How Snowball Earth Leveled Mountains and Created the Great Unconformity

yes this is how the Earth looked the oceans were completely Frozen or nearly so multiple times and for long periods the most recent snowballers started about 850 million years ago and lasted some 200 million years of course this was devastating for life on Earth but did you know that all of this ice destroyed the mountains and mercilessly ground the Continental Rock right down close to sea level this process created the Great unconformity why hello and welcome the great unconformity and snowball Earth I mean what a title that is a dramatic title and for good reason and we will be learning about that before we embark on this journey of seeing the actual rock of the great unconformity and putting our hand on the outcrop and and doing field geology and discovering it together I thought it'd be very important to do just a quick tiny lecture on what an unconformity is let's start with depositing layers of rock through time from the bottom up of course okay just layer upon layer now I like to think these this is like pages of a book this is what's recording the rock history The Rock record the record of the earth and so we have just a continuous in the optimal situation just a continuous record it just continually deposits new layers of rock now at times because of the mountain uplifting or or the Seas receding these layers of rock are no longer being deposited on top of each other bit erosion comes in and he rodes out uh some of the record so I'm going to take a little rag here and here we go I'll just maybe erode it out like this now there's a new a new surface of erosion like this okay and then new layers which I'll I'll put in red and it goes on again okay and then we can have erosion again but each time there is erosion and then deposition on top of it we have an unconformity and that's the beauty of the outcrop behind me it shows very clearly the elements of an unconformity the Red Rocks of the chugwater formation were deposited some 250 million years ago then they were uplifted and tilted about 65 million years ago and erosion occurred forming the unconformity surface finally new deposition occurred as travertine deposits within the last 10 000 years or so this means that there are about 250 million years of the geologic record missing now I want to make it clear this is just one unconformity of many many many in the Rock record and it is not the great unconformity which we will be focusing on in the end the principle of an unconformity is pretty simple as I've shown pages of the book meaning layers of rock have been eroded and we no longer have that history to look at there do we because it's been destroyed through erosion let's go into the beautiful Shoshone Canyon and see the Great unconformity well here we are at the great unconformity and I mean the great unconformity first of all let me point out the actual inconformity it's right up here where you see kind of a cup shaped disc shaped bottom that's the bottom of a river Channel right along here okay I can't quite reach it and underneath it are granites that are 2.7 billion years old so when you take these sedimentary rocks that are 540 million years old and underneath it are granites that's that old the 2.7 that's over 2 billion years of time that's missing right on that contact well one thing that's really cool to do is put your hand on the contact let's walk this in Conformity and follow me let's follow this contact you can follow it pretty easily you can see it we're coming down it's coming down this beautiful pink granite here it comes and right here I can put my hand on that contact so we come right down to where the unconformity comes to where I can touch it we have the granites here the paint granites right here and right here are the sandstones so that contact is right here where my hand is and that's that great period of missing time the great unconformity let me tell you it's pretty exciting for a geologist anyway to put your hand right there and and think about everything that has occurred during this period during this missing time period of 2 billion plus years we know that there were multiple episodes of mountain building and some of the mountains were ginormous like the Himalayas we know that there were periods of glaciation that lasted hundreds of millions of years and created what we call snowball Earth just amazing to think about all this that happened during this gap of time right here our next stop on this journey is the wonderful Wind River Canyon just south of Thermopolis Wyoming I've drawn the blue dash line to show the general dip of the formation layers as they come up the mountain the white dashed line is the trace of a massive fault which I'll be discussing on the Whiteboard well before we head into the great Wind River Canyon I wanted to show you sketch to help you understand what we're going to be seeing on drone video and understand the geology a little better for reference this represents the river that goes through the mountain this is the that cuts through the mountain the town of Thermopolis is back on this side to this to the north and on the south on the other side of the mountain is Shoshone the town of Shoshone so for reference these are the layers of rock of course this is the huge fault that brings up basement clear way up from great depths um I want to say there's 20 some thousand feet of displacement that has lit been lifted up on these rocks and we're