How do you measure a core?

Measurements on cores take many different guises and require many different experts. Here are just some of the standard things we look at:

We (Erwan, Abah, Giorgios, Mohammad, Mai Linh, Malka Leah, Emilio, Marco, Johanna, Leah, Natalia, Vera, Malgorzata, Nataliya, Laurence and Liane) look at the physical properties of a core (see also Leah’s blog entry):

  • How magnetic the core is. This tells us not only how much magnetic material the core contains, but by then de-magnetising it, we can get back to the original polarity of the Earth when the sediment was deposited. This gives us a rough timeline that can be applied to the cores.
  • How porous the core is.
  • What is the strength of the sediments (i.e. how much force can the sediments take before they fail and deform). We measure this using a torvane and a fall cone.
  • The gamma density of the core (i.e. how tightly packed or dense is the core material).
  • The colour reflectance of the cores. By looking at where on the scale each measurement sits with regards to yellow to blue, green to red, and black to white, we can work out what colour reflectance clay has as opposed to sand, giving us an automated way to look at lithology (see also below).
  • The thermal conductivity of the core material (i.e. how quickly can the core transfer heat, telling us something about how densely packed or “consolidated” the sediment is).
  • Do all the physical properties help plot the actual cores against the seismic data through a process called Core-Seismic Integration.
IODP OSP EXP 381
Line Scanning. Photo: VDiekamp, ECORD/IODP

We (Mary, Rob, Richard, Casey, Jack, Sofia, Romain, Liliana, Spyros, Shunli and Gino) look at the lithology, that is the physical characteristic of the material in the core:

  • Is it silt, sand, mud or clay or a mixture of all of those?
  • Is it all the same or are there layers of different types of different types of sediment?
  • Are the boundaries between different types of sediments sharp or gradual?
  • Is it all the same colour or different colours?
  • Has it been deformed or broken, either by faulting or by the actual drilling process?
  • What different minerals make up the sediment and so where might they have come from?

We (Clint, Carol, Joana, Simone, Luzie, Silvana, Brit and Christoph) also measure the geochemistry of the pore water – the water trapped between each particle of sand, silt or clay, and its neighbor:

  • Offshore we measure salinity, the pH, alkalinity and Ammonium.
  • Onshore we measure for a range of different elements including Calcium, Strontium, Chlorine, Potassium, Magnesium, Phosphate, Sulphate and Ammonium.
  • We also look at how much organic content is in the sediments.

We (Maria, Aleksandra, Marcie, Asli, Paula, Kostas and Katarina) look for evidence of past life by searching for microfossils – tiny fossils that are 1 millimeter or less in size, under microscopes. The type of microfossil can tell us whether it was land or water at that time, or if it was salty, brackish or freshwater. Certain species also prefer certain water temperatures, again giving us a clue as to what the environment was like in the past:

  • Diatoms – a type of microalgae
  • Foraminifera – single celled organisms with a shell or “test”
  • Nannofossils – a planktonic (floating) organism
  • We also look for pollens as different tree species can tell us about the climate at the time.
IODP OSP EXP 381
Paleontologist Kostas. Photo: VDiekamp, ECORD/IODP

And we can’t forget Lara and Alex – two more student helpers who keep the measuring machine going through copious supplies of coffee and cookies!

As you can see there are a lot of people involved in measuring the cores, but all of these different measurements, when combined, help tell the researchers the story of fault movement, changes in climate, whether the area was terrestrial, a lake, or fully marine, how much sediment was deposited (telling us something about erosion on land), and many other aspects. These measurements give us a fascinating insight into the past.

How do you…? Whilst the OSP is running we will post a series of blog entries, focussing on the different steps involved in processing and sampling the cores to IODP standards.

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