Hydrogen isotopes of n-alkanes in grasses, tree leaves and reeds from six regions with latitudes of 20° to 39°N in China are measured by GC-TC-IRMS analytical technique in order to understand their hy- droge...Hydrogen isotopes of n-alkanes in grasses, tree leaves and reeds from six regions with latitudes of 20° to 39°N in China are measured by GC-TC-IRMS analytical technique in order to understand their hy- drogen isotopic compositions and environmental significance. The results show that a difference in δ D values (from -42.1‰ to -66.6‰) of n-alkanes exists among the same kinds of plants from various re- gions. Hydrogen isotopic compositions of most even carbon numbered n-alkanes in every plant are slightly heavier than that of the odd homologues. A trend toward D-enrichment with increasing chain length of n-alkanes in most plant samples is observed. Mean δ D values of n-alkanes in the studied plants range from -202.6‰ to -130.7‰ and the reed from a salt marsh has the largest value. The mean δ D values of individual n-alkanes among the same kinds of plants from various regions have the characteristics of leaf > reed > grass. The hydrogen isotopic compositions of n-alkanes are apparently distinct among various kinds of plants from the same region and the mean δ D values exhibit a distri- bution of tree leaf > reed > grass. It is observed that the mean δ D values of n-alkanes and δ D values of C27 and C29 n-alkanes in the grasses and tree leaves from these studied regions correlate clearly nega- tively with latitude and positively with temperature, indicating that these values can be used as excel- lent indicators of environment and climate. These results provide important basic data for under- standing the distributional law of hydrogen isotopes of individual n-alkanes and their applied research.展开更多
N\|alkanes in extracts from possible carbonate source rocks of the Lower Ordovician Majiagou Formation in the central gas field of the Shanganning Basin and the Upper Sinian Dengying Formation in the Weiyuan gas field...N\|alkanes in extracts from possible carbonate source rocks of the Lower Ordovician Majiagou Formation in the central gas field of the Shanganning Basin and the Upper Sinian Dengying Formation in the Weiyuan gas field of the Sichuan Basin, are characterized by bimodal distributions with the dominant carbon numbers in the range C\- 17 \|C\- 21 and C\- 25 \|C\- 29 . In most samples, the lower carbon number components are present in greater abundance than the higher carbon number ones. Most samples contain significant concentrations of waxy hydrocarbons(C\- 22+ ) with C\- 21- /C\- 22+ ratios between 0.50 to 3.16, and an average value of 1.34. The n\|alkanes in extracts of outcrops and shallow core samples of Upper Proterozoic and Lower Palaeozoic carbonate rocks in the western and southern parts of the North China Basin are of unimodal distributions dominated by n\|alkanes maximizing in the C\- 25 \|C\- 29 range. These extracts have very high concentrations of waxy hydrocarbons with C\- 21- /C\- 22+ ratios all <1.0, ranging from 0 14 to 0 90 and averaging 0.36. All of the extracts have a marked odd/even predominance in the high molecular weight n\|alkane range regardless of whether they are from shallow or deep cores or outcrop samples. Simulation experiments were performed using typical sapropelic\|type kerogens from the immature Sinian Lower Xiamalin Formation carbonate\|rich shales collected at Jixian, Hebei Province, North China Basin, and the contemporary microplanktonic blue\|green algae Spirulina subsala. Results indicate that the unusual distribution of n\|alkanes in the extracts of Upper Proterozoic and Lower Palaeozoic carbonate rocks possibly originated from algae in the source rocks at high levels of maturity and overmaturity.展开更多
基金Supported by National Natural Science Foundation of China (Grant Nos. 40642007 and 40772069)National Basic Research Program of China (Grant No. 2005CB422105)Special Project for Winners of CAS President Award
文摘Hydrogen isotopes of n-alkanes in grasses, tree leaves and reeds from six regions with latitudes of 20° to 39°N in China are measured by GC-TC-IRMS analytical technique in order to understand their hy- drogen isotopic compositions and environmental significance. The results show that a difference in δ D values (from -42.1‰ to -66.6‰) of n-alkanes exists among the same kinds of plants from various re- gions. Hydrogen isotopic compositions of most even carbon numbered n-alkanes in every plant are slightly heavier than that of the odd homologues. A trend toward D-enrichment with increasing chain length of n-alkanes in most plant samples is observed. Mean δ D values of n-alkanes in the studied plants range from -202.6‰ to -130.7‰ and the reed from a salt marsh has the largest value. The mean δ D values of individual n-alkanes among the same kinds of plants from various regions have the characteristics of leaf > reed > grass. The hydrogen isotopic compositions of n-alkanes are apparently distinct among various kinds of plants from the same region and the mean δ D values exhibit a distri- bution of tree leaf > reed > grass. It is observed that the mean δ D values of n-alkanes and δ D values of C27 and C29 n-alkanes in the grasses and tree leaves from these studied regions correlate clearly nega- tively with latitude and positively with temperature, indicating that these values can be used as excel- lent indicators of environment and climate. These results provide important basic data for under- standing the distributional law of hydrogen isotopes of individual n-alkanes and their applied research.
基金This research project was financially supported by the Chinese Academy of Sciences (GrantNo .KZCX2 111)
文摘N\|alkanes in extracts from possible carbonate source rocks of the Lower Ordovician Majiagou Formation in the central gas field of the Shanganning Basin and the Upper Sinian Dengying Formation in the Weiyuan gas field of the Sichuan Basin, are characterized by bimodal distributions with the dominant carbon numbers in the range C\- 17 \|C\- 21 and C\- 25 \|C\- 29 . In most samples, the lower carbon number components are present in greater abundance than the higher carbon number ones. Most samples contain significant concentrations of waxy hydrocarbons(C\- 22+ ) with C\- 21- /C\- 22+ ratios between 0.50 to 3.16, and an average value of 1.34. The n\|alkanes in extracts of outcrops and shallow core samples of Upper Proterozoic and Lower Palaeozoic carbonate rocks in the western and southern parts of the North China Basin are of unimodal distributions dominated by n\|alkanes maximizing in the C\- 25 \|C\- 29 range. These extracts have very high concentrations of waxy hydrocarbons with C\- 21- /C\- 22+ ratios all <1.0, ranging from 0 14 to 0 90 and averaging 0.36. All of the extracts have a marked odd/even predominance in the high molecular weight n\|alkane range regardless of whether they are from shallow or deep cores or outcrop samples. Simulation experiments were performed using typical sapropelic\|type kerogens from the immature Sinian Lower Xiamalin Formation carbonate\|rich shales collected at Jixian, Hebei Province, North China Basin, and the contemporary microplanktonic blue\|green algae Spirulina subsala. Results indicate that the unusual distribution of n\|alkanes in the extracts of Upper Proterozoic and Lower Palaeozoic carbonate rocks possibly originated from algae in the source rocks at high levels of maturity and overmaturity.
