PlanetGeo: The Geology Podcast
PlanetGeo: The Geology Podcast
The White Cliffs of Dover - Nature's Chalkboard
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Welcome to another thrilling episode of PlanetGeo! In this episode, we dive deep into the jaw-dropping geology of the White Cliffs of Dover. We explore the formation and significance of chalk, a rock star in the geologic world. Learn about its formation during the late Cretaceous period, its economic uses, and its pivotal role as an aquifer system in Europe. From the fascinating microscopic coccolithophores to the sweeping landscape of the English coastline, this episode is sure to keep you on the edge of your rock hammer! Don't take it for granite! Tune in and discover the geological story behind one of the world's most iconic landmarks.
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And it's just this this famous beautiful exposure rock that has an exceptional geological story behind it. Chris. Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you. No, no. I remember that. Smudge thumb.
SPEAKER_01Smudge thumb. I do like that. And I like it when you get when you get like when you get the that processed cheese all kicked up on your fingers, and then you just save it up and then you lick it up. Yeah.
SPEAKER_02No, that's not what I'm talking about. It's mostly Dorito, Dorito powder that you're losing there.
SPEAKER_01Yeah, well, you call me smudge fingers, that's why.
SPEAKER_02And then you put your smudgy fingers all over the phone or over your computer camera and get your image all smudgy. It drives me nuts. You can't record good video anymore.
SPEAKER_01Well, nobody needs good video of Chris. Okay. Nobody needs to do this.
SPEAKER_02Yeah, these guys prefer to have it spongy. Hey, um, Chris, today. Yeah. This is listener question time. But is this here's a question for you The White Cliffs of Dover, the geology of the White Cliffs of Dover, and we're going to talk about the geology of chalk in general here. But is this Does that sound exciting, Jesse?
SPEAKER_01We're going to talk about the geology of chalk. You know, when when when we first started thinking about this, we're like, that's an interesting question. Well, let's do it. And then so I kind of have this idea. We j we did Potaski stones, you know. Now we're doing chalk. I I want to do one on stromatolites also.
SPEAKER_02Oh, yeah. It's all related.
SPEAKER_01You know, and so we'll have a little mini series on these microscopic organisms that were super important during their time.
SPEAKER_02Totally. Yeah. Is this, Chris, the first episode? It can't be the first. But it I couldn't remember one that that hadn't the first episode on an international outside the US location specifically.
SPEAKER_01That can't be right. No, uh-uh. No, it's not. Okay. Nope.
SPEAKER_02We've done uh we did one the Spartan the Hell Hell's Gate Hellgate, the Spartan 300. We did that.
SPEAKER_01We did that, the Spartan 300. Um, but we also did one on it was a mass wasting event that happened in the UK. You're right. Do you remember that? Yeah, so no.
SPEAKER_02That's right. Yeah, yeah, yeah. It was a weird, yeah, it was a weird uh soil creep phenomenon. Yeah, that's right. Okay, we've done a couple. This is our okay, second or maybe third on UK geology. But this, Chris, the white cliffs of Dover, this is really interesting geology for Europe generally and for the geology of chalk even more broadly. And we're gonna get into all that.
SPEAKER_01Hold on, hold on, hold on. No, no, no, no. It's the geology of the chalk.
SPEAKER_02Okay. The chalk. That's exactly right. Because this let's turn to image number one here. This first image that this is the white cliffs of Dover. This is a these are an internationally famous landmark. Would that be fair to say? I mean, do I Oh yeah, absolutely.
SPEAKER_01It's in with any every intro geology textbook, you got the white cliff over for sure.
SPEAKER_02Oh, absolutely. And it's they're spectacle-there's a reason. They're spectacular. I mean, these are beautiful. So these things, they're exposed around about eight miles along the the south southern English coastline, and they're made up of this extremely white chalk. Julius Caesar wrote about these chalk cliffs in 55 BCE. The Romans installed some lighthouses along here. France is only 21 miles away. This is a very narrow point along the English Channel, and it's just this this famous, beautiful exposure of rocks that has an exceptional geological story behind it. And Chris, I'll just flip to this next image because again, it's extremely beautiful. Like this is spectacular. This is as beautiful as a seascape as you can kind of get, and just speaks to English geology, I think, to me.
SPEAKER_01Well, I think I mean uh I do, but what also it is like shockingly beautiful, but also it's geologically really important.
SPEAKER_02Oh I mean very important.
SPEAKER_01You I mean this.
SPEAKER_02Geologically and historically, all sorts of you know interesting stuff tied up in this. This what is you said it before. It's called the chalk. This unit, this particular chalk unit is called the chalk. So we're reading a paper called The Petrology of the Chalk.
SPEAKER_01We both thought that was funny. I yeah, yeah. Um well the chalk, this formation formed uh during the late Cretaceous period, and we're talking about 126 million years ago. And actually, Jesse, if this is interesting, and I think maybe a lot of our listeners know this, but maybe not. Um the Cretaceous that period, that time period, and and it's marked by the the extinction event, uh, you know, many, many forms of life became extinct in a very short period of time, including the dinosaurs. But the route to Cretaceous is Creta, and that means chalk. So the time period, these were so abundant in every ocean that they named it an entire geologic period after these organisms.
SPEAKER_02It's very cool, Chris. And we're talking about the you said the late Cretaceous, that's exactly right. So that the entire Cretaceous period is 145 million years ago to about 66 million years ago, and so we're talking about the end of it, this 100 to 66 million year interval is the late Cretaceous. And I think that the naming, the origin of the naming and the subdivision of geological time is a really interesting topic, and it's frankly one that I don't know much about because I've spent most of my career studying the Archean, which is a huge time period with very few subdivisions in it, right? That's right. Like that's right. Um, but things like you know, the the Yeah, sorry, go ahead.
