Mass Physical Properties in Deep-Sea Sediment from the Clarion-Clipperton Fracture Zone, Northeast Equatorial Pacific

Deep-sea surface sediments acquired by multiple corer from 69 stations in the Clarion-Clipperton fracture zone of the northeast equatorial Pacific, were examined to understand the correlation of mass physical properties and sedimentological processes. The seabed of the middle part (8-12 degrees N) of the study area is mainly covered by biogenic siliceous sediment compared with pelagic red clays in the northern part (16-17 degrees N). In the southern part (5-6 degrees N), water depth is shallower than carbonate compensation depth (CCD). The mass physical properties such as grain size distribution, mean grain size, water content, specific grain density, wet bulk density, void ratio, and porosity of sediments are distinctly different among the three parts of the study area. Surface sediments in northern part are characterized by fine grain size and low water contents possibly due to low primary productivity and high detrital input. Conversely, sediments in the middle part are characterized by coarse grain size and high water contents, which might be caused by high surface productivity and deeper depth than CCD. The sediments show low water contents and high density in the southern part, which can be explained by shallower depth than CCD. Our results suggest that the variations in mass physical properties of sediments are influenced by combined effects including biogenic primary productivity of surface water, water depth, especially with respect to CCD, sedimentation rate, detrital input, and the geochemistry of the bottom water (for example, formation of authigenic clay minerals and dissolution of biogenic grains).