Climbing-Ripple Bedding in the Fluvio-Estuarine Transition: A Common Feature Associated With Tidal Dynamics (Modern and Ancient Analogues)
William P. Lanier, Bernadette Tessier, 1998. "Climbing-Ripple Bedding in the Fluvio-Estuarine Transition: A Common Feature Associated With Tidal Dynamics (Modern and Ancient Analogues)", Tidalites: Processes & Products, Clark R. Alexander, Richard A. Davis, Vernon J. Henry
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Climbing ripples characterize a variety of sedimentary depositional settings in which suspension sedimentation exceeds the rate of traction transport, but are poorly documented from tidal environments. Research within a modern macrotidal estuary (Bay of Mont-Saint-Michel, France) in comparison with a Carboniferous example of climbing ripples from tidally influenced sedimentary rocks (Tonganoxie Sandstone, eastern Kansas, USA), demonstrates that this form of stratification is very common and also closely associated with tidal dynamics along the fluvio-tidal transition zone of macrotidal estuaries.
In the modern example, flood- and ebb-dominated climbing-ripple facies (CRF) have been distinguished. Successive climbing-ripple units are up to 10 cm in thickness. Flood dominated CRF are associated with tidal channel levees found in the inner/straight channel zone of the fluvio-estuarine transition. In thicker CRF units, sedimentary structures indicate very high suspended sediment loads and rapidly decelerating flow velocity. Ebb-dominated CRF are found in chute channels and chute bars associated with the meandering zone of the fluvial-estuarine transition. The role of tidal dynamics in the formation of these CRF, both flood- and ebb-dominated, is indicated by the vertical organization and thickness evolution of the successive climbing-ripple units. They are frequently arranged in packages of strata that thicken and thin progressively. These packages are tidal rhythmites and correspond to the sedimentary record of the neap-spring-neap cycle. The increasing energy from neap to spring tides is indicated by an overall decreasing angle of climb in the generalized bedding sequence (progradation is dominant), whereas the decreasing energy from spring to neap is evidenced by an increase of this angle (vertical accretion is dominant).
Facies within the Tonganoxie Sandstone (Carboniferous) have identical climbing-ripple successions and similar vertical progressive thickening and thinning of strata in outcrop and in core, indicating a strong tidal influence on sediment deposition. Single sedimentation units in the Tonganoxie are up to 16 cm in thickness, but show an identical vertical progression of sedimentary structures as those from the modern facies in Mont-Saint-Michel. The physical sedimentary structures of both the modern and ancient are strongly comparable on a hydrodynamic basis insofar as silt-sized sediments dominate both systems. Furthermore, a variety of additional physical and biogenic sedimentary structures that require periodic or episodic exposure have been described from both the modern and the ancient. Sedimentation patterns in both systems suggest relatively rapid aggradation within the existing accommodation space, with soils and rooted horizons capping the units once this accommodation space is filled.