| 00:02 | Okay, well, as uh before listed what I think are some useful |
|
| 00:08 | , most of which are in the list, none are gonna be required |
|
| 00:16 | but add them to your pile of or future dates. So when we |
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| 00:25 | about river systems, obviously part of issue is the source area drainage area |
|
| 00:33 | mythology was talked about that vegetation in of climate, the type and amount |
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| 00:41 | sediment discharge coming through the system, type in a remount and variability of |
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| 00:49 | went to the system, the steepness the gradient of the river and accommodation |
|
| 00:57 | . If we want to have these deposits accumulate through time. All of |
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| 01:02 | are variables that really in a sense to all of the deposition environments that |
|
| 01:08 | talked about. Okay. And so back to the source to sink, |
|
| 01:13 | have this zone of sediment production transfer deposition. The flu real system is |
|
| 01:28 | , oops. Um in this area , I'm gonna change my color. |
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| 01:36 | don't like. There we go. mainly looking at this. When we |
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| 01:43 | at the sorcery, we're really looking a different kind of system. Bedrock |
|
| 01:50 | are more typical. Alluvial systems are . Course deltas on the topic of |
|
| 01:58 | . So here again, we got to sink and we've got the changes |
|
| 02:02 | are going on and among the things usual tectonics and climate seem to be |
|
| 02:09 | water scale drivers. So the first with rivers is the bedrock or an |
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| 02:19 | river. The bedrock river is basically entrenched river is basically eroding into the |
|
| 02:28 | and as you can imagine it is providing the bulk of the source of |
|
| 02:34 | set? Okay. As a we tend not to see these river |
|
| 02:44 | because they're in the eroding areas, eroded away unless we have some kind |
|
| 02:49 | a rise and base level to allow entrenched valleys to be filled. So |
|
| 02:56 | do see entrenched valleys, particularly in regions where the entrenchment and subsequent valley |
|
| 03:07 | is controlled by c local changing your changes to a lesser extent with |
|
| 03:14 | Okay, But we're not going to with the bedrock rivers per se because |
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| 03:19 | concerned with rivers that have a preservation . So we're gonna talk about alluvial |
|
| 03:26 | which are basically rivers that are cut unconsolidated stream deposited material. Okay, |
|
| 03:38 | . I'm not gonna look at the right now except to say sediment load |
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| 03:45 | of sediment. Qs uh some power . Stream power stream velocity slope that |
|
| 03:53 | to the gradient of the river and stability. We're looking at clay or |
|
| 04:00 | . We're looking at vegetated Aurand And when I say morphology, I'm |
|
| 04:05 | about if it's meandering, is it , what's its nur city wavelength radius |
|
| 04:12 | the depth ratio, single or multiple . Okay. Traditionally we classify stream |
|
| 04:22 | into meandering and braided straight in an straight or really rare? Okay. |
|
| 04:36 | they exist and estimate using exists. the question is, are they really |
|
| 04:44 | channels that have split with vegetation in ? Are they braided? Well, |
|
| 04:57 | we're thinking more about single channel versus channel. And so an estimate using |
|
| 05:05 | braided basically two forms of multi The big difference is with an estimate |
|
| 05:12 | the bars to become vegetated with single . Almost all single channel or |
|
| 05:22 | The reason that's important is because the between single and multi is easier to |
|
| 05:29 | make in the rock record. The other thing is there's a complete |
|
| 05:38 | , here's a meandering channel, a channel and channel the same river. |
|
| 05:46 | , so we're gonna look particularly at transition from meandering braided, in |
|
| 05:52 | see what's causing it. Now the of sediment um is thought to be |
|
| 05:59 | variable. There's a lot of discussion this and I'm not gonna get into |
|
| 06:03 | arguments but um a suspended load channel has more silt and clay, it's |
|
| 06:15 | a relatively lower amount of bedrock. . And one of the things that |
|
| 06:25 | these suspended channels or suspended load is lot of meandering um as you increase |
|
| 06:37 | slope for the power or the set meandering gets higher and in particular when |
|
| 06:46 | say meandering visualized city how windy it . Okay. Yeah, with mixed |
|
| 06:57 | which are more suspended load channels really better said channels that are predominantly mud |
|
| 07:07 | more restricted in downstream areas and coastal more typically we have a mixture of |
|
| 07:19 | low and so what we see there we increase the radiant or the power |
|
| 07:28 | the sediment load, you see an in sin you ah city. And |
|
| 07:32 | you begin to see a transition to channels to breed. In fact, |
|
| 07:42 | you can just take a straight increase the slope, it gives the |
|
| 07:47 | , increase the slope more meanders more increase it more, begins to straighten |
|
| 07:51 | and come breathe. So we see a primary variable here between meandering and |
|
| 07:59 | having to do with the slope. called bed load channels that are almost |
|
| 08:05 | bed load tend not to be They tend to be just multiple |
|
| 08:12 | So we might think of this High variability. Low variability. Um |
|
| 08:23 | with sediment load velocities, gradient. . Um I'm not gonna go into |
|
| 08:31 | detail because in fact we're not as in this except to recognize the |
|
| 08:44 | variables in pattern and variables in relative . Okay. Um these are still |
|
| 08:54 | to look at it in terms of load discharge, extreme palate. Los |
|
| 09:03 | city. Hi, below. so. Hello, The high. |
|
| 09:16 | . Little unclear what's going on here we're getting more and more. Let's |
|
| 09:23 | uh Upper cell plant model a plant . Bella kula model. Upper scott |
|
| 09:31 | . Forget it. We've gotten to point where it's counterproductive to deal with |
|
| 09:40 | models. This goes back to the lecture that said, we got more |
|
