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8247589 
Journal Article 
Geochemical appraisal of Stefanets Member (Etropole Formation) from the eastern part of the West Forebalkan, Bulgaria 
Botoucharov, N; Stefanova, M; Marinov, S 
2020 
Yes 
Bulgarian Chemical Communications
ISSN: 0861-9808 
Bulgarian Academy of Sciences 
52 
1 
62-67 
English 
The study presents a geochemical appraisal of key well core samples from Stefanets Member (Etropole Fm.), from the eastern part of the West Forebalkan, Bulgaria. Extractable organic matter, i.e. “free” and “bound” bitumens, was characterized by geochemical methods. Biomarkers were tracked, quantified and correlated. Parameters calculated on the base of n-alkanes, regular isoprenoids, hopanes, steranes and aromatic hydrocarbon distributions have determined organic matter as “mature” – early to late mature. The plots of the ratios Pr/nC17 vs. Ph/nC18 in a diagram were situated on the demarking line for Type II to mixed Type II/III kerogen. The magnitudes of Pr/Ph ratios < 1.0 have argued for reductive conditions in the depositional palaeoenvironment. There were proofs for hydrocarbons expelling and their total lack in “free” bitumen of the “late mature” sample. All calculated biomarker parameters have indicated that hopanes and steranes have attained their epimer equilibria. According to S29αα S/(S+R) vs. H31αβ S/(S+R) correlation one of the studied samples has been located in the “oil widow” area. Methyl phenanthrene index (MPI-3) has confirmed high samples maturity as the calculated values were in the range of 2.0-5.3. Results have demonstrated very good agreement between Rock Eval data, biomarker assemblages and set of calculated parameters. © 2020 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria 
Biomarker assemblage; Maturity; Stefanets Member; West Forebalkan