PlanetGeo: The Geology Podcast
PlanetGeo: The Geology Podcast
Eruptions and Extinctions - The Geology of the Gettysburg Sill
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In this episode of our visual podcast series, journey back to the battlefields of Gettysburg to unearth the geological forces that played a pivotal role in history. Dive deep with Herr Professor Dr. Reimink and Chris Bolhuis as they explore the York Haven Sill and Rossville Dykes, parts of the massive Central Atlantic Magmatic Province (CAMP). Discover how these ancient volcanic events potentially triggered the end-Triassic mass extinction. Packed with juicy geochronology details, this episode mixes wit, history, and science—one sedimentary layer at a time. Tune in to see how geology not only provides the high ground but also might have set the stage for a global biological turnover. Remember, in the battle of fossils and igneous intrusions, geology always wins!
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The database was instrumental in the battle. It set the stage for the topography. It's a large reason why the Union forces, I think, could defend this position, this fish hook that they had in Gettysburg. We'll talk about that. Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you. The good doctor.
SPEAKER_00Not getting any respect around here. You only get that when we're face to face. And we're in in front of your postdoc students or something like that.
SPEAKER_01And even then, maybe in a doctory way.
SPEAKER_00Did I drop any over-educated comments when I was? I don't think I did. I didn't, I was good. Yeah, you were good. You were well behaved.
SPEAKER_01You're well behaved.
SPEAKER_00Maybe in front of Tess I did, but not your little minions.
SPEAKER_01No, not not uh not everybody else. There was only like one PhD student of mine there, and then the rest were above me in the pay grade. That's true.
SPEAKER_00See, it was it was good to see Jesse graveling Jesse is a fun Jesse.
SPEAKER_01A few. Oh my gosh. Okay. Yeah. Well, uh today, Chris, this is chapter five. Part five, is that right? Yeah. Yes, it is. Yes. I gotta give you a little bit of a hard time here. Why? Am I allowed to do that? Yeah, absolutely. I don't ask permission.
SPEAKER_00Please, but take me down.
SPEAKER_01Take me down. We you know, we were putting this together and we were debating about what to what uh topics deserve standalone episodes in our kind of deep dive on the battle, the geology of the battle of Gettysburg. Yep. And 100%. You know, to me, this one stood out as like a very clear single episode. Like, no doubt we can do an episode on the diabase. And you were kind of uh hemmed and hot a little bit. You were easy to convince, but initially you were like, I don't know, I don't see if there's one there. How do you feel now after we've gone through and and scripted it all out and done the all the detailed? Write this down and take note.
SPEAKER_00Write this down and and uh you can timestamp and date stamp this, but I was 100% wrong. Okay. Uh in in my need to be persuaded. Um I think because the story really the geologic significance in the battle is easy. Diabase is easy, but then the importance of this large igneous province, that was something that I needed to dive deeper into. And then the story came, uh it revealed itself, and it's like, oh yeah, I was wrong.
SPEAKER_01And once again, one of the things that I I think there's a leg, you know, this points out the leg. So what do we oh let me just summarize what we're gonna talk about today here, real quick. We're talking about the diabase. The diabase was instrumental in the battle, it set the stage for the topography. It's a large reason why the Union forces, I think, could defend this position, this fish hook that they had in Gettysburg. We'll talk about that. But these diabase dykes, we're gonna talk about them. The sill in the dike, these are part of a huge igneous event that probably, quote unquote, probably, I emphasize probably, probably caused the end Triassic mass extinction event. And so that whole story, and this is one of the things that I find I don't know if it's frustrating, because I understood, but you know, the literature on the geology of Gettysburg is not updated with the geological story of, you know, the Rossville Dyke and the the broader regional significance of the York Haven Sill, right? Like you don't find that stuff written about on the literature on the bat the geology of the battle of Gettysburg yet. Right. Because they had a good point.
SPEAKER_00That's where that's where I was that's where I was like I needed to be convinced because the geology was pretty straightforward. You know, from the geology related to the battle of the the history of Gettysburg, and that was pretty straightforward. And I'm like, I don't think there's an episode there. I think this is like let's roll this into something else, right? Uh you know, it it comes down to the Confederates are trying to kick the Union forces off of this high ground sill. That's what it that's what the whole thing came down to. I'm like, how how what you know, where is it, Jesse? Where's the story here? What am I missing? And then and then you find it. And I think that this is a like a really interesting topic, and uh I'm looking forward to it. I I really am. So you were right, I was wrong. Um, that doesn't happen very often.
