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doi:10.2204/iodp.proc.319.105.2010

Site C0011¹

Expedition 319 Scientists²

Background and objectives

Integrated Ocean Drilling Program (IODP) Site C0011 (proposed Site NT1-07) is a riserless drilling site located ~30 km seaward (southeast) of the subduction trench and is the primary site for IODP Expedition 322 (Saito et al., 2009). Because of a combination of time constraints and the limited availability of coring technicians, the primary contingency sites for IODP Expedition 319, including drilling and casing a hole at IODP Site C0002 and drilling and coring proposed Site NT1-01, were not possible. After discussion with the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Project Management Team and the Co-Chief Scientists of Expedition 322 to define a plan that would best advance overall NanTroSEIZE scientific objectives, we opted to move to Site C0011 and drill with the same suite of logging-while-drilling (LWD)/measurement-while-drilling (MWD) tools used at IODP Site C0010.

The anticipated geology at Site C0011 was similar to previously drilled Ocean Drilling Program Site 1177 (Moore, Taira, Klaus, et al., 2001). The uppermost ~340 m was thought to comprise distal trench wedge turbidites overlying the hemipelagic mudstone of the upper Shikoku Basin facies. At ~340 meters below seafloor (mbsf), prominent reflectors were expected to coincide with the boundary between the upper and lower Shikoku Basin facies. From ~720 to 860 mbsf within the lower Shikoku Basin, a series of high-amplitude seismic reflectors were interpreted as turbidite sands (Moore, Taira, Klaus, et al., 2001; Ike et al., 2008). The depth to basement was expected to be ~1200 mbsf.

The results from the LWD/MWD data at Site C0011 will be described in the Expedition 322 Proceedings volume; here we provide a brief overview of the objectives and operations conducted during the final 5 days of Expedition 319. Our objectives/goals at this site were to:

• Set transponders at the seafloor in advance of Expedition 322, in order to gain time (~24 h) for their coring objectives;

• Drill with LWD/MWD; and

• Define sand body thicknesses and properties within the lower Shikoku Basin facies between ~720 and 860 mbsf using gamma and resistivity logs, which was one key scientific goal of Expedition 322 (described in detail in Saito et al., 2009).

LWD/MWD drilling included two phases: (1) drilling as fast as possible to 350 mbsf while recording data and (2) drilling at a controlled rate of penetration below 350 mbsf to a target depth of ~900 mbsf in order to obtain high-quality LWD resistivity image data in the lower Shikoku Basin facies.

¹Expedition 319 Scientists, 2010. Site C0011. In Saffer, D., McNeill, L., Byrne, T., Araki, E., Toczko, S., Eguchi, N., Takahashi, K., and the Expedition 319 Scientists, Proc. IODP, 319: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.319.105.2010

²Expedition 319 Scientists' addresses.

Publication: 31 August 2010
MS 319-105

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