--> ABSTRACT: Morphodynamics and Sedimentology of Channels in Tidal Bars and Tidal Flats, by Fagherazzi, Sergio; Mariotti, Giulio; Sun, Tao; #90135 (2011)

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Morphodynamics and Sedimentology of Channels in Tidal Bars and Tidal Flats

Fagherazzi, Sergio 1; Mariotti, Giulio 1; Sun, Tao 2
(1)Department of Earth Sciences, Boston University, Boston, MA. (2) Reservoir Characterization Division, Exxon Mobil Upstream Research Company, Houston, TX.

Deltas and estuaries are often characterized by tidal bars and tidal flats that collect and store sediments discharged by rivers. Both landforms are dissected by channel incisions that are critical for the redistribution of sediment and water and for the general evolution of these sedimentary deposits. Tidal flow concentrates in depressions leading to higher shear stresses thus promoting bottom erosion. At the same time a decrease of shear stress in higher locations promotes sediment deposition and accumulation. This combined mechanism is responsible for the formation of tidal incisions and the alternation of bars and channels in tidal environments. However, little is known about the complex feedbacks between tidal forcing and the formation of tidal channels. In fact, during a tidal cycle, the estuarine/deltaic bottom experiences a large range of velocities and water elevations, so that it is difficult to determine which event (or series of events) is responsible for channel formation. Here we compare extensive field measurements in Willapa Bay, Washington State, and Plum Island Sound, Massachusetts, two mesotidal environments in the United States. When the tidal flat is submerged, ebb-flood asymmetries in suspended sediment concentration are present. These asymmetries produce ebb and flood pathways with distinct morphological characteristics. We show that sediment deposition and erosion is clearly affected by this variability of flow along the bar/flat system. The redistribution of momentum between tidal bar and tidal channel leads to patterns of deposition and erosion that create distinctive layers of coarse and fine sediments, whose size and location are a function of tidal hydrodynamics and sediment availability.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.