SPEAKER_01And you'll get a signed contract coming to you there pretty soon to stay with that statement signed in effect.
SPEAKER_00Um I put it on record. It's there, it's on our podcast, it's on it's on our channel.
SPEAKER_01It's out there for real. The uh okay, so this episode's a beast. I mean, we could we're gonna avoid lots of rabbit holes and lots of weeds. And that's partly intentionally, I think, Chris, because this is part of a topic that is a huge topic in the earth sciences and the geosciences, which is the relationship between large igneous events, large intrusive and extrusive events, what we call large igneous provinces, LIPs, so lips, the correlation between those things and mass extinction events. And there is some correlation, there's probably some causation as well, but that's a big scientific debate, and it depends which one you're looking at, which pair you're looking at, uh, you know, the timing. And so that's a whole series, I think, that that we should definitely take a take a dive into at some point. But we're gonna kind of avoid some of those little rabbit holes as we go down and focus on.
SPEAKER_00Uh uh, maybe we will, maybe we won't, Jesse. Um we're we're gonna get we're gonna get into the well, let's get into this right or you know, like soon here. But I'm just gonna say that you you know you just scolded me before we jumped on here, and and so we're gonna bring that into the discussion today, I think. I can't help myself. We have a scolded bullet. We do.
SPEAKER_01Um, Chris, let's go. To start out, can you give us, can you just review what is the the sort of battlefield significance of the York Haven Sill and the Russell Diabites? And I just want to emphasize we saw this in the field, like the field trip video, we saw this in multiple locations. Little round top, devil's den, the weathering features were spectacular. So there's weathering differences that matter, but at a broader scale, set the stage and maybe look at this image number one here.
SPEAKER_00Sure. Yeah, if you're looking at this image, so you have three dashed lines on this little gif here. You have McPherson's Ridge on the northwest, you have Seminary Ridge right next to that, a little bit to the southeast of it, and then you have Cemetery Ridge with the fish hook dashed in blue there. So McPherson's Ridge is just it's a sedimentary anomaly with a little bit more resistant rock, and then you get to the Seminary Ridge, which is the Confederate and Warfield Ridge also. That's where the Confederates kind of position themselves during the three days. That's the Rossville Dyke, that's a diabase dyke. And then you have Cemetery Ridge down there in the southeast, the fish hook there in blue. And that is the York Haven Diabase Sill. And so that just that kind of like sets the stage. So all three of those are high grounds created by the resistance of each of those rock types that are involved.
SPEAKER_01So the the Confederates were sitting on the Rossville Dyke Ridge, and that was their strong point, their starting point, and the the Union was sitting on kind of this layer of hills that is within the York Haven Sill, and that was another high ground. And in between them, we had the sediments from the the Gettysburg Formation, which we've talked about before. The Gettysburg Basin, yeah, that's right. And so if you know, so this is a we're zooming in now on this thing. If you want all the other episodes, there's two more coming out yet still that are published on our app right now. If you want access to those, early access to those, you can download them in the Camp Geomobile app. First link in your show notes. We've also kind of covered a lot of this regional geology. We're gonna show some figures and we're gonna start to kind of be building this geological story now. And these these sills and dikes cross-cut the sediments, so they're younger, but it's unclear how much, or you know, we're kind of estimating how much younger. And geochronology plays a big role here, so it does.
SPEAKER_00And so, you know, everybody buckle in because Dr. Rymick is gonna go off on this. But the Yorkhaven diebase, you said this, you've said this many times to me personally, that it's been really precisely dated, and so has the Rossville Dyke, which is slightly younger. So, just to put timestamps on this, we're looking at the York Haven Dybase SIL. Should we define again?
SPEAKER_01Let me interrupt real yes, and let me interrupt before you do that, real quick. Two two quick points. First of all, York Haven Diabase, that's the the regional name for the Sill that some people, when you're in Gettysburg, they'll call it the Gettysburg Sill. So you'll see online things that are the Gettysburg Sill. We're talking about the York Haven Diabase, so those are one and the same. The Rossville Dykes, a series of dikes, are younger than that. And you can see in this map image that they're clearly cross-cutting. You can see this nice ridge, the the Warsville Dike.
