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GEOL6358 Terrigenous Depositional System - Day6 03-04-2023-Part2
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00:01 OK. Uh We, we have much done Marginal Marie. Uh We've
00:09 at ti flats, we've looked at Strand Plains, uh Barrier Islands,
00:17 , uh estuaries. Uh The trick is to see what is beyond
00:24 And, and let me just say the beginning, uh there was a
00:31 within my lifetime, at least that have what they call the sand line
00:38 the sand line was basically a line you draw someplace along the shelf beyond
00:48 there was no sand. So you sand love and, and of
00:54 we knew there was sand off but we thought uh it must be
01:01 sand from low stands. And as find out now, uh there's a
01:08 of sand on the shelf and there's lot of ways of getting sand to
01:11 on the shelf. So let's look some of the processes that are going
01:16 . Uh You're looking at oceanic you're looking at tides, you're looking
01:26 weather related uh wind generated waves and looking at the effect of density uh
01:36 uh being mainly the hyper and uh hugging flows and the homo uh
01:46 Uh One of which is you're looking right here that large plume uh crossing
01:53 , the Texas Coast. Uh The of the show is really important.
02:02 We can have broad shelves, we have a steep shelf ramps. Uh
02:07 can have V shaped of re entrance the shelf. Uh These are going
02:14 affect the relative importance of different kinds processes. We've, we've alluded to
02:20 with respect to the relative importance of versus tides on a V ship shaped
02:27 like uh the German bike. For , uh we've talked about the fact
02:32 as you get a delta pro grading deeper and deeper water, the shelf
02:40 is getting shelf edge is getting closer the shelf width, is getting
02:47 So there's less and less attenuation So, uh we're gonna see how
02:51 things interact, the the interaction of currents and shelves. And this is
02:57 much a function of the geometry of shelf. The shelf itself, of
03:02 , is to a large extent, function of the tectonic setting, which
03:07 the topic, the whole lecture we get into. But clearly the idea
03:11 a about passive margin, trailing margin a uh tectonic active margin is gonna
03:21 one you, you have in your in some place. So, Galloway
03:26 again, uh finds a way of a triangle of something. And so
03:31 , he envisions that you have tides and then storm slash currents.
03:43 the problem I have in part is storm and waves. It, it's
03:50 little unclear in, in my mind now, uh the distinction and when
03:55 talked about currents, um, that's actually a, a rather different
04:03 because those are oceanic currents which are up by movements of water masses.
04:10 , um, about the, pretty much the same time. Uh
04:18 and Baldwin published something they say, know, we really ought to pull
04:21 oceanic currents and that makes a lot sense. Um So I'm gonna treat
04:27 currents. Um And then tides not that order. And I'm gonna,
04:33 gonna kind of combine storms and Um And we'll, we'll kind of
04:40 with those main processes. Let's begin tides. If we look at the
04:46 tial areas, these are where we're have the tidal, the most extensive
04:52 of tidal flats. Uh We're gonna tide dominated estuaries and tide dominated
04:59 But let's look at this area right here where we can look at a
05:02 dominated shell. And so as we at various areas around um the United
05:10 , uh and France, we see uh the title prism if you like
05:19 , is funneled through uh the English and then it spreads out. And
05:25 there are significant accelerations of tides in of these areas. And in particular
05:35 area here, I'm gonna focus on because this is an area of major
05:40 sand deposition on the shelf. If look at the way tides generate,
05:48 I'm not gonna really go into this to say that uh there, there
05:54 co tidal lines which is say where high tide is at any one time
06:01 they kind of sweep around a center . And that shows the an increase
06:08 then decrease uh of tidal velocity which be measured by maximum near surface currents
06:17 spring tides. So we go from centimeters per second to 100 and 25
06:25 per second. As that tide is . I have envisioned that in your
06:31 of thinking that this is just we're focusing it into more and more
06:37 space. In reality, it has do with this warping of the tidal
06:42 . And frankly, it's too hard me to explain, but this is
06:47 easy to visualize and what we see that area if we were to look
06:52 the tidal ellipse. And what that is to look at the tidal direction
07:02 time over one title cycle. Uh not actually like this. It's gonna
07:10 some as it breaks down, it's dwp a little bit. So that's
07:14 , this is an area though, mean, uh uh it shows the
07:19 of the dominant uh titled direction as splays out. And as we look
07:29 that area, we find a whole of linear sand ridges that are aligned
07:36 to those tidal ellipses. So let's at one series of uh uh sand
07:51 right here. These are pretty Their heights are up to 40 m
08:00 . uh their crests are in water of 10 to 15 m and the
08:05 flank is about five degrees. And reason I focus on that is that
08:11 tend to exaggerate the steepness of these when we look at them in diagrams
08:18 seismic and we'll see an example of shortly. OK. Also notice that
08:24 are ridges that go deeper and deeper deeper in water depths. OK?