going to drive up the river and you're going to see these dipping strata these dipping layers which means we're going to drive into older and older rock as we get further and further up the river into the canyon and finally we will come to the great unconformity which is represented by this red line right here so just a general idea this the dips on here are I've exaggerated a lot on this sketch it's really only somewhere like 15 degrees of dip the the big layers this layer of rock or formation is the Permian age phosphoria as we cut deeper and deeper into the Rock we come to the Pennsylvanian age 10 sleep formation further into the canyon we see the Mississippian Madison formation the ordovician Bighorn Dolomite and Shaley limestones of the Gallatin and gervant formations up around the band we will finally come to the Flathead sandstone and the great unconformity finally we've arrived and I'm looking at the beautiful Flathead Sandstone overlying heavily weathered granite the great unconformity is right here as we continue to cut deeper and deeper into the mountain I want you to pay attention to the unconformity and what is underneath it here we see beautiful pink granites moving along we continue to see granites under the unconformity often the unconformity is difficult to identify because it is not a sharp contact I'm starting to see a change here do you do you see this layer of dark colored Rock here next to the pink granites let's turn the camera 180 degrees and look directly across the river to the other side of the canyon indeed we see dark colored metamorphic rocks that have been intruded by these granites and here we can clearly see the great unconformity with some granites and metamorphics underneath it can you see the layering or layers that are within the dark metamorphic rocks I really like this view because we can see these fingers of granite this light-colored paint Granite intruding into the metamorphic rocks often the layers within these beautiful metamorphic rocks dip steeply turning the camera to look yet deeper into the canyon we see that the canyon walls are dominated by dark colored metamorphic rocks the red dashed line is approximately where the unconformity is note the Steep dips on the beds or layers well now that we've seen this amazing video and made some observations with the Drone and about the metamorphics and the granites and everything I wanted to use the sketch board to help us understand the context and the geology so what I have sketched here is is the world 2.7 billion years ago more or less okay the mountains massive mountain ranges were around in Wyoming granite's head intruded they had eaten their way into the Rock through a process called stoping and other processes where the granite intrudes sometimes it kind of squeezes in other times big chunks of the of the metamorphic rocks uh get worked in and Cave off and spall off and Cave off into the into the hot molten rock now this Granite is about 20 million years younger than the surrounding rocks that we observe today the dark colored metamorphic rocks and here's the amazing thing is to be metamorphosed these rocks and for this Granite to be there this was about easily 15 miles deep buried about in this area some 15 miles underground that Granite cooled so the great unconformity hadn't occurred yet but now the process started the mountains were uplifted and over eons of glaciation and and not all glaciations some rivers and rain during periods started eroding off the mountain so I'm going to take a rag here as a big eraser and uh we're going to use that as erosion and erosion started occurring and going so 2.7 billion years ago what two and a half more or less started eroding down through time of course it was very rugged until it got closer and closer to sea level and then it started flattening the terrain out okay here it is through time through time and this red area is represents the granite as as we'll recall and it started it eroded some 15 miles deep let's just put a line right there okay that is the great unconformity now as you notice uh I have granites over here and metamorphic rocks over here from the ancient mountains that are preserved right but we're not finished so we eroded it all down and some 530 million years ago or so the oceans the warm oceans came back in as the ocean came in the the flat head Sandstone was deposited right on top and then the ocean just kept getting deeper and deeper and depositing more and more layers of rock so here we go layer after layer of rock that we saw as we came into the canyon with the drones some 11 000 feet of rock were deposited and then the new mountains the laramide mountains the mountain that created the canyon that we came up through uh deformed all this yet again to represent the laramide erogeny I'm just going to tip tip my uh board here so now it all got tipped like we observed and then the canyon came through and cut it all out wow what a sequence of events huh so I want to focus in here right here what we observed with the Drone is first we were in the granites down river to the north which is towards Thermopolis on that side of the mountain and then we got into a boundary area didn't we where we where we saw a granite mixed with metamorphics and then as we came further and further up the river it became completely dominated by the metamorphic rocks it turns out in the Wyoming provenance there's this mix of batholiths huge bodies of granite and then terrains of metamorphics for