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doi:10.2204/iodp.proc.340.102.2013 Methods1Expedition 340 Scientists2IntroductionInformation in this chapter will help the reader understand the basis for shipboard observations and preliminary conclusions for Integrated Ocean Drilling Program (IODP) Expedition 340. 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 U1393–U1401). 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 340 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 340 sites, GPS coordinates from precruise site surveys were used to position the R/V JOIDES Resolution. 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 calculated from the mean position of the GPS data collected over the time that the hole was occupied. Coring and drilling operationsThe advanced piston corer (APC) and extended core barrel (XCB) were used during Expedition 340. These standard coring systems and their characteristics are summarized in Graber et al. (2002). The APC 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 pressurized until the two shear pins that hold the inner barrel attached to the outer barrel fail. The inner barrel then advances with minimal rotation 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 is deployed when the formation becomes too stiff or too hard for the APC. 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. The XCB is a rotary system with a small cutting shoe extending below the large rotary drill bit. The smaller bit can cut a semiindurated core with less torque and fluid circulation than the main bit and thus optimizes recovery. In situ temperature measurements were made by replacing the standard APC cutting shoe with the advanced piston corer temperature tool (APCT-3). The APCT-3 includes a battery pack, a data logger, and a temperature sensor. During deployment, the APC inner core barrel is lowered to the mudline, where it typically sits for 5 min before being lowered to the bottom of the borehole and penetrating the sediment. The core barrel is then decoupled from the drill string and left stationary to record temperature. Heat is generated by friction produced during penetration. Temperature is therefore measured every 2 s continuously for 5–10 min after firing so that the decay of the thermal disturbance is recorded, allowing the formation temperature to be calculated. During this time, fluid circulation within the hole is turned off so that temperature measurements are not affected. The APCT-3 could therefore only be used when hole conditions were stable. Finally, the coring shoe and barrel are extracted and returned to the deck where data is recovered from the data logger. Formation temperature measurements were made using the APCT-3 at Sites U1395–U1400 (see “Downhole logging”). 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 a full or partial stroke is 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 further with the APC, the preferred coring tool. Nonmagnetic core barrels are commonly used during APC coring to reduce magnetic overprinting of paleomagnetic measurements; these cores can be orientated using the FlexIt tool (see “Paleomagnetism”). Standard steel core barrels are used when utilizing the drillover technique because they are stronger than nonmagnetic barrels. The XCB is used to advance the hole when APC refusal occurs before the target depth is reached. 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 varies. Core operations and recovery information are given in the “Operations” section of each site chapter.
The bottom-hole assembly (BHA) is the lowermost part of the drill string. The exact configuration of the BHA is reported in the “Operations” section of each site chapter. A typical APC/XCB BHA consists of a drill bit (11 Downhole logging operations were conducted in Holes U1394, U1395, U1397, and U1399 (see “Downhole logging”). Curatorial procedures and sample depth calculationsNumbering of sites, holes, cores, and samples followed standard IODP procedure (Fig. F1). 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 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 340, 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 “340-U1394B-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 U1394 during Expedition 340. For cores taken with the XCB, the core type is indicated by an “X” after the core number. 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 U1396B was designated 340-U1396B-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 U1396B after the drilled interval was designated 340-U1396B-2H (“H” for APC). 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 or longer because of sediment expansion. Method B (CSF-B) corrects for sediment expansion, mathematically ensuring depth overlap does not occur between sections. During Expedition 340, unless otherwise noted, all core depths below seafloor have been calculated as CSF-A and all depths have been calculated as CSF-B for plotting physical properties. 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. Core catchers were sampled for biostratigraphic analyses. Liner caps (blue = top; colorless = bottom) were placed onto cut 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 the freshly exposed end of a core section using a brass boring tool for immediate hydrocarbon analysis as part of the shipboard safety and pollution prevention program (see “Geochemistry”). Cores 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”). Once subsampling was completed, the remaining pieces of whole-round core sections were brought back to the Core Laboratory for routine core processing. As described in “Lithostratigraphy,” “Physical properties,” and “Paleomagnetism,” routine core processing in the Core Laboratory included whole-round logging of core sections and core splitting. Twenty-four whole-round samples from all sites were taken for geotechnical analyses following whole-round logging but before core splitting. Core sections were split lengthwise in the core splitting room to expose the split core surface. 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. The working half is defined by the double lines scribed on the outside of the core liner and denoted by a “W” after the core section in the full identifier (e.g., 340-U1396B-2H-5W); “A” is used to denote the archive half. Archive-half sections were then imaged with the Section Half Image Logger (SHIL), measured for point source magnetic susceptibility and reflectance using the Section Half Multisensor Logger (SHMSL), measured for natural remanent magnetization (NRM) both before and after alternating field (AF) demagnetization with the superconducting rock magnetometer (SRM), and visually described for lithologic and petrological properties. The working halves were sampled for standard shipboard analyses including smear slides, moisture and density (MAD) samples, paleomagnetic cubes, nannofossils, percent carbonate, total carbon, and X-ray diffraction (XRD) analyses. The working half split section was measured for shear strength and P-wave velocity. Taking of personal research samples was deferred to an expedition sampling party at the IODP Gulf Coast Repository in College Station, Texas (USA) in August 2012. After completing routine core processing, both halves of the core were wrapped in plastic wrap, 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 Gulf Coast Repository. 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; see “Core descriptions”). |
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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.