08:33 The short answer is those are old or those are old ridges that were
08:38 when sea level was a little So we're gonna see as sea level
08:43 , you begin to shut down the ridges and new ridges form.
08:50 we find these linear tidal sand ridges over the place, we find them
08:56 with the Amazon. We actually looked those uh when we were uh looking
09:03 uh and logs and Xan Del uh we get them over here.
09:09 We get them in uh also of Thai dominated deltas, but they go
09:15 the delta. In fact, we them down here in the Persian Gulf
09:20 in the China Sea. Um they in most of these high tidal range
09:28 . Now, this is that cross , I was talking to uh about
09:32 they are asymmetrical. They do have steep and gentle side, but that
09:37 side is Less than 5°. OK. but the other thing to notice is
09:44 the internal lamination at least based on suggests they are migrating laterally, migrating
09:54 the direction. Oh The steep even though the flow seems to be
10:03 right angles or along the face rather slip face. And, and the
10:09 happening is you've got a dominant flow this direction and then a subdominant flow
10:15 . And so the dominant flow goes the uh lee side or I'm
10:24 the stove side or gentle sleep but then wraps around and comes back
10:31 the steep side. OK. Um so what you end up having is
10:38 dominant flow causing erosion on the backside net deposition on the down on the
10:49 side. OK. And part of is that as we'll see in a
10:53 that oblique low here is gonna result sand waves working across and then down
11:04 steep face and back up to seat , the majority working back up to
11:09 face. We have sand waves sand waves here. Yeah. So
11:20 look at that in a second. Going back to this one here.
11:25 I want to look at in the right here. This is a,
11:32 sea Satellite image and the government put up in the 1980s to look at
11:41 sea surface L sat was basically designed look at the map. Uh Sea
11:47 looked at the water surface and there a shockingly good mimicry of the surface
11:58 the bottom. Now, what is is that it could be seen literally
12:07 the point of sand waves we're looking , in these linear sand dunes,
12:12 I mean, linear tidal ridges and asymmetry. I mean, just everybody
12:18 shocked when they saw that. Um began to imagine, oh what,
12:25 a wealth of information is gonna come of this. Uh The government shut
12:29 off or maybe better said it was longer available for the public. The
12:35 is it was too good and you see the wake of submarines. Uh
12:40 so uh that source of bath meric uh was lost. But uh when
12:48 look at this area, uh we've doing bath the metric surveys for a
12:53 time. And so these same sand that are climbing up these linear sand
13:04 , um The sand waves are up 15 m high Wavelengths of 20 to
13:12 m. And it turns out that an eight year period at an
13:17 you can see them migrate on the of uh hundreds of of, of
13:26 . OK. And so you can them migrate. But mathematically, and
13:34 you get side scans, this is uh reflector rather but you still see
13:41 internally, you're looking at net migration reactivation ridges. OK. Now,
13:56 reminds me of linear sand. This me of some large compound waves that
14:12 transfers that are in rivers and even transverse dudes, Edwards big slip faces
14:26 to 10, you know, 15 m high uh can occur in
14:32 lot of settings. And so you be thinking about a compare and contrast
14:46 uh transverse bed forms Idol fan So on blue sand. Yeah.
14:56 Now having said that, let's look at the maximum currents, remember I
15:02 it goes up to 100 and 25 spring tides. Uh You can look
15:11 the depth limit below which you cease have sand wave move. OK.
