Molecular characterization of fossil palynomorphs by transmission micro-FTIR spectroscopy: Implications for hydrocarbon source evaluation

Abstract

Transmission micro-FTIR spectroscopy has been conducted to elucidate the macromolecular structure of well-preserved fossil palynomorphs including prasinophycean algae, megaspores, chitinozoans, and scolecodonts. Plant and arthropod cuticles which may be present in palynological residues have also been investigated. Important differences are noted among these palynomorph groups regarding the intensities of CHx, CO and aromatic CC absorptions. Tasmanites, Leiosphaeridia, and plant cuticles are characterized by stronger aliphatic CHx stretching (3000–2800cm−1), strong CH3 (1460–1450cm−1), and intense CO group (1710–1700cm−1) absorptions. Aromatic CC stretching (1610–1560cm−1) absorptions are less intense and aromatic CH out of plane (900–750cm−1) absorptions are absent. In contrast, chitinozoans, scolecodonts, and arthropod cuticles show intense aromatic CC stretching (1620–1560cm−1) and aromatic CH out of plane (900–750cm−1) absorptions. Aliphatic CHx stretching (3000–2800cm−1) and CO group (1710–1700cm−1) absorptions are less intense. Megaspores are characterized by stronger aliphatic CHx stretching (3000–2800cm−1), strong CH3 (1460–1450cm−1), and moderate aromatic CC stretching (1610–1560cm−1) and CO group (1710–1700cm−1) absorptions. The CH2/CH3 intensity ratio has been used to assess the relative chain length and degree of branching. The aliphatic components in Tasmanites, Leiosphaeridia, and plant cuticles are longest chained and least branched whereas those in chitinozoans, scolecodonts, and arthropod cuticles are shortest chained and most branched. Megaspores show intermediate CH2/CH3 ratio. The present study demonstrates that palynomorphs differ in functional group chemistry and this spectroscopic technique can be useful to assign biological affinity of enigmatic palynomorphs. Furthermore, micro-FTIR spectroscopy provides insights into the hydrocarbon generating potential of different fossil palynomorph groups.