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The Geology of Petoskey Stones · PlanetGeo: The Geology Podcast

• 0:02
  SPEAKER_00: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:15
  SPEAKER_00: It's never happened.
• 0:17
  SPEAKER_00: Um Chris.
• 0:20
  SPEAKER_00: Christopher Bull, as my friend.
• 0:22
  SPEAKER_00: We're gonna talk about Potoski Stones today.
• 0:25
  SPEAKER_00: Potoski stones are if you're a Michigander, we probably have some Michiganders out there who are listening to this podcast.
• 0:33
  SPEAKER_00: You know what a Potaski stone is.
• 0:34
  SPEAKER_00: If you pro most likely, if you live in the state of Michigan, you know what a Potoski stone is.
• 0:38
  SPEAKER_00: I would I think that's a pretty safe bet.
• 0:40
  SPEAKER_00: Or you've heard of it at least, right?
• 0:42
  SPEAKER_01: I would think so.
• 0:43
  SPEAKER_01: If I mean it is our state stone.
• 0:45
  SPEAKER_01: I mean, like, and I hate that, I hate that verbiage stone.
• 0:49
  SPEAKER_01: It's our state fossil or it's whatever, but it's it's gotta be something else, right?
• 0:55
  SPEAKER_00: Patoski stones are amazing.
• 0:57
  SPEAKER_00: I've spent ever since growing up, you know, I I grew up going in the summers up to the northern parts of Lake Michigan, walking along the beaches where Potaski stones are really prevalent, and it is just like in me.
• 1:10
  SPEAKER_00: When I'm walking along a beach, I'm looking down, no matter what, even if I'm not on the stores of Lake Michigan, I'm looking for Potoski Stones just because it's kind of this innate thing.
• 1:18
  SPEAKER_00: They're a beautiful, beautiful fossil, beautiful, beautiful stone.
• 1:21
  SPEAKER_00: That's the state stone of Michigan, and collectors love this, you know, casual everyday beachgoers.
• 1:27
  SPEAKER_00: It's a fun thing to do to go look for Potoski stones.
• 1:30
  SPEAKER_00: It's great.
• 1:31
  SPEAKER_01: It absolutely is fun to do.
• 1:33
  SPEAKER_01: I have a I have a ton of them, you know, smaller pieces here and there and so on.
• 1:37
  SPEAKER_01: Um, hey Jesse, before we get into the geoscience of Potaski stones, we haven't done intros in a long time.
• 1:43
  SPEAKER_01: So can we real quick just take a second?
• 1:45
  SPEAKER_01: Like so you gotta do it quicker.
• 1:49
  SPEAKER_01: We'll be quick.
• 1:50
  SPEAKER_01: You are Dr.
• 1:50
  SPEAKER_01: Jesse Rymanck, you and I we have we go on the doctor.
• 1:54
  SPEAKER_00: Emphasis on the doctor, Chris.
• 1:56
  SPEAKER_00: You gotta say Dr.
• 1:57
  SPEAKER_00: Jesse Rymanck.
• 1:58
  SPEAKER_01: Yes, yes.
• 1:59
  SPEAKER_01: I roll my eyes when I say it, but you you and I go way back because you're one of my former high school students.
• 2:05
  SPEAKER_01: You were in one of my high school science classes, one of my earth science class.
• 2:09
  SPEAKER_01: And Jesse, after you left me, you eventually went on.
• 2:16
  SPEAKER_01: Yeah, yeah.
• 2:17
  SPEAKER_01: I love that.
• 2:19
  SPEAKER_01: Uh you actually went on and got your PhD in Canada, and now you landed, I think, the dream job to me.
• 2:27
  SPEAKER_01: Like you are a professor of geoscience at Penn State University, which is one of the you know most esteemed geoscience programs in the country, in my opinion.
• 2:37
  SPEAKER_00: So it's a pretty good gig, yeah.
• 2:39
  SPEAKER_00: And I'll expect you to refer to me as uh I think you should start calling me Professor, uh Professor Rhyming throughout this podcast, actually.
• 2:47
  SPEAKER_00: Okay, real quick, Chris Bullheis.
• 2:49
  SPEAKER_00: As you said, my former high school teacher, you've been teaching high school at a really elite level.
• 2:53
  SPEAKER_00: You've won national, regional teaching awards for earth science geology.
• 2:57
  SPEAKER_00: You run a geology field course in the summer.
• 2:59
  SPEAKER_00: You effectively teach AP geology, college-level geology.
• 3:03
  SPEAKER_00: You've built an astronomy course, and you know, you and I have a deep passion for rocks, and we've gone collecting a lot together in Michigan and out of Michigan.
• 3:11
  SPEAKER_00: We both grew up in the same you know area in Michigan.
• 3:13
  SPEAKER_00: And so, so that kind of leads us nicely into Potaski Stones because Potoski stones are on the collector's bucket list, I think, especially in this like part of the Midwest.
• 3:23
  SPEAKER_00: You know, if you're in the the upper nort the upper Great Lakes states, you're probably aware of Potoski Stones.
• 3:29
  SPEAKER_00: You've probably chased them down if you're at all interested in rocks.
• 3:31
  SPEAKER_00: If you go to rock shops in Michigan, in Indiana, in Wisconsin, you're gonna find Potoski stones.
• 3:37
  SPEAKER_00: Like it's getting unavoidable.
• 3:39
  SPEAKER_00: And actually, if you go to art shops, like little you know, art artist shops, absolutely often stuff made of Potaski stones in there, too, right?
• 3:47
  SPEAKER_01: Yeah, that's right, because it's so pretty, one, and then it's it's a soft rock, and so it's easy to do things with, like from a polishing perspective and jewelry making's perspective.
• 3:59
  SPEAKER_00: That's a really good point, Chris.
• 4:00
  SPEAKER_00: That we should definitely like emphasize how soft it is.
• 4:03
  SPEAKER_00: How you can you can polish this rock with just wet, dry sandpaper in your hands.
• 4:08
  SPEAKER_00: Like you just rub it around your hands with some wet, dry, you know, get the sandpaper wet and sand it down.
• 4:13
  SPEAKER_00: You can actually polish this really, really beautifully.
• 4:15
  SPEAKER_00: Um, Chris, I'm gonna let's turn to image number one.
• 4:17
  SPEAKER_00: Let's turn the images on here a minute and turn to image number one.
• 4:20
  SPEAKER_00: This is just a this is a photo of what a an unpolished Potoski stone looks like.
• 4:26
  SPEAKER_00: This is just to kind of give you a sense of the scale of these things.
• 4:28
  SPEAKER_00: So we got centimeters here in in the units, and we're looking at the scale of the fossilized, this is a fossilized coral, and we're seeing this white outer rind with the inner kind of darker gray, darker sort of uh tannish gray, maybe even color.
• 4:44
  SPEAKER_00: I don't know if that's appropriate, but this is what it looks like dry and not polished.
• 4:48
  SPEAKER_00: So this is like the least interesting version of a Potoski stone.
• 4:52
  SPEAKER_01: Yeah, yeah, but it's my to me, it's my favorite.
• 4:54
  SPEAKER_01: It's my favorite flavor of the Potaski Stone.
• 4:58
  SPEAKER_01: I love that.
• 4:59
  SPEAKER_01: Um, yeah, it forms this.
• 5:00
  SPEAKER_01: Uh when I look at that, I think honeycomb.
• 5:03
  SPEAKER_01: You know, it forms this these kinds of like hexagonal sides to it.
• 5:07
  SPEAKER_01: And and so yeah, today we're gonna get into why does Potoski stone look like this?
• 5:12
  SPEAKER_01: What were these organisms?
• 5:15
  SPEAKER_01: What setting did they thrive in?
• 5:17
  SPEAKER_01: Because that that all ties back into the geologic story of the great state of Michigan.
• 5:22
  SPEAKER_00: It's a and it's a it's a cool story.
