Amber from the Lower Cretaceous of Lugar d’Além Formation, Lusitanian Basin, Western Portugal: Chemical Composition and Botanical Source

The first comprehensive study about of amber from the Lower Cretaceous of the Lusitanian Basin, in the Estremadura region of western Portugal, is here reported. The amber was recovered as isolated clasts in the Portela da Vila outcrop section, near the small villages of Ramalhal and Ameal, from sedimentary deposits belonging to the Lugar d’Além Formation considered to be of Hauterivian age. The chemical composition of amber clasts was examined in order to infer their botanical source via biomarker analysis. GC–MS and GC×GC–TOFMS showed a strong predominance of abietane-type diterpenoids, including compounds such as amberene, ferruginol (phenolic abietane), kaurane and the derivative of clerodane. The dominance of abietane diterpenoids along with these specific biomarkers is consistent with resin exudation by Araucariaceae/Cheirolepidiaceae conifers, as supported by previous chemotaxonomic studies of Cretaceous amber. Palynological studies of the same sedimentary rock samples highlighted a pollen–spore assemblage characterized by low diversity and number of specimens, and dominated by conifer pollen assigned to the genera Classopollis, Araucariacites and coniferous bisaccate pollen, with relative occurrences of fern spores. The combined geochemical and palynological studies strongly support a source related to conifer plants for the amber here reported.