SPEAKER_00Which is so nice, which is so nice to have this clear cross-cutting relationship. Beautiful. Um, to to like timestamp things relative to each other.
SPEAKER_01Yes, exactly. And Chris was to me, go ahead. Just real quick, one thing that stood out to me just about the general topography, especially when we were when we were standing on the ridges. The first one we were looking at cemetery ridge, and then we went up into the tower, and we were looking out over the landscape, and we were kind of trying to figure out that was seminary ridge, actually. Excuse me, that's what sorry, but those are two very similar words that you know I get I just get flopped in my head. Yes, seminary ridge. We were up in the tower, looking over the landscape in that part of the world, all the little knobs. It took us a while to kind of figure this out, but there's a bunch of little knobs. Some of them are little ski hills and stuff like this, but all those little knobbly things, little knobbly hills, those are all in the York Haven diebase. Almost all of those weird little ridges and little roundtop and cemetery hill, those are all very similar, little knobbly. So there's a very different weathering feature to them. They don't have long linear ridges necessarily to them. So anyway, that that struck me. Anyway, we're talking about geographic.
SPEAKER_00I think I think you're right. I I I 100% back that up. These are subtleties that you can see on the battlefield, but the geology makes it make sense.
unknownYeah.
SPEAKER_00You know, like when I looked at it just strictly from a historical standpoint for the last two decades, that didn't really make a lot of sense to me until I dove into this. You know, those little nuances of the topography is what I'm talking about. So geology is the best. Let's put some timestamps on this. The York Haven diebase still or the Gettysburg still locally, 201.48 million years old. And that's with an uncertainty of 0.031 million years. So you know that's uh that's you're talking 200 plus million years old, but these these numbers matter, and and I think we're gonna get into this here in a little bit, right?
SPEAKER_01So Chris, uh I I don't know how you we talk a lot about how these numbers are hard to wrap your head around, especially when it's 201 point, you know, something. 201 million four hundred and eighty thousand years old. That's that. And the precision on that is 31,000 years. So that means plus or minus 31,000 years on the York Haven Sill. That's that that is just mind-boggling that we're going back 201 million years and we're saying we know that age, plus or minus 31,000 years. It never ceases to astound me how great, especially zircon uranium-led geocronology is these days.
SPEAKER_00It's spectacular. Yeah, I know. All right, Dr. Rymank, hold on a second. Okay, sorry. The Rossville dykes, which are younger because and they have to be because they cross-cut the York haven't here. Yep. So the Rossville dykes cross-cut the York Haven Sill. So they have to be younger, and the the uranium-to-lead geochronology backs this up. So you have 201.313 million years old, so slightly younger. We're talking on the order of you got the uncertainties in here, but 150,000 years younger, plus or minus. You have to throw the uncertainties in there.
SPEAKER_01So we're kind of broadly 150,000 years younger. Yeah, right.
SPEAKER_00So that's what we're talking about. That that's I think that's cool. Uh, that it has to be younger because of cross-cutted relations, but then the geochronology, people like you bear this out. The numbers support the observations, and uh, that's that's a cool thing.
SPEAKER_01Um, which I also think like it's cool to stand there, you know, stand on Cemetery Ridge or Seminary Ridge and look across the field and see the other one and say, you know, that's 150,000 years, younger or older. That's a that's a tractable amount of time. You can kind of see it because it's not insignificant. I understand that amount of time, it's a big amount of time, but I kind of can grasp it, right? And it's a really interesting feature of that landscape. So yeah. That's right. And that's as you said, that age, those that we people don't just date these things really precisely for the hell of it. There's a reason why they go to great lengths to get that uncertainty down to 31,000 years or 34,000 years. Like you you have to work really, really hard to get that level of precision. I mean, this is a years-long project to do that. And so guys really hard on that, and there's a reason for that.
