Facies and architectural analysis of fluvial deposits of the Nýřany Member and the Týnec Formation (Westphalian D - Barruelian) in the Kladno-Rakovník and Pilsen basins


Authors: Opluštil S, Martínek K, Tasáryová Z

Published in: Bulletin of Geosciences, volume 80, issue 1; pages: 45 - 66; Received 1 October 2004; Accepted in revised form 10 January 2005;

Keywords: Pennsylvanian, Pilsen and Kladno-Rakovník basins, fluvial architecture, facies analysis, sedimentary processes,

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The fluvial strata of the Nýřany Member (Westphalian D - Cantabrian) and of the lower part of the Týnec Formation (Cantabrian - Barruelian) have been the subjects of systematic sedimentological studies. Detailed analyses of the facies, paleocurrents, and sedimentary architecture were performed on the exposures. The cumulative stratigraphical thickness of the studied successions reaches about 100 m. Six sedimentary facies were distinguished: siltstone with plant material content (Fsm), fine-grained horizontal laminated sandstone (Sh), medium- to coarse-grained cross stratified sandstone (Sc), fine- to medium-grained massive conglomerate (Gm), fine- to medium-grained cross stratified conglomerate (Gcm), and coarse-grained cross stratified conglomerate (Gcc). Five architectural elements were identified: channels (CH), sand bed forms (SB), gravel bars and bed forms (GB), sediment gravity-flow deposits (SG), and downstream accretion macroforms (DA).
All of these sediments represent braided river systems, though the type or behaviour of these systems differs at individual localities. Most of them were high energy, braided rivers of low sinuosity. Laterally migrating braided streams of low sinuosity, possibly forming braidplain fluvial environments, were distinguished at the Hostibejk Cliff deposits and in the lower part of the Pecínov quarry succession. Deposits indicative of vertically aggrading streams of higher sinuosity and lower energy fluvial environments were recognized in the Lobeč Cliff deposits and in the upper part of Pecínov quarry. Radčice Cliff is dominated by laterally migrating channels, though multi-storey channel fills also occur.