15:18 that's basically saying there's some velocity below these sand waves don't move. The
15:27 is that that velocity in the winter much higher than the velocity in the
15:41 . Oh, I'm sorry. Uh , I'll show that in a
15:44 Uh But that velocity or maximum movement coincides with the maximum tide is different
15:55 on whether or not it's a ne mean tidal range which this is I'm
16:01 , with a maximum tidal range versus mean. And I actually don't remember
16:07 this is a mean or maximum during spring time. Ok. So
16:15 get under spring tide, you get tidal sand waves moving in great greater
16:22 that in times. Not a What is a surprise is that water
16:28 makes a difference, the warmer the , the deeper the band waves are
16:37 to move that. You know how in the world would, would
16:43 uh be a factor? Uh for viscosity, remember when we talked
16:50 the bed phase diagrams and we oh, there's a lot of
16:55 but we're gonna lump things and variables density and viscosity and blah blah
17:01 So we said, let's assume the is fresh water at 20 degrees
17:08 We did that to keep the salinity density of water this constantly and also
17:15 keep the viscosity because it turns out are big deals. And the temperature
17:22 of the water in the North Sea large enough. And I would argue
17:27 in the Bering Sea and certainly in Arctic but to significantly extend those uh
17:36 , and, or contract the uh that we uh are likely to see
17:44 of different forms. OK. Uh the title Sandridge 25m high. And
17:55 uh we see that same, same . Yeah. Uh This is the
18:01 from um and what I want to out is here is um one of
18:09 deltas, I forget which one in East China Sea and this whole area
18:18 areas of linear sand ridges. Um Down in here, these are
18:27 to as Paleo tributary, uh a mouth and they probably did initiate his
18:36 bars. But then as sea level and we kind of looked at that
18:42 tide dominated deltas, those linear Sandridge become detached, but they're still
18:51 except that at some point they become . So these way down here are
18:57 , these are variably active and these constantly active. So this is just
19:03 an interpretation of those deep ridges and some of the very uh some of
19:11 variability that you get. But most that the sand ridge is dominantly laterally
19:19 . OK. This room right we get huge sandwiches uh in m
19:27 many shelves. Uh This is actually of Newfoundland and it's the Georgia Banks
19:37 it's actually an important fishing area among . And we see that there are
19:42 long linear troughs, you've got these of tuning fork bifurcations. And as
19:49 get uh high up, you you have an asymmetrical uh bar and
19:56 you have these waves or proposed dunes coming up the, the flak,
20:07 less deeply dipping flank of this linear . OK. So the water is
20:14 up like this and back like this like this, back like this wavelengths
20:22 hundreds of meters and heights of 6 10 m, typically up to 18
20:30 , Current velocities up to 75 So it's pretty, it's certainly enough
20:36 move stand during uh certainly during spring and even during uh some uh
20:47 OK. So as we look at sand waves, um you can go
20:56 something that has a uh basically a of proposed death to one that has
21:11 reversal movement and the dip gets lower you begin at some point to have
21:19 migrate down that. So finally, looking at uh just an amalgamation of
21:27 riding up and then down the back . OK. Um I'm not gonna
21:34 into this right now. This turns to be a useful diagram for a
21:41 of reasons, but it's all I you to think about is simple sand
21:50 two complex compounds that way. As showed earlier, we've got this
21:58 it's comes going up and then back way, uh that reverse flow can
22:05 cause it to make a kink and separate. We see those kinks they
22:15 right here. We separated in here it's separated. OK. So that's
22:22 pretty common way and probably is what's those tuning fork ations. Now,
22:33 mentioned that there is a gradation from moving uh sand ridges and relatively shallow
22:47 to if you like relic sand ridges deeper water. Now, they're actually
22:55 mob sandwiches, which means in the of dying. Um And that's probably
23:03 a bad term. They are areas there was a, an active sand
23:09 , but now it's kind of being a little bit and eroded on the
23:14 , uh we saw this a little with the, with the sand ridges
23:21 were formed by submerges of uh the Delta. Uh They gradually got less
23:30 less active and began to be reworked other processes. So, on the
23:35 shelf, when they're active, they're steep and then eventually they begin to
23:41 eroded down. And so we get two stage morphology and package of sediment
23:56 structures active and then dying where it's being uh gradually reworked, still has
24:05 topographic expression. Uh But it's no uh the way it was.
24:13 So we can talk about then the ridges and we can talk about tidal
24:20 waves. Ok. Um So these two different large sand bodies. These
24:31 occurring in some cases, the sand on top of the sand ridges.
