Consolidation tests on silty mud samples from the Pleistocene upper continental slope at ODP Sites 902 and 903, off the New Jersey margin, reveal overconsolidation in the uppermost few meters, mostly normal consolidation to a depth of about 80 mbsf, and underconsolidation near 60 mbsf and from 80 to 130 mbsf, the maximum depth of investigation. In the underconsolidated section, excess pore pressures are estimated between 100 and 600 kPa. Underconsolidated intervals correspond to moderate to vigorous gas escape observed during recovery of the cores. If in situ methane production is the dominant cause of underconsolidation, free gas most likely exists somewhere within those intervals. Underconsolidation also appears to correlate with cyclic intervals of lower void ratio deposited during glacial times. Measured permeability varies only within a narrow range and is of the same one-half order of magnitude for most samples, about 3 x 10¹⁷ to 8 x 10¹⁷ m²; only one clayey silt sample is more permeable by almost one order of magnitude. In the absence of significant variations in permeability through the section, sediment texture and composition must be further investigated to explain the observed intervals of underconsolidation and their potential relationships with properties controlled by sea-level changes.

Date of initial receipt: 13 March 1995
Date of acceptance: 27 July 1995

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