Exploring the Precambrian igneous geology of the Ozarks' scenic St. Francois Mountains

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Were there volcanoes in the Missouri Ozarks? How old are the igneous rocks there? Where can you go to explore the Precambrian backstory of the region's scenic St. Francois Mts?
Join us in this episode of our Geology of the Ozarks series as we visit lots of scenic publics land in the Ironton / Pilot Knob / Arcadia Valley area to find and interpret evidence for widespread volcanic activity well over a billion years ago, such as lapilli (volcanic hail), columnar jointing, and massive ash deposits. Long erosion has also exposed a diverse set of related intrusive igneous rocks including various granites and mafic dikes, as well as possibly Missouri's only metamorphic rocks. Follow along as we present a relatively brief summary of an intensely complicated period of Ozark geologic history.
If you're able, please support our work with a one-time or recurring donation via Ko-Fi!: ko-fi.com/ozarkoutsider
Geology of the Ozarks series (playlist): • Geology of the Ozarks
Chapters:
00:00 Introduction
01:14 Ignimbrites a.k.a. Welded ash-flow tuffs (Johnson's Shut-ins State Park)
04:22 Lava flows (Taum Sauk State Park & Hughes Mt. Natural Area)
06:20 Interpretation part 1
07:07 How to support our content
07:27 Subvolcanic granites (Amidon Memorial Conservation Area)
08:18 Country rock (Hawn State Park)
10:27 Ring granites (Knob Lick Towersite)
12:14 Interpretation part 2
14:19 Mafic rocks (Silver Mines Recreation Area)
16:25 Hydrothermal mineral deposits (Shepherd Mountain & Einstein Silver Mine)
18:37 Interpretation part 3
20:23 Younger granites (Elephant Rocks State Park)
21:39 Summary & what's next in the series
Locations visited and featured include:
- Johnson's Shut-ins State Park: shepherdmountainmo.com/
- Taum Sauk State Park: mostateparks.com/park/taum-sa...
- Bell Mountain Wilderness: www.fs.usda.gov/recarea/mtnf/...
- Shepherd Mountain Bike Park: shepherdmountainmo.com/
- Knob Lick Towersite: mdc.mo.gov/discover-nature/pl...
- Royal Gorge Natural Area: mdc.mo.gov/discover-nature/pl...
- Hughes Mt. Natural Area: mdc.mo.gov/discover-nature/pl...
- Amidon Memorial Conservation Area: mdc.mo.gov/discover-nature/pl...
- Hawn State Park: mostateparks.com/park/hawn-st...
- Silver Mines Recreation Area: www.fs.usda.gov/recarea/mtnf/...
- Battle of Pilot Knob State Historic Site: mostateparks.com/park/battle-...
- Elephant Rocks State Park: mostateparks.com/park/elephan...
- Marble Creek Recreation Area: www.fs.usda.gov/recarea/mtnf/...
- Various roadcuts
Credits for images/materials not produced by Ozark Outsider. A full bibliography would overwhelm this section so here we only cite sources of specific materials shown in the video.
- Thanks to all agencies and organizations that provide public domain imagery, footage, and interpretive materials (e.g., National Park Service, US Geologic Survey, Missouri State Parks, Missouri Department of Conservation, State Historical Society of Missouri, Iron County Historical Society)
- Blades & Bickford (1976), Rhyolitic ash-flow tuffs and intercalated volcaniclastic tuffaceous sedimentary rocks at Johnson Shut-Ins, Reynolds County, Missouri, Studies of Precambrian Geology of Missouri, EB - Kisvarsanyi, Report, Investigations of the Missouri Geological Survey, n. 61, p. 91-104.
- Kisvarsanyi et al. (1981) Guidebook to the Geology and Ore Deposits of the St. Francois Mountains, Missouri, Report of Investigations Number 67: share.mo.gov/nr/mgs/MGSData/B... of Investigations/Guidebook to the Geology and Ore Deposits of the St. Francois Mountains, Missouri/RI-067.pdf
- du Bray et al. (2021), Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri, USGS: pubs.usgs.gov/pp/1866/pp1866.pdf
- Hong Kong ash-flow column image: By Minghong - Own work, CC BY-SA 4.0, commons.wikimedia.org/w/index...

