Criteria and methods of quantitative assessment of petroleum prospects in poorly studied large territories

The main anticlinal folds in the Donets basin arose in zones of deep-seated faults separating large, slightly disturbed basement blocks to which the synclines are confined. These blocks, in their descending and ascending movements, alternately passed each other, thus bending the sedimentary beds first on one then on the other side of the deep-seated faults. It was this, and not tangential pressure, that led to the formation of the steep anticlinal folds. In the initial stage (C₁, C₂, and the first half of C₃), very large brachyform anticlinal structures arose above the deep-seated faults. This is indicated by the reduced thickness of the Carboniferous rocks toward the crests of these structures. Later (In the second half of C₃and P₁), linear folds arose on the sites of the brachyform structures. The present inclination of the isometamorphic surfaces (surfaces of equal degrees of metamorphism) in the synclines and anticlines reflects the magnitude of the tectonic deformations that occurred in the course of the Inversion (P₂ - T). —Authors.