4. Explanatory Notes¹

Shipboard Scientific Party²

INTRODUCTION

This chapter includes information on shipboard methods that will help the reader understand the basis for our preliminary interpretations and also help the interested investigator select samples for further analysis. Coring techniques and core handling, including the numbering of sites, holes, cores, sections, and samples, are the same as those reported in previous Initial Reports volumes of the Proceedings of the Ocean Drilling Program and are only briefly summarized within this chapter.

Reference Depths

Seafloor depths and cored intervals below seafloor (meters below seafloor, mbsf) are determined by drill-pipe measurement.

Numbering of Sites, Holes, Cores, Sections, and Samples

Ocean Drilling Program (ODP) drill sites are numbered consecutively from the first Deep Sea Drilling Project (DSDP) site drilled by the Glomar Challenger in 1968. A site refers to one or more holes drilled while the ship is positioned over a single acoustic beacon. The first hole drilled at a given site is assigned the site number modified by the suffix "A," the second hole takes the site number and suffix "B," and so forth. These suffixes are assigned regardless of recovery as long as penetration takes place. This is exemplified by Hole 1108A, the first one drilled during Leg 180, which consisted of a jet-in test to 16.3 mbsf.

Each cored interval is generally 9.5 m long, which is the length of a core barrel. Coring intervals may be shorter and may not necessarily be adjacent if separated by intervals that are drilled but not cored. The depth interval assigned to an individual core begins with the depth below seafloor at which the coring operation began and extends to the depth at which the coring operation ended for that core.

A recovered core is typically divided into 1.5-m-long sections that are numbered serially from the top, from 1 through 7 (or less if partial recovery). 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. Also by convention, material recovered from the core catcher is placed in a separate section during the core description, labeled CC (core catcher), and placed below the last (bottom) section recovered in the liner. When material is recovered only in the core catcher, the core catcher is placed at the top of the cored interval.

Samples removed from a core section 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, and interval in centimeters measured from the top of the section (Fig. F1). For example, "180-1108B-26R-2, 20-25 cm" represents a sample removed from the interval between 20 and 25 cm below the top of Section 2, Core 26 (R designates that this core was taken during rotary core barrel coring) of Hole 1108B during Leg 180.

All ODP core identifiers indicate core type. The following abbreviations are used: H = advanced hydraulic piston core (APC); X = extended core barrel (XCB); R = rotary core barrel (RCB); and W = wash core.

Core Handling

As soon as a core is retrieved on deck, a sample of sediment is taken from the core catcher and given to the paleontological laboratory for an initial age assessment. The core liner with the core inside is marked into section lengths, each section is labeled, and the core is then cut into sections. If whole-round samples are to be taken, the desired intervals are identified and cut out of the core, and then the sections are cut. When possible, whole-round samples are taken from the bottom of sections. During Leg 180, whole-round samples were taken for interstitial water (IW) analyses, organic geochemistry, microbiology, and postcruise permeability measurements. For safety monitoring, small (~5 cm³) plugs of sediment are taken from the end of one section per core for headspace gas analysis. If pockets of gas are present, a vacutainer gas sample is taken through the core liner.

Each section is then sealed at the top and bottom by using acetone to seal color-coded plastic caps to the plastic core liner. A blue cap marks the top of a section, a clear cap marks the bottom of a section, and a yellow cap marks the end of a section from which a whole-round sample has been removed. The sample code (e.g., IW) is written on the yellow cap. The core sections are then carried into the laboratory where the length of the core sections and any samples taken are logged into the shipboard database.

After the core sections equilibrate to ambient lab temperature (~3 hr), they are run through the multisensor track (MST) and thermal conductivity measurements are made for soft sediments (see "Multisensor Track Measurements"). Cores are subsequently split lengthwise into working and archive halves. The archive half is used for nondestructive measurements: visual core description, paleomagnetics, magnetic susceptibility, and color reflectance. Samples are taken from the working half for shipboard physical properties measurements (see "Physical Properties") before being sampled for additional shipboard and postcruise studies. The archive halves are photographed a whole core at a time, and close-up photographs are taken as requested. Finally, the core sections are put into labeled plastic tubes, sealed, and transferred to cold-storage space aboard the drilling vessel. Following the cruise, the cores from Leg 180 were transported to the Gulf Coast Repository of the Ocean Drilling Program in College Station, Texas.