Earth Science Outside
EARTH’S MATERIALS ARE HISTORIANS… Sediments tell the history the present. Bedrock tells the history of the past.
Session 3 – April 9, 2018 – UofU Osher – Earth Science Outside. DRAFT for some details but logistics are solid.
Meet at the parking lot for the bicycle path.
Address: 2700 So. Wasatch Blvd. SLC 84108. Also known as a Grandeur Peak Trail Head.
NOTE: Thinking ahead of where you want to be may help you arrive there! (a) south side of Parley’s Canyon, (b) east side of I-215, and (c) the end of the road (Wasatch Boulevard).
BRING: your handout from Session 1 (Commander’s House) of the Geologic History of Salt Lake County shown as nine cross-sections.
NOTE: For Part 1, we’ll sit at a picnic table and extra lawn chairs will be provided.
NOTE: For Part 2, We’ll walk down the bicycle path about 200 feet (?) (please, someone with an altimeter, measure it). SAFETY FIRST. Some bicyclists careen by. Stay on the mountain side of the path.
NOTE: For Part 3, We’ll set up lawn chairs. If you have a favorite, light, lawn chair it’s fine to bring it. The mapping exercise takes about a half hour. Participants will use colored pencils (provided) and handout and be citizen scientists, mapping the bedrock units (based on patterns) and putting the units in order using the “rules” of younger than / older than.
NOTE: Safety first. ALL outdoor exercises have inherent safety concerns. Be prepared with sensible shoes, walking stick if desired, clothing appropriate for weather, etc. The path is relatively steep. We’ll take our time. SAFETY is a group endeavor. Speak up for safety! There’s never been an issue at this site, let’s keep it that way.
Map showing location of parking lot where we meet (2700 So Wasatch Boulevard).
Exit 33rd south, cross east toward Eastwood Elementary School. Turn north on Wasatch Boulevard and drive to the end of the street.
Alternate Site if bad weather
No alternate site will be posted until we know for sure bad weather. Weather looks great! But check back the Saturday before class.
Anticipated Schedule and Activities:
1:30 PM — Welcome and Practice Step One of Landscape Literacy… Breathe! and Be mindful of patterns.
ParleysNorth-PAlderman-2018-Patterns of Earth Materials.
Repeat to remember, Remember to repeat: Five steps toward the JOY of landscape literacy. Today we focus on Steps One and Two.
- Step one (Session 1): look around. Be mindful of patterns. Breathe deeply.
- Step two (Session 2… try your skills today, breaks in slope?): Look deliberately at patterns of shapes of landforms. PATTERNS… Deliberate awareness of landform shapes and consequences.
- Step three (Sessions one and two AND 3, today!): Look deliberately at patterns of materials, specifically sediment versus bedrock.
- Step four (Session 3, today!): Focus on patterns in bedrock. Be mindful of layering and patterns such as tilting or folding. Be mindful of crosscutting relationships, what cuts what, for example, does a stream channel cut the bedrock?
- Think about what you see (Session 3, today).
Practice looking locally (within a 1000 ft), and then mid-field (a couple miles away), and then far field (several miles away). What do we notice about repeated patterns, or patterns that don’t repeat.
1:45 PM — Earth materials – We’ll meet right at the bicycle parking area, table, north end.
2 PM — Walk a ways down the bicycle path. Observe patterns within patterns.
2:30 PM — Review the rules of younger than / older than (Superposition, Cross-cutting relationships, Original horizontality vs tilted.)
Participants as Earth scientists. “Map” the rock units of the vista ahead of you. And put them in order.
NOTE: Colored pencils and handout provided. Enjoy being a citizen scientist.
By the end of Session 2:
Participants should take their time and relish Step 1 of Landscape Literacy: PATTERNS. Mindful moments.
Participants should be able to practice Step 2: Deliberate awareness of PATTERNS of shapes of landforms and interconnections to the five subsystems of Earth systems (geosphere, hydrospere, atmosphere, biosphere, and anthrosphere). Participants should recognize some of the patterns from Faultline Park… and some not. Participants should appreciate the importance of tectonics to Utah’s landscapes. Tectonic forces largely set the stage for regions by changing what is high and what is low. Then agents of erosion / deposition modify the scene.
Participants should be able to recognize (pretty obvious) patterns of layered bedrock, specifically, layering and tilting of units.
