- [Dr. Jaffri] We've talked about grain sizes, and what we're gonna look at next are sedimentary structures. Now, some sedimentary structures are easier to see than others. So we're gonna start with the easier ones first. So going through this core, you can see this jumbled mess right there. You've got a lot of angular class of clay suspended in what appears to be a sandy matrix. Okay? So this brescha that we see here, let's talk about how that actually forms. But before we do that, let's move on to something easier. Okay? What you see are several mud drapes. Okay, when I say I see mud drape, we're talking about that thin parting of clay right there. And here, you can actually see some lenses. Here's a lens of sand, you can see that it gets encased in that mud drape. Here's one, here's another one, there are some more on top. When you see these lenses encased in mud, we call that lenticular bedding. Okay? When you get lenticular bedding, it tells you that you mainly have a mud bridge matrix with some sand coming in. Higher up, you can see that you've got a lot more sand, but on top of these sands are individual mud drapes, and they're actually getting thicker in one direction. So let's talk about how these actually form. That was lenticular bedding, This is flaser bedding. The transition between lenticular and flaser is wavy bedding, which is kinda what you see in this section of the core. So let's talk about a few of these things. Of course when you're in the core lab, you're only describing these, you're not gonna be interpreting them at the core facility, but because I am showing these to you, it would be nice if you could understand how they're actually formed. So this is the general idea. All right? So we are... Let's assume this right here is the base of a tidal channel or a tidal flood. And what happens is let's call this landwards, and we're gonna call this basinward. Now, when the tide comes in, the tidal currents have enough energy to start moving sand grains, and what they do is that they create a series of ripples. So this is when the tide is coming in. Now, what happens is, once the tide is in and you've got high tide, we have this nice, quiet period called a slack water period. And during slack water, clay particles that are in the water can floculate. Okay, so these are all our clay particles. They floculate and they all sank. Okay? And what they're gonna do is they're gonna cover everything with mud, all right? After the slack water period is over, this was our initial tide, this was our flood tide coming in. Now, tide's gonna go back out, and then once it goes back out, you get another series of ripples that are moved, which is basically sand, which is being moved by tidal currents, but this time in the opposite direction. Okay? So we had our flood tide, this is our ebb tide. Okay? So now these both are sitting on top of that mud drape. Once that tide goes out, it's slack water time again, clay floculates, and we get another mud drape. Now when you keep repeating this, what you get, you get sand in here as ripples, and then here is a mud drupe, and that is another mud drape. And that's what you're seeing in this core right there. So that's our, right there, that's our slack water mud drape, this is the tide coming in or going out, we don't know, because the core's not oriented, and we don't know the geography. But anyways, slack water mud drape, then that sand was moved by tidal currents, another slack water mud drape. Okay? And in this core, you see we've got a repetition of these mud drapes. All right? So whenever you see these mud drapes, it's one of the many indicators that you possibly have tidal currents. So let's focus on this brescha we saw earlier. How does this form? Well, these mud drapes form everywhere, so you need a tidal curve. You have tidal channels. I'm just drawing one of these in cross-sectional view. Okay? So basically this is what I'm drawing. You've got a tidal channel, that's a point bar. So we made a cross section going like this. Let's label this A, call this A prime. So this'll be A, which is the cutback, and A prime, so you've got lateral accretion going on here. See these surfaces right there? These are covered by mud drapes. So these surfaces right here, all of them are lined with mud. What happens sometimes is that if you keep building this guy up, this surface right here will act as a glide plane, and this entire package of sediment is gonna glide and fall into the channel. And it makes this chaotic, jumbled mess of sand and mud drapes. And this stuff is what you're seeing right there. Okay? This is extremely common in tide-influenced settings. Another thing you get, going up here, is you can see that there's a lag, which means this is probably material that was ripped up. You could see a lot of ripple paths up there. When you see that, those often mark the base of some sort of channel. What you also see here are water escape features. Okay? And these are very common, the most common type in tide-influenced settings. Here's a great example of that. Okay, these are known as syneresis cracks. And it's because of the salinity difference from the tide, from the water coming in, evaporation, that's how you get these syneresis cracks. Very common in tide settings. Now if we keep moving, you can see that there's quite a bit of bioturbation, we're not gonna talk about bioturbation in this particular module. So let's move on to our next core. Okay, this one is a very different core. We could see very bioturbated, salt stones, and shale right there. And then coming up here, what you can see is a very very sharp base, okay? Very sharp base, fine sand, and then it's got a nice concave up top, but that concave up top has been burrowed. Okay? So let's talk about that. What is going on there? Basically, what happens is, let's assume this is our sea floor on a normal day. Once a storm goes through, the sea floor gets undulating like that. Okay, and that's because of oscillatory currents. You get these bumps and you get the depressions. The bumps are known as hummocks, and these depressions are known as swales. Now, when a storm starts, it has a lot of energy. So you start with erosion, which is why you get this sharp base right there. Okay? And then storm energy is subsiding, which means waning flow conditions, waning means low velocities, decreasing over time. And then once the storm is over, organisms will show up and they'll start eating all the nutrients and all the organic material that was brought out into the ocean from the storm waves hitting the coastline, okay? And once these guys start feeding, you can see they start burrowing, and then you can see one of the burrows right there. So this is also, the succession is often called a tempestite. Okay? So let's draw that out for you. So you often get a sharp base. Okay? And then a gradational path. Okay, and lots of burrowing. Okay, so this right here represents our hummock, we'll just call it HCS for hummock cross-ratification. And then the top part of it is burrowed, and of course, all this is super burrowed. Okay? Because the burrowing happens during quiescence. All right? So that's what you're seeing in this succession. When you look here, there's a few things you should be mindful of. For example, this section right here. You see this? Now that is not a sedimentary structure. Basically those are saw marks. So whoever was slapping this core was supposed to pus the core slowly through the saw, but obviously they weren't as slow, they really pushed it, and as a result, they created these saw marks. So do not mistake these for sedimentary structures. Now when you're looking at this section of the core, it looks relatively blank, okay? And the reason it looks so blank is because the core's not wet. So what we're gonna do is we're gonna wet the core, and when we do, you're gonna see a lot more details.