Tidal Systems

Tidal flats represent the land area covered by sea water during high tide and exposed to the air during low tide.

Photo by W. W. Little

Oscillation (symmetrical) Ripples

Because of bi-directional flow, symmetrical current ripples are very common tidal structures.

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.

Photo by W. W. Little

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.

Photo by W. W. Little

Photo by W. W. Little

Interference Ripples

Surface ponding can lead to the development of oscillation ripples.

Photo by W. W. Little

Herring Bone Cross-bedding

Photo by W. W. Little

Dessicated Mud

Dessication cracks in mud can form during low tides.

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.

Photo by W. W. Little

Photo by W. W. Little

Root Casts

Salt tolerant vegetation, such as mangrove, commonly grow on tidal flats, causing bioturbation through root growth.

Photo by W. W. Little

Tracks

Animal tracks, including migratory trackways, are common on tidal flats.

Photo by W. W. Little

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.

Photo by W. W. Little

Photo by W. W. Little

Photo by W. W. Little

Photo by W. W. Little

Algal Mats

Algal structures are common features in tidal zones.

Photo by W. W. Little

Photo by W. W. Little

Photo by W. W. Little

Large-scale Architecture

Tidal deposits are characterized by horizontally-laminated mud with interspersed sand- or mud-filled channel forms.

Photo by W. W. Little

Photo by W. W. Little

Tidal deposits are often “bundled” into sand/mud couplets, related to annual neap/spring tidal cycles.

Tidal Bundles (parasequences)