2. Explanatory Notes¹

Shipboard Scientific Party²

INTRODUCTION

In this chapter, we describe the shipboard procedures used during Leg 193. This information concerns only shipboard operations and analyses described in the site chapters of the Leg 193 Initial Reports volume of the Proceedings of the Ocean Drilling Program. Methods used by various investigators for shore-based analyses of Leg 193 data will be described in the individual scientific contributions to be published in the Scientific Results volume and in various professional journals. Abbreviations of technical terms in this volume are listed in Table T1.

The Leg 193 Summary chapter and separate sections of the site chapters were written by the following shipboard scientists (authors are listed in alphabetical order; no seniority is implied):

Leg 193 Summary: Fernando Barriga, Ray Binns, Jay Miller

Operations Summary: Leon Holloway, Gerry Iturrino, Jay Miller, Mike Storms

Igneous Petrology: Wolfgang Bach, Ray Binns, Jay Miller, Holger Paulick, Dave Vanko, Chris Yeats

Hydrothermal Alteration: Wolfgang Bach, Fernando Barriga, Ray Binns, Klas Lackschewitz, Dave Vanko, Chris Yeats

Sulfide and Oxide Petrology: Fernando Barriga, Ray Binns, Terje Bjerkgard, John Kulange, Álvaro Pinto, Steve Roberts, Steve Scott, Ian Warden, Chris Yeats

Structural Geology: Terje Bjerkgard, Bob Findlay

Geochemistry: Wolfgang Bach, Fernando Barriga, Liane Benning, Ray Binns, Erika Elswick, Jay Miller, Dave Vanko

Microbiology: Ryuji Asada, Hiro Kimura, Andrew Masta

Physical Properties: Lizet Christiansen, Gerry Iturrino

Rock Magnetism: Sang-Mook Lee

Downhole Measurements: Anne Bartetzko, Gerry Iturrino

The summary core descriptions ("barrel sheets"), core photographs, and thin-section descriptions can be accessed from the "Core Descriptions" contents list.

Numbering of Sites, Holes, Cores, and Samples

The Ocean Drilling Program (ODP) drill sites are numbered consecutively and each site consists of one or more holes drilled while the ship was positioned over one acoustic beacon. For all ODP drill sites, a letter suffix distinguishes individual holes drilled at the same site. The first hole to be drilled is assigned the site number modified by the suffix A, the second hole takes the site number and suffix B, and so forth. Note that this procedure differs slightly from that used by the Deep Sea Drilling Project (DSDP; Sites 1 through 624), but prevents ambiguity between site- and hole-number designations.

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

Cores taken from a hole are numbered sequentially from the top of the hole downward. Core numbers and their associated cored intervals (in mbsf) are unique in a given hole. Normally, maximum recovery for a single core is 9.5 m of rock or sediment contained in a plastic liner (6.6-cm internal diameter) plus ~0.2 m (without a plastic liner) in the core catcher (Fig. F1). The core catcher is a device at the bottom of the core barrel that prevents the core from sliding out when the barrel is being retrieved from the hole.

A recovered core is divided into 1.5-m sections that are numbered serially from the top (Fig. F1). When full recovery is obtained, the sections are numbered from 1 through 7, with the last section possibly being shorter than 1.5 m. When less than full recovery is obtained, as many sections as are needed to accommodate the length of the core are used (e.g., 4 m of core would be divided into two 1.5-m sections and a 1-m section). If cores are fragmented and recovery is <100%, sections are numbered serially and the rest of the drilled interval is regarded as void, whether or not shipboard scientists think that the fragments were contiguous when in situ. In rare cases, a section <1.5 m in length may be cut to preserve features of interest visible through the core liner (e.g., lithologic contacts).

By convention, material recovered from the core catcher is placed below the last section. The core catcher is placed at the top of the cored interval in cases where material is recovered only in the core catcher. However, information supplied by the drillers or by logging may allow for a more precise interpretation as to the correct position of core-catcher material within an incompletely recovered cored interval.

Also by convention, when the recovered core is shorter than the cored interval, the top of the core is equated with the top of the cored interval. Samples taken from the cores are designated by distance measured in centimeters from the top of the section to the top and bottom of each sample.

