2. Explanatory Notes¹

Shipboard Scientific Party²

INTRODUCTION

This chapter is designed to document the primary procedures and methods employed by the various shipboard laboratories in order to clarify the basis for our preliminary interpretations. This information pertains only to shipboard methods described in the site reports in the Leg 186 Initial Reports volume of the Proceedings of the Ocean Drilling Program. Methods for shore-based analysis of Leg 186 samples and data will be described in the individual scientific contributions to be published in scientific journals and in the Scientific Results volume.

Numbering of Sites, Holes, Cores, and Samples

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 Ocean Drilling Program (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 is assigned the site number modified by the 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 m long, which is the length of a core barrel. Coring intervals may be shorter than 9.5 m 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 more than 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 "186-1150A-3H-5, 80-85 cm" would be interpreted as representing a sample removed from the interval between 80 and 85 cm below the top of Section 5, Core 3 (H designates that this core was taken during hydraulic piston coring) of Hole 1150A from Leg 186 (Fig. F1).

All ODP core identifiers indicate core type. The following abbreviations are used: H = hydraulic piston corer (also referred to as advanced hydraulic piston corer [APC]); X = extended core barrel (XCB); R = rotary core barrel (RCB); and M = miscellaneous material.

As soon as a core is retrieved on deck, it goes through a sequence of processing steps. First, a sample is taken from the core catcher and given to the paleontological laboratory for an initial age assessment. The core is then placed on a long horizontal rack. For safety monitoring, small (~5 cm³) plugs of sediment are 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. The core is then 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 organic geochemistry may also be taken at this stage if they have been requested. For 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 caps identify the top of a section, and clear caps identify the bottom of a section. 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 labeled with 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.

Before they are split, whole-round core sections are run through the multisensor track (MST) and thermal conductivity measurements are taken. Whole-round samples for shore-based studies of 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 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. Following the initial scientific measurements, both halves of the core are put into labeled plastic tubes, sealed, and transferred to cold-storage space aboard the drilling vessel. At the end of Leg 186, the cores were transferred from the ship in refrigerated containers to cold storage at the ODP Gulf Coast Repository in College Station, Texas.