3. Explanatory Notes¹

Shipboard Scientific Party²

INTRODUCTION

This chapter is designed to document the primary procedures and methods employed by the various shipboard laboratories to understand the basis for our preliminary interpretations. Shore-based methods used in subsequent work by various investigators should be explained in the publications produced by them.

Site Chapter Authorship

Descriptions of individual drilling sites, summaries of operations, and preliminary results and interpretations are contained in site chapters. This entire volume should be treated as a publication to which all scientists listed at the front of this volume contributed. The individual sections of site chapters were written by the following shipboard scientists listed in alphabetical order with no seniority implied:

Principal Results: Shipboard Scientific Party

Background and Objectives: Feary, Hine

Operations: Malone, Pollard

Lithostratigraphy: Andres, Betzler, Brooks, James, Machiyama,
Matsuda, Simo, Surlyk

Biostratigraphy: Brunner, Holbourn, Ladner, Li, Shafik

Paleomagnetism: Fuller, Molina Garza

Composite Depths: Mallinson

Organic Geochemistry: Mitterer

Inorganic Geochemistry: Swart, Wortmann

Physical Properties: Isern, Mallinson, Robin, Russell, Smart

Downhole Measurements: Huuse, Isern, Spence

Seismic Stratigraphy: Feary

Drilling Operations

Drilling sites are numbered consecutively from the first site drilled by the Glomar Challenger in 1968. Procedures for drilling multiple holes at one site involve removing the drill pipe from the seafloor, moving the ship a short distance, and then drilling a new hole. Multiple holes at one site are identified as A, B, C, and so on (e.g., 1126A, 1126B, 1126C, etc.).

Three coring systems were used during Leg 182: (1) advanced hydraulic piston corer (APC), (2) extended core barrel (XCB), and (3) rotary core barrel (RCB). The system type, the duration, and the rationale employed were designed to maximize core recovery and penetration rate; the details are explained in the "Operations" sections of each site chapter.

Drilled intervals are referred to in meters below rig floor (mbrf) measured from the kelly bushing on the rig floor to the bottom of the drill pipe. Meters below seafloor (mbsf) are calculated using the kelly bushing minus a sea-level correction factor. The mbrf depth of the seafloor is determined with a mudline core. Water depth is calculated by subtracting the distance from the rig floor height above sea level (determined at each site) from the drill-pipe mudline measurement in mbrf. This water depth typically differs from precision depth recorder measurements by one to several 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.

For Leg 182 multiple APC holes were cored at each site, where possible, to construct a continuous composite section. This produces a meters composite depth (mcd) scale for each site, using interhole correlation to accommodate drilling gaps and/or core expansion (see "Composite Depths").

Cores are taken in 9.5-m intervals. These intervals are cut into 1.5-m sections and are contained in a plastic liner with a 6.6-cm inside diameter. If recovery is less than 100% (as is frequently the case) and there are empty spaces in the core liner, the top of the core material in the 9.5-m interval obtained is equated with the top of the first section.

Curatorial and Core-Handling Procedures

Samples are identified with a curatorial code consisting of leg, site, hole, core number, core type, section number, and interval in centimeters measured from the top of the section. For example, 182-1126A-10H-1, 10-12 cm, would mean Leg 182, Hole 1126A at Site 1126, Core 10 (H indicating APC), Section 1, with the sample taken 10-12 cm down from the top of Section 1.

As soon as a core is retrieved on deck a sample is taken from the core catcher and taken to the paleontological laboratory for an initial age assessment. The core liner with the core inside is marked into section lengths. Each section length is labeled and the core is cut as marked. If whole-round samples are taken, the desired interval is identified and cut out of the core. When possible, whole-round samples are taken from the bottom of sections. During Leg 182 whole-round samples were taken for interstitial water (IW) analyses. 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 glue color-coded plastic caps to the plastic core liner. A blue end cap marks the top of a section, a clear one marks the bottom, 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 any yellow cap used. The core sections are then carried into the laboratory and the lengths of the core sections and any samples taken are logged into the shipboard database.

After the core sections equilibrate to ambient laboratory temperature (~3 hr), they are run through the whole-core multisensor track (MST), and thermal conductivity measurements are made for soft sediment (see "Physical Properties"). Cores are subsequently split lengthwise into working and archive halves. The archive half is used for nondestructive measurements: visual core description (VCD), paleomagnetics, magnetic susceptibility (MS), 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 Leg 182 all cores were transported in refrigerated containers to the Gulf Coast Repository of the Ocean Drilling Program in College Station, Texas.