SPEAKER_00Yeah, sorry. I have a question for you then. Uh, because you know, the like the literature is a little bit all over the place with with these numbers. You'll see variation in the 201 point, you know, the decimals, the hundreds or tens of thousands of years, right? But those numbers matter. Why is there so much variance? And it's very frustrating. It is from my standpoint, because I'm looking at this and and you're trying in your head as you're reading all this stuff to try to keep the numbers straight because there's a very important piece of this puzzle that we have yet to talk about, and you're trying to keep it straight because it has to work.
SPEAKER_01It ha yeah, that's right. Okay, uh the short answer is that techniques improve through time.
SPEAKER_00So old literature then.
SPEAKER_01All right. So older literature. The long answer is that there are different techniques at play, and so in even within one category of techniques, zircon uranium-led data, there's data treatment differences at play. So for instance, the the first point, older literature, much of the older literature on these things are were argon-argon geochronology, which just is inherently less precise. We don't have the dual decay system, it's not as well. I mean, it it works really well, but the uncertainties are ten times bigger than the zircon uranium lead uncertainties that we get here. So there it's just a sledgehammer, right? Not a chisel. And then that's fair. So the lot of the differences are yeah, it's those differences.
SPEAKER_00Then in the framer versus a finished carpenter, right? Yeah, exactly.
SPEAKER_01Yeah, it's exactly right, exactly right. Different tools in your toolbox. The small corrections, which are I think more frustrating, or could be more frustrating, like for instance, there's some some literature, some of the early literature, early, uh early in the latest phase of lit of zircon uranium lead your chronology from like 2013 or something like that. That type of data, it's zircon uranium-lead data, and then a recent paper came out and summarized a bunch of that, and there are little corrections that you do for things like what is the thorium-uranium ratio of the magma? That's a little input parameter into the cascading data reduction.
SPEAKER_00Yeah, well, can I just talk about that a second real quick, Jesse? Uh because thorium is a part of the decay series to get you down to lead. And and so that's what you're referring to is all these daughter isotopes that uh that happen along the way also have to be taken into account, right? That's right.
SPEAKER_01That's what you're referring to. So in this time scale, it's not going to change your age from 201 million to 202 million, but it can change it at the tens of thousands of years, maybe a hundred thousand years, if you change that thorium-uranium ratio. And we know the limits of it, it's just kind of picking which value. And uh, so people will go and take older data from the literature and recalibrate it using a different thorium uranium ratio and get a slightly different number, for instance. So, and there's valid reasons for doing that, and and there's debate about exactly which process you should use, which one's correct. Okay, but does that help?
SPEAKER_00Uh it does. I think that's helpful. Let's move on. Um, so let's talk about the York Haven and Dye base SILS in the larger context, then. Let's let's move to that. So these are a part of this. Are we ready for acronym?
SPEAKER_01We gotta get people ready for an acronym coming at you. Yes, which is a good one.
SPEAKER_00It's a m well, there are a couple acronyms involved in this. I mean, it's an L I P Lip, right? It's a large igneous province, but this one specifically, this massive event that happened is part of what's called camp. Not the camp that I love, dear near and dear to my heart. The the group camp, C A A M P. Okay, I love them. Um, but this is just C-A-M-P. So this is the Central Atlantic Magmatic Province. Um and so the name tells you a lot, Chris.
SPEAKER_01And this is so the Central Atlantic Magmatic Province. This is a lip, a large igneous province. These hills and dykes are part of that. The York Haven Diabase, the Rossville, or excuse me, the York Haven Sill, the Rossville Dike, these are part of the Central Atlantic Magmatic Province. And this is a map, this image number three here, this is a map that just I pulled in a bunch of the data points that people have analyzed samples from. And you can find these things all up and down the east coast of North America, all the way up into Newfoundland. You can find them down into South America, into the Amazon. You can find these things, very similar age, similar composition, etc. You can find them in in Africa and up in Europe as well, mainland Europe. So you can find these things.
SPEAKER_00And that's kind of important because if you zipper up the Atlantic Ocean, then these data points are connected. They're close together. It it there's a this is not random. This is a pattern that's that's established here.
SPEAKER_01In that time, 201, we talked about this a couple episodes ago in the Trasic Rift Basin, the sediments, the Gettysburg, you know, formation, these were formed in in kind of a rifting environment, a stretching environment. And so it makes sense that these basalt flows and these dye base intrusions go along with it.
