Abstract <p>For the first time, transformation of the molecular composition (based on infrared spectroscopy data) and thermal properties of fossil resins from the Taymyr Peninsula over geological time (from Albian to Santonian) were studied. This is important for understanding the processes of their formation and alteration. Fossil resins of this region are mainly brittle varieties (retinites). However, gedanite can also occur together with them. It was established for the first time that, in addition to the previously known finds of gedanite in the Hetian and Dolgan formations, gedanite can also occur in the Ognev and Begichev formations, suggesting a more wide distribution of gedanite in northern Eurasia than previously thought and pointing to general formation conditions of this resin type. It is shown that their molecular composition and thermal behavior change with time, but not significantly. Mechanisms of these alterations are different for gedanite and retinite.</p>