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doi:10.2204/iodp.proc.327.102.2011 Methods1Expedition 327 Scientists2IntroductionThis introductory section provides an overview of operations, depth conventions, curatorial procedures, and general core handling and analysis. This information will help the reader understand the basis of our shipboard observations and preliminary interpretations. It will also enable interested investigators to identify data and select samples for further analysis. The information presented here concerns mainly shipboard operations and analyses described in the site chapters, including a small number of shipboard samples that were analyzed on shore because of a lack of time or necessary instrumentation during Integrated Ocean Drilling Program (IODP) Expedition 327. Methods used by various investigators for shore-based analyses of Expedition 327 samples and data associated with separate scientific studies will be described in individual publications in professional journals. Site locationsGPS coordinates from precruise site surveys or preexisting Ocean Drilling Program (ODP) and IODP sites were used to position the R/V JOIDES Resolution at Expedition 327 sites. A SyQwest Bathy 2010 CHIRP subbottom profiler was used to monitor seafloor depth on the approach to each site to confirm depth profiles from precruise surveys or previous expeditions. Once the vessel was positioned at a site, the thrusters were lowered and a positioning beacon was dropped to the seafloor. The dynamic positioning (DP) control of the vessel uses navigational input from the GPS system 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 a significant portion of the time the hole was occupied. Drilling operationsThe advanced piston corer (APC), extended core barrel (XCB), and rotary core barrel (RCB) systems were used during Expedition 327. The APC and XCB systems were used to recover the sedimentary section and sediment/basalt interface at Site U1363. The RCB system was used to recover the basement section at Site U1362. 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 observation of the pressure gauge on the rig floor because the excess pressure accumulated prior to the stroke drops rapidly. 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 can be achieved but excessive force cannot retrieve the barrel, the core barrel can be “drilled over” (i.e., after the inner core barrel is successfully shot into the formation, the drill bit is advanced to total depth to free the APC barrel). The XCB system was used to advance the hole when APC refusal occurred before the target depth was reached or when drilling conditions required it. The XCB is a rotary system with a small cutting shoe that extends below the large rotary APC/XCB bit. The smaller bit can cut a semi-indurated core with less torque and fluid circulation than the main bit, potentially improving recovery. The XCB cutting shoe (bit) extends ~30.5 cm ahead of the main bit in soft sediments but retracts into the main bit when hard formations are encountered.
The bottom-hole assembly (BHA) used for APC and XCB coring was composed of an 11 The RCB BHA included a 9⅞ inch RCB drill bit, a bit sub, an outer core barrel, a modified top sub, a modified head sub, a variable number of 8¼ inch control length drill collars, a tapered drill collar, and two stands of 5½ inch drill pipe. The number of drill collars ranged from 8 to 26 during coring so that it was possible to position only 8¼ inch collars (rather than drill pipe) in the open hole. Keeping drill collars in the open hole helped to prevent basement rubble from falling in the hole, which could have caused the drill pipe to become stuck. Drill collars also help to maintain annular velocities that lift cuttings from the hole during drilling. We did not use nonmagnetic core barrels because of the nature of the formation and did not orient cores because of the lack of high-priority scientific goals requiring this procedure. Formation temperature measurements were made at Site U1363 to determine heat flow through the sedimentary section (see “Downhole measurements”). Most APC/XCB cored intervals were ~9.5 m long, which is the length of a standard core barrel and the length of a joint of drill pipe. In some cases the drill string was drilled or “washed” ahead without recovery to advance the drill bit to the target depth at which core recovery needed to resume. Depths of drilled intervals and core recovery are provided in the “Operations” section of each site chapter. IODP depth conventionsDeep Sea Drilling Project (DSDP), ODP, and IODP Phase 1 reports, diagrams, and publications used three primary designations to reference depth: meters below rig floor (mbrf), meters below seafloor (mbsf), and meters composite depth (mcd). These designations were combinations of origin of depth (rig floor or seafloor), measurement units (meters), and method of construction (composite). The designations evolved over many years to meet the needs of individual science parties. Over the course of ODP and IODP scientific drilling, issues with the existing depth scale designations and the lack of a consistent framework became apparent. For example, the application of the same designation to scales created with distinctly different tools and methods was common (e.g., mbsf being used for scales measured both by drill string tally and the wireline). Consequently, new scale type designations were created ad hoc to differentiate the wireline logging scale from the core depth scale so that depth-mapping procedures and products could be adequately described. However, the management and use of depth scales and splices for a site was problematic, and the requirement to integrate scientific procedures among three IODP implementing organizations (IOs) amplified the need to establish a standardized and