Investigating Rock Layers and Fossils to Infer Past Depositional Environments at Lilydale Park
Summary
This activity is an inquiry based field investigation of the sedimentary geology of Lilydale Regional Park's brickyards area, a bluff and slope location near St. Paul Minnesota's Harriet Island and Cherokee Heights Park. Students document their observations of rock outcrops and fossils, develop investigable questions, and infer past depositional environment changes at the site. Students relate relative sediment size and fossil content of rock layers to present-day marine and shoreline environments. By applying the guiding principal of "the present is the key to the past," students reconstruct a sequence of general changes in Lilydale's depositional environment and climate over geologic time. Students summarize and present their findings and engage in discussion with peers.
Collapse
Learning Goals
Goals
Students will apply geologic principals such as superposition and uniformitarianism to infer past geologic events at the site.
Concepts
The characteristics of sedimentary rock layers provide evidence of their depositional history.
Younger sedimentary layers are deposited on top of older layers.
Fossils provide insights into past climates and environments.
Vocabulary
superposition, transgression, regression
Students will apply geologic principals such as superposition and uniformitarianism to infer past geologic events at the site.
Concepts
The characteristics of sedimentary rock layers provide evidence of their depositional history.
Younger sedimentary layers are deposited on top of older layers.
Fossils provide insights into past climates and environments.
Vocabulary
superposition, transgression, regression
Context for Use
The field exercise at this site is appropriate for a group of no more than 20 students in grade 9-12. Space constraints, steeply sloping slippery land, deadly tunnels, and heavy vegetation make this site inappropriate for larger groups. Allow at least two or three hours to visit the site and make observations; 15-30 minutes will be necessary to walk between outcrops and the parking area.
Some previous knowledge of sedimentary geology may be useful to students before they conduct the field investigation. Knowledge of how sediment size and deposition relate to the speed of moving water near coastal environments is helpful. Prior to visiting the site students should also have experience recording rock observations in a science notebook and distinguishing observations from interpretations. This activity works best as part of a geologic history unit though it could also be part of a rock cycle unit. The activity may also be adapted to other sites where outcrops of different ages and rock types are exposed
Some previous knowledge of sedimentary geology may be useful to students before they conduct the field investigation. Knowledge of how sediment size and deposition relate to the speed of moving water near coastal environments is helpful. Prior to visiting the site students should also have experience recording rock observations in a science notebook and distinguishing observations from interpretations. This activity works best as part of a geologic history unit though it could also be part of a rock cycle unit. The activity may also be adapted to other sites where outcrops of different ages and rock types are exposed
Description and Teaching Materials
Introduce the activity by walking the students along the trail from the bluff's base to near its top. Explain that as they walk up the trail they will be viewing rock layers in order from oldest to youngest by the law of superposition. Pause at the St. Peter Sandstone at the base of the cliff. Provide the students with 10 minutes to examine the outcrop individually and record observations of the rock. Hand lenses, rulers, shovels, and collection bags make more detailed observations possible. Split the students into groups of three to discuss their observations and share them with the large groups. Repeat the same procedure at outcrops or debris of Glenwood Shale, Platteville Limestone, and Decorah Shale. Once all sites have been examined, compare and contrast the observations made at each site as part of a full group discussion.
Once the observations have been discussed, ask the students what they think led to the changes in the rock layers that they observed. Ask what questions they have about how each layer formed. Introduce the idea that "the present is the key to the past," meaning that they can interpret past depositional environments by relating the outcrop observations to today's depositional environments. For example sand size sediments may be from a high energy near shore environment while smaller clay size sediments may be from a lower energy environment far from shore.
