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Fingerprinting of Cretaceous higher plant resins by infrared spectroscopy and gas chromatography coupled to mass spectrometry.

Ambers from Peñacerrada (Basque Country, North Spain) have been analysed by IR spectroscopy and GC-MS in order to study the polymeric and solvent-soluble GC-amenable fractions, respectively. All samples showed branched monoalkybenzenes, bicyclic sesquiterpenoids and tricyclic diterpenoids related to pimaric acids precursors, suggesting a paleobotanic origin from araucarian species. Molecules containing oxygenated polar functionalities were not found, which is in agreement with the Cretaceous origin of the samples and in good correspondence with the IR spectra and with the low oxygen content estimated from elemental composition analysis. In addition, no IR bands for exocyclic double bonds and very few GC-amenable monounsaturated molecules were found, which provides further evidence of the loss of olefinic groups. These features show that the age-dependent loss of oxygenated and olefinic functions is a general process affecting the whole amber structure, not only the solvent soluble fraction.