IODP NanTroSEIZE Stage 1:
Expedition 316: NanTroSEIZE "Shallow Megasplay and Frontal Thrusts"
Weekly Report #2
Date 04/Jan/2008
Chikyu arrived on location at site C0006 (proposed NT1-03B) on December 27th and conducted tests of the underwater camera system, including untwisting the camera cable and tests of the camera system itself. Due to electronic problems, the camera operation test was cancelled at noon, December 28th.
The HPCS BHA (Hydraulic Piston Coring System Borehole Assembly) was rigged up and run to the seafloor at that time, and Hole C0006C was tagged at 19:15 PM December 28th. Due to full recovery and lack of a clear mudline, the vessel was repositioned, and Hole C0006D was tagged at 22:45 PM December 28th, again full recovery and lack of mudline required repositioning and reshooting. Hole C0006E was tagged at 00:00 (midnight) December 29th, with 5.19 meters of recovery including the mudline. HPCS coring with six APCT-3 temperature measurements was conducted to a depth of 79.3 meters below seafloor (mbsf). Refusal (no penetration) occurred on core C0006E-14H, and HPCS coring was halted.
Extended Shoe Coring (ESCS) commenced at that time, and has continued to the present, recovering 22 cores (C0006E-15X to 36X) with a total recovery of 138.8 meters, 66% recovery. Core quality has remained high throughout with some increase in coring-induced deformation in the lower section of the hole. Current depth is 286 meters below seafloor and ESCS coring is ongoing. During ESCS operations, the Davis-Villinger Temperature Probe has been deployed 6 times so far, at an interval of ~50 meters.
Repeated electrical troubles in the motor driving the lubrication system for the top drive forced several minor halts in drilling to wait for repairs. Identification of the source of these electrical failures (drilling fluid/seawater spray from the wireline blow-out preventer) allowed remediation and prevention, but has slowed the pace of coring operations. The wireline cable and sinker bar must be removed from the drill pipe before drilling begins and must be reinserted to recover core barrels, adding approximately 1 hour to each coring run.
Site C0006, proposed as Site NT1-03B, targets the main frontal thrust at the seaward edge of the accretionary wedge. The scientific objectives of drilling at Site C0006 are to clarify the function of the frontal thrust with respect to large earthquakes, the evolution of this thrust fault, and the relationship between fault slip and deformation. Drilling at this site has passed through slope deposits into the accretionary prism; however, the boundary between slope and prism sediments is not clearly defined. Poor recovery intervals may correlate with faults or sands tentatively identified in downhole logs during Expedition 314. Within the prism sediments, zones of deformation have been evidenced by the occurrence of shear bands and fractures. In situ temperature measurements are currently being evaluated.
Sampling for pore fluids, microbiology, void gas, head space gas, and imaging of cores for hydrate presence was carried out in the core cutting area. XCT scanning, Multi-sensor core logging, thermal conductivity measurement, and whole-round core sampling for geotechnical and physical properties analysis was carried out, followed by core description for structural, sedimentological and stratigraphic investigation. 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.
Minor repairs and maintenance on several pieces of lab equipment have been carried out, with no major failures in any systems.
