IODP NanTroSEIZE Stage 1:
Expedition 316: NanTroSEIZE "Shallow Megasplay and Frontal Thrusts"
Weekly Report #6-7 (Final report)
Date 5/Feb/2008
D/V Chikyu relocated to Site C0008 (proposed site NT2-10A) on January 26th, 2008. The Remotely Operated Vehicle (ROV) was launched in order to deploy seafloor transponders below the Kuroshio Current (running at 2.0-2.5 knots at the time), and the Hydraulic Piston Coring System (HPCS)/Extended Shoe Coring System (ESCS) Borehole Assembly (BHA) was rigged up and readied while the vessel was calibrating for Dynamic Positioning System (DPS) navigation and positioning over the site. The BHA was run to the seafloor, the ROV launched, position checked, and Hole C0008A was tagged at 1:30 AM on January 27th at a depth of 2751 meter below sea floor (mbsf), at location 33°12.8229’N, 136°43.5997’E.
The first core (316-C0008A-1H) was a successful mudline core that penetrated to 6.93 mbsf with 100% recovery. Cores 316-C0008A-2H to -28H, -29X to -42X, and -43H were collected with a total of 6.93 meters of recovery at a rate of 75.8% in interlayered mud, silt and sand. Near the bottom of the hole, starting from Core 316-C0008A-34X the drilling rate of penetration dramatically increased and recovery dropped to near 0%. After several repeated attempts to improve recovery by changing drilling and pumping parameters, and a final attempt to successfully Hydraulic Piston Coring System (HPCS) core the inferred unconsolidated sand at the bottom of Hole C0008A, the hole was abandoned. During this time, a request was made to CDEX and EPSP (Environmental Protection and Safety Panel) to shift 215 meters South East and core Site C0008, Hole B. This request was approved.
POOH (pull out of hole) and completing the Hole C0008A took place between 9:00 AM and 18:15 PM on January 31, 2008. The BHA was POOH to 200 meters above the seafloor and the rig was shifted to Hole C0008B between 18:15 and 19:30 PM on January 31, 2008. Table C0008-B-1 shows the cores collected, meters recovered, and recovery percentage for holes C0008A.
The vessel was positioned above Hole C0008B (C0008C is at the same location) at 21:30 PM, January 31, 2008; Latitude 33°12.7313’N, Longitude 136°43.6727’E, water depth 2797 meters below seafloor. The BHA was RIH (run in hole) to the seafloor, and the seafloor was tagged at 2828 meter below rotary table (mBRT). The first HPCS core (316-C0008B-1H) was shot at 21:35 PM, but did not successfully capture the mudline, Hole C0008B was abandoned and Core 316-C0008C-1H (5.51 meters of recovery, successful mudline) was shot in Hole C0008C at 0:05 AM on February 1, 2008. Coring operations in Hole C0008C resulted in the collection of cores 316-C0008C-1H to -21H, -22X, and 23X* to 25X* (0 - 176.2 mbsf) with total recovery of 189.7 meters of core and recovery rate of 108%.
During this operation, observations from previous Hole C0008A were used to adjust the determination of the advance of the piston core based on the drillers' information and the observation of large amounts of exotic material sucked into the bottoms of HPCS cores deeper in the section (316-C0008C-7H to -21H). This phenomenon resulted in initial recovery rates that in some cases exceeded 200 percent (i.e. with an advance of 5 meters and recovery of 10.2 meters). However, X-CT imagery and visual core description have confirmed that the drillers' advance data is a generally reliable measure of actual HPCS penetration. The intervals of each core occupied by exotic material pulled into the core bottom have been recorded, and use of the J-CORES depth processing and "D-Tunes" functionality will allow post-processing of the coring recovery and data registration with little difficulty.
After HPCS refusal was determined based on low-penetration, severe core liner deformation, and severe core expansion problems in Cores 316-C0008C-17H to -21H, the Extended Shoe Coring System (ESCS) was employed. However, the first ESCS core (316-C0008C-22X) was not of sufficient quality to justify further coring (preservation of the unconsolidated portions of the lithologic section and gas hydrates were particularly poor). The scientific goals of this site were deemed to have been accomplished, Target depth (TD) was declared and the newly developed ESCS "punch" coring system was deployed for testing. Three cores (316-C0008C-23X* to -25X*) were collected with this system with excellent results. A post-expedition report of the results of this coring system test, including X-CT scan, VCD, and chemistry data (for contamination analysis) will be produced to supplement this report.
Following collection of the final ESCS "punch" core at 20:35 PM on February 2, 2008, Hole C0008C was abandoned, the hole completed, and the BHA POOH to the surface. The BHA was recovered at 5:30 AM on February 3, 2008. The BHA was rigged down, excess drill pipe laid out, and the guidehorn rigged down. Transponders were recovered on the morning of February 4, 2008 and D/V Chikyu began transit to Shingu, Wakayama Prefecture, Japan.
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.
The weekly report about the Expedition 316 was reported by the Co-Chief Scientists (Dr. Elizabeth Screaton and Dr. Gaku Kimura), CDEX Operations Superintendent (Mr. Ikuo Sawada and Tsuyoshi Abe) and CDEX Expedition Project Manager (Dr. Daniel Curewitz).