instance the Bighorn mountains about half of it is metamorphic on the southern end of it the Northern end is dominated by granite in the Wind River mountains we have two major plutons of granite but we also have vast areas of metamorphic rocks so is a very complex mix of the of metamorphosed rocks sedimentary rocks and volcanic rocks that had been turned into metamorphic rocks through burial and then the granite's coming in and and intruding and invading shall we say all that I realized I needed to make something a little more clear to us and that is this idea of metamorphic rocks being buried 15 miles deep for the granite's cooling off 15 miles deep and then being eroded down to it how does that work okay this is phase one and that is we have a basin full of sediment this is a cross-sectional view with my little tree here this red area represents a granite intrusion okay into the metamorphic rocks that we've seen and it's way down deep 15 miles under the ground where you get this metamorphism it's not just 15. it can easily be 15 it might be a little less or it could be quite a bit more okay but very deep and that's where this occurs and then uplift starts to bring these up to the surface and that'll be phase two so phase two is you you bring these rocks up high through time they're being squeezed and compressed and bringing them up to be eroded now as mountains are uplift erosion is occurring and they reach an equilibrium so you can only get mountains about so tall I mean Mount Everest is just shy of 30 000 feet if I remember right so you have a maximum and the erosion keeps up and you keep bringing that those deep deep sediments that we had on the prior sketch uh get up above sea level okay eventually they get up above sea level as the erosion occurs and keeps coming up and they work together okay erosion and and the rising of the mountains now early on for the longest time they're big tall rugged mountains it's early after the uplift and it brings that up and you keep eroding down so continuing on in this journey of erosion of these mountains now we've taken it clear down we've eroded these mountains way down here's sea level right here I've symbolically show these metamorphic rocks I could put granites in here too but we've eroded some 15 miles easily 15 miles of rock to get down to this point okay in the core of the mountain and notice the relief that I've depicted here is very gentle compared to the rugged mountains that we get early on the big tall rugged mountains that we've seen and it's a natural process as you get closer and closer to sea level you have less and less relief which means less energy less potential energy Studies have been done here in Wyoming to show that the relief here the tallest Hills are only like 150 200 feet tall and they tend to be more gentle and and Broad okay there's a modern example of that situation in the Canadian Shield that's what we see everything is down close to sea level and has really been eroded down over a huge amount of time we've learned a lot here in the Wind River Canyon but believe it or not it has one more very important piece of Earth history to reveal to us I've mentioned a couple times about the warm ocean waters that came in finally and deposited the Flathead sandstone and you might ask well what evidence do you have for that and that's a fair question of course and that's what I love about this outcrop right here this is the Flathead Sandstone right here in the Wind River Canyon right above the great unconformity let's go take a look at it okay so here we are let's take a look here right where my hand is see the these looks like spaghetti in the rock just spaghetti hanging down these are worm Burrows vertical worm barrels these tubes are called scalithos we don't know exactly what the animal looked like but they were worms this outcrop is completely full of them just pretty amazing to think about because these worms like to burrow vertically in high energy environments like right on the shore face right at the beach where the water swashes around that's where these worms dig vertically down to stay away from the high energy so they don't get washed away right and they dig down and feed on the Organics within the sand on the beach so how did warmth arrive what caused that warmth to come and meld all these glaciers and bring warm water to the world well the best theory we have is that there was a period of intense volcanism which put tremendous amounts of CO2 into the atmosphere and helped us warm up I just love this outcrop it's the best outcrop I've seen for these vertical tubes scalithos and it is direct evidence that the whole world had changed that warmth had arrived and the life had begun to flourish and would continue to to explode in diversity and ultimately of course lead to well to us well I want to take you to a really special place it's a bit of a drive it's an eight-hour drive actually and it's to Antelope Island in the Great Salt Lake near Salt Lake City Utah and there there's some special deposits associated with the Great unconformity I think you're going to like this this is what it's all about right here this is why I drove all these miles eight hours and fought a snowstorm and was in three hours of traffic jams to show you this outcrop let me show you some details here if we come right up here and look at this rock it has some very surprising features so now that we've moved in a little closer I'm hoping you're starting to get excited like me looking