SPEAKER_01No, I just I agree. I I wish that I taught another class at the like the second or or maybe a historical geology class at my high school. That would be fun because you know, just to take it to that next level, we can dive into things like this. Because I think the divisions in the geologic time scale are they're really interesting, and like doing a dive into all of that, I think that would that's a that's a class.
SPEAKER_02That's a class I want to take. We can do it via the podcast. We should put this together for a podcast series here because it's famous, you know. Okay, Kreta means chalk, so therefore Cretaceous period is what we're talking about. There's things like the Jurassic is named after the Jura Mountains, uh, and you know, Switzerland and the and French border there. There are a lot in in Pennsylvania, you know, named for the Pennsylvanians. So there's a lot of these things in geology that go a long ways into explaining common themes in the geological record. And this is one of them. We're gonna come back to this topic, but I just wanted to highlight this point you made. We're gonna come back to this that the Cretaceous, the N Cretaceous, is a particularly chalky period of time. And uh there's chalk exposed in a lot of places that formed during this time interval here. The chalk, the chalk makes up the white cliffs of Dover. And I'm gonna skip ahead, Chris, to a very schematic geological map here. But this is mainland Europe down on the on the bottom right, and you can kind of see, you know, France there, you can see the English Channel, and the black outline is the country. So you can see the UK here with England, Scotland, and you can see part of the other British Isles there. But the dark green on this diagram are places where the chalk is outcropping at the surface, and then the light green are places where the chalk is underneath of the surface, what we call subcrop. So the rocks are there, they haven't been eroded away, but they're beneath the surface. That's what subcrop means. And for the listener, basically there's two basins of interest here. There's a North Sea basin, which is to the east of the UK, northern England and Scotland, that North Sea there. So under there, there's a big basinal depression, and then there's something called the Paris Basin, which is on the mainland European continent, mostly around the Paris area in France, but it is again a basement. And you can kind of see this, Chris, especially in the Paris Basin. You can see that the chalk is exposed in a ring-like structure, and then it subcrops it, you it dives down into the earth in the center of that. So we can kind of tell just by looking at one unit that it's it's buried beneath other rocks on top of it, you know. That's exactly right. And and this is this is the city.
SPEAKER_01Which is typical with the basin. If you think about that, right? If you think about a basin, the central part of the basin is gonna be because it's depressed more, you get more deposition there. And on the edges of the basin is where these where it outcrops more often. You know, I think of like Michigan geology. Let's jump back across into the US and and it's the same kind of thing. And you have that's right, and it and all these super old basement rocks, they're only exposed on like the perimeter of the Michigan basin, which extends actually beyond the state of Michigan, but same kind of thing going on here. Yep, it's this kind of bullseye pattern that you get.
SPEAKER_02And they'll be within the um those same rocks that are exposed on the outside will be present in the subsurface in the center of the basin. So the Michigan Basin of those rocks are exactly, they're just down beneath our feet, which will become really important here briefly. But so, okay, we've had an episode on how do basins form, basically the formation of a basin. And we're kind of looking, there's this Paris basin, there's this North Sea basin, there's a few little smaller basins, and in between on the margins of these basins, the chalk, the chalk, capital T, capital C, the chalk is exposed. And it's particularly exposed in southern England, southeastern England, and then in mainland Europe across the English Channel there. And these exposures take place along this really cool uplift, not really an anticline, but it's an uplift feature that spans the English Channel. And so the chalk was laid down and then it was kind of uplifted in between these two basins and exposed more readily there at the surface. And there's a really cool geological story of how the English Channel formed with glacial outbursts, floods, etc. But these cliffs, they're really cliff-forming units, which is an interesting point, Chris. That chalk, we'll come back to the formation here, they are a cliff former in this region, in part because they're why okay.
SPEAKER_01Why is that uh noteworthy to you? You know, we see that all the time. It's a c chalk is a form of limestone, and we see limestone forming cliffs quite a bit. You know, we did a whole series on the Grand Canyon, and a lot of those cliff-forming rocks are limestone, a flavor of, you know.
SPEAKER_02I think it's interesting, Chris, because of the region, the climate variability and what forms a cliff and what does not form a cliff. Like here in Pennsylvania, all of the valleys are limestone, shale or limestone. Because it's easily dissolved. And I live in a Karsty province in Pennsylvania, where we have sandstone, shale, limestone, and we have those repeated back and forth and back and forth. The ridges in the ridge and valley are all sandstones.
SPEAKER_01The ridges are sandstone, the valleys are going to be shales and your limestones are limestones, right? And that's because of your wet, wet climate.
SPEAKER_02Exactly. Wet climate, more easily, more easy to dissolve. So we have to think of like weak rock, but also chemically weak rock. Okay. And limestone is a chemically weak rock, but in the southwest, that you just mentioned the Grand Canyon, out there, there's less chemical weathering. And so then limestone's really resistant, really tough limestone.
SPEAKER_01And chalk is that's a good point.
SPEAKER_02So it ebbs and flows what's a cliff former and what's not a cliff former when we're talking about erosion hole.
SPEAKER_01Right. So that kind of leads into the next topic, I think, is that the chalk is a very important aquifer system in Europe.
SPEAKER_02You know, I mean, and some of the interesting, Chris. Yeah, it really got some stats into this. This is super interesting.
SPEAKER_01Well, it supplies about half the groundwater for the public supply to England, about one-fifth to a quarter for southern Belgium, about 10% to the public water system in France, about 10% in Denmark. I mean, so it's a it's this really like laterally continuous layer that's providing groundwater, which is super interesting. Now, you know, in Michigan, I don't think of limestone as being a particularly like important aquifer, but you do in Pennsylvania. It's an important aquifer system, and and it clearly is here too, in this part of Europe.