24:36 cases, we'll see the sand waves , can be uh disconnected from
24:43 OK. Well, we saw both of both. So this is a
24:48 diagram to kind of remember as a section to think about how they might
24:54 these might look and how they might . And as we'll see in a
24:59 , we can then compare these with generated waves on the shelf. But
25:05 we do this, let's look at title bet forms and realize that they
25:15 depending on whether that's a low sand high sand supply region. Now,
25:21 general with bye to low um bad . In fact, I'll skip over
25:32 . Uh We see this pro gradation this fay track with decreasing strength.
25:40 go for mainly erosion with these little ribbons to ridges to dunes, the
25:50 dunes with sand sheets. That's a good model for what we get
25:58 Low sand. We never really get bar cans. We don't get these
26:02 ridges unless you have a lot of . OK. We only get these
26:06 ridges. We have a lot of . And I think this is that
26:12 can imagine, yes, as analogous a wind field. Uh the Eoan
26:22 sheets that we get in the big earths where we have downstream changes in
26:29 velocity and in the rate of sand and therefore changes in the types of
26:36 . OK? And I think that be an interesting project to, to
26:40 as a term paper is not a quiz, but uh there are similarities
26:47 obviously differences as well. Now, look at one of these uh titled
26:54 bars. This would be one of sand waves made. Uh It also
26:59 be a sand ridge and we get a a complication we have right here
27:10 . We got a ridge with the going like this. So that this
27:18 a longitudinal bar, this is a bar yet in cross section they kind
27:25 look similar. And so in in field, it's sometimes questionable whether we're
27:34 at a laterally or rather a down I'm sorry, down tide transversing sand
27:44 or a laterally migrating longitudinal bar. , here we have a field example
27:56 um we've got it migrating seaward. In this case, the geometry implies
28:03 it is a more of a transverse or, or mouth bar. Uh
28:08 can break it up into packages and we could look here at one posting
28:18 sequence and we could look break that into a series of dead sets from
28:26 lithic to more uh standard units were um spring tidal bundles shown here.
28:39 co upward sequence is the same as see here. Worst thing upward
28:45 Uh We actually saw something like this the last lecture on uh tidal deposits
28:53 tidal sand bars. Now we're they're farther offshore with the same general
29:00 . Uh And we saw it here well now with these sand bars or
29:08 waves rather. Um Here it's earlier interpreted as a sand ridge, was
29:16 interpreted as a sand bar. It back and forth. But let's,
29:20 just look at it like this. is low sand supply to maximum sand
29:29 and maximum migration. This is now full ridge and then we're beginning to
29:35 the sand supply and the wave energy beginning to die down until finally,
29:44 this. Oops um the um I'm uh down in here is this model
30:01 where we have recorded the growth and the abandonment. OK. And
30:13 if that looks a lot like um inception, growth and destruction of San
30:20 I think there's a lot of analogies that. So let's look at a
30:25 example. This is the Santa Margarita my scene in California. I showed
30:31 this the very first day to emphasize you can get pro grading bed forms
30:44 very high ski uh a very uh and high um in non Eoan
30:55 Uh This is one set uh that you of what I said earlier.
31:01 is a zone of non erosion, non deposition or erosion that's full of
31:08 . So it's a marine surface. ? Uh Here we have that surface
31:13 and you can see the sets going as you look at that. I
31:18 you can see there are packages and surfaces within those packages and their course
31:38 fine packages. OK? You can a truncation reactivation surface here. There's
31:46 here and notice here, we've actually along here. A clay rape.
31:53 as we look at uh these because actually looking at grain flow but in
32:02 submarine package and these are, this actually a clay dye, but these
32:13 in here are clay drapes defining Uh This is that marine surface,
32:25 energy erosion on the back side. again an example of those clay drapes
32:34 on the bottom. Remember the reason not at the top is because they
32:38 removed uh by that reactivation surface. here we have some double mud drapes
32:44 in here on the bottom. And some cases, these are small sand
32:52 . Ok. So they vary in from that really thick one to these
33:02 small, suggesting at least two different of bar slash ridge. Wait,
33:13 turns out these are bars with two scale of transverse bed forms. And
33:22 one of those little mud drapes. you look at the paleo currents,
33:27 basically on a shelf where there was channel that was basically connecting the central
33:39 of California with the open marine Pacific . And so you had this funneling
33:44 tides uh in this particular area, was abdominal in other areas, it
33:52 flood dominant. And what we see uh in some areas, it's uh
34:03 bioturbated. Other areas, the bioturbated uh are either not present or oh
34:15 see laterally discontinuous. And then at areas, we see these huge corsets
34:24 in others, we get these smaller cents. So this is basically a
34:33 section of that large tract showing variations Large Scale four sets and then small
34:43 four sets. Now you look up . Uh This is a measured section
34:59 within that my so and we go transfer from, from tater cross strata
35:10 trough cross strata to more parallel laminated strata to bio. Now, the
35:21 debate, it basically says it stopped active and that could be sea level
35:28 too high or maybe the current channel . But bio turb took over.
