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. A center bit may replace the core barrel if it is decided to drill
without coring.In this chapter we describe the shipboard procedures used during Leg 197. This information concerns only shipboard operations and analyses described in the site chapters of the Initial Reports volume of the Leg 197 Proceedings of the Ocean Drilling Program. Methods used by various investigators for shore-based analyses of Leg 197 data will be described in the individual scientific contributions to be published in the Leg 197 Scientific Results volume and elsewhere.
The leg 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).
The "Core Descriptions" directories for each site include summary core descriptions ("barrel sheets"), core photographs, and thin section descriptions (see the "Core Descriptions" contents list.)
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 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 (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 sediment or rocks recovered from different holes usually do not come from exactly equivalent positions in the stratigraphic column.
The cored interval is
measured in meters below seafloor. 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. A center bit may replace the core barrel if it is decided to drill
without coring.
Cores taken from a hole are numbered sequentially from the top of the hole downward. Core numbers and their associated cored intervals in meters below seafloor 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 falling out when the barrel is being retrieved from the hole. In certain situations recovery may exceed the 9.5-m maximum. In hard rock cores, this probably happens when a pedestal of rock fails to break off and thus is not caught by the core catcher. When a subsequent core barrel is deployed, this pedestal enters the core barrel and, because it is from the previous cored interval, it can lead to >9.5 m of recovery for the next 9.5-m cored interval.
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 (rarely, an unusually long core may require more than seven sections). When less than full recovery is obtained, as many sections as are needed to accommodate the length of the core are used; for example, 4 m of core would be divided into two 1.5-m sections and a 1-m section. If cores are fragmented and recovery <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 situations, a section <1.5 m may be cut to preserve features of interest (e.g., lithologic contacts).
By convention, material recovered from the core catcher is placed below the last section when the core is described and is labeled "core catcher" (CC); in sedimentary cores, this is treated as a separate section. The core catcher is placed at the top of the cored interval in situations where material is recovered only in the core catcher. However, information supplied by the drillers or by logging may allow for more precise interpretation of the correct position of core catcher material within an incompletely recovered cored interval. 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 "197-1203A-25R-1, 10-12 cm" indicates a 2-cm sample removed from the interval between 10 and 12 cm below the top of Section 1, Core 25 ("R" designates that this core was taken during rotary drilling) of Hole 1203A during Leg 197.
As soon as a core is retrieved on deck, a sample is taken from the core catcher and taken to the paleontology laboratory for an initial age assessment. The core is then laid out on a long horizontal rack on the catwalk adjacent to the drilling floor. Next, the core is marked into section lengths, each section is labeled, and the core is cut into sections. The plastic core liner containing each section is then sealed at the top and bottom by gluing on color-coded plastic caps; blue to identify the top of a section and clear to identify the bottom. Caps are usually attached to the liner by coating the end of the liner and the inside rim of the cap with acetone.
Next, the sections of core are carried into the laboratory and each is labeled again using an engraver to permanently mark the full designation of the section onto the plastic core liner. 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 shipboard CORELOG database program. After cores have equilibrated to room temperature (~3 hr), they are run through the multisensor track (MST), probes are inserted through holes drilled through the liner to measure thermal conductivity on relatively soft sediment, and the cores are split.
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. During Leg 197, the wire-cut cores were split from the bottom to top; thus, investigators should be aware that older material may have been transported up the core on the split face of each section.
The working half of the core is sampled for both shipboard and shore-based laboratory studies. Each extracted sample is logged into the sampling computer database program by the location and the name of the investigator receiving the sample. Records of all removed samples are kept by the curator at ODP. The extracted samples are sealed in plastic vials or bags and labeled. Samples are routinely taken for shipboard physical properties measurements and for calcium carbonate (coulometric) analysis.
The archive half is described visually. Smear slides are made from sediment samples taken from the archive half. Most archive sections are run through the cryogenic magnetometer. The archive half is then photographed using both black-and-white and color film, a whole core at a time. Close-up photographs (color and black and white) are taken of particular features for illustrations in the summary of each site, as requested by individual scientists. Both halves of the core are then placed into labeled plastic tubes, sealed, and transferred to cold-storage space aboard the drilling vessel. At the end of the leg, the cores are transferred from the ship in refrigerated airfreight containers to cold storage at the Gulf Coast Repository of the Ocean Drilling Program at Texas A&M University.
Igneous rock cores are handled differently from sedimentary cores. Once on deck, the core catcher sample is placed at the bottom of the core liner and total core recovery is calculated by shunting the rock pieces together and measuring the total length to the nearest centimeter. This information is logged into the shipboard CORELOG database program. The core is then cut into 1.5-m-long sections and transferred into the laboratory.
The contents of each section are transferred into 1.5-m-long sections of split core liner, where the bottom of oriented pieces (i.e., pieces that clearly could not have rotated top to bottom about a horizontal axis in the liner) are marked with a red wax pencil. This is to ensure that orientation is not lost during splitting and labeling. Important primary features of the cores also are recorded at this time. Core pieces are then photographed digitally while being rotated to acquire a full, circumferential image for later correlation with the Formation MicroScanner (FMS) logs. The core is then split into archive and working halves. A plastic spacer is used to separate individual pieces and/or reconstructed groups of pieces in the core liner. These spacers may represent a substantial interval of no recovery. Each piece is numbered sequentially from the top of each section, beginning with number 1; reconstructed pieces are all assigned the same number, but with a consecutive suffix letter (e.g., Piece 1A, 1B, etc.). Pieces are labeled only on the outer cylindrical surfaces of the core. If the piece is oriented, an arrow is added to the label pointing to the top of the section. Because pieces are free to rotate about a vertical axis during drilling, azimuthal orientation during Leg 197 was possible only by using paleomagnetic data.
In splitting the core, every effort is made to ensure that important features are represented in both halves. The archive half is 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, are performed on the archive half of the core. The working half is 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 is then sampled for shore-based laboratory studies. Records of all samples are kept by the curator at ODP. Both halves of the core are then 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. As with the other Leg 197 cores, they are housed at the Gulf Coast Repository of the Ocean Drilling Program at Texas A&M University.
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.
Ms 197IR-102