SPEAKER_00Oh, oh, good point. Good point. So we are talking about the Rossville dykes and the the York Haven dye base sills. Those are intrusive things, those are intrusive bodies. But equally important, maybe more important, I don't know. You can weigh in on this, but you also have extrusive. You have flood basalts that are involved in the cloud.
SPEAKER_01Flip ahead to image number four here, Chris. And this is an image from some of the famous flows in Morocco. And I've just highlighted with a GIF here where the basalt flow is in this sequence. And it's pretty thick, right? This is a pretty, pretty voluminous basalt flow package, and just the aerial extent here is enormous. Camp, basalts, sills, and dikes have been found over 10 million square kilometers in landmass area reconstructed. So this is a huge area where this stuff is found. The volume erupted is not huge on the scale of large Igneese provinces, but it's still a ton, two to four million cubic kilometers of basalt erupted onto the surface. And some of these dikes are huge, 500 kilometers long and 30 meters wide. Like these are these are monsters. These are monsters.
SPEAKER_00Even the York Haven Dai Bay Sill is on the order of 330 meters thick to 600 plus meters thick, and maybe even 700 meters thick. So you're, you know, that's these are massive intrusions.
SPEAKER_01These are really big ones, and some famous ones that people might have heard as the Preakness flows up in New Jersey, the North Mountain Basalt in Nova Scotia. These are geological names that people might know if they've looked into this, or they've or they've thought about large igneous provinces and mass extinction events before. And so it's a lip. I I particularly like that acronym. It's a lip. Uh, it's a large igneous province. There are intrusive and extrusive parts to that, and that's going to be really important in the story of teasing apart how this may have or may not have influenced the mass extinction event at the end of the Triassic.
SPEAKER_00So that leads us to you know, kind of parsing out these igneous events, and there were different phases that were involved, and we know this in part, and this kind of leads us down to the discussion now of Chris getting scolded by Dr. Rymanc here. Um was your first scolding by Dr. Ryman? How'd that land? It's not my first. Are you kidding me? Um this so in the literature, you will read about these pulses that happen, these events that happened, maybe four of them over a 600,000-year time span. It's whatever, that's not important. But you'll read about the titanium levels, low titanium, high titanium. And I kind of went down a rabbit hole with it, you know, because the titanium levels in and of themselves is not important, other than okay, these magmas had different evolutions, they they they had different sources, they were a little they were different times that this happened. Um, but then maybe the link of low titanium to a lot of outgassing of carbon dioxide and sulfur dioxide, that's the hole I went down. And and kind of like I I just said that low titanium kind of coincides with a lot of this these really important gases that kind of set the thermostat for the planet. And you scolded me and said you need to back off on this because you know there's debate involved here. So well, what's the takeaway, Jesse? I mean I you know, my I I I think.
SPEAKER_01My take on it at least is that the titanium is important in that it's different flavors. It's a way that chemicals that petrologists, people who study these things, can chemically fingerprint these things. So say, Oh, this one's high titanium and is whatever quartz normative. It has high titanium concentrations in the rock. Like the rock has more titanium than the other flavor, which has low titanium. And those tell us something about the petrology, how that basalt or diabase got to be, and all the processes that happened before that. And there is a correlation between the high titanium and the low titanium and the ages. Like there's this sort of general theme. But I think it's kind of I I think it gets a little complicated in trying to match those up across this huge area. Understatement of the day. It gets kind of complicated. Kind of complicated. And so my sense was just this is a rabbit hole that we could that we don't need to go into to explain the the story here. Now, I would love to go down. I think this deserves many episodes in the in some series about the link between lips and large and uh mass extinction events because it's really a key point and there's some really interesting stuff in there. Or the debate existing, maybe.
SPEAKER_00That's fair, it's fair, and and uh I'm duly scolded. Um the the we're talking about the end Triassic extinction. So that's been dated at 201.36 million years ago, uh and so it's like it coincides with these igneous intrusions that we're talking about, and it coincides with these flood basalts. It's kind of like right in the middle of them. Right. The ETE, the N Triassic extinction event, is kind of straddled by these intrusions and extrusions, and so is it causal that's it causal? That's the key.
