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doi:10.2204/iodp.proc.314315316.122.2009 Expedition 315 methods1Expedition 315 Scientists2IntroductionThis chapter includes information on shipboard methods that will help the reader understand the basis for our preliminary interpretations and help the interested investigator select samples for further analysis. Authorship of site chaptersThe separate sections of the site chapters were written by the following shipboard scientists (authors are listed in alphabetical order; no seniority is implied):
Reference depthsSeafloor depths and cored intervals below seafloor (core depth below seafloor [CSF]) are determined by drill pipe measurement. When using Integrated Ocean Drilling Program (IODP) Method A, core expansion lengths overlap and are not scaled. We sometimes had more core recovery than coring advance (usually 9.5 m), especially in shallow sediments. These core lengths are linearly compressed to adjust to the coring advance and are labeled CSF-B to indicate core depth below seafloor calculated using IODP Method B (compression). Drilling engineers prefer to use pipe length to present the depth as drillers depth below rig floor (DRF). This measurement can be converted to CSF by subtracting water depth and the height of the rig floor from the sea surface. In some contexts referring to logging-while-drilling (LWD) results (as in “Core-log-seismic integration”), logging depths are presented as LWD depth below seafloor (LSF), which is also based on drill pipe measurement below seafloor. Numbering of sites, holes, cores, sections, and samplesSites drilled by the D/V Chikyu are numbered consecutively from the first site with a prefix “C.” A site refers to one or more holes drilled while the ship was positioned within 300 m of the first hole. 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 suffix “B,” and so forth. These suffixes are assigned regardless of recovery, as long as penetration takes place. During IODP Expedition 315, we drilled at Sites C0001 and C0002, both of which had been previously drilled during IODP Expedition 314. Therefore, hole names start with “E” for Site C0001 and “B” for Site C0002. 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 separated by intervals that were drilled but not cored. The core depth interval assigned to an individual core begins with the depth below seafloor at which the coring operation began and extends to the depth at which the coring operation ended for that core. A recovered core is typically divided into 1.5 m long sections that are numbered serially from 1 beginning at the top. When the recovered core is shorter than the cored interval, the top of the core is equated with the top of the cored interval by convention in order to achieve consistency in handling analytical data derived from the cores. Also by convention, material recovered from the core catcher is placed in a separate section during core description, labeled core catcher (CC), and placed below the last (bottom) section recovered in the liner. The core catcher is placed at the top of the cored interval in cases where material is only recovered in the core catcher. Samples removed from a core section are designated by distance measured in centimeters from the top of the section to the top and bottom of each sample removed from that section. A full identification number for a sample consists of the following information: expedition, site, hole, core number, core type, section number, and top to bottom interval in centimeters measured from the top of the section. For example, a sample identification of “315-C0001H-3R-2, 20–25 cm,” represents a sample removed from the interval between 20 and 25 cm below the top of Section 2. Core 3R designates that this core was taken using the rotary core barrel (RCB) in Hole C0001H during Expedition 315. All IODP core identifiers indicate core type. The following abbreviations are used: H = hydraulic piston coring system (HPCS; equivalent to the advanced piston corer), X = extended shoe coring system (ESCS; equivalent to the extended core barrel), and R = RCB. Core handlingAs soon as a core is retrieved on deck, a sample is taken from the core catcher and, if sedimentary, sent to the paleontological laboratory for an initial age assessment. The Curator immediately measures the total length of the recovered core and informs the Wellsite Geologist. The Wellsite Geologist then registers the core number in the shipboard database J-CORES together with the drilling advance and other additional drilling information. The core liner with the core inside is marked into section lengths by the Curator, each section is numbered, and the core is cut into sections. Usually all of Section 4 is dedicated to interstitial water analyses. Therefore, Section 4 is frequently significantly shorter than 1.5 m. Its length varies from 20 to 45 cm depending on depth. This short section is immediately removed from the core cutting area and scanned with the X-ray computed tomography (CT) scanner to investigate internal structures in order to avoid losing unique tectonic or sedimentary features. For safety monitoring, small (~5 cm3) plugs of sediment are taken from the bottom of Section 1 for headspace gas analysis. Each section is then sealed at the top and bottom with color-coded plastic caps and vinyl tape. A blue end cap marks the top of a section, a clear cap marks the bottom, and a yellow cap marks the end of a section from which a whole-round sample has been removed. The sample code (e.g., IW for interstitial water) is written on the yellow cap. Core sections are then carried into the laboratory, and the length of the core sections and any samples taken are logged into the J-CORES database. In the laboratory, X-ray CT images are taken for all core sections. As mentioned above, a short section for interstitial water analysis is given top priority for X-ray CT scanning. A structural geologist and a sedimentologist examine section’s internal structures with real-time axial images to judge whether the section can be squeezed or not. If they find any important structures inside, the section is preserved and another whole-round sample candidate is taken for interstitial water analysis. Other sections are scanned with the X-ray CT in turn. After taking X-ray CT images, microbial whole-round samples are taken from a nonstructured less-disturbed horizon based on information gained from the X-ray CT images. Samples for anelastic strain recovery measurement are also taken at this time. After core sections equilibrate to ambient room temperature (~3 h), they are run through the multisensor core logger (MSCL). For soft sediments, thermal conductivity measurements are then made (see “Physical properties”). After these nondestructive measurements, whole-round samples that are not time sensitive are taken. At the same time, 1 cm thick “cluster” slices are taken next to the whole-round sampling intervals. This thin round slice is divided into several pieces for different analytical purposes: X-ray diffraction (XRD; bulk), moisture and density (MAD), some organic chemistry analyses, and some shore-based analyses. This cluster sample provides a set of physical and chemical data for each sampling horizon, which enables more comprehensive geologic interpretation. Cores are subsequently split lengthwise into working and archive halves. The archive half is used for nondestructive measurements: visual core description, paleomagnetism, digital photo image scanning, and color spectroscopy. Samples are taken from the working half for shipboard physical property measurements (see “Physical properties”) before being sampled for additional shipboard and postcruise studies. Finally, core sections are wrapped in plastic bags (heat shrink wrap) and transferred to cold-storage space aboard the drilling vessel. Following the expedition, cores are transported to the Kochi Core Center in Kochi, Japan. |
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