Authors / CoAuthors
Sandison, C.M. | Alexander, R. | Kagi, R.I. | Boreham, C.J.
Abstract
The polar lipid and macromolecular compositions of three samples from the marine-influenced Heartbreak Ridge lignite deposit (Bremer Basin, Western Australia) were investigated for chemical changes wrought during early diagenesis. The results of Rock-Eval, microscope Fourier transform infrared spectroscopic and thermal extraction/pyrolysis-gas chromatography-mass spectrometric analyses indicate that the composition of the lignite and its extract are typical of immature Type III organic matter, and thus contain a high proportion of aromatic and oxygen-containing functionalities. Down-seam variation in the proportions of these functionalities, together with changes in the carbon preference index (CPI) of the pyrolysate n-alkenes, and the wax indices of straight chain n-alkyl pyrolysis products, is consistent with more pronounced degradation of the lowermost lignite horizon. This profile is also reflected in the diagenetic products of higher plant triterpenoids, identified in the lignite extracts by gas chromatography-mass spectrometry. The extent of aromatisation, demethylation, ring opening and defunctionalistion is recorded through this depth profile by the compositions of the free, sulfurised and oxygenated higher plant triterpenoids. In contrast, degradation of the extended hopanoids had come to a hiatus by the onset of sulfurisation in the Heartbreak Ridge lignite. Oxygen-containing lipids are implicated as the primary source of the sulfurised hydrocarbons, although not necessarily via direct sulfurisation of the identified oxygenated lipids, but through the formation of more reactive intermediate species. These results suggest that the onset of marine incursion and associated sulfur fixation inhibits, and through preservation illuminates, the typical biogeochemical transformation of lipids and biopolymers in coal-forming environments.
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nonGeographicDataset
eCat Id
40295
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- External PublicationScientific Journal Paper
- ( Theme )
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- organic geochemistry
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
Publication Date
2003-01-01T00:00:00
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geoscientificInformation
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34, 1081-1102
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