Pickering, KT; (2014) 338 Methods. In: Proceedings of the Integrated Ocean Drilling Program. (pp. 1-92). Integrated Ocean Drilling Program

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Abstract

This chapter documents the methods used for shipboard measurements and analyses during Integrated Ocean Drilling Program (IODP) Expedition 338. Riser drilling was conducted, including cuttings, mud gas, logging while drilling (LWD), and measurement while drilling (MWD) from 852.33 to 2005.5 meters below seafloor (mbsf) in IODP Hole C0002F, which had been suspended for 2 years since being drilled during IODP Expedition 326 by the D/V Chikyu in 2010 (Expedition 326 Scientists, 2011). Due to damage incurred to the intermediate flex joint of the upper riser assembly during an emergency disconnect sequence after the passing of a cold weather front with associated high winds and rapid changes in wind direction while in the high-current area, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC)/Center for Deep Earth Exploration (CDEX) decided to discontinue riser operations at Site C0002 on 23 November 2012 (see “Operations” in the “Site C0002” chapter [Strasser et al., 2014b]). In light of this decision, we completed riserless coring in IODP Holes C0002H (1100.5–1120 mbsf), C0002J (902–926.7 mbsf), C0002K (200–286.5 mbsf), C0002L (277–505 mbsf), C0021B (0–194.5 mbsf), and C0022B (0–419.5 mbsf). Riserless LWD operations were completed in IODP Holes C0012H (0–710 mbsf), C0018B (0–350 mbsf), C0021A (0–294 mbsf), and C0022A (0–420.5 mbsf) (Table T1 in the “Expedition 338 summary” chapter [Strasser et al., 2014a]). Previous IODP work at Site C0002 included logging and coring during Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Stages 1 and 2. LWD operations provided data from 0 to 1401.5 mbsf (Hole C0002A; Expedition 314 Scientists, 2009a) and 0 to 980 mbsf (Hole C0002G; Expedition 332 Scientists, 2011). Coring at Site C0002 previously sampled 0–203.5 mbsf (Holes C0002C and C0002D) and 475–1057 mbsf (Hole C0002B) (Expedition 315 Scientists, 2009b). During riser operations, we expanded the data sets at Site C0002. Gas from drilling mud was analyzed in near real time in a mud-gas monitoring laboratory and was sampled for postcruise research. Continuous LWD/MWD data were collected in real time for quality control and for initial assessment of borehole environment and formation properties. Recorded-mode LWD data provided higher spatial sampling of downhole parameters and conditions. Cuttings were sampled for standard shipboard analyses and shore-based research. Riserless coring in Holes C0002H and C0002J–C0002L provided additional core samples (whole round and discrete) for standard shipboard and shore-based research. Riserless operations at Site C0012 provided an extensive LWD data set for characterization of the sediment and basement conditions and properties. These logging data, which extend from 0 to 710 mbsf, complemented previous coring work at Site C0012 (Expedition 322 Scientists, 2010c; Expedition 333 Scientists, 2012b) and provided additional data in intervals where core recovery was sparse, especially within the basement. Hole C0018B was the logging complement to coring in Hole C0018A. The LWD hole provided in situ characterization of mass transport deposits (MTDs) that were cored in Hole C0018A (Expedition 333 Scientists, 2012c) as part of the Nankai Trough Submarine Landslide History ancillary project letter. Hole C0018A sampled a stacked series of MTDs that are related to active tectonic processes. Logging data provide additional characterization of the features in the MTDs and the sediments that bound them, which allows additional constraints on the evolution of MTDs. Riserless coring and LWD operations at Site C0021 (proposed Site NTS-1C) targeted a more proximal site for MTDs observed at Site C0018. Combined with LWD and core data obtained at Site C0018, LWD and coring at Site C0021 provide additional information on the nature, provenance, and kinematics of MTDs, as well as constraints on sliding dynamics and the tsunamigenic potential of MTDs. Riserless coring and LWD operations at Site C0022 (proposed Site NT2-13A) were initiated to provide new constraints on the timing of activity along the splay fault. Site C0022 is located between IODP Sites C0004 and C0008 (Expedition 314 Scientists, 2009b; Expedition 316 Scientists, 2009b, 2009c). The objectives of the site were to obtain samples for precise age dating of sediment deformation at the tip of the splay fault to determine the age of activity. Core data provided samples for dating and deformation analysis. Logging data provided in situ conditions and resistivity images of deformation features.

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