| 09:45 | and we have examples practically. So we're gonna start looking at the architectural |
|
| 09:55 | and create our own law, but still would like to know what are |
|
| 09:59 | of the variables and and certainly one the main variables is channel slope. |
|
| 10:05 | something about this charge. We've known a long time that if you increase |
|
| 10:11 | for a given discharge, you go meandering to brady. If you keep |
|
| 10:19 | constant and increased discharge, Did you from meandering debris? Okay, so |
|
| 10:29 | in a channel forming discharge, a of argument as to what that |
|
| 10:35 | But let's just assume that it's some of measure of the amount of |
|
| 10:46 | Okay, now, notice here, going from point bars. Two point |
|
| 10:54 | in mid channel bar's the dominantly mid to almost all mid channel borders. |
|
| 11:02 | gonna be our transition from meandering to . And this is an important |
|
| 11:11 | Senior velocity increases, then decreases the , the death ratio, and the |
|
| 11:18 | of braiding increases as well. Now can also see all sorts of bar |
|
| 11:30 | . Forget we're also getting out trying at least at this level classified bar |
|
| 11:40 | . Besides the very simplest point bar connected mid channel, we'll do a |
|
| 11:48 | more with braided, but not a lot. So let's focus on keeping |
|
| 11:52 | simple. Having said that the way going to create these interpretations influential deposits |
|
| 12:04 | by initially defining bounding surfaces just like did with Julian first order is migrating |
|
| 12:17 | for second order short term changes, a flood event. Third or fourth |
|
| 12:24 | systems. Growth of a macro growth of a point bar, fifth |
|
| 12:30 | base of the channel. Okay, we're going to create our own |
|
| 12:35 | if you like, by defining a point bars and mid channel |
|
| 12:47 | Now, I'm gonna focus initially on fact, today, almost completely on |
|
| 12:54 | systems. Okay, so here we've system that's basically got a 5th order |
|
| 13:03 | . The fifth order system here. amalgamated system. Yes, scott 3rd |
|
| 13:12 | 4th order boundaries. And then within third orders, we've got 1st and |
|
| 13:19 | order boundaries. Okay, so Between 5th order boundaries, we have what |
|
| 13:27 | gonna call a story. And the is essentially a single laterally meandering alluvial |
|
| 13:41 | system. And as it a crease , we have to have some kind |
|
| 13:49 | accommodation line, like a climbing We're gonna preserve at least the lower |
|
| 13:57 | of that story. Now, in rapidly subsiding or slowly meandering systems, |
|
| 14:06 | may preserve the entire channel. But all cases, that story will be |
|
| 14:15 | a measure of that channel migration. we're going to recreate that champion and |
|
| 14:25 | deposits and associated deposits by looking at various architectural elements. Okay, |
|
| 14:35 | lateral migration, downstream migration, gravel , laminated sand, easier to look |
|
| 14:43 | them individually. Okay, so the itself is going to be bound by |
|
| 14:49 | erosion of circus surface and that's gonna A 5th order Baljic service and it's |
|
| 14:55 | to be filled with a rather complex of channel deposits, bars, abandoned |
|
| 15:07 | deposits, etcetera. And what these symbols are here or of course are |
|
| 15:14 | hands, the types of sedimentary structures there's gonna be a lot of detail |
|
| 15:23 | here. For example, it could that we're looking at laterally accreting deposits |
|
| 15:34 | a point bar. Mhm. Now creating deposits are deposits are gonna be |
|
| 15:43 | a high angle to the channel They're typically fairly thick. This |
|
| 15:49 | by the way, is pretty much measure of the channel thickness. |
|
| 15:57 | dips can be fairly steep, 5 15 degrees. That is the dip |
|
| 16:03 | the 150.4. Okay, Now, downstream of creating bar deposit as as |
|
| 16:10 | would expect. It's a bar that's in the same direction as the |
|
| 16:17 | I'm sure they're thinner and the dips usually low. These are these deposits |
|
| 16:28 | . And just to go back uh are these laterally creating deposits. So |
|
| 16:43 | would be third or fourth, And would be 3rd or 4th. |
|
| 16:52 | you might look here, look at little truncation here, that's probably a |
|
| 17:02 | order reactivation circles here. Okay, I seem to misplace my photo of |
|
| 17:14 | creating deposits. But the downstream creating are pretty clear. We've looked at |
|
| 17:19 | before. Okay. And notice the depositing here like this. So the |
|
| 17:38 | surface, which is this here is in the same direction as The little |
|
| 17:48 | sets have a hard time. Draw downstream. Accreting laterally accreting downstream, |
|
| 18:03 | . So how do I know? , if you look at the cross |
|
| 18:10 | of the planer or tabular process, gonna give you a pretty good indication |
|
| 18:17 | the flow direction of the water, direction of those accretion surfaces. Those |
|
| 18:28 | or fourth order deposits tells you the of the migration law. They're the |
|
| 18:38 | . Okay. Now, if we at laterally recruiting deposit, we still |
|
| 18:46 | the direction of the water as determined the direction of the small dunes and |
|
| 18:58 | have the direction of the migration of bar. Is that right? And |
|
| 19:05 | laterally accreting. So the way we down frame from laterally creating is basically |
|
| 19:12 | at the flow direction as determined from dune, smaller dune uh migration. |
|
| 19:23 | to d. Dens plain across strategy the accreting bar surfaces. The third |
|
| 19:31 | fourth order. Now I mentioned Um It's I think it did that |
|
| 19:39 | have a shorthand that we use for and gravel. And this is kind |
|
| 19:44 | useful although again, I'm gonna show example that we can have horizontal lamination |
|
| 19:51 | . H. That are dipping at or 15 degrees. So they're not |
|
| 19:56 | horizontal, they're complaining. Uh But look at some of these deposits what |
|
| 20:01 | might look like. Okay. B. Sand bed trough cross |
|
| 20:11 | Ls laminated sand. Shh downstream. . We're playing across trap channel with |
|
| 20:30 | order sediment gravity floats like uh the flows. This massive grab, gravel |
|
| 20:45 | in bed forms, draw planer gravels sand. So all of these are |
|
| 20:53 | short hands for describing a measured We're cool. But what they will |
|
| 21:02 | is we will use them as packages reconstruct the geometry and type of flu |
|
| 21:08 | system. Now, when we look a meandering river and we look at |
|
