Week 3 Recap

On Monday, Chris and I went to the USGS in Menlo Park and split all the larger cores from the June cruise. The core splitter is a relatively simple device, but it works much better than cutting the cores free-hand or using a bandsaw. It consists of a frame that holds the core in place while a vibratory cutter and a razor blade pass down the core liner. We were able to finish the job in only a few hours. Half of each core was kept as an archive and the other half was purposed for subsampling of carbonates.

I photographed each core and looked for carbonates. Except for two, each core yielded only one sample, since there were no defined carbonate horizons.

One core had two clear sediment layers (mud overlaying sand), and I was able to take a sample from each of those layers. I subsampled the longest core (51") in 8 different places at similarly spaced intervals. On this core, the upper five sites yielded large shells whereas the lower three yielded only small shell fragments. However, one of the fragments from the very bottom of the core may be large enough to date, which is promising.

I cleaned all of these new samples according to the methods explained at length in the Week 1 Recap.

I sorted through the grab samples collected during Chris and Simon's cruise last summer, as well. I took sediment samples from each core and dried them in Mitchell A55. The next step is to sift them, as I did with the other sediment samples last week. I was fortunate to find two balanophyllia corals that had been overlooked in one of the sample bags. Though one is too small to use for U/Th dating, it is a good candidate for radiocarbon dating.

I met with Karrie in order to discuss the next step with lab work. We calculated that dissolving 1 mg of carbonate from potential candidates for U/Th dating would be sufficient for each of the prescreening measurements (on the EM1 ICP-OES to measure Ca, Sr, Ba, Mg, Mn, & Al, and on the Nu Attom ICP-MS to measure U concentration). Karrie scheduled me instrument time on the EM1 ICP-OES on August 4.

On Thursday, I spent the day near Watsonville with Rosemary Knight and members of the Environmental Geophysics group observing a cone penetrometer test at a site I investigated in GP 190 (Near-surface Geophysics) during spring quarter.