VideoPoints

• ••• • •• • ••••• • •
GEOL6358 Terrigenous Depositional System - Day4 02-25-2023-Part1
Help Tour
© Distribution of this video is restricted by its owner
Transcript ×
Auto highlight
Font-size
00:03 Okay. Um let me uh got it. All right. And
00:09 let's think about the Louisville system Um The last time we spent really
00:19 much the whole lecture talking about processes the channel and the processes of deposition
00:28 a latte predominantly laterally. Accreting Bar. Having said that the architectural
00:36 that I described that make up that bar um can also be applied to
00:42 migrating bars or downstream recreating uh and be applicable are applicable to graded bars
00:51 well. I want to leave the though for a minute and look at
00:55 bigger picture of the meander belt as whole. And clearly it's a complicated
01:01 . Meandering streams changed their course a . Really one of the first geological
01:08 of this was by Fisk and others of Louisiana. And uh Essentially,
01:16 Corps of Engineer wanted a map of floodplain. Now, ironically, they
01:22 a map of the floodplain in order find out where the clay 24th the
01:27 channels, because those were areas where river tended to be stuck.
01:35 it doesn't laterally migrate, whereas where sandy or it moved more. And
01:41 , uh this map, although it's geologic map um is really more about
01:47 physical processes of those deposits. And Fisk who ran that team was then
01:54 by Exxon. He and actually his eventually moved to Houston and they began
02:01 at de positional models for petroleum point view. It started with respect to
02:06 engineering. And sis took his group Exxon, another part of his group
02:13 to Shell. Shell did the point that we talked about. Exxon is
02:18 do the Mississippi River and the Mississippi . Uh And Shell also did the
02:26 area island. So really the beginnings our studies of deposition models really started
02:34 the 19 forties with the fisk work the Corps of Engineers. When we
02:41 at various species we're concerned with, pretty much have talked about the active
02:46 filled. Uh we're gonna talk about channel fill and then we'll look at
02:52 beyond the channel on the channel margins rivers changed course in a variety of
03:01 . Be the meandering or rated. tend to occur either as a shoot
03:08 off what you see on the, the left where it basically cuts through
03:12 existing bar. Uh And this is true in braided stream, but it
03:17 occurs in meandering. Uh It can a meandering neck cut off um and
03:23 can be avulsion. Avulsion is where is a large scale shift in the
03:28 of the river and this point at it migrates. Let me see if
03:34 can get my panda to work. This point right here. Uh That's
03:42 avulsion note and we actually talked about a little bit with uh alluvial fans
03:49 we'll come back to that story a later. Okay, when we look
03:53 net rather shoot cut off, we them. Obviously they're going to be
03:57 during flood. When the flood waters trying to take a shortcut over the
04:05 off of the point bar, so see them cutting through and at some
04:10 , what will happen is the river deepened so much here that it will
04:17 this off here. So this will abandoned. Okay, And so that's
04:22 shoot cut off. Uh this will a net cut off and we can
04:27 that in this particular case. Um neck was completely cut off.
04:33 and still there's a vestige of the river flowing into that cut off.
04:43 we look at this here, we actually that the cut off occurred not
04:50 much by the two eroding areas cutting each other, but well, it's
04:56 if you like a kind of shoot off where it simply skipped over,
05:00 a shortcut and left behind a man uh well, we'll call an oxbow
05:09 , it's an oxbow lake that's being and one of the things to notice
05:14 that it tends to be filled from upstream side. So even as this
05:23 and the sediment is heading down, of it continues to spill into this
05:28 , what that means is there's an downstream, a symmetry of the channel
05:35 . Uh we think of the channel as being kind of a blood
05:40 Uh and certainly it can be, in the latter stage, but there
05:45 be a lot of sediment, horse sediment coming into that upstream. Uh
05:53 . Okay, um it eventually fills into an oxbow medal, if you
05:58 . So we drilled into that would looking at the settlement that we're going
06:03 describe in a few minutes. there's the abandoned channel film. Here's
06:09 case of a river basically leaving its running down for a while and then
06:15 downstream. So this would be a of avulsion where it's not just within
06:22 river, uh but rather within the belt, but it's it's creating a
06:28 new meander belt. In this particular , you'll notice that there's kind of
06:34 hint of something down here. But this is a uh meander belt tend
06:40 be a relatively higher area because of build up of the levees. And
06:47 as we look, get farther and away from that meander belt, we
06:52 into the low lying flood basins. so this river, once it
07:00 went down that topographic law. we're looking at the topography on the
07:06 and the channel belt as a whole define to a large extent the relative
07:13 of future and past of options. basically gonna follow the low spot.