| 21:19 | in flood, let's look at Normal flow first. In normal |
|
| 21:26 | it tends to kind of flow as as it can. Okay, can |
|
| 21:33 | sorry, a normal flow, it as sinuous as it can. It's |
|
| 21:37 | kind of wandering around and flood. straightens out. Okay, so let's |
|
| 21:45 | at low flow, low flow, got this outer bed here and in |
|
| 21:53 | outer bands, it is deepest. , we have a pool at low |
|
| 22:00 | and then at the transition we have called a riffle and a riffle. |
|
| 22:05 | that zone between the deep pools where flow velocity crosses over during low |
|
| 22:16 | There's the pool opposite of the pool the bar in the riffle? An |
|
| 22:27 | court in flood, the river straightens . Okay, so we're gonna see |
|
| 22:40 | lot of deposition on the upper part the point. And a lot of |
|
| 22:46 | things we saw in lower flow are just not as important. So, |
|
| 22:51 | gonna look at low flow and high deposits. And we're gonna look at |
|
| 22:58 | point bar deposits as a portion of much more complex system which would include |
|
| 23:09 | Levee's displays, the flood basins, channels, etcetera. So we're gonna |
|
| 23:18 | at how you define those. But gonna focus just on this, the |
|
| 23:23 | channel fill, that's enough for right . And so let's look at that |
|
| 23:30 | channel fill. And what we see the meandering system is that as it |
|
| 23:35 | laterally, it leaves behind these this and uh swell topography. These little |
|
| 23:43 | and lows representing former locations of the of the point. Bar these meander |
|
| 23:51 | back here, We have them And what it shows in this particular |
|
| 23:57 | is that this river was meandering and actually became more and more well larger |
|
| 24:08 | larger Manders. And then something happened here and it was a band, |
|
| 24:20 | , rather not quite abandoned because it see more like that still has a |
|
| 24:27 | river. But look how much smaller is. Okay, so this river |
|
| 24:34 | abandoned and when it was active, was expanding. And what that means |
|
| 24:45 | that the amplitude of the meander was larger and larger. Now we could |
|
| 24:55 | a little different way of of uh Andrew, here's a river that basically |
|
| 25:03 | letters, It move like that. this would be translation. It could |
|
| 25:19 | or translate. And of course, it could do everything in between. |
|
| 25:31 | the shape of the meander scrolls is important in terms of defining the geometry |
|
| 25:39 | the point for deposits. So let's at this river here here, it's |
|
| 25:52 | as what, what would you say the pattern of Andrew, Is it |
|
| 26:07 | like we saw in the Yukon is downstream. There's something in between. |
|
| 26:23 | , I'll just tell you what, think this translation basically migrating gap street |
|
| 26:39 | eroding up hmm when we see those here, it's expanding. So this |
|
| 26:53 | a natural example and this is a . So what this paper does is |
|
| 27:00 | looking at the still, the point deposits will come back to this diagram |
|
| 27:09 | . Okay, now one of the we we see with bluegill systems is |
|
| 27:17 | even the same system can vary geometrically time. So what I want to |
|
| 27:27 | is look at some prices have seen along the trinity river, compare them |
|
| 27:38 | the whole scene, the monitor. to do that, we need to |
|
| 27:43 | just a little bit about the morphology the meandering river. So we can |
|
| 27:49 | about the wavelength, the amplitude and radius of curvature. We talk about |
|
| 28:08 | width of the radius of curvature as . Now, what's, what's important |
|
| 28:14 | this is that the wavelength is proportional some measure of meaning discharge and the |
|
| 28:28 | of the um meander, which is half the wavelength is also proportional of |
|
| 28:39 | kind of discharge this case, So the bigger the meander, the |
|
| 28:46 | the discharge. And so let's go to looking at the Louisville and the |
|
| 28:54 | and look at the channel with okay the and the width and aptitude and |
|
| 29:06 | of curvature of the meanders. What says is that 20,000, let's say |
|
| 29:17 | years ago there was a lot more flowing down the trinity roof. You |
|
| 29:24 | much larger rivers and point bars, larger abandoned champ fills and a geometry |
|
| 29:35 | flu real deposits is very different than forming today. So we can see |
|
| 29:42 | changes in the sedimentary record of a river due to climate changes that can |
|
| 29:54 | really very quickly. Well let's look the Yukon river. Okay. Um |
|
| 30:05 | think it's pretty clear that this was river when it was actively accreting and |
|
| 30:23 | pretty clear that something happened to cause decrease in discharge. Now the previous |
|
| 30:29 | , the decrease in discharge and therefore change in pattern of sin you ah |
|
| 30:35 | was due to a global climate change . It was due to avulsion. |
|
| 30:41 | river simply changed its, its um course leaving behind this abandoned river. |
|
| 30:51 | , um and so this is what looks like today and you can see |
|
| 30:59 | channel, the channel here is for . So that's the confusion here. |
|
| 31:07 | , so a channel abandoned is another of causing a change in channel because |
|
| 31:13 | abandoned. The channel doesn't necessarily shut entirely. Not like a little oxbow |
|
| 31:20 | . It can be a long term event. We can even see preserved |
|
| 31:27 | the rock record. These meander scrolls abetting plane And in some cases show |
|
| 31:38 | Meander Scrolls. And here's one where looking at 200 m. This is |
|
| 31:44 | Google Earth and we can actually reconstruct channel geometry. And from that began |
|
| 31:53 | better understand the paleo hydrology. our best Force is to look at |
|
| 32:07 | size and look at the seismic geo where we take a time slice in |
|
| 32:15 | particular case, a flu viel And we can literally see those meander |
|
| 32:21 | . Now, ironically we can see scrolls in a deep sea channel as |
|
| 32:28 | . So meandering deep sea channels have lot of similarity to meandering, flew |
|
| 32:32 | channels, which as I think about would make a great discussion question exam |
|
| 32:39 | those two channels. We're gonna focus this. And here is an example |
|
| 32:50 | the my scene of the gulf of of looking at the kinds of channel |
|
| 32:57 | based on the seismic. Got you seismic geo morphology. You see bar |
|
| 33:06 | , different types of cutoffs, bar , etcetera. So let's look at |
|
