Origin Of CH Research Articles

Isotopic signatures of CH 4 and higher hydrocarbon gases from Precambrian Shield sites: A model for abiogenic polymerization of hydrocarbons

Previous studies of methane and higher hydrocarbon gases in Precambrian Shield rocks in Canada and the Witwatersrand Basin of South Africa identified two major gas types. Paleometeoric waters were dominated by hydrocarbon gases with compositional and isotopic characteristics consistent with production by methanogens utilizing the CO 2 reduction pathway. In contrast the deepest, most saline fracture waters contained gases that did not resemble the products of microbial methanogenesis and were dominated by both high concentrations of H 2 gas, and CH 4 and higher hydrocarbon gases with isotopic signatures attributed to abiogenic processes of water–rock reaction in these high rock/water ratio, hydrogeologically-isolated fracture waters. Based on new data obtained for the higher hydrocarbon gases in particular, a model is proposed to account for carbon isotope variation between CH 4 and the higher hydrocarbon gases (specifically ethane, propane, butane, and pentane) consistent with abiogenic polymerization. Values of δ 13C for CH 4 and the higher hydrocarbon gases predicted by the model are shown to match proposed abiogenic hydrocarbon gas end-members identified at five field sites (two in Canada and three in South Africa) suggesting that the carbon isotope patterns between the hydrocarbon homologs reflect the reaction mechanism. In addition, the δ 2H isotope data for these gases are shown to be out of isotopic equilibrium, suggesting the consistent apparent fractionation observed between the hydrocarbon homologs may also reflect reaction mechanisms involved in the formation of the gases. Recent experimental and field studies of proposed abiogenic hydrocarbons such as those found at mid-ocean spreading centers and off-axis hydrothermal fields such as Lost City have begun to focus not only on the origin of CH 4, but on the compositional and isotopic information contained in the higher hydrocarbon gases. The model explored in this paper suggests that while the extent of fractionation in the first step in the hydrocarbon synthesis reaction chain may vary as a function of different reaction parameters, δ 13C values for the higher hydrocarbon gases may be predicted by a simple mass balance model from the δ 13C values of the lower molecular weight precursors, consistent with abiogenic polymerization. Integration of isotopic data for the higher hydrocarbon gases in addition to CH 4 may be critical for delineation of the origin of the hydrocarbons and investigation of formation mechanisms.

The role of Fischer–Tropsch catalysis in the origin of methane-rich Titan

Fischer–Tropsch catalysis, which converts CO and H 2 into CH 4 on the surface of iron catalyst, has been proposed to produce the CH 4 on Titan during its formation process in a circum-planetary subnebula. However, Fischer–Tropsch reaction rate under the conditions of subnebula have not been measured quantitatively yet. In this study, we conduct laboratory experiments to determine CH 4 formation rate and also conduct theoretical calculation of clathrate formation to clarify the significance of Fischer–Tropsch catalysis in a subnebula. Our experimental result indicates that the range of conditions where Fischer–Tropsch catalysis proceeds efficiently is narrow ( T ∼ 500 – 600 K ) in a subnebula because the catalysts are poisoned at temperatures above 600 K under the condition of subnebula (i.e., H 2/CO = 1000). This suggests that an entire subnebula may not become rich in CH 4 but rather that only limited region of a subnebula may enriched in CH 4 (i.e., CH 4-rich band formation). Our experimental result also suggests that both CO and CO 2 are converted into CH 4 within time significantly shorter than the lifetime of the solar nebula at the optimal temperatures around 550 K. The calculation result of clathration shows that CO 2-rich satellitesimals are formed in the catalytically inactive outer region of subnebula. In the catalytically active inner region, CH 4-rich satellitesimals are formed. The resulting CH 4-rich satellitesimals formed in this region play an important role in the origin of CH 4 on Titan. When our experimental data are applied to a high-pressure model for subnebula evolution, it would predict that there should be CO 2 underneath the Iapetus subsurface and no thick CO 2 ice layer on Titan's icy crust. Such surface and subsurface composition, which may be observed by Cassini–Huygens mission, would provide crucial information on the origin of icy satellites.

Affinities, origin and adaptive features of the Australian Desert GobyChlamydogobius eremius(Zietz, 1896) (Teleostei: Gobiidae)

The Desert Goby Chlamydogobius eremius (Zietz, 1896) is a gobiid teleost fish endemic to the Central Australian Basin, occurring mostly in artesian springs. Generic features for Chlamydogobius Whitley are supplied with emphasis on the modified head lateral-line system and on osteology. Comparisons with other Indo-Pacific genera suggest closest affinity with Mugilogobius Smitt, within a monophyletic grouping which also includes Weberogobius Koumans, Redigobius Herre, Pseudogobius Aurich, Brachygobius Bleeker, Hemigobius Bleeker, and Pandaka Herre. The origin of Ch. eremius is considered in the light of the Tertiary and Quaternary climatic history of the Central Australian Basin. The adaptiveness of certain morphological and life-history features found in Ch. eremius, such as elongate gut, black peritoneum, short pelvic disc, and large egg-size, is also discussed in relation to present habitat.

Core helium flash and the origin of CH and carbon stars

Core helium flash and the origin of CH and carbon stars