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Gravitational sliding on the Mid-Atlantic Ridge at the Kane Transform: Implications for submarine basin-slope degradation and deformation

¹ Marathon Oil Corporation, Houston, Texas 77056; dgao{at}marathonoil.com

Dengliang Gao received his B.S. degree (1983) in geology and his M.S. degree (1986) in structural geology from Hefei University of Technology (China). He also received an M.S. degree (1994) in petroleum geology from West Virginia University and a Ph.D. (1997) in marine geology and geophysics from Duke University. He has worked at Tongji University (1986–1991) (China) and Exxon Production Research Company (1997–1998) and is currently at Marathon Oil Corporation (since 1998). He published a conceptual model for a cuspate-shaped, active fault system in eastern China that predicted the 1991 earthquake ( M = 5.7) in Taicang and the potential environmental hazard in Shanghai (eastern China). He is currently interested in the application of the conceptual model to gravitational sliding structure and hydrocarbon system analyses in deep-marine basin slopes. He is also interested in developing three-dimensional (3-D) seismic texture theories and has patented several inventions for 3-D seismic structure and facies analyses. He is an active member of AAPG and the Society of Exploration Geohpysicists and serves on the Publications Committee of AAPG.

Deep-tow side-scan sonar imagery, along with submersible and camera surveys, provides a synoptic view of the sea-floor geology, leading to critical observations and new interpretations for previously unknown gravitational sliding features on the Mid-Atlantic Ridge at the Kane Transform (23°38'N). The sliding on the rift-valley wall occurred mostly as massive slumps of slope-forming gabbroic bed rocks, possibly along mechanically weak, low-angle (30°) detachment faults, creating frontal cuspate ridges and downslope-trending lineaments. The sliding on the transform-valley wall occurred mostly as debris avalanches, producing distributed surficial sediment and bedrock clasts in an apron of hummocky and chaotic terrain on the lower slope, steeply dipping (70°) amphitheaterlike escarpments on the upper slope, and downslope-trending ridges and lineaments on the middle slope.

Local and global comparative analysis suggests that distinct geologic settings of submarine slopes exert fundamental influence on the nature, style, and scale of gravitational sliding. The rift-valley wall differs from the transform-valley wall primarily because of their different structural grain, lithological complexity, and sediment thickness. The steeply dipping (25°), sediment-free rift-valley wall on the Mid-Atlantic Ridge contrasts strongly with the gently dipping (5°), passive continental margins loaded with thousands of meters of petroliferous sedimentary rocks. Results from comparative analysis not only add to the knowledge of complexities of submarine gravitational sliding structures but also contribute to a better understanding of the differences in sea-floor degradation and deformation processes in contrasting submarine geologic settings represented by mid-ocean ridges and passive continental margins.