| 33:17 | being deposited as that channel migrates. . You get the highest velocity, |
|
| 33:26 | highest shear stresses and the deepest part the channel. And so we tend |
|
| 33:34 | have a finding upward secrets force define we not only see a change in |
|
| 33:48 | size, but we'll see a change sedimentary structures. And by the way |
|
| 33:56 | that channel migrated. He leaves behind irrational base which is our service. |
|
| 34:07 | here's that meandering system finding upwards. these would be individual events oops hear |
|
| 34:25 | each of which is expressed in the as a meander road bridge and run |
|
| 34:33 | I run a rich and sweat. , now the an original point bar |
|
| 34:45 | from modern to ancient was really the room with a research group from shell |
|
| 34:52 | in the 50s, published in the 60s, 70s, 70s where they |
|
| 34:56 | a series of cores and looked at face, she's track. And if |
|
| 35:01 | like applying Walters law, looking at vertical sequence. It. And so |
|
| 35:07 | they found in the fall, wag deepest part poorly bed face off |
|
| 35:14 | Then quote giant ripple prosthetic. We them something different now horizontally bedded and |
|
| 35:22 | ripple bedded. That was the lateral . And so that was the vertical |
|
| 35:26 | they predicted and sought to a certain in their course. So here is |
|
| 35:33 | point bar. They looked at uh was the cut bank Uh in |
|
| 35:40 | Here's the cut bank today. So of this point bar was formed in |
|
| 35:47 | last now This particular period, maybe years. So here we see the |
|
| 35:55 | point by. So let's look at surface. This is that same |
|
| 36:04 | And here we have what shall originally uh giant mega reports. Well, |
|
| 36:12 | now know there are dunes and we that they are sinuous. So they |
|
| 36:17 | three details. And we see superimposed these ripples as the water continues to |
|
| 36:27 | . Actually, it was going like , the water in between the dunes |
|
| 36:35 | to drain. So we get ripples in the troughs and then their mantles |
|
| 36:42 | blood. So notice the direction of dunes is more or less down |
|
| 36:54 | but notice the direction of these ripples least is a right angle. So |
|
| 37:00 | you want to know what direction the is oriented. Don't rely on |
|
| 37:05 | rely on dunes. Okay. And this is some of the dune cross |
|
| 37:11 | . Okay. Uh and we've talked these kinds of things before about reconstructing |
|
| 37:20 | conditions and bounding surfaces. So here got a series of bounding surfaces separating |
|
| 37:33 | bed form. So what would that ? What would this, assuming that |
|
| 37:44 | and this are the same type of form? What would that surface founding |
|
| 37:52 | be separating the two or so? . Uh I think this it's what |
|
| 38:06 | gonna be calling you a unit door these, I'm gonna call dudes |
|
| 38:13 | if I'm right, what would that bounding surface bit second one. |
|
| 38:27 | okay, we'll talk about unit bars . Uh here we've got trough cross |
|
| 38:42 | . Okay, so again, we've large scale dunes uh or unit |
|
| 38:50 | We've got they are three dimensional Okay, uh This is the dip |
|
| 38:58 | strike direction. So that's the lower of the emergent bond. The poorly |
|
| 39:06 | gravels. You don't say there's always Now as you go up the |
|
| 39:16 | you get into a what they originally horizontal bedding. Plainer surface. |
|
| 39:25 | Uh And you've got basically plainer betting these ripples here, that's you only |
|
| 39:38 | . And so what you get is transition up into, I'd rather hear |
|
| 39:48 | . Uh huh. Plainer strap. the planer strata is inter bedded mr |
|
| 40:04 | strategy. Here's the ripples, no we went towards you. Okay, |
|
| 40:15 | there's climbing ripples, We've talked about one Mama Drake. So what would |
|
| 40:26 | bounding surface, B what the Right, okay, so this is |
|
| 40:39 | at the end of a flood The top of the mud would |
|
| 40:46 | What type of downing service? right, because it's the end of |
|
| 40:54 | event. Okay, and these will first year here and here we see |
|
| 41:04 | are three dimensional ripples because of the the mud draped by the way can |
|
| 41:11 | really thick and then as it you get these big cracks which in |
|
| 41:17 | next flood is going to be ripped as much chips. So much chips |
|
| 41:22 | often gonna be found at the base individual floods deposits. So here we |
|
| 41:34 | um two and 3 d. Dunes cross strata and ripples. And so |
|
| 41:43 | is supposedly the idealized vertical seats. problem with that is other than right |
|
| 41:57 | the very top where we get a of mud drapes. The assumption is |
|
| 42:04 | over yeah, five or 10 m only ripples than only plainer bedding then |
|
| 42:20 | then scale cross bedding. But this sequence, Yeah, maybe. I |
|
| 42:32 | read it. Uh but Maybe 15m more um was deposited in multiple |
|
| 42:44 | They were deposited like this here, another. And sure enough, it |
|
| 43:00 | like those transitions occurred at the same . But how likely is that? |
|
| 43:08 | likely is it that in flood the transition from ripples to cleaner bedded |
|
| 43:20 | doom scale occurred at this level throughout entire flood and the next flood the |
|
| 43:27 | thing. Not really because in point fact, even within a single |
|
| 43:37 | there's going to be a variation Between 3rd order sets based on how that |
|
| 43:45 | changed during the flood, how the discharge, philosophy discharge and death |
|
| 43:55 | So in one case, you might have planner going into dune to ripple |
|
| 44:00 | planer to ripple down here. This here is what might have been |
|
| 44:13 | but even then it varies during the flood deposit. So I I much |
|
| 44:22 | a diagram like this, which suggests individual floods have unique flood signatures. |
|
| 44:40 | this gets to the scale that we're at. Here's that 5th order bounding |
|
| 44:45 | . Again here is the packet during single chan hears this story by the |
|
| 45:00 | . So this is what we refer sometimes as a lap laterally creating |
|
| 45:08 | Each of those packages is separated into . Each of those chunks is separated |
|
| 45:21 | individual beds. Okay, so here's same thing laterally accrued ng lap eventually |
|
| 45:37 | the bed. Now this bed this is the third order bounding |
|
| 45:45 | So fly deposit Here we see 12 strata, planer ripple. Okay, |
|
| 45:52 | it's a record of a deposition Okay, so that could be this |
|
| 45:59 | here. The problem is it could more complex. Oops draw that agree |