SPEAKER_02So I yeah, Chris, I mean, I'm trying to uh I'm trying to remember what is the western uh the big western aquifer rock um out in the western United States that picks up water in the Midwest, has some like glacial water in there still. Um Yeah, sure.
SPEAKER_01That's called the the Lakota Formation, and it's got a lot of sandstone in it. It feeds the Ogallala Reservoir that runs under Nebraska and goes clear down to Texas. So super important. And I mean, you talk about um extending the railroads west through Nebraska, that was very important because that formation is exposed in the Black Hills, which is the structural dome. So the rock layers, it creates these confined aquifers where it has impermeable layers above and below these sandstones, and they're tilted, which means you kind of have this water tower effect. You have pressure, and so they were able to drill down to that in Nebraska. They knew if it was laterally continuous far enough that they would hit that, and then it's under pressure, so it required less pumping to bring the water to the surface for the steam engines and and all that. So, yeah, super important. And and that aquifer is really struggling right now. It's it's it's depleted. Yeah.
SPEAKER_02So, Chris, this is this links in nicely to the chalk, capital T, capital C chalk as an aquifer system. It's massively important for huge swaths of of the of Europe and the UK. And so this has been the focus of a lot of study. I mean, entire volumes of journal articles, of jerk entire journals have been written on the aquifer system that is the chalk, or just generally chalk aquifers in northern Europe. And it's a highly variable chalk system. And this is the the reason why it pulls together a bunch of threads we've talked about before. We've talked about karst systems and how limestone gets easily is easily dissolved, chemically dissolved. And so we get these fracture networks, we get little caverns, we get solution cavities, we get irregular flow as opposed to a sandstone, which has a a really regular, by comparison, flow network through the sand grains.
SPEAKER_01It doesn't have to create sandstone doesn't have to create its own channels and avenues, whereas whereas chalk and limestones do. They do this by solution. Exactly by solution.
SPEAKER_02And so some of these chalks, Chris, exposed in the chalk, and especially at the surface in England, along some of these cliffs, at the surface exposures of the chalk, which this is a beautiful photo that you can see nicely. This horizontal layering, which we'll touch on in a little bit. There's horizontal layers in the chalk. This stuff, some of these rocks have 40% porosity, which is just a mind-blowing amount of porosity. That's like loose sand level of porosity. Like, you know, pour sand in a bucket, how much water can you fit in there compared to the the amount of sand you have in there? 40% of the rock is porous.
SPEAKER_01But so a lot of that's can I throw some stats on that a second, Jess? Just real quick. Sorry to interrupt you. But if you think about a, let's say, a bucket of well-sorted beach sand, I think of like Lake Michigan beach sand. You take a five-gallon bucket or a five-liter bucket, I don't care, and you fill it to the brim with that sand, what is the porosity of that? Well, you can measure that by just how much water can you pour in that's going to sit in the pore space and force the air out. And with that kind of sand, it approaches 50%. That's a lot, right? That is a lot, right?
SPEAKER_02Because what is actual sediment? You're describing really well-sorted, really kind of rounded sand grains, which is almost as much porosity as you can possibly get. I mean, it's not exactly, but as soon as you get a mixed sediment, this the fine particles are going to fill in the gaps between the big particles, you're going to decrease the porosity. Here in the chalk, we're dealing with 40% in some instances at this surface exposed chalk. However, it doesn't drain very well, it's not very permeable. Those channels are not very connected. The flow paths are really irregular and difficult for reasons which we'll touch on later in the when we talk about how these things form. But link that process with you know a lot of room for water. Link that, especially at the surface, water, surface water can get in there, and then link that with the way it can be dissolved. And you can get these solution cavities, you can get fractures, you can get fissures and voids. That means that water, when it can get through, gets through really quick. And we talked about this actually in central Pennsylvania. We've had this before. The groundwater systems are really robust and reliable, but they're really interconnected through these voids and fractures, which means the water is not filtering through. It has a short residence time. Water can travel really fast through these things, which makes them more susceptible to surface contamination, to pollution, and it means that you're not undergoing as many chemical reactions as you push water through these rocks. And so therefore, it's kind of like more like a pipe rather than like a filter system. Exactly.
SPEAKER_01That's like a sewer system kind of. Yeah, yeah. I think so for sure. It's completely different. And the other thing is that a lot of this you you talked about how it's a cliff former, but it's not particularly what I would call stable. There are some really unstable areas within this. And actually, I I think you can see this pretty well in this image, the instability of it down near the water, down near the ocean level. There, some recent large landslides, some mass wasting events have taken place, and so it's not particularly stable.
SPEAKER_02And Chris, that also has to do with the karstiness of this rock. This is a karsty rock. It can be dissolved. We can get karst, exocarst. It's a nice aquifer system, but it's a very variable aquifer system. So many of the regions where this aquifer serves, the water quality is deemed moderate to pour because it's a really a carbonate-hosted aquifer system, which is again doesn't do as much filter pressing, really, is a kind of a simple way to think about it.
SPEAKER_01So there are some other geologically interesting things within the chalk that upon close examination you might be able to see. Things like Samara layers, which are these clay-rich layers that you get, which create these like impermeable uh perched water tables in within the chalk layer. Those are we think maybe formed by volcanic eruptions that had a lot of like silicate minerals in it. And usually silicate minerals that are not quartz will you know chemically weather into clay, and so that forms this clay-rich what we call a marl layer.
