Sedimentary processes on the continental slope off New England

• Main Author: MacIlvaine, Joseph Chad
• Format: Dissertation
• Language: English
• Published: Woods Hole Oceanographic Institution 01.09.1973
• Subjects: Continental slope; Quaternary sedimentation; Sedimentary processes

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August, 1973 A detailed study of a small (5000 km2) area of the continental slope south of Cape Cod, Massachusetts, was conducted. Bathymetry, 3.5 kHz profiles, seismic profiles, suspended sediment analysis, bottom photographs, television laboratory flume experiments, studies of surface sediments, and piston cores were combined to form the basis for understanding the sedimentary processes which control transportation, deposition, and erosion of sediments, and the geomorphic features of the continental slope. Gravitational processes (slumping, creep, and turbidity currents) are apparently the most effective erosional processes on the continental slope. Massive large-scalefailure occurs where the slope steepens from a gradient of 1.50 to 7.60, producing scarps hundreds of meters in height. Upslope propagation of slumping on the upper continental slope has formed steep-sided gullies with layers of disturbed residual material and humocky floors. On thesteep lower continental slope small slump scars on the order of 100 m in horizontal extent and several meters high arecommon. Material removed by slumping is emplaced at the foot of the continental slope as intact and disrupted blocks1 to 100 m thick. Turbidity currents generated by slumping have apparently eroded V-shaped gullies in the lower continentalslope.Bottom currents are most influential at the shelfbreak, where they produce sorting of surface sediments and suspension of fine material by erosion of the bottom. Internalwaves may be a significant source of high velocity bottom currents and turbulence. Laboratory flume experiments and observation of the bottom indicate that the sediments of most of the continental slope are not normally affected by bottom currents. Sediments at the foot of the continental slope on the upper continental rise arereworked by bottom currents.Biological activity causes both roughening and smoothing of the sediment surface. Tracking of the bottom produces small-scale roughness, and reworking of the bottomreduces larger roughness elements. Biological production of fibrous structures helps render the sediment surface extremely resistant to erosion by bottom currents. Biologicaleros ion of rock outcrops produces rubble slopes locally at the bases of scarps.Conditions have varied markedly during the Pleistocene and Holocene. During glacial periods rapid deposition increasedthe activity of gravitational processes, while during interglacial periods of slow deposition biological and hydrodynamic processes became relatively more important. Prepared for the Office of Navai Researchunder Contract N00014-66-C0241; NR 083-004.