07:21 , the so called mud plug itself , we're looking at that abandoned channel
07:26 and we see that they're all if you think back to that first
07:31 second slide uh look how many abandoned , look how much the abandoned channel
07:38 constitutes the floodplain between the meander rather the meander scrolls, which is
07:47 superficial expression of the point bar deposit these abandoned channels. That's that's the
07:54 of the floodplain until rather the meander until we get out to the
08:01 And when we look at that, this again just talks about the stages
08:06 filling. Uh so that uh we envision this thing, not just being
08:12 off into uh a an enclosed which is muds, but a lot
08:19 sediment coming in different directions. And with the decor is for, this
08:25 from the Brothers River, from the crew. Uh and here there's a
08:29 abrupt cut off. So, where poured, uh the channel floor still
08:38 its deposits and then set off to . Um On the other hand,
08:44 can see it varies a lot in of how much uh of the lower
08:50 was preserved before was cut off. see we can see a gradual decrease
08:58 settle on the left um as it's in. Uh and we can even
09:03 swamps coming in once this channel is and get channel failures as well in
09:09 diagram on the bottom basically shows the screen, that's as it come
09:17 Look at that gradual decrease in percent and gradual increase in percent blood.
09:24 , so that's really more realistic than shutting it off. Okay, uh
09:33 the lower parts of these channel fields be pretty androgynous. Now, if
09:39 look at the margin of the look outside the channel and look outside
09:43 point bar, we can see natural , crevasse, berries, uh There's
09:48 cheap flood bits and um flood So let's let's see what we're looking
09:54 here um when the river floods and specifically uh exceeds its channel, it
10:04 decelerates. And so it's going to that suspended sediment and even sediment that
10:09 be moving his bed load and start which of course this material first and
10:15 gradually find a material farther out and result is rebuild a natural levee,
10:21 shaped uh periphery to the channel It builds higher and higher.
10:28 in this particular example, there's no migrant lateral migration occurring. But I
10:34 you can imagine pretty easily that if migration is occurring, then levees are
10:41 to be pro grading as well. we're gonna see this gradual program creation
10:51 the levy in the same direction as lateral pro gradation of the channel
10:58 Now, levies tend to be particularly at the margin and as a
11:04 they often have different vegetation, a better sorted the uh little higher
11:12 So we're going to see uh more , perhaps uh different types of vegetation
11:21 those levees and we'll see in a , different types of soils development as
11:26 . So this is kind of a again, this is from fisk in
11:30 , um looking at the various geometries what we see. We've got lateral
11:37 book. What type of migration would describe the pattern shown by these?
11:47 was it more translation? More expansion something in between? What does it
11:55 like to you? Well, they , I think uh for what this
12:10 and expansion basically says that the roles concentric with the channel, whereas if
12:19 recall translation voting on the upstream migrating on the downstream side. And
12:27 the scrolls are located on the upstream . So you need to get comfortable
12:33 that geometry because that affects the pattern sand development. Okay, now we've
12:40 the leggings then notice panel eyes, got these crevasse channels for best place
12:47 into more muddy flood plain. So here we get a picture.
12:53 is time living here. It's a hard to society because you see that
13:01 channel ized flow that's coming and spilled . This has been abandoned channel,
13:08 when it was acted, this was a hard right hand turn. And
13:12 there was a lot of spillover. the stage was overflowing again, you
13:23 it here, here's a very nice the wrestling channel and so that basically
13:31 between what we refer to fizzy graphically levies and crevasse places the presence or
13:39 of the channel levees are generally thought be more sheep flow once it begins
13:45 be channel. Ized uh it becomes crevasse play and I think as you
13:49 see from this here, it's not that clear in real life down
13:56 Okay, so let's look at this , it's gonna be this prism shaped
14:05 geometry uh with decreasing rate of deposition the right, that is difficult to
14:15 channel, decreasing grain size and less less drainage because it's basically the water
14:22 is getting closer and closer to the . Tell, tell me I get
14:27 to the flood basin, it may be a marsh, you may well
14:30 the water table and the ground at same level. Um Now one of
14:35 things that happens is that the rate deposition of course is higher Jason sam
14:43 . So you don't have a stable soil storm sitting out here in the
14:50 , basically it is relatively mature, we get a lot of immature soils
14:57 there is constantly being coarser material. the other thing is the soils tend
15:02 be oxidized at least because you are the the water people. So you
15:10 sometimes called in uh a uh leech above a glacier horizon. The glaze
15:19 is basically the, the reduce er non oxidized muds that are typically kind
15:28 a grayish in color. Uh you leaching of calcium carbonate above the water
15:36 , whereas down here begin to get iron concretions as well as calcite concretions
15:43 well. Okay, and as I earlier, those levees can migrate with
15:55 migrating channel. So if we were take more here to customs levy,
16:01 we're getting progressively older. Got escapes levy deposits exposed. Uh and we're
16:09 going off the bottom from proximal to legend. And so we're seeing a
16:17 in the grain silo, basically sampling more distal parts of the levees.