SPEAKER_02So, Chris, the marl, a marl is a it's a very clay-rich layer typically. And when you're just describing the rock as a clay-rich layer, that's the term marl. If we know the origin, if we know, for instance, in some of these layers, we can almost you can kind of see some of the bands in this rock in this image here. You can see this horizontal banding here, darker colors. If we know it's volcanic origin, then we call it a bentonite because we know, especially with uh volcanic ash fall, that stuff's really fine-grained. And so it's really easy to turn that stuff to clay. I mean, you're many times it's often just volcanic glass, which has no internal crystal structure. So it weathers very quickly into clay minerals and it forms these really, really, really easily expansive units. So the clay will shrink without water and it'll expand a lot with water. Out in the western United States, in dry regions, that's a big problem for buildings and foundations because it can actually expand so much it just compresses.
SPEAKER_01Well, we use this sometimes to pack wells.
SPEAKER_02Yes, that's exactly right. Exactly right.
SPEAKER_01So, you know, you drill a well and you want this to be kind of like airtight, pressure tight system. So we'll pack the well, and this bentonite, when it gets wet, it kind of just seals the whole system up. So, Jesse, one other thing that you can see in this lenses of Marl, but you also get lenses of chert, which is this just uh really it's uh it's a form of quartz, it's the silica-rich, these lenses that occur within this.
SPEAKER_02One of Chris Bois's favorite rocks, if I if I dare uh hazard a guess. Chris is a chert man.
SPEAKER_01How can you not be, Jesse? Honestly.
SPEAKER_02I mean, I I agree. It's you know, it's a good one, it's a really good one. But how do you envision? I mean, what's your mental model for how chert forms? Well, apart from a lot of different ways.
SPEAKER_01Yeah, a lot of different ways. Um it's a microcrystalline flavor of quartz, and it forms diagenetically, which we're gonna get to. Are we coming up to that right now, Jesse? Are we moving in that direction? The diagenesis of okay, well then of this process.
SPEAKER_02Well, maybe before we get to that, because you're right, silica. So this silica, these silica bands, these chert bands, can form during diagenesis for sure. There's some other variety of ways you can get nodular chert in the chalk layer, in the chalk unit. You can get uh several different varieties of these. You can get flints, you can get stylolites as well, which are different feature in here.
SPEAKER_01It can be quite colorful too.
SPEAKER_02It's you know, yeah, it can be really pretty. And and there's a whole bunch of basically you got to think of this as a sedimentary rock unit that is laid down progressively over time, and there are time changes throughout this from the bottom to the top, things change. There's different categories. There's the gray chalk, the white chalk series, they've been subdivided to death. We're not going to get into all the details of all the subdivisions here, but there's a wide variety of different chert styles in here and different layers. These are really good index layers that sometimes are really horizontally expansive, so they can be mapped across huge swathes of the chalk outcrop, both in outcrop and in subcrop as well.
SPEAKER_01So well, before we get into that part, Jesse, let's talk about the Cretaceous what was the world like at this time? Because this was a very different looking world than what we have today.
SPEAKER_02It was chalky, Chris, right? The name tells us it was chalky.
SPEAKER_01There you go. That's right. That's right. And but but it's true. I mean, there was like chalk was forming everywhere. It was very, very prolific. So what was it like during the Cretaceous? We can to be really general, it was much warmer than it is today. I mean much warmer. Yeah. So in other words, we're talking about forests that went from the equator all the way to the poles. Now there were times where where there were probably glaciation, but these would have been glaciers that stuck to the poles during certain times and would have maybe sprawled to lower latitudes, but they they never extended very far during this time period.
SPEAKER_02So Chris, it's really important to think about what the relationship between glaciers, climate, and chalk deposition, especially chalk deposition in the areas that we're taught we're going to talk about, chalk being deposited, because the sea life changes dramatically when you do this. So think of all of the ice that we have tied up in the ice caps, the Antarctic ice cap, the Greenland ice cap, you know, Arctic Sea.
SPEAKER_01Yeah, about 10% of the land continental surface is covered in ice today.
SPEAKER_02And so that's a huge amount of water tied up in ice. And so you melt that and you raise sea level, and you raise sea level enough to basically flood the continents. And I always like to use this visual where I live in Pennsylvania. It's kind of an easy, easy visual, and I think where the chalk is exposed is a pretty easy visual. You don't need to raise sea level very much to flood all of the United Kingdom, much of mainland Europe. The same thing goes for here, Pennsylvania.
SPEAKER_01Yeah, if you East Coast and the Gulf Coast just destroyed it's really flat.
SPEAKER_02Like we have this whole Piedmont province that's like a couple hundred meters, not even several tens to a hundred meters above sea level. Soon as we get into Pennsylvania here, sure you got some ridge and valley province, but like you could easily flood this with a couple hundred, maybe five hundred meters of sea level rise. And so it's kind of this tipping point where where the continents, the continental, the low-lying parts of continents, which we talked about the hypsymetric curve, there's a very limited amount of Earth's area, of Earth's surface area that is high mountain ranges. It's a pretty small part, and there's a huge amount that is flat-lying continents kind of roundabout near sea level. And so if you melt all the ocean, all the glaciers rather, and dump all that water into the ocean, it's gonna raise sea level and it floods the continents. And what happens? Just that's just a it sounds okay. Let's it sounds like interesting. Let's just flood the continents. Okay, easy. But actually think about what happens. If you flood the continents, what's life gonna do? What are those oceans gonna look like? The climate's gonna be warmer, so the ocean water is gonna be warmer. I mean all the life, yeah. Yes, we have relatively shallow seas that are huge areas. I mean, you could imagine this being a really rich ocean life environment because it's all really shallow.
SPEAKER_01Yeah, and it's what it's we're talking about warm water, it's very shallow water, so photosynthesis is just booming. That's the scene during especially the late Cretaceous. That's what the world was like.
