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doi:10.2204/iodp.proc.334.102.2012 Methods1Expedition 334 Scientists2Introduction, operations, and curationInformation assembled in this chapter will help the reader understand the basis for shipboard observations and preliminary conclusions of Integrated Ocean Drilling Program (IODP) Expedition 334. It will also enable the interested investigator to identify data and select samples for further analysis. Information presented here concerns only shipboard operations and analyses described in the site chapters (Sites U1378–U1381). This introductory section provides an overview of shipboard operations, curatorial conventions, and general core handling and analysis. Methods used by various investigators for shore-based analyses of Expedition 334 samples and data will be described in individual publications in various professional journals and the “Expedition research results” chapters of this Proceedings volume. Site locationsAt all Expedition 334 sites, GPS coordinates from precruise site surveys were used to position the vessel on site. The only seismic system used during the cruise was the Syquest Bathy 2010 CHIRP subbottom profiler, which was monitored on the approach to each site to ascertain that the seafloor depth agreed with that from the precruise survey. Once the vessel was positioned at a site, the thrusters were lowered and a positioning beacon was dropped to the seafloor. The dynamic positioning control of the vessel uses navigational input from the GPS and triangulation to the seafloor beacon, weighted by the estimated positional accuracy. The final hole position was the mean position calculated from the GPS data collected over the time that the hole was occupied. Coring and drilling operationsThe advanced piston corer (APC), extended core barrel (XCB), and rotary core barrel (RCB) systems were used during Expedition 334. These standard coring systems and their characteristics are summarized in Graber et al. (2002). 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 near 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 the pressure gauge on the rig floor. The XCB system is deployed when the formation becomes too stiff or too hard for the APC system. The XCB cutting shoe (bit) extends as far as ~30.5 cm ahead of the main bit in soft sediments but retracts into the main bit if hard formations are encountered. APC refusal is conventionally defined in two ways: (1) the piston fails to achieve a complete stroke (as determined from the pump pressure 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 full or partial stroke can be achieved but excessive force cannot retrieve the barrel, the core barrel can be “drilled over”; after the inner core barrel is successfully shot into the formation, the drill bit is advanced to total depth to free the APC barrel. This strategy allows a hole to be advanced much farther with the APC, the preferred coring tool. Nonmagnetic core barrels are commonly used during all conventional APC coring, but the APC drillover technique is not typically conducted in the first hole at each site if hard rock might be encountered. Standard steel core barrels are usually used when utilizing the drillover technique because they are stronger than the nonmagnetic barrels. Most APC/XCB cored intervals are ~9.5 m long, which is the length of a standard core barrel. However, the amount of advance during coring varied case by case. Core operations and recovery information is shown in the “Operations” section of each site chapter. Some APC cores were oriented using the Flexit tool (see “Paleomagnetism”). Formation temperature measurements were made in Hole U1378B, Hole U1379C, and Hole U1381B (see “Downhole logging”). Downhole logging was executed in Holes U1378A and U1379A using logging while drilling (LWD). The XCB system was used to advance the hole when APC refusal occurred in a hole before the target depth was reached and when the formation became too stiff for the APC system or when drilling hard substrate. The XCB is a rotary system with a small cutting shoe extending below the large rotary drill bit. The smaller bit can cut a semi-indurated core with less torque and fluid circulation than the main bit and thus optimizes recovery.
The bottom-hole assembly (BHA) is the lowermost part of the drill string. The exact configuration of the BHA is reported in “Operations” in each site chapter. A typical APC/XCB BHA consists of a drill bit (11 The RCB system was deployed to drill the sediment and basalt at Site U1381 because the basalt was the main target at this site. The RCB is a conventional rotary drilling system and requires a dedicated RCB BHA and a dedicated RCB drilling bit (9⅞ inch outer diameter). A typical BHA for RCB coring includes an RCB drill bit, a mechanical bit release (MBR), a modified head sub, an outer core barrel, a modified top sub, and a series of drill collars followed by tapered drill collar and 5½ inch drill pipe. Curatorial procedures and sample depth calculationsNumbering of sites, holes, cores, and samples followed standard IODP procedure. Drilling sites are numbered consecutively from the first site drilled by the Glomar Challenger in 1968. IODP Expedition 301 began using the prefix “U” to designate sites occupied by the US Implementing Organization (USIO) vessel, the R/V JOIDES Resolution. For all IODP drill sites, a letter suffix distinguishes each hole cored at the same site. The first hole cored is assigned the site number modified by the suffix “A,” the second hole takes the site number and the suffix “B,” and so forth. For Expedition 334, each site has two or more cored holes (A, B, C, etc). A full curatorial identifier for a sample consists of the following information: expedition, site, hole, core number, core type, section number, and interval in centimeters measured from the top of the core section and also the sampling tools and volumes taken. For example, in sediment, a sample identification of “334-U1378B-1H-2, 10–12 cm” represents a sample taken from the interval between 10 and 12 cm below the top of Section 2 of Core 1 (“H” designates that this core was taken with the APC system) of Hole B of Site U1378 during Expedition 334. For hard rocks, a sample identification of “334-U1381A-3R-8 (Piece 1, 4–7 cm)” indicates a 3 cm sample of Piece 1 removed from the interval between 4 and 7 cm below the top of Section 8 of Core 3 (“R” designates that this core was taken with the RCB) in Hole A at Site U1381. For cores taken with the XCB, the core type is indicated by an “X” after the core number. During Expedition 334, Site U1380 sediment was drilled without coring because the target recovery was underlying basement rock. Drilled intervals are assigned double-digit numbers, and the cores recovered after a drilled interval are assigned the following number in combination with the corresponding letter for drilling/coring system. For example, the drilled interval in Hole U1381A was designated 334-U1381A-11, where the first “1” indicates drilled interval 1 and the second “1” indicates the first section of that interval that was drilled. The first core recovered in Hole U1381A after the drilled interval was