Tidal Systems
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Tidal flats are land areas that are covered by sea water during high tide and exposed during low tide. Sediment structures that commonly form on tidal flats include symmetrical ripples due to bi-directional tidal flows, flat-topped ripples when ripple tops are flattened during flow reversals, and flaser bedding where clay drapes form over silty sediments due to variable energy conditions. Burrows left by organisms moving between surface and subsurface areas during tides are also common, as are root casts from salt-tolerant vegetation and animal tracks.
Tidal Systems
- 1. Tidal Systems Tidal flats represent the land area covered by sea water during high tide and exposed to the air during low tide.
- 3. Photo by W. W. Little Oscillation (symmetrical) Ripples Because of bi-directional flow, symmetrical current ripples are very common tidal structures.
- 4. Photo by W. W. Little Flat-topped Ripples Tidal ripples are often flattened as their tops are planed upon reversal of flow direction. In some cases, a small flap of sediment will extend away from the crest toward the trough in the direction of the reversed flow.
- 5. Photo by W. W. Little
- 6. Photo by W. W. Little Flaser-bedded Mud Because of highly variable energy conditions associated with tidal flow, flaser bedding in the form of clay drapes over silty sediment is common.
- 7. Photo by W. W. Little
- 8. Photo by W. W. Little Interference Ripples Surface ponding can lead to the development of oscillation ripples.
- 9. Photo by W. W. Little Herring Bone Cross-bedding
- 10. Photo by W. W. Little
- 11. Dessicated Mud Dessication cracks in mud can form during low tides.
- 12. Photo by W. W. Little Burrowed Mud Vertically-oriented burrows are common as organisms surface to feed during high tide and return to the subsurface for safety at low tide.
- 13. Photo by W. W. Little
- 14. Photo by W. W. Little Root Casts Salt tolerant vegetation, such as mangrove, commonly grow on tidal flats, causing bioturbation through root growth.
- 15. Photo by W. W. Little Tracks Animal tracks, including migratory trackways, are common on tidal flats.
- 16. Photo by W. W. Little
- 17. Photo by W. W. Little Tidal Channels Much of the drainage on a tidal flat enters the sea through a highly complex system of tidal channels.
- 18. Photo by W. W. Little
- 19. Photo by W. W. Little
- 20. Photo by W. W. Little
- 21. Photo by W. W. Little Algal Mats Algal structures are common features in tidal zones.
- 22. Photo by W. W. Little
- 23. Photo by W. W. Little
- 24. Photo by W. W. Little Large-scale Architecture Tidal deposits are characterized by horizontally-laminated mud with interspersed sand- or mud-filled channel forms.
- 25. Photo by W. W. Little
- 26. Photo by W. W. Little Tidal deposits are often “bundled” into sand/mud couplets, related to annual neap/spring tidal cycles. Tidal Bundles (parasequences)