Structural and geomorphological conditions for the development of the river valley network in the Southwestern Black Sea shelf

The region studied is a specific tectonic knot due to the marine continuation of dry land first-order morphostructures described in the literature. The position and tectonic activization of morphostructures of lower taxonomic rank predestined the basic pattern of the ancient river valley network in the shelf. Among them Rezovo graben is of particular interest. It is located between the periclinal parts of Southeastern Strandža Mountain and the Northern Pontides. During the regressive stages in the development of the Black Sea basin two main river systems developed on the shell – that of Paleo-Sredecka River which follows the axis of Burgas depression and that of Paleo-Veleka – along the axis of Primorsko negative morphostructure.
   The southeastern centricline of Primorsko depression, cut from the south by the East Rezovo fault, was the location of the Rezovo paleo-lake in which Paleo-Veleka and Paleo-Rezovska emptied. From this lake eastwards ran the largest river Paleo-Veleka which was controlled by the subparallel East Rezovo fault and a number of local positive fault-bound structures. A considerable in size buried shelf delta of Paleo-Veleka has been established in the periphery of the shell. On the continental rise the fairway of this river is related along a considerable distance to the southern margin of Rezovo neotectonic graben. The results obtained and the conclusions drawn enable a considerable widening of the perspectives for prospecting for placer raw materials, construction materials, oil and gas.