16:22 go down low. Um in these cases, uh they are deposited from
16:29 flow most common. The high blasting then it wanes as the water drops
16:36 the floodplain. So we have a of course, uh systems uh increasing
16:43 and parallel beds ripple uh because these deposited on the levees hugely, they're
16:50 relatively fine grain. So we wouldn't to find dudes. So we're pretty
16:55 looking at plane uh bed to ripple and then mud drinks and not surprised
17:02 would expect to see them highly Uh and probably a lot of root
17:09 as well. So here's an example deposit here. You can see
17:19 This is not a matter of This is actually true thinning if you
17:24 farther and farther away in if that becomes fresh as they often do,
17:38 you get a portion of the water through the levee and then deposited into
17:44 look like. Ah it's giving you and it's giving you display which you
17:52 think of as a little adult. basically what is any fact? It
17:57 well have been a delta at the of flooding because the floodplain may have
18:01 had standing water. So when we at these uh here we have a
18:07 of different examples of uh we got on the left, um mid
18:16 bar the notice the right channel is little larger than the left. That
18:22 of majority of flow is being diverted the fight. And that the version
18:29 apparently enough to cause a breach at relatively single rather single point to give
18:37 this kind of uh single. down below. We get a lot
18:44 strength stretch. And so we have overlapping for basketball display. It's kind
18:52 hard to tell at what point or would be a levee versus a whole
18:59 of overlapping crevasse plays. Uh So would be an example of a single
19:07 . And this is more of an we talked about earlier where we we
19:13 this progression of channel. Ized well opposed to sheet flow, we can
19:20 of it as a delta. And if we were looking at through the
19:30 letting and we had a full breeding wedge or display into in this case
19:38 lake probably a temporary lake because the is there because the floodplain is
19:47 Uh But from the point of view deposition it much of this was deposited
19:53 a middle delta. Now we're going see the same thing when we get
19:57 to the Mississippi delta where we look crevasse plays into the bay and there
20:02 truly are many little deltas into standing . Uh Here on the floodplain,
20:10 water is going to to settle And if we look at a serious
20:16 section, what we see is uh of pod shaped areas there get smaller
20:32 smaller as we go farther offshore or farther and farther away from the
20:36 Um And and these again are are display itself which as it pro grades
20:47 to be uh course inning upwards. I'm sorry, um thickening upwards.
20:55 Individual splay events are gonna be typically upwards. So this is associated with
21:02 lateral pro gradation of that splay moving and just like the levee. That
21:08 be because of either increasing discharge during flood or because we see distinct flood
21:17 . Probably the lateral migration of that through a long lived crevasse play.
21:23 , these crevasse plays not only can long lived, they can actually be
21:29 inception of channel of ocean. So don't always just heal up and leave
21:34 . Okay, so we have a of um finding upward sequence in here
21:44 due to uh individual slaves and thickening . The channel itself is kind of
21:52 migrate. It's also gonna be finding , but it's going to be um
22:00 little coarser grain. It's gonna show of channel ized erosion Scout.
22:08 And so here's just some examples of sections through these little mini delta into
22:20 uh So the question is uh that lake deposits may have been A week
22:32 two deposition. Uh There's been a of recent papers on these. This
22:43 goes really in some of the A lot of climbing ripples within the
22:49 . That's because if you recall climbing are being formed as you have rapid
22:57 from suspension and traction. So where have rapid deposition, those ripple bed
23:03 creek a levee or a crevasse play going to be the classic area for
23:11 deposition. So, climbing ripples are form in these various sets and uh
23:20 can the coursing upwards or finding upwards on the nature of the flood.
23:28 all floods are created equal. Um we have some good examples forcing the
23:35 blood's blood uh in the crevasse Uh the channel belts are gonna tend
23:43 be always finding upwards. So, the coursing upward crevasse play is as
23:51 as the finding upwards. But the upwards channel is okay, and this
24:00 some of the channel eyes deposits that get from those crevasse. Blade
24:07 Uh There's been a lot of work on the geometry of these channels.
24:12 not gonna labor this picture except these just examples of them. But the
24:17 of course uh is because we would to know the geology of the sand
24:24 . These sand bodies can actually be . First of all, the sand
24:28 are architectural elements within a particular meandering , but there are also potential components
24:38 a reservoir. And so there's been lot of work done from the lateral
24:43 she's changes within crevasse plays such as and all and the proximal the distal
24:56 that we get, but also trying predict the geometry. Uh But one
25:04 the things we love to do uh our world at least as petroleum geologist
25:11 to be one dimensional, we have wealth and we want to extrapolate that
25:19 the areal extent. So can we thickness project the lateral extent of something
25:27 interest. And so we spend a of time trying to look at things
25:31 with the death ratios for with the ratios of various types of environments.
25:39 is the thickness versus its lateral R squared is not huge, but
25:46 begin to see that there are uh that you can use to get a
25:52 approximation uh from that thickness. And point is that used to be pretty
25:59 and pretty wide. Um This is Yeah, this is 50 ft.
26:12 sand is on the order of um 1000 ft. uh and and it's
26:23 and part of the isolation of that body is the main channel which is
26:30 fleshed. They've got a sad body pinching out into clay flood basin and
26:38 confined by the abandoned channel. Uh just another example of fields in
26:47 Um and you've got these crevasse blaze here you've got salt and so it
26:55 happening, the crevasse blaze was being off. And so you have an
26:59 strata graphic threat because a crevasse place there's a lot of features that you
27:07 um on the floodplain itself and in origin you get a lot of deposition
27:14 um water that are falling stage. get mud cracks, you get mud
27:19 ripples, you get vegetation, the cracks get broken up, the mud
27:27 can actually be filled. These are mud cracks within the morning coffee,
27:34 think it's dry, this is not um here we've got the mud chips
27:40 are typical influential deposits, particularly at base of a flood deposit where you're
27:47 up those chips and they're kind of along. Um We've got soils
27:55 we've got red paleo soils, we some touch soils, we get mud
28:02 , we need to pick up the cracks at core, we get a
28:07 of plant material, we get plant , ultimately we get cold, but
28:13 before coal we get just a lot leafy material and they're gonna be preserved
28:18 that more distal part because remember they to be below the water table.
