Lesson 1: Sedimentary Environments

The lesson will open with the teacher describing changes that the earth has gone through (in this case, that Salt Lake City was once on a beach, then in the middle of a desert, then underwater in a lake). This will intrigue students and prompt them to think about how we could know this.

Then, show images of three different environments. Ask students to write in their handout their observations, focusing on similarities and differences they see, sediment, and how that sediment could have gotten there. Then, hold an open discussion and invite students to share their answers. Through the discussion, we are looking for ideas about how sediment ends up in each place… that is, in the ocean there isn’t much movement, in the mountain stream the water moves quickly, in the desert the wind moves the sand. Likewise, the ocean floor has a lot of mud, mountain streams have larger rocks, and desert dunes are made of sand. After thinking a bit about these concepts, students should be ready to dive into the lesson.

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Explore

First, review a couple topics. Use the diagram from the Powerpoint to explain the relationship between grain size and transport energy. In particular, the big idea here is that the energy of the force carrying sediments is proportional to the grain size carried. Faster/ higher energey water can carry larger grains (like pebbles), while slow/lower energy water can only carry very small grains (like mud). So, different grain sizes will end up in different places/environments.

Next, review sedimentary rocks. Start by discussing the categories of sedimentary rocks. Clastic rocks are composed of rock fragments transported from other places. Chemical rocks are composed of minerals that precipitate in place. This lesson focuses on clastic rocks, as chemical rocks can get pretty complex and we’re discussing clastic grain sizes.

Move onto discussing characteristics of sedimentary rocks, particularly these:

• Grain size: how big are the grains?
  • gravel, sand, mud
• Sorting: are the grains the same size?
  • poorly sorted to very well sorted
• Sedimentary structures: what kind of layers are in the rock?
  • none, flat layers, or rippled layers

This is a simplification, but it works for this lesson. Grain size and sorting can tell you about the energy level of the environment the rock formed in. Sedimentary structures can tell you about forces at work in the environment. And, if there are fossils in the rock, fossils can tell you about the ecosystem of the environment the rock formed in.

Next, discuss the three rock types we will focus on in this lesson: conglomerate, sandstone, and shale. Use the images of the outcrops and the sketchfab links to look at these rocks at different scales (up close and from a distance). The biggest takeaway is that conglomerates form in high energy environments, sandstones form in medium energy environments, and shales form in low energy environments. Make sure the students know that these rock types can form in multiple depositional environments, so we need additional clues to figure that out.

Next, cover the basics of a few different depositional environments. Depositional environments are, in essence, places where sediments accumulate. Some examples are rivers, lakes, and the ocean. Sediments are transported by water, wind, or ice, and the specific environment will produce specific rocks according to the energy level, transport distance, and chemical and biologic processes. When discussing specific environments, make sure to emphasize the energy level and transport distance, as well as additional facts that can help students diagnose the environment. After discussing each environment, ask students if they can think of any places like that environment, or if they’ve been somewhere like this. The environments discussed here will be options for the following activity.

The activity for this lesson is to make observations of three unknown rocks to try to determine in which depositional environment they formed. The handout will guide students through the key observations. Rock A is a sandstone with ripples, Rock B is a conglomerate, and Rock C is a shale. In this exercise, students will note the grain size, sorting, and sedimentary structures. Then, based on these characteristics, the students will determine in which of the previously discussed depositional environments the rock formed. In addition, students will note what kind of fossils they might expect to see from an environment like that. While this is in progress, check in with students/groups to ensure they understand.

When the students have finished the activity, discuss their observations and conclusions as a group, and reveal the depositional environments of each rock.

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Explain

Concepts:

• Grain size is related to energy of the water carrying the particles.
• Different sedimentary rocks form in different environments based on the energy carrying sediments.
• Sedimentary rocks record the environment they form in, and these characteristics can be used to identify what environment a given rock formed in.

Vocabulary: 

• Depositional environment – places where sediments accumulate
• Sediment – fragments that have been weathered from the original rock and transported to another location

• Deposition – the laying down of sediment that was carried by wind, water, or ice

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Eloaborate

There are additional provided slides that cover a few more depositional environments and their characteristics. If you have time or wish to explore more depositional environments, you can add these in. These would also be neat to show the unique rocks that form there!

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Evaluate

Formative Assessment: 

Throughout the lesson, prompt students if they know or have been to any places in the environments like the ones described. As in, when discussing beach environments, ask if anyone can think of a place with an environment like that.

Summative Assessment:

The activity detailed in the handout will serve as an assessment, as the students should be able to use their knowledge to identify sedimentary rocks and depositional environments. The teacher should talk to each student / group during the activity ensure that they understand.