Cyclicity, lithofacial features and sedimentary environments of eifelian deposits of Dobrudja foredeep
Received: February 18, 2020
Institute of Geology and Geochemistry of Combustible Minerals of the National Academy of Science of Ukraine
Institute of Geology and Geochemistry of Combustible Minerals of National Ukrainian Academy of Sciences
Institute of Geology and Geochemistry of Combustible Minerals of National Ukrainian Academy of Sciences
Institute of Geology and Geochemistry of Combustible Minerals of NAS of Ukraine

Purpose. Demonstration of the lithofacial structure and reconstruction of the sedimentation conditions of the Eifelian deposits of the Biloliskyy block of the Dobrudja foredeep in the aspect of the formation of productive horizons and the localization of perspective objects. Methods. The complex of lithological, paleo-oceanographic, lithophysica, and well logging explorations. Results. Five sedimentary cyclites of regressive nature, which are traced throughout the study area, were identified in the section of the Eifelian deposits of the Biloliskyy block of the Dobrudja foredeep. Cyclites have a two-membered structure: the lower part is represented by carbonate or terrigenous-carbonate rocks, the upper part is represented by marl- sulphate and sulphate (anhydrites). Characteristic changes in the content of the main lithological differences of cycles in space and time and the rhythmic nature of their sedimentation conditions have been determined. The sedimentation features of the development of biostromic bodies during the Eifelian age were reconstructed. The study localized the areas of their maximum development which tend to the slopes of the Skhidnosaratske and Zhovtoyarske uplifts. The features of the lithophysical structure of the Skhidnosaratske deposit are clarified. The main reservoirs (anticlinal and lithological types) of all the five identified productive horizons of the deposit were discovered to tend not to the modern arch of the structure, but to its south-western pericline. Based on the lithological and facial features of the region's Eifelian sediments, prospects for lithological-type traps within the southern, eastern, and northern slopes of the Zhovtoyarska structure are highly estimated. Scientific novelty. The construction of  lithological, paleo-oceanographic, lithophysical models made it possible to determine the peculiarities of the spatial-temporal heterogeneity of the Eifelian deposits lithological structure of the Biloliskyy block of the Dobrudja foredeep and to correct the current estimation of their oil and gas prospects. Practical significance. The study of the features of the lithological structure of the strata, the creation of lithological, lithophysical, and paleo-oceanographic models will help to clarify the nature of the spatial-temporal development of sedimentary solids of various composition and genesis. All this will serve as a lithological basis for a more reasonable forecast of the distribution of oil and gas prospective objects.

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