|
| 46:11 | them. But there may be that that that laterally a creating surface could |
|
| 46:24 | simple or could be compound. And that means is that And and these |
|
| 46:31 | basically the same. What that what means is that here we've got a |
|
| 46:51 | . I mean a flood deposit but that bed we've got migrating bed forms |
|
| 47:04 | the slope. We actually saw that DUIs and we're gonna see it here |
|
| 47:14 | what I'm gonna call unit bar. what are called unit bars. So |
|
| 47:21 | simple flood with no bad forms migrating that surface would look like this. |
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| 47:37 | if we've got bed forms migrating across surface. It's going to be more |
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| 47:43 | . What that means. Is that ? The fourth mhm Order is the |
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| 47:55 | thing as the 3rd the single There's no difference. We make that |
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| 48:04 | because there's a 4th order boundary that separated by dunes. Migrating down here |
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| 48:16 | a third order and below. So same problem we had with simple versus |
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| 48:26 | aeolian dunes. We have with simple compound flood deposits on rivers and will |
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| 48:35 | into this more uh to make that that clear. But let's look at |
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| 48:43 | a simple point bar. Okay, among other things, as we get |
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| 48:50 | and higher in the sequence, we're it thinner and thinner blood deposits and |
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| 48:57 | finding up excuses. That's what that's we're looking at here. So, |
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| 49:03 | on the rate of migration and the of the river, we might only |
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| 49:10 | three or four flood sequences before that has completely filled that channel on lateral |
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| 49:20 | . Here we see three flood deposits on the upper part of the point |
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| 49:29 | , and notice the flood deposits are thinner and thinner. Yeah, |
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| 49:35 | when we look at these flood we can see first of all that |
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| 49:45 | the bulk of this one in the is horizontal. Strategy, claim it |
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| 49:52 | . The bulk down here, at as exposed as here, the plane |
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| 49:56 | great up in the ripple and then ripples truncated by horizontal. These are |
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| 50:08 | order bounding surfaces. These are 3rd . Each of these is a flood |
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| 50:19 | . Okay. In fact, we see them weathering out. And |
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| 50:27 | we're looking at is the planer beds up into rippled Rating up in two |
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| 50:44 | . Shh, S R fine. and then the earlier in the later |
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| 50:56 | deposit. Third, third. so when we look at those |
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| 51:06 | we're basically looking at the story of flood and they're different. Not all |
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| 51:17 | are gonna be the same. No surprise there. Now, in |
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| 51:25 | we see different blood packets depending on size and where they occur on the |
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| 51:41 | for example, remember in horse grain , we don't get ripples, we |
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| 51:50 | do this and fine grained sands, don't get dunes, we get rips |
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| 51:55 | of course planter beds, so the deposits on the top shows kind of |
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| 52:02 | waning flow from steady high, unsteady flow cleaner lamanna, the ripple to |
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| 52:15 | . Mhm. As we go farther , if it's all course, it's |
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| 52:23 | coarse grain sand or coarse grain But notice as we go down the |
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| 52:35 | bar or downstream in the flow the grain size gets fine. |
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| 52:48 | here is more poorly sorted, so get um planer again, um but |
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| 53:01 | don't get, you get a little of finer green ripple, but mainly |
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| 53:13 | then to play, these are downstream on a point bar under different waning |
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| 53:27 | conditions. In other words, finding , we normally assume that floods first |
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| 53:41 | is high velocity dropping blasting finding out it turns out that that's not always |
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| 53:53 | case. I had a student work a individual flood deposits. What she |
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| 53:58 | is the upper part of the park deposition was on the rising flow but |
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| 54:05 | coarsened uppers and on the downstream finding latter part and the dropping flow is |
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| 54:17 | the deposition occurred downstream. Okay, again is in the field, 5th |
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| 54:27 | bounding surface. Oops, sorry, these are creating laterally creating surfaces. |
|
| 54:36 | . And you can kind of see point bars Now in all these cases |
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| 54:44 | like pretty clear. But to wait a second, there's some something's |
