Core Description

Owned by jr_crowder (Unlicensed)
Last updated: Feb 06, 2023 by jr_vadman (Unlicensed)
4 min read

Core Description area on the Core Deck.




 

Overview

A description of each core recovered on the JR is among the primary deliverables of the shipboard science party. Core describers are also responsible for other tasks related to description, including instrument measurements, sampling of core sections, and general core handling. The core description team typically includes 5-10 scientists, and up to 15 have sailed on expedition with ambitious description objectives. Depending on the types of materials expected, specialists in sedimentology, igneous petrology, metamorphic petrology, volcanology and/or structural geology may be included.

Tasks that core describers are fully responsible for, or may be assisting technical staff with:

  • Core description

    • Macroscopic description of section halves, including structural measurements as appropriate

    • Microscopic description of smear slides and thin sections

  • Section half preparation

  • Whole-round and section half imaging

  • Measurement of diffuse color reflectance and magnetic susceptibility

    • Standard core logging

    • Handheld color reflectance measurements

  • SEM and/or EDS measurements

  • Sampling for shipboard analyses

  • XRD interpretations

  • Writing the lithostratigraphy and related sections for the site chapters (Proceedings), site summaries and preliminary report, including a descriptive summary of all observations, preliminary interpretations, and suitable illustrations.

Core description using GEODESC apps

The primary responsibility of the core describer is - core description! Therefore, this overview begins here even though the other tasks outlined below may have to be done before or in parallel to the actual description of each section half, smear slide or thin section.

Core description includes:

  • Macroscopic description of section halves, including structural measurements as appropriate

  • Microscopic description of smear slides and thin sections

You will be using GEODESC applications for these tasks. If you are new to GEODESC, you may want to read this introductory document first:

You have three browser-based GEODESC applications at your disposal (on shore, simply remove the .ship from the link!):

These applications have help buttons at the right top of their user interfaces, which link to the relevant sections in the user guides. You can also access the user guides directly:

These main user guides have embedded links to each other and, in particular, to the GEODESC glossary where general terms and concepts are explained.

The remaining user guides are mainly for the technical support staff:

  • GEODESC Catalog Manager: this is the final GEODESC tool still in development and will be used by subject mater experts to make gradual updates to the catalogs that projects copy at start-up.

  • GEODESC user guide editor: critical information on links and general tips for technical writing.

  • GEODESC IT support: evolving protocols for moving projects and data to the ship and back to shore.

Section half preparation

For soft sediment cores, the surface textural effect of core splitting can be mitigated by scraping the surface using glass slides and paper wipes. This process can be laborious and it should only be applied if the benefits outweigh the effort. In some material, scraping may created artificial effects that counter the purpose of making sedimentary structures more visible. The decision whether to scrape or not is the scientists'. If scraping, be sure to avoid contamination down or up the core section.

For igneous rocks, the question often arises whether to image the archive section half surface wet or dry. Wetting the surface 'ust right' before imaging is laborious.

Whole-round and section half imaging

Whole-round imaging using the section half image logger (SHIL) is typically only done on igneous rocks, although it could could also be done on sedimentary rocks if scientifically justified and time is available. Technicial support personnel typically carries out this type of imaging due to the equipment configuration changes needed.

Section half imaging is done on all sections and the core describers are typically doing it.

The detailed user guides are:

Measurement of diffuse color reflectance and magnetic susceptibility

Standard core logging

The physical properties (PP) specialists are typically analyzing and reporting the data from the magnetic susceptibility point sensor (MSP) and reflectance spectrophotometry and colorimetry (RSC) measured on the section half multisensor logger (SHMSL). However, given the physical locatin of the logger, general workflow, and often small PP team, the core describer are operating the systems.

The detailed user guides are:

Handheld color reflectance measurements

The old Minolta Spectrophotometer from the 90ies never went completely away. It may still be around as a backup if you ask a technician:

SEM and/or EDS measurements

If you have time and purpose, you can enjoy scanning electron microscopy (SEM) and/or energy-dispersive spectroscopy (EDS):

Sampling for shipboard analyses

In a nutshell

You are in charge of selecting certain samples for specific analyses bases on your assessment of the core material and the usefulness of the analyses:

  • 1~5 samples (~5 cm3) per core for carbonate (CARB) analyses

  • 1~5 samples (~5 cm3) per core for XRD analyses

  • 1~5 samples (~5 cm3) per core for ICP-AES analyses

  • etc.

Video Tutorials (Windows Media Player)

Thin Section Report Builder