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River Delta Behavior during Cross-Shelf Transits: a Step Forward toward Understanding Three-Dimension Architecture of the Continental Margin*
Cornel Olariu1 and Ron J. Steel1
Search and Discovery Article #50096 (2008)
Posted October 24, 2008
*Adapted from oral presentation at AAPG Annual Convention, San Antonio, TX, April 20-23, 2008.
1 Department of Geological Sciences, The University of Texas at Austin, Austin, TX ([email protected])
The river delta depocenter during cross-shelf transit will follow pathways that are influenced by previous cycles. The main pattern of sediment dispersal on the shelf is proposed to be a radial infill of accommodation space that occurs on time scales from channel mouth-bar growth (100’s of years) to entire delta complexes (10K’s of years). We argue that this inherent tendency of river deltas to fill shelf accommodation in a radial pattern allows the shelf prism to be constructed fairly evenly out from the contemporary shelf edge. Also, the radial storage of the river-derived sediments on the shelf will increase the time necessary for the delta distributary to reach the shelf edge and potentially deliver sediments to deep water. The radial growth of the shelf may be influenced by wave or tidal dispersal mechanisms on the shelf during sea level change, causing the radial pattern to be altered. Wave action will spread the river-derived sediments in a shore-parallel pattern over a broader area and will build wider radial delta systems. Tides will enhance sediment transport over narrow zones normal to the shore and the tidal systems will tend to have an elongated radial shape. The ideal radial pattern will also be modified during the sea level fall or rise when accommodation changes. With the sea level changes the center of the radial system (river mouth) will shift basinwards or landwards before being complete and will initiate a new radial complex. The formation of complete or incomplete radial delta complexes on the shelf will produce topographic highs that will cause deltas formed during successive periods to compensate topographically on the shelf.
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