35:36 . Um That's basically the same thing Galloway described um with respect to a
35:47 high dominated shelf and, and uh what oops, that's what Larry Phillips
35:57 as well. Uh We got reactivation . We have large scale four sets
36:03 small scale four sets we got in case, it's a basal lag grading
36:09 into finer grain bid centers. So you can think and then you
36:14 see the paleo currents here dominantly um in this particular case. And what
36:24 oceanic's currents? Um You will recall we have major currents set up by
36:34 global wind belts that are deflected by , the continents that basically circle and
36:47 parallel to the continental margins of the main um stream, uh the
36:53 uh continents. OK. And one them, it's down in here.
37:00 , I and if you look at , excuse me, um it's a
37:10 that actually impinges on part of the shelf and these currents can be pretty
37:18 . Interestingly, uh they can meander this one is forced against the,
37:26 current uh uh force against uh South . But notice others, it begins
37:34 move around and begins to meander and probably have heard of the meandering of
37:41 Gulf stream. Uh, but right it's confined to the edge of the
37:48 shelf and sometimes it actually impinges on shelf and sometimes it's offshore and
38:01 because it, even though it's relatively , it's still meanders, it's just
38:06 low seo meander. And the key that in those areas where it is
38:15 on the shelf, we have a dominated shelf Landor of that, we
38:22 a wave dominated show. Ok. what does it look like?
38:31 it is that current dominated shelf has in the higher areas, higher velocity
38:43 . Um sand waves, tidal sand and it even has as we get
38:51 the highest velocities that are on the edge. We see these linear sand
38:59 and grooves that we saw or at I just mentioned earlier in the highest
39:06 of that track with the North going the North Sea, we had
39:15 scour sand ribbons rating into either sand and or tidal ridges. And that's
39:25 we have here. And those sand are up to 17 m high And
39:31 are in 50 m water depth or and they're migrating high speeds off the
39:38 shelf. It uh this is the plume coming out of the Amazon.
39:49 This is a tide dominated delta and lot of the mud Is resuspended and
39:55 maximum and it's creating, we call mud uh concentrations up 20-30% by
40:03 And so it's moving as a slurry drift. And interestingly, the maximum
40:14 uh at least off the mouth of delta is offshore. But as we
40:22 laterally down drift to the north, begin to see these kind of waves
40:29 in and we see on land, arcuate features uh that are sometimes called
40:43 capes and they are essentially these mud that are migrating down drift. It
40:58 something like this. Here's that oblique bank giving you these holocene deposits uh
41:09 we talked about earlier with the, fluid buds and the sub A
41:16 OK. And actually, uh this their, by definition, these fluid
41:23 are greater than 10 g per liter 10% or they can be up to
41:29 m high and they've been measured as to 48% of the weight of the
41:38 and just uh almost unbelievable. So those are current, I'm gonna
41:46 of ignore storm for a second and storm down here. Those are um
41:51 current dominated shelves. OK. We about tide, tidal current shells.
41:59 Let's look at wave and storm dominated . Storm waves are up here,
42:08 with the, the 40 degrees north south. Uh We also get some
42:13 of uh tropical cyclones uh which we in there as well. So let's
42:21 at this area down here offshore Southwestern United uh southeastern United States shelf and
42:38 actually looks a lot different then the of texts, which is kind of
42:45 , we know it's a little higher , but we don't have any major
42:52 coming in. That's part of So the Gulf of Mexico tends to
42:57 been more muddy. Uh You can of the east coast of the United
43:03 is being more sediment starved. And we tend to have transgressive shorelines.