SPEAKER_01Yeah, you we we see this coincidence between them, and is it caused by the same process? And so let's skip ahead here to the fifth image, which I like this fossil reconstruction here, but the what is the end trassic extinction? Okay, let's just run through some numbers. We lost Trasic ammonites, devastated corals in the oceans. 25 to 30 percent of the genera were lost in the oceans, so a big extinction event in the oceans. On land, huge turnover in vertebrates. We lost 95% of the megaflora, 42% of the tetrapods, which went extinct. So we kind of I don't know how to think about this, Chris. I'm not a paleontology expert, but I kind of thought about it like these kind of crocodile-y, terrifying big land crocodile things became less important, and this extinction event set the stage for dinosaurs and really for mammals eventually to kind of take over and radiate. Is that I I don't know if that's accurate, like or that if that's a perfect framing of it.
SPEAKER_00Well, I yeah, I think it is. Um, it's adequate for what we're doing uh here. You know, we saw on the plum run bridge, we saw dinosaur footprints uh in the Heidlersburg member, which is older than this extinction event. So the dinosaurs were around, but they were different, they weren't very big at this point, and it kind of just set the stage for them to fill a niche. This biological niche, you know, and and also the mammals that were around as well. And so this kind of extinction event, I think what's important from that kind of historical standpoint is that it kind of just set the stage for them. Okay, it's your turn.
SPEAKER_01Yeah. Uh in Christmas image. That's how I feel about it. I like this image because it's a phytosaur, which is plant lizard, which I don't know. If I was naming this thing, I wouldn't think this thing looks like a plant lizard to me. You know, this is definitely not team walking around eating plants, I don't think. I I must say I'm I'm kind of happy that the uh N Triassic extinction occurred here because I I I don't want these things walking around with me. This is not good.
SPEAKER_00Yeah. Um so all right, Jesse, let's talk about the timing of the N Triassic extinction. How does that number happen?
SPEAKER_01Okay, maybe, Chris, let's I don't know how to do this. Maybe we set the stage again and and give a little bit of a historical background. So, like, there's this coincidence between the N-Triassic extinction event, which you see in the sediments. You have to see that in sediments, especially ocean sediments are the best ones for pending down an extinction event because those are the ones where there's higher fossilization rate. That's where the more fossils are. That's where the fossils are going to be preserved. Yep. Yeah, in an ocean basin. On land, you know, there are fossils in there, but they're they're less regularly preserved. It's it's more a random distribution of fossils, let's say. So, okay, people notice this extinction event here. They noticed that there's basalts and sills that broadly correlate. Like I said, a lot of the early geochronology, the argon geochronology, and some of the astronomical tuning stuff was coarse, a coarse thing that said, yeah, there's a correlation here. Maybe it caused it, some ideas about why it caused it. Later geochronology, especially when we started to really hone the zircon uranium-led geochronology, that started to notice that data started to show that a lot of the basalts post-dated the extinction event. Or probably post-dated the extinction event, just by a little bit.
SPEAKER_00Just by a little bit. So that's what I've done. That's important because if if that's important, because if the basalt happened after the extinction, this large igneous province, you know, then that couldn't have been causal.
SPEAKER_01And that's well, Chris, what is well let me ask you a question. What is the easy explanation, the easy cause, the easy causal relationship between a large igneous province and a mass extinction event? Like outgassing the outgassing. Okay, perfect. So you outgass a bunch of CO2, sulfur dioxide, mercury, and you kind of change climate, poison.
SPEAKER_00If these, okay, let's let's take this a little bit of chemistry and geochemistry here. The if you take these igneous intrusions and you inject them into hydrocarbons and hold on, hold on, no, no, no, no.
SPEAKER_01Chris, hold that story. Hold that. I want to talk about the extrusive thing a minute, because that comes later. The extrusive thing, if we were thinking, oh, if a large igneous province caused a mass extinction, outgassing CO2, then we'd say, oh, the basalts are the outgassing. They represent the outgassing, they represent magma making its way to the surface, right? So the fact that a lot of these basalts and even things like the Rosswell Dykes are after the extinction kind of brought this into question. However, more data and different data, especially focused on the intrusive rocks, has shown that these intrusive relationships or these intrusive magmatic rocks, especially down in South America, I'll go back to this, down in South America, especially, predate the extinction event. They're slightly older. So they're old enough to be a little bit before the extinction event. So okay, Chris, this begs the question then that what's the process? What's the link? We have again this correlation, but what's the causation theory behind this?
