 In this video, I'm going to provide an example that shows how chronostratigraphy and lithostratigraphy differ from each other. So the upper part shows a modern environment where we have a river flowing into a lake and waves influencing the shallow part of the lake. And then when too much sediment piles up in the shallow parts, you end up with turbidites that flow down into the bottom of the lake. And between turbidites, you just have mud settling out from suspension. So wave base is the water depth below which you no longer get waves influencing the sediment at the bottom. And so down here at the bottom, I have four stratigraphic columns. And we can think of these as cores that might have been drilled in the sediment of this modern environment with each core under the area that it was drilled. So this first one was drilled in a river channel, not very practical, but the deposits at the top part here represent a river with the mud and their mud cracks. I have my legend over here which shows what the symbols mean. And the mud cracks form when mud is drying out when they're exposed to air. And so we have a whole series, the first thing we intersect here is a series of river deposits which we would expect there. Then the next one was drilled in the lake, but at a water depth where the waves are influencing the sediment and we can see that there's some sandstones with the wave intervals, that's what this bumpy symbol represents. And then the last two cores were drilled in parts of the lake that were below wave base and they have mud at the top of them and then the core intersected some sandstones. So we know that we have the top surface, it represents the top of the cores. So that is this area here. And if we trace a timeline coming down here, we know that this is the modern surface here. We can trace a timeline coming down to the modern surface of this core and then down to this one here. So this is our modern surface. And one of the things that you can see is that the sediment type, which eventually could become rock type, is different in different places. And that's a manifestation of Walther's Law where you have a change in environments that produce different sedimentary structures and accumulate different rocks. And then if you look down in the stratigraphic columns, you see that the rock types are actually different. So for example, we have trough cross stratification from dunes, really common in rivers and ripples on top. Well, when we talk about rivers, you'll see that this is a very typical sedimentary succession going from coarser grain dunes to finer grain ripples. And then when we get down here, we have some of the wave ripples. Just like when we go from the river deposits laterally, we see wave ripples. From the wave rippled areas in the stratigraphic column, we go down. Eventually we get to upper planar lamination with ripples on top and mudstones as well. And this set of sedimentary structures looks a little bit like the river ones, but if we go laterally into the deeper lake, we see that there are upper planar lamination with ripples on top, and that's also characteristic of turbidites. And so we know we have turbidites going in this direction into deeper water here. So at the same time, the rock types are distinctly different. Now I've given us a cheat in some sense to help us with our stratigraphy, and I've provided an ash bed. So this bed right here has V's in it, which represents a volcanic ash, and we see the same bed here, where we see an ash bed here, here, and here. So I can hypothesize that those ash beds represent the same volcanic event, and if we looked in details at the crystals that were present in the geochemistry, we could actually test that. And since I made up this example, I will tell you that that's actually the case. So then in this particular case, we have a volcanic event, which gives us another timeline. So basically the point where this ash is present was all at the surface at the same time. And if we look at what's under it, we see, okay, well there's a river channel here, there are wave ripples here, there are turbidites here, and there are turbidites here. So that gives us the actual time events. However, what we just used was information that we don't often have in the rock record. So for example, we can't see a modern surface if the rocks are, say, several hundred million years old. When we have a volcanic event, it's really nice, but volcanoes aren't going off all the time. So what I'm going to show you is how it's easier to correlate by rock type, and it gives us different information. So I'm going to hide what I just drew. And we are going to define some facies and use those to correlate our rock types. Okay, so I'm going to define a group of facies that consist of the river and flood plains. So this facies group will include trough cross stratified sands with ripples, and they find upward in river rocks. And then it will also include mudstones with mud cracks, which show that they're getting exposed. Okay, so I'm going to color, I'm going to color the rocks that match that facies. So I'm going to interpret all of these as related to the river flood plains. The ash isn't, so I'll make a little bit of a jump for that. So we have some right here. The trough cross stratified sand would fit. The wave rippled sand does not, but then this rock does again here, okay, because it's got the