A complete 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 the section. For example, a sample identification of "Sample 193-1188A-1R-4, 80-85 cm" indicates a 5-cm sample removed from the interval between 80 and 85 cm below the top of Section 4, Core 1 (R designates that this core was taken during rotary drilling) of Hole 1188A during Leg 193 (Fig. F1).

Igneous and Hydrothermally Altered Rocks

There were special handling and curation requirements for all cores recovered during Leg 193. Plastic core liners were split into nominally 1.5-m lengths and total core recovery calculated by shunting the rock pieces together and measuring the total length in each section to the nearest centimeter. This information was logged into the shipboard Corelog database program as liner length (length of the plastic liner) and curated length (length of core inside the liner). The plastic core liner containing each section was sealed at the top and bottom by gluing on color-coded plastic caps: blue to identify the top of a section and translucent to identify the bottom. Caps were attached to the liner by coating the end of the liner and the inside rim of the cap with acetone. The core was then transferred into the core laboratory.

Because microbiological sampling was a primary objective of Leg 193, special precautions were taken to minimize contamination of the cores prior to sampling. Anyone handling the core prior to microbiological sampling wore latex gloves swabbed in alcohol. The contents of each section were transferred into 1.5-m-long sections of split core liner, and with the oversight of a co-chief scientist or designate, an interval of core was identified where appropriate for microbiological sampling. Because this interval had not been described, it was photographed on the core table with a handheld digital camera, and if deemed necessary a brief description was prepared. The whole-round section or piece was then transferred to the microbiology laboratory for processing. A representative length of Styrofoam was used to mark the location of the sampled interval in the split core liner. Residues from the microbiological sampling were returned to the core liner after processing, and we attempted to accurately curate these using the digital images and descriptions as guides.

After microbiological sampling, the bottom of oriented pieces (i.e., pieces that clearly could not have rotated top to bottom about a horizontal axis in the liner) were marked with a red wax pencil. This was to ensure that orientation was not lost during splitting and labeling. Contiguous pieces of the core with obvious features that allowed alignment were curated as a single piece and plastic spacers were affixed between pieces and/or reconstructed pieces in the core liner. In some cases, when we were concerned that structural features might be lost during core splitting, cores were photographed as whole rounds (see the "Core Descriptions" contents list). The core was passed through the shipboard multisensor track (MST) and then split into archive and working halves, either with a diamond saw or as described below for disintegrated core. For sawed core, each piece was numbered sequentially from the top of each section, beginning with number 1; reconstructed pieces were all assigned the same number, but with a consecutive suffix letter (e.g., Piece 1A, 1B, etc.). Pieces were labeled only on the outer cylindrical surfaces of the core. If the piece was oriented, that is, the piece was long enough that it could not have rotated about its long axis in the core liner, an arrow was added to the label pointing to the top of the section.

Many initially continuous core samples taken with the advanced diamond core barrel (ADCB) during Leg 193 tended to disintegrate during or after removal from the core barrel (see Fig. F2A, F2B). For curation, equivalent collections of fragments were placed into the working and archive halves, and "piece boundaries" were set at detectable changes in lithology. Because of this, digital photographs of the cores were taken immediately after recovery. Summary "prelogs" were also prepared to allow effective curation of the cores. These logs and images are presented in the "Core Descriptions" contents list.

In splitting the core, every effort was made to ensure that important features were represented in both halves. The archive half was described visually, then photographed with both black-and-white and color film, one core at a time. Nondestructive physical properties measurements, such as magnetic susceptibility, were performed on the archive half of the core. The working half was sampled for shipboard physical properties measurements, paleomagnetic studies, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), and thin-section studies. The working half of the hard-rock core was subsequently sampled for shore-based laboratory studies. Records of all samples are kept by the curator at ODP. Both halves of the core were shrink-wrapped in plastic to prevent rock pieces from vibrating out of sequence during transit, placed into labeled plastic tubes, sealed, and transferred to cold-storage space aboard the drilling vessel. Cores containing sulfides were placed in foil bags, evacuated, and filled with a nitrogen atmosphere prior to final packaging to minimize oxidation. All Leg 193 cores are housed at the Gulf Coast Repository of the Ocean Drilling Program at Texas A&M University.