The relationship between silica diagenesis and physical properties in the East/Japan Sea: ODP Legs 127/128

Abstract

Six sites were drilled on ODP Legs 127 and 128. One of the significant results of this drilling was the detection of an opal amorphous silica (opal-A) and opal cristobalite (opal-CT) transformation at all the drill sites. Laboratory measurements of electrical resistivity and physical properties (e.g., velocity, porosity, and density) were conducted on the sediments and rocks sampled from the four sites (Sites 794, 795, 796, and 797). Electrical resistivity and physical properties data show significant change at the opal-A/opal-CT and the opal-CT/Quartz boundaries, suggesting the effects of silica diagenesis. Electrical resistivity reflects the change of physical properties (esp., velocity, wet bulk density, and porosity) well throughout the sites. The transformation boundary is easily recognized in the electrical and physical properties. Electrical resistivity increases by about 50% and 950% across the opal-A/opal-CT and opal-CT/Quartz boundaries, respectively. Thus, electrical resistivity as well as physical properties may be used to identify lithology and diagenetic boundaries such as opal-A/CT, opal-CT/Quartz, and to estimate the reservoir character (e.g., permeability and pore geometry) of sediments and rocks.