GEOTECHNICAL PROPERTY VARIABILITY OF CONTINENTAL-MARGIN SEDIMENTS - HIGH-RESOLUTION VERTICAL AND LATERAL DATA FROM THE NORTHERN CALIFORNIA SLOPE

High-resolution vertical and lateral gradients and variations in sedim ent mass physical properties were derived fi om measurements in box co res, on the scale of millimeters, tens of centimeters, and kilometers from typical, relatively broad areas of the northern California contin ental slope in the Cape Mendocino area at water depths from 380 to 940 m. Such data are important as a control on comparisons of different s ediment suites, as well as providing limits for realistic flux calcula tions of dissolved inorganic and biochemical species and pollutants. T he sediments studied have relatively constant organic carbon contents (OC similar or equal to 1.75 wt%) and bulk mineralogy. They range from silty sands (similar to 45% sand, 40% silt) to clayey silts (similar to 63% silt, similar to 35% clay) and are extensively bioturbated. Phy sical property variations between subcores (similar to 25 to 35 cm in length), taken from the same box core, increase with increasing clay c ontent. For coarse-grained sediments, mean down-core differences in ph ysical property values between related subcores are small, averaging 3 .6% for water content, 4% for porosity, 0.026 Mg/m(3) for wet bulk den sity, and 0.1 for void ratio. Subcore variations for fine-grained sedi ments are generally significantly larger, averaging 9.8% for water con tent, 1.52% for porosity, 0.027 Mg/m(3) for wet bulk density, and 0.3 for void ratio (box core 125). Millimeter variations of physical prope rties from horizontal 12-cm-long subcores indicate a maximum range of lateral variation of 18.2% for water content, 8% for porosity, 0.14 Mg /m(3) for wet bulk density, and similar to 0.6 for void ratio.