Sulphur and oxygen sequestration of n-C37 and n-C38 unsaturated ketones in an immature kerogen and the release of their carbon skeletons during early stages of thermal maturation

M.P. Koopmans; C. Schaeffer-Reiss; J. W. De Leeuw; M. D. Lewan; J.R. Maxwell; P. Schaeffer; Damste J.S. Sinninghe

doi:10.1016/s0016-7037(97)00099-9

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Sulphur and oxygen sequestration of n-C37 and n-C38 unsaturated ketones in an immature kerogen and the release of their carbon skeletons during early stages of thermal maturation

M.P. Koopmans·C. Schaeffer-Reiss·J. W. De Leeuw·M. D. Lewan·J.R. Maxwell·P. Schaeffer·Damste J.S. Sinninghe

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Abstract

Sedimentary rock from the Gessoso-solfifera Formation (Messinian) in the Vena del Gesso Basin (northern Italy) containing immature ( R o = 0.25%) S-rich organic matter was artificially matured by hydrous pyrolysis at temperatures from 160 to 330°C for 72 h to study the diagenetic fate of n -C 37 and n -C 38 di- and tri-unsaturated methyl and ethyl ketones (alkenones) biosynthesised by several prymnesiophyte algae. During early diagenesis, the alkenones are incorporated into the kerogen by both sulphur and oxygen cross-linking as indicated by chemical degradation experiments with the kerogen of the unheated sample. Heating at temperatures between 160 and 260°C, which still represents early stages of thermal maturation, produces large amounts (up to 1 mg/g TOC) of S-bound, O-bound, and both S- and O-bound n -C 37 and n -C 38 skeletons, saturated n -C 37 and n -C38 methyl, ethyl, and mid-chain ketones, C 37 and C 38 mid-chain 2,5-di- n -alkylthiophenes, C 37 and C 38 1,2-di- n -alkylbenzenes, and C 37 and C 38 n -alkanes. With increasing thermal maturation, three forms of the n -C 37 and n -C 38 skeletons are relatively stable (saturated hydrocarbons, 1,2-di- n -alkylbenzenes and saturated ketones), whereas the S- and O-bound skeletons are relatively labile. These results suggest that in natural situations saturated ketones with an n -C 37 and n -C 38 skeleton can be expected as well as the corresponding hydrocarbons.

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Source-reported bounding extent: 44.137701903506894° to 44.45372242145541° latitude; 11.43641391587036° to 11.882839029932796° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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M.P. Koopmans, C. Schaeffer-Reiss, J. W. De Leeuw, M. D. Lewan, J.R. Maxwell, P. Schaeffer, Damste J.S. Sinninghe. 1997. Sulphur and oxygen sequestration of n-C37 and n-C38 unsaturated ketones in an immature kerogen and the release of their carbon skeletons during early stages of thermal maturation. https://doi.org/10.1016/s0016-7037(97)00099-9

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