From Source to Sink: How Sediment Reflects the Journey from the Mountains to the Sea
This is one component of the Source to Sink Mini Lesson Set
Continental margins are phenomenal places to study the modern sedimentary cycle because sediment in margin regions has been routed from mountains (source) through river systems to the sea (sink); in some cases, sediment has continued across continental shelves and been delivered to the deep sea. The goal of this mini-lesson is to let students explore the characteristics of some key regions in the modern sedimentary cycle to identify and relate the variables that control source-to-sink systems. Which areas are eroding most rapidly and why? Which systems are responsible for the most rapid transfer of sediments from continents to the oceans? How do the characteristics of river systems affect the properties of the sediments they discharge? How can we apply our knowledge of these modern source-to-sink systems to the ancient sedimentary rock record?
After completing this mini-lesson, students will be able to:
- Relate the variables that control sediment supply to the continental margin and apply these variables to compare and contrast source-to-sink systems
- Identify the first-order controls on the variables that control sediment supply
- Predict sediment yield and sediment maturity for a given source-to-sink system
- Relate the characteristics of continental margin sedimentary rocks to the ancient source-to-sink systems that produced them
Context for Use
This exercise may be modified for introductory students, but is probably more appropriate for upper division courses, such as Sedimentology & Stratigraphy, Basin Analysis, Earth History, and others. Students should know the basics of characterizing a river system, including river velocity, discharge, gradient, and channel and floodplain development. Students should understand the difference between active and passive continental margins, and students will need to have some understanding of sedimentary rocks, including the concepts of textural and compositional maturity and the processes that lead to mature sediment.
You will need computers for students with Excel (or similar spreadsheet program), GeoMapApp (free download from www.GeoMapApp.org), and possibly Google Earth (free download; not required for the activity, but may be helpful for students to have in addition to GeoMapApp). For the final two questions in this activity, you will need to provide several sedimentary rocks (and thin sections and microscopes as well, if you have them available) of varying maturity for students to describe and interpret in the context of the source-to-sink systems they have characterized through the preceding questions.
Students could work through most of the activity in one or two 50-60 minute classes, depending on student backgrounds and how much the students are working in groups and reporting out versus working through these questions on their own, as well as how much time the instructor allows for students to "explore" the different river systems in the data table. Allowing some extra time to resolve any technical difficulties with GeoMapApp may add to the time needed. The time needed to complete the final two questions of the activity, best done in a lab setting, will depend on the number of samples for students to describe, the level of detail in the descriptions, and the availability of thin sections. All of these are at the discretion of the instructor.
Description and Teaching Materials
In the first part of this mini-lesson, students will work with data describing several rivers around the world. Students will sort the data in a variety of ways to try to identify potential correlations between variables that describe rivers (e.g., sediment yield and river length). Students will then discuss these potential correlations and work through an activity to relate these variables to first-order factors such as tectonics and lithology.
Students will then compare and contrast the Fly River in Papua New Guinea and the Waiapoa River in New Zealand and make predictions about the maturity (textural and compositional) of sediment discharged by these two systems. These rivers were selected for study by the S2S initiative because they both have large sediment flux which increases the likelihood that signals of processes happening in the source will be detectable in the sediment arriving at the sink; despite this similarity, these systems represent very different types of source-to-sink systems.
In the final part of this mini-lesson, students will link what they have learned about modern source-to-sink systems with the sedimentary rock record. Students will examine hand samples, thin sections, and/or images of a variety of sedimentary rocks to determine which type of source-to-sink system and where within that system those sedimentary lithologies may have been deposited.
Introduction to River Systems (PowerPoint 2007 (.pptx) 1.6MB Oct6 14)
From Source to Sink - Student Version (Microsoft Word 2007 (.docx) 23kB Oct1 14)
From Source to Sink -Notes to Instructor (Microsoft Word 2007 (.docx) 13kB Oct1 14)
Students will demonstrate that they have achieved the learning goals through their group discussions of the potential correlation between variables describing different river systems, written answers to the provided questions, predictions about sediment properties for the Fly and Waiapoa River systems, and their interpretation of sedimentary rock samples in the context of source-to-sink systems. Instructors may also choose to assess student learning outcomes outside of the mini-lesson, perhaps through related exam questions.
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