To be able to study the stratigraphic sequences caught in our coring tubes, plastic liners first need to be opened. We use a specialised core splitter with two circular saws in order to make parallel, lengthwise incisions, which can be cut through easily with a knife. Once the liner has been divided into two halves, the inside sediment still has to be separated. Because surface deposits from the bottom of Lake Hamana appeared to be extremely runny and water saturated, we prefer to use metal plates for splitting. Two of these plates are being pushed through the lengthwise incisions and through the sediment until hitting the underlying table top, after which they can be pulled apart. One after the other, the metal plates are slid off the core halves, providing us with clean sediment surfaces.
Some additional, manual retouches might be necessary for acquiring good images with the linescan photography setup, which is part of the Ghent University GEOTEK Multi-Sensor Core Logger (MSCL) (http://www.geotek.co.uk/products/mscl-s-). The MSCL is a tool for non-destructive, downcore analyses of several geophysical properties of the sediment, such as density, magnetic susceptibility and colour spectrophotometry. Density values signify how tightly the matter is packed together and are a good indicator for porosity and lithology variations. Magnetic susceptibility (MS) is the degree in which a material magnetises in response to an applied magnetic field. Positive measurements suggest that the analysed sediment might be paramagnetic, ferromagnetic, ferromagnetic or antiferromagnetic. MS data can thus be extremely useful when looking for changes in sedimentary provenance and/or diagenetic processes. Colour records from the spectrophotometer provide true colour representations of split core surfaces before oxidation processes can take place. Therefore, it is of major importance that MSCL logging is done immediately after core opening. Moreover, sediment colour reflects compositional elements and mineralogy as well, complementing density and MS data.
Each of these properties are measured stepwise with contact point-sensors attached to the MSCL. Logging results in full downcore profiles of the above properties and can be used for further study. For instance, stratigraphic sequences will be described macroscopically, paying special attention to sediment colour, texture, structure, grain size, contacts etc. These macroscopic observations can then be correlated with the geophysical properties, hopefully enabling us to recognise some event deposits.
The below (highly speed up) timelapse video shows how split sediment cores move through the linescan setup of the GEOTEK MSCL. Meanwhile, several geophysical properties are measured and acquired data are shown on the computer screen.