SPEAKER_02We're talking about tens of if not hundreds of millions of years at this level. So this is like a just a very different planet. This is a very different planetary starting point for life. Like and you know, as we've talked about before, all biology does is respond to the geology. Of course, for the most part, it's not quite true, but we'll see.
SPEAKER_01Jesse, Jesse, something came across my feed uh the other day. There's somebody is starting to offer a degree in geobiology. Okay.
SPEAKER_02Well, we don't have a geobiology degree. Penn State has one. Yeah, it's a geobiology degree program. Yeah, yeah. We've got several geobiologists uh on our staff, and it was a big push like a couple years ago. Yeah. And uh what's the breakdown?
SPEAKER_01Is it like in terms of you know how much geology and how or is it just all blended together?
SPEAKER_02You know, it's a really tough thing. So our pro okay, well, we're getting into the weeds here, but our program, but our program has uh a limited number of requirement like hard requirements, even for a geoscience degree, there's like uh six or maybe it's eight classes that are required, and then the rest are kind of just take whatever you want in the three or four hundred level, whatever's offered at a time period. So it's kind of mix and match, even to begin with. I don't know exactly what the geobio degree program, what the requirement breakdown is, but I will look into it and report back to you.
SPEAKER_00All right.
SPEAKER_02Because yes, I mean, I don't know if it satisfies anybody, but Chris, this this time period we're talking about, what's called the Cretaceous Thermal Maximum in the peak temperature here is about 90 million years ago. So right smack dab in the middle of this late Cretaceous period where we're talking about the chalk being deposited. And you know, we're dealing with a big rise in CO2, uh high CO2, really a warm, warm, warm environment melting all of the glaciers. So that's kind of the the idea here.
SPEAKER_01So Jesse, let's then I think that's a good time and a good segue to transition into what is chalk, like a little bit of the biology combined with the you know, what was going on with the atmosphere, and like you said, carbon dioxide dissolving into the ocean. So chalk, these are microscopic organisms. Basically, these are single-celled algae. And so, like when you think about that, and you you think about how like how fine-grained the chalk is, that's what we're dealing with. You think about look at the white cliffs of Dover, this image that we have in front of you right now, hundreds of feet thick, but these are made up of, these are mats of microscopic organisms, and that's a crazy thing to kind of try to wrap your mind around for a second. Um, so these were photosynthetic single-celled organisms that were producing these calcareous plates. They're called coccoliths.
SPEAKER_02Um, here we go. Hold on, Chris. We got an image for that. Here we go. Skipping forward. Beautiful. I mean, these are these are SEM images of uh individual organisms, really.
SPEAKER_01Let me back up a second. The organisms themselves are called coccolithophores, which is they're they're a flavor of foraminiphora or what we call commonly forams, right? But they they made these look at these plates that they're making. They are very, very cool. So they're making these calcareous plates, and when they die, they just settle down and accumulate on the sea floor, and that's what the white cliffs of Dover or all the other chalk formations that outcrop, you know, throughout the whole world, basically. We've got a lot of it in the US as well. That's what it's made of. And that's a I don't know, that's a crazy thought because these are single-celled microscopic marine organisms. Super, super important, though.
SPEAKER_02I agree. It's a it's a extremely important and really cool story. So the depositional rates here are not crazy, you would think, oh, this is extremely low, but it's not actually that low. Do you know they're not a crazy slow depositional process because the ocean is teeming with life? There's so much of this biological activity going on. Again, because ocean water is warmer, the continents are flooded, all of this stuff is happening to keep the deposition rate from being like crazy low, basically. So this is a really productive time for these shallow ocean, um, shallow ocean shelf areas. And so, Chris, should we highlight, come back to home turf and highlight a couple examples of other important geographical examples of chalk?
SPEAKER_01Let's do that. But before we do, I want to just say, because we did talk about it a real the extinction event, the KT event.
SPEAKER_02Oh, yeah. Yeah, yeah, absolutely.
SPEAKER_01Many of the four minifera were, you know, became extinct after this, but and chalk did not. You know, they suffered greatly due to this event that happened. Um, but they're still around today. And that's amazing to me as well. That these same organisms, and and there are many, many different species of these coccolithophores, but they're still around. That's pretty awesome. They made it. It is, you know, yeah, which is you know, that's what happened, right? It during this KT event, most of the bigger ones died off much, much less diversity. But these, because they were so small, they made it.
SPEAKER_02So yeah. And uh it's not a huge um difference in the well, it's a big difference in the life forms, but you know, the temperature differences we're talking about five to seven degrees, ocean chemistry, something like that. But it does, it just makes that that knob can get turned up really quickly too, rapid, uh especially when you flood the continents, lots of deposition or lots of of life happening. And then the N Cretaceous, as you said, extinction event happens and it's a hard reset, basically. So, Chris, a couple other examples of chalk really that are are kind of famous. We talked about the white cliffs of Dover. This same the chalk, that's the chalk, capital T, capital C, uh, extends all over the Paris basin. So there's huge chalk cliffs as well as you get off into uh into um France and the northern European basin. We showed that image before, including parts of Germany, Denmark, and the Netherlands, even. So this is a very expansive unit across most of Europe. We also have Chris, here's a photo of the I think I'm pronouncing this right, Neo Barara or Neo Niobrara formation. I don't know. Do you know how to pronounce this particular one?
SPEAKER_01I primarily just I know it's a formation, but I refer to the pure shale, which is uh a whole sequence of rocks.
SPEAKER_02And this is uh a formation within the pure shale, yeah. So this is uh one that is very common in the western United States, which again was a flooded continental shelf at the same time period deposited.
SPEAKER_01Interior seaway, and yeah, yeah.
