ISSN:
1573-5117
Keywords:
Archaea
;
bacteria
;
biomarkers
;
carboxyl acids
;
hypersalinity
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract In this paper, we investigate the molecular characteristics of recent sediment from the Ejinur salt lake (northern China) and eight Tertiary (Eocene) core samples from Qianjiang Formation (Eq1-4) of Jianghan basin, central eastern China, focussing on the distributions and abundances of carboxylic acid isolated from extractable organic matter. n-Alkanoic acids in sediments from both study areas (Ejinur and Jianghan) show a pronounced even over odd predominance (EOP) and a bimodel distribution. In the lower molecular weight range C16 and C_18 components are prominent with the former dominant. For higher homologues (≥ C20), docosanoic (C22) and tetracosanoic (C24) acids dominant the n-alkanoic acid homologues for the Jianghan and Ejinur samples, respectively. Alkanoic acids with an isoprenoid skeleton are more abundant in Jianghan, including C20, C21, C24, C_25 and C30 homologues, with a C25 component (3, 7, 11, 15, 19-pentamethyleicosanoic acid) most pronounced in the lower part of the Qianjiang Fm. The carbon skeletons of these isoprenoid acids are identical to those of isoprenoid hydrocarbons previously recognized in source rocks and petroleums from Jianghan, and attributed to Archaea (formally called archaebacteria; e.g. halophiles, methanogens). The similarity in the distributions of isoprenoid alkanoic acids and alkanes suggests that these isoprenoid acids must derive from comparable biological sources, although they appear to be formed geochemically from biosynthetic precursors (e.g. alkanes, alkenes, alkanols or alkenols). The possibility that these acids are formed as oxidation artifacts from alkanes can be discounted because of the dissimilarity between the distributions of n-alkanoic acids and n-alkanes. Iso and anteiso branched carboxylic acids are prevalent in both the Ejinur sample and the upper portion of the Qiangiang Fm (Eq1-3). They derive from bacteria, perhaps sulfate reducing bacteria, and their abundances may aid assessment of the importance of bacterial contributions of organic matter in different sedimentary environments. The presence of hopanoid acids and a 3-carboxy steroidal acid further attest to contributions from bacterial and eukaryotic sources, respectively. The occurrence of carboxylic acids in the Jianghan samples confirms the potential for these compounds to survive in ancient sediments and source rocks, notably in hypersaline settings.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1003275523777
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