43:14 if we look offshore, the shelf a series of transgressive cheat sans,
43:27 . The presence of those sheet sands basically the relics of sands during the
43:36 . Now, earlier, you we had mentioned that during a rise
43:41 sea level, you get a wave and we often think of it as
43:47 basically an area of non deposition. then we have this regressive sequence on
43:59 of it, but we mentioned earlier that erosion only occurs to some depth
44:09 which we have offshore deposition, we onshore deposition here with the transgressive
44:17 That's this stuff here. We have here, but look at that accumulation
44:23 occurring offshore. OK. Now, can, that is our depositional record
44:30 a transgression. OK. In that record of the transgression can be pretty
44:40 if wave energy is low or sediment is high. In other words,
44:48 package here, his bigger with lower energy or greater sediments of life.
45:01 . Now, with low sediment supply high wave energy. That's that package
45:06 very thin. You get it. of this was erosion before the transgression
45:18 . So if we look at this here, we see and this is
45:24 in your notes, I apologize. , put him in later. Here's
45:29 surface, but here's actually our transgressive . And then we have the
45:41 This is the maximum flooding location. ? And we have a pro grading
45:51 or pro grading uh from offshore to shore face to over shore face just
45:59 we talked about earlier. But now beginning to look at the shelf and
46:04 pro grading, I'm sorry, that uh system here that's uh gonna be
46:13 uppers. This area is reworked. know this, this is pretty
46:20 What we're gonna look at is what when you with that sand where it
46:26 accumulate. Now, I'll just also this and that is that not only
46:31 it the effect of sediment supply and versus wave energy, but it's also
46:36 effect of that, that is, affects the shelf deposition, but it's
46:42 effect of sediment supply and accommodation space that affects the development of the land
46:50 . Uh what's sometimes called a back wedge. So we can think about
46:57 going on out here. But we think about what's going on up here
47:02 how that package will accrete uh that can see on really on a seismic
47:09 . Let's go back to that area the shelf. Now, if we
47:17 at it, we've always said that is a high wave energy setting.
47:23 look at this ridge here, look all these oblique ridges. Yeah.
47:39 if we get real close, they're attached, but we uh they're not
47:45 that way here, but uh they kind of in a bleak angle to
47:50 shore itself. And uh we even them some cases associated with these varied
47:58 , which we also have a Now, what we do have in
48:03 gulf and what we're actually thinking about is the fact that transgressions rarely occur
48:14 and uniformly, you can have rise sea level and a pulse, a
48:22 island can form, it can even grade a little bit and then it
48:29 be flooded again. So we actually on the Texas coast, some of
48:37 abandoned barrier islands that are sand Uh We're interested in them as we
48:45 for a source of uh offshore for beach nurse, but their sin
48:55 surround it land and sea by OK. And they result of barrier
49:05 . Well, in the east uh we do have barrier overstepping.
49:17 what's left behind are these relic near ridges? And that's what These are
49:26 . Here are the shore attached ridges one stage of, of transgression.
49:38 . When the shoreline was here, were sure attached now they've become detached
49:49 they're still pretty big and pretty steep they're still at least semi active and
49:59 interpreted cross section looks something like You no longer see anything that might
50:08 beach related or like, because even they were originally attached to the
50:16 but rather you see this offshore appreciate sandy ripples up the back dunes and
50:28 on the back side and the potential bi observation. Ok. Depending on
50:33 deep they are. Yeah. So we got three major sand bites that
50:44 can have and they're good potential reservoirs they're well sorted and they have the
50:51 of being sur completely surrounded by shel . Ok. So let's envision that
51:02 sequence again, it says storm think way dominated. I I treat
51:08 the same. Um Here's that ment and now we've got that Grimness.
51:22 is offshore deposit, storm sands from to five and then bioturbated muds.
51:36 . So that's pretty much from here that is the same track that we
51:42 in the pro gradation sequence as we from the inner fingered storm deposits.
51:50 cross strata going into thinner deposits, into muds. So let's look
51:57 at this transgressive sequence that we talked with um Mississippi Delta. We said
52:05 we can see barrier islands being flooded linear goals and those shows,
52:20 all over the shelf where those abandoned were. And this is one of
52:27 ship shoal is now completely disconnected from Mississippi Delta, but it still is
52:37 actively moving sand shoal. Now, those sand shows are gonna get buried
52:49 a transgression here. The model was they were sure face connected.
