| 00:01 | Yeah. OK. All right. Again, lots of more references than |
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| 00:07 | listed here. If you see a diagram or a topic that you're particularly |
|
| 00:14 | in. Look at the citation, if I put it in uh the |
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| 00:21 | boulder, if not uh send me email and I'll send you the PDF |
|
| 00:25 | I have it. OK. Um You know, we talked about |
|
| 00:37 | with respect to coastal variables, those in influencing deltas are the same ones |
|
| 00:44 | influence tidal flats and barrier islands and plants. Um We could look at |
|
| 00:53 | as a list or we could think it. Kind of like a geophysicist |
|
| 00:57 | think about it as a flow chart uh sediment input and reservoir energy and |
|
| 01:06 | to get to the delta. We think about like a geologist might look |
|
| 01:10 | it. Uh The, the key is look at all the feedbacks and |
|
| 01:15 | how complex that ultimate system is that up providing the sediment input to that |
|
| 01:25 | uh to that standing body of OK. Uh And the influences that |
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| 01:34 | variables that control the energy levels of standing body of water. OK. |
|
| 01:40 | we will talk about some though, not all of those. OK. |
|
| 01:46 | Early classifications were geom morph of uh elongate uh arguably strand plane. |
|
| 01:57 | The, the test of it here see was that beginning in the late |
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| 02:06 | uh fisher from U T. Um , and colleagues began to think about |
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| 02:13 | as being high destructive or high And again, the idea of being |
|
| 02:20 | relative to what Well, uh the between sediment input and we mainly wave |
|
| 02:30 | , sediment input is high. We elongate delta, sediment input is low |
|
| 02:35 | wave energy is high, high Uh Then they thought, oh, |
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| 02:39 | , you know, maybe we ought add the influence of tides. |
|
| 02:43 | uh then we get this diagram that destructive wave influence, high destructive tide |
|
| 02:51 | . Bill Galloway also, uh was uh U T at the time then |
|
| 03:00 | out? Well, let's do this a triangle diagram. And this pretty |
|
| 03:03 | has remained the way we think about the delta classification, uh some relative |
|
| 03:11 | of sediment waves and energy. Now , you'll notice that shape of this |
|
| 03:18 | shape uh um was sometimes called an delta. Uh Walker said that's not |
|
| 03:27 | a delta, it's an estuary uh then stick out. Um We basically |
|
| 03:34 | that uh and the confusion is that dominated estuaries and tide dominated deltas do |
|
| 03:43 | look pretty simple. So, uh confusion is less real now staying along |
|
| 03:51 | triangular input, the most recent to into the classification for is say, |
|
| 03:59 | , you know, I, we that there are great L L |
|
| 04:05 | don't fall at the end. So have a vocabulary that allowed us to |
|
| 04:14 | where they fall. Uh And that's reasonable. And, and that's |
|
| 04:19 | particular classification has been adopted uh more than not. But then what about |
|
| 04:28 | type? Maybe we could add 1/4 . Um And then all of a |
|
| 04:34 | you got all these different kinds of different great planes and, and, |
|
| 04:41 | well, uh we give them that's quite true. But the difficulty |
|
| 04:48 | first of all, the different especially sediment and put added to the |
|
| 04:53 | is going to affect the morphology of del secondly, delta has changed through |
|
| 05:00 | . And thirdly, delta's um are show even lateral changes with short periods |
|
| 05:11 | time. I don't mean changing from stand to high stand, I mean |
|
| 05:16 | left to right. So this was of illustrated the difficulty of describing the |
|
| 05:23 | Delta On the Danube Delta over the couple of 1000 years or in the |
|
| 05:29 | I stand um would variably a wave river dominated delta. In fact, |
|
| 05:37 | pretty much today, you see Delta three and four are very different. |
|
| 05:43 | . Uh This is in spite of fact that there are no tides in |
|
| 05:47 | Black Sea. So we're only looking sediments fly and wave energy? |
|
| 05:53 | So where would that delta fall? in terms of, is this gonna |
|
| 05:59 | ? Well, I don't know, it, is it one place or |
|
| 06:02 | ? Is it kind of in the ? Uh And that's a hard |
|
| 06:09 | that's one of the complexities that we of dealing with deltas. Uh Also |
|
| 06:15 | you only had a few wealth. Would you describe this delta complex uh |
|
| 06:23 | a wave dominate. Delta river maybe a barrier island, uh maybe |
|
| 06:29 | the C delta. So these are problems that we have to reconcile. |
|
| 06:37 | it, it begins with looking at variability of modern deltas to anticipate the |
|
| 06:46 | that we might expect with ancient delta . Well, going back to uh |
|
| 06:53 | classification, um let's look at something might be right here big. Um |
|
| 07:04 | is an attempt to classify the Mitchell delta. And at first, it |
|
| 07:11 | looks pretty straightforward. But when we at the delta plain, uh it's |
|
| 07:17 | a lot of Southern das those environments tidal related thing. Uh tidal |
|
| 07:26 | tidal channels, tidal marshes, it wave and uh blue things like channel |
|
| 07:37 | bar, uh play lagoon film, beach ridges, abandon channel. Uh |
|
| 07:47 | just a lot of different things that here. And so here, then |
|
| 07:55 | , in this case, oh, looking at spits that are clearly wave |
|
| 08:05 | , but we're looking at tidal channels are here that are clearly tidal |
|
| 08:11 | And then the river channel itself is channel influenced to. So we need |
|
| 08:16 | figure out the relative percentage of the plane. It consists of different types |
|
| 08:29 | tide wave and river morphology. When do that, you can actually quantify |
|
| 08:38 | being 62% tides, 25% fluvial and weights. OK. Um Well, |
|
| 08:49 | is at least a quantitative approach to modern deltas. Uh But how do |
|
| 08:58 | go to the rock record? Here's a core and here you can |
|
| 09:06 | at the relative percentage of waved dominated doin. Well, wave generated tide |
|
| 09:16 | in fluvial, generated sedimentary structures. ? And that puts it way over |
|
| 09:24 | . OK. Now, the key is that we know at this point |
|
| 09:31 | types of sedimentary structures associated with the tides and rivers, OK. |
|
| 09:40 | cross strata, um waves, um bundles tide. So meandering bar deposits |
|
| 09:52 | bar deposits of two of you. we've already got the ability in mind |
|
| 10:00 | on the previous lectures to take a call and look at this pro grading |
|
| 10:07 | and say the relative percentage of species have been preserved through time because the |
|
| 10:16 | when we go back to here, is not the delta in as it |
|
| 10:24 | is the delta at a snap in . Some of these environments have a |
|
| 10:30 | lower preservation potential than others. And notice that if you looked at |
|
| 10:39 | face sheets, the surface deposits, . Her title. If you look |
|
| 10:45 | the rock record, most of what's is wave gene. OK. So |
|
| 10:50 | this tells us is that the deltas mixed. Um And we can look |
|
| 11:03 | a vertical section and or a cross and begin to take into account the |
|
| 11:11 | percentage of the sediments as preserved in context of the process that and these |
|
| 11:20 | examples of some of the things we look for all of which we've talked |
|
| 11:25 | before. So here's an example of lower Wilcox delta in core, looking |
|
| 11:35 | the core to figure out the relative of fluvial and title and wave generated |
|
| 11:50 | depending on where you are. So we're beginning to see this approach |
|
| 11:57 | to the ancient record and it's got distinct advantages. Uh And it's one |
|
| 12:02 | the ways of trying to get past members and figure out where in this |
|
| 12:12 | uh processes did this particular delta exists the period of time that it for |
|
| 12:20 | that it can change through time. with that in mind, let's think |
|
| 12:25 | the processes that impact deltas. There's the sediment coming in. Uh |
|
| 12:35 | that really is influenced by the water sediment discharge. Uh the percent suspended |
|
| 12:41 | grain size, seasonality, the density between the receiving base and the input |
|
| 12:54 | depth bottom slope and sediment type on bottle tidal range and associating currents and |
|
| 13:03 | wave energy and associated currents. So these are the things that we're |
|
| 13:08 | at. So we kind of lump of them together into buoyant forces. |
|
| 13:14 | buoyancy forces, frictional forces and inertial being the primary things that affect deposition |
|
| 13:23 | the mouth of the river. And ironically, tides and waves are |
|
| 13:30 | they important secondaries. But uh we're ignore them for just a couple of |
|
| 13:36 | . So what we're gonna do, gonna look at the relative densities of |
|
| 13:42 | incoming out like flows. We're and we're gonna look at Hypo uh |
|
| 13:49 | pal flows where the river is less than the receiving basin hyper where it's |
|
| 13:59 | dense and Homo where it's about the . Now, in the case of |
|
| 14:04 | Homo, pital flows, they tend be dominated by friction and void forces |
|
| 14:10 | the cases of the hyper petal flows by inertial forces as are. So |
|
| 14:18 | see what that might look like if trying to describe the dispersal set. |
|
| 14:26 | . The Hyper with more dance since on the bottom by, let's look |
|
| 14:48 | the hypericum for a second. Uh We're seeing it's floating and the |
|
| 15:00 | to which this plume is floating is to be a function of the buoyancy |
|
| 15:05 | here. And so experimental and field show that the mouth bar is a |
|
| 15:17 | where the cross sectional area of the is decreasing. So the flow is |
|
| 15:30 | to reach a maximum right here at bar crest. So we've got increasing |
|
| 15:38 | in the back of the bar maximum here and then decreasing down here. |
|
| 15:46 | so one of the things we're getting lower flow regime, upper flow |
|
| 15:57 | no, no regime. And notice we're actually talking about rude ducks. |
|
| 16:07 | that food number is the den meric number. Talk about it more. |
|
| 16:14 | , we mentioned it early on and is the oh inertial de buoyant forces |
|
| 16:23 | this flow here. And we've actually a hydraulic jump that's occurring going from |
|
| 16:34 | critical to sub critical. We get high energy. So most of the |
|
| 16:39 | uh is occurring at our crest now that plume is a buoyant plume. |
|
| 16:51 | and it doesn't feel the bottom There's not much friction here. It |
|
| 16:56 | to spread but not real fast because internal to this, we've got a |
|
| 17:05 | of got flow patterns that keep it flowing too widely or dispersing too |
|
| 17:14 | So at what happens is we've got tone of deposition here is the bar |
|
| 17:25 | and we've got kind of a funnel shaped here that's flanked by levies and |
|
| 17:35 | bar channel going into bar or the going into bar crest. We're gonna |
|
| 17:43 | this expressed differently. And I think when we look at uh some more |