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5 июн 2024

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Комментарии : 72

@ozarkoutsider 2 месяца назад

Hi viewers & subscribers! This was by far our most complicated and time-consuming video yet. Lots of fun to research and film, but lots of work to develop and fact-check. We've done our best to present this complex story accurately and accessibly, but feel free to ask any questions right here; not only will this let us answer them, but it'll help us understand what uncertainty might still exist out there. Thanks for your interest, and check out our Ko-Fi account (linked above) if you're up for offering support for this work.

@intractablemaskvpmGy 2 месяца назад

I can tell. The Ozarks are fascinating; from the geology to the people. I've learned some interesting things from your presentations. Keep up the good work!

@robynsnest8668 2 месяца назад

Well done. I was stationed in Missouri and did a lot of exploring and remembered the area well. 40 years later and truly learning still is awesome. Quick question, on the age of this activity, is there a correlation to the kimberlite eruption at the diamond park? If not age, same structure maybe or root cause. Great video and funny "dad" jokes.

@ozarkoutsider 2 месяца назад

Good question! The Crater of Diamonds deposit is much, much younger (somewhere around 100 million as opposed to 1.4 billion) and formed in a completely different geologic context. It's understandable to wonder about a connection between the two, as it's the only other "eruption" event out there, but there definitely isn't one. If you want to learn more, here's a great (if slightly technical) report from the Arkansas Geologic Survey on the site: www.geology.arkansas.gov/docs/pdf/publication/state_park_series/crater-diamond-sps-06-24-8.pdf

@jmonty 2 месяца назад

Thank you for answering the question about the Arkansas diamond connection. My next thought was if there was a connection to Hicks Dome in Southern ILL. It is also igneous in nature.

@ozarkoutsider 2 месяца назад

No, there's no connection to the St. Francois Mts. That structure is a standalone feature of a very different nature, that has more in common with a whole line of crater-like structures that actually stretch across Missouri between eastern Kansas and southern Illinois, which have been variably interpreted as impact craters and cryptovolcanic structures (loosely meaning they're not actually volcanoes but relate to explosive underground movements of magma; it's complicated). We hope to cover those in a video later in this series.

@Dorpers89 2 месяца назад

im in sw missouri and have lots of neat rocks all over our farm

@mrblock1318 Месяц назад

THANK YOU! there was so much mis information on the Ozarks formations (this is just one series of its' formation also) and you have done an amazing job compiling and showing the information as needed. THANK YOU!

@stevewhalen6973 2 месяца назад

Such an amazing geological life span these mountains have seen.

@TerryBollinger 2 месяца назад

FANTASTIC video!! While I'm familiar with the post-unconformity geological history of my home county, Madison, and knew there had been some huge ash flows earlier than that, I never heard of the three gigantic Precambrian calderas! This must not have been known when I knew the former State Geologist, Tom Beveridge. I've looked out from Knob Lick over that very plain with the hills north of Fredericktown easily visible in the distance and had NO IDEA I was looking at a caldera rim. WOW! 15:50 I know both of those mafic dikes - this one and the earlier one from Silver Mines - very well. A small story from the construction of that roadcut: A friend of mine in high school had a house near the old 72, and his father was watching out his front window as they blasted in the distance, sending boulders visibly up in the air. Suddenly, one bolder went straight up, started looking... larger... and larger... and landed in the middle of their station wagon in the front driveway. No one was hurt, and the station wagon nicely cushioned the fall of the poor boulder, which was having an especially bad day. Needless to say, the road department stopped using illegal-sized charges after that. Tough rock, rhyolite! I would always point out the south exposure of the dike cut by 72 to friends, telling them how hundreds of millions of years ago, it was a streambed running down the side of a barren post-nonconformity hillside. At multiple scales, many fossil landscapes were buried under miles of dolomite and then re-exposed by the Ozark Dome, as I suspect you will address in your next video. The granite at the edges makes so much more sense now that you showed those calderas! Wow! Again, thanks!

