Geotechnical property variability of continental margin sediments: High-resolution vertical and lateral data from the northern California slope

• Published in: Marine georesources & geotechnology 1997-09, Vol.15 (3), p.283-304
• Main Authors: Sawyer, William B., Ransom, Barbara, Bennett, Richard H.
• Format: Article
• Language: English
• Subjects: bioturbation; California; continental slope; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Engineering geology; Exact sciences and technology; geotechnical properties; Marine and continental quaternary; Mendocino; oxygen minimum zone; physical properties; porosity; sediment variability; Surficial geology; water content
• ISSN: 1064-119X; 1521-0618
• DOI: 10.1080/10641199709379948

High-resolution vertical and lateral gradients and variations in sediment mass physical properties were derived from measurements in box cores, on the scale of millimeters, tens of centimeters, and kilometers from typical, relatively broad areas of the northern California continental 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 sediment suites, as well as providing limits for realistic flux calculations of dissolved inorganic and biochemical species and pollutants. The sediments studied have relatively constant organic carbon contents (OC ? 1.75 wt%) and bulk mineralogy. They range from silty sands (∼45% sand, 40% silt) to clayey silts (∼63% silt, ∼35% clay) and are extensively bioturbated. Physical property variations between subcores (∼25 to 35 cm in length), taken from the same box core, increase with increasing clay content. For coarse-grained sediments, mean down-core differences in physical property values between related subcores are small, averaging 3.6% for water content, 4% for porosity, 0.026 Mg/m 3 for wet bulk density, and 0.1 for void ratio. Subcore variations for fine-grained sediments are generally significantly larger, averaging 9.8% for water content, 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 properties 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 ∼ 0.6 for void ratio.