Ocean Drilling Program (ODP) Leg 201 was the first ocean expedition that focused on subsurface marine environments to study life in sediments deep beneath the ocean floor (Shipboard Scientific Party, 2003). During Leg 201, seven sites were drilled into a wide range of subsurface environments in both open-ocean and ocean-margin provinces of the eastern tropical Pacific Ocean. These subsurface environments include carbonates and siliceous oozes typical of the equatorial Pacific, clays and nannofossil-rich oozes of the Peru Basin, biogenic and terrigenous-rich sediments of the shallow Peru shelf, and clay-rich deepwater sequences of the Peru slope (Shipboard Scientific Party, 2003).
Fluid flow in sediments can transport nutrients that maintain microbial life in subsurface sediments (Chapelle, 1993); thus, it is important to quantify the rate of fluid flow. Permeability is an important property of the porous medium that controls fluid flow in sediments. In this study, we used core samples from five sites from Leg 201, including open-ocean Sites 1225, 1226, and 1231 and ocean-margin Sites 1227 and 1230 to measure vertical permeabilities (Fig. F1). Each site represents a different subsurface environment. Sites 1225 and 1226 represent the carbonate, siliceous, and chalk sediments of the equatorial Pacific; Site 1227 represents the biogenic oozes and terrigenous sediments of the shallow Peru shelf; Site 1230 represents the hydrate-bearing clays, biogenic oozes, and silt sediments of the lower slope of the Peru trench; and Site 1231 represents deep-sea clays and nannofossil oozes of the Peru Basin (Shipboard Scientific Party, 2003). Constant-flow tests were conducted on core samples to measure the vertical permeability of the sediments.