@ozarkoutsider 2 месяца назад

Wow, Terry, that's a fantastic story about the 72 cut getting blasted. We love hearing stuff like that, details we can't learn otherwise. Just to be clear, the caldera basin you can see from Knob Lick is off to the south and west of the towersite; I wasn't sure from your phrasing if you thought it was to the north and east. Interestingly, the du Bray (2021) paper from which those caldera maps are drawn cites studies going back as far as 1962 that defined the caldera boundaries, though the idea may not have percolated beyond specialists. Since you've been to the Silver Mines area, it's especially fun to explore the shut-ins there and realize that the river is essentially carving its way through the remnant of a caldera rim (defined there by a ring granite) to escape the basin, after entering the old caldera from the north near Knob Lick. So cool.

@TerryBollinger 2 месяца назад

Thanks! And, yes, I was talking about the view south and west towards Fredericktown. The ring of hills north of Fredericktown forms the edge of the caldera. I've noticed that abrupt transition driving south toward Fredericktown my entire life, but I did not know why. Now I do! I love the Silver Mines Valley. In retrospect, the sharpness of the valley makes sense if it's part of the edge of a caldera. Wow! There are black magnetite and ilmenite sands in eddy current areas around trees in the park where the old bridge used to be, but I’ve never found these minerals immediately below the mine area. I always wanted to track down the source of those sands, which may be a dike in the river itself. If you grabbed any quartz samples, some of the yellowish tint is topaz. It gave the miners a hard time since their bits were wearing out much faster than they were supposed to. There is also wolframite there. The government briefly reopened the mines during World War II to mine tungsten. My son found the largest (fist-sized) chunk of almost pure sulfide minerals I’ve ever seen from the tailings. The find annoyed his older rockhound cousin, who had looked for good pyrite specimens for many years and never found one so large. It sits on our piano. The Einstein mine is above the dam. If the one you went to was below it, that's a different one they've made more accessible. I don't recall its name if it had one. A tiny, classically local nitpick: It’s “town” versus “ton.” We kept our “w,” but Farmington lost theirs. (Silly northerners, they can't keep track of their w's!)

@ozarkoutsider 2 месяца назад

Thanks on the pronunciation correct, I'm the "outsider" in Ozark Outsider and am always fearful of slipping up on that regard. And Joanna's from the other end of the Ozarks! With regard to the Einstein mine, the Missouri Geologic Survey map and guide we were drawing on there clearly labels the Einstein mine as the adit just downstream of the dam, the site that now has the more modern wooden cover we showed and was the former site of the large processing complex we also showed (and the original use of the dam). That mine did have multiple access points across the hillside, as drawn in the cross-section diagram we showed. EDIT: The publication is linked in the video resources (look for the map on p 29 and various photo labels/text on surrounding pages); I tried linking it here as well but RU-vid's clunky comment system couldn't handle the URL.

@TerryBollinger 2 месяца назад

@@ozarkoutsider A fantastic resource; thank you! RU-vid messed up your link by not recognizing blanks, so here's another percent-encoded (no blanks) try at the same link: share.mo.gov/nr/mgs/MGSData/Books/Reports%20of%20Investigations/Guidebook%20to%20the%20Geology%20and%20Ore%20Deposits%20of%20the%20St.%20Francois%20Mountains,%20Missouri/RI-067.pdf The above link does seem to work. RU-vid then asks if you want to leave RU-vid and create a new tab. If you say yes, the report pops up. I seem to have given away a local secret, as the adit I was referring to is not on this map! A geology student at Rolla once gave me a considerably older report. In that one, the unmaintained, little-known adit above the dam on the same west side as the well-known (and well-maintained) River Tunnel adit was labeled "Einstein Mine." I thought it might be the Gabriel Shaft of this map, but it's an entrance much like the River Tunnel, not a shaft, and is also closer to the dam and river. Unlike the park-gated River Tunnel adit, this lesser-known entrance is (or used to be) open and accessible, provided you know where to find it. I am embarrassed to admit that my nephew has gone pretty deep into it in the past, which was ill-advised then and, I'm sure, even more risky now if it's still open. If my nephew had his way, he'd reopen that entire mine. We've had long talks about the politics and bad management of the early operation, and he thinks it's still a viable mining site. He may well be correct.