at this rock I mean you have this beautiful black background color which is a Shale or mudstone it's very dark colored it's a what we call a matrix and then you have these class these angular clasps some of them are kind of rounded as well uh they're kind of stretched that's because they've been squeezed and metamorphosed that's an entirely different discussion that isn't why I'm here with you uh but all these various shapes and they're beautiful they're made of quartz and various Granite types here uh this huge clasp here is quartz very large there's something odd about this for geologists anyway and that is we have a complete mix of class size we have the very fine-grained mudstone shales then we have class that get huge this is very unusual and can only happen in two ways one of two ways from debris flows that where you get lots of rain in the mountains and the and it's in a muddy Shaley area and it breaks loose and now you have mud and then it can go over areas that have rocks and all kinds of stuff and it all mixes it up and then it deposits at the bottom of the mountain okay those are debris flows the other way is deposits from glaciers okay now glaciers they don't care they grind up rock into really fine flour they carry huge rocks on top of them and within them and underneath them they push them I mean they just they don't care about size of rocks at all okay unlike a river which is very particular and in fact most depositional systems sort out the grain sizes really well and so this is why it's so unusual for geologists now this formation is called the mineral Fork tillite it's two throughout two to three thousand feet thick and this is the neat thing you can tie it right back to the great unconformity the great unconformity is above it aways okay not too far above it but these are deposits from these giant continental glaciers that I've been talking about that have eroded the entire continent right down to the roots this is the direct evidence of these glaciers that we're depositing this and in fact geologists have been able to go around the world and see these kinds of deposits at this age that uh near the equator or at the equator and that's why they start to go oh boy you know this probably means and the more we study it the more we think that that the Earth was entirely ice covered snowball Earth or nearly so there's some debate about how much and all that I don't want to go into those details but essentially let's just call it snowball Earth so my trusty white board with a sketch to help us out okay this black line represents the great unconformity as it was being formed okay this blue here is a big huge continental glacier that's eroding everything down and has eroded it right down to sea level okay the wiggly lines here represent metamorphic rocks where it's ground down into the core of the mountains just taking them right down to the roots right down to sea level here's sea level this well this is not well done this blue line here the wiggly blue lines is the ocean water okay we have these huge icebergs that just break away off the front of the glacier as it reaches the ocean so we have the glacier and Incorporated within it is it's tearing up these mountains as all this debris I'll put in red all the debris on it within it underneath it in front of it on the side you know wherever it can okay and it's carrying it out and it finally gets over this hinge point and starts heading into the ocean it starts dropping All That Rock that's within the glaciers and also I'm sure pushing some out too into these low areas but most of this here that we've been looking at is more Dr dropping out of the glaciers as they melt the icebergs and this red wedge here represents what we've been seeing here the mineral Fork till light now this wedge as I've said of the mineral Fork till light that we have recorded here in Utah is some two to three thousand feet I mean that's pretty spectacular and it's these rocks dropped into the shales these dark shales are the ocean sediments you know it's very quiet water and you deposit very fine-grained shales these black shales and mud Stones okay and then the glaciers bring in all this rock some big big boulders can be very large size and and dropping it in there and that's why you have this really bizarre situation where you have very low energy mixed with very high energy meaning very fine-grained stuff Rock mudstone shales mixed with very high energy rocks and and you can do that of course with these glaciers So eventually is the earth warm the glaciers melted of course started to melt that I'm sure took a long time sea levels started to rise bringing in sandstones across this great unconformity here that we've seen in Wyoming the Flathead Sandstone the very same Sandstone that's equivalent here in Utah is called the tintic and in the Grand Canyon it's called the tepeat sandstone and over in The Dakotas it's called the Deadwood Sandstone but they're all the same okay bringing in the Sandstone on top of here so a point I want to make here is in Wyoming this rock underneath the great unconformity is some of the oldest on the continent you have to go to the Canadian Shield to get older but it's 2.7 billion years old and the Sandstone the Flathead Sandstone is some 530 550 million years old so you have a huge gap in time however as you come over here into Utah this uh unconformity is underlying by well this mineral Fork tillite we've been looking at and a couple other thinner units and