|
| 17:48 | work, but this is just a because what it suggests is that in |
|
| 17:54 | hyper? I'm sorry. Um, hope it, don't saying it? |
|
| 18:03 | . Hi, Pope. Picked I get those confused even today. |
|
| 18:10 | , we have a crescentic bar levies because of that, if we look |
|
| 18:21 | the cross section through here, we that because the bar is scenic and |
|
| 18:28 | extend very far. It tends to us relatively confined for faces. |
|
| 18:38 | Now, what that means is that this plume. In fact, let's |
|
| 18:44 | at it here. This plume doesn't much. OK? Which means that |
|
| 18:53 | it extends, the sub aqueous levees sub aerial. So we've got levees |
|
| 19:03 | here that are gonna become sub aerial that bar crest will be limited to |
|
| 19:10 | area here. So in cross it's gonna be relatively confined la |
|
| 19:20 | So this is gonna be typical where have buoy and flow, especially a |
|
| 19:26 | of muds and deep water, deep because we wanna make sure that there's |
|
| 19:34 | interaction with the bottom. Ok. , consider something different where you have |
|
| 19:45 | water in the basin that's gonna be dominated. It's gonna spread laterally because |
|
| 19:58 | slowing down. The whole thing is as it slows down, it's dispersing |
|
| 20:07 | flow in all directions in distinct contrast that buoyancy quote. Now, the |
|
| 20:17 | result is you got the flow channelizing diverging and so you get it's more |
|
| 20:28 | middle ground bar in a lot of secondary bores again, we've got the |
|
| 20:36 | of sediment and greatest energy on the . But now look at the levees |
|
| 20:41 | beginning to display. So the Alya would be an example of that where |
|
| 20:50 | getting basically the shallow Alya Bay being receiving basin for the Fly River, |
|
| 20:59 | during floods because it wants to become Mississippi river. So we got a |
|
| 21:05 | bifurcation and as you might expect, gonna have a much wider sandy distribute |
|
| 21:18 | . OK. So we both can be hypo flow. It depends on |
|
| 21:27 | water depth to a large extent. is friction versus buoyancy dominated. |
|
| 21:33 | Well, muds tend to keep it in suspension, deep water keeps it |
|
| 21:40 | interacting with the bottom sands tend to lower in the water column. And |
|
| 21:47 | water means that there's more interaction with plot. OK. Now, even |
|
| 21:55 | that, we do begin to see influence of tides until finally, we |
|
| 22:03 | tis that become asymmetrical and we get linear tidal bars. So these river |
|
| 22:11 | bars, do them protic lo um one n member. Those linear tidal |
|
| 22:25 | I talked about uh are the other . So we'll talk more about these |
|
| 22:33 | . Now, an inertial dominated flow where there's more impact in slowing down |
|
| 22:46 | . This is deep water. It be hyper petals flow down and there's |
|
| 22:51 | spreading. OK. It's also decreasing , but it's not floating as |
|
| 23:01 | And so we get this um ex expansion. And the thought here was |
|
| 23:11 | that that is occurring when you had flu. It is to say that |
|
| 23:20 | was no a density Segre separation between incoming fluid which would tend to want |
|
| 23:27 | make it float. And the outlines um receiving basis for it. |
|
| 23:35 | Uh And that's why it expands And the other thought was that's gonna |
|
| 23:42 | us these Gilbert type deltas rapid deeper water, the over type. |
|
| 23:52 | . And that's shown here um for type deltas, I'm sorry down here |
|
| 24:00 | home. But we also get it hyper flow where we have so much |
|
| 24:11 | that uh rather, so much sediment that were slowing down the bottom. |
|
| 24:25 | we can get inertia dominating when it's down on the bottom is ect currents |
|
| 24:33 | we can get it when it's up top with home picked up. So |
|
| 24:41 | be looking especially at these various products we look at delta deposits. |
|
| 24:50 | more recently, we're looking at uh experiments. Uh I'm not gonna get |
|
| 24:57 | a lot of detail but notice how getting these elongated plums with narrow, |
|
| 25:10 | they increase levies. And this elongated , this bar is getting larger and |
|
| 25:16 | as it elongates. And this is couple of examples though, by the |
|
| 25:21 | we get down to here, notice more of a bar and even a |
|
| 25:27 | bar as it evolves uh with different this would be more um friction |
|
| 25:38 | more do it. So let's see , that we get when this channel |
|
| 25:54 | the standing body of water. Distribution channels, levies and the mouth |
|
| 26:03 | programing offshore. And we're gonna use Mississippi, not because it is the |
|
| 26:08 | typical of deltas, one of the , but simply because it is the |
|
| 26:14 | study. And if you recall, the study began when the L S |
|
| 26:26 | uh and uh coastal Research Center began the corps of engineers began studying the |
|
| 26:35 | River while they were studying the Mississippi and delta because the core is responsible |
|
| 26:40 | everything that's navigable. So They started the Mississippi River in the Mississippi |
|
| 26:50 | They started in the 40s and it's the best study delta we have. |
|
| 26:55 | let's look, first of all, one of the main tributaries or dis |
|
| 27:00 | rather. Here we have aqueous levee levee. Here we have an offshore |
|
| 27:10 | , kind of a protic offshore bar got a proximal part that we're gonna |
|
| 27:18 | the distributor mouth bars and a distal . And beyond that, we're gonna |
|
| 27:25 | a pro delta. And beyond that within that, we're gonna have some |
|
| 27:31 | these displays where there's remobilization by the delta nearby in the delta um |
|
| 27:43 | front. And we got winnowing by and storm waves, especially the |
|
| 27:52 | Winnowing is gonna be mainly the upper of the bar um storm waves will |
|
| 27:59 | the entire bar and you can get floods, increased pluvial deposits, giving |
|
| 28:10 | both these splays that are coming Think these may become eventually Hyro and |
|
| 28:22 | get reworking by slumping. Yeah. this is kind of a a general |
|
| 28:30 | of the river coming in the pausing . I've been depositing bars, those |
|
| 28:39 | being reworked by waves. And during , the bars are going to migrate |
|
| 28:47 | offshore and also generate offshore deposits. by the way, those deposits will |
|
| 28:59 | be generated by the storm waves. the talk, what we talked about |
|
| 29:06 | storm surge, wind set up and generated storm deposits going below storm wave |
|
| 29:14 | . Ok. That's some of these well, but we'll look for |
|
| 29:19 | Now, in the simplest term, got hyper protective floating deposits, sand |
|
| 29:31 | caused it then mixed sand and mud more or less settling out a |
|
| 29:43 | And what that would give us would a sandy portion and then a muddy |
|
| 29:51 | of that pro grading delta. Now sandy portion is typically called the delta |
|
| 30:02 | . OK. Uh Except here they the delta front extending all the way |
|
| 30:09 | here with the pro delta being mud below. Now, part of that |
|
| 30:19 | that even though uh Boa used this to uh as his model, the |
|
| 30:29 | here is that there's the sand does extend very far offshore and into very |
|
| 30:37 | water here. The implication is that delta front sand extends into much deeper |
|
| 30:47 | sand itself that suggests that the thickness the delta front may be a function |
|
| 30:57 | wave energy and type of setup. . Fair enough. But what that |
|
| 31:04 | begins to make it sound like is short face. Remember when we had |
|
| 31:07 | those discussions about where do you draw line with a pro grading system going |
|
| 31:15 | sand to mud? OK. And there's a similar confusion if you like |
|
| 31:23 | the use of the term delta And so I will show you examples |
|
| 31:28 | how this called different things. And want you to just imagine how is |
|
| 31:36 | might vary and this is just in at the dip section. Now, |
|
| 31:42 | other thing to keep in mind is when you're trying to correlate a |
|
| 31:48 | but from a couple of logs or roles, uh you need to be |
|
| 31:55 | about layer cake photography. When in , this is a delta. I'm |
|
| 32:04 | describe the sands as delta front, are not a straight line but form |
|
| 32:15 | um but likes to call shazam that extending into the offshore. OK. |
|
| 32:26 | each of these represents a major pulse by reworking and no pulse P |
|
| 32:37 | So we've got to just like we a meandering stream, uh which was |
|
| 32:46 | us series of packages that uh we to think about that pro grading delta |
|
| 32:57 | and pro delta So here is the Front, 1764 and here it is |
|
| 33:04 | 1779. And so we can actually at the pro gradation of that delta |
|
| 33:14 | . Notice it's not called the delta here. Here, it's called |
|
| 33:19 | the sand is distributing a mount Now, all of a sudden the |
|
| 33:24 | becomes delta front and the pro delta way down here. Uh well, |
|
| 33:30 | don't use that distinction anymore. They back in the 80s, but just |
|
| 33:35 | you have to often translate older literature modern thinking. Ok. So what |
|
| 33:47 | would call the delta front now extends this. Ok. Um And I'll |
|
| 33:54 | back to that but notice that here's same um Mathematic shorelines. But now |
|
| 34:04 | what happened from 79, The 28, the delta has stopped programing |
|
| 34:16 | even began to be wrote. if we look at the erosion of |
|
| 34:20 | delta as a whole, large areas that pro grading delta front have eroded |
|
| 34:28 | especially if we look from 1979 look how much erosion has been occurring over |
|
| 34:36 | . The fact is that if you at 1940 Green is 1979 and yellow |
|
| 34:49 | 2005, much of that delta Well, almost all of it has |
|
| 34:55 | depositing and much of it has actually . Ok. Now, what this |
|
| 35:02 | reflecting is the decrease in sediment load the 19 50s on with dams. |
|
| 35:13 | . Um so this delta is actually to be abandoned and we're seeing |
|
| 35:21 | the initial phase of it by erosion and what I couldn't find quickly, |
|
| 35:31 | I'll tell you is in the is there is that the marshland which is |
|
| 35:37 | measure of the sub sub aal delta disappearing as well. Now it's disappearing |
|
| 35:48 | two reasons. But the main reason the delta is subsiding at the same |
|
| 35:56 | , less sediment is being provided to the marshes. So all over Missis |
|
| 36:06 | is losing a huge amount of Siberia because submergence is greater than the sediment |
|
| 36:15 | can keep up. Now in natural or anthropogenic. And the answer |
|
| 36:23 | yes, both we had, we delta submerges because of compassion and this |
|
| 36:34 | compassion of the delta clay. We also get delta subsides because of |
|
| 36:44 | and oil and gas extraction causing the of clay. And if you wanna |
|
| 36:52 | into an argument, Pick one over other. Ok. Um Environmentalists want |
|
| 36:59 | say it's all anthropogenic petroleum companies want say no, it's all natural. |
|
| 37:07 | course, it's answer again is Uh But we're seeing the beginning of |
|
| 37:13 | transgressive phase of even this modern we'll talk more about that a little |
|
