Molecular composition and chemosystematic aspects of Cretaceous amber from the Amazonas, Araripe and Recôncavo basins, Brazil

Abstract

Amber occurrences in Brazil are rare. In this regard, the molecular composition of three such fossil resin samples from Brazilian Cretaceous sedimentary basins has been analyzed to determine the botanical origin of the resins. The samples were collected from the Amazonas (Alter do Chão Formation), Araripe (Santana Formation, Crato Member) and Recôncavo (Maracangalha Formation, Caruaçu Member) basins. The mono-, sesqui- and diterpenoids in the extracts were used as chemosystematic markers when compared with terpenoids in extant conifers. The compounds were mainly diterpenoids and their degradation products from the labdane, podocarpane, pimarane and isopimarane classes, in addition to paraffins, methoxyphenols and carboxylic acids. Tetracyclic diterpenoids such as phyllocladane, kaurenol and kauranol were also present. The biomarker compositions are certainly typical for conifers and, given the absence of triterpenoids and diterpenoids such as ozic acid, angiosperms can be excluded as a botanical source. The absence of phenolic diterpenoids (ferruginol, totarol) and their derivatives excludes podocarpaceous affinities for the ambers from the Amazonas and Araripe basins. The fossil records of the embedding sediments (e.g. Araucariaceae pollen and leaves) support the proposal of an Araucariacae origin for these ambers, but Cupressaceae and Cheirolepidiaceae cannot be excluded. On the other hand, the presence of phyllocladane and kaurane derivatives is evidence for Araucariaceae or Podocarpaceae origins for the amber from the Recôncavo basin, but Cupressaceae cannot be excluded.