IODP NanTroSEIZE Stage 1:
Expedition 316: NanTroSEIZE "Shallow Megasplay and Frontal Thrusts"
Weekly Report #4
Date 18/Jan/2008
Coring operations in Hole C0006F continued from cores 316-C0006F-14R to -23R (514-603 meter below seafloor, or mbsf) with total recovery of 26.44 meters of core and recovery rate of 31.58%. Following the collection of core 316-C0006F-23R, it was determined based on pump rates, pressure, torque, and rpm that the hole condition had deteriorated to such a degree as to make further coring too risky. The decision was made at 9:00 am January 13, 2008 to abandon Site C0006 and relocate to proposed Site NT1-03A as an alternative means to achieve the science goals for the NT1-03 family of sites. C0006F was killed with high-density mud, the Borehole Assembly (BHA) pulled out of the hole, drill pipe tripped and the RCB BHA was racked back at 21:00 PM, January 13.
Chikyu then relocated to Site NT1-03A (now renamed site C0007). The ROV was launched in order to deploy seafloor transponders below the Kuroshio Current (generally running at 2.0-2.5 knots), the HPCS/ESCS BHA was rigged up and readied while the vessel was calibrating for DPS navigation and positioning over the site. The BHA was run to the seafloor, and Hole C0007A was tagged at 22:30 PM on January 14th at a depth of 4081 mbsl, at location 33°01.23258’ N, 136°47.94852’ E.
The first core (316-C0007A-1H) was a successful mudline core that penetrated to 3.14 mbsf with 100% recovery. Due to operational and curatorial issues, the following core was labeled 316-C0007B-1H. This core was taken from 3.14 mbsf and it recovered 10.06 m of sediment with recovery of 105.9%. Because the bit came out of the borehole during recovery of this core, the following core was labeled 316-C0007C-1H. This core was taken from 12.64 mbsf and recovered 7.95 meters of sediment with 100% recovery.
All further coring was conducted in Hole C0007C continuously from this point. Cores 316-C0007C-2H to -4H, -5X to -15X, and -16H to -17H were collected with a total of 51.26 meters of recovery at a rate of 33.82% in interlayered silt, sand, etc. Jamming of the piston core barrel in the BHA following the shooting of core 316-C0007C-18H at ~15:00 PM on January 17th has required several hours of operational time.
Drilling at Site C0006 continued within the accretionary prism. The primary lithology was mudstone with volcanic ash layers. In general deformation was observed to be less than observed above, although several thrusts were inferred from the seismic interpretation. Because hole conditions prevented reaching the frontal thrust at Site C0006, an alternate location from the prospectus, NT1-03A, was selected to complete the objectives. Drilling was begun on Site C0007. Abundant sands have been observed (or inferred from poor recovery intervals) at this site.
Sampling for pore fluids, void gas (where appropriate), and head space gas was carried out in the core cutting area. XCT scanning, Multi-sensor core logging, and whole-round core sampling for geotechnical and physical properties analysis were carried out on whole round core sections, followed by core description (structural, sedimentological, stratigraphic), and physical properties measurements (thermal conductivity, moisture and density, P-wave velocity and electrical resistivity) were carried out on the split core section. This was followed by collection of a complete suite of samples for paleomagnetic, physical properties, paleontological, mineralogical, age-dating, geotechnical, and structural analyses. Following color and spectral scanning and paleomagnetic scanning, cores were packed for shipping to the core repository.
