Geochemical characteristics of Upper Cretaceous asphaltenes from bitumen seeps in the Kurdistan region, northern Iraq: Insights from trace metals and Fourier Transform Infrared (FTIR) spectroscopy

Abstract

Fourier Transform Infrared Spectroscopy (FTIR) and trace metal analysis were conducted on the set of 20 solid bitumen samples obtained from two geological formations; upper Campanian – lower Maastrichtian Bekhme Formation and Maastrichtian Aqra Formation. This study analyzes the infrared (IR) spectra of extracted asphaltene samples of both studied formations from two regions in northern Iraq (Bekhme region and Sare Sada region), focusing on key functional groups and molecular vibrations. The spectra reveal consistent peaks for alcohols (OH stretching), alkyl groups (CH₂ and CH₃ bending), and unsaturated bonds (alkenes and alkynes) across all studied samples. Additional peaks indicate the presence of CO stretching (suggesting alcohols and ethers) and metal-carbon stretching, pointing to metal coordination. The analysis highlights the complex structure of asphaltenes, which combine aliphatic chains, aromatic components, and trace metals. Peak intensities reflect slight similarities in composition. The stretching phenomenon can be attributed to the stretching vibration of hydroxyl groups. Comparing the aromatic, aliphatic, and long chains, together with the nickle to vanadium ratio, indicates that the examined samples originated from the same source of organic matter. Furthermore, it is highly probable that all samples from both studied regions originated from a mixed marine-terrestrial-oxic-dysoxic carbonate environment.