FORMATION OF THE SOUTH-EASTERN PART OF THE DNIEPER-DONETS DEPRESSION (DATA ON DIRECT AND INVERSE 2D TECTONIC MODELING)

Abstract

Forward and reverse numerical modeling was applied in studies of structure and stratigraphic features of the syn-rift (Late Devonian) and early post-rift (Carboniferous) evolution of the SE Dnieper-Donets depression (DDD). Modeling is presented both with and without the outflow of Devonian salt from the matrix complex onto the surface at the formation of salt stocks being taken into account. The huge thickness of Carboniferous deposits can be explained by the action of three processes superimposed on each other: post-rift thermal subsidence of the depression, the outflow of Devonian salt from the matrix layer during the salt diapir activity and the regional subsidence of the East European platform. No effect of other tectonic or non-tectonic processes is not required for this explanation. Forward syn-rift modeling using the "flexural cantilever" model of the sedimentary basin formation allowed us to predict the total syn-rift extension of the Earth's crust across the DDD, as being close to 65 km with its maximum β sextension factor being 2.4. The modeled syn-rift elevation of the Mohorovicic discontinuity is 15 km. It is forecast that it dropped at present to 4-6 km due to thermal subsidence and filling of the depression by sediments. At the termination of the rift stage, the thickness of the Devonian syn-rift sequence in the axial zone of the SE DDD have reached 7.5 km, which is 3-3.5 km greater than the modern thickness. The decrease in thickness of this sequence occurred due to the loss of Devonian salt, which outflowed onto the surface during the post-rift phases of salt diapirism in the Early-Visean, Mid-Serpukhovian and Early-Permian. The salt outflow from the matrix created extra space for sediment accumulation. This resulted in formation of up to 1.5-1.7 km of the total thickness of Lower-Carboniferous sediments.