Very impressed with your visual sense. The combination of drone, whiteboard, annotated photos, jeep shots, etc.....wow. Lots of planning to get good light. Congrats on making these so effective.
So glad to see Nick here; my first love, geologically speaking. You two need to do a joint something. Nick has mentioned how events further west impacted the mountains. Is the uplift part of the Exotic Terranes story?
The thing with the Rockies is, and a lot of people don’t realize this-even though the rocks were originally deformed and thrust upward during the Laramide orogeny, between 70 and 50 Ma, by Mid-Oligocene time (i.e. by around 30 Ma), those mountains/uplifts were already nearly completely buried by the sediments/erosional debris they shed into the basins and alluvial fans that surrounded them. It actually wasn’t until late-Miocene to Pliocene time (i.e. between 10 and 5 Ma) that the modern-day geomorphological features/landforms we call “The Rockies” were “exhumed” from their deep burial, and the landscape was rejuvenated. And actually, the specific landforms we see today as “The Rockies” for the most part were further sculpted and shaped by glacial erosion during the Pleistocene, and most recently, the Last Glacial Maximum. Geologists refer to this event as “The Exhumation of the Rockies”. So the Rocky Mountains that were originally uplifted by the great Laramide high-angle basement thrusts and reverse faults are not even the same mountains that we see today, though structurally they are their “children”, we might say, inheriting the same structures that permitted their original uplift. The Intermontane West of 30-10 Ma would have looked VERY different than the place we see today, being high elevation, but largely a flat plateau with a couple rocky knobs sticking out of it, kind of like the Granite Mountains of Wyoming today, but nothing like today’s Wind Rivers or Bighorns. This surface is known as a “plantation surface”, and represents a time of geologic stasis, when the highlands had largely been eroded, and the lowland basins were largely filled in, forming a broad, even surface. Once the mountains were rejuvenated between 10 and 5 Ma, this surface was also uplifted, but deeply incised into the valleys and basins we observe today. The “shoulders” or terraces of this “sub-summit surface”, as it is known by geologists, is located all over the Intermontane West between the elevations of 10 and 11,000 ft. You can observe this quite well in the Wind River mountains and the Beartooth Mountains, and in fact, if you follow the Beartooth Highway from the Chief Joseph Scenic Byway junction in Wyoming’s Absaroka Mountains, over the state line towards Red Lodge, MT, you will be driving along this elevated plantation surface, the sub-summit surface, the actual ancient Oligocene-Miocene paleosurface. This drive, at 10-11,000 ft elevation, and broadly flat, is called variously “The Highway to the Sky”, “A Drive Along the Roof of the Rockies”, “The Roof of the World”, and “The Most Beautiful Drive in America”. During the Pliocene, many parts of the landscape would have begun to look familiar to us, but the highest parts of the pre-glacial Rockies would have still had a very different character than today’s post-glacial mountain heights, which have been sculpted into arêtes, nunataks, cirques, U-shaped valleys, hanging valleys, and proglacial lakes, by the activity of vast glaciers during repeated ice advances in the last 2.5 Ma. Now the kicker is this: despite knowing the start-and-stop Cenozoic uplift history of the Rocky Mountains, Cordilleran Geologists actually haven’t a very clear idea to this day of what actually caused the Mio-Pliocene rejuvenation and “Exhumation of the Rockies”. Unlike the Laramide event described in this video, which was definitely a classical “orogen”, or mountain building event caused by plate tectonic collision along a convergent margin, the “Exhumation of the Rockies” occurred during a time of tectonic quiescence, which continues today. The active margin along most of the Western United States no longer exists, and the majority of the Intermontane West and Great Basin is currently in an extensional tectonic regime. There are two leading theories, but they are much contested, and the jury is still out. The first theory involves what is known as “epeirogenic uplift”, basically a broad, non-tectonic doming or uplift of a region. According to the proponents of this theory, such epeirogenic uplift was caused by thermal/dynamic uplift of the Intermontane West by hotter, ascending mantle flow under the region. To some extent, seismic tomography supports this, but it can often be like interpreting Rorschach tests, and there is no consensus on the matter. Another mechanism for epeirogenic uplift is “delamination” of lower crust. Essentially, mountain building events cause the earth’s crust to thicken, both upwards in the form of mountains, and even more so downwards, into the crustal roots of orogens. These downward-projected rocks in the thickest part of an orogen are under immense pressure, and this causes the minerals in the rocks to undergo structural and chemical changes that result in them becoming much denser, creating rocks like eclogite. These ultra-dense rocks are actually denser than the mantle below them, and at such depth, subject to immense heat and pressure, which causes them to deform in a ductile manner, downwards, and essentially whole areas of crustal root of the mountain belt form “drips” of dense material or peel off and fall into less dense mantle below, the same way that dense oceanic crust subducts into the mantle. In the absence of these dense crustal roots, the more buoyant magma rushes in to fill the void left behind, and the crust is now substantially thinner, and as a result, the whole area is uplifted by the dynamics of the upward-migrating hotter mantle material and increased thermal gradient. The second major theory of how the Rockies were reborn in the Mio-Pliocene primarily involves feedback loops between climatic change and erosion. Essentially, as climate became colder (and climate reached a Cenozoic maximum during the Oligo-Miocene) burial phase of the Rockies), during the Cenozoic, the climatic patterns of the Intermontane west changed, so as to cause more precipitation and thus more erosion, both chemical and physical, in the region. With more erosion and transport of the highlands (the area remained relatively high in elevation), river valleys and mountains begin to be incised into the plateau. Now, because the crust of the Earth floats on the mantle below it, the same way an Iceberg does, a portion of crust that consists of a flat plateau will sit lower in the mantle than the same size piece of crust that has many peaks and valleys. The reason for this is the piece of crust with many peaks and valleys has had a bunch of material carved out of it, so it is less dense. At the same time the peaks are at least as high as the original plantation surface, so this causes the crust to be isostatically uplifted, such that the average elevation is lower than the old plantation surface, but the peaks left behind are now substantially higher. As the peaks get higher, they begin to exert an orographic effect on the regional climate, and collect snow and glaciation as they get taller, and so a feedback loop is initiated, where the mountains continue to get taller as a result of erosion due to climate change, and climate change and erosion increase as the mountains get taller. But again, neither of these theories are “fact”…yet. The Rockies remain a mystery. In fact the cause of the original Laramide uplifts described in this video is itself still unknown by geologists…but that is a whole, other topic… :)
Nice summary of the regional geologic history! I plan on doing a video sometime on the basin filling and exhumation. This will be a nice reference...thank you
Thank you, I enjoyed reading this. I recently watched a video about the exotic terranes in the Pacific North West, and how their collision and accretion to the west margin could have created the compression needed to uplift the Rockies in the first place. This might be too out there a question but: do you know if we have identified the final destination or current location of all the sediment that eroded from the high-elevation flat plateau you described?