| 37:19 | , but that's really important to think this transition from Delta programing beginning to |
|
| 37:26 | abandoned. And just as a clue what's gonna follow what's gonna happen if |
|
| 37:33 | delta begins to be abandoned. one of the things is it's gonna |
|
| 37:37 | its river course, it's gonna shift form a new deal to low. |
|
| 37:42 | delta is forming today in Bay. we actually have some land rowing in |
|
| 37:53 | is the delta, which is the Mississippi delta. And most of the |
|
| 38:01 | that we're losing is a modern Mississippi . The loss of sediment and marsh |
|
| 38:09 | is in part coincident with and because the gaining of land and settlement with |
|
| 38:15 | fly delta. So just keep that mind. OK. So here we |
|
| 38:21 | this probating delta and up near the , we've got that bar crest and |
|
| 38:28 | bar and we'll talk about more This is that coarsening upward sequence that |
|
| 38:36 | the proximal out into frontal displays and delta. OK. So this is |
|
| 38:46 | delta front by the definition of being sand. This is clay. He's |
|
| 38:55 | pro delta and just like short we can argue left to right about |
|
| 39:01 | to call this. Is it distal front? Is it co pro |
|
| 39:07 | Does it have a new name? Well over here, uh it's called |
|
| 39:13 | pro delta. Yeah, that will . I'm not sure I care. |
|
| 39:19 | But uh and here it's called delta distributed him out. I'm gonna call |
|
| 39:25 | delta front. It's the same deposits it's just a matter of what do |
|
| 39:33 | call it? And going back to shore face, uh, foreshore |
|
| 39:42 | Welcome to the Real World. Uh I'm gonna keep this vertical section |
|
| 39:47 | though because it's from Boar. And got a lot of good examples of |
|
| 39:52 | these different face sheet by whatever Uh, cause here is that Hoing |
|
| 39:59 | sequence that we get, you notice in here, we get coarser splays |
|
| 40:09 | finally it's all delta front. let's begin with the offshore, highly |
|
| 40:19 | mud with intubated sand, but it's mixed up. It's really hard to |
|
| 40:25 | . Ok. What that says is low rates of deposition relative to rates |
|
| 40:31 | conurbation. Yes, mud is being out there, but it's beyond the |
|
| 40:37 | where the river sands over, they're relic duds left over when sea level |
|
| 40:44 | a little low. Ok. So primary sedimentary structures to speak of. |
|
| 40:52 | , we're beginning to get no primary structures, mainly graded beds of silt |
|
| 41:02 | mud, silk to clay. Um little bio, not much ur because |
|
| 41:11 | though we're beginning to get sediment that's derived from God, sediment plume, |
|
| 41:21 | sediment plume is also fresh pressure. we get a uh within the sediment |
|
| 41:28 | . We uh and because of the plume, we're getting a distressed uh |
|
| 41:35 | , how distressed. The relative amount bio depends on the subtleties of |
|
| 41:43 | frequency of floods. And so it's vary. Ok. And to get |
|
| 41:49 | up, we are getting into inner and mud and notice the sandstones are |
|
| 41:57 | to be a hum. Ok. the muds, they show these graded |
|
| 42:06 | that are more distal deposits of storms hyper pickle flows as we get a |
|
| 42:14 | higher up. You'll notice that some the sand has actually subsided for |
|
| 42:24 | This case is um completely separated from home layer. Uh And that's because |
|
| 42:31 | getting the sand coming out over very saturated, un compacted mud. |
|
| 42:41 | So it's loading, the sand is the underlying water, saturated blood. |
|
| 42:49 | we get a lot of soft sediment in that area here and that's shown |
|
| 42:53 | as well. Well, eventually we're then to thicker sand events associated with |
|
| 43:05 | pro grading point bar reworked by Uh It can be bioturbated. Uh |
|
| 43:15 | usually you're getting some kind of primary or structure in here. Again, |
|
| 43:24 | about that whole difference between the pro shore face and the pro grading river |
|
| 43:32 | delta. OK. Now, let's at that system as it pros and |
|
| 43:42 | is a real, this has been relatively narrowly confined lobe of the |
|
| 43:51 | So if we draw a cross section here, we're gonna see the pro |
|
| 43:57 | of that for delta and delta OK. And then we're gonna see |
|
| 44:13 | channel in the marsh deposits, marsh into bed. Now, this here |
|
| 44:25 | probation kind of begins to get a pack because it's mainly all sand. |
|
| 44:32 | this would be the distal and proximal delta. And this would be the |
|
| 44:37 | unit and some of that sand may be distributor channel and then very fine |
|
| 44:49 | get marsh. OK. Uh Here that pro grading system. Um |
|
| 45:04 | we might see, are they down ? Yeah. So by the time |
|
| 45:11 | get to this, actually, I you to mainly think about this diagram |
|
| 45:18 | in this diagram here. OK. In this transition here. So focus |
|
| 45:33 | what that looks like as that delta progra to the press you. That |
|
| 45:47 | what's called the bar finger sand. called the bar finger sand because |
|
| 45:58 | it has progra out digital digitate That is to say it hasn't bifurcated |
|
| 46:05 | lot. It bifurcated here and then kind of went on straight now that |
|
| 46:16 | finger sand is because of that hype flow and that deep water in the |
|
| 46:22 | plume, it just never, never widely. So we're seeing those plumes |
|
| 46:32 | out like this and the plumes are the sand will be deposited. |
|
| 46:39 | Now, if you look at it's pretty, I've messed it up |
|
| 46:43 | notice the variation of thickness From less 100 ft To over 200 ft. |
|
| 46:54 | fact, the pods are Of over m to six m. So what's |
|
| 47:08 | this very lumpy look? And I even add that if we look at |
|
| 47:15 | is a pack of uh I think a Pennsylvanian sandstone, the Antar |
|
| 47:20 | we get these same pods. There's about the pro, it's not exactly |
|
| 47:32 | . Ok. Yeah. The reason is that you pro grading over those |
|
| 47:45 | saturated muds again, easily compacted and forming these diap pes. And if |
|
| 47:52 | look at these dots, if you make a series of chores or |
|
| 47:57 | section, you see that this mud here is actually just the most recent |
|
| 48:09 | a series of older mud lumps. of course, the bar finger sands |
|
| 48:15 | sinking between the the dark periods. S U cord, a one of |
|
| 48:25 | mud lumps and they put down 300 of cool. And in 20 |
|
| 48:34 | every bit of that core Casey had to the surface. That's how rapid |
|
| 48:41 | rate of uplift was due to loading those uncoached muds. And that is |
|
| 48:48 | course why we get these knobs of thinking and sand. And that's really |
|
| 48:57 | kind of the beginning of what's going with deformation further offshore that loading of |
|
| 49:05 | mud and the mud failing it's in of itself is causing a huge amount |
|
| 49:12 | instability issues with respect to that muddy . Oh, we get these little |
|
| 49:22 | slump of gullies and loaves all along front. Uh We get pro grading |
|
| 49:36 | here, but we get large scale here. We get older slumps that |
|
| 49:43 | being filled. Ok. So let's at that and we realized that the |
|
| 49:51 | delta is a mess. It is but an area of gentle deposition of |
|
| 50:02 | over time. Ok. And you some of these mud diap here coming |
|
| 50:11 | and even disrupting the delta, the sands, the rather the uh delta |
|
| 50:17 | sands. And then beyond that, get these growth faults. Gullies lumps |
|
| 50:26 | we look at how much of the has been reworked, almost all |
|
| 50:34 | up to 40% on the shallow delta has been reworked. The non reworked |
|
| 50:44 | is that lighter colored yellow? And more recent surveys show that as |
|
| 50:51 | get farther down, virtually, all the delta has been reworked. |
|
| 51:02 | And especially here, the orange is loaves. They laterally coalesce and they |
|
| 51:11 | are, was forming that part of delta. Now, if we look |
|
| 51:18 | them inside scan sooner, we see shoot and this culling and then the |
|
| 51:26 | is coming in. So here, the load, here's another moment, |
|
| 51:37 | know, a uh compression ridges. . If we draw a cross |
|
| 51:46 | these mud flows or um may laterally . Ok. But here's what they |
|
| 51:58 | up and here's the crowns, the compressions. Uh We didn't know this |
|
| 52:10 | of all until we started looking for and we didn't start looking for it |
|
| 52:15 | we lost a drilling rig after Hurricane . And in one of the A |
|
| 52:23 | um in the late fifties, they because of the hurricane and tried to |
|
| 52:30 | back. It wasn't there. They it eight miles down down slope. |
|
| 52:37 | And at that point, they realized um there's a lot of foundation issues |
|
| 52:43 | lack of stability problems uh that they taken into account. It's now the |
|
| 52:49 | thing you do when you go into offshore area, you do a basically |
|
| 52:54 | an engineering geology study uh to look the, The mobility of that lower |
|
| 53:02 | 100 m. OK. Now, mentioned that the um delta today is |
|
| 53:15 | to submerge. OK? Uh It's to grow here. We'll talk more |
|
| 53:23 | that later, but I wanna focus the modern delta because it's what we |
|
| 53:30 | most about how this type of delta formed. It is a quote elongate |
|
| 53:39 | with the star finger sand. Um started out In 1874, very much |
|
| 53:49 | a bird today. It's not. and the reason is that much of |
|
| 53:59 | uh skinny leg of the bird's foot been fattened up with cress place. |
|
| 54:08 | most of the land that we see the more distal portion of the super |
|
| 54:17 | is actually for vast play and we monitor it by looking at Cubit's gap |
|
| 54:27 | right here, grew, grew, , grew and grew, OK. |
|
| 54:37 | By the way, it's now shrinking because of subsidence, but that's this |
|
| 54:43 | right here and these are some of oats, OK? Here's Cuba ga |
|
| 54:55 | one of the points about to And this has to CVAs places in |
|
| 55:01 | . What is a play in the ? It's just crevasse places that fall |
|
| 55:08 | that are associated rivers on deltas and into bays or going into rivers |
|
| 55:16 | going into floodplains. Uh Those gaps be long lived and can be |
|
| 55:25 | flood after flood as we've seen. here's the river Delt elongating and in |
|
| 55:35 | the lower delta plain is filling with blades. Ok? Now, if |
|
| 55:45 | look at one of those crevasse plays that view, we can look at |
|
| 55:51 | present active crevasse play and think of like a mini delta. We've done |
|
| 55:59 | like a pro delta delta front, tilt to play. But if we |
|
| 56:07 | more carefully, we've got evidence for older her vast play that it over |
|
| 56:19 | . But the expression of that, he is a little bit of a |
|
| 56:26 | marsh. Some Oyster reefs, the Wreaths were basically forming on the little |
|
| 56:35 | on the channels. And then of Bay itself. So we're gonna take |
|
| 56:41 | cross section down here is focusing on uh um modern, I'm sorry, |
|
| 56:55 | focusing on when this inactive distribution was and abandoned. And then we're gonna |
|
| 57:01 | a cross section more strike view to at the present day Travase play. |
|
| 57:11 | here's that channel, here was the play and here is that Crevasse play |
|
| 57:22 | into the bank. All the way here. Now that Crevasse play was |