28:22 gonna be oxidized for on the What will not be oxidized on the
28:27 ? That would be route. So likely to get a lot of root
28:33 as well. Um I'm sorry, . Okay. There's a possibility route
28:39 again, um coal deposits at the . So these are all basically um
28:49 of that flood basin and from a point of view is both a source
28:56 a seal. Okay. Ah What can we talk about the flood
29:03 Um Actually, let's let's look at for a second. Uh This is
29:09 continued template to organize your thoughts about of the trends that you get in
29:20 various environments. Uh So let's just for a second and some of
29:26 And I want you to interpret these as being present, sand and farther
29:32 to the left the course of the . Uh And on the right.
29:39 Think of it as share uh strictly , that's not true, but that's
29:45 pretty good first approximation. And that's we're gonna use. So we got
29:50 for C. It's going through what described yesterday as that laterally agreeing point
29:59 . It's gonna have that. Um me that uh the bounding surface,
30:12 order bounding surface of erosion scoured the is gonna be finding upward sequence
30:18 finding upward sequence will vary depending on you are at the bar. Uh
30:22 it will vary whether or not it's simple bar or bar with unit bars
30:28 it, but it's still gonna be finding upwards. And so when we
30:33 at that core, that's what we this shark base with order erosion.
30:40 then of course this is the So um what's here? It's not
30:49 . Is just finding out now. you should be able to do is
30:56 draw a core adjacent the difference as how you might in interpret or expect
31:08 vertical sequence to be based on what talked about earlier. Okay. Uh
31:14 on the other hand here, we've foot play. E. And pretty
31:19 that mud with a few spikes of so we can come over here to
31:27 . Which is a natural leading notice the panel has been migrating from right
31:34 left there for okay, uh right left. So it's gonna force it
31:42 . So we have basically a fund in. Is that uh vibrate.
31:53 then it's shown is happening off. And that strictly speaking, probably is
32:00 accurate for this gene this picture, certainly let these uh channels and uh
32:09 going they're gonna be abandoned whether Uh So we could go through and
32:13 at some of the others be let's what B. Is okay.
32:18 Is in the for that play. we have a series of course thicker
32:27 and and that would be the So this would be channel.
32:42 Um down here f uh it's basically abandoned channel then. Um So it's
32:54 meander cut off Where maybe it should off here again. 5th order bounding
33:01 channel margin for screen and then So you ought to be able to
33:10 at these various Elon's as surrogates for sections and visualize where in the floodplain
33:21 might occur. And not only think them with respect to maybe analog
33:27 but what a core might look like well. Now we talked about this
33:34 time, it's um it's worth repeating little bit. Uh We've got this
33:39 here, we have had a previous , a belt abandoned active challenge.
33:47 here we have these lateral lateral and within them we have a series of
33:58 flood events. And so we've talked what they may look like, but
34:04 is just a good example. Uh a single flood packed bounded by third
34:10 fourth one here, it's like Um or going to trawl parallel parallel
34:25 and gravel. Now, that's basically we're looking at right here. Now
34:37 can also do the same thing with 324. We can also be thinking
34:44 the fine grain film of a abandoned or what about a levee deposit or
34:51 about a prevents flood or what about flood basin? Each of these is
34:56 the component of the floodplain or rather the channel belt? Uh a single
35:05 cross section if you like. As begin to have that a grave through
35:14 we begin to see larger and larger here, they describe these components versus
35:23 and we're we're putting this together not a single. Um so we're building
35:34 a larger package. Finally. Now go here and occupied. I don't
35:40 these terms, but there's a continuum entering channel system and abraded channel
35:50 And as we go down, we begin to slice it up and their
35:55 were getting literally blood by flood and components within the floods. This is
36:06 the definition of what I've been talking the story. I will read it
36:12 , we've talked about it but again to the migration of a single
36:18 Excuse me. And so these are various types of components that fill that
36:27 associated with the single time period of laterally migrating or migrating channel. So
36:35 talked about this earlier. These are channel components and these would be the
36:41 components. So these are the components what we talked about earlier. And
36:49 when we finally get up to this is the big picture that we're
36:54 towards now. When we have this picture, let's look at this channel
37:00 , we're gonna uh we can talk the channel belt versus the floodplain
37:06 The channel belt, is that the extent of channel deposits makes sense.
37:12 , so it's gonna consist basically a and abandoned channels and maybe a little
37:18 elevens. The floodplain is gonna be levee's purpose plays in flood basin.
37:26 we can think of an individual what into the flood basin floodplain december.