@@amacuro (what follows I had to divide into three parts) Well, the thing is you are talking about what are actually many separate events. Exotic terranes of the Pacific Northwest collided with the North American continent during the Jurassic Nevadan Orogeny (about 170-160 Ma, locally different phases of it are also named as the Siskiyou, Klamath, and Sierran phases, or orogenies). This collisional event represents the docking of what is known as the “Intermontane Superterrane” (IMS), a collection/archipelago of both allochthonous (from abroad) and parautochthonous (originally rifted from North America and separated from it by the Carboniferous-Triassic Slide Mountain Ocean/Havallah Back-arc Basin) island arc terranes, including oceanic crust that was caught up that existed in between the two major sides of the intermontane superterrane, known as Cache Creek/Bridge River/Hozameen terranes (the IMS consists of an eastern and a western side, known as Quesnelia and Stikinia, respectively, which originated as a single long island arc that closed in on itself like a pair of scissors as it collided with North America, imbricating portions of the ocean floor that were caught in between), as well as additional ophiolite complexes that are thought to have either formed as inter-arc spreading centers within the archipelago, or as suprasubduction ophiolites formed in the forearc when the trench retreated or new subduction zone formed (Ingalls Complex, Josephine Ophiolite, Smartville Complex, etc). So the IMS was a very complex set of terranes, and they all accreted to North America during the Jurassic, and it is many of these that make up the majority of the “accreted terranes” of the PNW. Then, during Cretaceous time, between about 130 Ma and 80 Ma, there was another large, protracted collision, known as the Sevier Orogeny. This event involved the docking of another “superterrane”, known as the “Insular Superterrane” (INS), which consisted of a collection of allochthonous, exotic terranes, some of them showing evidence of having traveled all the way from the Tethyan realm, across the paleo-Pacific (Panthalassa) Ocean, others from as far away as the Arctic and Scandinavia. Primarily, the INS consisted of a vast oceanic plateau/large igneous province known as “Wrangellia”, which was erupted on to the Farallon plate (plate whose remnants include the Juan de Fuca and Cocos plates today, most of which subducted beneath North America) during the Carnian epoch of the Triassic Period, and which may have played a part in a mild extinction event that brought about the ascendancy of Dinosauria, the “Carnian Pluvial Episode”. This oceanic plateau, Wrangellia was partially emergent/subaerial for a good portion of its existence and would have formed oceanic islands, similar to the Kerguelen Plateau today, or Iceland or the Galápagos Islands, and sometime during the Carboniferous period, it collided with rifted fragments of the paleo-continent known as “Baltica”, which originated in the Arctic and were translated west and south, around North America, along with a host of other terranes such as the Peninsular terrane, Anguyaucham, etc which originated as intra-oceanic island arcs during the latter half of the Mesozoic, and which were connected to Wrangellia as part of a single archipelago and subduction system off the west coast of North America. Additionally, south of the aforementioned terranes, the INS was constituted by the Guerrero composite terrane, which now makes up a large part of western Mexico and Baja California. This superterrane, the INS, collided with North America obliquely, in a sinistral/left-lateral sense and caused parts of the INS to be sheared and spread all across the Cordilleran margin. The compressional deformation from the collision created a whole series of margin-parallel thrust sheets and faults, collectively referred to as the Sevier thrust belt, named after the area in Utah where they were first studied and are east exposed. As I mentioned before, this event lasted from around 130 to 80 Ma, and it created two distinct sets of arc volcanics, an older 100-130 Ma series of subduction-related arc plutons, and a 100-80 younger series of chemically distinct plutons that includes the Sierra Nevada and Idaho batholiths that may instead represent the magmatic, plutonic products of slab-break off post-Sevier collision. In the PNW, the INS and its related rocks are represented by rocks like the 93 Ma Mt. Stuart granodiorite, the Easton Metamorphic Suite, the Western and Eastern Mélange Belts, the Nanaimo Group, and of course rocks of Wrangellia exposed on Vancouver Island. The Sevier Orogeny represented a huge event which accreted a lot of new material to the edge of the continent, and the voluminous syn- and post-collisional magmatism thickened the crust of the Cordillera to an extreme degree. As a result of this crustal thickening, a vast high-altitude “crustal welt” or plateau formed that extended from as far south as Arizona all the way to the Canadian border, and because it would have been similar to today’s Altiplano in the Andes, it has been called the “Nevadaplano”. There are several lines of evidence, from geochemical, to fossil, to geothermobarometric that estimate the thickness of this post-collisional (Sevier) “Nevadaplano” crust at around 67km thick, around the same thickness as today’s Altiplano, but somewhat less thick compared to the Himalayan Plateau/crustal welt, representing a paleo elevation similar to that of today’s modern Altiplano. Now, my previous post focused on neither of these events, but rather yet another mountain building event that occurred later, from around 70-50 Ma, the Laramide Orogeny. The Laramide Orogeny actually had nothing to do with exotic terranes in the Pacific Northwest. The causes of the Laramide Orogeny remain mysterious, and its effects are seen in NW-SE trending, basement-involved, high angle reverse and thrust faults throughout the intermontane west of the United States, down into Texas and, as well as in Arizona (Maria Fold and Thrust Belt) and into Texas and northeastern Mexico. Unlike the Sevier Orogeny that occurred before it, the Laramide Orogeny is not associated with the accretion of any known exotic terranes, and its associated deformation almost exclusively occured far inboard of the continental margin, as much as 1000km or more. Additionally, unlike the “Thin-skinned” fold and thrust belt-style faults and folds of the earlier Sevier event, where only the weak, younger sedimentary and volcaniclastic layers above the basement are involved, Laramide deformation is what geologists call “Thick-skinned” deformation, involving crustal-scale, high angle faults, which thrust cratonic basement rocks up several kilometers. It is these basement-involved faults that form the cores of all the great mountain ranges of the central and southern Rocky Mountains, and which expose some of the oldest rocks known in the United States. The Rocky Mountains were formed by this event, though they were later buried and rejuvenated as I explained in my previous post. END PART I
@@amacuro (Part II) But as I alluded to in that earlier post, the jury is still out on what caused the Laramide Orogeny. Unlike the Nevadan and Sevier orogenies, which we know were caused by the collision of North America with the IMS and INS, respectively, the Laramide Orogeny involved no collision with continents or island arcs, and deformation was localized deep in the continental interior, far away from the active margin, as far east as the Black Hills of South Dakota. What’s more, unlike the Sevier Orogeny, which was associated with voluminous magmatism and emplacement of batholiths all along the Cordilleran margin, the Laramide Orogeny is actually accompanied by a prominent “magmatic lull” or “magmatic gap” in which arc magmatism basically shut off during the period concerned. The two major theories of what caused the Laramide Orogeny are “flat-slab Subduction”, and “far-field stresses”. Far-field stresses means the idea that plate-tectonic forces conspire to transmit compressional forces deep into the interior of a tectonic plate, causing it to buckle up, and this has also been implicated in the ancient intracratonic/intraplate orogenies of the US Ancestral Rocky Mountains of the US and Australia’s Alice Springs/Petermann Orogeny. But the majority of researchers implicate “Flat-slab Subduction” as the cause of the Laramide event. With flat-slab subduction, for some reason, the subducting plate (the ancient Farallon plate, in the case of the Cordillera) changes dip direction from its usual 30-60 degrees, to something much, much shallower, even completely flattening out, such that it is sub horizontal relative to the overriding plate and in physical contact with it. In this way, proponents of flat-slab subduction believe that the physical contact and impinging of the subducting plate underneath the upper plate caused the basement involved faults to form, and flat slab subduction additionally has the benefit of explaining the Laramide Magmatic Gap-a flat slab leaves no mantle wedge which can partially melt to form arc magmatism. Additionally, the process of flattening the slab and the later return of the slab to a normal angle of subduction in the Tertiary would suggest an initial migration of the arc towards the hinterland, before the magmatic lull, followed by a dramatic return to magmatism with the return of the mantle wedge, and with the upper plate heavily metasomatized by the volatile rich fluids released by the oceanic plate in contact with the lower crust of the upper plate-and, indeed, this is exactly what is seen with the Cordilleran arc-a migration of magmatism towards the hinterland, followed by a magmatic gap, followed by a dramatic return to highly silicic, evolved magmatism known as the “Mid-Tertiary Ignimbrite Flareup”. So IMO the flat-slab theory makes a lot of sense. Moreover, we actually know this happens, and we have imaged flat slab subduction under two portions of the Andes occurring today. In fact, one of these flat slab segments is also accompanied by basement-involved, thick-skinned thrusting in the deep hinterland and a magmatic migration followed by a magmatic lull-in Argentina’s Sierras Pampeanas, located over 500km from the crest of the Andes-not quite the 1000+ km of the Laramide hinterland thrusts, but definitely in the ballpark. So it seems clear that flat-slab subduction is a good explanation, but what is not so clear is what could have caused the flat-slab subduction in Laramide time. So, generally researchers fall into two camps about this: the “aseismic ridge” camp, and the “oceanic plateau” camp. Today’s flat-slab under the Andes and Sierras Pampeanas is caused by the subduction of an aseismic ridge. Aseismic ridges can be formed as either hotspot tracks in oceanic crust, or fossil spreading centers now stuck in the middle of an oceanic plate. Oceanic plateaus on the other hand are vast landforms like the aforementioned Wrangellia, which is no longer of course on the ocean floor, but has been sliced and diced and launched up into the mountains of Vancouver and Alaska. However, there are a lot of good examples of surviving oceanic plateaus, especially from a period of hyperactive magmatism in the Pacific, known as the Cretaceous Normal Superchron, in which some of the largest oceanic plateaus in the world formed, including the Ontong Java, Shatsky Rise, Manihiki, Hikurangi, and Caribbean oceanic plateaus. Oceanic plateaus can form in the middle of oceanic plates as well as at mid ocean ridges, where they often become even more massive, receiving extra magma from the spreading center, as can be seen in Iceland today. Proponents if the oceanic plateau theory for the Laramide flat slab specifically implicate a missing “conjugate” plateau of the surviving Shatsky Rise. These researchers cite plate reconstruction models that seem to suggest that the Shatsky Rise (now in the western Pacific) formed at a spreading ridge, and so as it formed, a conjugate to it would have formed on the other side of the spreading ridge, and the plate reconstructions suggest that this conjugate would have been located at the right latitude, at the right time, to collide with southwestern North America during the Laramide event. Some researchers go further to suggest that an additional “lost conjugate oceanic plateau” (namely the lost conjugate of today’s Hess Rise oceanic plateau, also in the western Pacific) also collided with Mexico during the Laramide, and is responsible for the Laramide thrusts and deformation observed in Mexico’s Sierra Madre Oriental and in southern Texas. But there is one big problem with the oceanic plateau theory of the Laramide flat slab-every single oceanic plateau that we know of in the geological record that has collided with a continent has ended up as an accreted exotic terrane, shredded into pieces. Wrangellia is a prime example, as