This chapter explains the techniques and procedures used during Leg 195 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 Initial Reports volume of the Leg 195 Proceedings of the Ocean Drilling Program. Methods used by various investigators for shore-based analyses of Leg 195 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, and the summary chapter is derived from all their contributions (authors are listed in alphabetical order; no seniority is implied):
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. Because a number of other factors may determine the rate of penetration, it is not always possible to relate drilling time directly to the hardness of the layers. Bit weight and revolutions per minute, recorded with a new acquisition program (Fusion), also influence the penetration rate.
When cores are split, many show signs of significant sediment 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, and 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 used by DSDP (Sites 1 through 624) but prevents ambiguity between site- and hole-number designations. It is important to distinguish between 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 core cutting began and extends to the depth where core cutting ended (see Fig. F1). The length of each cored interval is generally 9.5 m, the length of a core barrel; however, 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 meters below seafloor 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 other hole problems occur. Full recovery for a single core is 9.5 m of rock or sediment contained in a plastic liner (6.6 cm internal diameter) plus about 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. 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 at least partially a consequence of degassing. Each recovered core is divided while in its liner 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 generally being shorter than 1.5 m. Rarely, a core may require more than seven sections; this is usually the result of gas expansion having caused voids within some sections. When less than full recovery is obtained, sections are numbered as needed to accommodate the length of the core; for example, 4 m of core would be divided into two 1.5-m sections and a 1-m section. If a core is fragmented (recovery <100%), the sections are numbered serially and remaining or unused sections are noted as void, whether shipboard scientists believe that the fragments were contiguous in situ or not. 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 only recovered 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 deep-sea drilling), 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 section. For example, a sample identification of "195-1200A-7R-1, 10-12 cm" would be interpreted as representing a sample removed from the interval between 10 and 12 cm below the top of Section 1, Core 7 ("R" designates that this core was taken by the rotary core barrel) from Hole 1200A during Leg 195. A computer routine is available to calculate the meters below seafloor depth from any correctly formulated ODP sample designation; this avoids inconsistencies that could have arisen on those occasions where some sections were cut to nonstandard lengths. Although meters below seafloor depth is an invaluable convention, it is not ideal, especially for high-resolution work.
All ODP core and sample identifiers indicate core type. The following abbreviations are used:
APC, XCB, RCB, G, and W cores were cut during Leg 195.
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. Then, the core is 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. Headspace gas samples are taken from the ends of cut sections on the catwalk and sealed in glass vials for light hydrocarbon analysis as part of the shipboard safety and pollution prevention program. During Leg 195, headspace gas samples of sediment were taken at both Sites 1200 and 1201. 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 mark the full designation of the section permanently 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 Janus database program. At this point, whole-round samples are taken for pore water and microbiology studies. After the remaining cores have equilibrated to room temperature (~3 hr), they are run through the multisensor track (MST), thermal conductivity measurements are performed on relatively soft sediments, and the cores are split.
Cores 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 195, the wire-cut cores were split from the bottom to the top; thus, investigators should be aware that in the sediments 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 and paleomagnetic 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 chapter for 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.
Hard 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 Janus 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 to ensure that orientation is not lost during splitting and labeling. Important primary features of the cores also are recorded at this time. 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.
In splitting the core, every effort is made to ensure that important features are represented in both halves. The archive half is described visually and 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 then is 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 195 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 195IR-102