@AvanaVana 2 месяца назад

This is one of the best and most comprehensive overviews of this chronically-underrated geologic gem that I’ve ever seen. Submitted to the Earth Science Online Video Database!

@SB-qm5wg 2 месяца назад

An incredible tale from deep history

@dianespears6057 2 месяца назад

Very interesting and helpful. Thank you.

@jbroshar87 2 месяца назад

thank you for this. Ozark geology is so under represented

@db_illin 2 месяца назад

This is so interesting! Awesome video

@Idrinklight44 2 месяца назад

Great video!!! Didn't know that about elephant rock granite being younger! I really like Missouri's geology.

@Idrinklight44 2 месяца назад

Royal gorge is another great visit!

@blakeantos1301 2 месяца назад

Wow! Good timing. Heading to the area for the eclipse this weekend and I like to learn about the geology of places before I hike. Thanks for the great info!

@ozarkoutsider 2 месяца назад

If you recognize us, say hello!

@hgbugalou Месяц назад

I love what you are doing here. Please consider doing a video on the new New Madrid seismic zone. I've yet to hear a geologists take on latest theory about the farralon plate remnant slab sinking into the mantle being the stress source for seismicity for the reelfoot rift.

@ozarkoutsider Месяц назад

Thanks! It's on our long-term list but we have some work to do before we can discuss that intelligently.

@czarnick123 14 часов назад

This is incredible youtube. Outstanding research and presentation. Really enjoyed and learned a lot. Excited for the next one! Do yall ever do tours?

@ozarkoutsider 9 часов назад

Thanks so much! Hope you'll check out the entire series. We wish we had more time to work on these and get them out faster, but we're self-employed and juggle a lot of commitments. The tour question is one we've discussed often. The basic barriers are (a) the sheer size and relatively low tourist and local population density of the Ozark region, (b) the modern standards for liability when you do anything, and (c) the somewhat restrictive policies of our public-lands agencies on for-profit activities on those lands. In principle we'd love to do it; in practice we've yet to see a clear path forward that would pay for itself. Starting our Ko-fi account to accept simple tips for our work was a small step in the direction of looking for ways to make this project more self-supporting. Again, thanks for your awesome feedback!

@selcouthconcepts 2 месяца назад

These videos are phenomenal! They are the best Ozark Geology videos I have found online! I'm subscribed and looking forward to the next videos!

@am2dan 2 месяца назад

Thanks for the _great_ video! You hit a lot of my favorite spots, and I learned a lot. I _almost_ majored in geology ages ago. I went in an entirely different direction professionally but maintained the interest. Among my books are Unclesbay and Vinyard, Beveridge, and others on Ozark geology. And I hung out with a lot of geology/geologic engineering types in the caving club at UMR before it was MST but after it was MSM. :-)

@ozarkoutsider 2 месяца назад

You sound like our kind of follower, thanks for watching!

@MothShadow Месяц назад

Hey! Who is this? LOL, what years were you there? This is Rob / Hobbes...

@Idrinklight44 2 месяца назад

I really really enjoy Hughes Mountain

@ianbrown8408 Месяц назад

Love the video! Will have to rewatch it to get all the details. I'm up in eastern Ontario, Canada and live by what I believe is a resurgent caldera, with another volcanic crater near by. People here have no idea. Good to see somebody else that gets excited about very old volcanos.

@BenSHammonds 2 месяца назад

this was fascinating, I knew of the volcanic history in southwest Arkansas (Crater of Diamonds State Park) but never knew of this in Mo.

