engleski

Source potential and palynofacies of Late Jurassic "Lemeš facies", Croatia

Laminated limestone and calcareous shale outcrop samples from the Late Jurassic "Lemeš" facies (Croatia) were investigated to characterize their organic facies and palynofacies and their hydrocarbon generative potential.The results indicate that the organic-rich sediments of "Lemeš" facies were deposited within a relatively shallow marine environment at low redox potential, characterized as an oxygen depleted depositional setting with stratified bottom waters of the carbonate paltform (Adriatic Carbonate Platform). The organic-rich samples contain a high portion of lipid-rich amorphous kerogen of algal/phytoplankton origin, enriched by bacterial biomass. Most of the analyzed samples have total organic content (TOC) grater than 3%, Rock-Eval S2 higher than 20 mg HC/g rock, yielding Hydrogen Index (HI) values ranging from 503 to 610 mg HC/g TOC. According to these results, the analyzed samples have very good to excellent oil-generative potential. Relatively high sulfur content suggest that the kerogen is best described as Type II-S. Biomarker maturity parameters, as well as the fluorescence of the isolated kerogen, show that the organic matter is at early to peak oil thermal maturity. The observed level of thermal maturity indicates that these samples were once buried to depths of ~5.5 to 5.8 km befora being uplifted in the Late Terniary. The surface outcrops of the "Lemeš" facies suggest that these strata have significant source potential and are the likely source of oil in the Croatian External Dinarides

source rock; organic facies; palynofacies; biomarker geochemistry; hopanes; steranes; mono and triaromatic steroids; Lemeš facies; Late Jurassic; Adriatic Carbonate Platform; Croatia

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