Rocks, rocks and more rocks

Visual Core Description, also known as VCD, involves recording the composition and type of rock that has been cored, as well as the relationships between the types of material in the core. It is an important, exciting, and often frustrating job:

The rate at which core arrives on deck can be quite variable. If we are coring continuously we can get a 3 m core every hour and a half. However, if pipe is tripped to change the bit or case the hole, an entire shift can pass by with only a single core to keep us occupied. Shifts tend to be either very busy, or very quiet.

When the core arrives on deck, all everyone wants to do is to look at what has come up, including me. Nonetheless, the core has to be measured and curated before I’m supposed to look at it. Usually it takes around 30 minutes for the core to make it from the deck to the desk in my “office” (by which I mean a shipping container).

When chips of rock break loose from the core catcher, I have a very small sample to look at under the microscope. Otherwise the entire core is wrapped in 5 mm of (not very) see-through acrylic plastic. It is our job (mine and, on the night shift, Michael’s) to do a preliminary description so we know what to expect when we split the cores in Bremen in autumn. This isn’t the easiest of tasks as we cannot physically touch the cores and the core liner is often fogged up or masked by drilling mud!

Once I’ve completed my description, the core moves on to the petrophysicists and then into a refrigerator for storage until it gets opened up for re-description by the entire science party in 5 months’ time. In the mean time, the VCD made onboard is an important guide to help the rest of the science party make sample requests from the core. We have already made many interesting and exciting observations; we only have to wait 5 months to test any of them!

Auriol Rae – Petrologist

Featured Image: ELeBer@ECORD_IODP