C-S-FE GEOCHEMISTRY OF SOME MODERN AND ANCIENT ANOXIC MARINE MUDS ANDMUDSTONES

Citation
Ac. Aplin et Jhs. Macquaker, C-S-FE GEOCHEMISTRY OF SOME MODERN AND ANCIENT ANOXIC MARINE MUDS ANDMUDSTONES, Philosophical transactions-Royal Society of London. Physical sciences and engineering, 344(1670), 1993, pp. 89-100
Citations number
28
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Multidisciplinary Sciences
ISSN journal
0962-8428
Volume
344
Issue
1670
Year of publication
1993
Pages
89 - 100
Database
ISI
SICI code
0962-8428(1993)344:1670<89:CGOSMA>2.0.ZU;2-K
Abstract
Most sedimentary C, S and Fe occurs in marine muds and is originally p resent as an unstable mixture of dissolved sulphate, organic matter an d detrital Fe minerals. During early diagenesis, key reactants are eit her destroyed (reduction of Fe(III) and SO42- to form pyrite), created (organically bound sulphur (OBS)) or preserved (Fe-bearing silicates) . Pyrite formation is commonly limited not by sulphide availability bu t by the rate at which detrital Fe minerals react with sulphide. At lo w temperatures, detrital Fe(II) and Fe(III)-bearing clay minerals reac t very slowly with sulphide and are buried intact. The uptake of sulph ur into organic matter is not, as commonly assumed, sulphide-limited. We believe that polysulphides react rapidly with organic matter and th at the availability of reactive polysulphides may also influence the s ulphur content of kerogen. Polysulphide formation is favoured at stabl e aerobic-anaerobic interfaces and sediments deposited under weakly ox ygenated bottom waters are most likely to contain sulphur-rich kerogen . Deep burial (greater than 70-degrees-C) C-S-Fe diagenesis is charact erized by the loss and partial reduction of Fe(III) from smectitic and illitic clays and the conversion of limited amounts of OBS to lower m olecular mass S compounds. Pyrite formation is volumetrically insignif icant. More than 90% Of OBS remains within organic-rich mudrocks durin g petroleum generation and expulsion, preserving a sulphur-enriched re sidual kerogen. The extent to which OBS is eventually converted to H2S , and at what level of thermal maturity, is unclear. If, as may be lik ely, much of the sulphur in residual kerogen is thiophenic, it will be stable to at least 200-degrees-C.