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doi:10.2204/iodp.proc.343343T.102.2013 Methods1IntroductionThis chapter documents the procedures and methods employed in the shipboard work described in the Expedition Reports section of the Expedition 343/343T Proceedings of the Integrated Ocean Drilling Program volume. Methods for shore-based analysis of Integrated Ocean Drilling Program (IODP) Expedition 343/343T samples and data will be described in individual scientific contributions to be published elsewhere. All shipboard scientists contributed to the completion of this volume. Numbering of sites, holes, cores, and samplesSites drilled by the D/V Chikyu are numbered consecutively from the first site (drilled by the Chikyu during IODP Expedition 314) with the prefix “C” because the site is drilled using the Japan Agency for Marine-Earth Science and Technology (JAMSTEC)/Center for Deep Earth Exploration (CDEX) platform. A site refers to one or more holes drilled while the ship is positioned within 300 m of the first hole, and a letter suffix distinguishes each hole drilled at the same site. The first hole drilled at a given site is assigned the site number modified by the suffix “A,” the second hole takes the site number and the suffix “B,” and so forth. (Fig. F1). The cored interval is measured in meters below seafloor according to the depth determined by the procedures described in IODP Depth Scales Terminology version 2 (www.iodp.org/program-policies/). This depth scale is equivalent to the Ocean Drilling Program (ODP) depth scale meters below seafloor (mbsf). In general, 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 to which coring advanced. Each coring interval is generally ≤9.5 m, which is the length of a core barrel; however, coring intervals may be shorter. Cores taken from a hole are numbered sequentially from the top of the hole downward. Core numbers and their associated cored intervals are unique in a given hole. Generally, maximum recovery for a single core is 9.5 m of sediment in a plastic liner (6.6 cm internal diameter) plus ~0.2 m (without a plastic liner) of sediment in the core catcher, a device at the bottom of the core barrel that prevents loss of the core while the barrel is retrieved from the hole. In certain situations, recovery may exceed the 9.5 m maximum. In soft sediment, this is normally caused by core expansion resulting from depressurization. Recovered cores are divided into 1.5 m sections that are numbered serially from the top of each core. When full recovery is obtained, these sections are numbered from 1 to 7, with the last section usually being shorter than 1.5 m. When a recovered core is shorter than the cored interval, the top of the recovered core is equated with the top of the cored interval by convention to achieve consistency in handling analytic data derived from the cores. All sections recovered are placed immediately adjacent to each other in the core tray. Samples and descriptions of cores are designated by distance, measured in centimeters from the top of the section to the top and bottom of each sample or interval. By convention, when a core is described, material recovered from the core catcher is placed below the last section and labeled with the suffix “CC.” In sedimentary cores, core catcher sections are treated as separate sections. The core catcher is placed at the top of the cored interval when material is recovered only in the core catcher. However, information supplied by the drillers or logging may allow more precise interpretation of the correct position of core catcher material within an incomplete recovered core interval. Complete sample identification numbers include the following information: expedition, site, hole, core number, core type, and section number, followed by the interval in centimeters measured from the top of the section. For example, the sample identification “343-C0019E-17R-1, 4–7 cm” indicates a 3 cm sample removed from the interval between 4 and 7 cm below the top of Section 1 of Core 17 (“R” designates that this core was taken with the rotary core barrel [RCB]) in Hole E at Site C0019 during Expedition 343. Core handlingThe following sections describe in detail the flow of core from the drill floor through the laboratory. Core handling during Expedition 343 followed the general core flow procedure implemented during recent IODP expeditions on the Chikyu. (Expedition 331 Scientists, 2011; Expedition 322 Scientists, 2010). Modifications were made to the core flow when necessary to ensure that core sections of particular interest to the expedition (e.g., principal slip surfaces or zones) were not damaged. The specific core flow for this expedition is illustrated in Figure F2. Core cutting areaRotary cores were recovered from the drill site in 9.5 m long segments. As soon as the core was retrieved on deck, the core catcher was delivered to the core cutting area. A ~150 cm3 (~5 cm whole round) sample of material taken from the core catcher was preserved for micropaleontologic analysis, and the rest of the core catcher material was packed into a core liner and entered into the general core flow. Each core segment was then carefully transferred to the core cutting area. The recovered core length and the total length of void space were then measured and entered into the J-CORES database, along with core identification information, drilling advance, and depth information (Expedition 331 Scientists, 2011). Prior to cutting the core into 1.5 m sections, a visual inspection was made to try to identify structurally important features to avoid cutting directly through lithologic contacts or structures. If a structurally important feature was identified, the locations of divisions between core sections were modified to ensure the structure was not