they're around 700 million years old so that the Gap in time is much less and in the Grand Canyon The Rock underneath is some 1.7 billion years old instead of the 2.7 that's in Wyoming so how do we get changing gaps in time along the great unconformity how does that happen Okay so I have my sketch here this piece here represents continental crust the real old stuff Wyoming good old Wyoming right 2.7 billion years old and this represents oceanic crust that is plunged in a subduction has plunged down underneath another piece so they they come together right the oceanic crust comes meets and it plunges underneath like this that's plate tectonics you can study up on that a little more sometime I may do a lesson on that but anyway it subducts this whole plate goes underneath plunges underneath starts melting and that material works up and builds volcanoes we call this a volcanic Arc and there's a lot of sediment associated with shedding off these volcanoes and everything else but see what's happening is they're coming together through time and eventually this material this volcanic Arc and all its Associated sediments hit Wyoming the old Craton and these are younger so for instance the terrain that's in Southwest United States that includes uh the Grand Canyon it's one of these 1.7 billion years old and it hits Wyoming and Wyoming is kind of the center of the universe everything is accreting onto it sticking on to it as it comes around building the North American continent amazing so this comes in hits here now you have 2.7 billion year old rock and once this hits it you have next to it that's stuck onto the side here we can think of it that's glued together suture together is 1.7 billion years old so now you have dramatically different ages of rock next to each other right let's revisit the Rock and be right at the outcrop and we can put our hands on or at least I can I sure wish you could with me here because it it you can just feel the history in this looking one last time out over the Great Salt Lake shrouded in a beautiful fog I contemplate The Amazing Earth history of this area which overwhelms me with a sense of awe foreign [Music] well we've made it here to an Overlook of the last stop we're going to be stopping down below in this country way down here for the final stop to wrap up this great unconformity discussion but I wanted to see I wanted you to see this Overlook so that you get an appreciation for the vastness of the country and hopefully you'll see how amazing this place this is to see the Great unconformity so let's just take the Drone right down here right way down below to the tops of those Canyons to give you a broad scale feel for where the great unconformity occurs here I think I see the unconformity now do you here it is with the beautiful flat head Sandstone above it and the pink granites below let's move on to a new area these beautiful rugged Canyons have been cut deep into basement rock granites by the Clarks Fork River in most of this area the Flathead Sandstone has been eroded and stripped back along the great unconformity surface this happens because the Sandstone is easier to erode than the underlying granites this means that all these relatively flat areas along the canyons are the actual unconformity surface try to imagine this surface uncut by Canyons extending as far as the eye can see that scene is much like the world looked as the glaciers receded well now that we have a better understanding of this broader region let's go ahead and drive down way down there on the onto the rim of the canyon down there and have our final discussion well here is the Flathead Sandstone I'm standing just above the great unconformity so I'm going to walk along here around the corner we're going to look at a couple things at the sandstone first of all I want to look right here and just look at all the beautiful cross bedding we call it in the sandstone I've drawn a few blue lines here to help guide your eyes so you can see this cross bedding or cross stratification those are the along the fronts of the bed forms out in the in the ocean waters typically less than 200 feet of water where you get these four sets these cross beds coming in someday I'll do a lesson on that a lecture on on that and I'm just walking down through the Section down a little deeper into the sandstone a little deeper getting ever closer to the Great unconformity and come right around here around the corner where the parking is for the cars I'm going to come right around the corner in fact the flat area where you see the cars parked is the actual unconformity surface and this is where the Flathead Sandstone has been Stripped Away by the process of erosion here is a view of the same parking lot from across the river the steeple Canyon walls are the granites underneath the great unconformity surface the Flathead Sandstone is back in the trees back behind the parking lot and as I come around the corner you can see how this Sandstone weathers naturally instead of the road cut that we were just at typical weathering pattern of this beautiful sandstone well I finally made it to this surface I'm standing literally on the surface of the great unconformity my feet are on granites here in this area granites that are 2.7 billion years old I've got the sandstones that are 550 million years old or so behind me and it's being eroded and receded and stripped back that Direction behind me to reveal this surface now I've been talking about some big numbers in