|
|||||
|
|
Release of bound aromatic hydrocarbons from late Archean and Mesoproterozoic kerogens via hydropyrolysis |
|
| Authors: | Jochen J Brocks Roger E Summons |
| Institution: | 1 Department of Organismic and Evolutionary Biology and Department of Planetary and Earth Sciences, Harvard University, Cambridge, MA 02138, USA 2 School of Civil Engineering and Geosciences, Drummond Building, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, United Kingdom 3 School of Chemical, Environmental and Mining Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom 4 Geoscience Australia, GPO Box 378, Canberra ACT 2601, Australia 5 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA 6 Department of Earth and Space Sciences and Astrobiology Program, University of Washington, Seattle, WA 98195-1310, USA |
| Abstract: | Hydrogen-lean kerogens (atomic H/C<0.4) isolated from the 2.5-billion-year-old (Ga) Mt. McRae Shale, Hamersley Group, at Tom Price, Western Australia, were studied via hydropyrolysis, a continuous-flow technique that degrades organic matter in a stream of high-pressure hydrogen assisted by a dispersed Mo catalyst. The hydropyrolysates yielded predominantly phenanthrene and pyrene, and higher polyaromatic hydrocarbons and alkylated homologues were generated in low relative concentrations. Saturated hydrocarbons were not detected. The molecular and carbon isotopic compositions of the hydropyrolysates are very similar to aromatic hydrocarbons obtained by solvent extraction of the host rocks. Because molecular structures covalently attached to kerogen are unaffected by contamination, this indicates that both the bound and extractable aromatic fractions are syngenetic with the host rocks. Therefore, the results of the hydropyrolysis experiments provide compelling evidence for preserved bitumen of Archean age. The very high proportion of nonalkylated polyaromatic hydrocarbons in the hydropyrolysates is consistent with hydrothermal dehydrogenation of the kerogen, and a marked concentration difference of pyrene in rock extracts and hydropyrolysates might be explained by hydrothermal redistribution of the bitumen. The kerogen and bitumen composition is therefore consistent with models suggesting a hydrothermal origin for the giant iron ore deposits at Mt. Tom Price. Comparison of the Archean samples with hydropyrolysates from immature Mesoproterozoic kerogens from the Roper Group, McArthur Basin, Northern Territory, and with pyrolysis experiments on Proterozoic kerogens in the literature suggests that Precambrian kerogens are frequently highly aromatic and lipid-poor regardless of their degree of thermal preservation. |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ | |