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doi:10.2204/iodp.proc.344.102.2013 Methods1R.N. Harris, A. Sakaguchi, K. Petronotis, A.T. Baxter, R. Berg, A. Burkett, D. Charpentier, J. Choi, P. Diz Ferreiro, M. Hamahashi, Y. Hashimoto, K. Heydolph, L. Jovane, M. Kastner, W. Kurz, S.O. Kutterolf, Y. Li, A. Malinverno, K.M. Martin, C. Millan, D.B. Nascimento, S. Saito, M.I. Sandoval Gutierrez, E.J. Screaton, C.E. Smith-Duque, E.A. Solomon, S.M. Straub, W. Tanikawa, M.E. Torres, H. Uchimura, P. Vannucchi, Y. Yamamoto, Q. Yan, and X. Zhao2IntroductionThis introductory section provides an overview of operations, depth conventions, curatorial procedures, and general core handling and analysis during Integrated Ocean Drilling Program (IODP) Expedition 344. This information will help the reader understand the basis of our shipboard observations and preliminary interpretations. It will also enable interested investigators to identify data and select samples for further analysis. The information presented here pertains to shipboard operations and analyses described in the site chapters. Methods used by various investigators for shore-based analyses of Expedition 344 samples and data associated with separate scientific studies can be found in individual publications in various professional journals. Site locationsGPS coordinates from precruise site surveys or from preexisting IODP sites were used to position the vessel at Expedition 344 sites. A SyQwest Bathy 2010 CHIRP subbottom profiler was used to monitor seafloor depth on the approach to each site to confirm depth profiles. Once the vessel was positioned at a site, the thrusters were lowered and a positioning beacon was dropped to the seafloor at all sites except Site U1381. Dynamic positioning control of the vessel uses navigational input from the GPS system and triangulation to the seafloor beacon, weighted by the estimated positional accuracy. The final hole position was the mean position calculated from GPS data collected over a significant portion of the time the hole was occupied. Drilling operationsThe advanced piston corer (APC), extended core barrel (XCB), and rotary core barrel (RCB) systems were used during Expedition 344. The APC and XCB systems were used to recover the sedimentary section in Holes U1381C, U1412A, U1412B, U1413A, U1413B, and U1414A and the sediment/basement interface at Hole U1381C. The RCB system was used to recover sediment and basement sections in Holes U1380C, U1412C, U1412D, U1413C, and U1414A. The APC system cuts soft-sediment cores with minimal coring disturbance relative to other IODP coring systems. After the APC core barrel is lowered through the drill pipe and lands above the bit, the drill pipe is pressured up until the two shear pins that hold the inner barrel attached to the outer barrel fail. The inner barrel then advances into the formation and cuts the core. The driller can detect a successful cut, or “full stroke,” from observation of the pressure gauge on the rig floor because the excess pressure accumulated prior to the stroke drops rapidly. APC refusal is conventionally defined in two ways: (1) the piston fails to achieve a complete stroke (as determined from the pump pressure and recovery reading) because the formation is too hard or (2) excessive force (>60,000 lb; ~267 kN) is required to pull the core barrel out of the formation. When a full or partial stroke can be achieved but excessive force cannot retrieve the barrel, the core barrel can be “drilled over” (i.e., after the inner core barrel is successfully shot into the formation, the drill bit is advanced to total depth to free the APC barrel). The XCB system was used to advance the hole when APC refusal occurred before the target depth was reached or when drilling conditions required it. The XCB is a rotary system with a small cutting shoe that extends below the large rotary APC/XCB bit. The smaller bit can cut a semi-indurated core with less torque and fluid circulation than the main bit, potentially improving recovery. The XCB cutting shoe (bit) extends ~30.5 cm ahead of the main bit in soft sediment but can be retracted into the main bit when hard formations are encountered.
The bottom-hole assembly (BHA) used for APC and XCB coring was composed of an 11 The RCB BHA included a 9⅞ inch RCB drill bit, a bit sub, an outer core barrel, a modified top sub, a modified head sub, a variable number of 8¼ inch control length drill collars, a tapered drill collar, two stands of 5½ inch drill pipe, and a crossover sub to the drill pipe that extended to the surface. Nonmagnetic core barrels were used most of the time in the APC and RCB sections, and APC cores were oriented with the FlexIT tool when coring conditions allowed. Formation temperature measurements were taken in all APC holes to determine heat flow through the sedimentary section (see “Physical properties”). Most APC-cored intervals were ~9.5 m long, and XCB-cored intervals were ~9.7–9.8 m long, which is the length of both a standard core barrel and a joint of drill pipe. In some cases, the hole was drilled or “washed” ahead without recovering sediment to advance the drill bit to the target depth at which core recovery needed to resume. Depths of drilled intervals and core recovery are provided in the “Operations” section of each site chapter. IODP depth conventionsDeep Sea Drilling Project, Ocean Drilling Program (ODP), and IODP Phase 1 reports, diagrams, and publications used three primary designations to reference depth: meters below rig floor (mbrf), meters below seafloor (mbsf), and meters composite depth (mcd). These designations evolved over many years to meet the needs of individual science parties, but over the course of ODP and early IODP scientific drilling, issues with the existing depth scale designations and the lack of a consistent framework became apparent. A new classification and nomenclature for depth scale types was defined in 2006–2007 during the hiatus in IODP drilling operations to ensure that data acquisition, scale mapping, and the construction of composite splices are unequivocal (see “IODP Depth Scales Terminology” at www.iodp.org/program-policies/). The primary depth scales are measured by the length of drill string (e.g., drilling depth below rig floor [DRF] and drilling depth below seafloor [DSF]), core recovered (e.g., core depth below seafloor [CSF] and core composite depth below seafloor [CCSF]), and logging wireline (e.g., wireline log depth below rig floor [WRF] and wireline log depth below seafloor [WSF]). In cases where multiple logging passes are made, wireline log depths are mapped to one reference pass, creating the wireline log matched depth below seafloor (WMSF). All units are in meters. The relationship between scales is defined either by protocol, such as the rules for computation of CSF from DSF, or user-defined correlations, such as core-to-log correlation or stratigraphic correlation of cores between holes to create a common CCSF scale from the CSF scale used in each hole. The distinction in nomenclature should make the reader aware that the same depth value in different depth scales usually does not refer to exactly the same stratigraphic interval. During Expedition 344, unless otherwise noted, depths below rig floor were calculated as DRF and are reported as mbrf, core depths below seafloor were calculated as CSF-A and are reported as mbsf, and downhole wireline depths were calculated as WMSF and are reported as mbsf. Curatorial procedures and sample depth calculationsNumbering of sites, holes, cores, and samples followed standard IODP procedure. A full curatorial identifier for a sample consists of the following information: expedition, site, hole, core number, core type, section number, section half, piece number (hard rocks only), and interval in centimeters measured from the top of the core section. For example, a sample identification of “344-U1412A-2H-5W, 80–85 cm,” indicates a 5 cm sample removed from the interval between 80 and 85 cm below the top of Section 5 (working half) of Core 2 of Hole A at Site U1412 during Expedition 344 (Fig. F1). The drilling system used to obtain a core is designated by the core type: H = APC, X = XCB, and R = RCB. The “U” preceding the hole number indicates the hole was drilled by the U.S. Implementing Organization (USIO) platform, the R/V JOIDES Resolution. The depths of core intervals are defined by the length of drill string, the seafloor depth, and the amount the driller advanced the core barrel. The length of the core is defined by the sum of the lengths of the core sections. The CSF depth of a sample in a section is calculated by adding (1) the core-top depth measured with the drill string, (2) the lengths of all higher sections in the core, and (3) the offset of the sample below the section top. A soft to semisoft sediment core from less than a few hundred meters below seafloor expands upon recovery (typically a few percent to as much as 15%), so the recovered interval may not match the cored interval. In addition, a coring gap typically occurs between cores. Thus, a discrepancy between DSF and CSF depths can exist with regard to a stratigraphic interval. Furthermore, when core recovery is >100% of the cored interval, a sample taken from the bottom of a core will have a CSF depth deeper than that of a sample from the top of the subsequent core (i.e., the data associated with the two core intervals overlap on the CSF-A scale). If a core has incomplete recovery, for curation purposes all cored material is assumed to originate from the top of the drilled interval as a continuous section; the true depth interval within the cored interval is unknown. This should be considered a sampling uncertainty in age-depth analysis or correlation of core data with downhole logging data. Core handling and analysisCores were extracted from the core barrel in plastic liners. The liners were carried from the rig floor to the core processing area on the catwalk outside the core laboratory, where they were split into ~1.5 m sections. Blue (uphole) and clear (downhole) liner caps were attached with acetone onto the cut liner sections. SedimentAs soon as cores arrived on deck, core catcher samples were taken for biostratigraphic analysis. Once the cores were cut into sections, whole-round samples were taken for shipboard interstitial water analyses and postcruise microbiological studies. When a whole-round sample was removed, a yellow cap was used to denote the missing interval. Gas samples were taken using a syringe for hydrocarbon analysis as part of the shipboard safety protocol. Syringe samples were also taken for shore-based microbiology analyses. See Figure F2 for a schematic of core flow through the laboratories. Core sections were placed in core racks in the laboratory. When the cores reached equilibrium with laboratory temperature (typically after 3 h), whole-round core sections were run through the Whole-Round Multisensor Logger (WRMSL) for P-wave velocity, magnetic susceptibility, and bulk density measurements. In some cases, whole-round samples were taken for anelastic strain recovery analyses following this step. Whole-round core sections