is the Siletzia-Yakutat oceanic plateau that collided with Eocene Washington and Oregon (and the Yakutat half of it with Alaska), as is the Ontong-Java Plateau, which is currently colliding with the Australian plate to form the Solomon Islands and Bougainville. In the case of the Ontong-Java plateau, scientists estimate that as much as 80% of the vast oceanic plateau is being subducted, with only the top 7km of crust becoming accreted to the Australian plate. But seismic tomography shows that despite so much of an oceanic plateau being subducted, the angle of subduction is normal, not flat. And the bigger issue with the oceanic plateau theory is that if an oceanic plateau had subducted under North America (or two!), there would undoubtedly be scraped-off remnants of that plateau left behind as exotic terranes, exactly as we see in the case of Wrangellia, Siletzia/Yakutat, and Ontong-Java. But no such terranes exist, not even a hint of them. Therefore I personally find it very unlikely that an oceanic plateau was responsible for flat-lab subduction in the Laramide orogeny, and I am more in favor of the “aseismic ridge” explanation. After all, it is exactly what we see today in the Sierras Pampeanas, and uniformitarian principles like this are the rock (pun intended) on which we build the edifice of geology. But very little is known about the history of such an aseismic ridge, because whatever it was that caused the Laramide Orogeny, it’s long since been subducted, and left very little direct physical trace. The only rocks that might be directly related to this subduction event are a small group of rocks found in Southern California and Arizona, the Pelona-Orocopia-Rand Schist, which are actually several related units of highly deformed high-pressure, low-temperature metamorphic rocks that researchers believe may have been shoved down the subduction factory during the Laramide event. And very recent research suggests that there may even be related rocks all the way up in Washington State-the Swakane Gneiss of the North Cascades. And this leads me back to the Pacific Northwest and the rest of the story of its exotic terranes. END PART II
@@amacuro (Part III) While the Laramide Orogeny, was occurring, roughly 70-50 Ma, deep in the interior of the continent, there is more and more evidence that some interesting things were happening at the edge of the continent. Namely, there is increasing evidence, ever since Myrl Beck first proposed it as a theory 40+ years ago, that the entire outboard edge of the North American Cordillera was sheared and translated by continental-scale (1500-3000km offset) dextral/right-lateral transform faults, around the same time as the Laramide Orogeny. This theory is known as “Baja BC”, because it is analogous to the translation of Baja CA, today (and much of coastal California state), from its original position 500km further south, in just 12.5 Ma. There is increasing good paleomagnetic data, paleontological data, geological, and geochemical data to support it. However, researchers have had trouble finding the continental scale dextral transcurrent faults, the Baja BC equivalent of the San Andreas. It could be a combination of things, the fog of the past, that translation was distributed across many smaller faults, and or that the faults responsible have been overprinted, invaded, and erased by magmatic activity in the 50 million years since it happened. I am personally a supporter of a more moderate, 1500-2000km offset Baja BC scenario. The result of this translation was that many exotic terranes of the PNW, for example the Mt. Stuart Granodiorite and indeed the entire Northern Cascades Crystalline Core, and probably all the rocks west of it that are its age or older, including Wrangellia, and the rest of the INS, were probably translated from much farther south, to their current northern positions, during this time period. Last of all in the exotic terrane story of the Pacific Northwest, was the accretion of the Siletzia Oceanic Plateau. Like Wrangellia before it, Siletzia formed out at sea, but unlike Wrangellia, which seems to have traveled thousands of kilometers for hundreds of millions of years, before colliding with North America, Siletzia was formed at a spreading center, just off the coast of the newly-accreted INS, during the early Eocene epoch, and was very probably created by the same mantle plume that site under Yellowstone today, the North American continent having overridden the hotspot in the last 50 or so Ma. Like all large igneous provinces, of which oceanic plateaus are one type, Siletzia was extruded extremely rapidly, and just a couple million years after it formed offshore, it was accreted to the Pacific Northwest, shared between modern-day Washingtin state and Oregon. We know it formed across a spreading ridge, the ancient Kula-Farallon or Kula-Resurrection ridge (it is very difficult to know which for sure, but was more likely the former), because its conjugate oceanic plateau, which spread northward as Siletzia was pushed into west-moving North America, is the Yakutat terrane, geochemically and lithologically identical to Siletzia, which was transported north along the coast of British Columbia, along the Queen Charlotte fault, where it is currently colliding with Alaska and responsible in part for that state’s highest mountains, Denali and the Wrangell-St. Elias mountains. Siletzia marks the final exotic terrane to be accreted to the Pacific Northwest. After Siletzia, the modern day Cascades volcanic arc as we know it was established, and the Olympic subduction complex became imbricated against Siletzia to form Washington’s Olympic peninsula, but those rocks were formed in the trench system just off the coast-they aren’t exotic in the same way as Siletzia, or the INS before it, or the IMS before that. And as the majority of the East Pacific Rise has also subducted beneath North America, and the only remnant of the once-great Farallon plate that could potentially carry exotic terranes on it is the tiny, young Juan de Fuca plate, with the exception of a seamount here and there before the rest of the EPR is subducted, there probably won’t be any more exotic terranes accreted to the PNW for a long time. To summarize my response: exotic terranes of the PNW are not associated with the Laramide Orogeny that I described in my earlier comment, but with older events, the accretion of the Intermontane and Insular Superterranes in the Nevadan and Sevier orogenies, respectively, and the younger accretion of the Siletzia oceanic plateau. Although there may be some connection to a handful of units in the PNW, such as the Swakane Gneiss, and Laramide “flat slab subduction”, but this work is very recent and the jury is still out. END PART III
I discovered your channel by accident, just a geology search on youtube and now you are, along with Nick Zentner my favourites to watch. Thanks from the U.K. Cheers.
I've enjoyed your last four geology related videos a great deal and eagerly await more. You are an excellent teacher and have a gift both for the storytelling (content) and the delivery (video production) combined with superb vocal work and a likable, enthusiastic and easy manner. Whole thing is a winner. Thanks. PS: It would be fun to watch you tooling around the rockies in your jeep and explaining them to that Ned Zinger guy.
Having studied my geology at school and university, in the UK, it is very interesting to see basic geological principles being applied to an entirely different continent, on a different part of the earth's crust. I am glad you've stuck to explaining the idea of relative time, the sequence of events, without worrying too much about the later, more sophisticated methods of dating absolute time. Many thanks indeed, firstly for your enthusiasm, but also for your effective and skilled technique of combining different forms of explanation, using plain old eyeball - visual interpretation, white-board, drone photos and even your Jeep for scale. I hope to watch more of your videos, learning even more about the beds, formations and structures that form your part of the North American continent. But hey, maybe watch your step on those steep slopes !
Thank you so much for another wonderful video. I was raised as a fundamentalist young earth creationist, but taking a few geology classes helped me break free from that harmful ideology. Since then I've been in love with geology, and the amazing wealth of detail we find in the rock. I hope videos like yours will bring this realization to others like me, and help them experience the wonder of the world around them.
A lot more fun and believable than mind numbing nonsense of fundamentalists who refuse to be openminded about anything. Welcome to freedom of thought and enjoy the journey.
This was only the second video of yours I have watched and I am already awed and utterly fascinated by geology. You're an amazing teacher. Thank you so much!
My cousins own a ranch at the base of the Wind River Mountains outside of Boulder WY. I've camped there and also hiked across the mountain range from one side to the other, ten days in the wilderness. The horse flies were so big they could knock you down and take advantage of you. thank you
Another fantastic video. Loved it. That second outcrop, along with your diagram and the explanation of how it got that way, had great explanatory power. Really well done. Thank you.
👏🏼 Yayyy!! Outstanding! Your'e a very good teacher. No sensory overload. Your video pans the landscape without dramatic music and fast edits; yes! You've given me some keys, I can't unsee these tilted, layered formations. Your whiteboard ties it together. You got it together man.
Thank you for the time you spent doing this. I am heading to Utah tomorrow for a 4 day solo camp trip and i cannot wait to see what i've learned from your videos.
I learned a little about geology many years ago, mostly out of books. That was interesting, but getting these in situ lectures in the mountains is much more enjoyable. Thanks from the UK.
I moved to your general part of the country recently and doing so immediately resparked my latent interest in geology. There are so many interesting features in the landscape that are like giant puzzles. Your videos have been a great aid in enhancing my appreciation for the beauty that can arise from a few simple rules and the passage of time.
I'm in the process of catching up on your back catalog of videos, it's really fun when I can just go from one topic to another. Keep up the great work educating us! Really, really, really appreciate your work.
I just found your channel. I really appreciate your way of offering thoughts from a tiny rivulet forming in your back yard and showing how it relates to the grand canyon. I've shared you with friends. Thank you.
Thank you. I love your video. I’m interested in geology, ancient earth deposits, formations and life forms. I became interested in geology when I learned about herkimer crystals found in NY. But, Wyoming is extremely old and interesting as well. Parts of the Eastern Canadian coast are extremely old as well. I can’t believe how much we can learn about our Earth and about history by studying geology.
I'm working my way through Dr Cook's videos and have been inspired to uncover or erode the 50 years of life sediment that had covered my childhood interest in Geology. I have shared videos with many friends who are not science types and they have been able to gain a better appreciation of mountain building and erosion. They don't get as excited about it as I do but that's their loss. What I admire about Myron Cook is that he is a natural teacher. So often we hear those that can't teach turn the saying upside down. The reality is that very few people have the skills to pass their knowledge on to those with differing abilities to learn. I can't tell you how many professors I had that were either unintelligible due to language barriers, unable to organize and relate their thoughts (just read the chapter), or completely disinterested in teaching lowly under grads. Dr. Cook's Socratic approach teaches his audience to observe, think, and rationalize. When sprinkling the subject liberally with enthusiasm a teacher inspires. I don't know what Zuckerberg is paying Cook but it's not enough for the quality of entertainment and education that he provides. Personally I have no time for "influencers" but will binge watch Myron Cook every time I am on TH-cam.
I too just discovered your channel. I’m interested in so many different things, I did not know that I was interested in basic geological concepts but your video on the formation of the Gulf of Mexico and especially the delta deposits and fans hooked me. Thank you for introducing me to the fascinating world of geology.
If you ever come to Colorado on the front range, please come to my area and teach me about the geology here . I live on the Palmer Divide near Devils head.
