Facies and architectural analysis of fluvial deposits of the Nyrany Member and the Tynec Formation (Westphalian D - Barruelian) in the Kladno-Rakovnik and Pilsen basins

• Published in: Bulletin of geosciences Vol. 80; no. 1; pp. 45 - 66
• Main Authors: Oplustil, S, Martinek, K, Tasaryova, Z
• Format: Journal Article
• Language: English
• Published: 01.01.2005
• ISSN: 1214-1119

The fluvial strata of the Nyrany Member (Westphalian D - Cantabrian) and of the lower part of the Tynec 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 Pecinov quarry succession. Deposits indicative of vertically aggrading streams of higher sinuosity and lower energy fluvial environments were recognized in the Lobec Cliff deposits and in the upper part of Pecinov quarry. Radcice Cliff is dominated by laterally migrating channels, though multi-storey channel fills also occur.