SPEAKER_02Exactly. And and here we had a several examples of this, these interior seaways, but we had a Cretaceous example. And Chris, this is interesting to me. This is a photo from Kansas. So there actually is some topography in Kansas, it turns out. It's not just flat. If you would ask me before, I've I've driven across Kansas a couple times, and man, can it get flat. No offense to Kansas.
SPEAKER_01Okay, I I'm not gonna go there. I'll I'll rip on Nebraska all day long, but I'm not gonna I'm not gonna offend anybody from Kansas. Rip on Nebraska all day long, but Kansas is off limits to you. Yeah, Kansas is off limits. That's right. That's right.
SPEAKER_02It's funny. Why why's it why why is Kansas off limits? But Nebraska's fair game for you.
SPEAKER_01I don't know. I just feel like you know, if you if you find yourself living in Nebraska, I think you've made a poor life decision somewhere along the way.
unknownI don't know.
SPEAKER_01Please don't send me hate mail, but uh it's just it just doesn't do it for me. It's uh you know, you're driving and you're driving.
SPEAKER_02It's a it's a big state, and so many times I've driven through Nebraska. You're completely biased because you're driving. That's like for you leaving from Michigan at whatever 5 a.m. You leave from Michigan on the big yellow school bus and you head out west. Nebraska's where it gets a little bit starts to get painful length of drive, uh, and then it doesn't help pretty flat. Yeah, and then you're also like looking forward to the mountains by that point, too. And you're like, oh we just need to get to the mountains. So eastern Colorado has some of the same vibes sometimes, but you got that right of a long drive, that's all.
SPEAKER_01So okay, all right. So I alright, I take it back. I'm sorry, Nebraska. You're you're okay.
SPEAKER_02Okay, just a little bit.
SPEAKER_01I'll take it back.
SPEAKER_02Yeah, yeah.
SPEAKER_01But all right, so Jesse, let's get into the geologic setting for the formation of chalk. Okay, what do we gotta have? I like this. I like okay. This is like organization mentally. Uh my mind needs this. I don't know. Your mind is more scattered than mine, but what do we gotta have? You know, um, we need shallow, warm seas. Okay, we and we've established that. That's what the Cretaceous was like, especially the late Cretaceous. So continental shelves are submerged, so we need warm, shallow water, ideal for photosynthesis. What else do we need? We need the water to be relatively calm conditions. So these are low energy environments. So, because what happens then? They they're just allowed to settle out undisturbed. You don't have this, it's not very turbulent and things like this. Um, extremely important, right? Yeah, it is. It is extremely important.
SPEAKER_02And you look at this this photo here. I mean, you get these really fine laminations. I mean, I've seen this stuff, Chris, when uh when I was an undergrad, we went and drilled some of the post-glacial, post-dune lakes sitting behind, well, the in the in the west side of Michigan. We have these dunes along Lake Michigan, and there's lakes sitting right behind them, and they're really calm because all the storms come. The storms get kicked up over the dunes and don't really impact these lakes. And so you have really fine laminations in the sediment preserve, they're really small, really calm. So you get these tiny laminations that are preserved across it. And the same thing is going on at a continental scale in some of these. I mean, you can chase individual chert layers that are a couple inches thick, later miles and miles and miles. That only happens if it's a really calm, really homogeneous environment across most of that area.
SPEAKER_01And the other thing really that you touched upon already is you have very slow depositional rates. And we're talking fractions of a millimeter per year. So these are really, really slow rates. Um, and they're usually deposited in like, you know, how shallow is the water? On the scale of a couple to a few hundreds of meters deep. So not very deep. You know, this is like really broad, flat, submerged continental shelf areas where this is happening.
SPEAKER_02And Chris, the other the other thing that's interesting to think about here is, you know, okay, this is fractions of a millimeter per year. That's on the slow end of normal sediments, but it's in a normal sedimentary depositional range. It's not uh it's not chemical deposition, let's put it that way. It's not, we were talking about the manganese nodules on the sea floor that are doing you know, millimeters in in millions of years. I mean, really incredibly slow stuff. So this is much faster than anything you'd see in the deep, deep, deep ocean today. That's incredibly slow deposition. This is slow on the scale of sediments that occur on continental shelves. But you have to think if we flood the continents, again, I want to kind of paint this visual. If we flood the continents, there's a lot of activity that happens in a modern continental shelf environment. We have these submarine landslides that take out some of the transmission cables and the fiber optic cables that go across the you know the Atlantic. When you're on the edges of the continental shelf, that's a very dynamic underwater environment where you're getting deposition, you're getting sediment going out, you're getting plastic sediment going out into the ocean. So it's really dynamic. If you flood the continents, then you have this huge expanse where there's not much relief on the ocean bottom anymore. Whereas like our modern, our modern continental shelves, there's actually a decent amount of relief. There's a big slope drop-off there. Flood the continents, and and you know, that still happens, but you have this big expanse of, like you said, a couple hundred meter deep ocean water. So there's a lot of room to have really calm water, and the current cycle, the ocean currents are going to be totally different because you have this like really shallow continental part of the ocean and then the deep normal ocean basin. Whereas now we're really only have the deep ocean basin.
SPEAKER_01You touched on something that I think is worth noting. Why are the sediment accumulation rates so so slow in the deep ocean? A lot of different reasons for that, but the deep ocean, uh, you're not gonna get sediment that is land derived, what we call pyrigenous sediment, that's gonna make its way that far off into the deep ocean basin. It's gonna be deposited before it gets to that point. And then you talk about like maybe this kind of sediment accumulation, like this kind of bioclastic stuff. Well, even that's not gonna accumulate in the deep ocean waters very much because limestone, calcium carbonate, you have to saturate the entire column of water in order for that to happen. So even if these things are living in the shallow water.
