This chapter explains the techniques and procedures used during Leg 188 in order to help document the basis for our preliminary scientific conclusions and to provide the interested investigator with the information needed to select samples for further analysis. This information concerns only shipboard operations and analyses described in the site reports in the Leg 188 Initial Reports volume of the Proceedings of the Ocean Drilling Program. Methods used by various investigators for shore-based analyses of Leg 188 data will be described in the individual scientific contributions published in the Scientific Results volume and in publications in various professional journals.
The separate sections of the site chapters were written by the following shipboard scientists (authors are listed in alphabetical order; no seniority is implied):
1. The term Ma is equivalent to and replaces m.y.B.P. (million years before present); for example, 35-40 Ma.
2. The term m.y. is used in the context of duration, such as "... for 5 m.y. in the early Miocene."
Information concerning sedimentary stratification in uncored or unrecovered intervals may be inferred from seismic data, wireline-logging results, and examination of the behavior of the drill string, as observed and recorded on the drilling platform. Typically, the harder a layer, the slower and more difficult it is to penetrate. A number of other factors may determine the rate of penetration, so it is not always possible to relate the drilling time directly to the hardness of the layers. Bit weight and revolutions per minute (rpm), recorded with a new acquisition program (Fusion), also influence the penetration rate.
When cores are split, many of them show signs of significant drilling disturbance, including the concave-downward appearance of originally horizontal bedding, haphazard mixing of lumps of different lithologies (mainly at the tops of cores), fluidization, and flow-in. Core deformation may also occur during retrieval because of changes in pressure and temperature as the core is raised, as well as during cutting and core handling on deck.
Ocean Drilling Program (ODP) drill sites are numbered consecutively and refer to one or more holes drilled while the ship was positioned over one acoustic beacon. Multiple holes may be drilled at a single site by pulling the drill pipe above the seafloor (out of the hole), moving the ship some distance from the previous hole, and then drilling another hole.
For all 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 takes the site number and suffix "B," and so forth. Note that this procedure differs slightly from that previously used by the Deep Sea Drilling Project (DSDP) (Sites 1 through 624) but prevents ambiguity between site- and hole-number designations. It is important to distinguish among holes drilled at a site because recovered sediments or rocks from different holes usually do not come from exactly equivalent positions in the stratigraphic column.
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 operation began and extends to the depth at which the coring operation ended (Fig. F1). 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 continuous if separated by drilled intervals. In soft sediments, the drill string can be "washed ahead" with the core barrel in place, without recovering sediments. This is achieved by pumping water down the pipe at high pressure to wash the sediment out of the way of the bit and up the space between the drill pipe and the wall of the hole.
Cores taken from a hole are numbered serially from the top of the hole downward. Core numbers and their associated cored intervals (in mbsf) ideally are unique in a given hole; however, this may not be true if an interval is cored twice, if the borehole wall caves in, or if other hole problems occur. The full recovery length 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. F2). 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. In many advanced hydraulic piston corer/extended core barrel (APC/XCB) cores, recovery exceeds the 9.5-m theoretical maximum by as much as 0.60 m. The cause of this expansion is not fully understood. The recovered core in its liner is divided into 1.5-m sections that are numbered serially from the top (Fig. F2). When full recovery is obtained, the sections are numbered from 1 through 7, with the last section generally being shorter than 1.5 m. Rarely, a core may require more than seven sections; this is usually the result of voids within some sections caused by gas expansion. When less than full recovery is obtained, as many sections as are needed to accommodate the length of the core will be recovered; for example, 4 m of core would be divided into two 1.5-m sections and a 1-m section. If cores are fragmented (recovery <100%), sections are numbered serially and intervening sections are noted as void, whether or not shipboard scientists believe that the fragments were contiguous. In rare cases, a section <1.5 m may be cut to preserve features of interest. Sections <1.5 m in length are also sometimes cut when the core liner is severely damaged.