37:44 , now, as that meander belt altars, you don't have a,
37:55 just not story, but it's eventually grow up into a and you can
38:03 that has happened time and time again this valley has been filled my vertical
38:12 . And if we look at we're seeing what is happening literally at
38:20 same time as this. Here's that meander belt, actually, this is
38:24 new meander belt, the older And that's our, for the most
38:38 , we think most of oceans occur an initial from escalation, but for
38:46 reason, uh, that crevasse play a more optimal place for the river
38:54 to flow. And so we begin get a kind of disorganized global system
39:02 into the blood basis. And with it begins the organization, new meander
39:13 leaving behind the long gauges abandoned And you can kind of see that
39:26 cross section as well. And that's , this is basically showing a cross
39:31 here lateral migration. You cut the begin to have deposit, eventually the
39:41 channel is going to be abandoned. so now we're beginning to see the
39:48 . The new channel begin to integrate and this channel is now abandoned.
39:56 that happened repeatedly, uh, right the corner. In the process rumor
40:03 river or rather the plain of the contains three distinct meander belts,
40:11 the oldest city. And then as look to the north, we see
40:18 what is now Oyster Creek and the south and west, we see the
40:28 day Me Andri runs true. And also can see it here in a
40:38 , active channel, older channel and yet older channel as well.
40:45 now notice that this Um, Oyster is the abandoned channel, the abandoned
40:54 course of the Brazos and it was about 1000 years ago. And the
40:59 north of I-10 around city. It still is flowing. So even
41:07 it's an abandoned channel doesn't mean that gonna fill with water because it's still
41:12 water that's running off. And so just a a mere shell. It's
41:17 himself. So we still have water it, but it's not nearly the
41:24 that was here. And we also there are big me envelopes down here
41:30 well. So one of the things can envision is what this first of
41:37 here is the uh, terrace. , I don't know why I'm keeping
41:49 . Okay. And so here's the , but uh, the modern river
41:58 the Brazos. Here's a little older that's, this is Oyster Creek and
42:08 yet, yes, another one down That just has a little bit of
42:20 here. So it was one two Oyster Creek and three is modern.
42:28 what we're getting is down here, had a high, it's shifted to
42:36 to this side of that floodplain or meander belt here and then it shifted
42:44 here to fill this side. So something that's called compensation. All
42:50 It goes back to what I talked earlier with the topography on the
42:55 having positive relief because of the levees the relatively low areas are where the
43:02 channel is going to flow. okay. I'm not gonna go into
43:10 right now, but basically it was about um the various uh architectural
43:19 types of foundation surfaces. Uh They in here. It's useful to look
43:26 um and think about how vibration do have a sheet sand? Have my
43:33 order services. Uh This would be . So we talked about this and
43:43 is uh thinking about it as a building all the way up into a
43:48 belt. So this is useful at leisure to look at, to think
43:55 how that single din bound by that order bounding surface can grow up to
44:03 part of a mander boat. Uh these are just some pictures uh field
44:12 display showing the geometry here is a channel migrating belt. Uh Here is
44:20 meander belt series with multiple superimposed stories eventually varied amalgamated system with vertical
44:32 So we showed pictures, I showed of this earlier, we looked at
44:37 , just get a sense of how units in outcrop appear. Now there
44:47 an old idea that um suspended load maybe esta pero um mixed load or
45:00 and great bed load on by. this is way over simplified. So
45:14 I put it here just to let know that uh we sometimes correlate the
45:20 patterns with the type of bedroom type material. That's way to simplify,
45:28 the diagram here isn't bad uh in it says that this particular channel has
45:37 with the death ratio, certain with story or the the point bought.
45:46 This channel here has a larger way desperation. Uh This chap here is
45:53 narrow and impossible and as the Shannon uh we do get build ups.