SPEAKER_02Let me just jump in there. What do you mean by that? You mean that, okay, so in the upper part where the organisms live, they build their shells out of calcium carbonate, but you need to have that calcium carbonate skeleton, that their house, after they've died, it needs to sink down and it needs to not be redissolved by the water column, which means you have to have enough calcium carbonate, calcium carbonate, bicarbonate in the water so that it doesn't redissolve it. It's either precipitating or redissolving, it's not doing nothing. And so you have to have it, and that's what you mean by saturate the entire water column. So we get down in the deep ocean, you get down to a depth that that stuff is dissolved again.
SPEAKER_01Yeah, because the entire column of water with three miles deep or so, whatever you want to do, it's really, really deep water, is not entirely saturated in calcium carbonate. And the other thing that's happening too is that calcium carbonate is a little weird. It gets more soluble in cold water, which is not normal for we think of like dissolving salts or sugars in water, and and you know, you heat the water up and you you make it becomes more soluble. Limestone is the opposite of that. So deep oceans, colder water, that also favors the redissolving of these dead coccolithophores. So anyway, yeah, that's just a sorry, side note, but yeah.
SPEAKER_02So these these things get deposited, and we've talked about this the the slow deposition, calm conditions, warm, shallow water, the Lake Cretaceous thermal maximum here, very particularly very different world than what we think of today. Now we have to make a rock out of that. So we talk about diagenesis now. Now that's the term diagenesis. We're forming a rock out of this sediment. This loose sediment is going to get compacted, cemented together, those are the two processes to turn sediment into rock. That's the next step. And so it's really kind of simple to think about, but there are some dramatic things that can happen during this process, including forming some of these chert layers during this process, diagenesis. And we think of diagenesis happening in the many meters to deeper beneath the subsurface. And so I think it's it's important to kind of think of how this is going to change the chemistry here a minute. Because so compaction is kind of simple. You put more sediment on top, and the stuff beneath it gets squished and squeezed. And that can squeeze out the water that's trapped in there. But you're getting ocean water kind of trapped in the sediment as it's getting deposited. But that that water is also kind of flowing around and communicating with the surface water at some level, but there's a gradient, a chemical gradient from the top to the bottom. So deep down in the layer, still loose sediment. You can get chemistry, water chemistry, that's very different. Like all the oxygen could be gone out of it because let's say there's some organic matter being deposited along with it. That stuff's going to decompose, soak up all the oxygen out of the water, down the poor water now that's trapped in the loose sediment, and it's going to take that water and remove all the oxygen from it. And that's one of the processes that could dissolve and then reprecipitate silica-rich bands. So these silica-rich bands are these chert layers, some of them are certainly just silica being deposited as the sediment's getting undergoing diagenesis, really. Um, that it's part of the diagenesis process that there's fluid kind of moving through that is silica saturated, and then it hits a gradient, a chemical gradient, and starts to dump out, precipitate that silica into a chart layer or chert object.
SPEAKER_01I have a question for you. Do you call this in your class, your intro-level classes, anyway? Do you refer to this process as diagenesis or do you just call it lithification?
SPEAKER_02I I I call I talk about diagenesis as the term for no actual real good reason, I guess, now that I think about it. But yeah, I talk about it as diagenesis and compaction, cementation. We gotta cement the stuff together. Um how about you?
SPEAKER_01I usually refer to it as lithification, just you know, but the same thing. It's a two-step process, turning sediment into rock, basically, is what we're talking about. Um, and it gets complicated, especially in the deep oceans.
SPEAKER_02Um yeah, the the the chemical chemical reactions that can occur during gygenesis are incredibly important and they get really complicated really quickly. But they can do a couple things that we can see in these in the chalk and another chalk around the world.
SPEAKER_01So that's right. Yeah. Well, Jesse, we're about ready to wrap up our discussion, riveting discussion about chalk.
SPEAKER_02Oh man.
SPEAKER_01Um, but I I think like we need to I think we've talked about what chalk is, we've talked about the the geologic setting of the time period where these were so prolific. We've talked about the diagenetic processes. Now let's talk about why is chalk important. Is there an economic significance and importance to chalk?
SPEAKER_02So I think most people have probably heard of chalk or you even use chalk as like chalkboard chalk, right? You have stuff you use on the chalkboard. Um, and they they would uh assume maybe that's coming from the chalk uh layer, which the historically would not be wrong, right? Um, I use chalkboard chalk. I still use markers more, but there are many of our classrooms have the old chalkboards in. No way, really?
SPEAKER_01I would think only the physics department would have chalk. Only the physics department.
SPEAKER_02Chris, the one the one I lecture in, um I I mostly use PowerPoints every once in a while, go to the chalkboard, but it has those ones where there's like three chalkboards. Oh, yeah, yeah. Slides you slide them all over. Well, you slide them up. So there's an actually a three by three grid of chalkboards. So there's three horizontal, and then you can slide them all up. So you can write on it, slide it up, write on it. I used to have it slide it up. Um, it's totally cool. I mean, a huge lecture hall pole. Anyway, um yeah, but hold on.
SPEAKER_01It is it is yeah, it is hard. The numbers on chalk are difficult, right?
SPEAKER_02Because I couldn't find so I I I struggled. We struggled. To find hard and fast numbers to put on chalk mining and chalk extraction. It is often lumped in with aggregates and the other flavors of limestone, right?
SPEAKER_00Yeah.
