- [Instructor] So this is our tutorial on sequence stratigraphy. The core I have here is from a classic location. By classic location, I mean it's from the Mesa Verde Group in Colorado. The Mesa Verde Group was deposited along the Western Interior Cretaceous Seaway during cretaceous time. And the core that you see here was taken very close to the Book Cliffs and when Exxon came up with ideas of parasequences and parasequence stacking and how you could possibly identify key sequence stratigraphic surfaces in core, logs and outcrop, these are the exact same rocks they used. Okay so you're getting to see the same rocks that were used to create log, core, and outcrop base sequence stratigraphy. So the first, I'm going to do this in two parts. The first thing we're going to do is we're just going to run through the core, and I'm going through the inarments of that position because you don't do sequence stratigraphy until you've done sedimentology first. Okay so we've already gone through this core, we've identified grain sizes, sorting, sedimentary structures, trace fossils, and now we're just going to put it all together. Okay but, when you're doing sequence stratigraphy one of the key things we're looking for, what we're looking for are patterns and surfaces. So let's look at the overall pattern first. Shale of the base. The sandstone on top. Few tiny shale breaks. Okay so the whole package is generally coarsening, until another shale break. Another shale break. Another sandstone package. Sandstone package starts coarsening upwards until we get to the next shale break. Now the core continues on this table here. And you've got a nice thick, homogenous shale package. So what do we have? We've got two coarsening upwards packages, now bear in mind that each one of these sleeves represents one meter. Okay, so keep the scale in mind at which this coarsening is occurring, So that is our pattern. We've got two coarsening upwards packages. Now let's look at key surfaces. What do we see? Sharp contact between upper shoreface sandstones. Upper to middle shoreface sandstones. Two offshore shales. How do we know these are offshore? Well that's what the bio-oxidation tells us. How do we know these are middle to upper shoreface sandstones? Well, in the lower part we got oscillatory flow generated sedimentary structures like hummocks and swales. On top we've got wave induced uni-directional current structures, which is basically cross stratification. Okay, so we go through the cross stratification. Any time you see a shale break like this guy right here, you mark that. Like this guy here, you're going to mark that. Okay this is, every surface matters, so you can't ignore them. We come up here, we see rootlets at this surface, again very important. Rootlets represents paleo shale. Paleo shale tells us there was sub-areal exposure there. Those are basically non-marine rocks right there. But then right on top, starting with these shales, you've got bioturbation in here. Okay, if it's bioturbation, and with this soil bioturbation that we're seeing, transition zone to offshore, another sharp base, another sandstone package. This one happens to have low angle cross stratification, until we get to this point. This is where bioturbation stops. Bioturbation stops, very coarse grain sandstone starts. The course grain sandstone has tons of normal grading and it has no bioturbation. Loss of cross stratification until we get to that coal. More shale. And then we've got this thick homogeneous shale package. And if you look in here, there's almost no bioturbation. So this is fairly anoxic right there. There's just a few shots of cylindricness right there. But overall fairly fairly anoxic. And you can see how thick that shale is. Each box here represents three meters. So that's one, two, three, four, five, alright so that's almost 15 meters of shale right there. Alright so now let's walk you through the sequence stratigraphy. The description part included pattern recognition and recognition of every sharp contact that we see. So let's start with this guy. Base of the shoreface sitting directly on top of transition zone shales. That is what we call the regressive surface of marine erosion, or an RSME. Alright, that is when your shoreface is actually incising during force regression into underlying strata. A few shale breaks, every time you see a shale break like this, like that guy, you would mark that as a flooding surface. Okay, what's a flooding surface? Exxon definition is deep water strata over shallow water strata. So by definition, that makes that a flooding surface. We've got one there, we have got another one right there. So there's two distinct flooding surfaces right there. The subaerial exposure right there, represented by the roots is our subaerial unconformity, which is the SU. Back in the day we called that the sequence boundary. Okay so, regressive surface of marine erosion, at least two or three flooding surfaces, we're still in our upper shoreface, and that's capped by a sequence boundary. Then we've got, after the sequence boundary we've got this material here. And that's representing marine influence coming in. How do we know that? From the marine face fossils. Transition zone to offshore shales, until yet another RSME. Okay, regressive surface of marine erosion. Upper shoreface sandstones incising into transition zone shales. On top of that we've got our fluvial deposits. How do we know these are fluvial? Well they're coarse grained. Not only are they coarse grained, they got not bioturbation, loss of cross stratification, you can see several bases of channels, including this guy right here. Huge change in grain size, going from fine grain material to coarse grained, poorly sorted material right there. Again non-marine rocks cutting into marine rocks. That right there is another sequence boundary. So we've identified two different sequence boundaries now. Getting into fluvial strata, so this is all non-marine. Alright, there's our first shale coming in. That first shale coming in is our first flooding surface. Okay, some siltstone right here, until we get into this thick shale subsession which represents our condense section. We call it a maximum flooding surface but technically it's more of an interval than a surface. Okay so maximum flooding surface, sequence boundary here, represented by a fluvial channel cutting into upper shoreface sandstones, another sequence boundary here marked by the rootlets. Alright so those are our key sequence stratigraphic surfaces. Once you've mark the location of your key sequence stratigraphic surfaces, the packages in the middle you can start splitting up into systems tracks.