Your explanation with layers, their thickness, the uplifts and the time it took to erode mile high+ mountains, is very humbling in realization of how insignificant we are in the realm of things. and the worry of global warming. As if we are the only species that is too big and important to become extinct. Thank you very much for your time and teaching method. You are awesome.
Another wonderful video by Myron Cook that takes a complex geologic situation and is able to explain in an understand way. Thank you, I have learn a lot.
Myron the moment you tipped that marker board the light bulb instantly turned on for me with your previous image of the two different angles of those formations! That was amazing the way you articulated this lesson with the marker board! I love your channel.
Thank you. This confirms my trying to have people understand the full measure of kinetic force that was imparted from this asteroid collision, on the naturally occurring tectonic activity of the North American plate plate with consideration to the subduction of an eastern Pacific ocean plate of which the Juan de Fuco plate may be the final portion that is known. And that central midwest sea, had been due to a depression of subductive plate collision. Much as is observed with the Gobi Desert depression north of the Himalayas , beyond the Tibetan Plateau. And the reason for the eurasian steppes.
Wow! Now I understand more of how the Windriver range formed. Basically a giant plug, pluton, of granite exposed when the much, much larger mountain above it eroded away. Fascinating. Thanks.
This is great stuff. I just joined this channel. I Love geology but have no education on this subject expect for Caving. I want to learn more. This channel is providing that for me.
I learned so much from your video. Most of my life has been in the PNW with some trips through MT and WY. Then I lived in Kansas for 2 years followed by CO for 14 years. On my trips back to WA I would change my route to explore WY more. I have traveled through the places you talked about in this video. It is nice to learn more about what I saw. Thanks very much.
I did my field camp out of Dubois (Miami of OH)- way back in 1980. Nice to see the area again. I've always been amazed at the folding of the sedimentary cover as the core was thrust up. The rocks weren't that deep, relatively speaking, so how they folded w/o heat and compression alludes me.
I don't know how i ended up watching your channel. Never searched for such things but I am glad that it happened. Really loved all your videos. Thanks for sharing these great information.
You make me want to move to Wyoming and get my hands in the earth. Fascinating uplifting sequence, transformation of the land is sooo interesting over long geological time, I could listen to this story forever
I absolutely love your videos, Myron. You had mentioned the Chicxulub crater and I was recently studying about it. I would sincerely love a video from you describing everything you know about the Chicxulub crater. You are a wealth of knowledge and love hearing your thoughts and experiences.
Everything is good about your videos! Music, camera work, your friendly and accessible yet detailed explanations, your choice of topics, the trusty whiteboard and how well you draw on it, your Jeep driving around way ‘out there,’ and the absolutely spectacular and untrampled landscapes. I did almost tell you to “Be careful!” on that steep slope, though…. 😂
Myron, thank you for all the work and time you put into these lessons you provide for us to learn and enjoy. It shows on your face that you truly love taking us along, but I know you would accomplish more without all of us tagging along.... so thank you! But since you're taking us with you, I have one request. Can I sit up front for the ride back? SHOTGUN!!
Myron... Been watching several of your vids over the past few months! Really like your 'easy to follow' explaination of issues; also a 'Zentnerd' here! Enjoyed the graphics in explaining the way the Hawaiian Islands were formed, though I knew it before, the 'visuals' prompted me to 'Share' the link to others who were following the eruption of MaunaLoa... I'll be looking for more!! Thanks!
I LOVE Geology, esp out here in Nevada looking for gold deposits, well used to i don't get around anymore but that's life, but i'll never get tired of watching videos like this and staying up on my knowledge of Geology, this was a fantastic video !
wonderful! looking forward to the next video. your content is the next best thing to being on the field as the best lessons are those that we experience.
I REALLY appreciate these videos and look forward to more! I grew up on the coastal plains, became a physicist, and eventually moved to the llano uplift area which caused me to get curious about rocks and now I'm learning a bit about this fascinating subject My understanding is llano is a really interesting geological area and would love to see what you can teach us all about it!.
Thank you, very intersting lesson, I will try to determine "Relative Dating " of the formations out here in Southern California, hopefully I can find a Stratigraphic Column of this area and answer some questions I come up with as I travel this great location called Imperial County. I had just gotten into prospecting a couple of years ago, but between digs I enjoy the scenery and always find myself trying to reconstruct what happened and why.
Myron, it’s been a long time since we were in school together at UW. By chance I’ve stubbles on to your videos and have been enjoying them this past week. Love them. Keep it up fellow cowpoke! Cheers - Rich W.
@@myroncook Indeed, my career as a geologist in Houston has been good to me and my family. But I’m envious that you stayed in Wyoming. Best regards. Rock on brother! Keep making those videos.
Wonderful, thank you again for your terrific videos! I am learning so much. I have a newbie question though. You kept referring to rock sediment being “deposited “ in layers. This confuses me. Deposited from where? How does that sediment “fall and layer” horizontally? Thanks, hope you or some other knowledgeable person here sees this question.
@@myroncook Thank you for responding sir! But where does it come from? Is it primarily from volcanic activity? Or ancient oceans moving sediment around? By the way I absolutely love your videos and am so glad you make them! Please don’t stop. I got so much more out of a recent trip to Utah; went to Zion, Bryce, Capitol Reef, Arches, Canyonlands (among other travels through Utah’s breathtaking scenery)thanks to the knowledge I have picked up from you. You rock! (Bad pun intended 😄)
You are one cool cat!! I’m jealous of your life in Wyoming! I’ll never understand why I didn’t become a geologist because I get mesmerized by videos like yours. Thanks for keeping it simple for people like me. Oh, and your brothers cool too. I will watch all your videos I just subscribed to your channel. Thankyou!
I'm surprised you have not touched on the Black Hills yet. I use to live on the eastern flanks as a kid, and it always amassed me how the hills cross into Wyoming from South Dakota.
Mountain forming is awesome. We would not really have them if it wasn't for how active our planet is. It is not quick either. Really gives a good example of how much time went into the formation.
The C/T boundry ? I am impressed. I had no idea where ,in the US , i could find one. Grand Canyon of the Gunnison park, with my roadside geology book, one foot was on the basement rock and the other on a billion years newer rock. How something so simple can bring a a smile to a face😊
What would happen geologically if the iron rich granite in the northern hemisphere was attracted to the current northern crawl of the magnetic pole? Do you think it will create a "northern Pangea" in the eras to come? I had a thought that Iceland is a nexus point for North America and the EuroAsian continent to come together. Well... this would obviously happen a long time in the future. LOL! I just love this! You are amazing Myron Cook! Please keep posting your videos, they really make me think!
Fish the Green at Weeping Rocks annually. Traveled the Continental Divide from NM/MX border to AB, then up to Tuktoyaktuk, NWT on the Arctic Ocean in the last two years. Many AK trips. I’m subbed and love your content!
![ละลาย (LALALYE) - DAOU PITTAYA ต้าห์อู๋ พิทยา [OFFICIAL MV]](http://i.ytimg.com/vi/wo6r9TgausI/mqdefault.jpg)
Very impressed with your visual sense. The combination of drone, whiteboard, annotated photos, jeep shots, etc.....wow. Lots of planning to get good light. Congrats on making these so effective.
Thank you Nick. I'm a big fan of yours and you helped inspire me to do this.
Love both of you!
Yes, Nick, I enjoyed this video, too.
Still learning after all these years.
So glad to see Nick here; my first love, geologically speaking. You two need to do a joint something. Nick has mentioned how events further west impacted the mountains. Is the uplift part of the Exotic Terranes story?
The thing with the Rockies is, and a lot of people don’t realize this-even though the rocks were originally deformed and thrust upward during the Laramide orogeny, between 70 and 50 Ma, by Mid-Oligocene time (i.e. by around 30 Ma), those mountains/uplifts were already nearly completely buried by the sediments/erosional debris they shed into the basins and alluvial fans that surrounded them.
It actually wasn’t until late-Miocene to Pliocene time (i.e. between 10 and 5 Ma) that the modern-day geomorphological features/landforms we call “The Rockies” were “exhumed” from their deep burial, and the landscape was rejuvenated. And actually, the specific landforms we see today as “The Rockies” for the most part were further sculpted and shaped by glacial erosion during the Pleistocene, and most recently, the Last Glacial Maximum. Geologists refer to this event as “The Exhumation of the Rockies”.
So the Rocky Mountains that were originally uplifted by the great Laramide high-angle basement thrusts and reverse faults are not even the same mountains that we see today, though structurally they are their “children”, we might say, inheriting the same structures that permitted their original uplift. The Intermontane West of 30-10 Ma would have looked VERY different than the place we see today, being high elevation, but largely a flat plateau with a couple rocky knobs sticking out of it, kind of like the Granite Mountains of Wyoming today, but nothing like today’s Wind Rivers or Bighorns. This surface is known as a “plantation surface”, and represents a time of geologic stasis, when the highlands had largely been eroded, and the lowland basins were largely filled in, forming a broad, even surface. Once the mountains were rejuvenated between 10 and 5 Ma, this surface was also uplifted, but deeply incised into the valleys and basins we observe today. The “shoulders” or terraces of this “sub-summit surface”, as it is known by geologists, is located all over the Intermontane West between the elevations of 10 and 11,000 ft. You can observe this quite well in the Wind River mountains and the Beartooth Mountains, and in fact, if you follow the Beartooth Highway from the Chief Joseph Scenic Byway junction in Wyoming’s Absaroka Mountains, over the state line towards Red Lodge, MT, you will be driving along this elevated plantation surface, the sub-summit surface, the actual ancient Oligocene-Miocene paleosurface. This drive, at 10-11,000 ft elevation, and broadly flat, is called variously “The Highway to the Sky”, “A Drive Along the Roof of the Rockies”, “The Roof of the World”, and “The Most Beautiful Drive in America”.