versatile depth framework. A new classification and nomenclature for depth scale types was defined in 2006–07 during the hiatus in IODP drilling operations to provide a starting point from which the IOs could address more specific issues about the management of depth scales and splices (see “IODP Depth Scales Terminology” at www.iodp.org/program-policies/) (Table T1). This new depth framework has been implemented in the Laboratory Information Management System (LIMS) used aboard the JOIDES Resolution. The new methods and nomenclature used to calculate sample depth in a hole are now method specific, which ensures that data acquisition, scale mapping, and construction of composite splices are unequivocal. The primary depth scales are measured by the length of drill string (e.g., drilling depth below rig floor [DRF] and drilling depth below seafloor [DSF]), length of core recovered (e.g., core depth below seafloor [CSF] and core composite depth below seafloor [CCSF]), and logging wireline (e.g., wireline log depth below rig floor [WRF] and wireline log depth below seafloor [WSF]). In cases where multiple logging passes are made, logs are mapped to one reference pass, creating the wireline log matched depth below seafloor (WMSF). All units are in meters. The relationship between scales is defined by protocol, such as the rules for computation of CSF from DSF, or user-defined correlations, such as core-to-log correlation or stratigraphic correlation of cores between holes to create a common CCSF scale from the CSF scale used in each hole. The distinction in nomenclature should keep the reader aware that a nominal depth value at different depth scales usually does not refer to the exact same stratigraphic interval. During Expedition 327, unless otherwise noted, depths below rig floor were calculated as DRF and are reported as meters; core depths below seafloor were calculated as CSF Method A (CSF-A) and are reported as mbsf; and all downhole wireline depths were calculated as WMSF and are reported as mbsf (Table T1). In addition, some depths are reported in meters subbasement (msb), accounting for the thickness of the sediment section above the volcanic crust, because this depth reference is relevant to numerous aspects of borehole observatory system design and installation and to cross-hole lithologic correlation. Core handling and analysisCores were extracted from the core barrel in plastic liners. The 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. Blue (uphole direction) or clear (downhole direction) liner caps were glued with acetone onto the cut liner sections. Hard rocksPieces were pushed to the bottom of 1.5 m liner sections, and the total rock length was measured. The length was entered into the database as “created length” using the SampleMaster application. This number was used to calculate recovery. The liner sections were transferred to the core splitting room. Whole-round samples were taken for microbiological analyses following consultation with other members of the science party. The imaging specialist took photographs of these samples before they were bagged and processed. In cases where a whole round was removed, a yellow cap was used to denote the missing interval. The plastic liners were split lengthwise to expose the core. Oriented pieces of core were marked on the bottom with a red wax pencil to preserve orientation. In some cases pieces were too small to be oriented with certainty. Adjacent but broken pieces that could be fit together along fractures were curated as single pieces. The petrologist or assistant laboratory officer on shift confirmed piece matches and marked the split line on the pieces, which defined how the pieces were to be cut into 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 with acetone to the split core liner between individual pieces or reconstructed contiguous groups of subpieces. These spacers may represent substantial intervals of no recovery. The length of each section of core, including spacers, was entered into the database as “curated length,” which commonly differs by a few to several centimeters from the length measured on the catwalk. The depth of each piece was recalculated in the database on the basis of its curated length. Core sections were placed in core racks in the laboratory. When the cores reached equilibrium with laboratory temperature (typically after 3–4 h), the whole-round core sections were run through the Natural Gamma Radiation Logger (NGRL) and the Whole-Round Multisensor Logger (WRMSL), which was configured for hard rock to measure magnetic susceptibility and gamma ray attenuation. Each piece of core was split with a diamond-impregnated saw into an archive half and a working half, with the positions of plastic spacers between pieces maintained in both halves. Pieces were numbered sequentially from the top of each section, beginning with 1. Separate subpieces within a single piece were assigned the same number but were lettered consecutively (e.g., 1A, 1B, 1C, etc.). Pieces were labeled only on the outer cylindrical surfaces of the core. An arrow pointing to the top of the section was added to the label of each oriented piece, and the orientation was recorded in the database using the SampleMaster application. The working half of each core was sampled for shipboard physical properties, bulk X-ray diffraction (XRD) and inductively coupled plasma–atomic emission spectroscopy (ICP-AES) analyses, and thin sections. Thermal conductivity measurements were taken on selected samples (see “Physical properties”). The archive half of each core was scanned on the Section Half Imaging Logger (SHIL) and measured for color reflectance and point magnetic susceptibility on the Section Half Multisensor Logger (SHMSL). The archive halves were also described visually and by means of thin sections. Some archive-half