Organic geochemistry of seasonally flooded rain forest soils: molecular composition and early diagenesis of lipid components

Ten soil samples from the Orinoco River Basin, Venezuela, were studied in order to characterize the molecular distribution of lipids and to determine early diagenetic degradation processes in these environments. The sample set contained six soil samples that were collected directly adjacent to large tropical rivers, and that were, therefore, subject to seasonal flooding. Molecular evidence for the formation of anaerobic microenvironments in these soils during the flooding period was obtained; this was based on the presence of several ring-A-degraded higher plant triterpenoids, products of the anaerobic degradation of 3-oxy-triterpenoids. The molecular distribution of other lipid classes such as n-alkanes, n-alkanols, fatty acids and sterols are also reported here and compared to the organic matter of rivers from the Orinoco Basin.