application of the ancient trace fossil group in deep sea to the sedimentology

Extremely abundant trace fossils are associated with the deep-sea deposits, especially in turbidite measure and flysch facies. And these trace groups then become the effective indicators to reconstruct the ancient depositional environment and the palaeogeography. This paper focuses on ( ⅰ ) the formational features of deep-sea fossil and its assemblage feature, and further recongnizes that the coexistence of the shallow and deep water trace group in a depositional sequences is the identification mark of turbidite sequence; ( ⅱ ) thought and methods using the trace fossil to restore their environmental parameters such as the ancient sea depth, oxygenbearing condition and sedimentation rate, etc.; ( ⅲ ) the application and significance of deep-sea ichnofacies in environment interpretation.

Variation of iron species in sliding mud

Results of Mossbauer spectroscopy and ICP-AES measurement revealed a special distribution pattern of iron species in four crossing profiles of the Tertiary Formation Type of Landslides in Japan. In comparison with host rocks, the sliding mud in the landslide slip zone contains the higher ferrous iron content and/or trace pyrite, which indicates that the forming environment was relatively reducing. The total iron content also increased with an increase in ferric iron and pyrite, in contrast, decreased with an increase in ferrous iron content. The deep-gray and black mud layers formed and accumulated in various volumes within landslide slip zones are treated as the basic criteria for the slipping activity, because the soft mud saturated with groundwater is easy to create a plastic deformation.

Permian palynofioras from Yongchang and Sunan of Gansu Province and their phytoprovincial characteristics

The Early Permian (Shansi + Lower Shihhotse Formations) palynofloras of Longshoushan are dominated by Cathaysian-Euramerican common forms, mainly composed of pteridophytic and pteridospermous spores. But up to the Lower Shihhotse Formation, gymnosperms greatly developed, and they possibly already dominated the vegetation in the Upper Shihhotse Formation; while in the late Late Permian, they indicate a strong colour of Subangara area. In other words, during the whole Permian, the Cathaysian flora had a history from prosperity to decline, and Subangara plants might have had a reverse tendency there.

Carbon isotopic composition of mantle xenoliths in alkali basalt from Damaping, Hebei

The carbon isotopic composition of CO-2, CO and CH-4 extracted by pyrolysis from spinel lherzolite and black pyroxenolite xenoliths in alkali basalt from Damaping has been measured with GC_MS. The results show that, at heating temperatures from 400 to 1 140℃, the δ 13C of CO-2 and CO is -22‰--27‰, and that of CH-4 -30‰--50‰. The data imply that the magma which was generated in the upper mantle by partial melting in the area has experienced the multistage degassing process, and the δ 13C values represent the carbon isotopic composition of CO-2, CO and CH-4 remaining in it, respectively.

Leakage of mantle helium from the Liaodong Peninsula, China

The isotopic compositions of helium have been investigated in hot spring gases sampled from the Liaodong Peninsula, China. The 3He/ 4He ratios range from 0.14 Ra (0.14 times the atmospheric 3He/ 4He ratio of 1.40×10 -6) to 0.72 Ra. 3He/ 4He versus 4He/ 20Ne ratios and He contents suggest that a small amount of mantle-derived helium reaches the earth’s surface. Helium isotope ratios of the hot spring gases show a distribution pattern similar to the regional heat flow values, indicating that the positive thermal anomaly occurring in the area is closely associated with the presence of mantle-derived helium. The observations described above provide some significant evidence that the molten magma originating from partial melting of the upper mantle may have intruded into the continental crust along the activity fault. The coupling of the presence of mantle He and heat flow anomalies to seismic activity in studied region seem to imply that there is an internal relationship between mantle degassing and seismic

Thermal-induced polycondensation of soluble organic matter in coal of lower maturation stage

A brief discussion is given to the thermal-induced polycondensation of soluble organic matter (SOM) in coal during lower maturation stage, based on laboratory simulation on hydrocarbon generation from coal and on correlation with natural maturation of coal. An essential relationship between the retrogressive variation of SOM and thermal-induced polycondensation during the lower maturation stage has been established.

The simulation of the formation of dibenzothiopheneand dibenzofuron

The results of simulation indicate that biphenyl (BIP) is one of the original materials of dibenzothiophene (SF) and dibenzofuron (OF). It has the fundamental structure of SF and OF. As the radicals that attract electron, its two aromatic nucleuses influence each other, which make the α-H active. The strong electronegative sulphur or oxygen atoms attack the two places of the two aromatic nucleuses, seize the hydrogens and form H 2S or H 2O, the other sulphur or oxygen atoms attacking the two places which have lost hydrogens can put up a bridge and make the BIP molecule which can freely turn become a stable SF or OF molecule. So SF and OF have no definite relation with fluorene (F).

A model for carbon isotope distribution of methane duringdiagenesis

The evolution of methane carbon isotope with depth has been discussed based on diagenetic reaction kinetics and isotopic Rayleigh fractionational theory. A mathematical model to describe data of methane carbon isotope for the Liaohe oil field has been established.