General core description
By: K. Gajewski
When the sediment cores are returned to the lab, they should be stored in refrigerators in room 0012. You will need some stiff support so the cores are not crushed when they are stacked. Square white plastic gutter pipe is a good size, stacks easily, is relatively cheap and can be cut to proper length. Write the core name and drive number on the outside surface.
Splitting the core
Whne you are ready to begin, the core should be split. Unwrap the aluminum foil and place the core in the plastic wrap in the split black PVC pipe. This will support it properly during the description and subsampling. Place the core and 1/2 tube in the splitter. Use the cheese cutter to split the core. One half should be wrapped in double plastic and alumnimum foil and stored as an archive. Don't forget to label it with core name, drive number, depth and an "up" arrow. The other half can be kept in the black tube for the subsequent steps. Always rewrap the core if yuou are leaving it for a few minutes to prevent excessive drying.
Description of cores
The level of the core description depends on the question under investigation. Carefully clean the split face, taking care to not remove too much sediment. Look for changes in the stratigraphy, changes in texture, distinctive layers or transitions. Note down all these by depth. The colour should be estimated with the Munsell chart at any layer or at regular intervals. Moss or wood layers should be noted and sampled. The visual description is only the first step, as x-rays, magnetic susceptibility and weight loss will provide more information. If you are working with bog or marsh sediments, you could use the Trolls-Smith system (see the book in the library), but this is not very useful for lake sediments.
Note the presence of macrofossils. You may wish to sample them immediately as you may not be able to find them later. They may be useful for dating, and can be identified to indicate presence of the taxon on the landscape.
One helpful way to organise this information is to take two facing pages of your lab notebook; a lab notebook with gridded pages works best. At the far left draw a long, thin rectangle from the top of the page to the bottom. This represents the core, and you can locate all information on this picture. Each line of your grid can be 5 cm or so. You can write your description on the rest of the page. I also note the location of any subsamples on this diagram as well. This can help to properly locate yourself if you return to the core after a period of time. There is frequently some shrinkage, but if the location of the subsamples is known, you can accurately align your stratigraphy.
The following procedure was developed by several people, including C Duschesne, M Frappier, T Lacourse and K Gajewski. Note that all cores are different, and you will need to experiment with the method.
Set up the copy stand, ensuring the camera is snugly attached. Place the black towels on the table and the wall to absorb any reflections. The floods are clamped onto the open cabinets above. They should be symmetrically placed on both sides at a moderate angle. You will have to adjust them to minimize reflection from the wet core surface. Covering the reflectors with a cloth reduces reflection, but be careful that they don't burn! Use the circular level to ensure the camera is level, and adjust the height of the copy stand depending on how much of the core you wish to photograph at each exposure. Don't use too wide an angle, as this distorts the image, around 50 should be ok.
To determine the exposure, use the gray card. The card should be covering most of the field of view and set the f-stop and speed to centre the exposure needle. You shouldn't use too long an exposure to avoid camera shake - depth of field is not critical if you focus carefully. Once you have the exposure determined, take a photo of the MacBeth Colour Card; you can later use this to ensure the colour rendition is correct. As a rough guide, a good exposure was obtained at f11; 1/8 sec or f8 at 1/15 second. Note the exposure in the lab book.
Place the core in the black tube on the black towel. Place a metre stick above it, and on each exposure place the small colour card in the field of view. Make sure you get all three objects in each exposure. If you wish, you can place a sheet with the core name and drive number in the picture as well. The metre stick can be located for actual depth of core, or for the depth along the particular drive, but be consistent.
(a) use the slowest film speed you can get
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