vickyveritas

vickyveritas, 1 year ago to random

@geomannie @mike_malaska Wow, Bob! Fascinating! Would love to learn more, too!

vickyveritas, 1 year ago to Geology

Snowball Earth

Through many posts we have talked about the Great Unconformity (yes, you must capitalize it) and how it occurs worldwide in different rock sections. Why? Scientists believe that at several times in Earth’s history the planet was buried in a blanket of ice. Oceans were nearly frozen. This is what scientists call Snowball Earth, or sometimes Slushball Earth.

The last occurred sometime before 650 million years ago, during the aptly named Cryogenian period. In 200 million years, uplift and the giant erosive conveyor belts of ice eroded continents down to the roots of the ancient mountains and left the land at sea level. Think the Canadian Shield. This scraped bare land is the base of the Great Unconformity. As the glaciers melted, sea level rose and covered the land and deposition of sedimentary layers began. Variations of this happened worldwide. We can focus on the North American continent which looked much different at that time. Forget anything west of Idaho or so. It wasn’t there yet.

Wyoming Geologist Myron Cook does a much better job than I could of explaining Snowball Earth, the Great Unconformity, and why different gaps, between hundreds of millions to billions of years of time, exist across what was North America at the time in his great video published only 11 days ago. Throw in a master-class in Deep Time, and you have it all put together as only a master story teller can. And there are lots of rocks, yay! Watch this wonderful video. Yes, it’s long, but you’ll absolutely hate yourself if you don’t get to see the Mineral Fork Tillite and how the story ends. Trust me.

https://youtu.be/LXzDfQyUlLg

Follow it up with further findings on Snowball earth using thermochronology by Kalin T. McDannell, et. al. including our own @brenhinkeller as they work to help determine if glaciation or the recent hypotheses of tectonic influence had more impact on denudation of the continent. Spoiler alert: read the title of this post again.

https://www.pnas.org/doi/full/10.1073/pnas.2118682119

Another version here: https://eos.org/articles/erasing-a-billion-years-of-geologic-time-across-the-globe

Pinging @BoxcarMurphy who probably knows all about this already :)

#SnowballEarth #SlushballEarth #Glaciation #Cryogenian #TheGreatUnconformity #NorthAmericanContinent #DeepTime #MyronCook #HowSnowballEarthLeveledTheContinentsAndCreatedTheGreatUnconformity #WatchTheDamnVideo #geology #ScienceMastodon @geology

vickyveritas, 1 year ago to random

If you are an Earth Scientist and new here you are going to want to do 2 things.

1. Go to the Earth Scientist on Mastodon list below and add your information to the form by using the link in the list.
2. Download the list as a .csv file (there’s a link on the page for that) and import it to your mastodon account in your settings. This will let you automatically follow all of the Earth Scientists! It’s easy! You may have to be on the desktop app and logged onto your server instance to do this.
   This list is made possible by @allochthonous
   #EarthScience #Geoscience #NewHere
   https://all-geo.org/mastodon-earthsci/

vickyveritas, 1 year ago to Geology

Mount Laurel "Roof Pendant"

The volcanoes, whose inner-most workings are exposed in the granitic rocks of the Sierra Nevada, transformed the ancient sediment layers into which they were intruded. Erosion later isolated the remnants of the metamorphosed rock, suspending them above the granite as "roof pendants." The folding of these layers is most dramatically illustrated at Convict Lake when the lighting is just right. Click on the photo to below to expand.

"The story of the mountains around you began half a billion years ago when sand and gravel washed off an ancient continent and built up in layers beneath a vast ocean. Changed by extreme heat and pressure, most of these rocks have eroded away, but some remain.

Embedded within them are fossils of organisms that lived in the ancient sea and are some of the oldest rocks in the Sierra Nevada Mountains.”

#geology #RoofPendant #MountLaurel #ConvictLake #MetamorphicMonday #ScienceMastodon

vickyveritas, 1 year ago to Geology

Heart Mountain, Wyoming Revisited

Heart Mountain, a 8,123 feet high peak, is composed of dolomite,limestone and volcanic rocks formed several hundred million years ago, and is lying atop, and surrounded by, younger rocks formed around 55 million years ago. Older rocks atop younger rocks rarely happen, but do occur in geologic features such as igneous intrusions into older rock, recumbent folds, thrust faults, detachment faults, and -spoiler alert- landslides.

