Porosity and sound velocity measured in sediment core CIROS-1, supplement to: Bücker, Christian J; Henrys, Stuart A; Wonik, Thomas (1998): Revision of the Cenozoic seismic velocity structure of the CIROS-1 drillhole, Antarctica, and implications for further drilling off Cape Roberts. Terra Antartica, 5(3), 281-289

• Main Authors: Bücker, Christian J, Henrys, Stuart A, Wonik, Thomas
• Format: Dataset
• Language: English
• Published: PANGAEA - Data Publisher for Earth & Environmental Science 1998
• Subjects: DEPTH, sediment/rock; Porosity; Velocity, compressional wave; Drilling/drill rig; Calculated; CIROS; Sampling/drilling ice; Cape Roberts Project CRP; Ross Sea; Victoria Land; McMurdo Sound; Cape Roberts; Antarc*; Antarctica; antartic*
• Online Access: https://dx.doi.org/10.1594/pangaea.54717; https://doi.pangaea.de/10.1594/PANGAEA.54717

The CIROS-1 drillhole, which in 1986 reached a depth of 700 m below the seafloor, is still the only deep hole that can provide information on the velocity structure of the upper crust in McMurdo Sound and the Ross Sea, Antarctica. A careful review and quality control of the downhole logging data of CIROS-1 resulted in a new porosity depth function that is consistent with porosity data from the MSSTS-1 and CRP-1 drillholes. Using existing porosity-velocity equations, it was possible for the first time to obtain reliable velocity information for the upper 700 m of strata off the Victoria Land coast. The calculated synthetic seismograms, based on downhole velocity and density data, fit very well with the existing seismic lines IT90A-71, PD90-12, and NBP9601-89. The quality of the correlation confirms that the average velocity of the top 700 m of strata is about 2 000-2 300 m/s, and not 2 800-3 000 m/s, as was previously assumed. In consequence, these distinctly lower velocities result in shallower depths for the seismic unconformities V3/V4 andV4/V5 and thus may have important implications for further drilling off Cape Roberts.