Hydrodynamics of the United States mid-Atlantic continental slope, offshore New Jersey

Fluid pressures in Miocene-Pleistocene sediments of the US mid-Atlantic continental slope approach the lithostatic stress and control the stability of the slope. Fluid pressures in excess of hydrostatic were generated by regional depositional patters and sedimentation rates. Fluid migration within porous and permeable Miocene silty sand layers redistributed fluid pressure and generated low vertical effective stress where Pleistocene overburden is thin. Fluid pressures that equal the overburden stress cause lower slope failure and initiate headward erosion; this process is interpreted to form canyons along the US mid-Atlantic margin. Fluid overpressures and effective stresses were estimated from porosity of samples from Ocean Drilling Program (ODP) Sites 902, 903, 904, and 1073. Stress and pressure interpretations from consolidation experiments on cores from ODP Site 1073 were consistent with porosity-predicted conditions. The borehole data were used to calibrate a seismic interval velocity-effective stress model that was used to predict regional pressure and 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, quantified how rapid deposition of Miocene and Pleistocene sediments on 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, sedimentation and pressure generated near-failure conditions, but stability analyses did not predict large 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; it is interpreted that the combined Miocene-Pleistocene deposition generated excess fluid pressures and a flow field that generated failures and formed canyons on the middle and lower slope.