Tuesday, 19 July 2016

40,000 Points

It has been more than one month since the end of the offshore phase of IODP expedition 364. I wanted to wait a bit to review this experience, because writing something just after would have been a mix of “it was so hot”, “I think I had too many cookies/brownies” and “that was intense”. Now I am rested and relaxed, I can look back at these 58 days spent offshore Mexico on the 42-meter-long Liftboat Myrtle. A tiny, yet impressive place where I was part of such a fantastic scientific expedition: to drill the peak ring of the Chicxulub Impact Crater . That was my first offshore experience.

So, yes it was hot, and yes it was intense. But there are more important things to report from this experience. First of all, even if I heard of what a mission specific platform was and what the missions of the IODP  (International Ocean Discovery Program) were, it was impressive. It was impressive to see such a geoscientific operation taking place, just to bring rock samples to the surface, describe and analyse them. Just science.

My main role offshore was to measure physical properties of the cores, using a multi-sensor core logger (MSCL). It was not only me on the MSCL; we worked on 12-hour shifts to ensure a continuous workflow. Analysing cores for 12 hours in a row, 90 minutes for every 3 meters of core material, can be long. But it can also be rewarding: other scientists were really interested in this petrophysical data. We provided instant valuable information like rock density and magnetic susceptibility. Density was probably the most useful while offshore, for scientists to better understand what they described and how it fitted with their model. On the other hand, the magnetic susceptibility data (usually useful for correlations between boreholes and cores) was more of an amazement, to see the range of responses measured from the different materials recovered from the peak ring. I am sure that even if we do not use magnetic susceptibility as a correlation tool here, it will give scientists crucial information about the variation in composition of the rocks formed or affected during the impact.

The MSCL lab
Some feelings now about the measurements:

  • Satisfying: we were lucky enough to have a measurement time that fitted perfectly with the core recovery rate, never too far behind the drilling team;
  • Mildly frustrating: it was a single well and we did not know what lithology will be recovered in the next core, making it difficult to visualise the big picture;
  • Highly satisfying: to look at the MSCL dataset now; measurements every 2 cm across a total length of 830 m of core: more than 40000 measurement points in total;
  • Even more satisfying: to see that downhole logging data I helped to collect (with EPC staff from the University of Montpellier ) match very well with the physical properties measured on the cores. The hole was very nice and we collected good data; the cores were continuous, fairly well preserved and we collected good data. Of course it is not possible to show them now because they are under moratorium.

I think it was good to wait a bit before reviewing this experience; to dim the excitement of the expedition and of coming back home; to forget about some unimportant but inevitable technical problems; to relax. What I will remember from this first expedition is satisfying: good data, good team effort and epic geological setting.


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