Soft sediment thin section procedure

From Susan-  this sounds like an awesome method! pictures please! I don't understand about making the box out of foil

Note: before preparing a thin section using this procedure, talk to the requesting scientist and ask them what they are hoping to address by looking at the thin section. If they would like to see laminations, a thick section might be more suitable. If they're trying to identify a crystal, a grain mount might suffice. Remind the scientist that standard acetone-replacement procedures for soft sediment thin section making are not performed on the ship due to shipboard time limitations, and that the following procedure is IODP's best substitute procedure.

This procedure may not be suitable for the long-term storage of sediments containing calcareous nannofossils or any material that is especially water soluble.

Steps to be tested are in bold.

1. While sampling sediment from core, try to extract sediment in a standard billet shape with a nominally flat side on the face to be sectioned.

2. Prepare a small mold out of a double layer of aluminum foil, by using a form and folding the box around it. The box should be slightly (2-5 mm) larger than the billet on all sides and should have no visible holes. The plasticized tin foil from the wine bottle wrap for hardrock cores works well too, I have some scraps of that hoarded underneath the forward sink.

3. Place the wet sediment billet into the box and freeze-dry for 12-24 hours until no interstitial water remains. If, upon removal from the freeze-dryer, the billet is cold to the touch, there may be interstitial water ice remaining in the pore space. At this stage, the dried sediment is very fragile and should be treated with care.

4. Still inside the box, embed the sediment billet in Petropoxy by dripping the epoxy into the gap between the billet and the box wall most of the way up the billet, leaving the top of the billet dry. After an hour or so, check to see if epoxy has been absorbed into billet and add more. This step will take 12-24 hours, and will take ~5-10 mL of Petropoxy. In the case of exceptionally good permeation, by the end of the impregnation the top of the billet will appear wettened by permeated epoxy.

5. Preheat the heat block or oven to 135°C. (If using the heat block in the thin section lab, the dial needs to be set to 150°C)

6. If possible, remove the billet from excess epoxy and place on an aluminum weigh boat. You can also just cure it in the box, however I have had NO luck getting the aluminum foil off of the cured billet. If you just take the wet billet out and put it on a weigh boat, it doesn't seem like the billet will unimpregnate itself very quickly.

7. Heat the billet at 135°C until cured. Avoid fumes, and note that any plastic used (e.g. tape on the aluminum foil box, Peel-A-Way molds) may melt at this temperature. Seems like it needs at least 1-2 hours on the heat block, this might be faster in the oven. The manufacturer stated cure time for Petropoxy on a thin section is 10 minutes at temperature but in my experience it has been more like 30 minutes for a thin section so adjust accordingly.

8. Dry lap bottom surface (to be sectioned) on sandpaper, frequently wiping away dust. Aim for as flat a surface as possible, however expect that the surface will not be as hard as a traditional billet and can be a little gunky.

9. After a bottom surface is prepared, bond the billet to a clean slide (ultrasonicated in DI water, then wiped with isopropanol alcohol) using Epotek epoxy or Norland 61 and cure accordingly. Petropoxy should not be used at this stage, since it has a high degree of thermal expansion and will not form a good, flat bond with the slide. Note: At this stage we have been having some trouble with tiny bubbles, so I have been having the best luck doing a surface impregnation with abundant Epotek on the exposed surface, then heat-setting the Epotek.

10. Section with Petrothin, using a low spray of water. The remaining billet be gently rinsed of saw cuttings, and placed on the heat block at low temperature to dry it for additional sectioning or storage.

11. From this point on, the slide can be treated as a standard (albeit delicate) thin section and lapped using the Petrothin cup wheel, LP-50 with PLJ2 jig, or hand lapped as usual. Exhibit a degree of caution while thinning, since the bottom surface may not have been as smooth as a normal billet due to delicacy taken at step 8 (dry lapping bottom surface on sandpaper), and thus evenly lapping the top surface may result in patchiness or overthinning in portions. Generally, err on the side of slightly thicker than 30 um, and communicate this with the requesting scientist. If lapping with the LP-50 with PLJ2 jig, should use AlO abrasive and tend towards slower plate speeds.

12. Apply a coverslip if desired, using your choice in epoxies/adhesives (Petropoxy, Norland 61, Epotek).