SPEAKER_02Or or even just like sand and gravel and crushed aggregates, like you know, stuff that's going on roads, which is not necessarily chalk, right? So there's very few even US geological survey reports that tease out chalk as separate from limestone coring in limestone uses. But it's safe to say that in countries where chalk is is mined regularly, um, for instance, like France or the UK, has uh relatively, I wouldn't say prolific, but the chalk cores are around, it's on the order of tens of millions per year US dollars at the least, you know, in in recent years. But it's hard to put really hard and fast numbers on the economic importance of chalk in the modern era. Chalkboard chalk used to be real chalk rock, but now is more what they call mineral chalk. So it's like crushed gypsum, it's manufactured gypsum. It's so disappointing.
SPEAKER_00Yeah.
SPEAKER_02I know it is. I you know what would be a good here. Okay, here's the thing, Chris. Do you use a chalkboard in your do you have a chalkboard in your classroom?
SPEAKER_01No more. Nope, I don't. Oh, okay.
SPEAKER_02Well, you get a chalkboard. And uh, you know, if there's a listener out there, especially from the UK, who wants to send us a nice gift, give us some chalk pieces from the chalk that I could use in my classroom. That'd be kind of nice. I'd love to teach with chalk from the chalk. That'd be pretty good. That's a really good point. Excellent.
SPEAKER_01That's a good point.
SPEAKER_02Etsy must somebody on Etsy must make these, Chris. Don't you think? I would love to get it. You would think.
SPEAKER_01Somebody's got to do so.
SPEAKER_02No, no, I'm focused on this. I want to I want to. I know you are. I gotta we gotta find this out. I want to get this. All right, sorry.
SPEAKER_01Well, you go to the UK quite often. You you do your doctory presentations over in the UK, so you're gonna have to make this happen.
SPEAKER_02You'll give a chalk at Oxford and they'll give me a piece of chalk from the chalk.
SPEAKER_01That'd be good. That's right. Yeah. Uh another thing is like cement production, um, mortar, concrete, things like this, plaster. They use chalk as this kind of binding agent in it. And and this is something too. I I've worked with this extensively, actually, when I made my uh my beautiful rock pillars that line my driveway. Oh, yeah. You know, because uh when you clean it, you use myriatic acid or hydrochloric acid, and you get that reaction with the lime, the calcium carbonate that's in the the binding agent holding the mortar together.
SPEAKER_02So like the Portland cement, yeah. For sure. Okay, yeah. So you can see it. Do you feel you don't see it fizz, do you?
SPEAKER_01Oh, yeah, absolutely fizzes like crazy. Yeah.
SPEAKER_02Oh, interesting.
SPEAKER_01Yeah, good.
SPEAKER_02Be careful. Dissolve away your uh your nice columns there, Chris. You gotta be careful.
SPEAKER_01Oh no, no, no, no, no, no, no. But it does like it's havoc on your hands, you you know, like seriously. It's oh yeah.
SPEAKER_02Well, I mean, you should probably be wearing leather gloves or not. I know, but sometimes you just can't. You just can't sometimes. Sometimes you just health be damned. Don't follow Chris's um health and safety advice.
SPEAKER_01Generally, that's bad advice anyway, so yeah.
SPEAKER_02Yeah, it's definitely true. Um, soil treatments, lime, ground chalk is used for this, any kind of calcium carbonate can be used for this, and it can be used as a livestock feed additive.
SPEAKER_01So I gotta do this. I I have to do this in my own yard. I have a pine tree that is making my soil very low pH, too acidic, so I gotta add some lime to it. Yeah, I can't get grass to grow in a certain certain spot.
SPEAKER_02Yeah, dump it around there. Okay. I'm sure the pine tree is super happy about that. That you dumping lime on its roots, but I'm on it. I'm on it. You're on it. You gotta do what you gotta do. That's right. You gotta get the grass going. So there's a whole host of these. Toothpaste often has chalk in it as an abrasive. And that's interesting, right? Because you imagine, I'm gonna go back to this image. Imagine these little guys, these little fossils, they're pretty abrasive, right? There's a lot of sharp edges on this stuff, right? So it's a it's a really good abrasive, no real health effects when you eat calcium carbonate like this. So it's a good thing to use. Antacids have this, and in the coming energy landscape, carbon sequestration, chalk has been highlighted as a potential use for carbon sequestration mechanisms as well, too. So lots of potential uses and lots of very active uses for chalk.
SPEAKER_01Yeah. We use it for antacids. I've used it personally for antacids many times out in the field. Never from the chalk, though, just from not the chalk, yeah. But we use it as a filler in paint and also in paper manufacturing. It makes paper smooth, which is kind of cool.
SPEAKER_02Okay, there we go. The great many uses of chalk.
SPEAKER_01Yeah, just some uses. There we go.
SPEAKER_02You know what, Chris? It's a beautiful rock, chalk, and it makes some beautiful terrain. I uh the white cliffs of Dover, it's a really cool geological story. We can talk maybe next another episode about you know how the cliffs themselves actually formed and what cut the English Channel and all that kind of stuff. Very exciting geological stories to tell over there, you know, far across the pond. But the white cliffs of Dr. Hey, you know what?
SPEAKER_01Who would have thought the importance geologically and economically, and it's got a it's an interesting story. Chalk has historically very interesting story.
SPEAKER_02Yep, absolutely. And you know what? There's historical stuff to tell uh here as well. I mean, it's just a very striking feature of the landscape in southern England there, across the English channel. Hey, that's the story of chalk. What do you think, Chris? Good, good, are we done? Rap? I think that's a wrap. Yep, wrapped. Hey, you can find us on all social media, we're at Planet Geocasts. Go to our website, planetgeocast.com, shoot us an email. There's a contact us link there at our website. We love hearing from you. If you're listening on YouTube or Spotify, please subscribe and leave a like, review, and a comment. We always love hearing that.
SPEAKER_00Cheers.