Participants should be pretty confident that they know the rules for “relative age” meaning younger than / older than.
Review terms and concepts:
What are landforms?
What are physiographic provinces?
What is bedrock versus sediment?
Erosion, transport, and deposition.
What is meant by an “environment of deposition.”
What evidence do you see?
What evidence do you witness of the most recent “superposition” of sediments? What do they lie across?
What evidence do you witness of cross-cutting relationships? What rock units (bedrock units) are cut by the Wasatch fault zone?
Embrace the JOY of landscape literacy. The five steps to landscape literacy:
- Step one: look around. Be mindful of patterns. Breathe deeply.
- Step two: Look deliberately at shapes of landforms.
- Step three: Look deliberately at patterns of sediment versus bedrock.
- Step four: Focus on patterns in bedrock. Is there evidence of layering? What about crosscutting relationships or folding, or tilting of layers?
- Think about what you see.
Repeat to remember: Tectonics Rules!!
Repeat to remember. Remember to repeat.
What looks familiar, like these blocks of last time?
Content: Earth’s materials… there are two types of materials. Bedrock and sediment.
All sediments came from bedrock. There are three types of bedrock: sedimentary bedrock, metamorphic bedrock, and igneous bedrock. When a geologist hands you a rock, they hand you a piece of sediment that once was bedrock. When a geologist asks a buddy, “what kind of rock is this?” it is shorthand for: what kind of sediment did this rock come from.
Content: Sediments tell the story of the present. They tell what processes left them where they are: wind? water? glacial ice? ground failure? or, now humans.
Imagine: what do the rock materials in a stream look like?
What about a dune? How did it get there? What is it made of? How big are its individual pieces of sediments?
When you find a dune, what does it tell you about Earth processes. Earth’s climate near the dune?
Here is an image from NASA’s picture of the day — what environments are there? and what sediments are being deposited?
Content: Sediments document “environments of deposition.”
Sediments become sedimentary bedrock.
Sand becomes sandstone.
The muds of coastal floodplains become shale.
Stream deposits become conglomerates.
Content: Sedimentary bedrock tells the story of the past.
Step 3 of landscape literacy is to appreciate patterns of bedrock and their layering. And then to think about it. Here at Parleys Canyon we see abundant red shales, and some have wave ripple marks. We find fossilized sand dunes. We find evidence of stream beds of the past. We can leap to the conclusion that Utah, back then, looked like the northern Sahara along the Mediterranean Sea does today!
Content — some terms
Environments of deposition.
Examine the patterns of rock units.
Apply the rules of superposition, cross-cutting relationships, and tilting of rock units to figure out which units are the oldest and the youngest.
These rock units have been mapped by geologists as well as by you.
Here is their interpretation.
This map shows the rock units at Earth’s surface.
The following cross-section shows a slice looking sideways, of the rock units of the map, much as we saw at Parleys Canyon.
What evidence was there that the sediments in Salt Lake Valley, and in the canyons today are the youngest, even younger than the youngest bedrock?
What evidence was there that the rock unit colored purple on your map and called J-tc was younger than the unit called J-n. (Note: M.D. Crittenden used diverse shades of green because that’s how geologists color rocks of this age).
What evidence was there that the tilting of the rock units happened long before the Wasatch Range was exposed?
By the end of Session 3:
Participants should not yet be confident in their skills to read patterns of rock units or how to put the rock units in order. However, participants should recognize how geologists figure out series of rock units such as at the mouth of Parley’s Canyon.
Participants should take joy in recognizing that landforms (the natural features on Earth’s surface) are younger than the bedrock that makes them.
Participants should realize that Utah’s Chapter 9 – Now stretch to the west is the chapter of the present tectonics that has resulted in the basins and ranges of the Basin and Range province and, specifically our bold beautiful Wasatch Front.
Participants should realize that Utah in the past did not look like Utah today. Sediments of today record the environments of today. Sedimentary bedrock once was sediments of the past and records the environments back then. The mudstones of Parleys Canyon today were mud on shores of a sea perhaps similar to today’s Mediterranean Sea. The sandstones of Parleys Canyon today were sand of sanddunes as impressive as those of the Sahara Desert today.
To figure out the history of how Parleys Canyon came to be… don’t forget Tectonics Rules!
Geologic History of what is now the mouth of Parleys Canyon.
