This chapter contains information that will help the reader understand the basis for our preliminary conclusions and help the interested investigator select samples for further analysis. This information concerns only shipboard operations and analyses described in the site reports in the Initial Reports volume of the Leg 187 Proceedings of the Ocean Drilling Program. Methods used by various investigators for shore-based analyses of Leg 187 data will be described in the individual scientific contributions published in the Scientific Results volume and in various professional journals.
The separate sections of the site chapters were written by the following shipboard scientists, listed in alphabetical order:
Drilling sites are numbered consecutively from the first site drilled by the Glomar Challenger in 1968. A site refers to one or more holes drilled while the ship was positioned over a single acoustic beacon. Multiple holes are often drilled at a single site by pulling the drill pipe above the seafloor (out of the hole), offsetting the ship some distance from the previous hole (without deploying a new acoustic beacon), and drilling another hole.
For all Ocean Drilling Program (ODP) drill sites, a letter suffix distinguishes each hole drilled at a single site. The first hole at a given site is assigned the suffix A, the second hole is designated with the same site number and the suffix B, and so on. Note that this procedure differs slightly from that used by the Deep Sea Drilling Project (DSDP) for Sites 1 through 624 but prevents ambiguity between site- and hole-number designations. These suffixes are assigned regardless of recovery, as long as penetration takes place. Distinguishing among holes drilled at a site is important because recovered rocks from different holes, particularly when recovery is <100%, often represent different intervals in the cored section.
The cored interval is measured in meters below seafloor (mbsf); sub-bottom depths assigned to individual cores are determined by subtracting the drill-pipe measurement (DPM) water depth (the length of the pipe from the rig floor to the seafloor) from the total DPM (from the rig floor to the bottom of the hole; see Fig. F1). Water depths below sea level are determined by subtracting the height of the rig floor above sea level from the DPM water depth. The depth interval assigned to an individual core begins with the depth below the seafloor at which the coring operation began and extends to the depth that the coring operation ended for that core (see Fig. F1). Each coring interval is equal to the length of the joint of drill pipe added for that interval (~9.4-10.0 m). The pipe is measured as it is added to the drill string, and the cored interval is usually recorded as the length of the pipe joint to the nearest 0.1 m. However, coring intervals may be shorter and may not be adjacent if these are separated by intervals drilled but not cored or by washed intervals.
Cores taken from a hole are numbered serially from the top of the hole downward. Core numbers and their associated cored intervals (in mbsf) are usually unique in a given hole; however, this may not be true if an interval must be cored twice because of caving of cuttings or other hole problems. The maximum full recovery for a single core is 9.5 m of rock contained in a core barrel (6.6-cm internal diameter). Only rotary coring bits were used on Leg 187.
Leg 187 targeted exclusively hard-rock cores, which were curated following ODP protocols. According to these protocols, cores are pulled from the core barrels in butylate liners, split into ~1.5-m sections, and transferred into split, 1.5-m butylate core liners for curation and storage. The bottoms of oriented pieces (i.e., pieces that could not have rotated about a horizontal axis in the core barrel) are marked with a red wax pencil to preserve orientation during the splitting and labeling process. Contiguous pieces with obvious features allowing realignment are considered to be a single piece. Plastic spacers are used to separate the pieces. The cores are then split into archive and working halves. In splitting the core, every effort is made to ensure that important features are represented in both halves. Each piece is numbered sequentially from the top of every section, beginning with number 1; reconstructed groups of pieces are lettered consecutively (e.g., 1A, 1B, 1C, etc.; see Fig. F2). Pieces are labeled only on external surfaces, and, if oriented, a way-up arrow is added to the label. Visual core descriptions are prepared for the archive half, which is then photographed with both black-and-white and color film, one core at a time. Nondestructive paleomagnetic measurements are performed on the archive halves of cores, unless the cores were broken into pieces too fine to make the measurements meaningful. The working half is sampled for shipboard and shore-based studies. Records of all samples are kept by the curator at ODP. Both halves of the core then are shrink-wrapped in plastic to prevent rock pieces from vibrating out of sequence during transit, placed into labeled plastic tubes, sealed, and transferred to cold-storage space aboard the drilling vessel. All Leg 187 cores are stored at ODP's Gulf Coast Repository at Texas A&M University in College Station.
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 when 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 complete 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 the section. For example, a sample identification of "187-1152A-10R-1, 10-12 cm" represents a sample removed from the interval between 10 and 12 cm below the top of Section 1, Core 10 (R designates that this core was taken with a rotary coring bit) of Hole 1152A, cored during Leg 187.
Recovery rates are calculated based on the total length of a core recovered divided by the length of the cored interval (see Fig. F1). As hard-rock coring operations are characterized by <100% recovery, the spacers between pieces can represent intervals of no recovery up to the difference in length between a cored interval and the total core recovered. Total core recovery is calculated by shunting the rock pieces together and measuring to the nearest centimeter; this information is logged into the shipboard database. Most cores are designated R for curatorial purposes. In instances where coring intervals exceed the 9.5-m length of the core barrel, cores are curated as wash intervals and labeled W. Photographs of each core and detailed descriptions of each core sampled and of thin-sections are provided (see the "Core Descriptions" contents list).
Sediment cores commonly include material recovered in the core catcher. Unlike hard-rock recovery, this material is not included in the lowermost section of core but is curated as Section CC. During Leg 187, rare intervals were recovered without new penetration because of hole collapse or other fill. An artifact of the curation database requires these cores to be archived as G (ghost cores).
To aid the interested investigator, we have compiled summary information of core descriptions on a section-by-section basis and presented these on hard-rock visual core description (HRVCD) forms (see the "Core Descriptions" contents list). These forms (Fig. F3) summarize the igneous, alteration, metamorphic, and structural character of the core; they also present graphical representations of the pieces recovered and the lithologic units defined. In the CD-ROM and World Wide Web publication formats, these forms contain a link to an image of the archive half of the core captured shortly after splitting. On the left-hand side of the form, several columns record information about the core. In right-to-left sequence, these columns include (1) archived piece numbers; (2) sketches of each piece with details (veins, fractures, etc.) added to help distinguish features in the image; (3) arrows indicating way up for oriented pieces; (4) the next locations of shipboard samples marked according to the sampling code in the Janus database (XRF = X-ray fluorescence analysis; TSB = polished thin-section billet; XRD = X-ray diffraction analysis; ICP = inductively coupled plasma spectrometry analysis; BIO = microbiological sample); and (5) a unit number for each lithologic unit. On the right-hand side of these forms is a text summary of observations from every section, including (1) upper and lower contacts of each lithologic interval; (2) primary lithology; (3) comments summarized from rock descriptions; and (4) structural information.
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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