@bobaloo2012 Месяц назад

Thanks for the video. I grew up in the hills around Knob Lick many years ago and always wondered about the geology. I remember digging up big chunks of galena and wondered how such a thing could occur in a state known for its limestone.

@ozarkoutsider Месяц назад

For what it's worth, a lot of Missouri's galena isn't directly related to the St. Francois igneous activity. We'll be covering the broader question of mineral resources later in the series, but the short answer is that minerals like lead were also often deposited within the limestone much, much later through a different form of hydrothermal activity. That's why there are lead belts that aren't centered on the igneous areas, like in southwest Missouri. It really depends on context. Thanks for watching!

@2Goiz_1ShanDA 2 месяца назад

Now do Cincinnati... That's where geology goes to die!❤ taste the total frustration & challenge that edu. Be alive 💫. Great editing guys🤙

@billwilson-es5yn 2 месяца назад

I wasn't aware of all that mess being there. Thought it mostly flat like the rest of the region that the Mississippi River ran thru. Their age should predate the rifting that detached Amazonia and created the two fail rift zones in Southern Oklahoma and the nearby Reelfoot Rift. The Mid Continent Rift was already present. I've been watching Myron Cook's videos to get a better idea of why there's so much oil and gas here in East and West Texas.

@ozarkoutsider 2 месяца назад

We're going to stay out of tectonics discussions in the comments for now, leaving that for a later video. The Ozarks aren't the only rugged terrain bordering the Mississippi, though, check out what's called the Driftless region of southwestern Wisconsin.

@garyb6219 2 месяца назад

Wonderful video. Thanks. I'm sure you guys will be watching the eclipse, especially with totality going right over the Ozarks. Hopefully you'll share some pics or video in an upcoming post. I saw the total eclipse in 2017 and it was amazing!

@garyb6219 2 месяца назад

I got some nice gneiss from my niece in Nice. Sorry...

@ozarkoutsider 2 месяца назад

LOL well done! Or should I say, niiiiice.

@ozarkoutsider 2 месяца назад

Overall we'd rather focus on the experience for ourselves as we're not sure we could take any footage that would be as good or better than lots of other peoples' with better equipment. We kinda want this to be a personal joy, it's such a rare event. We did get to view the 2017 one as well and very much intend to repeat the wonder.

@alanpeterson4939 Месяц назад

I retired to that area. You can easily see the Great Unconformity at the road cut at Hwy 67 and Hwy E on the southwest side of Fredericktown. The road cut has an intersection of red/ dark purple rhyolite, overlain by Lamotte sandstone, visible on the south side of the road cut.

@ozarkoutsider Месяц назад

Yes, that will be one of the sites featured in the upcoming video.

@alanpeterson4939 Месяц назад

Another interesting spot (in my opinion) is some flat rhyolite, just below the dam at Marble Creek Park, that appears to have small flow waves frozen in time. I’ve spent fifty years wandering those hills.

@ozarkoutsider Месяц назад

That sounds cool, we didn't notice it when we were there but we were focused on tracking down the mafic outcrops further uphill from the dam.

@robynsnest8668 2 месяца назад

@4:18 epic dad joke. Lol. And then @10:07 lmao. This is an awesome video.

@ozarkoutsider 2 месяца назад

We do enjoy our puns...

@robynsnest8668 2 месяца назад

@@ozarkoutsider they are punny. Two thirds of a pun are p u.

@jbroshar87 2 месяца назад

Also, consider visiting Grand Gulf please!!!

@ozarkoutsider 2 месяца назад

We've been there, neat place! Not sure when it'll feature on the channel, there are just too many neat places to cover.

@edwarddesoignie1194 2 месяца назад

So why is there a hot spot in middle of the North American plate and has it drifted like the Yellowstone hot spot?

