Šujan M., Fordinál K., Šarinová K., Rybár S. & Pelech O., 2021: Upper Miocene colluvial and alluvial fan deposits of the Modrová Mb.: A window to palaeogeography of the Považský Inovec Mts. (Western Carpathians). Acta Geologica Slovaca, 13, 1, 27–47.

Upper Miocene colluvial and alluvial fan deposits of the Modrová Mb.: A window to palaeogeography of the Považský Inovec Mts. (Western Carpathians)

Michal Šujan¹, Klement Fordinál², Katarína Šarinová³, Samuel Rybár¹ & Ondrej Pelech²

¹Department of Geology and Paleontology, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, 842 15 Bratislava, Slovakia; miso@equis.sk
²State Geological Institute of Dionýz Štúr, Mlynská dolina 1, 817 04 Bratislava 11, Slovakia; klement.fordinal@geology.sk
³Department of Mineralogy, Petrology and Economic Geology, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, 842 15 Bratislava, Slovakia

Abstract

The study focuses on the upper Miocene colluvial to alluvial fan deposits of the Modrová Mb., which accumulated on the marginal blocks of the Považský Inovec Mts., transitional to surrounding depressions of the Danube Basin. These blocks are delimited tectonically according to the geophysical evidence, and the late Miocene normal faulting produced fault scarps causing rapid sediment supply. However, the supply of coarse clastics composed mostly of Mesozoic dolomites was of intensity sufficient only to fill the accommodation of the marginal blocks. The sediment input to the surrounding Danube Basin is on the both sides of the Považský Inovec Mts. not traceable, probably due to an overwhelming alluvial redistribution. Facies analysis of the Modrová Mb. implies an environment of colluvial fans with prevalence of cohesive debris flow deposition, associated with less frequent rockfall, grain flow and sheetwash processes on the western side of the mountains in the area of Modrová village. In contrary, the easterly situated area of Tesáre village exhibits dominance of debris flow deposition with more than one third of the succession deposited by channelized and unchannelized shallow traction currents, indicating sedimentary environment of an alluvial fan close to its transition to colluvial sediment-feeder system. Petrographical and geochemical study showed extremely low content of siliciclastic component in the colluvial deposits of the Modrová area. Dolomite clasts form a major part of the sediment and are covered by a coating of clay minerals. The coatings and sediment matrix contain iron oxides possibly derived by fersiallitic weathering and by oxidation of pyrite scattered within the matrix. Geochemistry of muddy layers in the Tesáre succession implies either cold or dry weathering conditions. However, weathering proxies are considered to be biased due to the rapid denudation in the colluvial to alluvial fan environment, since observed facies and published regional studies imply rather warm and humid climate. Several examples of simultaneous comparable depositional settings in the broader region imply, that these colluvial to alluvial fan successions could be related to a mild phase of regional tectonic activity at ~8 Ma.

Key words: facies analysis, Pannonian Basin System, late Miocene, palaeoenvironment, weathering, syntectonic deposition

Manuscript received: 2020-10-14

Revised version accepted: 2021-03-29