• 5:24
  SPEAKER_00: It ties in a whole bunch of different stuff here, um, from you know, Devonian history of the region to this you know exposures today in Michigan.
• 5:32
  SPEAKER_00: But the Potaski stones are really they're they're found all along the shores, especially on the Lake Michigan side, so the western side of Michigan.
• 5:40
  SPEAKER_00: They're found in the in the sort of gravel along the shores there, gravel and pebbles.
• 5:44
  SPEAKER_00: Um, they don't get huge, so you're not gonna find a massive boulder of Potaski.
• 5:49
  SPEAKER_01: You might hold on, hold on, Jim.
• 5:52
  SPEAKER_01: Hold on.
• 5:54
  SPEAKER_01: So there's a law apparently that you're not allowed to collect a sample that is more than 25 pounds.
• 6:01
  SPEAKER_01: And a few years ago, this guy found a 90-pound chunk of Potaski stone and he posted it on Facebook.
• 6:09
  SPEAKER_01: Yeah, posted it on Facebook, and the DNR came and took it.
• 6:13
  SPEAKER_00: Oh my goodness, really?
• 6:14
  SPEAKER_00: Yeah.
• 6:15
  SPEAKER_00: Oh, so DNR is the Department of Natural Resources in Michigan.
• 6:18
  SPEAKER_00: Um okay, so this caught enough online traction that they came and took it from him.
• 6:22
  SPEAKER_00: That's very funny.
• 6:23
  SPEAKER_00: I so I'm aware of this rule, Chris.
• 6:25
  SPEAKER_00: It's designed for rock collectors, basically, on the beaches, because the you can take some samples, like check your local areas, because some of these areas are in national national seashore, and it's a completely different ballgame there.
• 6:36
  SPEAKER_00: But in many areas, you can collect little pieces, but you can't collect more than 25 pounds per person per year.
• 6:42
  SPEAKER_00: So obviously 90 pounds exceeds that by quite a lot.
• 6:45
  SPEAKER_00: So that's a really funny story.
• 6:47
  SPEAKER_01: Um and and the the the person did not intend to break the law at all.
• 6:52
  SPEAKER_01: This was just, you know, he was proud as can be.
• 6:55
  SPEAKER_01: Like, hey, everyone, look at what I found.
• 6:57
  SPEAKER_01: And took a little bit of heat for it.
• 6:59
  SPEAKER_00: So I think Chris, we should we should mention that you know the these things are often kind of small.
• 7:03
  SPEAKER_00: And here's another photo of these things stacked on, you know, Potoski stones stacked on top of one another.
• 7:08
  SPEAKER_00: They have a lot of different character, uh different color characteristics to them, but this the same hexagonal pattern.
• 7:13
  SPEAKER_00: You'll often find them this size.
• 7:15
  SPEAKER_00: Like if it's to if the rock is totally Potaski, this fossil, they'll usually be this size.
• 7:21
  SPEAKER_00: If you start getting bigger, you'll have you know one corner that is fossil.
• 7:24
  SPEAKER_00: You won't have the whole rock that's often fossilized.
• 7:27
  SPEAKER_00: It's really rare to find a a monster one, and that is because of the history of these rocks.
• 7:33
  SPEAKER_00: These are these are fossilized coral and colonial corals.
• 7:37
  SPEAKER_00: And so those those colonies did not grow to the size of house-sized boulders often.
• 7:42
  SPEAKER_00: They're kind of smaller colonies that then became fossilized.
• 7:46
  SPEAKER_00: So that's kind of the the story behind just the sizes that you find here.
• 7:50
  SPEAKER_00: But Chris, paint us a picture.
• 7:52
  SPEAKER_00: Like we, you know, every rock tells a story.
• 7:54
  SPEAKER_00: What's the story that these rocks tell us about the ancient planet?
• 7:58
  SPEAKER_01: So you're talking about like the paleocetting?
• 8:00
  SPEAKER_00: Is that what you're what you're asking about the new forming in, like set the scene for us?
• 8:04
  SPEAKER_01: Yeah, so I I think that yeah, that's a good place to start.
• 8:06
  SPEAKER_01: So you're talking about five years old at this time or something?
• 8:10
  SPEAKER_01: Yeah, I knew that was coming.
• 8:11
  SPEAKER_01: Yes, I was 370 million years old at the time.
• 8:15
  SPEAKER_01: Um so yeah, this was in the middle Devonian, and so this is you know in the time frame of 375 to 360 million years ago.
• 8:24
  SPEAKER_01: And the region that is now northern Michigan, and I'm gonna do this.
• 8:28
  SPEAKER_01: Uh Jesse, is this is this right right here, like this?
• 8:31
  SPEAKER_01: Is that it's right.
• 8:33
  SPEAKER_01: Is this yes?
• 8:34
  SPEAKER_01: Is it is it correct?
• 8:35
  SPEAKER_01: Okay, all right.
• 8:37
  SPEAKER_01: We're talking about like wet up in this area, right up in here.
• 8:40
  SPEAKER_01: This is the part of Michigan that we're talking about because Michigan is the mitten state.
• 8:44
  SPEAKER_00: Yeah, for those are Chris is holding his hand up to the camera, uh, which is the classic.
• 8:48
  SPEAKER_00: If you're not if you're not familiar, is the classic Michigander person from Michigan thing to do?
• 8:53
  SPEAKER_00: Is like when you ask where you're from, hold up your hand because the state looks like a hand, so you point out.
• 8:58
  SPEAKER_01: It's yes, that is so common that you know I run into a lot of people from out of state, and they always ask where I'm from, and you know, we're talking, and so I got I got sick of like trying to pinpoint exactly where southwest Michigan is, uh, you know, where I'm from, and so I got it tattooed on my hand.
• 9:14
  SPEAKER_01: So I have a star on my hand.
• 9:16
  SPEAKER_01: Hold it up to the camera, Chris.
• 9:18
  SPEAKER_01: You're holding it up properly.
• 9:19
  SPEAKER_01: There, there you go.
• 9:20
  SPEAKER_01: Chris's got a star right in there, yep.
• 9:22
  SPEAKER_00: In Hudsonville, Michigan, star on the hand.
• 9:25
  SPEAKER_00: That's amazing.
• 9:25
  SPEAKER_00: That's right.
• 9:26
  SPEAKER_00: So, where okay, back to the Potaski.
• 9:28
  SPEAKER_00: If you hold your hand up, you hold your hand up, your thumbs to the right.
• 9:31
  SPEAKER_00: Uh the Potoski stone rocks are exposed up in your fingertips.
• 9:35
  SPEAKER_00: Not quite your fingertips, but your your you know, your top knuckle there.
• 9:39
  SPEAKER_00: That's right.
• 9:40
  SPEAKER_00: And so, Chris, I'm gonna skip ahead an image here.
• 9:42
  SPEAKER_00: And again, we can if you're listening on the podcast or if you're on YouTube and you want these images, we've got them on the app.
• 9:47
  SPEAKER_00: You can go to our app and the visual podcast series, we've got these images displayed there too, um, just under the Planet Geo stuff there.
• 9:53
  SPEAKER_00: So download first link in your show notes.
• 9:55
  SPEAKER_00: But Chris, this is setting the scene.
• 9:57
  SPEAKER_00: Like, what did the world look like?
• 9:58
  SPEAKER_00: I I love, and you're you're the best at this at painting pictures that the rocks tell us.
• 10:03
  SPEAKER_00: So about that.
• 10:04
  SPEAKER_01: But so this is 375 to 360 million years ago, and this part of Michigan at the time was uh warm, shallow sea, and and that's pretty typical because the Devonian period is generally considered to be warmer than before that and after that.
• 10:22
  SPEAKER_01: So this was a warm time, and so during this time then sea level was higher all across the board for the for the most part.
• 10:29
  SPEAKER_01: So um well, Chris, let's look at this image here a minute.
• 10:32
  SPEAKER_00: I I you're exactly right, and we have to visualize.