sections or pieces were run through the cryogenic magnetometer. Sampling for shore-based studies was delayed until the end of coring in each hole, except when samples had to be taken rapidly, generally for microbiology studies. Sampling was conducted based on the sampling plan agreed upon by the science party and shipboard curator. SedimentsOnce the cores were cut into sections, whole-round samples were taken for microbiological or pore water analyses. When a whole round was removed, a yellow cap was used to denote the missing interval. Core sections were placed in core racks in the laboratory. When the cores reached equilibrium with laboratory temperature (typically after 3–4 h), whole-round core sections were run through the WRMSL to measure P-wave velocity, resistivity, magnetic susceptibility, and bulk density. Thermal conductivity measurements were taken at varying intervals (see “Physical properties”). Sediment cores were split lengthwise from bottom to top into working and archive halves. Investigators should note that older material may have been transported upward on the split face of each section during splitting. The working half of each core was sampled for various shipboard analyses. The working half of each core was also sampled for shore-based studies based on the sampling plan agreed upon by the science party and shipboard curator. The archive half of each core was scanned on the SHIL and measured for color reflectance and magnetic susceptibility on the SHMSL. At the same time, the archive halves were described visually and by means of smear slides. Finally, some of the archive halves were run through the cryogenic magnetometer. For both sediments and hard rocks, cores were put into labeled plastic bags, sealed, and transferred to cold storage space aboard the ship. At the end of the expedition the cores were transferred from the ship into refrigerated trucks and transported to cold storage at the IODP Gulf Coast Repository in College Station, Texas (USA). Curatorial procedures and sample depth calculationsNumbering of sites, holes, cores, and samples follows standard IODP procedure. A full curatorial identifier for a sample consists of the following information: expedition, site, hole, core number, core type, section number, archive or working half (if taken from a section half), piece number (hard rocks only), and interval in centimeters, as measured from the top of the core section. For example, a sample identification of “327-U1362A-5R-2 (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 2 of Core 5 of Hole A at Site U1362 during Expedition 327 (Fig. F1). The “U” preceding the hole number indicates the hole was drilled by the US implementing organization (USIO) platform, the JOIDES Resolution. The drilling system used to obtain a core is designated in the sample identifiers as follows:
Core intervals are defined by the length of drill string, the seafloor depth, and the amount the driller advanced the core barrel; they are reported in DSF. The length of the core is defined by the sum of the lengths of the core sections. The CSF depth of a sample is calculated by adding the offset of the sample below the section top and the lengths of all higher sections in the core to the core-top depth measured with the drill string (DSF). A soft to semisoft sediment core from less than a few hundred meters below seafloor expands upon recovery (typically a few percent to as much as 15%), so the recovered interval does not match the cored interval. In addition, a coring gap typically occurs between cores, as shown by composite depth construction. Thus, a discrepancy between DSF and CSF depths can exist with regard to a stratigraphic interval. Furthermore, when core recovery is >100% of the cored interval, a sample taken from the bottom of a core will have a CSF depth deeper than that of a sample from the top of the subsequent core (i.e., the data associated with the two core intervals overlap). If a core has incomplete recovery, for curation purposes all cored material is assumed to originate from the top of the drilled interval as a continuous section; the true depth interval within the cored interval is unknown. This should be considered a sampling uncertainty in age-depth analysis or correlation of core data with downhole logging data. Core sample disturbanceCores may be significantly disturbed and contain extraneous material as a result of the coring and core handling process. In formations with loose sand layers, sand from intervals higher in the hole may be washed down by drilling circulation, accumulate at the bottom of the hole, and be sampled with the next core. The uppermost 10–50 cm of each core must therefore be examined critically during description for potential “fall-in.” Common coring-induced deformation includes the concave-downward appearance of originally horizontal bedding. Piston action may result in fluidization (“flow-in”) at the bottom of APC cores. Retrieval from depth to the surface may result in elastic rebound. Gas that is in solution at depth may become free and drive core segments within the liner apart. When gas content is high, pressure must be relieved for safety reasons before the cores are cut into segments. This is accomplished by drilling holes into the liner, which forces some sediment as well as gas out of the liner. These disturbances are described in each site chapter and graphically indicated on the visual core descriptions (VCDs), also known as “barrel sheets.” |
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inch (~29.05 cm) drill bit, a bit sub, a seal bore drill collar, a landing saver sub, a modified top sub, a modified head sub, five 8¼ inch control length drill collars, a tapered drill collar, two stands of 5½ inch transition drill pipe, and a crossover sub to the drill pipe that extended to the surface.