Influence of paleoenvironmental conditions on distribution and relative abundance of saturated and aromatic hydrocarbons in sediments from the NW part of the Toplica basin, Serbia

The investigation of the relationship between paleoenvironmental conditions and distribution and relative abundance of specific saturated and aromatic hydrocarbons was the main objective of this study, thus marking the parameters, which were most sensitive to environmental changes. Insights on the type, generative potential, and maturity of organic matter (OM), as well as paleoclimate conditions, along with the reconstruction of depositional settings of the northwest part of the Toplica basin (Serbia), were provided. Organic petrographic, palynofacies, organic geochemical, mineralogical, and XRF analyses were carried out to investigate 40 sediment samples of the Prebreza and Čučale sedimentary units. Investigated samples were deposited in the saline and anoxic environment, under semi-arid to semi-humid/humid climate conditions, along with the constant inflow of volcanoclastic material. The predominance of δ-methyltrimethyltridecil chroman (δ-MTTC) within euxinic portions of the stratified water column was associated with an increase in salinity, which was noticed for sediments of the Prebreza unit. Sediments from this stratigraphic unit showed a higher contribution of algae precursor, whereas sediments of the Čučale unit suggested higher participation of microbiologically reworked OM. Most of the samples contained oil-prone kerogen type II. Maturity of the OM for sediments of the Prebreza unit ranged from immature to early-mature, while for samples of the Čučale unit varied from early-mature to mature stages. Distribution of hopane biomarkers typical for crude oil indicated that depth of 1 km was a boundary for the genesis of thermodynamic, more stable compounds. A significant portion of semifusinite was correlated with the paleofire event, which affected the distribution of n-alkanes. The high production of hydrocarbons was related to volcanic activity. Parameters, which proved to be highly susceptible at the stratigraphic boundary between the Prebreza and Čučale units, were C-value, S/H, α-MTTC, δ-MTTC, β-/γ-MTTC, and (1,3- + 1,6-)/(1,4 + 1,5-DMC), respectively