Mohr, Jeré A.¹, John B. Swenson¹, Chris Paola², Lincoln F. Pratson³ 
(1) University of Minnesota Duluth, Duluth, MN 
(2) University of Minnesota, Minneapolis, MN 
(3) Duke University, Durham, NC

ABSTRACT: Sedimentation at the Foreset Toe as a Choke Point in Clinoform Dynamics

We present results from flume experiments that show how the foreset toe is a critical point—a “choke” point—for sediment transport in the coupled fluvio-deltaic system. Small changes in sedimentation at the foreset toe can control the entire upstream behavior of the system. During clinoform progradation, fluvial aggradation and shoreline behavior are controlled by the ability of the system to clear sediment from the foreset toe. We first examine how basement geometry controls sedimentation at the foreset toe, and ultimately, the behavior of the system upstream of the toe. If the basement slope exceeds the angle of repose of the sediment, failure occurs in the toe region and sediment is unable to accumulate there. As a result, shoreline regression and fluvial aggradation cease, the clinoform upstream of the toe becomes a bypass system, and all sediment is routed to the deep marine environment. A second set of experiments show how basement geometry in concert with turbidity currents can clear sediment from the foreset toe. Turbidity currents reduce the foreset angle by 20-30%. If the basement angle is greater than the reduced foreset angle, sediment is unable to accumulate at the toe, halting shoreline regression and fluvial aggradation and, despite the increase in sediment load to the fluvial system, generating autocyclic fluvial incision and shoreline transgression. Scale-up to field conditions shows that this phenomenon may occur with weak turbidity currents and basement slopes on the order of the continental slope.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.