International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

RECONSTRUCTION OF FLUVIAL BARS FROM THE LOWER TRIASSIC “BUNTSANDSTEIN FACIES” (LUZNA FORMATION) IN THE WESTERN CARPATHIANS (SLOVAKIA)

Pages: 41 - 55

Authors: ANNA VOZAROVA

Abstract: The 50–150 m thick Lower Triassic Luzna Formation quartzose sandstones and conglomerates are widespread in the Tatricum, Northern Veporicum/Fatricum and Zemplinicum (Western Carpathians). Several braided fluvial facies are well developed in the vertical sections from the Tribec Mountains, the Ciertaz Mountains and the Starohorske vrchy Hills. The channel lag and planar cross-bedded bar facies overlie major erosional surfaces and are characterized by complex interlayering of planar cross-beds 25–125 cm thick and trough cross-beds 15–50 cm thick. Paleocurrent data (both planar and trough cross-beds combined) indicate downcurrent, oblique or symmetrical accretion of the bars with respect to the local channel direction and are inferred to document lateral or mid-channel braid bar deposits. The thickness of the bar deposits suggests a shallow depth to the channels (~2 m). Paleohydrological data for mean and bankfull channel depth and width, mean annual discharge and mean annual bankfull discharge, paleoslope, drainage area and principal length of river are estimated. Paleoslope values estimated for the Luzna Formation braid-channels lie between those generally found for alluvial fans and modern rivers (mean S=0.0099). These higher paleoslopes, combined with shorter principal stream lengths, indicate a tectonically active, fault-segmented margin of the source area, from which were derived braided fluvial wedges of clastic sediments on the piedmont braid-plain.

Keywords: Western Carpathians, Lower Triassic, braided river, channel bar, paleohydrological data

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