IODP NanTroSEIZE Stage 1:
Expedition 316: NanTroSEIZE "Shallow Megasplay and Frontal Thrusts"
Weekly Report #5
Date 25/Jan/2008
Piston core jamming required abandoning Hole C0007C, pull out and recovery of borehole assembly (BHA) took place between 12:00 and 24:00 PM on January 18, 2008. During this operation, request for permission to drill an alternate hole at a distance of 185 meters NW of C0007C was made, and permission was granted via CDEX and IODP Environmental Protection and Safety Panel (EPSP). Due to consideration of both science target and time requirements, decision was made to run the RCB coring system. The BHA was made up and run in the hole, and Hole C0007D was spudded on January 19, 2008 at 3:30 AM, water depth 2049 meter, Lat: 33°1.3167’N, Lon: 136°47.8872’E.
We conducted jet-in and wash down to 18 meter below seafloor (mbsf), and drilled down to 175 mbsf to the first coring point, which was reached at 00:00 AM on January 20th. Coring operations in Hole C0007D resulted in the collection of cores 316-C0007D-1R to -35R (175 – 493.5 mbsf) with total recovery of 87.9 meters of core and recovery rate of 27.61%. A combination of: 1) determination that the scientific target had been reached, 2) deteriorating hole conditions, 3) repeated zero-recovery cores, and 4) recovery of small amounts of loose, fine sand in the final core resulted in the determination to pull out of the hole, finished the hole with dense drilling fluid, and recover the BHA to the surface at 15:00 PM on 24th January, 2008. The BHA was recovered at 1:30 AM, January 25th, 2008.
Hole C0007D, located 185 m upslope from Hole C0007C, was selected to target the frontal thrust in an area with less coarse material than encountered at Hole C0007C. Deformation observed within the cores and possible repetition of beds provides evidence of fault activity within the hanging wall of the frontal thrust. The region of the frontal thrust was associated with a wide array of deformation fabrics, with variable intensity and spacing, ranging from foliated gouge to coarse breccia. A no- to extremely low-recovery zone that drilled extremely quickly below this was inferred to be unconsolidated sand-rich material, and this inference was confirmed in the last core where ~0.4 meters of fine, black, soupy sand was collected.
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.