By convention, material recovered from the core catcher is placed immediately below the last section when the core is described and is labeled core catcher (CC); in sedimentary cores, it is treated as a separate section. In cases where material is recovered only in the core catcher, it is assigned the depth of the top of the cored interval (this convention differs from that used in the early days of DSDP), although information from the driller or other sources may indicate from what depth it was actually recovered.
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 when 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 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 "188-1165A-11H-6, 10-12 cm," would be interpreted as representing a sample removed from the interval between 10 and 12 cm below the top of Section 6, Core 11 (H designates that this core was taken by the APC) of Hole 1165A during Leg 188. A computer routine is available to calculate the mbsf depth from any correctly formulated ODP sample designation. This avoids any inconsistencies caused by cutting some sections to nonstandard lengths.
All ODP core and sample identifiers indicate core type. The following abbreviations are used: H = hydraulic piston core (HPC; also referred to as APC), X = XCB, and R = rotary core barrel (RCB). APC, XCB, and RCB cores were cut during Leg 188.
As soon as a core was retrieved on deck, a sample taken from the core catcher was given to the paleontological laboratory for an initial age assessment. Special care was taken in transferring the core from the drill floor to a long horizontal rack on a catwalk near the core laboratory so that the core did not bend or twist excessively. The core was capped immediately, and gas samples were taken by piercing the core liner and withdrawing gas into a vacuum tube. Voids within the core were sought as sites for gas sampling. Some of the gas samples were stored for shore-based study, but others were analyzed immediately as part of the shipboard safety and pollution-prevention program. Next, the core was marked into section lengths of 150 cm, each section was labeled, and the core was cut into sections. Interstitial water (IW) and whole-round samples were also taken at this time. In addition, headspace gas samples were taken from the end of cut sections on the catwalk and sealed in glass vials for light hydrocarbon analysis. Afterward, 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 clear for the bottom. A yellow cap was placed on the section ends from which a whole-round sample was removed. The caps were usually attached to the liner by coating the end liner and the inside rim of the cap with acetone.
The cores were then carried into the laboratory, where the sections were labeled with an engraver to permanently mark the complete designation of the section. The length of the core in each section and the core-catcher sample were measured to the nearest centimeter. This information was logged into the shipboard Oracle database (Janus).
After equilibrating to room temperature for ~3-4 hr, whole-round sections from APC and XCB cores were routinely run through the multisensor track (MST). The MST includes a gamma-ray attenuation (GRA) bulk densiometer, a P-wave logger, natural gamma-ray emission measurement, and a volume magnetic susceptibility meter. Soft sediments were measured for thermal conductivity before being split lengthwise into working and archive halves. Softer cores were split with a wire; harder cores were split using a diamond saw. The wire-cut cores were split from top to bottom so that sediment below the empty space or soupy intervals (as are sometimes present at the top of Section 1) would not be drawn into the empty space or compress the soupy materials at the top of a section.
After splitting, the halves of the core were designated as working and archive halves, respectively. Archive halves were then described visually and run through the ODP Minolta color scanner and the cryogenic magnetometer. Finally, the cores were photographed with both black-and-white and color film, a whole core at a time. Close-up photographs (black-and-white and color) were taken of particular features, as requested by individual scientists, for illustrations in the summary of each site.
The working half of the core was measured first for sonic velocity. After physical properties and paleomagnetic sampling, the working half was sampled for shipboard and shore-based laboratory studies. Each sample taken either for shipboard or shore-based analysis was logged into the Oracle database (Janus) by the location and name of the investigator receiving the sample. Records of all of the samples removed are kept in the Janus database and by the curator at ODP headquarters. The extracted samples were sealed in plastic bags and labeled.
Both halves of the core were placed into labeled plastic tubes, which were then sealed and transferred to cold-storage space aboard the drilling vessel. At the end of the leg, the cores were transferred from the ship in refrigerated air-freight containers to cold storage at the ODP core repository in Bremen/Germany.
1Examples
of how to reference the whole or part of this volume can be found under "Citations"
in the preliminary pages of the volume.
2Shipboard
Scientific Party addresses can be found under "Shipboard
Scientific Party" in the preliminary pages of the volume.