were run through the Natural Gamma Radiation Logger (NGRL). Additional whole-round samples were taken for shore-based physical properties analyses. Thermal conductivity measurements were made at varying intervals (see “Physical properties”). Sediment cores were split lengthwise from bottom to top into working and archive halves. Investigators should note that older material may have been transported upward on the split face of each section during splitting. The working half of each core was first described by the structural geologists. Samples were taken first for discrete physical properties and paleomagnetic analyses, followed by samples taken for shore-based studies based on the sampling plan agreed upon by the science party and shipboard curator and for remaining shipboard analyses such as bulk X-ray diffraction and carbonate. The archive half of each core was scanned on the Section Half Imaging Logger (SHIL) and measured for color reflectance and point magnetic susceptibility on the Section Half Multisensor Logger (SHMSL). Labeled foam pieces were used in place of missing whole-round intervals in the SHIL images. Archive halves were then described visually and by means of smear slides. Finally, the magnetization of archive halves and discrete pieces was measured with the cryogenic magnetometer and spinner magnetometer. Hard rocksPieces were pushed to the bottom of 1.5 m liner sections, and the total rock length was measured. The length was entered into the database using the SampleMaster application as “created length.” This number was used to calculate recovery. Liner sections were then transferred to the core splitting room. Whole-round samples were taken for postcruise microbiological and geochemical analyses following consultation with other members of the science party. Images were taken of these samples before they were bagged and processed. In cases where a whole-round sample was removed, a yellow cap was used to denote the missing interval. Oriented pieces of core were marked on the bottom with a red wax pencil to preserve orientation. In several cases, pieces were too small to be oriented with certainty. Adjacent but broken pieces that could be fit together along fractures were curated as single pieces. The petrologist on shift confirmed piece matches and marked the split line on the pieces, which defined how the pieces were to be cut in two equal halves. The aim was to maximize the expression of dipping structures on the cut face of the core while maintaining representative features in both archive and working halves. A plastic spacer was secured with acetone to the split core liner between individual pieces or reconstructed contiguous groups of subpieces. These spacers may represent substantial intervals of no recovery. The length of each section of core, including spacers, was entered into the database as “curated length,” which commonly differs by a few to several centimeters from the length measured on the catwalk. The database recalculated the depth of each piece based on the curated length. Core sections were placed in core racks in the laboratory. When the cores reached equilibrium with laboratory temperature (typically after 3 h), whole-round core sections were run through the WRMSL and the NGRL. Each piece of core was split with a diamond-impregnated saw into an archive half and a working half, with the positions of plastic spacers between pieces maintained in both halves. Pieces were numbered sequentially from the top of each section, beginning with 1. Separate subpieces within a single piece were assigned the same number but were lettered consecutively (e.g., 1A, 1B, 1C, etc.). Pieces were labeled on the outer cylindrical surface of the core. For oriented pieces, an arrow pointing to the top of the section was added to the label. The piece’s orientation was recorded in the database using the SampleMaster application. The working half of each core was first described by the structural geologists. Samples were taken for shipboard analyses, and thermal conductivity measurements were made on selected samples (see “Physical properties”). The archive half of each core was scanned on the SHIL and measured for color reflectance and point magnetic susceptibility on the SHMSL. Archive halves were then described visually. Because there was insufficient time to produce and describe thin sections on board, thin section description was completed on shore and the data were entered into the database postcruise. Finally, the magnetization of archive halves and discrete pieces was measured with the cryogenic magnetometer and spinner magnetometer. Sampling for shore-based studies was delayed until the end of coring. Sampling was conducted based on the sampling plan agreed upon by the science party and shipboard curator. When all shipboard measurement steps were completed, cores were wrapped, sealed in plastic tubes, and transferred to cold storage aboard the ship. At the end of the expedition, the cores were kept on the ship, and at the conclusion of Expedition 345 and the transit to Victoria, British Columbia (Canada), they were transferred into refrigerated trucks and transported to cold storage at the IODP Gulf Coast Repository in College Station, Texas (USA). Core sample disturbanceCores may be significantly disturbed and contain extraneous material as a result of the coring and core handling process. In formations with loose sand layers, sand from intervals higher in the hole may be washed down by drilling circulation, accumulate at the bottom of the hole, and be sampled with the next core. The uppermost 10–50 cm of each core must therefore be examined critically during description for potential “fall-in.” Common coring-induced deformation includes the concave-downward appearance of originally horizontal bedding. Piston action may result in fluidization (“flow-in”) at the bottom of APC cores. Retrieval from depth to the surface may result in elastic rebound. Gas that is in solution at depth may become free and drive apart core segments within the liner. When gas content is high, pressure must be relieved for safety reasons before the cores are cut into segments. This is accomplished by drilling holes into the liner, which forces some sediment out of the liner along with the gas. These disturbances are described in each site chapter and graphically indicated on the visual core descriptions (VCDs or “barrel sheets”). Authorship of methods and site chaptersThe separate sections of the site chapters were written by the following scientists (authors are listed in alphabetical order; see “Expedition 344 science party” for contact information):
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inch (~29.05 cm) drill bit, a bit sub, a seal bore drill collar, a landing saver sub, a modified top sub, a modified head sub, five 8¼ inch control length drill collars, a tapered drill collar, two stands of 5½ inch transition drill pipe, and a crossover sub to the drill pipe that extended to the surface.