Uses of the desktop deltaThe desktop delta is effective at demonstrating the major controls on sedimentary basin stratal architecture and the major concepts of sequence stratigraphy. Sediment and water supply can be precisely controlled, as well as base level. Subsidence can be simulated by a change in relative base level. Different channel margin geometries can be simulated by changing the shape of the foam core insert on the bottom of the tank. Most importantly, students can predict, observe, and explore how changes in these fundamental parameters impact stratal stacking patterns.
An example exercise using the desktop delta model
Desktop Delta exercise: student handout (Microsoft Word 789kB Jun17 08)
Desktop Delta exercise: key (Acrobat (PDF) 2.3MB Jun17 08)
The key includes:
- An example of a target deposit created in the desktop delta suitable for immediate use.
- Images of the target deposit that students can use for sketching their interpretation(s).
- A key to the steps that were used to create the deposit.
- A sequence stratigraphic interpretation of the deposit.
- Examples of deposits created by students in an effort to replicate the target deposit.
By the end of this exercise, students should be able to:
- Predict how changes in base level, sediment supply, and/or water supply effect sedimentary basin architecture in a fluvio-deltaic basin margin setting.
- Delineate sequence boundaries, marine flooding surfaces, and highstand, transgressive, and lowstand systems tracts on a cross sectional image of an experimental basin margin deposit.
- Infer from an experimental deposit what the real-world signature of these sequence stratigraphic entities will be, at an introductory level.
Exercise context:This exercise serves as an excellent stand-alone experiment and activity in a number of course contexts, including:
- A course section on sequence stratigraphy or basin-wide controls on sedimentary basin architecture.
- A portion of a course on deltaic sedimentation; the DD creates a spectacular Gilbert-type delta and, with wind modification (see the plans for how to use a blow-dryer effectively), can create a storm-dominated shelf!
- As an introduction to marginal marine depositional systems.
In my course, specifically, this exercise is part of a larger project (basin-scale stratigraphy using the Experimental Earthscape Facility - "Jurassic Tank") where students are learning about the broad controls on sedimentary basin architecture and sequence stratigraphy. This project relies heavily on experimental data from the Experimental Earthscape Facility ("Jurassic Tank") at the St. Anthony Falls Lab, so students need to have a very solid grasp of how the data were produced. In many respects, the delta desktop is a small-scale, two-dimensional version of Jurassic Tank, so it accomplishes this goal perfectly. However, it does not have to be used in concert with Jurassic Tank data.
This project and exercise come late in my course, probably 2/3 of the way through. Students will have exposure to some sedimentation mechanics, depositional systems, sedimentary petrography, and other basic information. However, I do not lecture on sequence stratigraphy or the controls on basin architecture before this exercise. Instead, I explain to them how the desktop delta works and I ask them, in a discussion, how this experiment might simulate real-world processes. In effect, I get them to figure out the controls on stratal architecture by
- using a group discussion centered on the desktop delta;
- having them play with the desktop delta; and
- having them attempt to replicate a deposit that I made in advance (and imaged for their use). In effect, this exercise serves as the introduction to, the FIRST experience in, basin-scale controls on stratal architecture and I want them to discover these controls on their own and in small groups.
- I set up the desktop delta a day or so in advance and I run it, varying only one parameter. I then take digital images of the deposit. These images become the 'target' images for the students.
- In class, I walk the class through how the desktop delta works and lead a brief (15 minute) discussion on how it applies to the broad controls on sedimentary basin architecture. I then split them into two groups (it is a small class). One of these groups gets the opportunity to 'play' with the desktop delta to get a feel for how it works. The other groups is assigned a different task; in my course sequence they are finishing up a peer edit of a prior project write-up, but you could have work on a reading assignment or similar, depending on where this exercise comes in your course.
- I then hand out the assignment to the class.
- They see the target deposit that I want them to create.
- Alone, they make a prediction as to how the deposit was made
- In pairs, they revise this prediction.
- In groups of 4 to 6 they agree on an experimental plan and they try to replicate the target deposit.
- After completing their experimental plan, they photograph their attempt then, alone, they describe what they did and why their attempt worked or did not work.
- In subsequent group discussions and mini-lectures, I walk them through the 'answer', telling them what I actually did to create the deposit and gradually introducing sequence stratigraphic terminology to the discussion, so that they can link this terminology to the deposit(s) we made.
Construction plans for the desktop delta modelDesktop Delta construction guide (Acrobat (PDF) 879kB Jun27 08)
The desktop delta was designed to be made from easily-available materials and with fairly limited machine-shop skills. Perhaps the two hardest things to find are 2-inch-wide aluminum channels and crushed anthracite coal. Sources for these are listed in the plans. Most everything else can be purchased at a good hardware store or through a good supply catalog (such as McMaster-Carr) or a local metal supply company. If you have access to a drill press and a table saw, you have most of what you need.
Other examples of using the Desktop Delta in teaching sedimentary geology
Glumac and Shafer Poster (Acrobat (PDF) 7.9MB Jun10 11)
Glumac and Shafer Video (Quicktime Video 12.4MB Jun16 11)
Bosiljka Glumac and Catherine Shafer have provided this example poster that illustrates how the desktop delta can be used to illustrate the 'slug model' of sequence stratigraphy. The related video is an excellent example of the Desktop Delta in action. It is a fast-action trip through one base level fall and rise, followed by a concluding fall. For a higher resolution version of the video, click here (Quicktime Video 92.6MB Jun16 11).