| Continental slopes represent the fundamental topographic boundary between the elevated continental crust and the deep ocean basins. The primary shape and bathymetric expression of this boundary on sediment-controlled slopes manifests itself in a variety of ways, from steeply dipping, canyons incised regions to gently sloping, smooth regions. This range in morphology reflects the different types of sedimentary environments that feed the margin. The following thesis examines the primary geomorphic expression of modern, sediment-controlled continental slopes, the global variability of slope morphology, and the mechanisms behind its formation. In this analysis, recent global bathymetry, and numerical modeling are used to help understand the modern variability of slope morphology and the underlying sedimentary and geologic factors that control primary sedimentary geomorphology of continental slopes. A main conclusion of the thesis is that the rate of sediment supply to the margin exhibits first-order control on the steepness of the continental slope and its relative incision by submarine canyons. In a global study of margin bathymetry in Chapter 1, five fundamental patterns of slope geometry are observed, ranging from low-angle slopes, to high-angle slopes, with differing degrees of erosion or incision by submarine canyons. These patterns relate to classes of margin stratal architecture defined by past studies, and both appear to be ultimately controlled by long-term sediment delivery to the slope. High sediment supply will cause margin progradation and a sigmoid profile geometry. If sediment input is too high or if a mobile subsurface (e.g. salt) is present, large-scale margin collapse will occur. This results in the continental slope exhibiting a low (<2°) gradient. Sediment starved margins do not prograde and remain steep (>5°) in response to shallow bedrock and/or the dominance of slope erosional processes. Similarly, for margins where sediment influx was initially high but has subsequently been reduced, slope erosion outpaces slope deposition and controls surface morphology. Glaciated margins show a similar sensitivity to sediment input. Particularly on glacial margins where sediment is rapidly delivered to the slope by intermittent ice streams, leading to the development of a debris-flow fan. The basic morphology of these fans appears to be directly related to the supply of glacial sediment eroded from the adjacent shelf.; A second-order control on slope morphology is observed for stable progradational margins. Numerical experiments in Chapter 2 show that these margins develop an equilibrium profile geometry when sediment flux is relatively constant. This equilibrium geometry is governed by basin depth such that deeper basins promote steeper slopes and shallow basins are less steep. The scaled geometry, however, is the same. Empirical data show that prograding margins may exhibit this equilibrium shape though their overall size varies. It is not evident through the experiments, how the effect of basin depth interacts with sediment input in determining the first order shape. It is probable that sediment input and depth act as dual geomorphic controls. |