During the Pliocene, many parts of the landscape would have begun to look familiar to us, but the highest parts of the pre-glacial Rockies would have still had a very different character than today’s post-glacial mountain heights, which have been sculpted into arêtes, nunataks, cirques, U-shaped valleys, hanging valleys, and proglacial lakes, by the activity of vast glaciers during repeated ice advances in the last 2.5 Ma.
Now the kicker is this: despite knowing the start-and-stop Cenozoic uplift history of the Rocky Mountains, Cordilleran Geologists actually haven’t a very clear idea to this day of what actually caused the Mio-Pliocene rejuvenation and “Exhumation of the Rockies”. Unlike the Laramide event described in this video, which was definitely a classical “orogen”, or mountain building event caused by plate tectonic collision along a convergent margin, the “Exhumation of the Rockies” occurred during a time of tectonic quiescence, which continues today. The active margin along most of the Western United States no longer exists, and the majority of the Intermontane West and Great Basin is currently in an extensional tectonic regime. There are two leading theories, but they are much contested, and the jury is still out.
The first theory involves what is known as “epeirogenic uplift”, basically a broad, non-tectonic doming or uplift of a region. According to the proponents of this theory, such epeirogenic uplift was caused by thermal/dynamic uplift of the Intermontane West by hotter, ascending mantle flow under the region. To some extent, seismic tomography supports this, but it can often be like interpreting Rorschach tests, and there is no consensus on the matter. Another mechanism for epeirogenic uplift is “delamination” of lower crust. Essentially, mountain building events cause the earth’s crust to thicken, both upwards in the form of mountains, and even more so downwards, into the crustal roots of orogens. These downward-projected rocks in the thickest part of an orogen are under immense pressure, and this causes the minerals in the rocks to undergo structural and chemical changes that result in them becoming much denser, creating rocks like eclogite. These ultra-dense rocks are actually denser than the mantle below them, and at such depth, subject to immense heat and pressure, which causes them to deform in a ductile manner, downwards, and essentially whole areas of crustal root of the mountain belt form “drips” of dense material or peel off and fall into less dense mantle below, the same way that dense oceanic crust subducts into the mantle. In the absence of these dense crustal roots, the more buoyant magma rushes in to fill the void left behind, and the crust is now substantially thinner, and as a result, the whole area is uplifted by the dynamics of the upward-migrating hotter mantle material and increased thermal gradient.
The second major theory of how the Rockies were reborn in the Mio-Pliocene primarily involves feedback loops between climatic change and erosion. Essentially, as climate became colder (and climate reached a Cenozoic maximum during the Oligo-Miocene) burial phase of the Rockies), during the Cenozoic, the climatic patterns of the Intermontane west changed, so as to cause more precipitation and thus more erosion, both chemical and physical, in the region. With more erosion and transport of the highlands (the area remained relatively high in elevation), river valleys and mountains begin to be incised into the plateau. Now, because the crust of the Earth floats on the mantle below it, the same way an Iceberg does, a portion of crust that consists of a flat plateau will sit lower in the mantle than the same size piece of crust that has many peaks and valleys. The reason for this is the piece of crust with many peaks and valleys has had a bunch of material carved out of it, so it is less dense. At the same time the peaks are at least as high as the original plantation surface, so this causes the crust to be isostatically uplifted, such that the average elevation is lower than the old plantation surface, but the peaks left behind are now substantially higher. As the peaks get higher, they begin to exert an orographic effect on the regional climate, and collect snow and glaciation as they get taller, and so a feedback loop is initiated, where the mountains continue to get taller as a result of erosion due to climate change, and climate change and erosion increase as the mountains get taller.
But again, neither of these theories are “fact”…yet. The Rockies remain a mystery. In fact the cause of the original Laramide uplifts described in this video is itself still unknown by geologists…but that is a whole, other topic… :)
Nice summary of the regional geologic history! I plan on doing a video sometime on the basin filling and exhumation. This will be a nice reference...thank you
Thank you, I enjoyed reading this.
I recently watched a video about the exotic terranes in the Pacific North West, and how their collision and accretion to the west margin could have created the compression needed to uplift the Rockies in the first place.
This might be too out there a question but: do you know if we have identified the final destination or current location of all the sediment that eroded from the high-elevation flat plateau you described?
@@amacuro (what follows I had to divide into three parts) Well, the thing is you are talking about what are actually many separate events. Exotic terranes of the Pacific Northwest collided with the North American continent during the Jurassic Nevadan Orogeny (about 170-160 Ma, locally different phases of it are also named as the Siskiyou, Klamath, and Sierran phases, or orogenies). This collisional event represents the docking of what is known as the “Intermontane Superterrane” (IMS), a collection/archipelago of both allochthonous (from abroad) and parautochthonous (originally rifted from North America and separated from it by the Carboniferous-Triassic Slide Mountain Ocean/Havallah Back-arc Basin) island arc terranes, including oceanic crust that was caught up that existed in between the two major sides of the intermontane superterrane, known as Cache Creek/Bridge River/Hozameen terranes (the IMS consists of an eastern and a western side, known as Quesnelia and Stikinia, respectively, which originated as a single long island arc that closed in on itself like a pair of scissors as it collided with North America, imbricating portions of the ocean floor that were caught in between), as well as additional ophiolite complexes that are thought to have either formed as inter-arc spreading centers within the archipelago, or as suprasubduction ophiolites formed in the forearc when the trench retreated or new subduction zone formed (Ingalls Complex, Josephine Ophiolite, Smartville Complex, etc). So the IMS was a very complex set of terranes, and they all accreted to North America during the Jurassic, and it is many of these that make up the majority of the “accreted terranes” of the PNW.
Then, during Cretaceous time, between about 130 Ma and 80 Ma, there was another large, protracted collision, known as the Sevier Orogeny. This event involved the docking of another “superterrane”, known as the “Insular Superterrane” (INS), which consisted of a collection of allochthonous, exotic terranes, some of them showing evidence of having traveled all the way from the Tethyan realm, across the paleo-Pacific (Panthalassa) Ocean, others from as far away as the Arctic and Scandinavia. Primarily, the INS consisted of a vast oceanic plateau/large igneous province known as “Wrangellia”, which was erupted on to the Farallon plate (plate whose remnants include the Juan de Fuca and Cocos plates today, most of which subducted beneath North America) during the Carnian epoch of the Triassic Period, and which may have played a part in a mild extinction event that brought about the ascendancy of Dinosauria, the “Carnian Pluvial Episode”. This oceanic plateau, Wrangellia was partially emergent/subaerial for a good portion of its existence and would have formed oceanic islands, similar to the Kerguelen Plateau today, or Iceland or the Galápagos Islands, and sometime during the Carboniferous period, it collided with rifted fragments of the paleo-continent known as “Baltica”, which originated in the Arctic and were translated west and south, around North America, along with a host of other terranes such as the Peninsular terrane, Anguyaucham, etc which originated as intra-oceanic island arcs during the latter half of the Mesozoic, and which were connected to Wrangellia as part of a single archipelago and subduction system off the west coast of North America. Additionally, south of the aforementioned terranes, the INS was constituted by the Guerrero composite terrane, which now makes up a large part of western Mexico and Baja California. This superterrane, the INS, collided with North America obliquely, in a sinistral/left-lateral sense and caused parts of the INS to be sheared and spread all across the Cordilleran margin. The compressional deformation from the collision created a whole series of margin-parallel thrust sheets and faults, collectively referred to as the Sevier thrust belt, named after the area in Utah where they were first studied and are east exposed. As I mentioned before, this event lasted from around 130 to 80 Ma, and it created two distinct sets of arc volcanics, an older 100-130 Ma series of subduction-related arc plutons, and a 100-80 younger series of chemically distinct plutons that includes the Sierra Nevada and Idaho batholiths that may instead represent the magmatic, plutonic products of slab-break off post-Sevier collision. In the PNW, the INS and its related rocks are represented by rocks like the 93 Ma Mt. Stuart granodiorite, the Easton Metamorphic Suite, the Western and Eastern Mélange Belts, the Nanaimo Group, and of course rocks of Wrangellia exposed on Vancouver Island.
The Sevier Orogeny represented a huge event which accreted a lot of new material to the edge of the continent, and the voluminous syn- and post-collisional magmatism thickened the crust of the Cordillera to an extreme degree. As a result of this crustal thickening, a vast high-altitude “crustal welt” or plateau formed that extended from as far south as Arizona all the way to the Canadian border, and because it would have been similar to today’s Altiplano in the Andes, it has been called the “Nevadaplano”. There are several lines of evidence, from geochemical, to fossil, to geothermobarometric that estimate the thickness of this post-collisional (Sevier) “Nevadaplano” crust at around 67km thick, around the same thickness as today’s Altiplano, but somewhat less thick compared to the Himalayan Plateau/crustal welt, representing a paleo elevation similar to that of today’s modern Altiplano.
