The "Explanatory Notes" chapter is designed to document the primary procedures and methods employed by the various shipboard laboratories during this leg. This information concerns only shipboard methods described in the site reports in the Leg 200 Initial Reports volume of the Proceedings of the Ocean Drilling Program (ODP). Methods for shore-based analysis of Leg 200 samples and data will be described in the individual scientific contributions to be published in scientific journals and in the Scientific Results volume.
Drilling sites are numbered consecutively from the first site drilled by the Glomar Challenger in 1968. 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 ODP 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 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 (measured in meters below rig floor [mbrf]), from the total drill pipe measurement. Each cored interval is generally 9.5 to 9.6 m long, which is the length of a core barrel. Coring intervals may be shorter and may not necessarily be adjacent if separated by drilled intervals.
A recovered core is divided into 1.5-m sections that are numbered serially from the top. When full recovery is obtained, the sections are numbered from 1 through 7, with the last section possibly being shorter than 1.5 m (Fig. F1); rarely, an unusually long core may require >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 placed in a separate section during the core description, labeled core catcher (CC), and placed below the last 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.
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 to achieve consistency in handling analytical data derived from the cores. Samples removed from the cores 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: leg, 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 "200-1224D-2R-1, 80-85 cm" would be interpreted as representing a sample removed from the interval between 80 and 85 cm below the top of Section 1, Core 2 (R designates that this core was taken with the rotary core barrel) of Hole 1224D from Leg 200 (Fig. F1).
All ODP core identifiers indicate core type. The following abbreviations are used:
As 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 an initial age assessment. In the case of Leg 200, no paleontologists were on board, so paleontological samples were not taken. Bob Goll and John Firth of ODP-TAMU (Texas A&M University) performed postcruise analyses of the siliceous (at Site 1223) and calcareous (at Sites 1223 and 1224) nannofossils, respectively. The core is then placed on a long horizontal rack. For safety monitoring, small (~5 cm3) plugs of sediment are also usually taken from the end of one section 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 vacutainer samples). Because gas hazards in the areas being drilled during Leg 200 were negligible and the sediment cover above basement was thin, no vacutainer samples were collected. Next, the core is marked into section lengths; each section is labeled; and the core is cut into sections. Interstitial water (IW) whole-round samples are then taken as a matter of ODP policy (typically on every third core); whole-round samples for microbiology studies may also be taken at this stage if they have been requested. For some of the cores that contain gas, several small holes are drilled into the core liners to allow gas to escape.
Each section is then sealed at the top and bottom by gluing on color-coded plastic caps—blue to identify the top of a section and clear for the bottom. A yellow cap is placed on the section ends from which a whole-round sample has been removed, and the sample code (e.g., IW) is written on the yellow cap. The caps are usually attached to the liner by coating the end liner and the inside rim of the cap with acetone, and then the caps are taped to the liners. The core sections are then carried into the laboratory, where the individual sections are again labeled using an engraver to permanently mark the full designation of the section. 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 ODP Janus database program.
After a core has equilibrated to room temperature, which usually takes ~1-3 hr, each whole-round core section is run through the multisensor track (MST), and thermal conductivity measurements are made on soft sediment cores. Whole-round samples for shore-based studies of paleomagnetism, consolidation, shear strength, and other elastic properties may be taken at this stage if they have been requested.
Cores of soft material are split lengthwise into working and archive halves. The 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. The wire-cut cores are split from bottom to top, so investigators should be aware that older material could have been transported up the core on the split face of each section.
Igneous 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. The core then is cut into 1.5-m-long sections and transferred into the laboratory.
The contents of each section are transferred into 1.5-m-long sections of split core liner, where the bottom of oriented pieces (i.e., pieces that clearly could not have rotated top to bottom about a horizontal axis in the liner) is marked with a red wax pencil. This is done to ensure that orientation is not lost during the splitting and labeling processes. Important primary features of the cores also are recorded at this time. A plastic spacer is used to separate individual pieces and/or reconstruct contiguous groups of pieces in the core liner. These spacers may represent a substantial interval of no recovery. The length of each section is then 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 then 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 is added to the label pointing to the top of the section.
For both sedimentary and igneous cores, the archive half is described visually (see "Core Descriptions"). Smear slides are made from small amounts of sediment samples taken from the archive half. Digital images of the archive halves are made on a digital imaging system installed prior to Leg 198. Most archive sections are run through the archive multisensor track (AMST) for color reflectance spectroscopy measurements and susceptibility measurements with a point susceptibility meter and then through the cryogenic magnetometer for magnetic remanence measurements. The archive half then is photographed using black-and-white and color film. Close-up photographs (color and black and white) 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 extracted sample is logged into the sampling computer database program by the location and the name of the investigator receiving the sample. Records of all removed samples are kept by the curator at ODP. The extracted samples are sealed in plastic vials, cubes, or bags and labeled. Samples are routinely taken for shipboard physical properties, paleomagnetic, thin section, and geochemistry analyses, and microbiological and molecular investigations as described in the sections below.
Following the initial 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. The working and archive halves of sedimentary and igneous cores are then put into labeled plastic tubes, sealed, and transferred to cold-storage space aboard the drilling vessel. At the end of Leg 200, the cores were transferred from the ship in refrigerated containers to cold storage at the ODP Gulf Coast Repository at TAMU in College Station, Texas.
1Examples of how to reference the whole or part of this volume can be found under "Citations" in the preliminary pages of the volume.
2Shipboard Scientific Party addresses can be found under "Shipboard Scientific Party" in the preliminary pages of the volume.
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