An Integrated Assessment\nof Different Depositional\nPaleoenvironment Using Nitrogen Markers and Biomarkers after Chromatographic\nMethods Optimization

In this study, chromatographic methods were first optimized\nto\nensure the robustness of the identification and quantification of\nnitrogen markers and biomarkers. Then, the optimal conditions were\napplied to 14 crude oil samples deposited in distinct paleoenvironments\nfrom Brazil, Venezuela, and Colombia to perform an integrated geochemical\nassessment. Analytical standards, certified reference material, and\nretention indices were used to confirm the identification of biomarkers\nand N-markers. The results of geochemical interpretations based on\nunresolved complex mixture (UCM), pristane/<i>n</i>-heptadecane\n(Pr/<i>n</i>-C<sub>17</sub>), and phytane/<i>n</i>-octadecane (Ph/<i>n</i>-C<sub>18</sub>) ratios and concentrations\nof carbazole and benzo[<i>b</i>]carbazole indicated that\nall oils are not biodegraded. The Pr/<i>n</i>-C<sub>17</sub>, Ph/<i>n</i>-C<sub>18</sub>, and Pr/Ph ratios showed that\nthe organic matter that generated the oils from Brazil and Venezuela\nwas deposited under anoxic conditions and Colombia oil reached dysoxic\nconditions. Some samples present a greater abundance of low- to high-molecular-mass <i>n</i>-alkanes, indicating freshwater lakes’ organic matter\n(Brazil oils). In contrast, other samples showed a lower abundance\nof high-mass <i>n</i>-alkanes, suggesting marine and saline\nlake origins (Colombia and Venezuela oils). The tricyclic/hopane ratio,\nthe ternary diagrams using 1-methylcarbazole, 2-methylcarbazole, and\n4-methylcarbazole, and regular steranes C<sub>27</sub>, C<sub>28</sub>, and C<sub>29</sub> suggested a contribution of algae to the formation\nof kerogen present in the source rocks of all petroleum samples. The\nhigh concentrations of carbazole in oils generated by marine organic\nmatter confirm the more positive δ<sup>13</sup>C values compared\nwith those generated by lake organic matter (Brazil samples). The\nuse of chemometric tools as principal component analysis exhibited\na grouping of samples according to the depositional environment using\ncarbazole and tricyclic/hopane ratio. The integration of all parameters\nanalyzed provides a guide for refined interpretations and differentiation\nof oils according to their depositional environments.