Late Miocene fluvial distributary system in the northern Danube Basin (Pannonian Basin System): depositional processes, stratigraphic architecture and controlling factors of the Piešťany Member (Volkovce Formation)

Abstract

Aim of the study was to investigate the detailed stratigraphic architecture of the alluvial Volkovce Formation, which was deposited in the northern Danube Basin during the interval between 10 and 6 Ma. Two type locality exposures were subject to facies analysis and interpretation of depositional processes and >500 boreholes served for correlation of spatial variability in the character of the formation. The study was focused on the northern Blatné and western Rišňovce depressions, which are partly separated by the Považský Inovec Mountains horst. It was revealed, that a mostly gravelly fluvial distributary system of the Piešťany Member was deposited in the northern Blatné depression, partly confined by the exposed horst and by incised palaeotopography. The sequence is composed of amalgamated braided river channel bodies with no overbank strata, in response to high sediment supply and low accommodation. The palaeo-stream then crossed the horst in its southern part towards the Rišňovce depression, where there was four times more accommodation. The submerged horst acted as a boundary, where the depositional processes changed to a meandering river and significant overbank deposits started to be preserved. Only small streams were present in the northern Rišňovce depression, which led to very low sediment supply compared to the high accommodation there. The depositional system was affected mainly by the incised palaeotopography, by the location of sediment input together with spatial differences in accommodation rate caused by the activity of the Ripňany Fault on the southeastern side of the Považský Inovec Mts.