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| 54:51 | on here. It doesn't look like all exactly parallel. In fact, |
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| 54:58 | can't even correlate some and that's because point bars don't accrete as similar shaped |
|
| 55:13 | . Everything I showed before really kind implied that, but the type of |
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| 55:20 | bar oppression depends on the pattern of And if there's typically one big flood |
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| 55:28 | year and if they're all the you get something like this. |
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| 55:36 | now, what happens if you got lot of floods of different magnitude? |
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| 55:46 | , you get what's called a fragmented bar, one flood may deposit like |
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| 55:52 | , another here here. In other , the blood, individual flood deposits |
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| 56:03 | disconnected or can be, So you what's called a fragmented point bar. |
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| 56:09 | this isn't a dream case, but just illustrates how the variability in water |
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| 56:17 | or the flood can affect the variability those flood packets. Okay, But |
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| 56:24 | they keep it simple here, we've a point bar. Okay then a |
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| 56:34 | section. Um Let's say through the bar might look something like this, |
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| 56:43 | is the middle or downstream portion of point block, right channel bottom finding |
|
| 56:55 | . Now we're beginning to get little portions which are individual portions of the |
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| 57:06 | migrating bar. Okay, And then kind of fairly abruptly is truncated these |
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| 57:19 | here. He's laterally accreting bedding those or fourth order bounding surfaces. I'm |
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| 57:30 | call epsilon cross strap. I'm not be outlook. So just so |
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| 57:47 | So that's my verbal shorthand for these accreting flood deposits on a point |
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| 57:55 | Yeah, they are preferentially preserved in upper part of the point bar, |
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| 58:03 | because by the time you get down here, they're amalgamated so much erosion |
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| 58:10 | now up in here on the I'm sorry. Um On the downstream |
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| 58:22 | . Uh they're still relatively well But if we look at the upstream |
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| 58:29 | , there's a lot of truncation, only see the lower portion of the |
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| 58:34 | bar preserved. You can kind of that here. And the reason for |
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| 58:46 | is all explain in a couple of is the erosion on the backside of |
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| 58:54 | meander loops and the presence in some of erosion, all scholars associated with |
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| 59:03 | bars, but the upstream a portion a point bar can look different than |
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| 59:10 | downstream. Now, that's especially true somewhat unusual cases where there is deposition |
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| 59:30 | actually extends into the concave a portion a meander. It's right in |
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| 59:41 | In other words, it's not just and cut back. There's actually a |
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| 59:50 | that extends into the cut bank when got deposition in this area, that's |
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| 60:00 | you think of as erosion. It's tail end of the point bar. |
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| 60:08 | often find a great, which is say, as we go from force |
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| 60:16 | find on the point bar it may drift into mud couples. And that |
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| 60:23 | was implied here, stand the mud downstream thinner deposits downstream and there's a |
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| 60:45 | of ways of doing that. But most common way is what's called a |
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| 60:51 | ball where there's a fine grained Eddie at the distal or downstream portion |
|
| 61:00 | Okay, and if we look at size over here, notice how the |
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| 61:07 | size raids from sand to muddy On .4, okay, this cross section |
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| 61:21 | is of the muddy portion of that . This is the cutback. |
|
| 61:31 | look how sin those individual bed Those are the flood packets here, |
|
| 61:42 | got a channel is migrating like this are the point bars, this is |
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| 61:59 | upper point, the downstream counterpoint bar channel. Here's another counterpoint bar migrating |
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| 62:17 | this direction. Okay, that's this here, look how different this vertical |
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| 62:32 | is from this or even from Mhm. Where we have these counterpoint |
|
| 62:40 | , we have uh very marked decrease grain size, decreases permeability, decreasing |
|
| 62:55 | potential. We're gonna see when we at some of our case studies how |
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| 63:00 | can affect how you your reservoir is . Now, just going back to |
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| 63:08 | of bar accretion extension, translation. can actually see that those meander |
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| 63:20 | The individual loops can vary in shape lateral continuity. I'm not gonna get |