• 10:35
  SPEAKER_00: Like, think about think about the continent.
• 10:37
  SPEAKER_00: We've done episodes on hypsometry or the hypsymetric curve.
• 10:40
  SPEAKER_00: Think about what happens if you flood the continents.
• 10:43
  SPEAKER_00: Think about what happens if you raise sea level a kilometer or let's say 500 meters.
• 10:47
  SPEAKER_00: Most of the eastern part of North America and actually all of the Canadian shield is very flat and very close to sea level within a couple hundred meters.
• 10:56
  SPEAKER_00: So if you just raise it a couple hundred meters, you flood the entire part of the continent.
• 11:01
  SPEAKER_00: And the only thing that's left sticking up is the high relief stuff.
• 11:03
  SPEAKER_00: You know, once you get out to the Rockies or once you get out into the western United States, that's high relief.
• 11:07
  SPEAKER_00: So this image is a really good sorry, go ahead.
• 11:10
  SPEAKER_01: No, I was just gonna say that's a really good point because this is a part of the broader Michigan basin.
• 11:15
  SPEAKER_01: You know, Michigan Basin is like this this down warped, but it's it's uh it's like a circular sincline or like a big broad salad bowl sitting right side out together.
• 11:25
  SPEAKER_01: You know, that's the that's the geology of of Michigan.
• 11:29
  SPEAKER_01: And so this was allowed, this is this like subsiding, this kind of sinking intracretonic basin that was sinking due to the sediment that you know it was like a this ideal setting for a really warm, shallow sea.
• 11:45
  SPEAKER_01: Yeah, yeah, yeah.
• 11:45
  SPEAKER_01: Totally.
• 11:46
  SPEAKER_01: And the deposition that was happening then just allowed for more deposition because of all the weight of the sediment uh that was accumulating.
• 11:54
  SPEAKER_00: And so Chris, again, this is sitting on continent.
• 11:57
  SPEAKER_00: So we're we're depositing, we often think of sediments going out into the ocean basin.
• 12:01
  SPEAKER_00: This is sediments being deposited on the continent, you know, on a submerged part of the continental crust.
• 12:07
  SPEAKER_00: And you're as you said, it's kind of subsiding as you as you put that weight, distribute, redistribute that weight around the continent, it it sloughs down.
• 12:14
  SPEAKER_00: We've talked about how you form basins before.
• 12:15
  SPEAKER_00: So go back to an episode, I don't know, six months ago on the Michigan basin and how you kind of can start to form these little basins.
• 12:21
  SPEAKER_00: And and there's bait little basins all over this part of North America.
• 12:25
  SPEAKER_00: The Michigan Basin is one of them that started to deposit these rocks.
• 12:28
  SPEAKER_00: We're also, Chris, near nearer the equator or near-ish to the equator, right?
• 12:32
  SPEAKER_00: So it's kind of this is a warm period.
• 12:34
  SPEAKER_00: The Bahamas is kind of a good analogy.
• 12:37
  SPEAKER_00: So picture the Bahamas.
• 12:39
  SPEAKER_00: Yes, not necessarily tectonically, but as far as like a surface environment, we've got this subsiding platform that's sort of shallow, warm, probably very beautiful.
• 12:49
  SPEAKER_00: Uh if you ignore all the scary creatures going around.
• 12:52
  SPEAKER_01: The water's beautiful too, right?
• 12:54
  SPEAKER_01: Then that's an important part of this, is that we kind of need this setting to be a sediment-starved kind of situation where because that allows for this really clear, sunlit waters that are good for reef development, which is essentially what coral is.
• 13:11
  SPEAKER_01: It's this is a part of the reef family.
• 13:14
  SPEAKER_00: You know, okay.
• 13:16
  SPEAKER_01: A part of what Potaski is.
• 13:18
  SPEAKER_01: This this organism that forms the Potaski stones is a part of that reef family.
• 13:23
  SPEAKER_00: Yeah.
• 13:23
  SPEAKER_00: So you picture, you know, you get out in the Bahamas a little bit and you you have this shallow setting.
• 13:28
  SPEAKER_00: There's all sorts of life going on, coral reefs around, they're growing.
• 13:32
  SPEAKER_00: As they grow, they build up that system, and there's some balance between sea level and where they're the creatures are happiest in there, and you know, sediment is kind of coming off.
• 13:41
  SPEAKER_00: And you think of like a carbonate mud, these sort of muddy, oozy carbonate sequences that are being deposited down, burying, you know, reef gets built up, it gets buried by you know carbonate kind of sloughing off, and then a new one pops up, and that's what's kind of going on here in this sequence of carbonates.
• 13:58
  SPEAKER_00: And this is in a sequence of sediments that are exposed all throughout Michigan.
• 14:01
  SPEAKER_00: We're gonna we're zooming in on one particular unit here that is exposed, as you said, in those upper knuckles of your hand in Michigan.
• 14:08
  SPEAKER_01: Yeah.
• 14:09
  SPEAKER_01: I want to have you take a step back, Jesse, because I don't want to be confused.
• 14:14
  SPEAKER_01: We're talking about these like sediment-starved water, and then you talked about this kind of muddy ocean bottom, which is not to be confused with muddy water, right?
• 14:24
  SPEAKER_01: Just can you clarify that point a second before we move ahead and use it?
• 14:28
  SPEAKER_00: So we're I mean, a lot of these rocks we transit so it's a time period where we're transit we transition from when you say sediment starved, you mean not a lot of mud cleaning dumped by the Mississippi River into the ocean basin nearby?
• 14:43
  SPEAKER_00: It's clear water.
• 14:44
  SPEAKER_00: There's not a lot of sediment, not a lot of uh sand grains or mud pieces, clay particles being dumped in by the river system.
• 14:51
  SPEAKER_00: When I say clay mud or carbonate mud, I mean um, you know, chemical precipitate.
• 14:57
  SPEAKER_01: Yeah, more like a jelly ooze, right?
• 15:00
  SPEAKER_01: Kind of this silicious or not silicious, this carbonaceous ooze.
• 15:04
  SPEAKER_00: Or actually kind of storm broken apart pieces of reef systems.
• 15:08
  SPEAKER_00: So storm comes in and kind of breaks apart the stuff that's on the bottom and reworks it over time.
• 15:13
  SPEAKER_00: And so that that's kind of what we're what we're talking about here.
• 15:16
  SPEAKER_00: Okay, so we're on this muddy thing where we, you know, there's a whole sequence of rocks that we can we don't want to we're gonna ignore for now the sequence of rocks.
• 15:23
  SPEAKER_00: We're gonna focus in on this this traverse group, which is Wow, hold on.
• 15:28
  SPEAKER_01: Is it really the Traverse group though, Jesse?
• 15:30
  SPEAKER_01: Is it really the Traverse group?
• 15:32
  SPEAKER_01: It's a traverse.
• 15:33
  SPEAKER_00: Let me let me let me let's move forward in one image here.
• 15:36
  SPEAKER_00: So this is a this is a geological map.
• 15:38
  SPEAKER_00: This is not this is ignoring the till.
• 15:40
  SPEAKER_00: All the till that's on uh covering Michigan, this is the bedrock map of Michigan.
• 15:44
  SPEAKER_00: And all we've highlighted here is the traverse group.
• 15:48
  SPEAKER_00: And the way to think about sedimentary packages is we break them apart into different different units, and one unit is a group, a group is a a group of formations uh that all kind of share similarities.
• 15:58
  SPEAKER_00: So the traverse group will be kind of a a limestone dominated sequence with variations, there's always variations in here, and then we've put a star on here for the gravel point formation, or one of the locations where the gravel point formation is exposed at the surface, which means a potential source for Potoski stones.
• 16:18
  SPEAKER_00: This is where one argument for one play, one of the many places that Potaski stones could actually be coming from, which is a question that we'll we'll touch on later.
