A multiproxy kinetic–isotopic framework for constraining the maturity of Baltic Amber

Baltic amber (succinite, sensu stricto) represents the most abundant and chemically complex fossil resin derived from Eocene conifers, but its authentication is often challenged by the presence of composite materials and subfossil resins. Here, we show that integrating thermogravimetric, kinetic, elemental, and carbon isotopic data provides a quantitative framework to constrain amber maturity, thereby allowing maturity to be distinguished from bulk chemical composition. Structural stability is assessed using the maximum decomposition temperature (Tmax) and the glass transition temperature (Tg), the latter reflecting cross-link density, whereas kinetic maturity is quantified by the Normalized Maturity Index (MInorm), which tracks diagenetic progression through activation energy. Our results demonstrate a clear decoupling between chemical stoichiometry and structural evolution. While elemental composition reaches a plateau early in the resin's history, kinetic and thermal parameters continue to evolve, providing a highly sensitive "geological clock". delta 13C values show moderate variability (-23.5%o to-20.9%o), consistent with a C3 resin-producing plants; however, highly mature samples cluster tightly around-23.0%o, indicating isotopic homogenization at advanced stages of maturation. This multiproxy framework enables identification of lower-maturity samples that exhibit reduced energy barriers and structural rigidity despite high organic purity. The findings support the assignment of the analyzed samples to the Baltic succinite lineage, representing various diagenetic stages within a chemically comparable fossil-resin system rather than clearly distinct source materials. This approach provides a robust methodology for identifying authentic succinite and precisely evaluating the maturation state of fossil resins.