Guide the discussion toward investigable questions about the geologic story of the sequence of rocks at the site. Ask questions similar to "Now that we have observed the rock layers, what data could we collect?" or "What could we measure that would help us explain how this area changed?" Then help students generate ideas for possible investigations. For example students could investigate how the sediment size changes as the rock layers from young sandstone to shale. Another possibility is to have the students compare the Decorah Shale fossils and present day sea life. Provide students with additional time for small groups of three to develop protocols, revisit outcrops, and seek answers to the investigable questions. Once the small groups of three have attempted to answer their questions, gather them together to present and discuss their findings with the large group.
Move on to an overview of the general geologic history of the area after the students' presentations have concluded. Show a geologic column of the layers at the park. Ask questions to judge if students can determine whether the water was getting deeper or shallower as each layer of sediment was deposited. Refer to the students' observations and ask which layer could have been near shore and which layers may have been deposited deep underwater. Ask how tropical sea fossils could be found in such abundance this far from the equator. Have students consider how the fossils could be so far above sea level today. This discussion also presents many opportunities to incorporate the vocabulary words noted earlier. Provide closure with a chronological summary of the geologic events from the bottom to the top of the column.
Once the observations have been discussed, ask the students what they think led to the changes in the rock layers that they observed. Ask what questions they have about how each layer formed. Introduce the idea that "the present is the key to the past," meaning that they can interpret past depositional environments by relating the outcrop observations to today's depositional environments. For example sand size sediments may be from a high energy near shore environment while smaller clay size sediments may be from a lower energy environment far from shore.
Guide the discussion toward investigable questions about the geologic story of the sequence of rocks at the site. Ask questions similar to "Now that we have observed the rock layers, what data could we collect?" or "What could we measure that would help us explain how this area changed?" Then help students generate ideas for possible investigations. For example students could investigate how the sediment size changes as the rock layers from young sandstone to shale. Another possibility is to have the students compare the Decorah Shale fossils and present day sea life. Provide students with additional time for small groups of three to develop protocols, revisit outcrops, and seek answers to the investigable questions. Once the small groups of three have attempted to answer their questions, gather them together to present and discuss their findings with the large group.
Move on to an overview of the general geologic history of the area after the students' presentations have concluded. Show a geologic column of the layers at the park. Ask questions to judge if students can determine whether the water was getting deeper or shallower as each layer of sediment was deposited. Refer to the students' observations and ask which layer could have been near shore and which layers may have been deposited deep underwater. Ask how tropical sea fossils could be found in such abundance this far from the equator. Have students consider how the fossils could be so far above sea level today. This discussion also presents many opportunities to incorporate the vocabulary words noted earlier. Provide closure with a chronological summary of the geologic events from the bottom to the top of the column.
Teaching Notes and Tips
This activity is quite different from most classroom lessons in its location, the challenges that it places on students, and the teaching strategies involved. Safety is of high concern. Steep slopes, slippery surfaces, limited sightlines, and drop offs are among the hazards. Scout this area well before bringing students to the site; obtain a fossil permit from St. Paul Parks and Recreation at https://www.stpaul.gov/departments/parks-recreation/permits-rentals and follow the safety guidelines outlined at the website.
Other practical considerations include appropriate clothing and preparations for sun and insects. Boots and long sleeved clothing are best. Insect repellent, sunscreen, and extra drinking water are also recommended.
Explanations of the park's geologic history, maps, geologic columns, diagrams, and other information may be found at the following website:
https://www.stpaul.gov/departments/parks-recreation/permits-rentals
Other practical considerations include appropriate clothing and preparations for sun and insects. Boots and long sleeved clothing are best. Insect repellent, sunscreen, and extra drinking water are also recommended.
Explanations of the park's geologic history, maps, geologic columns, diagrams, and other information may be found at the following website:
https://www.stpaul.gov/departments/parks-recreation/permits-rentals
Assessment
Assessment may take several forms in this activity:
-informal assessments of students conducting field work
-examination of student notebooks
-review of student presentations
-informal assessments of students conducting field work
-examination of student notebooks
-review of student presentations
Standards
9-12 Earth and Space Science III A 7 earth changes over time