Hydrodynamics of the Us mid - Atlantic Continental Slope , Offshore New Jersey A

Fluid pressures in Miocene-Pleistocene sediments of the US mid-Atlantic continental slope approach the lithostatic stress and are an important control on the stability of the slope. Fluid pressures in excess of hydrostatic were generated by regional depositional patterns and sedimentation rates. Fluid migration within porous and permeable Miocene silty sand layers redistributed pressure and generated low vertical effective stress where Pleistocene overburden is thin. Fluid pressures that nearly equal the overburden stress cause failure on the lower slope and initiate headward erosion; we interpret this process is contributes to canyon formation along the US mid-Atlantic margin. Consolidation is a function of stress history; therefore we can interpret fluid overpressure and effective stress from porosity of samples from Ocean Drilling Program (ODP) Sites 902, 903, 904, and 1073. Stress and pressure interpretations from consolidation experiments on samples from ODP Site 1073 are consistent with porosity-predicted conditions. The borehole data were used to calibrate a relationship between seismic interval velocity and vertical effective stress. Seismic analyses predict low effective stress and high overpressure in Miocene and Pleistocene sediments where Pleistocene accumulation was greatest. Two-dimensional sedimentation-flow models, using laboratory-measured rock properties, simulated how rapid deposition of Miocene and Pleistocene sediments along the upper slope generated significant excess pressures that drove fluids upward toward the seafloor and laterally to the middle slope in permeable Miocene sediments. Along the Hudson Apron, sedimentaiv tion and pore pressure generated near-failure conditions, but stability analyses did not predict failures. This is compatible with observations of the smooth apron. Southwest of the Hudson Apron, where canyons exist, Pleistocene accumulations are thin and Miocene sedimentation rates were high. We interpret that the Miocene-Pleistocene deposition generated excess fluid pressures and a focussed flow field that generated failures, which in turn led to the formation of canyons on the middle and lower slope.