• 16:26
  SPEAKER_00: Like, where did all these Potaski stones distributed all over Lake Michigan?
• 16:30
  SPEAKER_00: Where'd they come from?
• 16:30
  SPEAKER_00: It's an interesting problem.
• 16:32
  SPEAKER_01: So right, but Jesse, are we gonna get some blowback from people that say it's not called the Traverse Group, it's called the Alpina limestone, you know?
• 16:40
  SPEAKER_01: And Okay, yes.
• 16:42
  SPEAKER_00: Okay, that's that's a good that's a good question.
• 16:44
  SPEAKER_00: Alpina, if you're holding back to your hand, if you what which which way is right for me?
• 16:48
  SPEAKER_00: Is this correct for for you?
• 16:50
  SPEAKER_00: The hand?
• 16:51
  SPEAKER_00: Or is that my backwards?
• 16:52
  SPEAKER_00: Is this right?
• 16:53
  SPEAKER_00: No, that's right.
• 16:54
  SPEAKER_00: That's right.
• 16:54
  SPEAKER_00: No, you're right, you're right.
• 16:55
  SPEAKER_00: No, this is right.
• 16:56
  SPEAKER_00: Alpina's on No, that's not right.
• 16:58
  SPEAKER_00: Flip it back.
• 16:59
  SPEAKER_00: Flip it back.
• 17:00
  SPEAKER_00: This way's right.
• 17:00
  SPEAKER_00: Okay, there are cameras my camera's getting reversed in the thing.
• 17:03
  SPEAKER_00: Anyway, if you look at your hand, the Alpina's on the thumb side.
• 17:07
  SPEAKER_00: It's on the eastern side.
• 17:08
  SPEAKER_00: The northern, it's like your index, your index finger, upper knuckle of your index single.
• 17:12
  SPEAKER_00: And there's a famous limestone quarry up there.
• 17:15
  SPEAKER_00: And so the the limestone there has been named the Alpina limestone.
• 17:19
  SPEAKER_00: It is correlative, you can correlate that across to the western side of the state.
• 17:24
  SPEAKER_00: And it ebbs and flows throughout this sequence, this purple traverse group that is highlighted here in this map, in this image.
• 17:30
  SPEAKER_00: Um, you can kind of trace it discontinuously across, but if you go in different areas, they've they've seen different names.
• 17:36
  SPEAKER_00: And this is like one of the problems in geology, actually.
• 17:40
  SPEAKER_00: Chris, have you ever looked at a geologic map that is a big compilation map, and there's a really sharp straight line on the map separating units before?
• 17:51
  SPEAKER_00: Like you have one unit on one side and a straight north-south line and a different unit on the other side.
• 17:56
  SPEAKER_00: Have you ever seen that in in geologic maps?
• 17:59
  SPEAKER_00: Well, up in northern Canada, this happens a lot because there'll be people who compile the map for the geological map for the slave craton.
• 18:07
  SPEAKER_00: Oh, okay.
• 18:08
  SPEAKER_00: In one different region in 1980, they mapped one quadrangle, and in 1995 they mapped the neighboring quadrangle, and they kind of have slightly different nomenclature on either side of that boundary line.
• 18:20
  SPEAKER_00: And so, you know, the compiler is like, I don't know which one to call it.
• 18:23
  SPEAKER_00: It's clearly the same rock unit, but there's different descriptions, and you know, maps kind of have just the people who do the maps kind of develop these different sort of mental models for it.
• 18:32
  SPEAKER_00: So I think this this happens frequently in geology.
• 18:34
  SPEAKER_00: You kind of have to say, okay, the Traverse group, the this limestone that we're interested in, which on the west side is the gravel point formation.
• 18:42
  SPEAKER_00: That's the what people think as the source of Potaski stone fossils.
• 18:47
  SPEAKER_00: That's probably or almost certainly correlated to the Alpina limestone, which I've been to.
• 18:52
  SPEAKER_00: We went an undergrad field trip in this great um invertebrate paleontology class.
• 18:56
  SPEAKER_00: We went up to the Alpina limestone area and quarry and then the beaches and saw these carbonate reef systems.
• 19:01
  SPEAKER_00: Probably this if the same time frame, if not the exact same layer.
• 19:05
  SPEAKER_00: Uh, it's probably pretty damn close to the exact one.
• 19:08
  SPEAKER_01: It's just it's nomenclature, it's more geography related than you know where you happen to be from in terms of what you prefer to call it for sure.
• 19:15
  SPEAKER_00: Yeah, it's a human division, and Chris, as we know from your watermelon days, you're a lumper and not a splitter, right?
• 19:22
  SPEAKER_01: I'm a lumper, I'm world-class lumper, Jesse.
• 19:25
  SPEAKER_01: Hey, don't you forget the class?
• 19:26
  SPEAKER_01: But uh real quick, before we move on to the like the reef ecosystem part of this of this talk, is if you look at this image though, you can kind of see the structure of the basin of that surrounds and defines Michigan here.
• 19:41
  SPEAKER_01: You kind of see these concentric rings.
• 19:43
  SPEAKER_01: And if we zoomed out more from this, you would see that it forms this bullseye pattern where the rocks crop up, the same rock types crop up all around the state, and and they get progressively younger toward the center of it, which is what you get in a basin.
• 19:57
  SPEAKER_00: I was gonna ask you that question.
• 19:59
  SPEAKER_01: Okay, give me an analogy.
• 20:00
  SPEAKER_01: Come on, really.
• 20:01
  SPEAKER_00: I know a quiz for you.
• 20:03
  SPEAKER_00: Well, okay, so it's like what hold on, hold on, back out and tell me the rule of a dome versus a basin, because domes have the same bullseye geological map expression.
• 20:14
  SPEAKER_00: Um but dome versus basin, tell me the rule.
• 20:17
  SPEAKER_01: Well, imagine a uh uh like a bunch of sedimentary strata stratigraphically spread way out, right?
• 20:25
  SPEAKER_01: And then a piston like a slug of magma shoves the the sedimentary rocks up, it's gonna that's gonna accelerate weather and erosion there, and so you're gonna get old rocks exposed in the center of the dome, and the younger rocks are gonna be exposed on the edges, and that's that's switched around with the basin.
• 20:42
  SPEAKER_01: Because if you imagine a bunch of uh let's say you have five meter sticks stacked up on top of each other, and the one in the bottom is the oldest in sedimentary rocks, and the one on the top is the youngest.
• 20:54
  SPEAKER_01: And if you bend those up like a syncline, like a trough, okay, the bottom part, the oldest one, is gonna show up then way, way out on the edge of where you bent the meter sticks.
• 21:08
  SPEAKER_01: Yeah, and a basin is just a circular sincline, so it's yeah, that's the rule.
• 21:12
  SPEAKER_01: Youngest in the center, oldest on the edges, and and that's like that defines Michigan.
• 21:17
  SPEAKER_01: Like you want to find the old rocks, go way to the UP.
• 21:21
  SPEAKER_01: And that's where you're gonna get into you know the the very, very old Precambrian greenstone belt rocks and so on.
• 21:28
  SPEAKER_00: Yep.
• 21:28
  SPEAKER_00: So, Chris, another question for you.
• 21:30
  SPEAKER_00: Um, do you still carry around a wooden yardstick in your class all day, every day?
• 21:35
  SPEAKER_01: Oh my gosh, I just broke one the other day.
• 21:37
  SPEAKER_01: I I didn't intend to.
• 21:39
  SPEAKER_01: Yep.
• 21:40
  SPEAKER_01: I I use it all the time.
• 21:41
  SPEAKER_01: I uh let me see.
• 21:43
  SPEAKER_01: What was I talking about?
• 21:44
  SPEAKER_01: How did you break it?
• 21:46
  SPEAKER_01: Oh, you know what I was doing?
• 21:47
  SPEAKER_01: Okay, I was showing um I was showing how subduction zones can generate tsunamis.