52:59 Uh There's a variety of ways that things can get started and then be
53:05 . Here's an old valley, And here's the high stand Delta girl
53:14 of this as being transgressive and This is basically I'm sorry, this
53:25 the high stand, this is the and low stand. Ok.
53:35 one of the things we've seen, it's not a bath, the metric
53:44 that provides the source of the sand be reworked into a ridge or,
53:49 rather if it is a high, associated with the levee or a
53:57 And so here we have a, inlet, we've got a ridge and
54:05 it is the, it initiates the migration and the sand continues to migrate
54:12 away from the right away from the original precursor which may be associated with
54:21 champ. There's a series of shelf , this described offshore Indonesia and they
54:34 to have a sharp edge and kind elongate on this area here. And
54:47 we look at those in well we see that these are sandy ridges
55:00 that what we're looking at is a that the interpretation is started here and
55:12 migrated. So here is the, it started and then it began to
55:20 in this direction. And so that edge is called the leading edge.
55:24 that straight slip face. And if were to look at the, it's
55:41 got this distal erosional surface and then mud. But basically, this is
55:54 to be that eroded area of as linear Sandridge migrated away from the
56:02 So this is kind of what it like in cross section. And this
56:07 some suggestions of where they are. it turns out these are Strat graphic
56:15 in offshore uh deals in Indonesia. , looking at that transgressive sequence
56:27 uh we know that transgressions uh and occur, they can get stacked on
56:33 another is one cycle, two three cycles. OK. Each is
56:41 represent a transgression. Yes. And we just flipped it on edge.
56:50 is the prorated cycle. We've actually a lot about this portion. And
56:58 , now all I'm doing really is it on to the rest of the
57:07 . Now, this is a very thickened regressive cycle. Let's see this
57:13 . This, that's this here And where's, oh I'm sorry.
57:22 Excuse me, what I wanna do combine it with this. I I
57:27 do it. OK? Uh Let just say that our pro grading
57:32 the Mike cross Strat is way up top. And then above that though
57:37 the short face. You know, uh transgressive cycles. The mike strata
57:45 here, there is no shore face gone and we grade up into
57:50 And this is just and a real example in the organ region of a
57:57 transgressive sequence. And these are basically amalgamated, single transgressive sequences followed by
58:11 uh regressions. Now, there's one study that's kind of interesting. Uh
58:19 in the lake cretaceous in the shell , and you'll recall the Lake Cretaceous
58:25 is really an epi continental seaway. underlain by continental uh deposits. It's
58:34 shallow. OK. There are some in size valleys and some, some
58:41 in thickness. But think of it a mainly shallow shell with sands migrating
58:51 the northwest, which is the So here is the, the uh
58:57 may recall uh this, these are the shore face sands. Uh The
59:05 mass is here. This is where saw those big distributer fluvial systems.
59:11 grade it into deltas graded into near face sands. And then we go
59:17 the inner and outer shelf. There is a slope, but it's pretty
59:23 . And we see these big sand that are disconnected from the inner sands
59:34 they're right along in here. Here's here. Now, this is
59:41 is a pack of, one is Herzog draw unit. And in cross
59:53 , this is the field, a goes from shale to lenticular bedded to
60:03 bedded to Frazer bedding to sandstone. almost an inverted title that sequence.
