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doi:10.2204/iodp.proc.309312.102.2006 Methods1Expedition 309/312 Scientists2IntroductionThis chapter documents the procedures and methods employed in the various shipboard laboratories during Expedition 309/312 of the Integrated Ocean Drilling Program (IODP). This information applies only to shipboard work described in the “Expedition reports” section of the Expedition 309/312 Proceedings volume. Methods for shore-based analysis of Expedition 309/312 samples and data will be described in the individual scientific contributions to be published in the “Research results” section of the Expedition 309/312 Proceedings volume and elsewhere. AuthorshipAll shipboard scientists contributed to the completion of this volume. The separate sections of the chapters were, however, written by groups of scientists as listed below (in order of contribution where appropriate and alphabetically otherwise): Combined Expedition 309/312
Basement drilled in Hole 1256D during Expedition 309
Basement drilled in Hole 1256D during Expedition 312
Numbering of sites, holes, cores, and samplesDrilling sites are numbered consecutively from the first site drilled by the Glomar Challenger in 1968. Starting with IODP Expedition 301, the prefix “U” designates sites occupied by the U.S. Implementing Organization (USIO) vessel. Site 1256 does not follow this nomenclature because it was started during Ocean Drilling Program (ODP) Leg 206. At a site, multiple holes can be drilled by removing the drill pipe from the seafloor, moving the ship a short distance, and then drilling a new hole. For all IODP drill sites, a letter suffix distinguishes each hole drilled at the same 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). 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 (measured in meters below rig floor [mbrf]), from the total drill pipe measurement. While on site, ship location over a hole is maintained with respect to a positioning beacon deployed on the seafloor and in active communication with the Nautrinix dynamic positioning system on the JOIDES Resolution. In general, the primary reference for dynamic positioning was the Global Positioning System (GPS); the beacon reference acts as a backup in the event that GPS is unreliable. During most IODP expeditions, each cored interval is generally 9.5–9.8 m long, which is the length of a core barrel. However, one potential cause of poor recovery in hard rock coring is core jamming in the bit or throat of the core barrel. Once the opening in the bit is jammed, core may be prevented from entering the core barrel. During ODP hard rock coring missions, a novel coring approach employed to improve recovery was to extract the core barrel at shorter penetration intervals in order to mitigate loss of core when the bit was blocked. Following this strategy, several cored intervals during Expedition 309 and all cored intervals during Expedition 312 were reduced to 4.5–5 m (half cores). Each recovered core is divided into 1.5 m sections that are numbered serially from the top. When full recovery is achieved, sections are numbered sequentially as recovered, starting with 1 at the top of the core; the last section may be shorter than 1.5 m (Fig. F1). When the recovered core is shorter than the cored interval, the top of the core is equated with the top of the cored interval (in meters below seafloor) by convention to achieve consistency in handling analytical data derived from cores. All pieces 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. A full identifier 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 “309-1256D-80R-1, 30–32 cm” represents a piece of core removed from the interval between 30 and 32 cm below the top of Section 1, Core 80 (R designates that this core was taken with the rotary core barrel) of Hole 1256D from Expedition 309 (Fig. F1). Core handlingSome cores recovered during Expedition 309 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 glued with acetone onto liner sections on the catwalk. The 1.5 m sections were transferred to the core splitting room, where the plastic liners were split lengthwise to expose the core. Most cores during Expedition 309 and all cores during Expedition 312 were recovered without plastic liners. Core pieces were extracted from the core barrel and placed in consecutive order in a split plastic liner. In either case, pieces of core were pushed together and the length of the core in each core liner was measured to the nearest centimeter; this measurement was entered into the IODP curation data acquisition program as liner length (LL in the database), and cores were transferred to the core splitting room. Most pieces of core were marked on the bottom with a red 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. Therefore, the red wax mark does not universally indicate that the core piece was oriented. Adjacent core pieces that could be fit together along fractures were curated as single pieces. A plastic spacer was secured to the split core liner with acetone between individual pieces and/or reconstructed contiguous groups of pieces. 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 the curated length. Curated length commonly differs by a few centimeters from the liner length measured on the catwalk. Subsequently, cores were marked to indicate a split line, ideally maximizing the expression of dipping structures on the cut face of the core while maintaining representative features in both archive and working halves. Each section was scanned using the shipboard multisensor track (MST) (see “Physical properties”), and the outer cylindrical surfaces of the whole-round pieces were scanned with the Deutsche Montan Technologie (DMT) Digital Color CoreScan system, using the split line marking for registration (see “Digital imaging”). Each piece of core was then split into archive and working halves, with the positions of plastic spacers between pieces maintained in both halves. Pieces are numbered sequentially from the top of each section, beginning with number 1; reconstructed groups of pieces are assigned the same number but are lettered consecutively. Pieces are labeled only on the outer cylindrical surfaces of the core. If the piece is oriented with respect to the way up, an arrow was added to the label, pointing to the top of the section. The archive half of each core was described, and observations were recorded on IODP templates and spreadsheets developed by the expedition scientists (for details, see individual disciplinary sections in this chapter). Digital images of the dry, cut faces of the archive halves were captured with the IODP digital imaging system (DIS). Archive-half sections were also passed through the cryogenic magnetometer for magnetic remanence measurements. Finally, digital photographs of the archive half were taken. Digital color close-up images were taken of particular features for illustrations in the summary of each site, as requested by individual scientists. Working halves of cores were sampled for both shipboard characterization of cores and shore-based studies. Samples were routinely taken for shipboard physical properties (minicore or 8 cm3 cube), paleomagnetic (minicore or 8 cm3 cube), thin section (billet or slab), and geochemical (billet or quarter-round) analyses, as described in the sections below. Each extracted sample was logged into the sampling database program by location and the name of the investigator receiving the sample or by type of shipboard sample. Records of all removed samples are kept by the IODP Marine Curatorial Specialist. Extracted samples were sealed in plastic vials, cubes, or bags and labeled. Following shipboard initial scientific measurements and sampling, both halves of the cores were shrink-wrapped in plastic to prevent rock pieces from moving out of sequence during transit. Working and archive halves were then put into labeled plastic tubes, sealed, and transferred to an onboard cold-storage space. At the end of Expedition 312, cores from both Expeditions 309 and 312 were transferred from the ship for permanent storage at the IODP Gulf Coast Repository in College Station, Texas (USA). Hard rock core descriptionHard rock petrographic observations made during Expedition 309/312 are stored in both written and electronic media. All descriptions and measurements were made on the archive halves of the cores, except where otherwise noted. A summary of macroscopic features observed in the cores is presented in visual core description (VCD) forms (Fig. F2). In VCD forms, individual piece numbers are noted along the left-hand side of the core image. In the column labeled Orientation, arrows indicate pieces large enough to be oriented with respect to the top of the core. The location of shipboard samples are noted in the Shipboard Studies column. Complete macroscopic descriptions and measurements are available in spreadsheet form (see the HRVCD directory in “Supplementary material”). For details on observations recorded in the spreadsheets, the reader is referred to the disciplinary sections in this chapter. Complete microscopic descriptions on petrographic thin sections are available (see “Thin sections” in “Core descriptions”). |
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