Main regularities in the development of the morphostructures in Bulgaria

Abstract

Morphostructures of Bulgaria and eastern Balkan Peninsula underwent changes and transformations more than once during their long and complicated development. Hence their base is heterogeneous, the morphostructural integration was not achieved until the neotectonic stage when the present day orography came into being. The morphostructural differentiation reveals block structures of the earthcrust and deep faults control.

The largest morphostructures are as follows: I - the Danubian (Mizian) epiplatform plain, II - the Rhodopes median mountain massif, III - Kraisht-id-Srednuogora block-faulted low mountains, IV - Stara Planina epigeosynelinal mountain system, V - complex of accumulative surfaces within the limits of young foretroughs and intermountain depressions, VI - the Black Sea basin.

An alternation of geocycles and morphocycles in the relief development resulted in planation surfaces formation and changes of drainage pattern. Five main erosion surfaces can be identified, which belong to the neotectonic stage: two summit levels (Late Oligocene-Early Miocene and Tortonian- Sarmatian) and three lower post orogenic levels (Early Pliocene, Late Pliocene and Late' Pliocene-Early Pleistocene). There is also a broad regional Meso-Cenozoic planation surfaces as well as buried levels, the latter being formed before Permian, before Triasic, before Early Cetaceous, before Late Cretaceous - Early Tertiary and before Late Eocene-Oligocene. Drainage pattern reflects main features of the morphostructural plan. Its changes mainly date back to L.ate Pliocene and Pleistocene. Pre-neotectonic river valleys are practically of no significance to the recent topography.

The morphostructural differentiation is in close connection 'with deep structures of the earthcrust and the upper mantle, both direct and inverse relation being traced. Structural geomorphological studies are conducted with the aim of search of minerals and mineralizing faults, metallogenic and seismotectonic zonation of the Bulgaria, studies of recent crustal movement, thermal spring activity etc.