Boxcore Processing

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Core Extraction | Core Logging | Xrays | Developing Xray Film | Relief Peels

Core Extraction

1) Collect boxcore.

2) Remove boxcore door and allow sediments to dry. If sediments are very wet, the base of the core may be elevated 5-10 cm to prevent sediments draining from the core. Process the core while the sediments are still moist but not saturated. If you cannot process the core within 48 hours, keep the door on the boxcore until you are ready to process the core.

3) Remove uppermost sediments from corer with 4" putty knife.

4) Subsample core for grain size and composition analyses.

5) Leave a level 2 cm thick slab of sediment.Remove 1 cm or less of sediment from the sides of the boxcore to allow a 13 cm x 30 cm plexiglass tray with 1 cm molded sides to securely cover the core sediments. Be careful not to make the slab too thin. The core should never be less than 1 cm thick.

6) Label sides and base of plexiglass tray with top and bottom of core, orientation (note: when core is flipped, the orientation with respect to observer will change), and core label (e.g.-971013-8).

7) Invert plexiglass tray on top of sediments. Place 14 cm x 30 cm metal slide between the sample and boxcore. Maintain pressure on the metal slide to keep it flush against the boxcore, particularly near the top of the core.

8) Keeping a light pressure on the tray and metal slide, lift the sediments from the corer. Invert or ‘flip’ the sample so the boxcore sediments now rest in the tray. Note that orientation of the sediment has changed.

9) ‘Slide’ the metal slide off the sediment surface. Shave the surface of the tray sediments in the direction of the bedding until the thickness of the sediment is even with the height of the tray. Shave around gravel or shell fragments that originate in the lower 1 cm of sediment.

Core Logging

1) Place scale next to core.

2) Describe primary sedimentary features (grain size, grading, bedding, etc.) and secondary sedimentary features (e.g.-bioturbation).

3) Photograph and digital image core.

Xrays

Operating Instructions for the Vet-Ray VR8020LBC

1) Prepare core sample.

2) Wear radiation detection badge.

3) Securely mount the portable Vet-Ray unit on the stand. Connect the unit to an electrical outlet. Insert the exposure hand switch plug into the connector.

4) Turn on the light beam collimator lamp and adjust the beam to highlight the approximate area to be exposed.

5) Turn on the LV (line switch) and gradually increase the settings until the LV pointer is in line with the red diamond.

6) Set distance from xray unit to film. Recommended settings are in Table A.1.

7) Set the exposure time.

8) Select the proper Kv/Ma setting. Higher Kv (kilivolts) increase penetration, and higher Ma (miliamps) produce better contrast. Proper exposures of core sediments may require a high Kv and low Ma.

9) When changing parameters, change distance (6), time (7), and Kv/Ma (8), in that order. The ideal xray is low penetration (Kv), high contrast (Ma), and a short distance. Increasing Kv/Ma decreases the required exposure time.

10) Place film under xray unit. Position the core on top of the film.

11) Place lead letters and numbers for the sample name and an arrow with ON indicating onshore on left side of sample. Place letters BOT on left side at the base of the core. It is often easier to secure lead letters on duct tape, and place near the sample.

12) Direct and center the xray emission port (collimator cross mark) on the sample.

13) Confirm the film to tube focus distance with tape measure.

14) Stand behind a radiation barrier.

15) Start the exposure by pressing and holding the exposure hand switch. During the exposure, the exposure light will illuminate. The Ma meter shows the actual Ma. Amperage of the xray unit changes from 17 to 26 amps. A 20 amp breaker will work, but it is recommended to increase amperage of breaker to 30 amp.

16) Turn the line switch off.

17) Allow the xray unit to cool between xrays for 2 minutes for every second of xray.

18) Mark the yellow paper cover of industrex film with the core identification. Place film in cover and archive.

Table A.1. Recommended settings for core xrays.

Material

Sand boxcore

Silt boxcore

Epoxy peel

Sample thickness

w/ 1/8" plexi-glass 1.27cm (1/2")

w/ 1/8" plexi-glass
1.27 cm

1.27 cm

Height of camera

53 cm

53 cm

53 cm

Kv/Ma

60/20

70/15

70/15

Exposure time

2.5 s

3.5 s

2.4 s

Developer time

2.5 min

2.5 min

2.5 min

Fixer time

2.5 min

2.5 min

2.5 min

Film size

8" x 10"

8" x 10"

8" x 10"

Developing Kodak Industrex film

1) Place developer, fixer, and water in plastic bins. Place separate "drip" bins for excess developer, fixer, and water near the respective bins.

2) Seal off all light coming into the room, and turn on the red darkroom lights.

In darkroom

3) Remove film from the film envelope.

4) Place the film in the developer bin. There should be enough solution to completely submerge the film. Do not place more than one film in the developer solution simultaneously. Developing time will vary according to the temperature of the solution that is a function of the temperature of the room.  The temperature of the xray room (behind Mr. Scarborough's office at the FRF) is 72°. Develop for 3 minutes at 72° or 75°, 5 minutes at 68° (preferred), and 7 minutes at 62°.

5) Agitate the solution every 30 seconds for 5 seconds.

6) Before placing film in the fixer, let the excess developer drip from the film into the drip bin.

7) Repeat steps 4-6 for the fixer bath with the exception that you can place more than one film in the fixer at the same time.

8) Before placing film in the water bin, let the excess fixer drip off the film into the drip bin.

9) Place the film in the water bin for a minimum of 20 minutes. At this point, the lights may be turned on.Change the water often.

10) Frequently agitate the film in the water to rinse chemicals from the film.

11) Before hanging the film to dry for 24 hours, let the excess drip off film in the drip bin.

Relief Peels

1) Process and xray boxcore.

2) Cut cheesecloth into 18 cm x 35 cm pieces. Place 3 layers of cheesecloth over 1 cm thick core in plexiglass tray.

3) In a sturdy container, mix resin and hardener in the following ratios:

4) Use a disposable paintbrush to paint resin on cheesecloth until the cheesecloth and uppermost core sediments are saturated. The thickness of the peel should be 3-8 mm thick, so avoid applying too much resin.

5) Place labels for core identification and orientation on cheesecloth and affix with resin.

6) Allow the peel to harden.

7) Remove the peel from the plexiglass tray. It may be necessary to use a spatula or other utensil to pry the peel from the tray. Be careful not to break or crack the tray or peel.

8) Remove excess sediments from the peel with running water (a garden hose is great for robust peels) or knock the side of the peel against a hard surface.

9) Trim excess cheesecloth from peel edges with scissors. Affix the peel to a labeled masonite board with additional resin.


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The content for this web page was taken from the Dissertation Storm Sedimentation on the Surf Zone and Inner Continental Shelfof Rebecca Lenel Beavers in the Department of Geology of Duke University

This web site was created by Doug Call (Contract Student, University of Virginia) on July 31, 2001.