3. Explanatory Notes1

Shipboard Scientific Party2


In this chapter, we have assembled information that will help the reader understand the basis for our preliminary conclusions and also help the interested investigator select samples for further analysis. This information concerns only shipboard operations and analyses described in the site reports in the Leg 179 Initial Reports volume of the Proceedings of the Ocean Drilling Program. Methods used by various investigators for shore-based analyses of Leg 179 data will be described in the individual scientific contributions published in the Scientific Results volume and in publications in various professional journals.

Authorship of Site Chapters

The separate sections of the site chapters were written by the following shipboard scientists (authors are listed in alphabetical order; no seniority is implied):

Leg Summary: Casey, Miller
Operations: Holloway, Miller, Pettigrew
Igneous Petrology and Geochemistry: Casey, Guo, Miller, Shibata, Thy
Metamorphic Petrology: Casey, Miller, Shibata
Structural Geology: Casey
Physical Properties: Miller, Rao
Downhole Measurements: Boissonnas, Einaudi, Hoskins, Myers
Seismic Experiments: Busby, Gerdom, Hoskins, Myers
Appendix: Shipboard Scientific Party

Numbering of Sites, Holes, Cores, and Samples

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 assigned suffix B, and so on. Note that this procedure differs slightly from that used by the Deep Sea Drilling Project (Sites 1-624) 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 less than 100%, are likely to 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 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 separated by intervals drilled but not cored or 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; Fig. F2). Only rotary core barrel bits were used for recovering core during Leg 179.

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 clearly 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. Each piece is numbered sequentially from the top of each section, beginning with number 1; reconstructed groups of pieces are lettered consecutively (e.g., 1A, 1B, 1C, etc.; see Fig. F3). Pieces are labeled only on external surfaces, and, if oriented, a way-up arrow is added to the label.

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. Most cores are designated "R" (rotary drilled) 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 given the designator "W." Detailed descriptions of each core sampled, thin-section descriptions, and photographs of each core are presented (see the "Core Descriptions" contents list).

Summary Core Descriptions

As an aid to 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 summarize the igneous, metamorphic, and structural character of the core and present graphical representations of the pieces recovered and the lithologic units identified (Fig. F4). The far left side of these forms present an image of the archive half of the core captured shortly after splitting. On the right side of the image, several columns record information about the core. In left-to-right sequence, these columns include archived piece numbers and a graphic representation of piece shape with additional details (veins, fractures, etc.) added to help distinguish features in the image. Next to these is a column indicating pieces that could be oriented relative to way up. The next column indicates the location of shipboard samples. For reference, the samples noted conform to the sampling code in the JANUS database (XRF = X-ray fluorescence analysis; TSB = polished thin section billet; PP = physical properties analysis; and XRD = X-ray diffraction analysis). A graphic lithology column illustrates changes in lithologic units (see "Igneous Petrology and Geochemistry"); lithologies recovered are represented by the patterns illustrated in Figure F5 . A unit number corresponds to each lithologic unit and is recorded in the next column. Metamorphic intensity intervals are represented by uppercase letters (see "Metamorphic Petrology"). We also present a graphic representation of structural features in the core noting particular structural features (see "Structural Geology"). On the right side of these forms is a text summary of observations from each section. The upper and lower contacts of each lithologic interval are noted, as well as primary lithology and other comments summarized from igneous descriptions. Text summaries of metamorphic and structural description for each section are also compiled on these forms.

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 "Leg 179 Partipants" in the preliminary pages of the volume.

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