In this study, we analyzed the molecular and stable carbon isotopic composition (δ¹³C) of pollen and spores (sporomorphs) that underwent chemical treatments that simulate diagenesis during fossilization. We show that the successive removal of sugars and lipids results in the depletion  of ¹³C in the residual sporomorph, leaving rich aromatic compounds. This residual aromatic-rich structure likely represents diagenetically resistant sporopollenin, implying that diagenesis results in the depletion of ¹³C in pollen.