Now, my previous post focused on neither of these events, but rather yet another mountain building event that occurred later, from around 70-50 Ma, the Laramide Orogeny. The Laramide Orogeny actually had nothing to do with exotic terranes in the Pacific Northwest. The causes of the Laramide Orogeny remain mysterious, and its effects are seen in NW-SE trending, basement-involved, high angle reverse and thrust faults throughout the intermontane west of the United States, down into Texas and, as well as in Arizona (Maria Fold and Thrust Belt) and into Texas and northeastern Mexico. Unlike the Sevier Orogeny that occurred before it, the Laramide Orogeny is not associated with the accretion of any known exotic terranes, and its associated deformation almost exclusively occured far inboard of the continental margin, as much as 1000km or more. Additionally, unlike the “Thin-skinned” fold and thrust belt-style faults and folds of the earlier Sevier event, where only the weak, younger sedimentary and volcaniclastic layers above the basement are involved, Laramide deformation is what geologists call “Thick-skinned” deformation, involving crustal-scale, high angle faults, which thrust cratonic basement rocks up several kilometers. It is these basement-involved faults that form the cores of all the great mountain ranges of the central and southern Rocky Mountains, and which expose some of the oldest rocks known in the United States. The Rocky Mountains were formed by this event, though they were later buried and rejuvenated as I explained in my previous post.
END PART I
@@amacuro (Part II) But as I alluded to in that earlier post, the jury is still out on what caused the Laramide Orogeny. Unlike the Nevadan and Sevier orogenies, which we know were caused by the collision of North America with the IMS and INS, respectively, the Laramide Orogeny involved no collision with continents or island arcs, and deformation was localized deep in the continental interior, far away from the active margin, as far east as the Black Hills of South Dakota. What’s more, unlike the Sevier Orogeny, which was associated with voluminous magmatism and emplacement of batholiths all along the Cordilleran margin, the Laramide Orogeny is actually accompanied by a prominent “magmatic lull” or “magmatic gap” in which arc magmatism basically shut off during the period concerned. The two major theories of what caused the Laramide Orogeny are “flat-slab Subduction”, and “far-field stresses”. Far-field stresses means the idea that plate-tectonic forces conspire to transmit compressional forces deep into the interior of a tectonic plate, causing it to buckle up, and this has also been implicated in the ancient intracratonic/intraplate orogenies of the US Ancestral Rocky Mountains of the US and Australia’s Alice Springs/Petermann Orogeny. But the majority of researchers implicate “Flat-slab Subduction” as the cause of the Laramide event.
With flat-slab subduction, for some reason, the subducting plate (the ancient Farallon plate, in the case of the Cordillera) changes dip direction from its usual 30-60 degrees, to something much, much shallower, even completely flattening out, such that it is sub horizontal relative to the overriding plate and in physical contact with it. In this way, proponents of flat-slab subduction believe that the physical contact and impinging of the subducting plate underneath the upper plate caused the basement involved faults to form, and flat slab subduction additionally has the benefit of explaining the Laramide Magmatic Gap-a flat slab leaves no mantle wedge which can partially melt to form arc magmatism. Additionally, the process of flattening the slab and the later return of the slab to a normal angle of subduction in the Tertiary would suggest an initial migration of the arc towards the hinterland, before the magmatic lull, followed by a dramatic return to magmatism with the return of the mantle wedge, and with the upper plate heavily metasomatized by the volatile rich fluids released by the oceanic plate in contact with the lower crust of the upper plate-and, indeed, this is exactly what is seen with the Cordilleran arc-a migration of magmatism towards the hinterland, followed by a magmatic gap, followed by a dramatic return to highly silicic, evolved magmatism known as the “Mid-Tertiary Ignimbrite Flareup”. So IMO the flat-slab theory makes a lot of sense. Moreover, we actually know this happens, and we have imaged flat slab subduction under two portions of the Andes occurring today. In fact, one of these flat slab segments is also accompanied by basement-involved, thick-skinned thrusting in the deep hinterland and a magmatic migration followed by a magmatic lull-in Argentina’s Sierras Pampeanas, located over 500km from the crest of the Andes-not quite the 1000+ km of the Laramide hinterland thrusts, but definitely in the ballpark. So it seems clear that flat-slab subduction is a good explanation, but what is not so clear is what could have caused the flat-slab subduction in Laramide time.
So, generally researchers fall into two camps about this: the “aseismic ridge” camp, and the “oceanic plateau” camp. Today’s flat-slab under the Andes and Sierras Pampeanas is caused by the subduction of an aseismic ridge. Aseismic ridges can be formed as either hotspot tracks in oceanic crust, or fossil spreading centers now stuck in the middle of an oceanic plate. Oceanic plateaus on the other hand are vast landforms like the aforementioned Wrangellia, which is no longer of course on the ocean floor, but has been sliced and diced and launched up into the mountains of Vancouver and Alaska. However, there are a lot of good examples of surviving oceanic plateaus, especially from a period of hyperactive magmatism in the Pacific, known as the Cretaceous Normal Superchron, in which some of the largest oceanic plateaus in the world formed, including the Ontong Java, Shatsky Rise, Manihiki, Hikurangi, and Caribbean oceanic plateaus. Oceanic plateaus can form in the middle of oceanic plates as well as at mid ocean ridges, where they often become even more massive, receiving extra magma from the spreading center, as can be seen in Iceland today. Proponents if the oceanic plateau theory for the Laramide flat slab specifically implicate a missing “conjugate” plateau of the surviving Shatsky Rise. These researchers cite plate reconstruction models that seem to suggest that the Shatsky Rise (now in the western Pacific) formed at a spreading ridge, and so as it formed, a conjugate to it would have formed on the other side of the spreading ridge, and the plate reconstructions suggest that this conjugate would have been located at the right latitude, at the right time, to collide with southwestern North America during the Laramide event. Some researchers go further to suggest that an additional “lost conjugate oceanic plateau” (namely the lost conjugate of today’s Hess Rise oceanic plateau, also in the western Pacific) also collided with Mexico during the Laramide, and is responsible for the Laramide thrusts and deformation observed in Mexico’s Sierra Madre Oriental and in southern Texas.
But there is one big problem with the oceanic plateau theory of the Laramide flat slab-every single oceanic plateau that we know of in the geological record that has collided with a continent has ended up as an accreted exotic terrane, shredded into pieces. Wrangellia is a prime example, as is the Siletzia-Yakutat oceanic plateau that collided with Eocene Washington and Oregon (and the Yakutat half of it with Alaska), as is the Ontong-Java Plateau, which is currently colliding with the Australian plate to form the Solomon Islands and Bougainville. In the case of the Ontong-Java plateau, scientists estimate that as much as 80% of the vast oceanic plateau is being subducted, with only the top 7km of crust becoming accreted to the Australian plate. But seismic tomography shows that despite so much of an oceanic plateau being subducted, the angle of subduction is normal, not flat. And the bigger issue with the oceanic plateau theory is that if an oceanic plateau had subducted under North America (or two!), there would undoubtedly be scraped-off remnants of that plateau left behind as exotic terranes, exactly as we see in the case of Wrangellia, Siletzia/Yakutat, and Ontong-Java. But no such terranes exist, not even a hint of them. Therefore I personally find it very unlikely that an oceanic plateau was responsible for flat-lab subduction in the Laramide orogeny, and I am more in favor of the “aseismic ridge” explanation. After all, it is exactly what we see today in the Sierras Pampeanas, and uniformitarian principles like this are the rock (pun intended) on which we build the edifice of geology. But very little is known about the history of such an aseismic ridge, because whatever it was that caused the Laramide Orogeny, it’s long since been subducted, and left very little direct physical trace. The only rocks that might be directly related to this subduction event are a small group of rocks found in Southern California and Arizona, the Pelona-Orocopia-Rand Schist, which are actually several related units of highly deformed high-pressure, low-temperature metamorphic rocks that researchers believe may have been shoved down the subduction factory during the Laramide event. And very recent research suggests that there may even be related rocks all the way up in Washington State-the Swakane Gneiss of the North Cascades. And this leads me back to the Pacific Northwest and the rest of the story of its exotic terranes.
END PART II
@@amacuro (Part III) While the Laramide Orogeny, was occurring, roughly 70-50 Ma, deep in the interior of the continent, there is more and more evidence that some interesting things were happening at the edge of the continent. Namely, there is increasing evidence, ever since Myrl Beck first proposed it as a theory 40+ years ago, that the entire outboard edge of the North American Cordillera was sheared and translated by continental-scale (1500-3000km offset) dextral/right-lateral transform faults, around the same time as the Laramide Orogeny. This theory is known as “Baja BC”, because it is analogous to the translation of Baja CA, today (and much of coastal California state), from its original position 500km further south, in just 12.5 Ma. There is increasing good paleomagnetic data, paleontological data, geological, and geochemical data to support it. However, researchers have had trouble finding the continental scale dextral transcurrent faults, the Baja BC equivalent of the San Andreas. It could be a combination of things, the fog of the past, that translation was distributed across many smaller faults, and or that the faults responsible have been overprinted, invaded, and erased by magmatic activity in the 50 million years since it happened. I am personally a supporter of a more moderate, 1500-2000km offset Baja BC scenario. The result of this translation was that many exotic terranes of the PNW, for example the Mt. Stuart Granodiorite and indeed the entire Northern Cascades Crystalline Core, and probably all the rocks west of it that are its age or older, including Wrangellia, and the rest of the INS, were probably translated from much farther south, to their current northern positions, during this time period.