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| 63:29 | that particularly except to say that this affects the pattern. A bar records |
|
| 63:41 | pattern of bar migration, which in affects grain size. So here we |
|
| 63:48 | a situation where we see a downstream in grain size, upper part, |
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| 64:02 | coarser, few little parts of very associated with the counterpoint. Yeah. |
|
| 64:13 | here's a case we've had a valley and this meandering stream is migrating through |
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| 64:25 | by translation. Okay, As long in this direction, for some reason |
|
| 64:40 | stops right about here, and this here stopped right here, it stops |
|
| 64:45 | here, there's something that's preventing it expanding. Yeah. And that something |
|
| 64:55 | the incised channel incised valley. When in the narrow part of this incised |
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| 65:02 | and the stream will migrate until it off this so hard it's easier to |
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| 65:08 | downstream then expand. And what that is that in this portion of the |
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| 65:19 | fill, we tend to get the preferentially recorded by abandoned champs because that's |
|
| 65:32 | they saw. But as the river and expanded beyond the incised valley. |
|
| 65:42 | what happens. It expands over those and we get expansion. So we |
|
| 65:55 | translation below when you're confined to the part of the size valley expansion laterally |
|
| 66:05 | it spills up. Okay, now can occur with vertical accretion or can |
|
| 66:12 | occur with lateral accretion. Yeah, on but it encounters in the cut |
|
| 66:31 | . Yeah, here is a change the ST mud, lateral expansion. |
|
| 66:49 | , up until this point stay Now look what happens at stage four |
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| 67:05 | 56 we reached the end of this buffer and it began to expand. |
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| 67:21 | this was due to a lateral change the month if you like. |
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| 67:29 | in both cases, you went from to expansion as that river got to |
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| 67:36 | point where it could expand. Now, here's this point bar that |
|
| 67:43 | Herrera looked at this was those flood . It went from pebbly, the |
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| 67:50 | core sand, very fine grain And one of the things to notice |
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| 68:01 | these bars here turns out these bars related to what had been described earlier |
|
| 68:12 | shoot bars, where the flow is over the point bar is having a |
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| 68:22 | of a little channel or erosion on upper point bar in deposition of a |
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| 68:27 | grain load downstream. Yeah, Back 1970, that's what we called |
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| 68:35 | But fast forward 30 years. These are now called unit owners. |
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| 68:46 | And the downstream equivalent of these. are scroll bombs and these scroll boners |
|
| 69:03 | , or the downstream approval of these bars here. Or I'm sorry. |
|
| 69:11 | unit bars. Here's our unit Here's our crowbars, here's our unit |
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| 69:18 | , Here's the schools. Unit bars most common and greatest dreams, but |
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| 69:35 | importantly, they're associated or or rather they are more typically associated coarser grained |
|
| 69:48 | and they're not the same as These are the dudes. These are |
|
| 69:56 | unit bars bars adjust to flow width depth, not dept alone. And |
|
| 70:11 | can accrete actually all the way to top of the channel. So they're |
|
| 70:18 | distinct from dudes dunes. Never fill chance. They're restricted to about a |
|
| 70:28 | or sixth water debt. They vary a function of water debt. Unit |
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| 70:36 | can fill the chance. It turns here is a channel. I'm in |
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| 70:45 | bar point bar. And here we have a series of unit bars. |
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| 71:00 | the point bar is really a compound . And remember when we talked about |
|
| 71:06 | order versus fourth order a compound bar forms bed forms migrating along the surface |
|
| 71:18 | now what's migrating along that surface. by the way, what we did |
|
| 71:23 | say on the Gaza Strip, are migrating unit farms. So the flood |
|
| 71:32 | will include the flood migration of these unit bars like this? Here's our |
|
| 71:47 | , here's our unit bars. And we take a trench right here, |
|
| 71:53 | we see is that a creating point ? I mean recruiting unit bar. |
|
| 72:02 | when we look at it here, is the base of it and what |
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| 72:06 | can't see here, but there would another reactivation surface marking the flood |
|
| 72:21 | Okay, so here's our simple unit . It may have ripples on the |
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| 72:34 | , could even have backflow ripples It's migrating down the bar for |
|
| 72:44 | So here are reactivation surfaces. here we've actually got them migrating down |
|
| 73:02 | surface until they form basically have filled whole water. Each of these are |
|
| 73:14 | services. Okay, if we look where is it? Well, if |
|
| 73:30 | look at this in his backwards, couldn't figure out how to get this |
|
| 73:37 | . Notice these downstream migrating dunes rolling four packages. That's what we see |
|
| 74:06 | downstream, migrating dunes growing into full in this case downstream dipping bar. |
|
| 74:25 | , You can look at this, I think you get the idea uh |
|
| 74:33 | depending on what the water level is , you can get different things eroding |
|
| 74:39 | that's a detail you don't need to but the idea of reactivation and migration |
|
| 74:46 | important. Going back to the coarse , you can have erosion at the |
|
| 74:53 | part of the dune, deposition of lower part and deposition of that unit |
|
