Red rock and concretion models from Earth to Mars: Teaching diagenesis

Marjorie Chan
University of Utah
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This activity teaches students concepts of terrestrial diagenesis (cementation, fluid flow, porosity and permeability, concretions) and encourages them to apply those concepts to new or unknown settings, including extraterrestrial examples (e.g., Mars, which is often a big "wow" factor).

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This can be used for a variety of students of different levels from introductory to more advanced students- integrating the appropriate level of supporting activities (e.g., simple measurements of concretion sizes and shapes to more advanced activities of outside journal article reading to actual concretions analyses geochemical modeling, or petrography).

Skills and concepts that students must have mastered

Students typically understand what sandstones are, how fluids move through sandstones (porosity and permeability), and the concepts of cementation.

How the activity is situated in the course

The activity can be based on images and samples provided by the teacher, or images students can find on the internet. This seems to work best as a topic aligned with diagenesis, or as a "hot topic" at the end of a course where students attempt to apply what they have learned to a new, planetary setting.


Content/concepts goals for this activity

To understand an aspect of diagenesis (spatially and at different scales).

Higher order thinking skills goals for this activity

To learn to make careful observations and link products with the process that formed the products.

Other skills goals for this activity

Description of the activity/assignment

Terrestrial diagenesis of the Jurassic Navajo Sandstone in Utah explains both sandstone color and iron oxide concretions in "redrock" country. Students look at pictures and can physically examine concretion examples in the laboratory. Important concepts include: porosity and permeability, mobility of iron (through chemical reduction), and sandstone cementation. Complications include nucleation phenomenon (no obvious nucleus in the iron oxide concretions), self organization (relationship of size and spacing of concretions), chemical constituents, and potential multiple events over time in an open system.

The activity utilizes new NASA Mars Exploration Rover data from the Opportunity Rover's pictures of the Burns formation, Meridinani Planum (see Mars Exploration Rover Mission (more info) ). Students can compare different characteristics of terrestrial concretions based on visual images plus perform some limited analyses.
Examples include:
  • Similarities and Differences in Characteristics:
  • Outcrop scale distributions
  • Weathering and Accumulations
  • In situ distribution
  • Sizes, Shapes (sphericity, joined forms)
  • Degree of cementation
  • Mineralogical composition

Questions the students ponder include:
  1. Are the processes for the formation of Mars "blueberries" similar, despite physical and chemical differences?
  2. What controls the formation of concretions (terrestrial or extraterrestrial)?
  3. What are the implications for the presence of water and the movement of fluids?
  4. What inferences can be made about the host rock properties based on the textural, shapes or other characteristics of the concretions?

Determining whether students have met the goals

The reasoning presented by the students allows evaluation of if/how they have met the goals.
Students become exposed to the NASA web site (sometimes for the very first time) and are excited about applying their geologic knowledge to a different setting. They gain an appreciation for planetary geology that often isn't covered in geology curriculum.
Students gain the important perspective on the value of geologic analogs to understanding unknown settings. They see the need for interdisciplinary interactions to arrive at the best science. They realize the many applications of sedimentary geology.

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