Evidence for the rapid incorporation of hopanoids into kerogen

• Published in: Geochimica et cosmochimica acta Vol. 67; no. 7; pp. 1383 - 1394
• Main Authors: Farrimond, Paul, Love, Gordon D, Bishop, Andrew N, Innes, Helen E, Watson, Diane F, Snape, Colin E
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2003
• Subjects: Freshwater; Marine; ANE, Norway, Vest-Agder, Framvaren Fjord; British Isles, England, English Lake District, Priest Pot L
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/S0016-7037(02)01287-5

Hopanoids bound into the insoluble organic matter (kerogen) of Recent sediments from a freshwater lake (Priest Pot) and an anoxic sulphidic fjord (Framvaren) were released by hydropyrolysis and examined by gas chromatography-mass spectrometry. Bound hopanoids are present in high concentration (190–1400 μg/g TOC) and represent 22 to 86% of the total analysable hopanoids (i.e., bound and solvent-soluble), this proportion increasing with depth in Framvaren Fjord. The hopanes generated by hydropyrolysis contain higher amounts of the C 35, C 32, and C 30 homologues, reflecting the carbon number distribution of the bound hopanoids and indicating that both biohopanoids (C 30 and C 35) and their diagenetic products (dominated by C 32) are incorporated into the kerogen on a timescale of only 0 to 350 years. Sequential (multiple temperature) hydropyrolysis experiments gave an indication of the relative strengths of bonds being cleaved in association with hopane generation: The hopanoids of a sediment from Priest Pot are almost entirely bound by strong covalent bonds, interpreted to be mainly ether linkages, whilst a Framvaren sediment contains hopanoids that are bound by a mixture of weak di-/polysulphide linkages and stronger ether bonds. Labelling with deuterium indicated that the strong covalent linkages dominate, even for the Framvaren sediment.