SPEAKER_00Can I talk now about that? Yes, I want you to. Okay, all right, all right. Well, if you take these uh really massive intrusions and you you inject them or squirt them into hydrocarbons, uh, you know, like petroleum and natural gas-filled rocks, these sedimentary rocks, or you inject them into carbonates, you're gonna get two gases in abundance that are gonna be outgassed into the atmosphere then. They're gonna be basically liberated from the rocks, and that's carbon dioxide and sulfates. Okay, and both of those are greenhouse gases. So if you get a lot of that in a short period of time, which is what they think happened, this early stage that predates the ETE, the extinction event, then that could have been the driver of the extinction that is observed in the sedimentary rock record.
SPEAKER_01Which is such a cool um I'm biased. I must say I'm biased because one of the people involved in this work is a friend of mine from graduate school. But it's such a cool theory or or or or such a cool process as it's like, okay, it's not what we thought, it's not the normal thing that we thought, it's not the simple explanation. It's actually more complicated than that. And it's this to cause a mass extinction, you might need basalts, basaltic magma injecting into carbonates, these rock types that contain all this stuff that send mercury, that that this volatilization big sedimentary package sends mercury.
SPEAKER_00Well, hold on, let's let's talk about that a second. Because if you do this, what I just talked about, injecting these sedimentary rocks with this massive amount of magma, another thing that's going to be released is mercury. And you just alluded to that. And and that also gets liberated. And so what we find in the sedimentary rocks that happen after these intrusions in these shallow basins is a spike in mercury that lends credibility to the idea that that it did indeed happen before the extinction event. These gases were put into the atmosphere, liberated and put into the air before, and maybe driving the extinction then. But it makes sense too that that this would continue after the extinction, you know. So it happened before, during, and after, because this large igneous province spanned a pretty significant amount of time. We're talking to 600,000 years, uh, you know, ish, plus or minus. The extinction event probably didn't take that long.
SPEAKER_01Well, yeah, but but it wasn't it, it it also wasn't like an instant in time, right? It's you know, things are 40,000 to 100,000 year estimates for the the length of the extinction event. And the question, you might be sitting there listening to this thinking, well, why is this so hard? It seems like it's been nailed, right? Like, why's this seems simple now? It's not because think about how would you, I find this fun to kind of think about. Like, how would you identify an extinction event if you wanted to put your finger on it? How would you identify it? Well, you'd have to say, okay, what is the fossil that represents the next phase? What's the best fossil that represents the Jurassic? And I'd have to find that fossil somewhere and say, okay, that's the beginning of the Jurassic. Okay, then go back and say, well, what fossil do we not find, you know, after the Trasic? What goes away, what dies out, and find a fossil from that that's a Trasic one. But then you've just got a bracket. You've got a bracket in time, and you don't actually know if there's an extinction, if there's some preservational bias in there, if there's an extinction event, or if that bracket is actually the time that it took for the extinction event to happen. And so there's all these time lags in it. And then can I interrupt a second?
SPEAKER_00Yeah, absolutely. So bracketing an extinction event is exactly that's the correct way to put this, because sedimentary rocks are really difficult to put an exact timestamp on because they're made of detrital grains, which means that if there's any zircon in this in the sediment, you're not dating when the sediment was deposited, which is what we want to know. You're dating when those detrital grains formed. So it had to be form, get weathered out, eroded, and then deposited and lithified into rock. You know, so they're just really hard to do, they're hard to date this way. So you need other things, you need the fossils, like ash is important, right?
SPEAKER_01Because Chris, this is a great point. And this is uh ash is super important. And why is ash important? Well, because you can find zircons in it, and it's a distinct event. You know, the volcanic eruption happened, sediment and the ash came in, and the zircons came from the volcano. So we can date that really precisely. And if we can date a bunch of ash layers in a sedimentary sequence, then we get we can get an age model through that sediment. We can figure out deposition rate through that sediment, and that's really valuable. But the problem with these large igneous provinces is that we don't have a lot of ash. This is basaltic eruption. This stuff doesn't create huge volcanic eruptions that sends ash everywhere. And so a continent that's extending produces that's kind of breaking apart, produces a lot of basalt. That basalt is preserved on land, not in the oceans. So the ocean sediments are better at capturing the extinction event, the land sediments are are better at capturing the basaltic lavas, but the two don't often correlate, and they're kind of hard to match up in different ways. So it's just a complicated. I mean, we don't need to get any more in the weeds, it's just a point to say this is a little bit more.
