- [Instructor] This modules focuses on sedimentary structures in deep water sandstones. We've already covered sedimentary structures and trace fossils in fluvial shell and marine successions. And now we're gonna look at a deep water settings. What we have here is a core taken by Chevron at the Colorado School of Mines from the dat sandstone which is crustaceous in age from Wyoming. And we're gonna take a look at what we find in here. So, the first thing that I wanna focus on is this unit right here. You can see a bunch of laminated mud stones, sharp base. You've got a bed standing, starting there and then, it continues onwards. Now, what I have done is I have checked the grain size at the base of this bed and I've checked for grain sizes in the middle and the grain sizes remain fairly constant. Not only are the grain sizes pretty much the same, there are no sedimentary structures in here. In this case, we would call is a structureless or massive sandstone. Now, the term massive has been misused quite a bit in stratigraphy. Just because something happens to be thick doesn't mean it's massive. I've heard of people call carbonates massive. There's a massive carbonate or it is the massive formation, that's the worst. If you're gonna call something a massive formation, massive in sedimentology, by definition, is referring to something which is structureless such as this bed right here. If you're familiar with the nether grainy energy matrix, these massive sandstones develop and you have steady, uniform flows. So flows and better in which the velocity is not decreasing over time or distance. Okay. Massive sandstones make best reservoirs and if you see amalgamated massive sandstones, which you kind of do in the middle right here. Amalgamating mean one massive sandstone is cutting into another massive sandstone underneath it, you're probably looking at either the axis of a deep water lobe or you're looking at the axis of a channel. In this case we know that this is a channel-like succession so we're looking at the axis of a deepwater channel right here. On the right, you see these inter-laminated facies. So let's take a look at these real quick and see what's going on. If you look right here, you could see that there's a sharp base and a gradational top with a mud cap. So that, by definition is a waning flow. Waning meaning it's not steady. In this case, flow of velocity is decreasing over time. This is a much better example. Sharp base and then gradational top. These are low density turbidites. Okay. So, massive beds we get with high density turbidites. And then those laminae I showed you are from low density turbidites. You look at this inter-laminated succession right here and the other thing you notice, right where I have my measuring tape are climbing ripples. See, you can get climbing ripples in a deep marine environment. You can see that's the first ripple. There's another grain. Here's another group of grain. Here's another group of grain, so they're all stacked up. And if you remember from the module on fluvial and shallow marine successions, climbing ripples are what we get from rapid deceleration of flows. The other feature you see quite a bit in here is convoluted bedding, okay? So, right there. You can see a lot of convoluted bedding. So that's soft sediment deformation. And when you, there's a term that Roger Walker used for these. He called these CCC turbidites. C for climbing ripples. C for convoluted lamination. And, C for clasts, grip of clasts. And, those are characteristic of levees associated with deep water channels. And so, what we're looking at here are most likely external levees because they're super mud-rich. Internal levees would be a little more sill prone. But, that's what you're looking at right here. So, if you keep moving on, we've got some excellent examples of sub-sediment deformation. You can see a classic flame structure right there. You can see balls. Ball and pillow structures. In this succession more climbing ripples. There's more examples of soft sediment deformation right there. Okay. Where we can see there's plenty of evidence for liquefaction and fluidization in here. Now, when we're moving up in the core, you can see that there's super large clasts and the clasts that you see are made up of the same material as the quote, unquote, the over bagging marman. Which means basically the mud stones beyond the channel. And some of these clasts can be fairly large. If you look at this guy, here's my pencil for scale. You can see this clast is very large, very angular, which means it hasn't been passported too far. So you're probably getting closer towards the margins of the channel. And, a lot of times the margins of these deep water channels are characterized by large scale soft sediment deformation and large chunks like that. So, there's a few more things we're gonna look at here. What I'd like to focus on are collections of clasts like this. Okay. Now, what happens is is when one turbidity current is going through these channels, it's losing competence over time. Which, competence is the