• 21:54
  SPEAKER_01: So I I took a meter stick and I had most of it on a lab table, but I had this.
• 22:00
  SPEAKER_01: Like the uh, you know, the last 12 to 20 centimeters sticking off the lab table, and I bent it down like what happens to the overriding plate in a subduction zone.
• 22:10
  SPEAKER_01: Gotcha.
• 22:11
  SPEAKER_01: Yep.
• 22:11
  SPEAKER_01: And I was showing how when you bend that down, it kind of curls down.
• 22:15
  SPEAKER_01: It arches up the coastal area, it kind of bulges it up and can actually elevate it above sea level, right?
• 22:22
  SPEAKER_00: And then the yardstick that's on the on the table, but just near the edge of the table gets bowed up a little bit.
• 22:27
  SPEAKER_00: Yeah.
• 22:28
  SPEAKER_01: Bowed upward, right?
• 22:29
  SPEAKER_01: And so then when the it eventually breaks and gives way, the the you know, the subducting slab dives down and the overriding plate rebounds and snaps back up, and it makes a really loud noise on a slapping noise on the lab table.
• 22:42
  SPEAKER_01: And I I bent it too far and it just broke.
• 22:45
  SPEAKER_01: It just broke scares me every time it happens.
• 22:47
  SPEAKER_00: So another question what's your annual budget for yardsticks in your clock?
• 22:51
  SPEAKER_01: I buy 30 at a time.
• 22:52
  SPEAKER_01: Yep.
• 22:53
  SPEAKER_01: I do.
• 22:54
  SPEAKER_00: That's so good.
• 22:56
  SPEAKER_00: Hilarious.
• 22:57
  SPEAKER_00: Okay, well, that's a good analogy, a good deviation here.
• 23:00
  SPEAKER_00: Um, on to okay, so we've painted the picture.
• 23:02
  SPEAKER_00: We here's where the rocks are that we're looking at.
• 23:04
  SPEAKER_00: You know, we've got this ancient Devonian Bahamas style.
• 23:07
  SPEAKER_00: Picture the Bahamas, that's what's going on.
• 23:09
  SPEAKER_00: Here's where it's located now on the planet Earth.
• 23:12
  SPEAKER_00: Get us from the Bahamas to the deposits now.
• 23:15
  SPEAKER_00: Like what happened in between there to get to these really cool Potaski stone characteristics.
• 23:20
  SPEAKER_00: What do we have to have happen, basically?
• 23:22
  SPEAKER_01: Okay, so Jesse, like let's establish a little bit about this like reef ecosystem going on here.
• 23:28
  SPEAKER_00: Um it's a I think it's important to be fun to visualize.
• 23:31
  SPEAKER_00: It's really fun to try and visualize these things, right?
• 23:33
  SPEAKER_01: Yeah, because the you know, when you look at the Potoski stones themselves, you can't help but notice the honeycomb look to them, that kind of hexagon look to this.
• 23:43
  SPEAKER_01: And so these were called.
• 23:46
  SPEAKER_01: Here's the sciencey nerd term for it, but the hexagonaria precarinata, which we call Potosky stones, okay?
• 23:55
  SPEAKER_00: These were the that's the genus and species of this particular organism, right?
• 24:00
  SPEAKER_00: That's the fossil organism that we're talking about here.
• 24:04
  SPEAKER_01: Yes.
• 24:05
  SPEAKER_01: I mean, look, I think it's important to note that these are colonies, and these colonies are very, very diverse.
• 24:12
  SPEAKER_01: You know, we've seen these, Jesse, you and I personally, many different flavors of these kind of reef colonies, right?
• 24:19
  SPEAKER_01: Um Yeah, think of in Glacier National Park, you have these stromatolites, which were very similar to this, much, much older, but similar because they've they formed these like um cabbage head colonies, you know, and they literally looked like leafy cabbage heads, and then you'd see these other ones that look like stacked construction cones, and they're really like nearby, they're in close proximity with each other.
• 24:46
  SPEAKER_01: So you had these different colonies grown at the same time, and and this is just a type of colony that it's a it's a reef organism, essentially.
• 24:55
  SPEAKER_00: So, Chris, yeah, the re the reef part, let me just touch on that and build on that a little bit, is what visual should if you've never you know gone snorkeling on a reef or something like that, had the benefit of of doing something like that, what should you imagine?
• 25:08
  SPEAKER_00: Um, finding Nemo.
• 25:10
  SPEAKER_00: Imagine you know, this finding Nemo vision of the world where you know that there's a bunch of fish, they're they're living in all the there's all these creatures around, and then there's a pretty steep drop-off down into deeper water somewhere.
• 25:22
  SPEAKER_00: And the colony, the reef system, all these creatures building their homes out of minerals, calcium carbonate and aragonite, kind of build up this complex until it gets to really shallow water, and then you have this this water that's trapped between the reef and the land surface, but it's the they they they build up and get destroyed, and they kind of this kind of ebbs and flows.
• 25:43
  SPEAKER_00: But the the reef is a whole bunch of organisms, and we're focusing on one of the organisms in this particular ancient Devonian reef system that looked Chris.
• 25:52
  SPEAKER_00: This image is a diorama of a rugos coral, it's not a colonial version, these are singular ones, but it kind of gives us an idea of what the coral organism might have looked like in a healthy form, obviously.
• 26:04
  SPEAKER_01: I I I like this diagram, but or image, it the only thing that would make it look more real would be to have this kind of hexagonal top to it, which is what we see when we polish up a good size Potoski stone.
• 26:21
  SPEAKER_00: That's right.
• 26:22
  SPEAKER_00: So, Chris, these are the this particular species represented in this diet in this um in this diorama is uh an isolated, uh, a lone Rugos coral.
• 26:30
  SPEAKER_00: So they grow on their own.
• 26:32
  SPEAKER_00: The ones that make Potoski stones are a colonial fossil, which means that they grow together.
• 26:37
  SPEAKER_00: These these things grow up, and basically what you got to envision is they start small, and uh as the colony grows, you have more organisms, and they're six-sided.
• 26:46
  SPEAKER_00: I'm gonna skip ahead here.
• 26:47
  SPEAKER_00: They're six-sided because that's or generally kind of they're trying to be six-sided mostly, because that's the most efficient way to share sides, right?
• 26:56
  SPEAKER_01: They're sharing walls, right?
• 26:57
  SPEAKER_01: They're sharing walls growing, right?
• 26:59
  SPEAKER_01: Yeah, that's right.
• 26:59
  SPEAKER_00: So it's a big apartment building of corals, and as this colony grows, think of like a a half moon on the ground.
• 27:06
  SPEAKER_00: And as the colony grows, you get more organisms, they have to grow upward and outwards.
• 27:11
  SPEAKER_00: And so the colonies, the little organisms only exist, the polyps exist right on the surface.
• 27:16
  SPEAKER_00: And as the colony grows, they kind of have to build floors underneath of them.
• 27:20
  SPEAKER_00: And as they get more organisms, it has to kind of expand outwards.
• 27:23
  SPEAKER_00: And so all the all the creatures, all the polyps have to have to kind of move their apartments up a floor.
• 27:29
  SPEAKER_00: They got to add another floor to their apartment, move to the outside so they can go grab some grab some food from the from the water around it.
• 27:35
  SPEAKER_00: And so what we end up doing is this this colony gets bigger and bigger and bigger, more organisms get added to it, it grows upwards, and so it gets segmented.
• 27:43
  SPEAKER_00: And so if we look, this is the really beautiful view of a Potoski stone here.
• 27:47
  SPEAKER_00: If you cut this in half, like cut a slice of this, you would see that these things get smaller.
• 27:53
  SPEAKER_00: And if you look at the cut it longitudinally, cut it in half, you'd see these segmented floors that look like they look like floors, and and that's actually the polyp kind of growing, and then it built it says, Oh, I'm too deep.
• 28:04
  SPEAKER_00: I my walls are too high above my head.
