Research Update

After a successful field excursion in June, I brought back samples from four roadcuts:

• Old Wauneta Roadcut (OWR). A detailed description of this site can be found in Jacobs and Mason (2004). This site is probably second only to Bignell Hill for the late Glacial and Holocene stratigraphic record. Holocene loess, termed Bignell loess, is six meters thick at this site, and contains up to four buied paleosols. Underlying the Bignell loess is another paleosol termed the Brady soil, which has been dated to the Glacial-Interglacial transition. OWR is a great site to sample from not only because of its great stratigraphy, but it has also been extensively dated by radiocarbon and optically stimulated luminescence (OSL). An earlier researcher (Feggestad) took a transect of cores downwind from the OWR, which I will also use in my research.
• Lewis site. This roadcut is approximately two kilometers north of OWR. The Lewis site contains a Brady soil equivalent, which was laid down in an old sand dune swale. This is overlain by Holocene slopewash fill. This site is interesting because it offers the opportunity to document the silica biogeochemical cycle in a vastly different setting than OWR. Namely, how is silica entrainment and recycling effected by these different processes?
• Courthouse Rock (CR). CR is located in the Nebraska panhandle, and is the farthest north of the four sites. It has slightly larger particle size than the Lewis and OWR, and offers an opportunity to see how this effects the silica biogeochenical cycle.
• Wach Site. This site is composed of sand size particles. The Wach site was deposited from an old sand dune blowout. How will this effect the silica biogeochemical cycle?

Now that I have my samples, I'll be looking at two things. First, how does varying sediment accumulation rates effect the silica biogeochemical cycle? Second, how does particle size effect this cycle as well?

Tentative Si extraction methods 2

Sample size: ~5 g

1. Dry sample overnight. Weigh and record sample weight.
2. Remove organics with HNO3 and a pinch of KClO3. Place sample in boiling water bath. Digest for 1.5 hours. Centrifuge and decant supernatant (3x).
3. Remove carbonates with 10% HCl. Digest for 15 minutes or until reaction stops. Centrifuge and decant supernatant (3x).
4. Deflocculate sample with 5% (NaPO3)6. Place in mechanical shaker for 8 hours. Do not centrifuge.
5. Extract clays (less than 4 microns) using float times outlined by Tanner & Jackson (1947).
6. Float sample using 3NA2 • (WO4 •9WO3)• H2O. Set specific gravity to 2.3. Extract pytoliths using pipette. Centrifuge and decant supernatant (3x).
7. Place extracted phytoliths in 1 dram vial.