Last of all in the exotic terrane story of the Pacific Northwest, was the accretion of the Siletzia Oceanic Plateau. Like Wrangellia before it, Siletzia formed out at sea, but unlike Wrangellia, which seems to have traveled thousands of kilometers for hundreds of millions of years, before colliding with North America, Siletzia was formed at a spreading center, just off the coast of the newly-accreted INS, during the early Eocene epoch, and was very probably created by the same mantle plume that site under Yellowstone today, the North American continent having overridden the hotspot in the last 50 or so Ma. Like all large igneous provinces, of which oceanic plateaus are one type, Siletzia was extruded extremely rapidly, and just a couple million years after it formed offshore, it was accreted to the Pacific Northwest, shared between modern-day Washingtin state and Oregon. We know it formed across a spreading ridge, the ancient Kula-Farallon or Kula-Resurrection ridge (it is very difficult to know which for sure, but was more likely the former), because its conjugate oceanic plateau, which spread northward as Siletzia was pushed into west-moving North America, is the Yakutat terrane, geochemically and lithologically identical to Siletzia, which was transported north along the coast of British Columbia, along the Queen Charlotte fault, where it is currently colliding with Alaska and responsible in part for that state’s highest mountains, Denali and the Wrangell-St. Elias mountains. Siletzia marks the final exotic terrane to be accreted to the Pacific Northwest. After Siletzia, the modern day Cascades volcanic arc as we know it was established, and the Olympic subduction complex became imbricated against Siletzia to form Washington’s Olympic peninsula, but those rocks were formed in the trench system just off the coast-they aren’t exotic in the same way as Siletzia, or the INS before it, or the IMS before that. And as the majority of the East Pacific Rise has also subducted beneath North America, and the only remnant of the once-great Farallon plate that could potentially carry exotic terranes on it is the tiny, young Juan de Fuca plate, with the exception of a seamount here and there before the rest of the EPR is subducted, there probably won’t be any more exotic terranes accreted to the PNW for a long time.
To summarize my response: exotic terranes of the PNW are not associated with the Laramide Orogeny that I described in my earlier comment, but with older events, the accretion of the Intermontane and Insular Superterranes in the Nevadan and Sevier orogenies, respectively, and the younger accretion of the Siletzia oceanic plateau. Although there may be some connection to a handful of units in the PNW, such as the Swakane Gneiss, and Laramide “flat slab subduction”, but this work is very recent and the jury is still out.
END PART III
I discovered your channel by accident, just a geology search on youtube and now you are, along with Nick Zentner my favourites to watch. Thanks from the U.K. Cheers.
Thank you for the feedback!
I agree, these two genuinely love sharing their knowledge.
You explain geology better than anyone I've ever listened or watched!
Wow
I've enjoyed your last four geology related videos a great deal and eagerly await more. You are an excellent teacher and have a gift both for the storytelling (content) and the delivery (video production) combined with superb vocal work and a likable, enthusiastic and easy manner. Whole thing is a winner. Thanks. PS: It would be fun to watch you tooling around the rockies in your jeep and explaining them to that Ned Zinger guy.
Wow, thank you!
Having studied my geology at school and university, in the UK, it is very interesting to see basic geological principles being applied to an entirely different continent, on a different part of the earth's crust. I am glad you've stuck to explaining the idea of relative time, the sequence of events, without worrying too much about the later, more sophisticated methods of dating absolute time.
Many thanks indeed, firstly for your enthusiasm, but also for your effective and skilled technique of combining different forms of explanation, using plain old eyeball - visual interpretation, white-board, drone photos and even your Jeep for scale. I hope to watch more of your videos, learning even more about the beds, formations and structures that form your part of the North American continent.
But hey, maybe watch your step on those steep slopes !
Thank you, David
Thank you so much for another wonderful video. I was raised as a fundamentalist young earth creationist, but taking a few geology classes helped me break free from that harmful ideology. Since then I've been in love with geology, and the amazing wealth of detail we find in the rock. I hope videos like yours will bring this realization to others like me, and help them experience the wonder of the world around them.
Thanks for sharing!
You may like the vids by Stellium7 here on youtube, pretty amazing work actually, change the way you think about some of the rocks around you. :)
A lot more fun and believable than mind numbing nonsense of fundamentalists who refuse to be openminded about anything. Welcome to freedom of thought and enjoy the journey.
This was only the second video of yours I have watched and I am already awed and utterly fascinated by geology. You're an amazing teacher. Thank you so much!
Wow, thank you!
What a blessing. ❤
Humans don’t live long enough. Geology is amazing. 🤩
You just made my drives through the Big Horn Basin and South Pass more interesting. Much appreciated.
My cousins own a ranch at the base of the Wind River Mountains outside of Boulder WY. I've camped there and also hiked across the mountain range from one side to the other, ten days in the wilderness. The horse flies were so big they could knock you down and take advantage of you.
thank you
Interesting story! Thanks for watching
Mr. Cook - you make me cry,every time, at the beauty and majestic vistas of America
Mr.Cook, YOU are the BEST instructor I’ve ever heard, I wish all of my instructors were as well educated…
Another fantastic video. Loved it. That second outcrop, along with your diagram and the explanation of how it got that way, had great explanatory power. Really well done. Thank you.
Thanks again!
Love your videos, Myron. Being from Wyoming makes these familiar places and formations even more impressive. Thank you.
Glad you like them!
That was a great way of communicating things so simply. It's all accumulating dust turning to rock, collisions of plates and the aftermath. So simple.
👏🏼 Yayyy!! Outstanding! Your'e a very good teacher. No sensory overload. Your video pans the landscape without dramatic music and fast edits; yes! You've given me some keys, I can't unsee these tilted, layered formations. Your whiteboard ties it together. You got it together man.
Wow, thank you!
Thank you for the time you spent doing this. I am heading to Utah tomorrow for a 4 day solo camp trip and i cannot wait to see what i've learned from your videos.
I really like your channel. This is the kind of info that should be on Discovery Channel and PBS.
Thank you!
I learned a little about geology many years ago, mostly out of books. That was interesting, but getting these in situ lectures in the mountains is much more enjoyable. Thanks from the UK.
I moved to your general part of the country recently and doing so immediately resparked my latent interest in geology. There are so many interesting features in the landscape that are like giant puzzles.
Your videos have been a great aid in enhancing my appreciation for the beauty that can arise from a few simple rules and the passage of time.
I'm glad you enjoyed it.
I love your video and your explanation is clear. I look forward to explore Wyoming soon.
Have fun!
I'm in the process of catching up on your back catalog of videos, it's really fun when I can just go from one topic to another. Keep up the great work educating us! Really, really, really appreciate your work.
Glad you like them!
I just found your channel. I really appreciate your way of offering thoughts from a tiny rivulet forming in your back yard and showing how it relates to the grand canyon. I've shared you with friends. Thank you.
Thanks and welcome!
Thank you for explaining in a simplified way so people like me can more easily grasp what you know.
Glad it was helpful!
Thank you Myron. I really appreciate the time you take to make these videos
Glad you like them!
Outstanding effort being geophysicst I love each and every information. Keep it up ❤❤❤
I agree with Nick! Very well done and great information. Looking forward to your exhumation video!
Awesome, thank you!
Thank you. I love your video. I’m interested in geology, ancient earth deposits, formations and life forms. I became interested in geology when I learned about herkimer crystals found in NY. But, Wyoming is extremely old and interesting as well. Parts of the Eastern Canadian coast are extremely old as well. I can’t believe how much we can learn about our Earth and about history by studying geology.
I'm so glad you enjoyed it!
I'm working my way through Dr Cook's videos and have been inspired to uncover or erode the 50 years of life sediment that had covered my childhood interest in Geology. I have shared videos with many friends who are not science types and they have been able to gain a better appreciation of mountain building and erosion. They don't get as excited about it as I do but that's their loss.
What I admire about Myron Cook is that he is a natural teacher. So often we hear those that can't teach turn the saying upside down. The reality is that very few people have the skills to pass their knowledge on to those with differing abilities to learn. I can't tell you how many professors I had that were either unintelligible due to language barriers, unable to organize and relate their thoughts (just read the chapter), or completely disinterested in teaching lowly under grads. Dr. Cook's Socratic approach teaches his audience to observe, think, and rationalize. When sprinkling the subject liberally with enthusiasm a teacher inspires.
I don't know what Zuckerberg is paying Cook but it's not enough for the quality of entertainment and education that he provides. Personally I have no time for "influencers" but will binge watch Myron Cook every time I am on TH-cam.
Thank you!
I too just discovered your channel. I’m interested in so many different things, I did not know that I was interested in basic geological concepts but your video on the formation of the Gulf of Mexico and especially the delta deposits and fans hooked me. Thank you for introducing me to the fascinating world of geology.
Myron, we love your videos. Keep them coming!
I appreciate that
If you ever come to Colorado on the front range, please come to my area and teach me about the geology here . I live on the Palmer Divide near Devils head.
Colorado has some fascinating geology...maybe someday. Thanks!
Really like your teaching. Enlightening to us amateurs. Thank you.
Very interesting. It must get tricky to look at timing because both tilting and deposition occur at different rates but at the same time.
Your explanation with layers, their thickness, the uplifts and the time it took to erode mile high+ mountains, is very humbling in realization of how insignificant we are in the realm of things. and the worry of global warming. As if we are the only species that is too big and important to become extinct. Thank you very much for your time and teaching method. You are awesome.
Geology humbles me as does space. Thank you for watching!
Another wonderful Video! Thankyou for your wonderful presentation!
Thank you!
I've learned so much already from this video. Thank you!!!
