Near-seafloor overpressure in the deepwater Mississippi Canyon, northern Gulf of Mexico

Abstract

Laboratory experiments constrain overpressure (25-50% of hydrostatic effective stress) above 30 mbsf at two sites in the Mississippi Canyon region, northern Gulf of Mexico. Overpressure at site 2562 is less than that at site 2567; however site 2562 has accumulated faster. One-dimensional sedimentation-consolidation models cannot recreate the overpressure without external fluid sources. A fluid source (specific discharge, q = 2-7 mm/yr) is required for site 2567, whereas a fluid sink (q = 10-12 mm/yr) is required for site 2562 to simulate the constrained overpressure. Although basal conditions differ, specific discharge of 2.1-4.2 mm/yr occurs at the sea floor. Shallow upward flow at each site, deep upward flow at site 2567 and deep downward flow at site 2562 is consistent with a two-dimensional flow field where sites 2562 and 2567 are hydrologically connected at depth by a regional aquifer. Copyright 2008 by the American Geophysical Union.