SPEAKER_00Well, actually, I'm gonna get a little bit more into the weeds. I have a question. All right, perfect. Um so going back to the mercury issue, is it enough mercury to because mercury is a toxin, it's a neurotoxin, and not just to us, to to just a lot of forms of life. Was the mass extinction then also maybe a a kill shot that involved carbon dioxide outgassing, sulfate outgassing, and an abundance of this neurotoxin that was liberated too? Could that have had something to do with it?
SPEAKER_01I mean, it's certainly possible. I think the mercury thing, to my knowledge, is you know, people have focused on on mercury uh for a while, but it's a it's kind of a blossoming field. I mean, we have a uh a new faculty member um on our staff here who is a mercury expert in mercury in these large in these provinces, and there's a lot of new research coming out on mercury specifically, and people are kind of focusing in on it. It's a big, it's a growing field, I would say, because you're highlighting the importance of why. Like, is it is it enough? Is it the thing, or is it in order to do a mass extinction, do you need one thing or do you need a whole bunch of little things? Yeah, um, yeah, yeah, okay. That's a great question.
SPEAKER_00Yeah, all right, Jesse. Well, let's let's begin to wrap this episode up. What is why did you put back in this last image here uh showing you know, we used this in previous episodes too. So let's bring this full circle.
SPEAKER_01This is our timeline uh image that just shows back to the Gettysburg Basin how these things are are preserved, and we have yeah, 230 million years ago this thing starts as just a stratigraphic column that goes up from 230 to about 190 million years. We have the sedimentary rocks on the bottom, the new Oxford Formation, which we don't see in the Gettysburg Battlefield. Then we see the Gettysburg Formation, the Heidlersburg member, which are very important features, and then right at the Jurassic Trasic boundary, we have probably two, it's certainly too thick on this, but you have to make it thick enough to represent some amount of time here to see it. But the York Haven Sill and the Rossville dykes, just to kind of bring this back and highlight that the Rossville dyke post-dates the extinction event, the York Haven Sill kind of overlaps maybe a little bit, depending upon which of these small number changes you see which reference you're you're looking at. Um, but they are related. This event, they're related to this central Atlantic magmatic province event, the camp event, which to my reading, Chris, I think it's a pretty, I would say the the working model is that it did cause the end Turassic mass extinction by exactly the process you described. These intrusions, especially in South America and Africa, intruded into the sediments that helped outgas the sediments, which created this climate perturbation that ended up um inducing an end-Turassic mass extinction event that took several tens of thousands of years to kind of play out. I don't know. Is that a good time you know wra wrap up? Yeah. Um it's a it's it's a good story, Jesse.
SPEAKER_00It's a good story. I think it's good to emphasize.
SPEAKER_01You know, what we haven't talked about at all is any of the weathering features, but I feel like we covered that pretty well in our field trip episode, talking about the cool problems.
SPEAKER_00How the edges weather slower than the middle part of it and so on. Yeah, that is that's in our field trip episode, yeah. Field trip episode.
SPEAKER_01And it's just kind of nice to walk when we were walking around walking around the field trip, we looked, I mean, walk around in Devil's Den or on Little Round Top and thinking, you know, this rock had something to do with a mass extinction event 201 million years ago. Is a it's a fun thing to think about. It's you know, a somber thing, and and you know, you just saw some dinosaur footprints down the hill, and now you're standing on the die base that probably cause the extinction of those those creatures that left those footprints. Geology is powerful.
SPEAKER_00It all comes down to geology. Geology wins. I love that. Geology wins.
SPEAKER_01All right. Well, hey, that's a wrap on this episode. Uh, we've got a couple more coming at you later. If you want early access to those, download the Camp Geo Mobile app first link in your show notes. We have a Gettysburg Geology Visual Podcast series there. You can get early access to that. Follow us on all the social media. We're at Plant GeoCast. We have a contact us link on our website, plantgeocast.com. Cheers.