Breaching the Shelfbreak: Passage from Youthful to Mature Phase in Submarine Canyon Evolution
John A. Farre, Bonnie A. McGregor, William B. F. Ryan, James M. Robb, 1983. "Breaching the Shelfbreak: Passage from Youthful to Mature Phase in Submarine Canyon Evolution", The Shelfbreak: Critical Interface on Continental Margins, Daniel Jean Stanley, George T. Moore
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Mid-range side-scan sonar images of the U.S. Middle Atlantic continental margin show the presence of a variety of erosional features. Amphitheatre-shaped scars are present on the continental slope near Carteret Canyon. Several slope canyons, whose heads do not appreciably breach the shelfbreak, have a pinnate drainage pattern on the upper, sediment-draped slope. The thalwegs of these canyons follow nearly straight paths down the slope. In contrast, Wilmington, a shelf-indenting canyon, follows a curved to meandering path down the slope.
On the basis of these and other data, we propose a preliminary explanation of evolution of canyons on the middle Atlantic slope. In this model, localized slope failure begins the process of canyon formation. By headward erosion, these depressions extend upslope and form linear sediment chutes. These slope canyons represent the youthful phase in canyon evolution. Slope canyons begin the transition to a mature phase when the canyon heads breach the shelfbreak. Access to the continental shelf leads to the transport of shelf-derived materials through the canyon.
During the youthful phase, the dominant mechanism of canyon erosion is the failure of the slope itself. In the mature phase, entrenchment is augmented by the episodic cutting by turbulent sediment suspensions enroute from the shelf to the continental rise and abyssal plain. The shelfbreak, in this model, is an important factor in the evolution of a passive continental margin.
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The Shelfbreak: Critical Interface on Continental Margins
The shelfbreak is that point where the first major change in gradient occurs on the outermost edge of the continental shelf. Although this environment delimits the boundary between two principal and well-defined provinces, the continental shelf and slope - and thus is of the first order of importance on continental margins - it has received surprisingly little specific attention in either modern oceans or in the rock record. This volume, the first compendium dedicated specifically to the shelfbreak, was derived from an SEPM Research Symposium convened at the joint Annual Meeting of SEPM and AAPG on June 2, 1981. The material is organized in a manner to illustrate examples of the shelfbreak in both modern oceans and the rock record.