time and I want to help you understand deep time I think that's critical when we're talking geology so let me get something here I have this book and I think this is appropriate because books record history we use them to record our history let's imagine for a minute that each page in this book is one year [Applause] each page is one year now I've been talking about 500 million year old sandstone a little older how thick would this book be with 500 million Pages any guesses well it turns out it's 40 miles this book would be 40 miles thick now I've talked about two billion years of missing time on this surface that's well it's easy to do the math it's about 160 miles thick this book would be that's just the missing time on this surface wow it's it's rather overwhelming okay I want you to think of something to to really think in your minds creatively and imagine this surface is being eroded back right slowly and if I dig down with this handy little garden trowel I am revealing the unconformity just bringing it back right and I could keep going back a little and I am revealing this unconformity which hasn't seen the light of day for some 600 million years wow [Applause] as I walk along this amazing surface I Ponder the massive amount of the Iraq record that was relentlessly eroded away by huge glaciers and I imagine a Barren strip land with absolutely no vegetation of any kind then I see an ocean in the distance with a beautiful beach and I think about the miracle of the warmth that arrived and now I want to walk right over to the beautiful sandstones deposited by this beach that came in as the ocean rose right into this beautiful Sandstone what Joy this brings to me to think about the life the warmth and the wife the explosion of life that occurred represented by these sandstones which ultimately led to you and me to be and for me to be right here I've mentioned a few things about sea level rising glaciers receding and all this and I wanted to show you this sketch to help it put it all together this is so important this is a cross-sectional sketch with the glacier here okay represented in the blue the land surface the great unconformity at the time so this is some 550 million years ago is this black heavy black line okay uh this is a pluton of granite that is intruded into metamorphic rocks so these black squiggly lines represent the metamorphic rocks that we've seen I'm going to put a line right here for the moment that's just ocean okay that is the ocean at the time as this Glacier receded the sea level is rising now I want to mention this pluton remember it was at least 15 miles deep when it cooled off so we know that the erosion by these glaciers and primarily the great glaciers eroded down some 15 plus miles down to it just erode the continent down right now as these glaciers melt sea level is rising so here's time one time two as we continue to raise sea level and guess where the beach is it's right here huh if you were to walk on the beach so let's pretend like I'm standing right now on this great unconformity right here okay so as sea levels continue to rise they're coming my way the beach is coming my way and the sand zones are deposited so here we go through time oh finally got got my feet wet huh and keep going and actually sea level is these glaciers melted sea level Rose to the point where it essentially covered the entire continent of North America wow so now that we've seen in cross-sectional view what happened I want to show you in map view what the world looked like it turns out that the gentleman that created these maps that I'm going to show you his name is Dr Ron Blakey and I studied under him for my graduate work in fact he was the my advisor for my thesis and it was a great privilege to work under him and he's well known very well known because of these Maps you see him in museums and in many Publications probably the best known geologist on the planet right now so let me grab these Maps here and show you okay here's the first map uh this is represents during the deposition of this Flathead Sandstone are actually yeah right after right during deposition some 500 550 million years ago this is the state of Wyoming heavily outlined here in Black okay and this is all of North America the continent of North America and this is the western edge of Idaho so you see we had a lot of North America that still didn't exist at the time so the deeper waters were out here and as these glaciers mounted the Water started encroaching and coming in and coming into Wyoming and depositing the Flathead sandstone and other formations above that is the water continued to get deeper and deeper let me show you the next map here so here's the next period of time some 50 million years later is in the ore division so this is when the waters had come up to their maximum and you see an entire most of all of North America had been covered with is covered with shallow Seas another reference point by the way this is Hudson Bay here and we're getting down here's the panhandle of Texas to give you a feel okay for the lay of the land so here North America unlike any other time was covered in water in Shallow Seas primarily thank you for watching this video I hope you've enjoyed it and I hope you'll enjoy some of the other videos I've made and those that I make in the future

Channel: Myron Cook

Views: 612,133

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Id: LXzDfQyUlLg

Length: 45min 53sec (2753 seconds)

Published: Thu Dec 15 2022