46:03 , so here, for example, some ways in which a single channel
46:08 develop an individual story and then as have accretion, we can begin to
46:17 those stories become multistory channel bodies. again, notice the, notice the
46:27 on dimensions here. Uh This is given, see some more about
46:32 but this is again a similar story here we're looking at Wilson who was
46:41 more with the outcome package. Um again as you look at this,
46:49 about what you're looking so present. here are laterally accreting uh What
46:56 Uh This is a single story. is that different from this? Well
47:03 the channel has shifted and come So if a channel migrates and shifts
47:12 , that channel is abandoned for a , if it's been reoccupied and migrates
47:18 two stories it's multiple stories. But there's been no vertical aggression it's still
47:23 to be at the same. Well the other hand if there's vertical accretion
47:30 then it'll be amalgamated more. So they're vertically super closed less so if
47:38 compensation stacking like we see in So I think this is just so
47:47 might you think about the geometry? think about the rate of bank
47:56 Person channel of region. Um And respect to channel oppression. Think of
48:04 as subsides. Uh it doesn't have be subsided but that's the easiest way
48:09 do it. Okay. Um now need to read think about panel of
48:18 ships as well. Maybe the So maybe um we should think about
48:29 , both occurring as well. Now it not a single store all but
48:39 still gonna be a thin section because basically don't have any discretion here instead
48:45 a single uh it's big. Uh now that helps a little bit but
49:00 easier to visualize if we put that the third dimension. So we've
49:07 well, who was the high town , low to high aggravation and infrequent
49:15 frequent alcohol as we get more and frequent avulsion, the individual stories are
49:26 separated more and more lateral. And here we got high degree of lateral
49:40 with oppression, high rates of channel and high rates of channels. So
49:50 can begin to see how these can it melts Evolve over time and
49:59 a basement again. This is a study 2020 but essentially is talking about
50:05 same thing, frequency for Boston. sometimes right now when we talk about
50:18 systems and let's talk about a source sink. Uh The base level for
50:26 offline base level for river systems is ocean. And the thing is is
50:35 have static changes in sea level. influence decreases with this. If we
50:45 up here about relative importance. Climate is important throughout, you know,
50:51 a river system. Used to see greatest, but then it decreases with
51:00 a nick point beyond which we don't entrenchment. For example, if the
51:06 level drops, okay. Uh So as we go inland, we see
51:14 and less subsided related rather use static base level changes, determining rates of
51:24 . Example, what we see four basement basement society being more towards the
51:33 margin stores of towards the inland affecting . So if we want to get
51:47 lot of deposition in this basis and this is gonna be um it's beyond
52:07 influence of the changes. And it actually have to be a closed
52:13 It could be an open basis. just that that river is so far
52:18 that it doesn't know what's going on coast. It's only influenced by what's
52:22 up and down and if it's gonna preserved, it's going to be preserved
52:27 the basin. Tectonic subsidence. one of the ways in which we
52:36 the upstream influence of your static change something called backwater. That and basically
52:44 we have the largest physical profile of , the point at which the channel
52:54 drops below ceiling. It is in extent of the background backwaters. Tell
53:06 you have a river like this could 100 ft. You know, we
53:14 that rivers are, but eventually most and that point tends to be an
53:24 point that controls the pattern of a upstream. So rivers tend to shift
53:33 fourth by avulsion at a point proportional him more or less at the same
53:41 as the upstream influence of tobacco. the case of the Brazos, that
53:48 be around seal, that's where it and the ship for different rivers.
53:55 bigger the river, the deeper it , the wider the back. So
54:00 can imagine that same thing with Mississippi where backwater sent is upstream, in
54:08 , I think it shows here Mississippi on the order of that word,
54:15 hundreds of my hundreds of people. when we look at avulsion patterns,
54:27 of the is look at the geology here we got um splitting off the
54:40 . That's that's what the current Okay, we can actually see uh
54:48 events from satellite imagery. Now we've satellite coverage now for about 50
54:53 Uh we started getting satellite coverage, sat around 1970 so we've got a
55:01 record of looking at how some of abortions against occur will ever be analogous
55:07 this path. But we also can a Lordship Pence that look more like
55:15 uh laterally dispersing from some place. this particular spot is probably not so
55:23 controlled by the backwater as it it's changed and slowed from. And
55:35 pattern is called a distributed flu viel . It looks like a distributor.
55:41 kind of looks like a big It was too big for kind of
55:48 like alluvial fan except it's way too . So what we're looking at here
55:56 basically things that we used to call fans that are basically distributed systems that
56:05 that are beginning to diverge when they released from confinement. There are some
56:14 of note here upstream of which prevents river from shifting once it gets out
56:24 that confined area, then it keeps . Okay. And it gives you
56:28 fan life or distributive system now in case it's due to an active fault
56:38 fault marginal on the Himalayas. It also occur when you simply have a
56:47 play and there's a ridge and more center. If you've driven to austin
56:55 on 71 heading through lagrange uh turns you go through a a ridge is
57:06 and it's cemented, it stands as high and blend the rivers reach that
57:17 and then they can begin to split . So we could have distributed alluvial
57:24 even in the coastal plain where the is not a large mammal, itis
57:30 um, well cemented cement, well question and here we've got a distributed
57:38 coming into a lake is a distributed system are not what we normally call
57:46 fans. Yeah, too big to . Delta deltas are really at the
57:55 of them. Uh they, they're another and so what we used to
58:00 faithful fans in this system here and really aren't uh, I mentioned there
58:09 a great vacation in magnitude but that's because there's a gradation in size of
58:18 . Uh rather sources. So a of these see some of these others
58:30 really just distributed flu mobile systems and again we're talking is, were the
58:39 were the alluvial fans. Ah I'm even gonna call him fancy. Thank
58:47 . Sometimes you see mega teen but best uses the best term to
58:56 I think it's distributed influences and that's one that you'll see in the literature
59:01 . Um This does suggest that there gradations of magnitude and that is
