The skills of a geologist – Visual Core Description of the core surfaces

Investigations towards uncovering the secrets of the Chicxulub cores are not all covered by instruments. With a lot of expertise and experience the researchers directly undertake detailed observations. With eyes wide open and a pencil in their hands they report their findings in different columns on a special sheet. These observations may range from different rock types (lithologies), colors, structures or alterations coming to light. Along all the information the scientists divide the cores into separate units.

For initial color characterization they use a MUNSELL color chart. The pages of this book show fields with different colors with a circular recess inside. By direct comparison one can create a reproducible description of the core color.

The Munsell colorchart allows an exact description of the colors by direct camparison and numerical designation for up to 199 different color standard chips.

The MUNSELLcolorchart allows an exact description of the colours by direct comparison and numerical designation to 199 different colour standard chips.

Several additional categories and properties such as rock type (e.g. granite), shape of grains (rounded or angular?), or pebble size are looked into as well.

The scientists eventually carefully rinse a drop of a fluid on the core and I see rising gas bubbles: this simple test is a proof that the core material contains carbonate! Carbonate reacts with the liquid, diluted hydrochloric acid, and producing carbon dioxide (gas bubbles). (The calcium chloride  is rinsed off with distilled water.)

The scientists compare the real core half with the digital core image as well as the CT scan images that provide detailed insights into density variations. The observations of the visual core description (VCD) are noted on paper (so called VCD sheets), which exhibit the digital linescan of the actual core on the left side to add the notes.

At the VCD station you can also use an exceptional increasing magnifying lense. I can even see beautiful shells of foraminifera!

Even at first sight, all core sections acquired from the crater show a very different appearance from core to core … and every core section is observed and investigated by the researchers with great curiosity. From time to time they leave their working station and have a look at the new cores to come – this keeps the curiosity alive!

Written by Barbara Matyssek

Images: BMatyssel@ECORD_IODP



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