Fluorescence spectrosocopy of amber of different botanic origins

Resin is one of the few plant chemical defenses which commonly fossilizes, resulting in amber. There are many different approaches to chemically characterize amber, which can provide information about the original chemical composition of the resin, the fossilization processes that turned the resin into amber, and its botanic origin. Here we apply two-photon fluorescence micro-spectroscopy to a variety of amber samples – Cretaceous amber from Lebanon, Spain, and France, Eocene Baltic amber, and Pleistocene Araucariaceae copal from New Zealand – to characterize and quantify their fluorescence properties and determine if this provides information about their botanic origin. The fluorescence emission spectra of the amber samples can each be modeled as a linear mixture of four Gaussian components, with the mean emission wavelength of each component varying between the samples. These differences in Gaussian means allowed us to separate the samples into four groups. Based on previous analyses, both geochemical and paleobotanical, of amber from the same localities as our samples, we assigned each sample to a likely botanic origin. Based on this, the four groups identified in our fluorescence spectroscopy analysis generally correspond to ambers of different botanic origin. Group 1 is Cupressaceae amber. Groups 2 and 3 are likely a mix of Araucariaceae or Cheirolepidiaceae amber, with group 2 dominated by Araucariaceae amber and group 3 dominated by Cheirolepidiaceae amber. Group 4 is Baltic amber, with uncertain affinities within conifers, but likely not Cupressaceae, Araucariaceae, or Cheirolepidiaceae. These results demonstrate that fluorescence spectroscopy is a novel and useful approach for characterizing amber, and, in particular, may be useful for determining its botanic origin.