designated 334-U1381A-2R (“R” for rotary core barrel). The cored interval is measured in meters below seafloor (mbsf) according to the core depth below seafloor, method A (CSF-A), depth scale (see IODP Depth Scale Terminology at www.iodp.org/program-policies/). In general, the depth below seafloor is determined by subtracting the water depth estimated from the initial drill pipe measurement to the seafloor from the total drill pipe measurement. The depth interval assigned to an individual core begins with the depth below seafloor at which coring began and extends to the depth that coring advanced. Each coring interval is generally ~9.5 m, which is the length of a core barrel; however, coring intervals may be shorter. During Expedition 334, unless otherwise noted, all core depths below seafloor have been calculated as CSF-A and all LWD depths calculated as LWD depth below seafloor (LSF). For ease of communication of shipboard results, all depths are reported in this volume as “mbsf” unless otherwise noted. Core handling and analysisAs soon as cores arrived on deck, they were extracted from the core barrel in plastic liners. These 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. Liner caps (blue = top, colorless = bottom) were placed onto liner sections on the catwalk by the curator. Hard rock pieces were pushed to the top of the liner sections and total rock length was measured. The length was entered into the database using the SampleMaster application as “created” length. Created length is used to calculate recovery. Headspace samples were taken from freshly exposed end of a top core section and next to the interstitial water sample immediately after core retrieval using a brass boring tool or plastic syringe for immediate hydrocarbon analysis as part of the shipboard safety and pollution prevention program (see “Geochemistry and microbiology”). Typically this procedure is done in the first hole drilled at a site. However, the Environmental Protection and Safety Panel and the Texas A&M University Safety Panel approved our proposal to first drill a logging dedicated hole at Sites U1378 and U1379 using LWD techniques. This procedure was considered safe, as methane wasn’t expected to be a problem at the sites drilled during Expedition 334 and borehole pressure was constantly monitored during the LWD operation (see “Downhole logging” for detailed information on the LWD operation). The first core from each hole (i.e., Core 1H) was sampled for bottom water if a mudline was recovered and seawater was present inside the top of the core liner (see “Operations” in each site chapter). The bottom seawater was used for comparative studies of microbial communities between seawater and subseafloor habitats. Cores from subsequent holes were processed on the catwalk, and whole-round sections were routinely taken and transferred immediately to the Geochemistry Laboratory for a wide range of geochemical and microbiological subsampling, including interstitial water extraction (see “Geochemistry and microbiology”). Once the subsampling was completed, the remaining pieces of the whole-round core sections were brought back to the Core Laboratory for routine core processing. Basalt cores were brought to the Core Laboratory for routine core processing. After splitting, the cores were visually examined and described in detail by the shipboard petrologists and structural geologists. Subsequent to this, the scientists interested in this material for diverse geochemical and petrological studies were able to mark their samples, and, after approval by the Sample Allocation Committee, the curator proceeded to cut the samples. As described in “Lithostratigraphy and petrology,” “Physical properties,” and “Paleomagnetism,” routine core processing in the Core Laboratory included whole-round logging of core sections and splitting into working and archive halves. Archive-half sections were then imaged with the Section Half Image Logger (SHIL), logged with the Section Half Multisensor Logger (SHMSL), and visually described for lithologic and petrological properties. The working halves were sampled for shipboard analyses and personal postexpedition research. In the Core Laboratory, whole-round sections were split lengthwise in the core splitting room to expose the core. For hard rock cores, oriented pieces of core were marked on the bottom with a blue wax pencil to preserve orientation, either before they were extracted from the core barrel or when they were removed from the split core liner. In some cases, pieces were too small to be oriented with certainty. Adjacent but broken core pieces that could be fit together along fractures were curated as single pieces. The petrologist on shift confirmed piece matches, corrected any errors, and marked the split line on the pieces, which defined how the pieces were 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 to the split core liner with acetone between individual pieces or reconstructed contiguous groups of subpieces. These spacers may represent a substantial interval of no recovery. The length of each section of core, including spacers, was entered into the curation database as “curated” length. Curated length commonly differs by a few to several centimeters from the created length measured on the catwalk. The database recalculates the assumed depth of each piece based on the curated length. Core description as well as sampling for shipboard analyses and personal research was done onboard. After completing the description of the archive half and sampling of the working half, both halves of the core were then shrink-wrapped, put into labeled plastic tubes, sealed, and transferred to cold storage space aboard the ship. At the end of the expedition, the cores and samples were transferred from the ship to refrigerated containers and shipped to cold storage at the IODP Gulf Coast Repository in College Station, Texas (USA). Drilling-induced core deformationCores may be significantly disturbed and contain extraneous material as a result of the coring and core handling process. Therefore, the top 10–50 cm of each core must be carefully examined for potential “fall-in” during description. Common coring-induced deformation includes concave-downward appearance of originally horizontal bedding. In APC cores, the motion of the piston may result in fluidization (flow-in) at the bottom of the cores. Retrieval from depth to the surface may result in elastic rebound. Observed core disturbances are described in the “Lithostratigraphy” section in each site chapter and graphically indicated on the core summary graphic reports (barrel sheets). Authorship of site chaptersThe separate sections of the site chapters and methods chapter were written by the following shipboard scientists (authors are listed in alphabetical order; no seniority is implied):
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inch outer diameter), a bit sub, a seal bore drill collar, a landing saver sub, a modified top sub, a modified head sub, a nonmagnetic drill collar (for APC/XCB), a number of 8 inch (~20.32 cm) drill collars, a tapered drill collar, six joints (two stands) of 5½ inch (~13.97 cm) drill pipe, and one crossover sub.