|
| 57:35 | when this, when it shifted this here, notice it's still staying in |
|
| 57:39 | same location as the levy, but , it's shifted in the bay. |
|
| 57:46 | now we've got a transgressive phase erosion a beach and there's oyster reefs occurring |
|
| 57:57 | period in various Bethy metric highs. I've got a transgressive, I'm |
|
| 58:04 | a regressive transgressive cycle. Now, we look at it in cross |
|
| 58:11 | here's that older play again. But it has been covered by this |
|
| 58:24 | newer Vast Slight. OK. And this has the destruction of phase here |
|
| 58:33 | we don't have that here yet. let's see what uh a core might |
|
| 58:40 | like through here and basically, it's be coarsening upward and it's gonna go |
|
| 58:51 | the play and they use the delta here. Um I guess I'm OK |
|
| 58:59 | that, but I'm gonna use you Crevasse play, Andres Chen 12. |
|
| 59:08 | . So that's what you see here that's what you see for this part |
|
| 59:11 | here. Now, in fact, these are some of the faces that |
|
| 59:19 | vertical uh faces, you'd see uh upwards into the CVA play, then |
|
| 59:27 | upwards into the Crevasse channel. We talked about these before. We've |
|
| 59:33 | talked about the probating. OK? I'm not going to go over that |
|
| 59:42 | . Um But let me just remind that the same variables that we saw |
|
| 59:49 | the fluvial setting for Cres places is same in the, they aren't delta |
|
| 59:57 | except you're moving into a bay. bay is going to be brackish |
|
| 60:03 | It's gonna have a different set. gonna be standing water. It's gonna |
|
| 60:07 | a different set of benthic fauna and fossils and pelagic faunas and paleobiology. |
|
| 60:15 | . So, uh, and it's an area that's more rapidly subsiding. |
|
| 60:21 | . The deltas are gonna subside much rapidly than the fluvial settings. And |
|
| 60:28 | you got a lot more opportunity for of curves place. OK. And |
|
| 60:34 | here we have these uh series of upward and finding upper sequences and I'm |
|
| 60:46 | to suggests that they in part reflect th th this is channel abandonment, |
|
| 60:58 | here's a Creve uh channel and I this wrong. Um This, this |
|
| 61:09 | , this is coarsening up or this be, yeah, finding upwards, |
|
| 61:14 | sorry. Uh And then it may coarsening upwards again. So the channel |
|
| 61:22 | finding upwards, the plays are horsing . So let's look at what we |
|
| 61:31 | here. This is usually a uh I do in class, but we |
|
| 61:37 | , we're running a little short of . Uh So we have a series |
|
| 61:41 | these cyclic, small coarsening upward except for right here, we've got |
|
| 61:56 | chains that we can track all the across the area. So this is |
|
| 62:00 | flooding surface and then we get a from binding upwards to coarsening upwards and |
|
| 62:13 | getting thicker and thicker and somehow these to merge here. And then up |
|
| 62:23 | again, we've got a surface when go from binding upwards to questioning |
|
| 62:31 | Again, simply we lose it In short, we have a series |
|
| 62:44 | a complex vertically accreting series of crevasse bars, then crevasse channels. These |
|
| 62:54 | the little finding upper sequences and we a larger channel, this distribution |
|
| 63:02 | OK? And um this is an of a crevasse complex. OK. |
|
| 63:14 | This is an example of a dis channel with the erosion surface here. |
|
| 63:28 | . Now, the the one of points here is that correlation is really |
|
| 63:36 | . OK? I mean you not it, it's heterogeneous and it's in |
|
| 63:41 | dimensions. So these extremely, these river dominated deltas are just a nightmare |
|
| 63:51 | . Now let's also look at what is that delta begins is growing and |
|
| 64:00 | switches from a uh say it was distribution channel or there was a channel |
|
| 64:09 | that was active, smaller channel I mean a larger channel but still |
|
| 64:14 | channel. There are two small This channel begins to take all the |
|
| 64:20 | . OK? So we see a I'm here to there. All the |
|
| 64:28 | we have subsides, hey, as channel on the left gets bigger and |
|
| 64:37 | , it gets deeper and deeper, getting more and more discharge. The |
|
| 64:42 | are getting thicker and extending farther I mean the end of the bay |
|
| 64:50 | marsh, ok? Because the discharge getting bigger and bigger with that bigger |
|
| 64:57 | bigger channel. The levies are getting and notice you're going from a fresh |
|
| 65:07 | water marsh versus um failing to freshwater swamp in March. So you're |
|
| 65:23 | changes and those, the peat is thicker. So you're getting changes from |
|
| 65:31 | silt to brackish to freshwater marsh. all of this is happening as you |
|
| 65:42 | causing this delta to subside. And distributor is getting more and more of |
|
| 65:52 | , the water and set it. this coarsening upward sequence here would be |
|
| 65:58 | to this little core right here. . So here we have that uh |
|
| 66:05 | distributor, that active distributer and we a sense of that prorating uh levy |
|
| 66:14 | thick a grading swamp peat. This finger sand. Yeah. No, |
|
| 66:29 | is pretty much how this delta pro out into deeper water. So remember |
|
| 66:36 | is also what I would call a water delta then 150 ft of water |
|
| 66:43 | more. OK. Yet we know are older river courses and older |
|
| 66:57 | The whole scene depositional environments within the are really complicated. And this |
|
| 67:07 | well, the, the sequence we one to three or by actually six |
|
| 67:23 | 7, if we draw a cross through here would look something like this |
|
| 67:33 | Valley Field, then a delta That's actually um around 6000 years |
|
| 67:40 | that's below present sea level. And by the time we get to the |
|
| 67:45 | , the younger deltas, they're more less at the present high stand and |
|
| 67:50 | get the seminar, the force, plucking line and the, at you |
|
| 67:58 | , there's more numbers here because you divide it up or not, you |
|
| 68:02 | or a splitter basically. Ok. this would be more of a lump |
|
| 68:09 | I'm gonna look at in particular, this pattern of delta and that's really |
|
| 68:23 | common. Uh Here we have it the Mississippi. Uh This is from |
|
| 68:30 | yellow. Um And this is not we think of and normally as the |
|
| 68:42 | of a delta that's occurring way down , that's occurring down here. |
|
| 68:51 | It's an avulsion that's occurring up street it's an evo that's occurring pretty much |
|
| 69:03 | a distance equivalent to the back water where we go from the channel is |
|
| 69:14 | mean sea level to the channel dips mean sea level. And even though |
|
| 69:19 | tidal effects may only extend to there is a backing up the water |
|
| 69:27 | backs up uh to a distance far and that's what's causing these big shifts |
|
| 69:35 | big rivers. Ok? And this the abortion length, the calculated backwater |
|
| 69:44 | . And you see it's a pretty estimate for all these rivers. |
|
| 69:50 | Well, if we look at think , this, uh you know, |
|
| 69:57 | X get this, I wanna look um, this sound right in |
|
| 70:11 | I'm sorry. No, I I, I wanna look at a |
|
| 70:17 | and they had to fly at That's this zone here. Here's the |
|
| 70:22 | you fly river coming in. here's another spray of the river has |
|
| 70:34 | brought, has been channelized down to . So there's two deltas here, |
|
| 70:39 | into a fly a bay. It's delta in the Wax Lake Delta. |
|
| 70:48 | , the Wax Lake Delta is is the younger of the two deltas |
|
| 70:55 | it's relatively undisturbed. There's been a bit of dredging occur here, but |
|
| 70:59 | is the older delta. So it's more work done. And here we |
|
| 71:04 | a study from 1973 to 1982. notice it starts with these little, |
|
| 71:10 | , little uh isolated bars, distributor bars and they tend to coalesce laterally |
|
| 71:26 | downstream and upstream. Notice how the bar has grown both upstream and |
|
| 71:34 | In fact, we can look at , this was the original bars and |
|
| 71:43 | at how much upstream migration as well downstream migration as these little bars laterally |
|
| 71:51 | . Ok. Now, what that is that when we look at the |
|
| 71:55 | little bar, little and as it to accrete at some point, begins |
|
| 72:11 | elongate and migrate upstream as well as , she kind of show like this |
|
| 72:18 | notice where we're beginning to get upstream . Yeah. So this is the |
|
| 72:30 | is nucleated here. It grew down and up street. Well, Exxon |
|
| 72:41 | and did a detailed study of Wax and it was, it's more of |
|
| 72:44 | pristine Delta. You need a lot coy. And what they found was |
|
| 72:51 | you look at the, the it consists of a series of these |
|
| 72:58 | . That's not a big surprise because what was seen with. Um, |
|
| 73:06 | had to fly, but these lobes , they call depositional packages and they |
|
| 73:16 | decided to say let's call this a deposit complex because they found that those |
|
| 73:27 | were the result of a creating jet . So what a jet deposit? |
|
| 73:41 | , this is the beet right This is what's happening has that jet |
|
| 73:51 | river water empties into the reservoir, forms a jet and a deposit |
|
| 73:59 | And so the delta itself is going be an amalgamation of those and that |
|
| 74:06 | deposit. This is what would look here and this is the pattern and |
|
| 74:13 | flu. Ok. Notice we get elongation of levies, they're called pseudo |
|
| 74:24 | here for some reason. And we this pod uh where the bed load |
|
| 74:31 | deposited. And that would be analogous that present bar and back bar, |
|
| 74:39 | back slope and down slope bar that saw earlier. And then down in |
|
| 74:47 | , we get the deposition of suspension set. That's analogous to this opal |
|
| 74:57 | that was described by are modified from right. OK. There's a |
|
| 75:04 | in here where the velocity stays high turbulent mixing hasn't really closed it |
|
| 75:16 | So the high velocity means there's erosion then is followed by that I drive |
|
| 75:29 | that rapid deposition to belong erosion to . And that's what we say |
|
| 75:39 | This is actually an eroding channel and is sediment is depositing in the core |
|
| 75:52 | bed load to distance suspended. And you look at in cross section, |
|
| 76:00 | see that this starts as a little , the bar begins to grow and |
|
| 76:11 | it begins to erode on the backside grow on the downside. He rode |
|
| 76:16 | the backside, rode on the the road here and also starts to |
|
| 76:27 | in here and fill up and that bar was here and it shifts to |
|
| 76:41 | and then to hear and here and forming a to get deposit complex and |
|
| 76:52 | add those complexes together and they get delta. OK. This, by |
|
| 77:00 | way is that or again? And what we saw here. Yeah. |
|
| 77:24 | this is again, uh what you see in cross section, the scour |
|
| 77:33 | grading bar, shift, scour pro bar. So here is the axis |
|
| 77:42 | the main channel. Is it a ? And then Phils here is those |
|
| 77:51 | those pro grading uh jet deposits as go extend offshore? Ok. And |
|
| 78:02 | is that erosion on the back scow or Phil erosion on the backside |
|
