Sampling of Cores

Planning and organization of Science Party Sampling

The Onshore Science Party is considered to be part of the actual expedition, where the entire group of expedition scientists meets for the first time. The cores are split, described, and analyzed according to the IODP minimum and standard measurements. In addition the science party takes the samples for expedition-related analyses and for individual post-cruise research projects according to the moratorium sampling plan. All this work is carried out in the IODP laboratories of the BCR in the MARUM buliding.

- The Sample Allocation Committee (SAC), comprising the Co-chief scientists, the ESO staff scientist, and the IODP Curator, meet before arrival of the Science Party to review and evaluate the submitted sample and data requests. The goal of this meeting is to make sure that the scientific objectives of the expedition as represented in the proposed research projects are met, and also to identify potential overlap of or conflicts between different requests.

- On the first day of the Onshore Science Party, the SAC discusses the sample and data requests with the different groups (e.g., micropaleontologists, geochemists, petrophysicists, sedimentologists, etc.) and in the case of overlap they try to resolve the potential conflicts.

- The SAC then develops a specific sampling plan to be carried out through the course of the science party. This involves establishing the volume of each sample as well as the precise placement of samples for each investigator within each section, depending on the stratigraphic interval required, and the spacing between individual samples. Good planning at this stage is critical so that when possible each section must only be opened once to get all samples for all of the investigators.

All sampling follows the IODP Sample, Data, and Obligations Policy.

Three general sampling types are discussed:
Hard Rocks, Sediments, and Paleomagnetism Samples:

Hard rocks

Hard-rock sampling is usually carried out using a rock saw or a drill.

Various shaped samples can be cut with the saws, using blades of different thickness or diameter, depending on the purpose of the sample and hardness of material. For most sampling with the saw, the sample is hand-held and cut to shape as needed.

Drilling uses a cylindrical bit, usually with a one-inch inside diameter, but smaller diameter bits are also available. Hard-rock samples for paleomagnetic analyses (mini-cores) are often taken using the cylindrical drill bits. Mini-cores are most commonly drilled perpendicular to the long axis of the core, and perpendicular to the cut face of the core.

Both sawing and drilling techniques require a water source for cooling the cutting tools.

Hard rocks in marine geology are usually considered to be igneous ocean crustal rocks such as basalt or gabbro. The same sampling techniques, however, are employed in the lab for massive coral skeletons and indurated sedimentary rocks.

Sediments

For the purposes of describing sampling techniques, sediments are considered to be those sedimentary units that are soft enough to be sampled without the use of the saw or drill.

For the softest sediments, usually the most efficient technique makes use of plastic receptacles for relatively standard sample sizes of 5 or 10 cc. They are pressed into the soft sediment and removed with the sediment sample inside. There are two basic forms of these:

- Tubes: the plastic tubes are cylinders with an inside diameter (i.d.) of ca. one inch (10cc sample) or ca. 1/2 inch i.d. (5cc). In order to take a 10 or 5 cc sample, the tube is inserted into the cut section face in the middle, where the thickness of the sediment is greatest. Smaller samples can be taken away from the center, for example, a 2cc sample using a 5cc tube placed closer to the edge of the core liner. Volumes are only approximate.
- Scoops: the plastic scoops are rectangular at the top with the sides curved toward the bottom to match the curvature of the core liner (see photo). They are pressed into the soft sediment on the sides of the core so that the curved side matches the curve of the liner, and the straight side does not go all the way to the center of the core half. The scoop is then rolled out with pressure against the outside of the liner to leave a rectangular hole. These also come in two sizes: 10cc (2cm wide samples) and 5cc (1cm wide samples).
When the sediments are too hard to press in the plastic receptacles, or when geochemistry samples require avoiding contact with plastic (e.g., alkenone samples), then the sediments have to be scooped out with a metal tool such as a small spatula or knife, and a mallet may be necessary to drive the tool in. In this case, the volume is calculated such that a one cm-wide sample half the width of a section half is about 8cc. In addition, stainless steel scoops of various widths can be used.
Two types of samples are commonly taken from sediments for paleomagnetic studies. These are continuous u-channels and discrete paleomag cubes. The orientation of the sediments must be maintained in both cases. That is, the "up" direction has to be indicated on the sample.

Paleomagnetic samples: u-channels and cubes

U-channels commonly extend as a single sample through an entire section for continuous measurement. They are taken by pressing a long, rectangular plastic "tube" closed on three sides and open on the other (thus the term, u-channel) into the cut surface of the section half. The inside cross-section area of the u-channel is 2X2 cm (see photograph). After insertion into the sediment, a thin wire or plastic fishing leader is inserted so that it runs beneath the sampler, across the open side and up each side on the outside of the plastic u-channel. The wire is pulled along the length of the sample to separate the sediment cleanly across the open side from the sediment remaining in the section.
Paleomag cubes are discrete oriented samples of a specific, relatively accurate volume for paleomagnetic measurements. Various shapes and sizes have been used in the past. Examples for external dimensions:
• IODP standard: 25 x 25 x 19 mm
• Cubes for use in Bremen autosampler: 23 x 23 x 19 mm
The volume is about 8 cc.
The plastic cubes are pressed into the cut face of the core section with an arrow indicating the "up" direction. The top of the cube has a small hole to allow air to escape as the cube fills with sediment. When the cube is completely depressed and filled with sediment, a tool with a stiff wire is inserted and pulled below the cube, across the open side to separate the sample within from the sediment remaining in the liner. The cube, containing the sample can then be removed and cleaned, and a form-fitting top is then put on to cover the open side.