Alluvial Ridge-and-Swale Topography: A Case Study from the Morien Group of Atlantic Canada
- M. Marzo and
- C. Puigdefábregas
Published Online: 14 APR 2009
Copyright © 1993 The International Association of Sedimentologists
How to Cite
Gibling, M. R. and Rust, B. R. (2009) Alluvial Ridge-and-Swale Topography: A Case Study from the Morien Group of Atlantic Canada, in Alluvial Sedimentation (eds M. Marzo and C. Puigdefábregas), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303995.ch11
- Published Online: 14 APR 2009
- Published Print: 16 SEP 1993
Print ISBN: 9780632035458
Online ISBN: 9781444303995
- Alluvial ridge-and-swale topography(RST);
- exposition of channel deposits in cliffs;
- Alluvial ridge-and-swale topography;
- slightly asymmetric ridges and swales from Symmetric;
- Type lb ridges -largest and stratigraphically highest observed;
- abundance of claystone intraclasts
Ridge-and-swale topography (RST), a prominent feature of meander lobes in modern rivers, is generally attributed to scroll-bar accretion. An exhumed meanderbelt in the Silesian Morien Group of Nova Scotia, Canada shows four types of RST, three of which are attributed to scroll bars. Asymmetric ridges (type 1) contain single or stacked planar cross-sets that advanced up inclined surfaces that strike parallel to the ridge crests. Type 1a ridges show 0.5 m relief, 5 m mean spacing and low-angle (5°) inclined surfaces in sandstone. Type 1b ridges are larger in scale (1 m relief, 10 m mean spacing); their thin-bedded sandstone and siltstone show inclined surfaces that dip at up to 20°. Type 1 RST is attributed to scroll bars, and probably originated in part from the inward migration of two-dimensional dunes.
Symmetric (type 2) ridges consists of thick-bedded, trough cross-stratified sandstone with ridge-parallel palaeoflow. Type 2a ridges (up to 1.2 m of relief, 12 m average spacing) underlie scroll-bar ridges (1b), and probably represent initial scroll-bar deposits. Type 2b ridges are paired, with well-marked erosional swales, and are attributed to levees bordering chute channels.
Sandstone-rich ridges (1a, 2a, 2b) are resistant to weathering and form the most pronounced exhumed topography. Such ridges are preserved at a story boundary within the meanderbelt deposit.