In this chapter, we have assembled information that will help the reader understand the procedures of shipboard data acquisition and our preliminary conclusions. This information concerns only shipboard operations and analyses described in the site chapters of the Leg 177 Initial Reports volume of the Proceedings of the Ocean Drilling Program. Methods used by various investigators for shore-based analyses of Leg 177 data will be described in individual scientific contributions published elsewhere.
Two coring systems were used during Leg 177: the advanced hydraulic piston corer (APC) and the extended core barrel (XCB). Either of these systems was applied to maximize core recovery in the lithology being drilled. Each cored interval was about 9.5 m long, which is the length of a core barrel. In some cases, the drill string was "washed ahead" without recovering sediments to advance the drill bit to a target depth where core recovery needed to resume. Drilling systems and their characteristics, such as drilling-related deformation, are summarized in the "Explanatory Notes" chapters of previous Initial Reports volumes. The Leg 139 Initial Reports volume (Davis, Mottl, Fisher, et al., 1992) includes a particularly detailed description.
Drilled intervals are referred to in meters below rig floor (mbrf), which are measured from the kelly bushing on the rig floor to the bottom of the drill pipe, and meters below seafloor (mbsf), which are calculated by subtracting the seafloor depth in mbrf. In the case where sediments of substantial thickness cover the seafloor (as at all sites drilled during Leg 177), the mbrf depth of the seafloor is determined with a mudline core, assuming 100% recovery for the cored interval in the first core. Water depth is calculated by subtracting the distance from the rig floor kelly bushing to the sea level from the mudline measurement in mbrf. This water depth usually differs from precision depth recorder measurements by a few meters. The mbsf depths of core tops are calculated by subtracting the seafloor depth in mbrf from the core-top depth in mbrf. The core-top datums from the driller are the ultimate depth reference for any further depth calculation procedures.
Numbering of sites, holes, cores, and samples follows the standard Ocean Drilling Program (ODP) procedure. A full curatorial identifier for a sample consists of the following information: leg, site, hole, core number, core type, section number, and interval in centimeters measured from the top of the core section. For example, a sample identification of "177-1088A-1H-1, 10-12 cm" would represent a sample removed from the interval between 10 and 12 cm below the top of Section 1, Core 1H (H designates that this core was taken with the APC system) of Hole 1088A cored during Leg 177.
Cored intervals are also referred to in curatorial meters below sea-floor (mbsf). The mbsf of a sample is calculated by adding the depth of the sample below the section top and the lengths of all higher sections in the core to the core-top datum measured with the drill string. A sediment core from less than a few hundred meters below seafloor expands upon recovery (typically 10% in the upper 300 m) so that its length does not match the drilled interval it originates from. In addition, there is typically a coring gap between cores, as shown by composite depth construction (see below). Thus, a discrepancy exists between the drilling mbsf and the curatorial mbsf. For instance, the curatorial mbsf of a sample taken from the bottom of a core may be larger than that of a sample taken from the top of the subsequent core, which creates a stratigraphic dilemma. To avoid this problem, multiple holes (typically three to five) were drilled at a site to construct a continuous composite section. This resulted in a "meters composite depth" (mcd) scale for each site that accommodates core expansion and drilling gaps through interhole correlation using closely spaced measurements of core physical properties (see "Composite Depths," p. 3).
General core handling procedures, described in previous Initial Reports volumes and the Shipboard Scientist's Handbook, are summarized here. As soon as cores arrived on deck, core-catcher (CC) samples were taken for biostratigraphic analysis. After the core was cut in sections, whole-round samples were taken for shipboard interstitial water analysis. In addition, headspace gas samples were immediately bored from the ends of cut sections and sealed in glass vials for light hydrocarbon analysis.
Before splitting, whole-round core sections were run through the multisensor track (MST) and thermal conductivity measurements were taken. The cores were then split into working and archive halves, from bottom to top, so investigators should be aware that older material could have been transported upward on the split face of each section. The working half of each core was sampled for both shipboard analysis, such as physical properties, carbonate, and bulk X-ray diffraction (XRD) mineralogy, and shore-based studies. Shipboard sampling was kept at a minimum during Leg 177 to allow construction of a detailed sampling plan after the composite section was built. The archive-half sections were passed through the cryogenic magnetometer and described visually and by means of smear slides. The archive half was then photographed with both black-and-white and color film, a whole core at a time, and close-up photographs were taken of particular features for illustrations in the site reports, as requested by individual scientists. The working half was analyzed using an automated color reflectance scanning system.
Both halves of the core were then put into labeled plastic tubes, sealed, and transferred to cold-storage space aboard the ship. At the end of the leg, the cores were transferred from the ship into refrigerated trucks and were shipped to the ODP Bremen Core Repository for cold storage.
1Examples
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