| 78:13 | deposition. Here's the erosion on the downstream deposition. OK. This idea |
|
| 78:27 | these bars nucleate and then pro grade and at least initially upstream with erosion |
|
| 78:38 | the back side is seen almost Once we start to look, this |
|
| 78:48 | in Pennsylvania. This is, of , the anti um here is the |
|
| 79:00 | looking at these bars and erosion of backside. Here it is. And |
|
| 79:09 | , uh crop. Here we're actually a little bit of the backfield uh |
|
| 79:14 | re notice how this bar nucleates. grows upstream and downstream and then it |
|
| 79:24 | to be scoured, nucleates and grows and downstream with one shoot Deposit, |
|
| 79:36 | shoot complex. So what this this is based on fieldwork but it |
|
| 79:46 | the work that uh welder and others on uh the low uh growth. |
|
| 79:58 | . Uh More recently, we've got data showing that with a hyper pina |
|
| 80:09 | , we can still get the same downstream. And even with hoopy of |
|
| 80:21 | grain, we can still get So this would be, let's say |
|
| 80:28 | grained stratified hyper course, your grains up bigger. Homo builds up a |
|
| 80:41 | , doesn't build down as fault. , a picture you'll recall. It's |
|
| 80:49 | plume spreads out more deposits quicker. it's steeper. OK. That's a |
|
| 80:58 | place to stop. What was, was the? Oh the great is |
|
| 81:03 | seven. Uh So this is the lay layered uh water. Uh It's |
|
| 81:11 | dense then the incoming reservoir in the case. So it's hyper the um |
|
| 81:22 | trying to figure out what to do that. Like is that, is |
|
| 81:28 | suspended on the top? On the side? Yeah. Yeah. Um |
|
| 81:37 | , that's in suspension. So um the hyper pick flows um it can |
|
| 81:47 | in suspension but it can actually become concentrated that it begins to move by |
|
| 81:55 | . That would be the hyper. . Uh Notice in here is behind |
|
| 82:02 | bar, it's all below. I'm , it's not true. On the |
|
| 82:06 | , it's gonna be bed load and here suspended, you're increasing velocity |
|
| 82:16 | peak velocity breaking waves, deposition go to thinking about, yeah. |
|
| 82:27 | Here where we got this increasing and here they actually suggest that the water |
|
| 82:42 | be uh uh less dense. Um Here they're arguing that there's so |
|
| 83:01 | sediment that it's more dense. It up the back, increasing velocity, |
|
| 83:09 | erosion deposition, relatively rapid deposition. , steeper force sets. Then if |
|
| 83:21 | depositions occurring over a longer area, also the deeper the water this deep |
|
| 83:27 | the four, we'll talk more about changes. But uh this is actually |
|
| 83:35 | you change notes. OK. um I'm gonna take about a five |
|
| 83:41 | break. Um We'll quit recording but keep uh this on. Uh You |
|
| 83:47 | need to get your notes out, a break if you need it and |
|
| 83:51 | um 3 40 now, About five 10 minutes. OK. Any questions |
|
| 83:59 | , before I think? No. . Recording again. OK. |
|
| 84:10 | we spent a lot of time looking two parts of the modern Mississippi |
|
| 84:18 | Uh, the bird food. It's called the Bali Lobe. And, |
|
| 84:26 | , that, that here. Oops the a of lion down in |
|
| 84:35 | Uh, yeah. Yeah. And about the differences. The, |
|
| 84:44 | Bali or modern bird foot is an digitate. Uh Delta is one that |
|
| 84:56 | in relatively deep water. It is that um has very much brilliance. |
|
| 85:08 | dominated uh to configuration which confines us these bar finger sans. The A |
|
| 85:22 | a much more low delta. It's friction dominated dispersion because it's emptying into |
|
| 85:32 | shallow bag. They are both modern of the Mississippi Delta and also mentioned |
|
| 85:42 | there are quite a few older lobes in particular, I want to look |
|
| 85:52 | the lobe that is in this area . It came in like this and |
|
| 85:59 | can see good evidence. It was by the day's delta, good evidence |
|
| 86:10 | this contributory pattern. OK. And called the LA delta the four. |
|
| 86:27 | it really is very distinct from the day. It's got a lot of |
|
| 86:38 | , all of which are more or active at the same time. Uh |
|
| 86:44 | got a wide fringe of delta front because sand is coming in from |
|
| 86:52 | many places. And of course, does have a pro delta for the |
|
| 87:01 | . If we look at the uh we've got basically, I, |
|
| 87:05 | need to enlarge this one day but we're looking at distribution channels and notice |
|
| 87:13 | they're getting smaller and smaller these that be shown like this because they're |
|
| 87:23 | At the same time, we get broad. Yeah. S the front |
|
| 87:31 | is uh consists of distributed amount bars a slope and they uh the margin |
|
| 87:44 | it's kind of interesting here. Uh call right one which is they |
|
| 87:54 | they sub differentiated the delta front into and then more vital delta fronts and |
|
| 88:05 | how widespread it is. The the delta front extends laterally really even |
|
| 88:13 | little bit beyond the uh the friendship the Isaac as you might expect is |
|
| 88:23 | be much more low paid compared to bird flu. Yeah. And if |
|
| 88:30 | look at it in three dimensions, you find is that delta front is |
|
| 88:36 | a sheet sand. If you could a look through here, it, |
|
| 88:40 | basically a sheet sand, a low sheet. If you like going into |
|
| 88:46 | clay and clay with channel field sitting and there, that's in contrast to |
|
| 88:55 | bird foot with the nearly confined she is so we, we can automatically |
|
| 89:08 | to see the difference between the LA and, and about A little over |
|
| 89:19 | 1000 years ago. And uh the , the and the digit. And |
|
| 89:32 | we've got at albeit at different scales much better view of what a cross |
|
| 89:43 | might look like. This one, digitate one we talked about should be |
|
| 89:50 | by now, why it's so Ok. And it should begin to |
|
| 89:57 | apparent why the delta front here. why if we look at the vertical |
|
| 90:09 | of that bird foot, we go the pro delta and, and these |
|
| 90:21 | are kind of crazy. Uh but coarsening upwards with the cleanest sand at |
|
| 90:31 | top. Uh This would be also mouth or uppermost delta front. I |
|
| 90:41 | know what you like. OK. here and compare it with the low |
|
| 90:52 | , we got our mouth bars coarsening to pro delta and distribution channels. |
|
| 91:00 | strip channel wasn't shown on this Well, the first thing that comes |
|
| 91:07 | mind you might say is why, is uh it got so much more |
|
| 91:13 | in the mouth bar? Um My is that because in this zone |
|
| 91:22 | uh you're getting more river influence, down here, you're getting more |
|
| 91:28 | OK? But in any case, important to, to look at the |
|
| 91:35 | shape, OK? And coarsening And one of the things that's kind |
|
| 91:51 | interesting, the I need to read more carefully. Uh They're putting the |
|
| 92:00 | here, but uh then here they the, the distributor champ. I |
|
| 92:11 | know why it's not here, but should be ok. And it's pretty |
|
| 92:17 | . With the exception of some of the muds here. What is not |
|
| 92:31 | is the thickness. This is 80 , I'm sorry, 80 m. |
|
| 92:42 | is 20 m. Yeah, you've a very exaggerated thickness of this bird |
|
| 92:56 | delta and it's exaggerated for two It's being deposited in deeper water. |
|
| 93:04 | they have more accommodation space so the can extend into deeper waters. There's |
|
| 93:14 | subsidence going on. So we saw over thickening of those mouth bars as |
|
| 93:20 | paraded through time because of the compassion that over thick delta wedge compare that |
|
| 93:30 | the very thin pro delta clays of shallow water delta. There's not much |
|
| 93:40 | space. The muds frankly are gonna washed away. The muds are gonna |
|
| 93:45 | up in Western Louisiana and sheer They're gonna even end up in |
|
| 93:52 | but they're not gonna end up underneath within the a fly bay or |
|
| 94:00 | So to me, the most important to think about in these two deltas |
|
| 94:09 | one, the geometry of the, the delta front is I'm using it |
|
| 94:14 | also how thickness it is a depth water um significantly modifies both the process |
|
| 94:28 | the void versus frequent versus uh friction uh river processes and how the sand |
|
| 94:38 | deposited. Ok. Now, I go more as to what happened |
|
| 94:48 | Now, the delta when it was and when the new delta formed. |
|
| 94:57 | mean, we went through a phase a that now evolution is different than |
|
| 95:02 | , switching, contributory switching or is basically gonna oh the same lobe to |
|
| 95:14 | a little more complicated but distribution. a A V means all of the |
|
| 95:24 | are abandoned. Like is what's happening in the Mississippi and have been transferred |
|
| 95:31 | what probably would be they had to at. Now, I I described |
|
| 95:37 | this constructional phase where the distributor was bigger. And now I want to |
|
| 95:47 | about the destruction of phase as the is abandoned. It's abandon, it |
|
| 95:56 | to fill. Subsidence continues. So marsh will continue to grow. It's |
|
| 96:07 | thicken, but it's going to go um fresh water to brackish water vegetation |
|
| 96:20 | it continues to subside. The entire a plane is filled. You're, |
|
| 96:32 | not gonna have the distribution channel It's probably just be a little and |
|
| 96:39 | you're bumped. Now, look what's over here. You've got erosion of |
|
| 96:50 | what is now a salt marsh and level continues to rise and we're beginning |
|
| 96:57 | see a dissection of the salt marsh title a chance. Now, remember |
|
| 97:04 | said as sea level rises, but a relative rise, sea level, |
|
| 97:09 | whole abandoned low is sinking. So can think of that as the whole |
|
| 97:16 | lobe being flooded. Now, it's flooded over here, but the water |
|
| 97:24 | reached this particular spot. The ground has, it's become more contaminated. |
|
| 97:33 | getting more salty marsh, going from water to brackish water marsh now, |
|
| 97:39 | water. But now we're beginning to erosion as well. So let's imagine |
|
| 97:44 | active delta, let's imagine that it's . And now that act of delta |
|
| 98:01 | all of it is subsiding. at the front edge of the delta |
|
| 98:13 | being eroded by waves and we're gonna this arcuate string of barrier islands. |
|
| 98:22 | behind that, the delta plane is be flooded with Bay Marsh, the |
|
| 98:31 | delta plain and the upper delta plain continue to be marsh will vertically accrete |
|
| 98:38 | PETE but will gradually become more So let's look in for a section |
|
| 98:46 | was that original delta and here's to and it's been reworked. This is |
|
| 98:59 | Ravi and this is an emergent sand barrier island or bar or show |
|
| 99:10 | We got the flooding and actually eroding the edges and the subsides and abandoned |
|
| 99:19 | the chance. Ok. Now, thing is, let me just |
|
| 99:30 | notice we've got hence of these abandoned here, we're gonna see later. |
|
| 99:40 | gonna be outlined by oyster reefs typically of the higher levies of those abandoned |
|
| 99:49 | . Yeah. Uh This area here is here, beginning had the flooding |
|
| 100:01 | erosion of the bay and this is it would look like more or less |
|
| 100:10 | the wave erosion, uh wave uh uh Raven and we might get a |
