It's now been just over a month since I started my dissertation, and I'm loving every bit of it!
As mentioned in my last post, I'm researching OSL dating of marine sediments, specifically Ocean Drilling Program (ODP) Site 658B in the equatorial Atlantic. My first task is to address the issue of erroneously old ages yielded when measuring fine silt grains (4-11μm), attributed to lateral sediment reworking of fine silt at the ocean floor without further exposure to light, and thus these grains possess a residual luminescence signal at the time of deposition. This involves separation of samples in to seven different size fractions (ranging from 0-5μm to 40-60μm) and measuring their equivalent doses (i.e. the radiation dose received since last exposure to light) to determine the finest silt that can be accurately dated, since not all marine sites may have a high supply of coarse silt. I've been working in the dark lab using Stokes settling to isolate the finest grain sizes and sieving to separate the coarse silt. I've found working in the dark pretty straightforward, actually; I've not found it difficult to adapt my eyes to the orange/red light conditions in the lab and can still work as I can in the light. I've just finished my fourth week of working on this experiment, and I have some really great, interesting data back so far! The datasets just need the addition of the coarse fractions measurements (preparation of which is underway), and then I will be able to move on to my next experiment.
Next, I will be looking at light penetration in to the marine core. The issue here is that previously no attempts have been made to shield marine cores from light during their collection and archival. As a result, the outside of the core has been exposed to light (bleached). This means that only the material in the middle of the core that is shielded is useful, potentially leaving you with very little material to work with. I will be attempting to quantify the depth in to the core required to access material that is unbleached, and thus dateable. I will attempt to sample in to the core at mm intervals to achieve this, so my hand-eye coordination will definitely be tested!
Finally, I'll be looking to date Oxygen Isotope Stage 5 (the last interglacial, ~70-125k years ago) material in attempts to accurately extend the range of OSL dating for marine sediment. Climatic peaks and troughs during this time period are very well defined; if OSL ages can match these then its potential as a chronometer in marine sediments is increased.
I've been thoroughly enjoying undertaking this research. I can't believe a month has gone by already. I have a feeling the next two will go by in a flash, and I really, really don't want to finish just yet!! Nonetheless, my initial results are very promising and I think this work will provide some valuable insights to the application of OSL dating on marine sediments.