59:12 But again uh ironically they're all distributed . Notes. Uh the alluvial fans
59:19 not distributed alluvial systems. The reason is there not channel up slow is
59:25 is defined here. Uh These are gonna be distributive patterns or fan patterns
59:35 by non chancellors flow, sheep sheep blood. And uh but here
59:45 mean if you want to subdivide and can't certainly there are large gradations um
59:52 there's variations and added from um Well show. Um uh So and the
60:09 for uh relative width and depth of channels. He's all vary. And
60:16 there's been a lot of work done uh trying to get a sense of
60:22 these things look like and this is the satellite that because we no longer
60:26 to deal with isolated case studies, can go all over the world with
60:32 computer. And so we have multiple that are single. Ah So this
60:53 kind of the most of the geometries we're gonna see on these distributed flu
61:00 . So here for example rated bifurcated single threat uh seniors me Andrew and
61:07 threatening only one is active at a multiple threats. Um They're coming in
61:17 and being abandoned welcoming. Um well these are going from proximal to
61:27 um system. So this is what , the variability that we can get
61:34 these distributed systems, what's controlling them accommodation space? How far is it
61:45 ? In a foreland basin? It be the maximum basin with in the
61:52 region, it might be the distance the apex to the beach. Uh
62:01 . I gotta get graded low is be. And the discharge,
62:07 tectonics and climate are old friends. High discharge were typically graded, lower
62:14 Henry, high sediment supply typically graded the end. Yeah, you can
62:23 this later. This just kind of what was very sorry. So here
62:28 , we go back to this stream fan. This turns out to be
62:34 cosi in fact, this is this is what Galloway kind of gauge
62:43 a general pattern changes, but this what it's based on. And so
62:48 see that the coach's been shifting, the ship back. Um and so
62:55 got we can date the various channels all come into. Um And we
63:04 say that over here, it's beginning evolve with satellite data and see now
63:11 the recent floods are coming down this . So this portion of the the
63:19 , the river is in the process the abandoned and you're gonna have a
63:24 river course here. Now, if look at the modern river is greater
63:33 mainly launch total bars. and then meandering, is to go farther
63:40 In fact, if we look at middle part of the you see all
63:45 meandering rivers and those meandering rivers I add are being handed in the sense
63:57 they were the main river, they be headed and now either like or
64:04 , uh they're just little. now, if we look at downstream
64:12 in brain size over gravel, rich streams standing braided stream, the
64:18 meandering streams, we go from gravel sand and from graded two P.
64:24 now the other thing is, and is the nature of distributed alluvial
64:30 There's not a lot of lateral mobility revulsion. Nearly eight things. So
64:40 gonna have superimposed stories, but if go farther and farther down the uh
64:48 the fan, persistent, uh there's more and more separation of the individual
64:57 and so you're beginning to get more more separation. So you're getting um
65:02 the same amount of avulsion here, got to very distinct channel panel
65:09 They're super. That's going to affect an activity. The other thing is
65:18 this particular example, there's a that um X is abandoned. The point
65:36 is that that, well, we'll leave it for a second. I'll
65:41 more about it and see how vertically here in the lab, we separated
65:48 below. Now there's another mega fan the Okavango, Okavango fan or delta
66:00 sits here and it sits in the again, you've got this river,
66:06 trench, It can't migrate laterally. here into the is split here,
66:20 channels are all operating at the same . It literally splits up into multiple
66:27 channels. Um Now that's that's an distinction and we didn't know it a
66:35 of other things. Um here we the annual channels within confined and then
66:45 got straight to stable sinuous down Okay, um it's relatively low gradient
66:53 most any losses. The fans each of the, I'm sorry the
67:02 in what they call fans are literally terry's with small amounts of discharge in
67:11 lot of vegetation. This is the . So here we have pretty stable
67:17 that lowers the sin you ah It lowers the rate of lateral
67:25 Uh we tend to have more less sinuous chance and that is related
67:33 both the climate and uh the fact we are reducing the discharge. So
67:41 of those, this tributaries is more and has a lower width to
67:53 Now, in that particular case we have agents application multiple of the
68:03 So multiple channels at the same remember what I said about decreasing discharge
68:11 with changing here we go. Each these channels. So the channel dimensions
68:24 on the lower are gonna be awful you go. Whereas here they're going
68:33 merge, That would be the unknown that would be as examples and why
68:42 that important because, and this system , these are all laterally connected.
68:50 are if you think reservoirs, these connected residents here. These are three
68:59 present wars. There's no connection between separated by I'm in. So there's
69:09 important distinction between the style and one the ways you figure it out is
69:16 compare the paleo hydrology various components. the so called fans and now really
69:35 a lot better even though I mentioned , there's some in between them.
69:43 these actions here is the uh, one in brazil. Um, these
69:52 small compared to some of the others the endings. There are fans.
69:59 particular one's by the largest. And it's 22 times as large as
70:06 coast. This is a huge Okay. And it's basically sitting in
70:13 form of base. Thanks for the and it owns one of the series
70:24 things or flu the assist. And we look at it because I speak
70:35 lower grades, it goes from brady me Andrew. So it begins,
70:45 shows the same general panic. I these are just what rivers do.
70:52 , and if we look at look at this one, this is
70:55 different one, whole series of these uh, in the basin.
71:03 the span is here. Uh, this is a newer fan. It
71:22 we've got an incised river here, intersection point in the whole scene
71:33 okay, if we look at the seen fan, this is the place
71:39 fan here. They are distinct channels are more braided. If we look
71:52 the modern fan, they're much more Andrew. So what we're getting at
72:01 even with the same slow gradient, a change in the nature of the
72:09 because of the change in discharge from pleistocene to the whole scene. We
72:19 something similar in uh the alps, got the alps and then that piedmont
72:25 that um Goes to the coast. got some of these fans up to
72:37 braided upstream, meandering downstream, steep , graded, sinuous with the intermediate
72:50 and distribute terry. They're all beginning look the same in the sense that
72:59 is and sediment supply or whether determining versus me Andrew. Okay.