|
| 100:18 | bit of Todd limit, uh save here. Now again, we've got |
|
| 100:26 | abandoned lobe is being submerged. we'll see complete submergence of this area |
|
| 100:40 | this lobe continues to grow. we can look at these different lobes |
|
| 100:47 | they actually represent different stages of abandonment better said they've been abandoned for longer |
|
| 100:57 | of time. So if we look the youngest lobes like the Saint |
|
| 101:05 | which they hear it in the, we look at older loaves of some |
|
| 101:12 | and even older, the we're looking older and older, progressively more abandoned |
|
| 101:23 | . So let's look at the Saint lo and look at the chandelier is |
|
| 101:29 | right here. Those islands are basically realm of eroded delta frog with the |
|
| 101:43 | behind. And so what we can is that the active delta is here |
|
| 101:53 | the delta fro it's abandoned. So gonna have less sediment coming in |
|
| 102:02 | It's gonna begin to erode and spit accretion will give us elongated spits and |
|
| 102:14 | islands. It'll continue to si This is now gone. It's now |
|
| 102:22 | detached island and then as relative sea continues to rise, the island has |
|
| 102:34 | some merged shots. OK. So kind of imagine this transition is illustrated |
|
| 102:45 | various stage like as we see OK. Well, here we've got |
|
| 102:52 | series of uh planking barrier islands which sorry. Um The sequence here would |
|
| 103:10 | now let's see. Now, I be more like here would be our |
|
| 103:16 | barrier island sequence, vertical sequence. . Now, right now the uh |
|
| 103:24 | the uh the bay has come in two sides, but it is still |
|
| 103:31 | here here. Ignore this for a . Hair is completely detached. |
|
| 103:43 | it's now a transgressive barrier island which this now is a transgressive buried is |
|
| 103:53 | seeds and you recall what that it was lagoon or if you like |
|
| 104:01 | Flo Tale Delta, wash over etcetera. OK? Now, eventually |
|
| 104:06 | gonna subside and it's gonna be completely . And when it does that, |
|
| 104:14 | continue to trans uh move la but barrier island core is being reworked into |
|
| 104:25 | sand and that shelf sand now is OK. And so what you see |
|
| 104:34 | is the crest of the should and the front and then kind of the |
|
| 104:41 | . So it's gonna give us a upward sequence and it's also going to |
|
| 104:50 | increasingly bioturbated at the ball. that be the same here. And |
|
| 104:58 | it sinks far enough, it's down . This is ships. So, |
|
| 105:06 | , which is oh in water, it's uh several meters thick but in |
|
| 105:13 | depth. So well, I can't now. OK. So each of |
|
| 105:21 | sequences is a reflection of the abandonment of this deep water delta. |
|
| 105:37 | Now, put those together, here's pro grading sequence active and then a |
|
| 105:56 | . So eventually sands moving landward to us shoal and Shoal crest. |
|
| 106:04 | So the constructional phase destruction phase now that but a chart, OK. |
|
| 106:20 | The destruction of phase is almost completely . So we're gonna see that where |
|
| 106:27 | not a lot of subsidence, you get this thick bay accumulation. The |
|
| 106:36 | problem though is scale This scale here maybe four m that reflects what might |
|
| 106:46 | going on today. If you look some of the older um shoals during |
|
| 106:54 | sea, this constructional phase 10 Now it's more like 30 or 40 |
|
| 107:04 | . This is kind of compressed. the construction phase is actually much greater |
|
| 107:11 | thickness and the destruction of face even where you get these migrating barrier elements |
|
| 107:19 | , OK? Now, I wanna back to thinking about this transgressive regressive |
|
| 107:32 | , the sand and mud geometries in of the reservoir characteristics. Um Here |
|
| 107:45 | got a they uh our finger sand down to pro delta modes so we |
|
| 107:57 | envision it right about here. Let's at something a little different, maybe |
|
| 108:04 | for a second that we've got a section. So now we've got three |
|
| 108:13 | mouth bars and now let's imagine they've abandoned. OK. So what we're |
|
| 108:22 | at here is a pro grading phase gross and then a channel abandoned. |
|
| 108:36 | . Now again, different terms, bar, outer bar, call it |
|
| 108:43 | you like. You're looking at increased size better sorted the channels where they're |
|
| 108:51 | , they're gonna be pretty well mud filled when they're active. And |
|
| 108:56 | what we find is not a your best reservoirs within the channels are |
|
| 109:02 | be in the base. Your best in the bars will be at the |
|
| 109:07 | . Your non reservoirs are gonna be pro delta and to a certain |
|
| 109:12 | the outer uh bars uh your marsh the shelf. Yeah. So if |
|
| 109:23 | looked at the active or the mouth , let's say here in proximal |
|
| 109:35 | that is closest to the land, gonna be funnel shaped where you call |
|
| 109:44 | and outer and pro delta, you're as me. But then let's go |
|
| 109:49 | . Let's look at this in this . OK? We're seeing, pouring |
|
| 109:57 | wedges and even farther little places. what we're looking at is oops the |
|
| 110:28 | out of the sand giving me Now you saying that, isn't that |
|
| 110:38 | ? Hang on while I figure out to un animate this. Oh, |
|
| 110:50 | . OK. I guess that's Uh And you learn something every |
|
| 110:55 | even things you don't wanna learn. . So we see this as basically |
|
| 111:01 | pro grading strand line, pro grading island, pro grading delta front. |
|
| 111:11 | . With the contributory channels. Think how they feel. OK. And |
|
| 111:30 | saw this with any river deposit, can fill abruptly or I can fill |
|
| 111:42 | . Ok? And that will determine nature between uh the top cap sealed |
|
| 111:50 | the lower most active part reservoir. . So, oops. So let's |
|
| 112:07 | a cross section or rather making a section Based on four logs in |
|
| 112:14 | in a delta that's been abandoned. , we got certain profiles here. |
|
| 112:23 | got a relatively homogeneous mud with the , a little bit of thickening or |
|
| 112:35 | here. Then we got a worsening package serrated, abruptly kept and I'm |
|
| 112:54 | kind of just correlate the base of . Now above that, forcing up |
|
| 113:05 | sand in this place, we have course defining upwards package look kind of |
|
| 113:14 | this. It's separated by something And then on top of this and |
|
| 113:23 | , we've got delta plate. So on top of the delta plane |
|
| 113:33 | you got a pot of sand over , here's delta plane again and then |
|
| 113:55 | delta plane is capped by nothing It was hard to see what's going |
|
| 114:01 | here. But if this little, is a little bit of delt playing |
|
| 114:14 | , but it looks like something I to figure out is this relative with |
|
| 114:24 | and these two thick sand to finding their sands are distributor chance the coarsening |
|
| 114:36 | sequences the delta uh delta fraud. I might imagine this being a channel |
|
| 114:49 | . Now, the problem is mhm is has dealt a plane here. |
|
| 114:57 | I'm I must cut this off here maybe even to hear and this might |
|
| 115:06 | another little chat. And up here may be a transgressive face. So |
|
| 115:15 | see how we might do this. . Well, sure enough, here's |
|
| 115:23 | channel. Here's our, our finger , here's our delt to plane. |
|
| 115:41 | here the interpretation is this big It's probably not a crevasse channel. |
|
| 115:45 | another channel. Ok. Here. this is all a grading channel. |
|
| 115:59 | mean, a grading delt to playing grading Delt. And this truncation up |
|
| 116:06 | is basically the flooding during the destruction phase. OK. So you see |
|
| 116:18 | importance of being able to correlate the , the pro delta and the delta |
|
| 116:26 | environments. Now, this is a more complicated and I'm not gonna go |
|
| 116:31 | it, but uh I'm gonna let look at this at your leisure uh |
|
| 116:37 | think about this cross section worsening OK? Uh think about one, |
|
| 116:52 | , six up here. Uh And now is more like a low |
|
| 117:01 | OK? But think about how they about correlating these sands, you |
|
| 117:09 | I'm not gonna ask you to do on the quiz, but it's useful |
|
| 117:14 | have a look at the difficulties in . Um And where these came |
|
| 117:25 | OK. Now, clearly, sea is one of the major triggers and |
|
| 117:36 | regressive cycles and deltas and everything And if we think about pro grading |
|
| 117:46 | in programing delta packages, we could of a normal regressive or forced |
|
| 117:52 | you might actually have the deltas down which occurred during the last drop in |
|
| 117:58 | level. Yeah. And you can packages pro grading transgressing, pro grading |
|
| 118:10 | transgressive, probing less and transgressive or grading transgression, probating more transgression probating |
|
| 118:22 | transgressions. Now, what we we're at here is a retrograding pair sequence |
|
| 118:31 | . Each of these is a pair . This is a set of pair |
|
| 118:37 | . And in essence, what we're at is that there's an increasing ratio |
|
| 118:44 | A S. What is that accommodation to sediment supply, sediment supply is |
|
| 118:53 | . But when the accommodation stress, space rises gets deeper and then when |
|
| 119:03 | stable, it pro grades out because accommodation is not changing. SAS supply |
|
| 119:09 | still being added and it's accumulation rises . So these pulses of delta pro |
|
| 119:19 | during a relative rise in sea OK? And there's a back stepping |
|
| 119:27 | these packages. Here's that prograde uh gradation we looked at right two and |
|
| 119:40 | down here during a high stand and even older down here. So this |
|
| 119:49 | a retro gradation of sequence set of lobes With the oldest three being formed |
|
| 120:00 | rising sea level and the most recent during the high stance. OK. |
|
| 120:08 | what happens if sediment accumulation is faster sea level rise? That is a |
|
| 120:14 | A to S ratio, you get net c advance of the sea. |
|
| 120:20 | that's what we see here in the off trend dances. So we are |
|
| 120:35 | filling that base. Now imagine you've a seismic lion, the side MCLA |
|
| 120:48 | show very nicely these large slopes and really the growth of the shelf |
|
| 120:59 | Those are Sheth margin kind of But in fact, what we see |
|
| 121:07 | here are thin packages that we may be able to resolve initially, but |
|
| 121:12 | are the delta kind of forms. what we're looking at is basically a |
|
| 121:22 | probing until it eventually it gets to edge of the delta. At that |
|
| 121:30 | , the shelf can throw gray. you got this little bitty delta, |
|
| 121:37 | say a little bitty, they're, as thick as the shelf is |
|
| 121:43 | OK? And then we got these of creating content. Ok? |
|
| 121:54 | before we get too complacent, let's one confusion. Let's look at the |
|
| 122:03 | and add a sub aqueous delta. we've got two clients and those |
|
| 122:11 | by the way or up here, on the shelf, the Saville Delta |
|
| 122:24 | , which is what we've been talking and something that's been happening offshore. |
|
