PETROLEUM BIOMARKERS AS INDICATORS OF OIL ORIGIN AND MATURITY IN THE SOUTH-EASTERN PRECASPIAN BASIN

This study investigates the origin of oil from the south-eastern Precaspian Basin through biomarker analysis of five crude oil samples using gas chromatography-mass spectrometry (GC-MS). Biomarkers serve as molecular fingerprints to elucidate hydrocarbon origin, source rock characteristics, and thermal history. The analyzed samples revealed: a marine depositional environment (C₂₆/C₂₅ terpane ratios = 0.59–0.79), carbonate-dominated source rocks (C₂₉/C₃₀ hopane ratios = 4.78–5.55), sourcing from Paleozoic (Permo-Carboniferous) strata (C₂₈/C₂₉ sterane ratios = 0.44–0.57), and peak oil window – late maturation according to Ts/T, C 29 Ts/ C 29 Tm, C₂₉ sterane isomerization ratios. These findings demonstrate the basin's complex hydrocarbon generation history, with biomarker distributions indicating: marine organic matter input under anoxic conditions, carbonate-evaporitic source facies and thermal equilibrium consistent with primary oil generation. The results provide valuable insights for exploration strategies in similar frontier basins, with implications for reducing exploration risk and optimizing resource development. Future studies should combine these geochemical data with structural and stratigraphic analyses to refine migration models.