Consider this DRAFT as I blasted it out this evening (April 8, 2018).
Chapter 1: Metamorphic basement. Rocks from this chapter underlie the region, but neither the rocks nor the landforms that we see at Parleys Canyon were present during Utah’s Chapter 1.
Chapter 2: Metamorphism Lite. This chapter affected the region that would become Parleys Canyon, but neither the rocks nor the landforms of Parleys Canyon were present during Utah’s Chapter 2.
Chapter 3: Seas come in and seas go out. This chapter laid down rocks that record a marine (ocean) environment, near sea level, and near the equator. That’s where what-would-become Utah was at the time of trilobites. Neither the rocks nor the landforms that we see today at Parleys Canyon were present then.
Chapter 4: Broad basins. This chapter laid down uneven thicknesses of rocks that record broad basins perhaps like today’s Gulf of Mexico’s thick sections of sediments. Neither the rocks nor the landforms we see today at Parleys Canyon were present then.
Chapter 5: Deserts and Dinosaurs. This is the chapter of the rocks that we mapped in Parleys Canyon. It was a time when what-would-become-Utah had environments similar to those of today’s north Africa including those of the shores of the Mediterranean Sea. Environments included mudflats, stream deposits, beach deposits, sand dunes, and sand deposits off shore. This was the time of dinosaurs. These rock units stretch from Wyoming to Arizona. They were deposited here at what-would-become Parleys Canyon and also in what-would-become Utah’s Colorado Plateau. So the rocks of Parleys Canyon existed then, but not the landforms we see today.
Chapter 6: Scrunch from the west and swamps in the east. The tilting of the rock units at today’s Parleys Canyon is evidence that Tectonics Rules! The rocks that we see at Parleys Canyon today were buried miles below Earth’s surface as compressional tectonics resulted in mountains as impressive as the Andes or Himalayas across what is now western Utah. Thus the rocks and their tilting were present during Utah’s Chapter 6, Scrunch and Swamps, but the landforms we see today were not present. The region looked so different.
Chapter 7: Seven up! During this chapter of Utah’s past, the region of western North America rose almost a mile. The terrain may have looked like the Tibetan Plateau looks today. The rocks of Parleys Canyon were present at depth, but the landforms of Parleys Canyon and the mountains we know so well today, were not present yet.
Chapter 8: Impressive Igneous. The evidence of this chapter is not that far from Parleys Canyon, for example at Park City and at Big and Little Cottonwood Canyons where tectonics had melted bedrock that became mineral rich bodies. But these intrusive igneous rocks are not present at Parleys Canyon although ashes and volcanic debris probably buried the terrain and covered the rocks that would eventually be exposed at Parleys Canyon. However, the features we see at Parleys Canon were not present then.
Chapter 9: Now stretching to the west. This is the chapter when erosion finally exposes the rocks of Chapter 5: Deserts and Dinosaurs that form Parleys Canyon. Tectonics Rules! The downdropping of Salt Lake Valley along the Wasatch Fault exposes the Wasatch Front to erosion. Erosion exposes the rocks. Erosion has created the landforms we see today at the mouth of Parleys Canyon. The sediments of the region and even here at Parleys Canyon tell, for example, the contrasts of today’s climate with Parleys stream laying down sands and gravels in the creek bed below where we sat versus the sands and gravels of Lake Bonneville on the hill slopes opposite us and above us. During the recent (30,000-15,000 years ago) Ice Ages, the environment was wetter and colder. Lake Bonneville rose, and eventually was at the mouth of the canyon at the level of I-80, and then even above where we sat. Parleys Creek was carrying abundant sediment eroded from the west end of the Uinta Mountains. When the sediment reached Lake Bonneville, it became a delta right where we sat. We would have been under dirt as well as under water! But when climate changed back to our hot dry climate, the lake dried up and Parleys Creek cut through its own delta and formed the scenery we see today.
And that entire history, or close to it, is recorded in the materials (bedrock and sediment) and landforms we see today.
Next session, Session 4 – Focus on Chapter 9 – Now, stretching to the west.
We will study sediments of Salt Lake Valley including evidence of Lake Bonneville and Great Salt Lake.
Remember to check HERE for links to the latest information on all sessions of the course.
No homework. Just breathe! and be mindful of the Earth science that surrounds you.