| 122:31 | see it in this area here is a pro delta Clione. Where is |
|
| 122:39 | coming from? It's coming from a of setting is being transported down, |
|
| 122:51 | displacing that kind of, I mean uh mud clini here it starts and |
|
| 123:04 | it migrates down is going to become and more detached. It is in |
|
| 123:18 | a mud fluke and it forms this Delt. OK. So when we |
|
| 123:32 | of those clients, again, in cases, we would actually have a |
|
| 123:43 | of form of that sub aqueous delta across the show. We'll come back |
|
| 123:55 | this a little later, but because talking about, I wanted to mention |
|
| 124:00 | . Now, here's those three Actually, the two that I talked |
|
| 124:04 | earlier, the the back stepping in pro grading delta. And you could |
|
| 124:11 | imagine it vertically accreting it'll vertically accrete a high stand and a low |
|
| 124:18 | it'll backs step during the transgression and uh prograde uh during the high stand |
|
| 124:25 | drop. Now, Doris Curtis early suggested that the type of delta that |
|
| 124:36 | get in each of these cases, gonna be a different type of delta |
|
| 124:46 | it will have a different style of a OK. Here you got it |
|
| 125:00 | very much of a wave doin delta it will a grade or, or |
|
| 125:10 | will accrete in the back lapping port . Here we have a low be |
|
| 125:17 | and it will a grade vertically. , you have a river dominated delta |
|
| 125:23 | it will prograde. Oh, So there's a couple of things she |
|
| 125:32 | that hadn't been noticed before or hadn't published before. Then, as delta's |
|
| 125:42 | offshore and onshore, they change. the delta that's at the shelf edge |
|
| 125:49 | gonna be different than the delta back the shallow water and of course, |
|
| 125:55 | those iso pas vertically accrete will depend whether or not it's a grading, |
|
| 126:01 | grading or back stepping. Now, got into this and started thinking, |
|
| 126:08 | , let's, let's think of maybe have river dominated here, more fluvial |
|
| 126:14 | wave dominated here. And then he , you know, maybe as this |
|
| 126:19 | gonna be even more wave dominated. . So the difference of opinion |
|
| 126:26 | but the key is with this wedge sediment, we, if we had |
|
| 126:31 | , we could talk about the But this is basically something like the |
|
| 126:43 | delta here hasn't yet pro graded across shelves. The prediction is when the |
|
| 126:52 | regression or pro pro gradation is going morph into a fluvial wave dominant |
|
| 127:00 | which by the way, we'll call delta. So let's look at something |
|
| 127:11 | we might imagine occurring with the As the progress is offshore, it's |
|
| 127:21 | go from a shallow water inner shelf to a deep water shelf margin |
|
| 127:30 | Now notice the shallow here is actually LaForce delta, yellow water friction |
|
| 127:39 | What is not shown is a mid birds foot delta. OK. But |
|
| 127:47 | it would hit the shelf edge, got a lot of sediment. So |
|
| 127:58 | got a river component, but it's exposed to high waves because there's no |
|
| 128:05 | across the shelf. So high And so this is delta is gonna |
|
| 128:12 | to begin to prograde. The show mean prograde the slope. It's made |
|
| 128:17 | across the shelf and now it's pro into deep water. So here are |
|
| 128:24 | you kind of forms and here are clients and these are the things you |
|
| 128:35 | think about is that delta went from delta to show margin. Um The |
|
| 128:44 | of pro gradation of the high here here. Why? Because there's more |
|
| 128:52 | to fill wave influence, relatively low the inner shelf, high on the |
|
| 129:00 | she growth faulty. We'll see, gonna start getting a lot of growth |
|
| 129:06 | when we get off here. Uh gonna get a lot of gravity |
|
| 129:13 | When we're in the deeper waters deeper slope, the slope itself will be |
|
| 129:18 | higher. So shell margins, different margin, deltas are really different. |
|
| 129:32 | ? Now, that isn't to say there's not defamation occurring on a mid |
|
| 129:39 | March, if there's a lot of , uh you can have a pretty |
|
| 129:45 | slope, all of maybe a Anything about a 5th of a degree. |
|
| 129:52 | there is some deformation but is the gets deeper, the defamation gets |
|
| 130:02 | And now we're getting a lot of , a lot of slumps and even |
|
| 130:13 | and shape like paradis. Ok. this shelf edge margin is really a |
|
| 130:21 | structurally active self. And one of that's gonna happen is we're gonna have |
|
| 130:27 | lot of these hypericum flows that are be coming down. I mainly river |
|
| 130:39 | . Now, you can also get hyper flow that is do too. |
|
| 130:47 | lot of sediment plunging down. I'm gonna talk about that for right |
|
| 130:56 | But these hyper pial flows are basically to be clothes that are, that |
|
| 131:03 | across the shelf and will become active the shelf margin to help accrete the |
|
| 131:12 | . I suggest you read these on own. But here's that high protective |
|
| 131:19 | here, it's forming that mud plume I talked about where you got that |
|
| 131:31 | . Ok. And here's that mud crossing the shelf. But for right |
|
| 131:44 | , at least I'm not gonna talk much about these in, in |
|
| 131:51 | about the fluid mud. But fluid is a type of low fluid rather |
|
| 132:04 | has concentrations of mud up to 30% weight. Normally, it's a couple |
|
| 132:11 | 1%. It's such a high concentration silt and clay that it is a |
|
| 132:21 | flow. It's a density forms a float and it can it be formed |
|
| 132:31 | that zone of maximum turbidity in a , in an equator, in an |
|
| 132:39 | . Uh or it could be associated waves. A storm comes in d |
|
| 132:47 | it or it can be associated with . There's such a high influx of |
|
| 132:53 | that it's super concentrated and we actually about that a little bit with |
|
| 133:00 | Lakes are really good place. Hyper are very well developed in lakes less |
|
| 133:07 | in marine settings. But you get are are things that at first blush |
|
| 133:13 | like intertidal deposits. So this goes to my earlier comments at the very |
|
| 133:21 | day. Don't be too fooled by particular sedimentary structure. These are hetero |
|
| 133:29 | sediments. I've already mentioned probably five places where you find these hetero lithic |
|
| 133:38 | . Ok. But going back to margin, some margins are pretty |
|
| 133:50 | That doesn't mean there isn't very much and sediment slumping as material is coming |
|
| 134:02 | from the delta plane. But there's the large growth vaulting, for |
|
| 134:09 | OK. And so here you're getting , pro grading is coming down, |
|
| 134:15 | it's still pretty much pro gradation. ? And so here is a pro |
|
| 134:22 | shelf margin. Now, they would your stuff down here. But consider |
|
| 134:31 | alternative where it's an unstable margin. of growth faulting. It may be |
|
| 134:37 | master regional fault fitting right here. ? It's a very different stories. |
|
| 134:47 | know, if we look at just forget about the master faults, but |
|
| 134:51 | smaller growth faults is in here might something like this. We'll roll over |
|
| 135:00 | over thickening. These are sin depositional . These are the growth faults. |
|
| 135:07 | ? You see it here and you it in here. Now here is |
|
| 135:19 | is bypassing the shelf through some kind a channel submarine fan, but you're |
|
| 135:29 | getting slumps and failure up here. you get a little delta, they |
|
| 135:36 | be stacking up behind a, a here. You got a shale, |
|
| 135:46 | salt core or shale coal where it have a, a to a to |
|
| 135:55 | where it's extension here. Compression And I've got another little package for |
|
| 136:03 | . A lot of growth falls in . Ok. That here we got |
|
| 136:12 | programing margin. Here's our unstable Here's the big growth. You got |
|
| 136:20 | pond areas and maybe the, the down here, Compression ridge. In |
|
| 136:30 | , what we're looking at at the edge is a lot like a |
|
| 136:35 | It has a lot of same characteristics terms of the extensional head compression |
|
| 136:45 | Now, here is a cartoon that's a lot of backing to it in |
|
| 136:52 | shelf show margin. Think la fouche grading offshore mid shelf deltas depending on |
|
| 137:04 | sea level is doing. That could the Mississippi Delta. If it's a |
|
| 137:09 | sea level, if it's a forced , that is to say you're moving |
|
| 137:17 | , but you're also staying in shallow , still gonna be a shallow water |
|
| 137:25 | , but the wave energy will be because you're reducing the fetch. Is |
|
| 137:30 | clear that when you go from this the water depths and stay shallow |
|
| 137:47 | the delta, but the shoreline has that are higher because they haven't been |
|
| 137:55 | as much because the delta is closer the shelf age, you get to |
|
| 138:04 | shelf edge, it's gonna be still lot of fluvial sediment, but a |
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| 138:11 | more waves as well and it's in water and it has the potential for |
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| 138:18 | defamation. Then as sea level rises the rot in the deltas, a |
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| 138:26 | of them are gonna form ASU. we've got a lot of estuaries that |
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| 138:32 | forming so that the deltas are basically head deltas building the estuary. We |
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| 138:42 | about earlier, we talked about the in sea level causing the flooding of |
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| 138:47 | rivers going from delta to estuary. it's not until high stamps that the |
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| 138:59 | can fill those estuaries and begin progra again. Yeah. So here we |
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| 139:10 | the situation where we're looking at the or, and it's a wave dominated |
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| 139:26 | and it started during the transgression is migrating, waved dominated barrier island when |
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| 139:42 | filled, it became a wave dominated . That's exactly what we talked |
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| 139:54 | Last time we talked about that in dominant deltas when they failed. So |
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| 140:00 | looking at the transgression, an eventual of that and then it's gonna start |
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| 140:12 | its way out across the delta across shelf. Yeah. Now, in |
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| 140:19 | cases, there was um it goes wave dominated to a little more wave |
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| 140:26 | uh I rather uh river dominated as get across. Um Here it's getting |
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| 140:34 | to the shelf edge. So we're a little more sediment deposit offshore here |
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| 140:45 | crossing, should note that it's crossing shelf. Now, it's beginning to |
