The fantastic and massive Z-fold at the Wheeler Canyon trailhead in Ogden Canyon, Utah
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- Опубліковано 21 лип 2024
- While motorists zip by on Utah Highway 39, geology professor Shawn Willsey shares the story of the awesome Z-fold on full display just north of the Wheeler Canyon trailhead. This huge fold was caused by east-west compression about 100 million years ago during the Sevier Orogeny, a mountain building event that affected much of Utah and adjacent states.
GPS location: 41.25315, -111.84356
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Thanks for taking the time to educate us about something I drive by often but completely miss.
So true. This is one of the largest Z-folds I've ever seen. Would be cool if the Forest Service put an informational display here.
Wow... I'm totally in awe of the unbelievable forces at work here that created this Z-fold! Thanks for the diagrams and the explanation, Shawn :)
Thanks!
I'm a geologic formation nut as I'm out driving about this country, so I've seen this one with my own eyes and beheld it's remarkable appearance. I'm glad you made a video about it and explained how it was formed. Thank you.
Thank you for the diagrams!
Yes, I was hoping they would help explain the story.
Great video and grafics. You have an ability to explain the geology and bring the event to live action.
that really is fantastic! I'm always amazed to think of the forces that drive these kinds of formations. So, this limestone Is Mississippian. Formed during the Kaskasia sea, yes? As was the 574 feet of the redwall limestone of the Grand Canyon,? I've read some about the Sevier orogeny, with horizontal displacements of tens of miles and vertical displacements in thousands of feet. all in a short period of ten million years or so! Unbelievable forces at work. Really liked this video.
Yes, the Z-fold is almost entirely in Mississippian formations (mostly limestone): Deseret Limestone, Gardison Limestone, and Humbug Formation. These are correlative to the Redwall Limestone in the Grand Canyon.
We are interested while they are not, Thank you Brother👍🏼❤️
Thanks for the very engaging, information packed video. I am subscribing and can’t wait to see more. I love Geology!
Great news. Glad you enjoy these. Its fun to share Earth's stories with folks.
Amazing. Stuff ive seen and thought about but never actually learned about! Great education! Thank you!
Thank you Shawn have been watching all your videos they are all very informative
Another interesting study so well explained. Thanks heaps Shawn for quenching my thirst
Glad you enjoyed it
Impressive fold. Thanks for sharing, Prof!
The rock's plasticity is a huge part of getting folds like that as opposed to faults. Temperature, pressure, depth, and solubles content help make otherwise crystalline, somewhat brittle rock more like fresh Play-Doh. Kinda nature's material science in action 😀
I have phylite behind the house that has folds on the order of mm size, immediately adjacent to quartzite veins that were likely emplaced later, but then deformed as well. Deformations of deformations!
Totally "AWESOME" Thanks 4 Posting!!!
I love finding fellow UA-camrs in the Wasatch Hikers group. Great explanation of the z fold. Very interesting.
Thanks. The geology of the Wasatch is totally world class. I plan to launch more so be sure to subscribe.
Great job
I thought I'd viewed all your videos Shawn, but apparently I missed this one. I always wondered how those Z formations came about and now I know. Always think of large thrust faults on the edges of the continental plates, yet this is a smaller version that (check me if I'm wrong) occurred during the making of a mountain range.
I've driven through there a few times, but while everyone was sightseeing I was sight-glancing and driving. lol
It amazes me how geologists worked all that out. Who was the first to realize rocks could fold? That had to be quite shocking to some.
One thing I've always wondered when looking at folds like this - and I probably don't know enough to use the right terminology here: are the rocks deforming "plastically"? So, maybe the rocks were being subjected to enough heat to actually soften them so they could bend without fracturing - but not enough so they undergo metamorphism. Or do the rocks remain brittle and simply become fractured enough to allow the bending and folding to take place? Not sure if that makes sense... 😅🤷♂
Great question, Brian. Yes, rocks fold via plastic deformation (also called ductile deformation). In other words, the rock changes its shape due to stress without fracturing or breaking. Rocks will behave differently to stress depending on temperature, pressure, the composition of the rock, and other factors (such as layering). In general, rocks do need to be buried and therefore, heated somewhat to bend like the Z-fold. However, the temperatures did not reach those that begin metamorphism (about 200 C or 400 F). Hope this helps.
@@shawnwillsey Yes, that helps a lot! Thanks for taking the time to answer my question. :)
❤
marked on google earth thanks! So the hanging wall is on the east side of the fault - is it a large back-thrust? i thought the hanging walls would be be on the west side
Yes, the hanging wall of the Willard Thrust is exposed just east of this location......and further west as well out at Antelope Island. Imagine the thrust forming a large dome (rainbow shape). This structure is called the Wasatch Anticlinorium. Hanging walls can be on any side so compass direction is irrelevant. The hanging wall is the side of the fault above the fault, footwall is side below the fault. Hope this helps.
Thanks for the response! I did not realize the Wasatch was an anticlinorium. So are the normal faults reactivated high-angle thrusts? What I was asking did have a directional component to it though (i.e. compass direction - also some context I'm a 17 year petroleum geologist).
I guess what I was surprised by is the granite thrusting up and over from the east. I pictured low angle ramps dipping to the west that got progressively steeper as leading edge propagated along the detachment from west to east. Hope that makes sense. The explanation of the anticlinorium cleared a few things up for me. But I just need to pull up some cross sections through the Wasatch to see what the fault geometry is. Thanks again!
Dude, collaboration with Zetner, make it happen
Is the quartzite from eroded Mississippian era mountains?
No, the quartzite is a Cambrian aged unit called the Tintic Quartzite. So its much older than the Mississippian rocks which were deposited on the seafloor. I feature the quartzite and some other cool stuff on this video: ua-cam.com/video/WlfA0jnUySg/v-deo.html
Is the dam at risk from these folds?
Not really. The folding event occurred about 80-100 million years ago and also caused the rocks to fracture so you could argue that this deformation event weakened the rocks that the dam is abutted against. Overall, I would say the strength and integrity of the rock is probably fine. The bigger risk is if there was a large earthquake, the earthen dam may be compromised and cause flooding down the canyon and into Ogden. Good question.
I think its false to say sea levels were once higher than the mountains and all the water drained and left this. I think its more like this mountain was made up of ancient rock that formed for millions of years below ground and though the mountains seem old themselves, they just appeared in geologic time. What was once a sandy beach 520 millions years ago is partially sticking out of the ground sideways now. I think mountain form in two ways basiclly. Uplift from earthquakes and/or as molten lava composed of ancient rock.
These rocks are limestone; therefore they formed in shallow seas. The sea level was never above this _elevation_ , but the water was over the top of the original formations. Then, the formations were buried long enough to become rock, then they were uplifted and folded, or folded then uplifted-not sure of the sequential order. The technical name for the overthrust rock layers is _horse_ . en.wikipedia.org/wiki/Horse_%28geology%29