Neotectonic and geomorphological characteristics of the western part of the Aydemir Lowland, Silistra District

Abstract

Neogene, Quaternary and recent characteristics of the western part of the Aydemir lowland are presented in this paper. The "Srebarna" swamp is situated in this region being a biosphere reserve under UNESCO protection as well as their results-relief and substrate. There are some geodynamic development differences of various blocks of the investigated region found on the basis of correlative deposition age determinations. A paleoseismodislocation named "Srebarna" bound to the Pleistocene-Holocene boundary and aged 10500 ± 250 yr. has been found for the first time. It has a length 2750 m, a width varying from 750 up to 1000 m and a vertical amplitude – 20 m. The paleoseismodislocation is situated at a tectonic junction of a first-rank longitudinal tectonic zone and a third-rank meridional tectonic zone. It marks the epicentral zone of the earthquake. A block has been broken off as a result of one-act seismic event (intensity of 8-9 degree and supposed depth of 30-60 km). As a result of this event, the Srebarna and Kalnezhka River mouths have been naturally embanked by the gravitationally subsided block. It has been a natural barrage for the rivers' waters. The block has caused water baffling to its base, and thus their loss in the karstic underseams. The investigations presented in this paper are of practical importance due to the value of the biosphere reserve and the respective natural-geomorphological phenomenon.