The Palaeozoic Terrestrialisation

Abstract: The aliphatic and aromatic biomarker content from terrestrial and marine sediments of Late Ordovician to Early Carboniferous age have been related to their palynomorph assemblages (e.g. acritarchs, prasinophytes, chitinozoans, cryptospores, trilete spores and megaspores) in order to contribute to the knowledge of land plant evolution during the Palaeozoic. This investigation is therefore focused on the land-derived biomarkers and their attributions to specific kind of plants. The biomarker record of middle Silurian – lower Devonian sediments from southern Tunisia, Ghadamis Basin (Gondwana) reveals the presence of retene, cadalene, kaurane, norabietane, tetrahydroretene, C19 isohexylalkylnaphthalene and simonellite. The early Palaeozoic bryophytes and tracheophytes (e.g. Cooksonia, lycophytes and zosterophylls) may therefore be considered as potential precursors for retene and its related molecular compounds in sediments of Middle Silurian to Early Devonian age. In contrast, the Early Carboniferous flora formed by arborescent lycopods, sphenopsids and pteridosperms have been suggested here as a possible terrestrial source for phyllocladane, abietane, ent-beyerane, bisnorsimonellite, diaromatic totarane, diaromatic sempervirane and 2-methylretene in the Lower Carboniferous (Viséan) coal deposits at Dunbar (East Lothian, Scotland). Among the other biomarkers detected in our samples, ionene, alkyldibenzofurans, perylene and combustion-derived polycyclic aromatic hydrocarbons (PAHs) indicate pollen, lichens, fungi and vegetation fire contributions, respectively. Most of the biomarkers identified here had been so far generally associated to conifers, though conifers only evolved during Late carboniferous. These compounds therefore are also characteristic of early land plants.