@ozarkoutsider 2 месяца назад

We avoided discussing the tectonic setting because it would have lengthened the video unacceptably. But the short answer is the St. Francois Mt. volcanism wasn't a hot spot like Yellowstone but part of a much larger tectonically active zone, most of which is now buried deep beneath the overlying sedimentary rocks (see the previous video in this series). There actually seems to be some ongoing disagreement about just what WAS going, another reason why we decided not to venture into it. Good question!

@twotone3471 2 месяца назад

Think the best analogy to the St Francois volcanic period is The Phillipines of today. We know that the Volcanoes when active were part of a Exotic Terrane called Yavapai that collided onto North America not long before the Greenville Orogeny. A similar story played out in Australia's Southeast where a similar collision with a Exotic Terrane formed many, many calderas that hide in plain sight.

@ozarkoutsider 2 месяца назад

Thanks for your thoughts, but we're making an executive decision to not get sucked into tectonics discussions in the comments. It's just too complicated and would take too much time. We're hoping to cover the collective tectonic history of the region later in the series.

@twotone3471 2 месяца назад

@@ozarkoutsider No problem, after all we don't know exactly where Yavapai came from before hitting North America as far as I know. But when this area is called "The North American Craton" when it's barely older than the Grenville Orogeny (relatively speaking) is something odd to me when pretty much everything south of Minnesota was added on piece by piece.

@alanpeterson4939 Месяц назад

There are two very distinct rhyolites in the St. Francois Mountains, pink, and dark purple. I have always wondered, which one is older, and what is the cause of the color difference?

@ozarkoutsider Месяц назад

Great question and one I don't think we can answer. Speaking very loosely, I feel like many outcrops of the Grassy Mt. Ignimbrite tend to be pinker, almost light orange (Knob Lick is a good example), while other rhyolites (like those in the Taum Sauk area) tend to be that darker purple you describe. If there is a consistent pattern, it could have to do with subtle differences in the source magma or even eruption style. But it's not something we're equipped to give a definitive answer on, sorry.

@shieldofthebear1784 2 месяца назад

I have samples of what I believe may be lava deposit from Poplar Bluff, MO. HOW CAN I FIND OUT FOR SURE¿

@ozarkoutsider 2 месяца назад

Thanks for the question! So it really depends on what exactly you have and where. If you're looking at bedrock near Poplar Bluff, the answer is no, it's not igneous of any kind, lava or otherwise. If you're looking at loose material in a river, like the Black or St. Francis Rivers, it's possible, because both of those drainages reach up to areas of igneous bedrock exposure and could have carried some material down that far. One suggestion I always consider when something thinks they've found lava or other igneous material in an unusual location, is whether it's actually industrial slag of some kind, which is pretty easy to find in certain locations (especially along transportation routes). I'd suggest checking out our video on how to use GeoSTRAT, Missouri's online geologic mapping server, which you can use to look at geologic maps and compare what you're seeing to what bedrock is mapped in the area AND where drainage basins reach: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-PP2ky8mz3NE.html

@shieldofthebear1784 2 месяца назад

@@ozarkoutsider thank you

@psikeyhackr6914 Месяц назад

This frozen lava is from Missouri. Show me!

@missourimongoose8858 2 месяца назад

Haha i used to get stoned at the knob lick lookout tower lol they took out one of the stair sections back in the day so you dont get to see all the awesome artwork at the top anymore unless you climb up the side which i dont recomend Edit: you were within a few miles from where i grew up lol we own property from deer run lake to coppermines road

@ozarkoutsider 2 месяца назад

Gotta say, I was pretty relieved the tower was blocked off above that halfway platform...

@missourimongoose8858 2 месяца назад

@@ozarkoutsider another cool place that's close to there is mill stream gardens if your ever back to the fredericktown area, and you should eat at the pig if you get a chance it's awesome

@ozarkoutsider 2 месяца назад

Yep, we explored Millstream as part of this filming trip, but it didn't make the final cut. We did get some fun footage of kayakers running the rapids.

@missourimongoose8858 2 месяца назад

@@ozarkoutsider ya they had the kayak Olympics there when I was in high school