Paleowave

iMonsoon: Life of a Sedimentologist

The main job of the JOIDES Resolution (or JR for short) is to drill beneath the seafloor and to collect intact sediment cores. Once it gets started, the JR does a really, really efficient job of retrieving core. Every fifteen minutes or so (depending on the water depth at a location, the type of drill bit used, and the characteristics of the material being drilled), one can hear ‘Core on Deck!’ This chant is frequent enough to develop a Pavlov-like reflex.

‘Core flow’ is a JR term to describe the journey of a piece of mud from its inception at the drill rig to its resting place in a U-tube in the basement refrigerator. The scientists at the foremost part of the core flow are those in charge of measuring physical properties on the whole-round core (imagine a clear, plastic cylinder filled with sediments and rocks).

Next, the technicians onboard (who brought out the core from the drill rig via the ‘catwalk’ in the first place) proceed to split the whole-round core into two halves: the working half and the archive half. Many scientists now descend upon the working half, carefully sampling the mud for various chemical and physical measurements. It’s quite a spectacle – especially when we’ve hit a transition or a well-known boundary! What about the archive half? Well, this is where the sedimentologists come into the picture.

The main job of the sedimentologists (8 of us in total on this expedition, with one soon to join) is to describe, characterize, and make detailed reports about the contents of the mud. We are also responsible for walking the archive halves through the SHIL and SHMSL: two fancy imaging instruments that can take high-resolution photographs, and make color-based and magnetic susceptibility measurements which become important for the stratigraphic correlators onboard.

Once these scans are finished, the fun begins. Using tried and tested, yet basic, tools (see picture) we try and characterize the makeup of the mud. We document the colors using Munsell charts, note the texture of the sediments using the spatula, and then try and see interesting features using our hand-lens. It is also our job to document how the drilling process might have disturbed the recovered cores. Another vital aspect of the description process is making smear slides, where a small amount of sediment is taken on a glass slide for observation under a powerful microscope. This can be really handy for distinguishing the amounts of clay, silt, sand, and even identifying minerals or volcanic ash!

After the first five cores or so, all of us sedimentologists (4 in the day shift) became cogs of a bigger, well-oiled machine. Mind you, there were ~50 cores in the first hole, each composed of 4-7 1.5 m sections (!) – so we see a LOT of core, and during most parts, it can be run-of-the-mill. However, when something exciting does pop up (which can happen quite frequently at times), we usually all gather around the description table, huddle together, take notes and photographs, and have lively conversations and debates, and ultimately marvel at how we can catch glimpses of a world that was millions of years younger…