BIOLOGICAL ORIGIN OF TETRACYCLIC DITERPANES, N-ALKANES AND OTHER BIOMARKERS FOUND IN LOWER CARBONIFEROUS GONDWANA COALS (NIGER)

The saturated hydrocarbons of coal samples of the Anou Araren mine (Tim Mersoi basin, Niger Republic) have been studied by GC and GC-MS. Chromatograms revealed rather unusual n-alkane distributions, dominated by compounds in the C20-C23 range and showing a rapid and irregular decrease towards higher molecular weights. These signatures appear to be typical of the Paleozoic Gondwana swamps' flora, unlike typical low-maturity terrestrial organic matter characterized by a dominance of odd carbon number n-alkanes in the C27-C33 range, which could be attributed to angiosperms. The presence of large amounts of polycyclic diterpanes (ent-beyerane, phyllocladanes and kauranes) is unexpected in samples of that age since these compounds are usually thought to be derived from conifers which supposedly had not yet evolved at the time. A more likely explanation is that these diterpanes could be derived from biological precursors of the conifers.