DIAGENESIS OF HIGHER-PLANT TRITERPENES IN EVAPORITIC SEDIMENTS

Several samples from a Tertiary carbonated evaporitic series (Sainte-Cecile, Camargue, France) were investigated. Their analysis revealed a high abundance of new or uncommon hydrocarbons and organic S compounds related to higher plant triterpenes. Several of them, in particular, 12,29-cyclolupa-12,18,20(29)-triene 1, could be positively identified. These triterpenoids are generally absent from non-evaporitic sediments which contain essentially aromatic triterpenoids resulting from microbially mediated aromatization processes starting in ring A (or in ring B when preceded by the loss of ring A). The uncommon transformations undergone by higher plant triterpenes in the highly anoxic sediments from Sainte-Cecile are specific for each series of triterpenes (i.e., oleanane, ursane, lupane) and are probably linked with the rapid disappearance of the functionality located in ring A by reduction or by the incorporation of the triterpenes in S-rich macromolecules by reaction with inorganic S species. These biological markers represent new source parameters which may be quite useful as indicators of terrestrial inputs in evaporitic deposits.