| Popis: |
This paper summarises different results acquired on the short-term organic cycles (about 30 000 years for one metre thick) from the Kimmeridge Clay Formation (Yorkshire, G.B.). The results, as a whole, support the fundamental interpretation that considers primary production as the main factor influencing organic cyclicity. Other developments specify that in addition to the high organic primary production, the consecutive microbial sulphate reduction, the intensity of which strictly depends on the organic-walled phytoplanktonic production, emphasises the accumulation of the produced hydrocarbon-rich organic matter. This specific accumulation is possible through the selective preservation of bioresistant macro-molecules already present in living organisms and/or through early vulcanisation of lipidic molecules (Boussafir et al.; Gelin et al., this volume). The latter is favoured by the low availibility of reduced iron species compared to the massively produced HS− and consequently by the incorporation of HS− in excess within the organic matter. Here, this interpretation is presented as a mathematical model whose results are compared to measured data (for microcycles having organic carbon contents ranging from about 2 to 9%) and which account for the cyclic variation in both quantity and geochemical quality of organic matter. |
