BURIAL AND THERMAL HISTORY MODELLING OF THE EDIACARAN SUCCESSION IN WESTERN AND SW UKRAINE AND MOLDOVA

N. Radkovets^a*, P. Kosakowski^b, J. Rauball^c and A. Zakrzewski^b

^a National Academy of Sciences of Ukraine, Institute of Geology and Geochemistry of Combustible Minerals, Naukova 3a, 79060 Lviv, Ukraine.

^b AGH University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, al. A. Mickiewicza 30, 30-059 Kraków, Poland.

^c Chair Petroleum Geology, Montanuniversitaet Leoben, 8700 Leoben, Austria.

^* Corresponding author: radkov_n@ukr.net

The Ediacaran (Upper Neoproterozoic) succession in west and SW Ukraine and Moldova rests on a Cryogenian succession or basement. The succession is exposed at the surface along the southern margin of the Ukrainian Shield and dips to the SW towards the Carpathian Overthrust; where burial depths are sufficient, it is mature for oil and gas generation. The Ediacaran succession is made up of terrigenous siliciclastics ranging from conglomerates and sandstones to siltstones and mudstones, and includes a shale interval (the Kalus Beds) which may have source rock potential. Organic matter in the Kalus shales includes Vendotenides sp. (colonial bacteria) together with amorphous OM. This paper presents a study of the Kalus Beds and is based on data from surface and core samples and thin sections, and the results of Rock-Eval pyrolysis and reflectance analyses. TOC contents in the Kalus shales are in general <0.5 wt%, although the measured TOC was 0.89 wt% and 0.84 wt%, respectively, in samples from the Sokal-1 borehole and the Mynkivtsi outcrop location in SW Ukraine. The low present-day TOC in borehole samples may be due to the thermal transformation of the OM originally present. Reflectivity as measured on vitrinite-like macerals and bitumen in samples from outcrops ranges from 0.63 to 1.28% VR_oeq indicating a relatively low level of thermal maturity. However, the generally low TOC values in the outcrop samples mean that the Kalus Beds in general have little hydrocarbon potential in the study area.

The burial and thermal history of the Ediacaran succession in SW Ukraine and the Moldovian Platform was reconstructed, and 1D modelling was carried out at the Brody-1, Chernivtsi-1, Dobrotvir-1, Kolynkiv-1, Litovyzh-1, Ludyn-1, Lyman-1, Peremyshlyany-1, Sokal-1 and Voyutyn-1 boreholes. The results of modelling indicate that maturities equivalent to the onset of the oil window were reached from the Early Devonian through the Early Carboniferous. Slightly higher modelled maturities occurred in boreholes located near the Teisseyre-Tornquist Zone. The modelled transformation ratio for kerogen in the Kalus Beds is high and may exceed 90% in the boreholes studied.

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