Intra-Slope Canyon Morphology and Its Modification by Rockfall Processes, U.S. Atlantic Continental Margin

摘要

Side-scan sonar data have been acquired at three different range settings and scales for a section of the continental slope. The data allow new perspectives on canyon morphology at varying complementary resolutions. Both regional context and site-specific details are provided. Intra-slope canyons on the lower slope are associated with outcrops of Middle Eocene carbonate rocks. Canyon geometries are heavily influenced by structural patterns of intersecting joints. Drop core analyses of surface sediments suggest that intra-slope canyon formation is not a geologically recent event, but occurred before 50,000 yrs B.P. Within the canyons, rocky debris results from episodic rockfall activity from the steep canyon walls. Dating of canyon floor sediments with inclusions of rockfall debris at one location suggests the last discrete period of rockfall there began about 10,000 yrs B.P. and ended about 6000 yrs ago. The rockfall activity may have coincided with a period of increased submarine dissolution along the margin that accompanied the upslope migration of the Western Boundary Undercurrent. Elements of the lower slope terrain may reflect surface solutional degradation of the joint patterns associated with the Eocene outcrops over longer time periods. (Author)