From Triassic to moderinity: Raman spectroscopy for differentiation of fossil resins age by age

The results of studies of fossil resins of different geological ages and geographic origins are presented. A new method of spectral analysis for differentiation of fossil resins by age from the Triassic period to Modernity is developed. Raman spectra of fossil resin of the late Triassic period are obtained for the first time. The possibility of using the method for differentiation of resin from the late Triassic period to the Moderiny is shown. The studies were carried out using Raman spectroscopy. The spectra were obtained using a Renishaw Virsa spectrometer (UK) with an excitation wavelength of 785 nm and a Raport 1064 portable Raman spectrometer (Russia) with an excitation wavelength of 1064 nm. The range of the studied spectra was 400–3200 cm–1. 27 samples of fossil resins from Eurasia, Africa, America, and Australia were studied. Based on the results of studies of fossil resin samples from different geographic locations and ages, differences were found in the values of the ratio of vibrational modes of the valence skeletal vibrations (ν(C=C)) and the deformation vibration of the CH2 bond (σ(CH2)) in the wavenumber ranges of 1650–1600 cm–1 and 1440–1460 cm–1 in fossil resins aged from late Triassic to Modernity. It was found that with increasing age of amber, the degree of their polymerization decreases. For amber of age Triassic, the absence of ν(CH2,CH3) signals in the high-frequency region for the labdanum skeleton of the resin structure was shown, which indicates an extremely low degree of polymerization of it structure. The obtained results potentially allow using the Raman scattering method for additional differentiation of the age of fossil resins, in case of limitation of the application of the radiocarbon analysis method by age (40,000 years). The advantage of the proposed method is the possibility of rapid, with minimal sample preparation, determination of the age of fossil resin of ages Triassic, Cretaceous, Modernity. At the same time, the accuracy of differentiation of the ages of fossil resins in the age range from Cretaceous to Oligocene to Middle Miocene still remains low, which requires additional research. Also, at the current stage of development, the method does not take into account the influence of environmental conditions: climate, fossilization conditions under which the oleoresin was transformed into resin.