Palynofacies analysis, sedimentology and hydrocarbon potential of the Menilite Beds (Oligocene) in the Slovakian and Romanian Outer Carpathians

Abstract

The sedimentary organic matter (SOM) assemblages and sedimentology of the Menilite Beds from the Dukla, Grybów and Vrancea units in the Slovakian and Romanian Outer Carpathians are described. Qualitative and quantitative analyses of the SOM help ascertain depositional conditions, while the thermal maturity of the organic matter studied is estimated utilizing the Spore Colour Index and UV light excitation techniques. The sedimentary organic particles were grouped into ten SOM categories: marine palynomorphs (dinoflagellate cysts), sporomorphs (saccate and non-saccate, pollen and spores), freshwater algae (Botryococcus sp., and other freshwater microplankton), phytoclasts (cuticles, translucent wood, opaque wood), resin and amorphous organic matter (AOM). All samples are dominated by AOM. The presence of Botryococcus sp., Pediastrum sp., Pterospermella sp. and Campenia sp., in some samples points to deposition under hyposaline conditions. It is interpreted that the freshwater influx induced water column stratification in the basin, leading to the development of dysoxic to anoxic bottom-water conditions that enhanced the preservation of AOM. Kerogen analysis in UV light and evaluation using the Spore Colour Index demonstrated different thermal maturation patterns from the Slovakian (post-mature) and Romanian (immature) sections. Integrated palynofacies analysis (notably, the presence of freshwater algae) and sedimentological observations (e.g., hummocky cross-stratification) lead to the conclusion that the deposition of the Menilite Beds in the Vrancea Unit (Romania) was relatively proximal to the shoreline, above storm wave base, whereas the Slovakian units (Dukla and Grybów) were deposited in a more distal setting.