disturbed. The length of the modified sections was ≤1.4 m, the maximum length of core that can be run through the 3-D X-ray computed tomography (CT) scanner (GE Medical System LightSpeed Ultra 16). The core was then cut into sequentially numbered sections. A 5 cm3 sample was taken from the bottom of the first core section for headspace gas analysis. A 1 cm3 sample was taken from the bottom of each section to test for the presence of hydrogen gas. Pertinent members of the science party then decided on the preferred order of the X-ray CT scanning, such that sections of the core that appeared to contain enough intact rock to facilitate time-sensitive whole-round core (WRC) sampling for interstitial water, microbiology, and anelastic strain recovery were scanned first. Core processing deckEach core section was imaged using the X-ray CT scanner, with priority given to sections containing the proposed time-sensitive WRCs. X-ray CT scans were performed on complete sections, and data were reviewed in real time by the X-ray CT watchdog, a structural geologist, who used the scans to approve the location of each WRC sample. If the watchdog identified a feature of specific interest to the expedition coincident with a proposed WRC location, the core section in question was set aside and a second section from which time-sensitive WRC samples could be taken was scanned. After approval of time-sensitive WRC locations by the X-ray CT watchdog, these samples were cut for immediate analysis. The remaining core sections were then allowed to rest in order to reach thermal equilibrium with the temperature in the laboratory (~0–1 h, or until core temperature reached ~20°C). Once equilibrium was reached, the sections were scanned for gamma ray attenuation (GRA) density, P-wave velocity (PWV), magnetic susceptibility, noncontact resistivity (NCR), and natural gamma radiation (NGR) using the multisensor core logger system (Geotek, Ltd.) for whole-round (MSCL-W) analysis. MSCL-W analysis was conducted at 4 cm intervals for GRA, PWV, magnetic susceptibility, and NCR and at 15 cm intervals for NGR. Core sections possibly containing features of structural interest identified by the X-ray CT watchdog were scanned at the highest resolution possible given time constraints and the length of the core section, up to a maximum resolution of 1 mm for GRA, PWV, magnetic susceptibility, and NCR and 25 mm for NGR. If high-resolution MSCL-W analysis appeared to confirm the presence of a structurally important feature, a structural WRC was cut, sealed, and placed in –4°C storage for separate processing (with advice and consent of the Co-Chief Scientists). The rest of the core was returned to the general core flow. Following MSCL-W analysis, the X-ray CT and MSCL-W scans were oriented with respect to two longitudinal lines drawn on the core liner that demarcated the working half from the archive half. WRC samples were then taken for analyses that were not time sensitive. After all WRC samples were taken, the core section was split lengthwise along the lines delimiting the archive and working halves, which were then sent for further processing. Working halfHard rock thermal conductivity measurements were conducted on the working half of the core. After these measurements, the following time-sensitive physical properties samples were taken as close together as possible:
MAD samples were taken once per section; in some cases more samples were taken if the section contained more than one distinct lithology. Cubic samples for resistivity and discrete PWV were taken once per core, depending on core quality. A total of five cubic samples were used for elastic wave velocity measurements under high pressure. The locations of these samples were carefully chosen to ensure they did not coincide with areas of particular structural interest. Visual core description (VCD) of the working half of the core primarily focused on structural geology, although lithologic units of interest were also noted. Members of the science party representing geochemistry, physical properties, core description, microbiology, and paleomagnetism then used the VCD observations to determine discrete sampling locations for
The samples for XRF and XRD analyses were located as close as possible to the time-sensitive physical properties samples already taken from the core. Once all locations were agreed upon, the samples were taken from the core and processed (for detailed methodologies related to a specific analysis, please refer to the appropriate section below). The working half was then wrapped in plastic film, shrink wrapped, and placed in cold storage (–4°C). Archive halfNondestructive digital photo image scanning and color spectrophotometry were carried out on the archive half using the photo image logger (MSCL-I) and the color spectroscopy logger (MSCL-C), respectively (Expedition 331 Scientists, 2011). The archive half was then sent to the core description scientists for visual core description. Description of the archive half focused primarily on lithologic description, but features of possible structural interest were noted so that their complement could be identified in the working half for additional description, measurement, and subsampling, if warranted. Minuscule samples (approximately the amount that could easily be picked up on the end of a toothpick) were taken from the archive half in areas of lithologic interest for smear slide analysis. Selected sections of the archive half were sent back through the X-ray CT scanner to document any structural damage done to the core during core splitting or as a result of desiccation during description. The archive half was then wrapped and sealed following the same procedures described above for the working half. |
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