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| 140:54 | the shelf itself. So now it's stable pro grading shelf. So here's |
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| 141:03 | shoff delta pro grading stable margin. it's kind of like what's happening |
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| 141:13 | We had the delta pro grading across shelf and then extending to be on |
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| 141:23 | shelf and notice at love stand, begins to vertically acc predict again. |
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| 141:30 | then during transgression, it basically And here we have that bahe delta |
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| 141:38 | . OK. That they had delta still become a either wave or river |
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| 141:53 | delta and it'll prograde across the shelf start the cycle again. Now |
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| 142:03 | so in this case, what has the pro gradation is the sediment supply |
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| 142:15 | the shelf. So the argument would that we're at a relative high stand |
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| 142:21 | the Mississippi Delta has prods the shelf . Now notice there's some submergence going |
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| 142:30 | here. Um A little hard to this graphically, but you know, |
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| 142:35 | Delta four sets are getting a little thicker rather. Uh And that's in |
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| 142:43 | because the shelf is getting deep. shows as a horizontal shelf. It's |
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| 142:49 | OK. So it's, it's getting little deeper, but still it's moving |
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| 142:54 | pro grading. It is a normal . OK. Now, is that |
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| 143:02 | ? Well, let's see if you at the rate at which a delta |
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| 143:11 | is moving versus seven input. Uh Well, let's see how to |
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| 143:22 | this. Um The Mississippi is I'm sorry, have to ignore this |
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| 143:30 | just a second. Look at the at its sediment rate in the shelf |
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| 143:39 | . It would take 10,000 years. had 1000, it would take 10,000 |
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| 143:49 | to migrate across the ship. The Take 25,000 years. The Brazos. |
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| 144:02 | , it'll never get across. So it's really hard. There are |
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| 144:08 | few deltas in the world that have much set that you could envision them |
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| 144:16 | the shelf without a drop in Now, forced regressions exist but on |
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| 144:25 | very wide, almost epic Contin epic shelf. OK. So here are |
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| 144:34 | of those place to see shelf edge and they were formed during low stands |
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| 144:40 | sea level and here's just a kind a vertical section. I'll let you |
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| 144:47 | at it and think about uh what fluvial cycle might look like why we |
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| 144:53 | some things down here. But it's a forced regression until we get to |
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| 145:03 | low stand. OK. And actually it out. Then it stopped here |
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| 145:14 | then began to pro out again, here in his trunk. Yeah, |
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| 145:23 | is a Wheeler diagram. So it chosen it, it's not a cross |
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| 145:29 | per se. It's just saying what's on. OK. Now what happens |
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| 145:35 | this point here where it begins to past the previous show? The suggestion |
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| 145:45 | is that it's a stable programing But what Doris Curtis saw in the |
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| 145:53 | scene was that as the shelf began prograde, that is to say, |
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| 146:01 | the subsequent regression began to go beyond shelf margin here, it began to |
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| 146:19 | . This was the o shelf margin here. This is a newer she |
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| 146:27 | failed here. So we're getting these regional roof falls that were occurring in |
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| 146:38 | new one will form here where there been a long well established shelf. |
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| 146:50 | as the, the delta crossed the due to drop in sea level, |
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| 146:56 | it reached that point, it began have a growth fault. And those |
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| 147:01 | falls can be seen all along the , the Gulf coast. These are |
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| 147:05 | major regional growth falls that extend for of miles, ok? That delineate |
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| 147:14 | old shelf drinks. Now, there's way that it could happen and does |
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| 147:24 | you begin to prograde across the remember that there is some mud that |
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| 147:32 | progressing over and that can cause a of head were migrating scarfs or |
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| 147:47 | ok? And as they migrate they're gonna form a large in embayment |
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| 147:56 | indentation into the shelf or rather into shelf and delta deposits. And it's |
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| 148:06 | sold right here on the old It's gonna be a on the shelf |
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| 148:13 | in some point it's gonna stop. there's one possibility for how it |
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| 148:20 | it's gonna be like a big It's a slop skull with landslide, |
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| 148:27 | material here. Extensional faulting in here this big regional bit, this big |
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| 148:36 | here that slows down in a series smaller growth folds all sowing into this |
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| 148:46 | decor. Now, ironically within that , there are pieces of delta slope |
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| 148:54 | could be reservoirs even down in But the bulk of that scar will |
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| 149:06 | filled with something else and it could filled with mud or it could be |
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| 149:13 | with Progra Delta again. So let's a look and a system here. |
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| 149:24 | these are growth faults, small OK. This is the how you |
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| 149:32 | to try to correlate them. But is a system in Utah and you |
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| 149:41 | a fault right here. It souls here. Another false here sold out |
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| 149:46 | . There's even a little roll over . A little thickening here. |
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| 149:53 | You can see how that thickens this section is not this the photo, |
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| 150:01 | it shows the same things. So see these small growth faults that are |
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| 150:07 | out basically along the pro delta. ? This is the delta front and |
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| 150:13 | there's the pro delta clays below. of this is clay. OK? |
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| 150:20 | down there at that transition, we over thickening. Now we have at |
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| 150:28 | larger scale here is a section preserved fiord collapse, big blocks and then |
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| 150:46 | pro grading still with the upper part a delta and the lower part being |
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| 150:58 | , sandy to Shay turbinates. That's of what we see here. Slump |
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| 151:09 | prorating fill down in here. Um flow deposits. That's what we saw |
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| 151:24 | . Yeah. This particular diagram on top is based on uh Wilcox uh |
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| 151:44 | . This diagram on the bottom is on exposures in the Norwegian fjords. |
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| 151:52 | a surprise, Edwards worked at the fjords and then he started working in |
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| 151:58 | subsurface of the Wilcox in scout And he brought that with him, |
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| 152:05 | he had seen in the exposures led to recognize what was going on. |
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| 152:11 | , look what we got here. got edge of a delta collapse and |
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| 152:19 | with delta a gift and that, scar here. We've got big fault |
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| 152:29 | . I mean, scoured blocks, block build with pro grading series of |
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| 152:40 | going into delta plane. OK? we see the effect of slope edge |
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| 152:49 | . OK? I'm gonna skip this I'm gonna skip that. I'm gonna |
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| 152:53 | it quits here. Uh We pretty have talked about the types of failures |
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| 152:59 | we get on unstable slope edges and edge deltas. OK? We're gonna |
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| 153:09 | to talk about deltas and more specifically and tide dominated deltas tomorrow after the |
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| 153:19 | . So that's it for today. |
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