| 75:02 | can occur on the upper dune. gonna be during floods. Remember the |
|
| 75:08 | straightens out deposit sediment on top of foreign point bars. So here we |
|
| 75:16 | these unit bars or shoot colors covering the downstream portion of the point bar |
|
| 75:29 | , a lot of erosion. So getting that erosion going on here and |
|
| 75:36 | just have the lower part of the . There's no shoot bars here, |
|
| 75:42 | do get him here and notice the actually can see finding upwards forcing upwards |
|
| 75:54 | that coarse grained material rags over the of the of the point block. |
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| 76:03 | what we got here, coarser grained . His bar champ can fill now |
|
| 76:29 | and bridge and time. Um have at lower bars. This is mainly |
|
| 76:36 | great extremes. What they find is greatest dreams. You tend to get |
|
| 76:41 | channels sometimes and get channel grading into . What is most interesting here is |
|
| 76:52 | downstream unit bars. Thanks depending on they are on the point bar that |
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| 77:08 | be in the middle. They're on bottom. They tend to not be |
|
| 77:12 | the back because of erosion. And this again very quickly, just |
|
| 77:22 | me add that big rivers have even bed forms uh in the amazon river |
|
| 77:32 | are compound dunes, Simple news. on top of them. Compound dues |
|
| 77:42 | cross strata. It's on the order 10 m height. So we can |
|
| 77:50 | 10 m high compound dudes that are the bottom of the champ, so |
|
| 78:05 | have to think about scale most of we have recorded in both modern and |
|
| 78:13 | ancient had been relatively small channels. , meandering dudes. The amazon locally |
|
| 78:20 | me Andrew and yet big tunes. as we'll see, we're we got |
|
| 78:25 | pretty big great extremes as well. we're gonna get big scale cross |
|
| 78:32 | Okay, so some generalizations. If wanna try to interpret ancient alluvial |
|
| 78:40 | Uh, irrationally based 5th order, individual channel will deposit a story. |
|
| 78:48 | group into channel belts, mainly finding the net to gross for the percent |
|
| 78:57 | channel versus or other bar versus overbanked in continuous outcrops. You can begin |
|
| 79:07 | reconstruct the paleo chance. Absolutely, tend to have a lot of |
|
| 79:16 | And so as they a grade, upper part of the channel stories are |
|
| 79:23 | wrote it off. So this would a way in which a sand body |
|
| 79:32 | be preserved. Mhm. Uh It's single linear sand body. It might |
|
| 79:44 | due to lateral accretion. That might a single story. That would be |
|
| 79:54 | of a multiple laterally accreting a Here's a lateral Ukrainian unit is more |
|
| 80:06 | complicated. Uh still though even up here, we only have a single |
|
| 80:18 | chance it may shift, but there's net vertical accretion beyond what's happening in |
|
| 80:27 | channel itself. Now, if we to allow vertical accretion, we can |
|
| 80:33 | to amalgamate these channels. Okay, we're getting one on top of |
|
| 80:39 | Yeah, so here we have lateral . We can also have downstream accretion |
|
| 80:45 | the same channel, we could have . This is a single story, |
|
| 80:52 | laterally shifted. So we have different and the same deposit. So here |
|
| 81:01 | got, we tried to create rather these deposits, something like we did |
|
| 81:15 | . The problem is, we'll see . Um this correlation has very thin |
|
| 81:29 | migrating over tens of kilometers. The to death rate is huge, but |
|
| 81:41 | you take a thickness versus uh the were dressing the thickness of the fill |
|
| 81:54 | the width of the channel. um the time you get way up |
|
| 82:01 | here, these things are braided meandering streams are way down here and |
|
| 82:10 | turns out as they began to look the core. And also to run |
|
| 82:18 | test turns out those were not laterally channel belts at all. They were |
|
| 82:26 | channel belts for stories. Now, can see that in alcohol, we |
|
| 82:32 | see how this channel was broken up various stories. Okay. Oh, |
|
| 82:47 | , by the way is true While lower vertical exaggeration and this is |
|
| 82:57 | and then modified or annotated here, actually have a channel filled in the |
|
| 83:11 | . So that be something analogous to here, we have a channel that |
|
| 83:18 | of spilled over. Got this kind wing to it. These will be |
|
| 83:24 | deposits here we have multiple channels, of these is 1/5 order bounding |
|
| 83:36 | And so multiple stories, same thing , many stories giving you a sheet |
|
| 83:46 | pat and here we've actually got these scour down valley fill and then filled |
|
| 84:04 | like this. And this is just similar example and he's just moving the |
|
| 84:13 | um point bar deposit. Overbanked basic channel two channel filled with lateral filled |
|
| 84:39 | downstream, creating parts. This one kind of interesting because you got a |
|
| 84:47 | coat that was actually a thicker peak that was channel filled but when it |
|
| 84:59 | , you had kind of an inversion topography so that this drapes down for |
|
| 85:07 | exaggerated topography. Okay, that's something this. Now, here we've got |
|
| 85:22 | is away from the view. So it laterally accreting or downstream and |
|
| 85:41 | I got five minutes. So that's . It's the flow is into the |
|
| 85:51 | or out of the screen? It's creating to the right. So is |
|
| 86:00 | lateral or downstream? What's the direction flow? No, I just said |
|
| 86:11 | flow is downstairs down into the, viewing, your your view direction. |
|
| 86:21 | . Is flowing into the screen. . It's gonna be laterally agree. |
|
| 86:30 | , yes. Okay, now close this direction, laterally. Accreting. |
|
| 86:52 | , so if it were flowing, should say this, this is also |
|
| 86:59 | , so we've got lateral accretion The flow actually here is flowing in |
|
| 87:06 | direction, so it's down street Ah I forgot my own storyline, |
|
| 87:23 | flow is flowing in this direction. bed forms are creating upstream. What |
|
| 87:31 | that tell you? Upper floor Shoot pool. So here we have |
|
| 87:39 | accreting upstream, even though the flow down street. So we got, |
|
| 87:47 | you like really 33 geometries to think bar accreting laterally, bar creating downstream |
|
| 88:00 | like form of creating up street in of poles and upper floor regime. |
|
| 88:07 | , and that's all we have time today. So let's call it quits |
|
| 88:15 | um stop sharing. We can stop |
|
