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Previous | Next doi:10.2204/iodp.proc.301.105.2005 Methods1Expedition 301 Scientists2IntroductionThis "Methods" chapter documents the primary procedures and methods employed by the various shipboard laboratories during Integrated Ocean Drilling Program (IODP) Expedition 301. This information concerns only shipboard methods described in the site report chapters. Methods for shore-based analysis of Expedition 301 samples and data will be described in individual scientific contributions to be published after the cruise. Detailed drilling and engineering operations are described in the "Operations" sections of the individual site report chapters. Shipboard scientific proceduresNumbering of sites, holes, cores, and samplesExpedition numbers for IODP expeditions are sequential starting with 301. Drilling sites are numbered consecutively, and for the U.S. Implementing Organization (USIO)-operated platform, numbering starts with Site U1301 (the U indicates the USIO-operated platform). Multiple holes may be drilled at a single site. For all IODP drill sites, a letter suffix distinguishes each hole drilled at one site. The first hole drilled is assigned the site number modified by the suffix "A," the second hole takes the site number and the suffix "B," and so forth. The cored interval is measured in meters below seafloor (mbsf). The depth below seafloor is determined by subtracting the water depth estimated from the initial drill pipe measurement, which gives the length of pipe from the rig floor to the seafloor (meters below rig floor), from the total drill pipe measurement. Each cored interval is generally 9.5 m long, which is the length of a core barrel. Coring intervals may be shorter and may not necessarily be adjacent if they are separated by drilled intervals. A recovered core is typically divided into 1.5 m sections that are numbered serially from the top. When full recovery is obtained, the sections are numbered from 1 to 7, with the last section generally being <1.5 m (Fig. F1); rarely, an unusually long core may require more than 7 sections. When less than full recovery is obtained, there will be as many sections as needed to accommodate the length of the core recovered. By convention, material recovered from the core catcher of a sedimentary core is treated as a separate section labeled "core catcher" (or "CC") and placed below the last section recovered in the liner. The core catcher is assigned to the top of the cored interval in cases where material is recovered only in the core catcher. When recovered core is shorter than the cored interval, the top of the core, by convention, is equated to the top of the cored interval to achieve consistency in reporting depth-in-core. Any sample removed from a core is designated by distance measured in centimeters from the top of the section to the top and bottom of the sample removed. A full identification number for a sample consists of the following information: expedition, site, hole, core number, core type, section number, piece number (for hard rock), and interval in centimeters measured from the top of section. For example, a sample identification of "301-U1301A-3H-3, 80–85 cm," represents a sample removed from the interval 80–85 cm below the top of Section 3, Core 3H (H designates that this core was taken using the advanced piston corer [APC]), from Hole U1301A from Expedition 301 (Fig. F1). All IODP core identifiers indicate core type. The following abbreviations are used:
Core handlingSedimentary coresAs soon as a core is retrieved on deck, it goes through a sequence of processing steps. Usually, a sample is first taken from the core catcher and given to the paleontological laboratory for initial age assessment, but no micropaleontologic analyses were conducted during Expedition 301. The core is placed on a long horizontal rack outside the laboratory. For safety monitoring, small (~5 cm3) plugs of sediment are usually taken from the end of a few sections per core for headspace gas analysis. Gas samples may also be taken by piercing the core liner, typically at voids, and withdrawing gas into a syringe (referred to as vacuum-seal tube samples). Next, the core is marked into section lengths, each section is labeled, and the core is cut into sections. Whole-round samples for interstitial water (IW) and microbiological analyses are taken. Each section is sealed at the top and bottom by attaching color-coded plastic caps—blue to identify the top of a section and clear at the bottom. A yellow cap is placed on section ends where a whole-round sample has been removed, and the sample code is written on the yellow cap. Caps are usually secured to liners by coating the liner ends and inside rims of caps with acetone before attaching the caps. The core sections are carried into the laboratory, where individual sections are permanently labeled with an engraver. The length of the core in each section and the core catcher sample are measured to the nearest centimeter; this information is logged into the IODP database. Once they are in the laboratory, labeled, and equilibrated to ambient laboratory temperature (~1–3 h), whole-round core sections are run through the multisensor track (MST) and thermal conductivity measurements are made on soft-sediment cores. Whole-round samples for shore-based studies (e.g., consolidation, shear strength, permeability, structure, etc.) may be taken at this stage. Cores are split lengthwise into working and archive halves. Softer cores are split with a wire or saw, depending on the degree of induration. Harder cores are split with a band saw or diamond saw. Wire-cut cores are split from bottom to top, so investigators should be aware that older material could have been dragged up the core on the split face of each section. Igneous coresIgneous rock cores are handled differently from sediment cores. Once on deck, the core catcher sample is placed at the bottom of the core liner and total core recovery is calculated by pushing the rock pieces together and measuring to the nearest centimeter. Small fractured samples for microbiological cultivation experiments are collected from the catwalk immediately after the core liner is cut into sections. The core is cut into 1.5 m long sections and transferred into the laboratory. Whole-round samples are collected at this point for microbiological studies; these are handled using latex gloves, photographed, and removed to an anaerobic chamber as quickly as possible. The contents of each section are transferred into 1.5 m long sections of split core liner, where the bottoms of oriented pieces (i.e., pieces that clearly could not have rotated top to bottom about a horizontal axis in the liner) are marked with red wax pencil. This is done to ensure that orientation is not lost during the splitting and labeling processes. Macroscopic description of the core surface can be performed at this time. Plastic spacers separate individual pieces and/or reconstruct contiguous groups of pieces in the core liner. These spacers may represent substantial intervals of no recovery. The length of each section is recorded and entered into the database as the curated length. The curated length will commonly differ by a few centimeters from that measured on the catwalk. Each piece of core is split into archive and working halves, with the positions of spacers maintained for both halves. Each piece is numbered sequentially from the top of each section, beginning with number 1; reconstructed groups of pieces are assigned the same number, but they are lettered consecutively. Pieces are labeled only on the outer, cylindrical surfaces of the core. If the piece is oriented, an arrow pointing to the top of the section is added to the label. All coresFor both sedimentary and igneous cores, the archive half is described visually. Smear slides are made from small sediment samples taken from the archive half (all shipboard samples are analyzed on board and either archived at the IODP core repositories or made available to shipboard scientists for postcruise research). Digital images of the archive halves are made with a digital imaging system. Archive sections of sediment sections are run through the archive MST (AMST) for color reflectance spectroscopy measurements and susceptibility measurements with a point susceptibility meter. Both sedimentary and igneous sections are passed through the cryogenic magnetometer for magnetic remanence measurements. The archive half is then photographed using color film. Close-up color photographs are taken of particular features for illustrations in the summary of each site, as requested by individual scientists. The working half of the core is sampled for both shipboard and shore-based laboratory studies. Each sample is logged into the sampling database program by location and by the name of the investigator receiving the sample. The IODP curator and database maintain information about all samples taken. Samples are sealed in plastic vials, cubes, or bags, labeled, and stored as appropriate. Samples are routinely taken for shipboard physical properties, paleomagnetism, thin section, and geochemistry analyses, which are described in the sections below. Following initial shipboard scientific measurements and sampling, both halves of igneous cores are shrink-wrapped in plastic to prevent rock pieces from vibrating out of sequence during transit. Working and archive halves of both sedimentary and igneous cores are put into labeled plastic "D" tubes, sealed, and transferred to cold-storage space aboard the drilling vessel. During Expedition 301, the cores were shipped in refrigerated containers to cold storage at the IODP Gulf Coast Core Repository in College Station, Texas (USA). Top of page | Previous | Next |
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