The first discovery of amber resin in Lichi Mélange, Eastern Taiwan

Abstract

Amber is fossilized tree resin produced by the metabolism of vascular plants that has experienced various geological processes, including burial, compression, and heating. Therefore, most of the previously reported amber pieces were unearthed from sedimentary rocks. The record of amber in tectonic active regions, e.g., Taiwan, is extremely poor and has not been scientifically certified, leading to a poor understanding of the history of prehistoric flora in this region. This study reports a 1-cm yellow-brown amorphous resin interspersed in sandstone blocks in the Lichi Mélange at the southernmost tip of the Coastal Range in eastern Taiwan, representing the first official record of amber from the mélange unit and as well as in Taiwan. The results, in addition to the affirmation of the amber, show that the amber is composed of sesquiterpenes and triterpenoids, indicating a possible origin of dipterocarp trees that are absent in the paleobotanic record and modern flora in Taiwan. Furthermore, infrared spectra analysis shows its compositional similarity to the amber from Sumatra, Indonesia, which boasts modern dipterocarp forests. Petrographic analysis of the surrounding sandstone suggests that the amber was deposited into the continental margin and allocated to Taiwan through the arc-continental collision in ∼6–7 Ma. In summary, this study represents the first report of amber unearthed in the mélange unit and Taiwan. It shows that amber is a durable and reliable information carrier in accordance with biogeographic and tectonic evidence.