Experimental Study of Deep-Sea Fan Evolution and Sedimentology

Frank G. Ethridge and Gary A. Daub

A series of analog experiments, designed to investigate a number of different aspects of deep-sea fan formation, development, and morphology were conducted in two different flumes at Colorado State University. Earlier experiments, using a continuous flow method, resulted in overlapping sand lobes that formed on the lower part of a simulated continental slope and canyon as a result of non-turbulent grain flows. Relatively small amounts of sand reached the continental rise, where the predominant deposits were clay. These lower slope fans resembled subaqueous portions of fan deltas rather than deep-sea fans

Recent experiments involved the release of a series of turbidity current pulses. These turbulent pulses accelerated down the canyon until they reached the slope-rise break, where they experienced a rapid decrease in velocity and an increase in height as they spread onto the rise. These changes resulted in the deposition of significant amounts of sand on the continental rise, as well as in the lower canyon. Fans grew landward by onlap onto the canyon and slope, and reveal a retrogradational stacking pattern of successive sand beds. The sand fan also extended basinward on the upper continental rise eventually merging with clay deposits on the lower rise. The hydraulic jump, that occurred at the slope/rise break, was probably responsible for the initiation of sand waves, which developed in a radial zone that migrated basinward as the fan enlarged with each successive run. Sediment waves, that may have a similar origin, are described from density-current experiments and from modern deep-sea fans.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California