Chemical relationships of ambers using attenuated total reflectance Fourier transform infrared spectroscopy

Amber is known for its remarkably well-preserved fossils, but the chemical complexity of amber and its history are less well known. Amber is highly variable in both its physical and chemical properties, which are dependent on factors such as the source tree and the diagenetic history. Amber from a given locality therefore has a unique chemical composition. Fourier transform infrared (FTIR) spectroscopy is often used to determine the chemical composition of amber and to provide a fingerprint for amber samples. We used FTIR spectroscopy to analyse samples spanning the time period from the Early Cretaceous to the Oligo-Miocene from 17 localities in the Americas, Europe and Asia. We then used cluster analysis to examine the trends in amber chemistry and to increase our understanding of its formation through time. A detailed analysis of the clustering followed by modelling of the variables of importance suggested that the exocyclic methylene group content and conformation play a major part in explaining the clustering. Other variables, such as the ester and alkyl contents, contribute to identification. Placed in a broader perspective, our study indicates that the dominant factor in clustering is the age of the amber, followed by the locality.