73:09 when we look at these tectonic li belts, we get some of these
73:16 fans distributed flu real system mega what do you want to call
73:20 And then little bitty woods out And what's happened is we've had river
73:30 . We used to have a lot rivers that came like this, forming
73:38 little fans, But one Big River in and begins to capture beheaded.
73:50 smaller rivers is Thohir's what they looked originally, this fan beheads this
74:07 It shrinks this gross. So one grows at the cost of others.
74:15 so eventually we have this chain of are called here enter mega fans areas
74:26 then big mega fans here, the is called exit gorge. It grades
74:38 some kind of an axial channel. If it's the Himalayas, uh it
74:43 be the Ganges. Yeah. Um this model ironically was developed not for
74:51 Himalayas, but for the cordillera, cretaceous of western us. They're the
75:03 . And here's the cordillera flow and big mega fans. Now distributed systems
75:16 filling in the cretaceous seaway. so what we see here in cross
75:28 as foreland basin, these are really alluvial systems. And as we look
75:37 and more into these basins, we more and more of the pattern we
75:43 about with little alluvial fans and then rivers giving distributed systems. We've got
75:53 in our fuel camp called the bear conglomerate along the front of the bear
75:58 range. When you look at it is more proximal position, you
76:03 there's a series of angular in oldest fan deposits or proximal deposits,
76:11 almost 40°, then 20° and 15°. And that is reflecting is the progressive uplift
76:22 this big thrust that's coming up so older fans are being rotated and the
76:33 fans are less steep as we look this, we see inter bedded Raval
76:42 more plainer zones. Uh we're looking channel Ized gravels here probably my laterally
77:06 and in between, we've got non eyes deposits. Okay. Uh This
77:13 a downstream migrating channel bar. We've um massive class supported ravel's here.
77:28 we know they were not transported by flows, but rather by channel.
77:34 . Yeah, here we've got a distributed over a fan. This is
77:49 km. This is this one This is the exit gorge. Uh
77:59 and notice this is kind of where big thrust zones come together. So
78:05 these fold and thrust belts, the of thrusting tends to control the exit
78:13 , which again, not a Uh but that also shows where the
78:20 are going to be coming from and they're expanding. Okay, so these
78:26 the paleo currents. If we look the percent sand as we go farther
78:33 farther from proximal to distal is decreasing thickness of the flu viel section,
78:42 decreases and decreases lens. Mean grain is decreasing. And if we look
78:52 in cross section in the proximal we have a lot of superposition of
78:58 channels as we go farther and farther . There's more lateral separation of the
79:06 stories until finally, as we get the distal portions, they're relatively small
79:12 with widely separated by flood based So, this is kind of the
79:20 for this, this particular kind of flu real system and this one is
79:28 the cretaceous of the US. Uh if we get into the distal
79:33 we can actually see preserved in the planes. The various types of truly
79:43 patterns that would be thought of as more like real deltas down here.
79:51 the big distributed pattern. And then we get down to this spot,
79:58 getting a series of little literally crevasse in small deltas. Okay, this
80:11 an earlier model of how as you downstream, get more and more crevasse
80:21 and you get a proximal to distal . Okay, um sometimes called the
80:29 fan is now a flu or D. S model here, it
80:35 as a distributive system. Okay, look at the channel pattern as we
80:45 down the system. Uh Here's another . Still terminal suggestion here is that
80:56 some of these may be less active others. Uh that would depend on
81:01 relative size of these at any one . But again, look at the
81:12 of the channel deposits that we see all of these big fancies. We
81:20 go to uh to uh south same thing. We can go to
81:30 of the largest, if not the natural gas uh basins in the green
81:42 . You see the same thing. , as we go from proximal DFS
81:47 distal DFS And here we're looking at base in center gas field wall.
81:59 fact is that when you begin to at satellite data as we look at
82:05 fill particularly of areas that are tectonic tectonic relief. These D.
82:14 S. S really are the dominant . The channels themselves, The main
82:27 viel channels really are relatively small in of the percentage over 90 R.
82:38 . F. S. S. you include the fans. Okay,
82:42 axle systems here Less than 10%. can see that here. Look how
82:50 of this area his fan. Well are real fans but they're really just
83:01 little example of what's happening in, Argentina or the alps. Okay,
83:12 point here, is that most of Himalayan foreland basin. The Andean foreland
83:23 . The Alaskan foreland basis. The river graph. Uh Robin field All
83:31 over 90%. Just DFS is so that's a good place to
83:39 Let's stop recording. Take a take little bit of a talking break,
83:45 me try you know that. And we'll start again in about, It's
83:55 . Do you want to take your break now or do you want to
83:58 it more like 12:30? What do what do you want? Robin?
84:09 it matter? Okay, but Yeah. Okay, nobody cares.
84:19 . Uh let's um let's take about short break, finish this up and
84:25 we'll go to lunch.
-
+