ability of a flow to carry a particle of a certain size. As it's losing competence, it's dropping the coarsest load in the channels. And this is a great way to differentiate deep water channels from deep water lodes. By the time you get into an unconfined setting, most of these flows are fairly well-sorted and you're not gonna get clasts that are pebble sized like these guys right here. So why weren't these clasts dropped at this particular location? Well, there could be a few different reasons. This could either represent and amalgamation surface, which means this is one channel story. Here's another channel story above it. This happens to be the lag associated with the channel above. Okay. And, as successive flows go through, they all drop the coarsest grain particles right here. That is one possibility. Another possibility is this happens to be a sinuous deep water channel and this is right at the bend. And when you're at the bend, one of the things that happens if flow stripping. The channel is sinuous and but the flows that are going through it, they have a certain momentum. When they hit the bends, the clay-rich portion in the billows of your turbidity current, the clay-rich part, that goes through. When you get rid of the clay, you've decreased sediment concentration in the turbidity current and that decreases its competence and the grains drop out. Alright? We also have, again, more massive sandstones in the middle. Okay? And, this one has a nice, clay-rich cap on top. So does that one right there. Some of these are normally graded. You can see this one, sharp base, largest grains at the base. Smallest grains towards the top. And at the top, you also have the organic flakes. Okay, so that's making up your fine grain component. More inter-laminated facies in here. And then, you look at this part and we've covered this. We've touched on this in the section on barriers to fluid flow. Again, very laminated here. You can see the some sort of convoluted bedding in that zone but what happens here, not only is this white, there's no sedimentary structures in here. And, this is where someone actually dropped some acid on the core and of course they've stained it which is a horrible thing to do. If you want to test whether it's calcite, the smart thing would've been to turn this thing around, poured the acid on the back. Whoever did that has permanently damaged the core right there. But, that's what it is. That right there is the cemented zone. And then here, this is fairly interesting. What you've got is slump folding right there. Okay? This is important. We've got a scale right here, 15 centimeter scale. This is important because turbidites, the product of turbidity currents, this is not the only sediment gravity flow type out there. We've got debris flows as well and then we've got hybrids which we're gonna look at in a little bit. But when a debris flow is moving over a substrate, it is shear at the base so a debris flow has two parts. It's got a basal shear zone and then it's got its pluck flow on top. Okay. And when you see something like this, this is most likely due to shearing along the base of the debris flow as it's moving over the substrate. Alright. So, let's take a look at, so we've looked at high density turbidites, we've looked at low density turbidites, what we're gonna focus on now is a mixture between the two. We're gonna look at some hybrid beds. These hybrid beds are fairly common in this particular core and they actually tell you quite a bit. So, here's one example of these hybrid beds, okay? It starts right there, okay? It's a high density turbidite until you get to this part and here, we've got a debris flow. So what's going on? Well, it's the same event. The same event produces two types of flows. We've got a turbidity current that travels faster which is why it arrives sooner at this location, depositing this mass of sand. The debris flow is slower. It arrives later and then it sits on top of that high density turbidite. Okay? So in this case, it's a hybrid bed and more specifically it's what we call a linked debrite. Here's another example right here. High density turbidite, we get up here. And here it's actually a mix. You've got a lot of organic debris in it. In this case, the way it's convoluted, everything's kind of lined up so it's getting more towards laminar flow. You'd most likely call this a some sort of slurry flow. Then, here's another one on top. Here's the base of this turbiditity current and then on top is most likely another transitional flow. You're going from some sort of frictional debris flow to a slurry flow right there. The terminology I'm using is by Jeff Lowe, professor Stanford. You can use different terminology if you want. You just split this stuff down the middle likeand call everything either a debrite or a turbidite. Or, you could go with Arnold Bouma's classification scheme or Emiliano Montes and go with F ones, F fours, all that stuff. But, we're gonna stay out of that. So these are some of the most common sedimentary structures you'll find in a deep water environment.