trough cross stratification and the current ripples. I look over in these columns, I don't have any other facies with that composition. So next I'm going to define a facies with the wave ripples and color those areas. So we have a wave rippled rock there, wave rippled sandstones here. We have wave rippled sandstones here, then we have a volcanic ash, more wave rippled sandstones, and then this one has planar lamination, which doesn't quite fit. Now I can define turbidites, and I'm going to include the turbidites with the mud that's interlayered with them. I'm going to color that yellow. So these are all turbidites. There's some mud at the top, but that counts as part of my turbidite facies. When I get to here, there aren't any more turbidites down here, so I'm not going to color that for now. Then we have the mudstones and the turbidites, and then it's just mudstone down here. So I'm going to define a third facies that includes mudstones with no turbidites, and so that would be here and here. And now if we're going to do the lithostratigraphy part, we would match rocks of the same type. So those rocks and these rocks are pretty much the same. There's not anything like the orange ones here. There's a little bit of the wave-rupled rocks that are like the wave-rupled rocks over here. We have turbidites in this zone and this zone here, and we have turbidites in this zone and this zone here, facies division, but we have one among the mudstones down here. So I correlated the rocks roughly with those arrows, but we can actually correlate them more precisely at the boundaries between them. So this boundary is the easiest to draw because we have the contacts between the facies here and here. So this one down here would be my mudstone facies and this one up here would be my turbidite facies. So I also have turbidite facies here and now the way I want to correlate them, I need to think about what might have happened with Walther's Law. In general, what we see is that the deeper water rocks are below the shallower water rocks in each one of these columns. For example, we have river deposits sitting on top of wave deposits, and we can look at our modern environment and also just think about it, the rivers are not underwater whereas the waves are. And the same is true, the turbidites are in deeper water, the wave ripples, and I didn't show it in the diagram, but the further you are from the source of turbidites, the fewer you have, so the mudstone can be possibly way offshore from the turbidites. So if I was going to imagine that this middle core here was even longer, I might expect eventually to see the mudstone deposits down below. And so I'm going to interpret that the mudstones would be somewhere below this core. So that's a guess that that would be here. And if we can use the same thing to basically say, okay, this correlation, basically there's some boundary in here, in the lake, where you're going from wave ripples to the turbidites through time. Could look at the modern environment and maybe see that variation. So I'm going to define this, basically I'm going to project that the boundary between the wave ripples and the turbidites is somewhere between these two columns here. So I again have my turbidite facies here, and I'm going to wave ripple facies here. Similarly, I can predict that the boundary between the wave ripples and the turbidites is going to be somewhere deeper in this core here. And I have my turbidite facies here, my wave ripple facies here, and then there's some boundary up here between my river and flood plain facies and the wave rippled ones here. So I missed this little bit right here though. So one of the things that happens is that the boundaries between the facies aren't always nicely drawn, easy to draw lines. So I'm going to actually delete this line and improve my interpretation with a new one and say that, okay, this is the main boundary between the river deposits and the wave ripple deposits. And I'm going to say that maybe the river made an incursion into the lake when lake level was low, but then lake level went back up again here. So this will be my river facies in a little blob in the middle, and I still have my wave rippled facies in this zone here. Okay, so now this is our lithostratographic correlation. So I took a moment to remove some of the words and color in the facies. And so this zone that has the red-orange lines represents the river and flood plain facies. The orange ones represent the wave rippled facies, yellow turbidites, and the green, the mudstone. And so I'm going to show our prior correlations with the chronostratigraphy to compare and contrast. All right. So if we go along the modern surface here, we see river facies going into the wave rippled facies, and then the turbidites, like we see at the top. And then we have our volcanic ash. And you can see that the volcanic ash shows that the timelines cut across the facies lines at various points here, right? Not all the time, but a lot of the time. And this demonstrates that as if you correlate rocks by the rock type, you end up with the same rock type deposited at different times, right? And then you can have this different rock types deposited in different places at the same time. So this shows the difference between lithostratigraphy and chronostratigraphy. They have different purposes, and they answer different scientific questions.