The official CASEIS Cruise Blog is located here: http://www.ipgp.fr/caseis This official blog is written by my shift-mate Lola Johannes.
We continue to collect sedimentary cores...
- Here is a site map for the cores that we have collected so far. This is similar to maps that I have previously posted. The planned sites are in green, yellow, and red that are ranked by color from high to low priority. The dots in blue show the locations of our actual core sites.
- This is the Multi Sensor Track (MST), also known as the Multi Core Sensing Logger (MSCL) manufactured by GeoTek. In prior posts I show how this device is used to scan real color imagery (RGB) of the split cores. Here the MST is configured to collect four principle geophysical properties of the cores. These properties are the first that are measured after the core is cut up into 1.5 m segments and labeled. From right to left, the properties include: Gamma Density, P-Wave Velocity, Resistivity, and Loop Magnetic Susceptibility. Below is a general description of each of these measurements.
June 6, 2016
- Gamma Density Here, there is a source of gamma radiation, 137Cs located in a canister with yellow stickers. The stickers warn the user of the source of radiation. The gamma rays are emitted away from the operator of the instrument. As they pass through the core, they are absorbed differently by materials with different density. The sensor (out of view on the far side of the track) measures the amount of radiation that makes it through the core. This is, in essence, a way of measuring the density of the material in the core.
- P-Wave Velocity The blue parts of this instrument send seismic P-Waves through the core. The P-Wave velocity will vary depending upon the density, bulk modulus, and shear modulus of the material in the sediment core. The bulk and shear moduli are two measures of elastic properties of materials.
- Resistivity There is a source and sensor on the bottom of the track that measures the conductivity of the materials in the sediment core. These data are integrated over a large portion of the core and are generally of little use for us. The data typically have a long wavelength signal and we are interested in short wavelength signals (like found in mag sus and density data).
- Loop Magnetic Susceptibility As the core is passed through the white plastic device, it passes through a wire that applies a magnetic field through the core. Mag Sus is essentially a measure of how well the sediment can hold a magnetic charge. In other words, how much of the material in the sediment core is composed of magnetic minerals, like magnetite. Because these magnetic minerals tend to be more dense, the mag sus data generally covary (i.e. match) the density data. There are some cases when these data do not covary, like in tephras. Tephras will have high mag sus values, but low density values (in general).