60:15 And it's one that you might think is maybe could be associated with the
60:20 sandwich. OK. Now, that's we look at the field that we
60:30 porous sandstone here, hike sandstone And so there take a look at
60:43 asymmetry here. The asymmetry is such the interpretation is this ridge is actually
60:59 migrating like this and is eroding over . Ok. So when we look
61:09 those sand ridges in the North Sea other areas, that's the interpretation of
61:16 Shannon sandwich or at least an early . And so the vertical section here
61:26 from a bated sand, well bated stone to bioturbated sandstone and the shelf
61:33 central ridge going up near the top and it looks something like what Galloway
61:40 have predicted. And so the interpretation , this is a separate sand ridge
61:56 a big question is how to get . Uh This interpretation is it is
62:04 title sandwich. Um But how did bypass the show? How did that
62:14 get there? It, it was part of a transgressive sand sheet that
62:21 see in the east coast? Not . I mean, it doesn't fit
62:27 . Um Well, maybe it's a stand delta. So it's a relic
62:39 that was reworked or maybe it was , in fact, it could have
62:52 this unit that was reworked during the transgression dope. Most of the thinking
63:02 is that kind of like the abandoned that are now ridges in the Gulf
63:12 Mexico. These bridges that are in Cretaceous were low stand sand features that
63:23 then buried. But with a significant tidal range in tidal influence,
63:32 opposed to let's say the um Gulf Mexico, which is a micro title
63:40 . Now, the last example I'll be discussing is the pro grading storm
63:49 wave dominated shelf. This is the . We no better what I was
63:55 about earlier. That's the system here we can have that occur under tidal
64:01 or storm and wave settings. I'm focus now on the things we talked
64:07 earlier, the storm dominated short face show these are the estates in those
64:16 are basically going to give you uh storm generated sand bodies extending onto a
64:27 shelf. They are in essence the bed that we talked about and um
64:34 or, or rather well in the in Canada, ok. Uh We
64:42 about what they look like. Um talked about little question about whether or
64:51 there's actually a liquefied or, or a massive uh graded stone
64:57 Uh Sand here, we talked about happens when they're modified and of
65:02 they're gonna be capped with mud. ? Uh We can skip that,
65:08 here, here's some of those muds can cap the sands, ok?
65:19 here's that case where we talked earlier some of these muds piling up offshore
65:29 this is associated with a down slope . So now we're beginning to
65:35 well, maybe there are some currents might affect the formation of this downslope
65:43 . And, and that, that's basically down here, that's what
65:46 looking at with the sub aqueous OK. And so here there are
65:52 oriented currents. Here are waves. Hey, we've got that Delta Clii
65:59 again. Here we don't. And the difference between this portion and this
66:14 of that mud being deposited down Ok. Now, what kind of
66:20 that is, is it an oceanographic or is it just longshore currents?
66:28 it a storm generated current? It's not quite clear. Some cases.
66:32 may well be an oceanographic occurring in case is more analogous to what we
66:36 talking about in the Amazon. But the case, here's that high,
66:43 hypo pial fluid that flow that's transporting mud offshore is a plume. And
66:56 it gives us this offshore mud like . Well, that's really important,
67:06 we've also and had described sand plumes the delta is actually transporting sand as
67:23 as mud. And these were described Lisa sand bodies. Yeah, in
67:39 , um yeah, this description here the shaped of those sand bodies sitting
67:54 top of the mud. Ok. the idea is that when there's a
68:04 promenade, we've got longshore currents that being deflected and moving offshore. So
68:20 suggestion is that those offshore fields in cretaceous of Wyoming are not relic low
68:30 features that are reworked, but might been actually parts of these sand shows
68:38 street and, and we see what's as one of these downstream from the
68:48 dominated Nile. Hey, other people argued. Well, no, you
68:55 . Yeah, you might say but I think it's part of a
68:59 stand feature. So we're still arguing this stuff. And one of the
69:08 I will point out is that the literature has kind of ignored the shelf
69:16 PLOS. Now, I don't think really been ignored, but the focus
69:21 been on these mud bloops. And the reality is those mud plumes
69:32 be pretty sandy and they can form pics. And you'll recall that Hyper
69:40 can be sandy so they could actually generated from the river flooding itself.
69:48 maybe some of these shelf sand plumes simply the proximal portions of these hypopnic
69:58 . I think that's part of the . Um We've focused on the,
70:04 mud as a driving process or The other thing is these are,
70:10 be two fundamentally separate processes. One a hyper flu which will be
70:29 The other is unrelated to the hyper rather is sediment that is deflected
70:44 In which case it san and the of this would be longshore drip,
70:52 source of this would be the So we really haven't reconciled the ways
71:04 which we get these elongate sands. . But I'll just note that when
71:13 look at the Yukon Delta, we a whole series of shows offshore and
71:24 we core offshore, they're sandy and get similar Lesia shows when there are
71:37 rivers. I rather just promenades with . So the sandy plumes and sandy
71:51 side shows exist. They're not They're not the topic of much discussion
71:58 now, but it's, it's important think about them in the context of
72:03 is being discussed. Relic sands, of relic sands and hypopnic plumes and
72:11 plumes. Ok. Oh, that's good place to stop. So,
72:18 let's stop
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