• 28:06
  SPEAKER_00: I need to move outwards a little bit.
• 28:08
  SPEAKER_00: So it builds a floor, moves itself outward, and this happens as the colony gets bigger and bigger and bigger.
• 28:12
  SPEAKER_01: So it's almost it was like an upside-down construction cone.
• 28:15
  SPEAKER_00: I think that's the way to think of it as it that's a really good way to describe it, Chris.
• 28:19
  SPEAKER_00: Yeah, I and I think it's almost as beautiful cut in the other direction.
• 28:23
  SPEAKER_00: Like this is the classic view of a Potaski stone here, but it's almost as pretty cutting in this direction, where you kind of see the the floors of the segment in that um, I have a question um stone.
• 28:34
  SPEAKER_01: What builds the floor though?
• 28:36
  SPEAKER_01: Is it algae that helps them secrete this kind of uh jelly-like calcareous ooze that makes the floor then?
• 28:43
  SPEAKER_00: Yeah, I know you referred to the coral lights, like the the individual the individual apartments here.
• 28:49
  SPEAKER_00: Um I don't know that actually.
• 28:50
  SPEAKER_00: I think I'm not sure what what initiates that growth.
• 28:53
  SPEAKER_00: Um that's a good question.
• 28:54
  SPEAKER_00: Again, see above, we're not biologists.
• 28:58
  SPEAKER_01: We're not, we're not.
• 29:00
  SPEAKER_00: We can appreciate the biology here, but yeah, that's right.
• 29:03
  SPEAKER_00: Here we can.
• 29:03
  SPEAKER_00: Here's one where it is we can.
• 29:06
  SPEAKER_01: So, Jesse, how about we transition then into like this?
• 29:11
  SPEAKER_01: It's I think of this as like a three-step process.
• 29:15
  SPEAKER_01: We have sedimentation going on, we have diagenesis, and we have then fossilization happening.
• 29:22
  SPEAKER_00: You mean you mean taking this live colony and turning it into the rock we see today?
• 29:26
  SPEAKER_00: Into the rock.
• 29:27
  SPEAKER_00: Absolutely.
• 29:28
  SPEAKER_00: Yes, absolutely.
• 29:29
  SPEAKER_01: Perfect.
• 29:30
  SPEAKER_01: So let's take each of these segments kind of briefly here in terms of it's in this order.
• 29:36
  SPEAKER_01: So, like when the corals die, think about what happens to them.
• 29:41
  SPEAKER_01: Well, they got buried.
• 29:44
  SPEAKER_01: They got buried by more limestone, right?
• 29:46
  SPEAKER_01: Now this is different.
• 29:48
  SPEAKER_01: This was a a transition from a reef kind of paleo setting into just simply more of a more typical limestone sedimentary rock deposit.
• 29:59
  SPEAKER_01: Is that a fairly fair?
• 30:02
  SPEAKER_00: And you just think of uh think of there's all sorts of reasons that a reef, an entire reef ecosystem, or just particular colonies could die, right?
• 30:11
  SPEAKER_00: And then get buried by this mud, this limestone, this this calcareous mud gets buried, and you can have whole reef systems that that pass away and die for climate reasons or or perturbation reasons.
• 30:23
  SPEAKER_00: They get a big storm comes through and just floods this thing with with a whole bunch of sediment.
• 30:27
  SPEAKER_01: The whole reef system dies, muddy the waters and and things change, right?
• 30:31
  SPEAKER_01: And and this is what go ahead.
• 30:33
  SPEAKER_01: Well, I was just gonna say, Jesse, when that sediment, when when the when the coral dies, it's getting buried by this by this limestone.
• 30:40
  SPEAKER_01: That's the reference to the traverse group that you talked about before.
• 30:43
  SPEAKER_00: Right.
• 30:44
  SPEAKER_01: So these really finely laminated traverse group right on top of the Potoski stones.
• 30:50
  SPEAKER_00: So and Chris, this speaks to to kind of the the background, or actually the rock exposure itself.
• 30:56
  SPEAKER_00: If you think about a reef system and you think about the Bahamas, you know, the reef is a relatively small part of the entire sedimentation system.
• 31:05
  SPEAKER_00: That's true in a lot of places.
• 31:06
  SPEAKER_00: There's a lot more basic limestone being laid down than there is reefs getting buried.
• 31:12
  SPEAKER_00: And that's true back in the past too.
• 31:14
  SPEAKER_00: Reef fossils are they're not rare, they're all over the place, but they're but they're not incredibly common.
• 31:20
  SPEAKER_00: There's a lot more rock that is just in my mind a little bit of a boring limestone than there is Potowski stone part of this rock.
• 31:28
  SPEAKER_00: Does that make sense?
• 31:29
  SPEAKER_00: Yes, yeah, yeah, that's a totally fair thing.
• 31:32
  SPEAKER_01: And and uh you're not you're not offending me by calling it more of just kind of this boring limestone.
• 31:37
  SPEAKER_01: You're definitely offending some people though.
• 31:38
  SPEAKER_01: I I guarantee that.
• 31:40
  SPEAKER_00: But you know, we're among friends here, so it's all good.
• 31:43
  SPEAKER_01: That's right.
• 31:45
  SPEAKER_01: That's right.
• 31:46
  SPEAKER_01: It's all tongue in cheek, everyone.
• 31:47
  SPEAKER_01: It's all yeah.
• 31:48
  SPEAKER_01: So all right.
• 31:49
  SPEAKER_01: Well, uh this gets a little little doctory actually, professor.
• 31:54
  SPEAKER_01: There I just called you professor, but where we get into so you have the sedimentation process and then then you have the diagenesis process.
• 32:02
  SPEAKER_01: And diagenesis is this like techie word, I think it's a I don't know.
• 32:07
  SPEAKER_01: This is not really an intro level word, I wouldn't say, would you?
• 32:11
  SPEAKER_01: I don't I don't use diagenesis in my classes, I just don't.
• 32:14
  SPEAKER_00: Yeah, I I use it, but not not it's not uh it's not on the need-to-know basis for sure.
• 32:18
  SPEAKER_00: Okay, yeah, that's right.
• 32:19
  SPEAKER_00: That's right.
• 32:20
  SPEAKER_00: Yeah.
• 32:20
  SPEAKER_01: Diagenesis is this kind of garbage can term that refers to the series of physical and chemical changes uh that occur or that happened to the system.
• 32:31
  SPEAKER_01: And in this case, it refers to per mineralization, recrystallization, and then lithification.
• 32:38
  SPEAKER_01: So let's talk about each one of those, Jesse.
• 32:43
  SPEAKER_01: Just a brief synopsis of what what's involved in diagenesis.
• 32:48
  SPEAKER_00: Ooh, diagenesis.
• 32:50
  SPEAKER_00: This is taking a sediment and turning it into a sedimentary rock.
• 32:53
  SPEAKER_00: You can also think of it as low-grade metamorphism.
• 32:56
  SPEAKER_00: Those are two, I think, kind of interchangeable ways to think about it.
• 33:01
  SPEAKER_00: So, how do you take sand grains and uh make it a sandstone?
• 33:06
  SPEAKER_00: You gotta kind of bond the sand grains together in some way.
• 33:09
  SPEAKER_00: You can cement those things together, you can precipitate quartz or or something in there to precipitate them.
• 33:15
  SPEAKER_00: You can put it under a little bit of heat, a little bit of pressure, and that also does the kind of bonding uh together.
• 33:20
  SPEAKER_00: And the same types of processes can happen to rock.
• 33:24
  SPEAKER_00: So digenesis is that category of things.
• 33:26
  SPEAKER_00: And you laid out three really, I think, three different ways to do it, or three overlapping ways to do it is a better way to describe it.
• 33:33
  SPEAKER_01: I think they're all involved in this though, in terms of the like the preservation, exactly.
• 33:39
  SPEAKER_00: So overlapping processes that they feed back into each other a lot.
