CHARACTERIZING BOTANICAL SOURCES OF CRETACEOUS AND PALEOGENE AMBERS FROM ALASKA

Amber, a fossilized resin, stands as a valuable repository of paleoecological information due to the biological inclusions it often preserves within. These lagerstatte provide an unprecedented window into the terrestrial ecology at the time of formation. While much work has focused on the diversity of faunal, floral, and fungal inclusions at known amber localities throughout the world, the botanical origins of the amber resin itself at some sites remains incompletely explored.

In this study, we analyzed the chemical signature of Alaskan ambers from four localities spanning Cretaceous to Paleogene time. We performed Fourier-Transform Infrared (FTIR) Microspectroscopy on multiple samples each from Koalak (Cretaceous), the North Slope (Cretaceous), Chickaloon (Paleocene/Eocene), and California Creek (Oligocene). The analytical technique reveals an amber’s chemical composition by generating an infrared absorbance spectrum, facilitating a comprehensive examination of the molecular bonds within the amber. Amber color variations (milky, light, medium, or dark) within each locality were examined to discern if unique chemical profiles existed among them and to discriminate potential taxonomic sources.

While our findings indicate minimal chemical disparities across and within color variations within a particular amber site, the botanical sources between sites appears to be different. By comparing the spectra of Alaskan amber samples with those of modern conifer resins, we identify several possible amber sources.

The two Cretaceous samples display chemical similarity in 5 of 6 characteristic peak ratios that can be used in conifer amber discrimination. These samples are more similar to each other than they are to the Paleogene ambers which themselves share a different set of peak ratios. Among the peak ratio signatures in the FTIR spectra of the Cretaceous ambers most are shared with modern Pinaceae. The Paleogene ratio data show a less clear affinity to reference conifer families, sharing peak ratios with Pinaceae, Araucariaceae, and Cupressaceae.

This taxonomic characterization of each amber locality contributes essential insights into the paleobiological community in the fossil forest, providing further context for biological inclusions and the paleoclimate of the respective sites.