But how exactly this mass of older rocks, part of a much larger mass of rocks, managed to overcome gravity and slide 28 miles in under 30 minutes became the controversy of its day. Turns out, Wyoming geologist Myron Cook has the answer due to tons of work by hundreds of geologists, and it is a much larger story than just Heart Mountain. The link below is to his fascinating, but very long video on the Heart Mountain Detachment fault and landslide. I encourage you to watch it, but have recapped it below.

The first image, a Google Earth map below, shows the area of Wyoming near Cody where the landslide occurred. The arrows point to two volcanic systems, even larger than Yellowstone, that lay northwest (map looking to the southeast towards Heart Mountain, small green dot) that existed around 50 million years ago. These stratovolcanoes were 20,000 feet high above the Bighorn basin, and the magma fed up dikes through the hundreds of millions year-old sedimentary rocks.

These volcanoes were explosive and the earthquakes they generated were enough to “rattle things around” and crack open a detachment fault along a bedding plane of the Bighorn Dolomite. Recent research suggests the detachment was caused by collapse of one of the volcanic flanks. Nevertheless, the red outline shows the area of the Heart Mountain detachment/ landslide zone along which about 20 miles by 30 miles of 800 + feet of sedimentary rock topped with (maybe) thousands of feet of volcanic deposits that slid catastrophically, very quickly, and all at once.

The second image shows the detachment fault, a hairline thin contact in the dolomite (carbonate rock) with a very shallow dip of only 2%, just feet above a shale horizon. Once movement was initiated, the mass began to slide. The heat from the friction extracted and superheated CO2 gases buoying the rock. The shallow slope became “frictionless” and in areas there is no deformation of the underlying base.

The slide caused the mass of rock to break into blocks, some have estimated over 100 blocks slid during the slide at a speed well over 100mph. The directions of the sliding bifurcated, (image 3) and some blocks slid towards where Heart Mountain stands now, and some slid more southerly where other blocks now lie.

The last image (4) shows something startling - if you drilled through Heart Mountain down into Bighorn Basin, you would reach Bighorn dolomite again 15,000 feet down, and mirroring the stratigraphy of Heart mountain. This is because between 75 and 50 million years ago, a period of mountain-building called the Laramide Orogeny caused uplift of the area the detachment formed in, and subsidence of the Bighorn basin. The Bighorn basin filled with thousands of feet of newer sedimentary rock including the 55 millon year-old Willwood formation on which Heart Mountain lies.

Learn how Supervolcanoes caused the World’s Largest Landslide in Wyoming by Myron Cook: https://youtu.be/CYS3r3tk2GI

Here is some more technical information for those so inclined: http://faculty.mnsu.edu/stevenlosh/research/block-sliding-heart-mountain-detachment-wyoming/

And more recent info here: https://www.researchgate.net/publication/254617445_Recent_Contributions_to_the_Understanding_of_the_Heart_Mountain_Detachment

Pinging @BoxcarMurphy again. Sorry Boxcar!

#HeartMountainDetachment #HeartMountainLandslide #DetachmentFault #Landslide #BighornBasin #BighornDolomite #WyomingGeology #RecommendWatchingTheVideo #LearnHowSupervolcanoesCausedTheWorldsLargestLandslideInWyoming #MyronCook #Geology #ScienceMastodon @geology

The cliffs of Bighorn dolomite, a tannish layered and hard sedimentary rock, is shown with arrow tips along the razor-thin Heart Mountain detachment fault.
This shows a diagram indicating the direction of travel of the massive blocks of the Heart Mountain landslide. Some slide directly away from the break away fault, and some rotated and slid off at a different angle around the Rattlesnake and Pat O’Hara mountains.
Geologist Myron Cook illustrates the path of sliding of the detachment block along a very shallow dip, and how the block managed to crossover a ridge and into the Bighorn basin miles, and miles away. He also illustrates how the older rocks of Heart Mountain lie above the younger rocks, but at depth below the same older rocks lie.

vickyveritas, 1 year ago to random

"The Mole was bewitched, entranced, fascinated. By the side of the river he trotted as one trots, when very small, by the side of a man who holds one spell-bound by exciting stories; and when tired at last, he sat on the bank, while the river still chattered on to him, a babbling procession of the best stories in the world, sent from the heart of the earth to be told at last to the insatiable sea."
~ The Wind in the Willows by Kenneth Grahame

#TheWindInTheWillows #KennethGrahame #TuolumneMeadows