• 33:43
  SPEAKER_01: They do, absolutely.
• 33:44
  SPEAKER_01: It's a positive feedback loop, but this this permineralization is uh um I think of it a lot like how I think about petrification of wood.
• 33:53
  SPEAKER_01: You know, you have these wood fibers that are soaking up this water that's rich in usually silica in terms of petrification processes, and then that silica gets precipitated inside the wood fibers and it it's turning this into rock.
• 34:07
  SPEAKER_01: That's I think similar to what's happening here with the corals themselves.
• 34:12
  SPEAKER_01: You have groundwater then that is kind of permeating its way through these skeletal structures, but the water is uh saturated with calcium carbonate.
• 34:23
  SPEAKER_01: And so it just it's kind of precipitating calcite essentially, limestone, within the pore spaces of what was left of now these dead corals.
• 34:34
  SPEAKER_01: Does that make sense?
• 34:34
  SPEAKER_01: So we're we're like we're just adding uh you know calcium carbonate as a filler inside of these these kind of like horn-shaped corals.
• 34:46
  SPEAKER_00: Okay, gotcha.
• 34:46
  SPEAKER_00: Yeah, that's that's a that's a good description.
• 34:49
  SPEAKER_00: And so then we're we're gonna you know build on to that and what what's the next what's the next process or the next overlapping process that can relate to this?
• 34:58
  SPEAKER_01: Well, uh recrystallization.
• 35:00
  SPEAKER_01: This is a bit of a rabbit hole though, because most of the Potoski stones were originally aragonite.
• 35:08
  SPEAKER_01: And uh aragonite is a calcium carbonate, it's a polymorph of of calcite.
• 35:14
  SPEAKER_01: In other words, same chemical formula but slightly different crystalline structure, right?
• 35:19
  SPEAKER_01: And so what we had going on is the aragonite was stable when it was forming, but then later on, calcite's more stable.
• 35:30
  SPEAKER_01: And so the calcite structure replaced the aragonite structure in this recrystallization process.
• 35:38
  SPEAKER_01: The net effect is of this recrystallization process of turning it back into calcite is that it made it tougher.
• 35:44
  SPEAKER_01: Yeah, made the Potosky stones resilient.
• 35:47
  SPEAKER_00: More yes, that's it, that's a that's a good way to do it.
• 35:50
  SPEAKER_00: Adding survivability to, I guess, the rock itself.
• 35:52
  SPEAKER_00: Yeah.
• 35:53
  SPEAKER_00: That recrystallization is essential, right?
• 35:55
  SPEAKER_00: It's essential to the kind of fossilization part and and and it and it helps explain the softness.
• 36:00
  SPEAKER_00: You described very, very well how the the sort of lapidary enthusiasts love this rock because it's so easy to polish, it's really easy to cut.
• 36:10
  SPEAKER_00: I mean, a rock saw just churns through Potoski stone like butter.
• 36:14
  SPEAKER_00: It's amazing how quickly you can cut through a Potoski stone.
• 36:17
  SPEAKER_00: Like if you're cutting a granite on your rock saw and then you cut through Potaski, it just rips through Potoski stone because it's so soft and because it's it's mostly made of these relatively soft minerals, you know, calcite.
• 36:29
  SPEAKER_00: There is a little bit of quartz recrystallization in here as well, and and sort of replacement texture, but you know, the calcite's very soft uh when it comes to a diamond impregnated steel blade, right?
• 36:41
  SPEAKER_00: Or even just your your sandpaper um can polish this stuff really well.
• 36:45
  SPEAKER_00: And then we end up getting to sort of lithification, right?
• 36:48
  SPEAKER_00: And and how how does that play out in these rocks?
• 36:51
  SPEAKER_01: Well, it's lithification is burial and and kind of further cementation.
• 36:57
  SPEAKER_01: It's it's like you said, there's overlap between this and recrystallization.
• 37:00
  SPEAKER_01: There's overlap between all three of these diagenetic processes.
• 37:03
  SPEAKER_01: But lithification, you know, just it made it uh tougher yet again.
• 37:10
  SPEAKER_01: This kind of compaction and further cementation, kind of gluing everything together one last time.
• 37:19
  SPEAKER_01: This allowed it to endure, you know, one of the final steps is we gotta take this stuff and we gotta move it.
• 37:26
  SPEAKER_01: We gotta move this from due to glaciers, and that's not a like a that's not a non non-violent process.
• 37:34
  SPEAKER_01: That's it's not you know, it's not a passive process.
• 37:36
  SPEAKER_01: And so that lithification helped it kind of and gave it the last strength that it needed to and to make the final journey, I guess, if you will.
• 37:46
  SPEAKER_00: Yeah, to endure that.
• 37:47
  SPEAKER_00: And that brings us really nicely, Chris, into like how do you how do you get this stuff spread all over the state of Michigan?
• 37:52
  SPEAKER_00: Let's go back to this, let's go back to this map here, man, and go to image number four in our stack, which is showing this traverse group, which again is kind of if you if you're not looking at at the app, you're you're looking at the knuckles, the upper knuckles of your your four fingers, not your thumb, but your four fingers, that's where we're kind of exposed there.
• 38:08
  SPEAKER_00: And the gravel point formation is kind of your ring finger, up upper knuckle of your ring finger on your left hand if you look looking towards you.
• 38:15
  SPEAKER_00: It's a really limited area of where we've seen a lot of these fossils in outcrop, and there's a bunch spread throughout here, but how do we get this stuff all over Michigan, all over Lake Michigan, the shores of Lake Michigan?
• 38:28
  SPEAKER_00: It's a really well, I think it's a it's a cool question to ask with a very simple answer.
• 38:34
  SPEAKER_00: And it's really glacial transport.
• 38:36
  SPEAKER_00: Like we talked about when we were talking about putting stones, Chris, in the Lorraine quartzite and the Lorraine group um putting stone in Lake Huron, when the glaciers scraped across here, they ripped up a ton of that stuff, deposited it in till all over Michigan, and then that stuff has just been continually reworked over time by all the sort of surficial processes for the last 10,000, 20,000 years that we've that that we've experienced um on the surface.
• 39:04
  SPEAKER_00: It got exhumed.
• 39:05
  SPEAKER_00: It got exhumed.
• 39:06
  SPEAKER_00: Yeah, that's exactly right.
• 39:07
  SPEAKER_00: It got exhumed and then it got transported, it got plucked, and there you go.
• 39:11
  SPEAKER_00: Yeah, exactly.
• 39:12
  SPEAKER_00: And Chris, I've like I've found Potoski stones up in, you know, up in that that especially that northwest part of the lower part of Michigan on the eastern side of Lake Michigan, there's a ton of sand dunes all the way down to you know Holland and this the all the way down south, hundreds of feet high sandstone or sand um sand dunes on the edge of Lake Michigan.
• 39:33
  SPEAKER_00: And I've been up in this part of Lake of Michigan, up by the the Potoski Stone area, Grand Travers Bay area, on big sand dunes.
• 39:41
  SPEAKER_00: You know, you're 300 feet above the surface of the water, and you're, you know, looking around, you you find a rock buried in the sand dune.
• 39:49
  SPEAKER_00: This is all glacial till that's been reworked, and some of the sand dunes are just windblown parts of that.
• 39:54
  SPEAKER_00: And you pick it up, and it's an amazing Potoski stone that's been weathered by the sand.
• 39:59
  SPEAKER_00: Like it's clearly been sandblown and sand, it's not polished because the pits, the the inner parts get get more weathered than the outer white rinds of it.
• 40:08
  SPEAKER_00: And so I've found these things, you know, certainly no longer an outcrop, but in glacial till before.
• 40:13
  SPEAKER_00: Have you found Potoski stones in gravel pits before?
• 40:16
  SPEAKER_01: Oh, absolutely, for sure.
• 40:18
  SPEAKER_00: Okay, yes, yeah, yes.