Glad it was helpful!
Another wonderful video by Myron Cook that takes a complex geologic situation and is able to explain in an understand way. Thank you, I have learn a lot.
This channel deserves ten times more views
Myron the moment you tipped that marker board the light bulb instantly turned on for me with your previous image of the two different angles of those formations! That was amazing the way you articulated this lesson with the marker board! I love your channel.
Thank you. This confirms my trying to have people understand the full measure of kinetic force that was imparted from this asteroid collision, on the naturally occurring tectonic activity of the North American plate plate with consideration to the subduction of an eastern Pacific ocean plate of which the Juan de Fuco plate may be the final portion that is known. And that central midwest sea, had been due to a depression of subductive plate collision. Much as is observed with the Gobi Desert depression north of the Himalayas , beyond the Tibetan Plateau. And the reason for the eurasian steppes.
Incredible videos, sir! Absolutely LOVE your teaching methods that make grasping the information so much simpler. Thank you kindly, Professor
You're very welcome!
Wow! Now I understand more of how the Windriver range formed. Basically a giant plug, pluton, of granite exposed when the much, much larger mountain above it eroded away. Fascinating. Thanks.
Love your videos Myron. I knew absolutely nothing about Geology until I started watching your TH-cam videos.
Awesome! Thank you!
Very nice information Myron Cook! Awesome videos and an amazing showcase of these unique locations of nature! Like 99 ✅
Many thanks
I really enjoy the way you teach
Thank you Richard.
I grew up in Green River, Wyoming. I always liked driving through Red Canyon. It's a beautiful place. Lots of cool mountains there to see up there.
Great work sir
Thanks
Great info here. looking forward to more video's from you.
Awesome, thank you!
This is great stuff. I just joined this channel. I Love geology but have no education on this subject expect for Caving. I want to learn more. This channel is providing that for me.
Awesome, thank you!
I learned so much from your video. Most of my life has been in the PNW with some trips through MT and WY. Then I lived in Kansas for 2 years followed by CO for 14 years. On my trips back to WA I would change my route to explore WY more. I have traveled through the places you talked about in this video. It is nice to learn more about what I saw. Thanks very much.
Great teaching style. Your videos are easy to digest and remember.
So beautiful to think about. Definitely going to study geology more
That makes me smile!
This video is so cool! I'm glad I found your channel.
Glad you enjoy it!
I did my field camp out of Dubois (Miami of OH)- way back in 1980. Nice to see the area again. I've always been amazed at the folding of the sedimentary cover as the core was thrust up. The rocks weren't that deep, relatively speaking, so how they folded w/o heat and compression alludes me.
I don't know how i ended up watching your channel. Never searched for such things but I am glad that it happened. Really loved all your videos. Thanks for sharing these great information.
Amazing stuff Myron keep it up!
Thanks, will do!
You make me want to move to Wyoming and get my hands in the earth. Fascinating uplifting sequence, transformation of the land is sooo interesting over long geological time, I could listen to this story forever
I absolutely love your videos, Myron. You had mentioned the Chicxulub crater and I was recently studying about it. I would sincerely love a video from you describing everything you know about the Chicxulub crater. You are a wealth of knowledge and love hearing your thoughts and experiences.
Great suggestion!
Always love when the Whiteboard of Understanding comes out
Everything is good about your videos! Music, camera work, your friendly and accessible yet detailed explanations, your choice of topics, the trusty whiteboard and how well you draw on it, your Jeep driving around way ‘out there,’ and the absolutely spectacular and untrampled landscapes. I did almost tell you to “Be careful!” on that steep slope, though…. 😂
Thanks! 👍
another awesome video! Makes the subject of Geology much easier to comprehend. Thank you!💕
Myron, thank you for all the work and time you put into these lessons you provide for us to learn and enjoy. It shows on your face that you truly love taking us along, but I know you would accomplish more without all of us tagging along.... so thank you! But since you're taking us with you, I have one request. Can I sit up front for the ride back? SHOTGUN!!
Another very good video. Not easy to see/imagine what it was like. Easier to know it after your explanations.
Myron... Been watching several of your vids over the past few months! Really like your 'easy to follow' explaination of issues; also a 'Zentnerd' here! Enjoyed the graphics in explaining the way the Hawaiian Islands were formed, though I knew it before, the 'visuals' prompted me to 'Share' the link to others who were following the eruption of MaunaLoa... I'll be looking for more!! Thanks!
Thank you!
these are the best. I love your work Myron
I LOVE Geology, esp out here in Nevada looking for gold deposits, well used to i don't get around anymore but that's life, but i'll never get tired of watching videos like this and staying up on my knowledge of Geology, this was a fantastic video !
wonderful! looking forward to the next video. your content is the next best thing to being on the field as the best lessons are those that we experience.
Thanks so much!
I REALLY appreciate these videos and look forward to more! I grew up on the coastal plains, became a physicist, and eventually moved to the llano uplift area which caused me to get curious about rocks and now I'm learning a bit about this fascinating subject
My understanding is llano is a really interesting geological area and would love to see what you can teach us all about it!.
Just found your channel, by luck no doubt. What a treat. Ima binge these videos.
Welcome aboard!
Knowledge with a Zen flair....thank you
I will watch all of your videos, it is fascinating to learn geology, Thank you.
I just want to say that I really enjoy these videos.
Great job on your video that made a complex subject understandable that shows the earth was once flat.
Your video are so informative and makes geology so easy to understand. As a student of geology I really love your videos.. Love from India 🇮🇳.......
Great educational show--thanks!
You are an amazing teacher. I learned so much!
Thank you, very intersting lesson, I will try to determine "Relative Dating " of the formations out here in Southern California, hopefully I can find a Stratigraphic Column of this area and answer some questions I come up with as I travel this great location called Imperial County. I had just gotten into prospecting a couple of years ago, but between digs I enjoy the scenery and always find myself trying to reconstruct what happened and why.
Wonderful!
Thank you. I love to sit and consume your videos. Most excellent.
Love your videos, deep time history is fascinating.
Very interesting video. Beautiful scenery as well. Also excellent camera work. Clearly you picked your times to film well.
Myron, it’s been a long time since we were in school together at UW. By chance I’ve stubbles on to your videos and have been enjoying them this past week. Love them. Keep it up fellow cowpoke! Cheers - Rich W.
Thank you so much, Richard, and I hope life has treated you well over these many many years!
@@myroncook Indeed, my career as a geologist in Houston has been good to me and my family. But I’m envious that you stayed in Wyoming. Best regards. Rock on brother! Keep making those videos.
That was a very well explained analysis of geological dating.
Wonderful, thank you again for your terrific videos! I am learning so much.
I have a newbie question though. You kept referring to rock sediment being “deposited “ in layers. This confuses me. Deposited from where? How does that sediment “fall and layer” horizontally? Thanks, hope you or some other knowledgeable person here sees this question.
thicker layers always have gravity take over through time. Like pouring honey on the floor....most of it will end up very flat
@@myroncook
Thank you for responding sir! But where does it come from? Is it primarily from volcanic activity? Or ancient oceans moving sediment around?
By the way I absolutely love your videos and am so glad you make them! Please don’t stop. I got so much more out of a recent trip to Utah; went to Zion, Bryce, Capitol Reef, Arches, Canyonlands (among other travels through Utah’s breathtaking scenery)thanks to the knowledge I have picked up from you.
You rock! (Bad pun intended 😄)
Really great video, easy to understand thank you.
Great stuff - I enjoyed watching and re-learning
Glad you enjoyed it
Lovely video thanks
this is by far my favorite channel
Thank you!
@@myroncook do you think you can do a video on the KT layer boundary sometime?
Have you made a video on the different causes of uplift? Thank you!
You are one cool cat!! I’m jealous of your life in Wyoming! I’ll never understand why I didn’t become a geologist because I get mesmerized by videos like yours. Thanks for keeping it simple for people like me. Oh, and your brothers cool too. I will watch all your videos I just subscribed to your channel. Thankyou!
Wow, thanks!
I'm surprised you have not touched on the Black Hills yet. I use to live on the eastern flanks as a kid, and it always amassed me how the hills cross into Wyoming from South Dakota.
Mountain forming is awesome. We would not really have them if it wasn't for how active our planet is. It is not quick either. Really gives a good example of how much time went into the formation.
Thanks Myron. Great info
The C/T boundry ? I am impressed. I had no idea where ,in the US , i could find one.
Grand Canyon of the Gunnison park, with my roadside geology book, one foot was on the basement rock and the other on a billion years newer rock.
How something so simple can bring a a smile to a face😊
What would happen geologically if the iron rich granite in the northern hemisphere was attracted to the current northern crawl of the magnetic pole? Do you think it will create a "northern Pangea" in the eras to come? I had a thought that Iceland is a nexus point for North America and the EuroAsian continent to come together. Well... this would obviously happen a long time in the future. LOL!
I just love this! You are amazing Myron Cook! Please keep posting your videos, they really make me think!
Great work Myron always excellent illustrations thank you 🙏🙏🙏
My pleasure
Fish the Green at Weeping Rocks annually. Traveled the Continental Divide from NM/MX border to AB, then up to Tuktoyaktuk, NWT on the Arctic Ocean in the last two years. Many AK trips. I’m subbed and love your content!
Thanks for sharing!
myron. love your videos ive told people thayt t i wish i could have been a geologist. i am enthralled with the subject.
If you're ever in Arizona check out barnhardt trail.