• 40:19
  SPEAKER_00: So these are things that are reworked and dumped off in a gravel pit as the glacier meltwater is retreating, right?
• 40:25
  SPEAKER_00: And it's just glacial erosion picking up this stuff and dumping it in a big amalgam down further to the south and southwest.
• 40:33
  SPEAKER_01: Yeah, yeah, it's interesting that you know with the Michigan basin kind of protected this since Devonian until the Pleistocene glaciations took place, which is amazing.
• 40:44
  SPEAKER_01: You know, that's a long time, Jesse.
• 40:46
  SPEAKER_01: We're talking 350 plus million years where it was just stable, because if it weren't stable, this rock would have been erased quite easily.
• 40:56
  SPEAKER_01: That's right.
• 40:57
  SPEAKER_01: Actually, and so the fact that it's still around is a little bit shocking to me, and and just uh it's a really cool piece of the story.
• 41:04
  SPEAKER_01: It was protected, really, by the stuff all on top of it, and and by the just the structure of the basin geology.
• 41:11
  SPEAKER_00: And Chris, these you know, it's an important point, is that we talked about this basin geology, we talked about this back in previous episodes, and there are basins all over this part of North America that are similar age, have similar kind of depositional histories, and there are actually many very different but very related species of fossils to the one that has been designated the Potaski stone, the the state stone of Michigan.
• 41:36
  SPEAKER_00: And there's like at least seven and more than that species that are quite related that are actually, I mean, I'll be honest, I wouldn't be able to tell the difference between a lot of these because it comes down to you know the the number of segments and and what the structure of these things looks like, and and it comes a little bit to the lumper splitter argument of which are what are species and what are not different species, but there's a lot of different variations on this that are not necessarily the exact species that has been designated as the Botoski Stone, but look quite similar.
• 42:05
  SPEAKER_01: Yeah, I mean they're they're in Canada, they're in England, Germany, even in Asia.
• 42:11
  SPEAKER_01: So there were a lot of shallow seas that had the same kind of setting that had they could have been called Potaski Stones too, or they would have been called something else, obviously.
• 42:21
  SPEAKER_01: But it's it's very similar to the species.
• 42:23
  SPEAKER_01: Yes.
• 42:24
  SPEAKER_00: Yeah, that's right.
• 42:25
  SPEAKER_00: For this this is just uh well, if you're from Michigan, you know this rock.
• 42:30
  SPEAKER_00: If you're from it, it's a very common collector's rock, too, kind of like Pudding Stone, and maybe even more so than Pudding Stone, I'd say.
• 42:38
  SPEAKER_00: You'll see it in rock shops all over the Midwest and all over North America, really.
• 42:43
  SPEAKER_00: And I think part of the reason, Chris, that it's a spectacularly beautiful rock and that people really like it.
• 42:49
  SPEAKER_00: It's it's um how do I say this?
• 42:52
  SPEAKER_00: It's like a um it's like a little kid's dream rock because it changes color.
• 42:58
  SPEAKER_00: It or not doesn't change color, but the the color change is so dramatic between wet and dry.
• 43:03
  SPEAKER_00: That's right.
• 43:03
  SPEAKER_00: And this and this last photo is just a great one from the web that that just shows if you're wading in these beautiful clear waters of Lake Michigan and you you look at a dry Potaski stone on land, you could easily walk across it.
• 43:16
  SPEAKER_00: It's just a plain old, generally kind of drab gray rock, and it you'd have to look kind of closely to see that there's these cool coral fossils in there.
• 43:25
  SPEAKER_00: But if you get that thing wet, the white coralite, the the white parts around the coral, each corallite stand out like crazy, and the dark little eyes in the center stand out really well.
• 43:36
  SPEAKER_00: And it's a it's really stunning.
• 43:38
  SPEAKER_00: You kind of look at it and you think, what is that rock?
• 43:41
  SPEAKER_00: That's really cool, that's really pretty.
• 43:42
  SPEAKER_00: And then you polish it and it gets even more beautiful.
• 43:45
  SPEAKER_00: Um, so this is I just like this photo.
• 43:47
  SPEAKER_00: It's a nice example of it.
• 43:49
  SPEAKER_00: Just reminds me of walking along the shores of Lake Michigan in the summer, which you just you just can't beat that sometimes.
• 43:55
  SPEAKER_01: No, it's hard to beat.
• 43:56
  SPEAKER_01: It absolutely is hard to beat.
• 43:58
  SPEAKER_01: I mean, we're biased, everybody, but you know, that's okay.
• 44:00
  SPEAKER_01: It's it's our podcast, so we can beat it.
• 44:03
  SPEAKER_01: That's right.
• 44:04
  SPEAKER_00: But it but at least we're biased towards cool stuff.
• 44:07
  SPEAKER_00: Great rock.
• 44:09
  SPEAKER_00: Right?
• 44:09
  SPEAKER_01: Yeah, it is a cool story.
• 44:11
  SPEAKER_01: I mean, you know, because think about this a second.
• 44:14
  SPEAKER_01: This is a reef.
• 44:16
  SPEAKER_01: It's a part of a reef system.
• 44:18
  SPEAKER_01: And we're in the middle of a the North American Kraton.
• 44:23
  SPEAKER_01: That's not an easy thing, I think, for a lot of people to imagine.
• 44:28
  SPEAKER_01: Wait a second, what?
• 44:30
  SPEAKER_01: And and then you look at other parts of of the surrounding geology, you know, where we have gypsum all over the place, and these other evaporate deposits and limestone and dolostone, and we have in between the gypsum shale layers where there's shark teeth preserved in these shale deposits and coprolites, shark poop, and things like this, and and it's all a part of the story.
• 44:54
  SPEAKER_01: It's a cool part of the story because it's so vastly different from what we see today.
• 45:00
  SPEAKER_01: And I love that about geoscience is just contemplating things like that.
• 45:05
  SPEAKER_00: I think you're you're exactly right, and it just brings to mind that every rock tells a story, and the story is often a story of a very different world than we currently inhabit.
• 45:18
  SPEAKER_00: And in a world where the continents, the flat lying parts of continents are flooded, is a very different world than the one that we currently inhabit, and it has very different creatures on it, and it has very different life forms, and the rocks tell the story.
• 45:32
  SPEAKER_00: And I love these instances, Chris, where we get beautiful rocks that tell a really interesting story.
• 45:38
  SPEAKER_00: I'm used to studying really not beautiful rocks that tell an interesting story about the early earth.
• 45:44
  SPEAKER_00: Oh, come on.
• 45:44
  SPEAKER_00: That's they're not pretty.
• 45:46
  SPEAKER_00: They're not pretty.
• 45:47
  SPEAKER_00: They're not as pretty as Potaski stones.
• 45:49
  SPEAKER_00: So it's always like a really good thing when it's also a pretty stone that tells a pretty good pretty good story, right?
• 45:54
  SPEAKER_00: And so I uh we like to focus on those ones.
• 45:57
  SPEAKER_02: Yeah, yeah.
• 45:59
  SPEAKER_00: Um what do you say, Jess?
• 46:01
  SPEAKER_00: Is that a wrap?
• 46:02
  SPEAKER_00: Yeah, I want to go look at I want to go look for some Potaski stones, man.
• 46:05
  SPEAKER_00: We gotta we'll try and make a trip this summer.
• 46:07
  SPEAKER_00: Go look at some Potaski stones.
• 46:09
  SPEAKER_00: That'd be great.
• 46:09
  SPEAKER_00: That'd be great.
• 46:10
  SPEAKER_00: Hey, I think that's a wrap.
• 46:11
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• 46:12
  SPEAKER_00: We're at Planet GeoCast.
• 46:14
  SPEAKER_00: Send us an email, planetgeocast at gmail.com.
• 46:16
  SPEAKER_00: We always appreciate getting those.
• 46:17
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• 46:25
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• 46:34
  SPEAKER_00: Cheers.