WEBVTT 00:00:00.000 --> 00:00:01.480 align:middle line:90% [SQUEAKING] 00:00:01.480 --> 00:00:03.440 align:middle line:90% [RUSTLING] 00:00:03.440 --> 00:00:06.870 align:middle line:90% [CLICKING] 00:00:06.870 --> 00:00:18.017 align:middle line:90% 00:00:18.017 --> 00:00:20.600 align:middle line:84% JOHN SOUTHARD: And this is where we are, cross-stratification. 00:00:20.600 --> 00:00:24.240 align:middle line:84% As I remember, this is what we got to-- 00:00:24.240 --> 00:00:27.480 align:middle line:84% very useful for depositional interpretations. 00:00:27.480 --> 00:00:31.240 align:middle line:84% Here's the official definition, and just make sense. 00:00:31.240 --> 00:00:33.900 align:middle line:84% That's the official definition of cross-stratification. 00:00:33.900 --> 00:00:38.000 align:middle line:90% 00:00:38.000 --> 00:00:43.000 align:middle line:84% I think that it's probably the best 00:00:43.000 --> 00:00:48.320 align:middle line:84% way of making interpretations from looking at Strata. 00:00:48.320 --> 00:00:52.720 align:middle line:84% So it's caused by the action of bed configurations in a flow 00:00:52.720 --> 00:00:54.280 align:middle line:90% during aggradation. 00:00:54.280 --> 00:00:57.240 align:middle line:84% And we typically see sets of conformable laminae, 00:00:57.240 --> 00:01:00.890 align:middle line:84% called sets, separated by truncation surfaces. 00:01:00.890 --> 00:01:04.349 align:middle line:84% Or maybe not-- Maybe no truncation surfaces in there. 00:01:04.349 --> 00:01:06.910 align:middle line:84% You're going to see what I mean by that. 00:01:06.910 --> 00:01:08.750 align:middle line:84% So the basic idea is pretty simple. 00:01:08.750 --> 00:01:12.650 align:middle line:84% There's a flow over a sediment bed, and there's deposition. 00:01:12.650 --> 00:01:15.730 align:middle line:84% And then at a certain time later, the flow changes. 00:01:15.730 --> 00:01:17.270 align:middle line:90% Flows change all the time. 00:01:17.270 --> 00:01:19.270 align:middle line:84% It erodes downward into that deposit. 00:01:19.270 --> 00:01:20.830 align:middle line:84% And then it starts to deposit again. 00:01:20.830 --> 00:01:24.050 align:middle line:84% And you're left with two sets separated by a truncation 00:01:24.050 --> 00:01:24.790 align:middle line:90% surface. 00:01:24.790 --> 00:01:26.530 align:middle line:90% That's the basic idea. 00:01:26.530 --> 00:01:29.610 align:middle line:84% And I don't think I'm telling you anything new. 00:01:29.610 --> 00:01:33.250 align:middle line:84% But there's a problem, because if you have erosion, 00:01:33.250 --> 00:01:35.650 align:middle line:84% there's a certain amount of time that's not recorded. 00:01:35.650 --> 00:01:37.830 align:middle line:84% Only when there's aggradation enough 00:01:37.830 --> 00:01:39.610 align:middle line:84% so there's never any truncation do 00:01:39.610 --> 00:01:42.250 align:middle line:84% you have a complete record of the time involved 00:01:42.250 --> 00:01:45.010 align:middle line:84% in the process, which is unfortunate, but that's the way 00:01:45.010 --> 00:01:45.630 align:middle line:90% it is. 00:01:45.630 --> 00:01:48.450 align:middle line:90% 00:01:48.450 --> 00:01:51.530 align:middle line:84% So the way you can get around that is 00:01:51.530 --> 00:01:54.870 align:middle line:84% to run the flow over a bed of sediment 00:01:54.870 --> 00:01:57.485 align:middle line:84% over a wide range of conditions, either in the laboratory 00:01:57.485 --> 00:01:59.110 align:middle line:84% or in the natural environment, and keep 00:01:59.110 --> 00:02:01.097 align:middle line:84% track of what's happening, because then you do 00:02:01.097 --> 00:02:01.930 align:middle line:90% have a record of it. 00:02:01.930 --> 00:02:03.490 align:middle line:84% Even there's some erosion later on, 00:02:03.490 --> 00:02:05.170 align:middle line:84% you know what's happening through time. 00:02:05.170 --> 00:02:08.150 align:middle line:84% But the problem is only in certain situations 00:02:08.150 --> 00:02:12.110 align:middle line:84% can you actually do that, unfortunately. 00:02:12.110 --> 00:02:16.870 align:middle line:84% So I've been interested, fascinated, 00:02:16.870 --> 00:02:21.070 align:middle line:84% by cross-stratification since I was a grad student in the early 00:02:21.070 --> 00:02:24.890 align:middle line:84% '60s, and not a lot was known about it then. 00:02:24.890 --> 00:02:26.582 align:middle line:84% We've made a lot of advances since then. 00:02:26.582 --> 00:02:27.290 align:middle line:90% Oh, look at this. 00:02:27.290 --> 00:02:29.630 align:middle line:90% Oh, thank you. 00:02:29.630 --> 00:02:34.370 align:middle line:84% And so in the old textbooks you'd see diagrams like this 00:02:34.370 --> 00:02:35.250 align:middle line:90% and like this. 00:02:35.250 --> 00:02:37.550 align:middle line:84% They're sets separated by laminae, separated 00:02:37.550 --> 00:02:39.130 align:middle line:90% by truncation surfaces. 00:02:39.130 --> 00:02:43.952 align:middle line:84% But when you look more closely, if you look at a block diagram, 00:02:43.952 --> 00:02:45.410 align:middle line:84% you often see something like this-- 00:02:45.410 --> 00:02:47.555 align:middle line:84% I'll be getting to this-- in which these are not 00:02:47.555 --> 00:02:48.930 align:middle line:84% really different from each other, 00:02:48.930 --> 00:02:52.810 align:middle line:84% they're just different sections through a unified deposit. 00:02:52.810 --> 00:02:55.640 align:middle line:90% 00:02:55.640 --> 00:02:57.440 align:middle line:84% I was looking at this upside down once 00:02:57.440 --> 00:03:00.200 align:middle line:84% and, holy mackerel, large scale trough 00:03:00.200 --> 00:03:02.160 align:middle line:90% classification in a cookbook. 00:03:02.160 --> 00:03:04.903 align:middle line:90% Isn't that amazing? 00:03:04.903 --> 00:03:06.320 align:middle line:84% You're going to get the impression 00:03:06.320 --> 00:03:09.160 align:middle line:84% that I see cross-stratification wherever I look. 00:03:09.160 --> 00:03:13.160 align:middle line:84% OK, so if you're lucky, you have two angles like that, 00:03:13.160 --> 00:03:15.660 align:middle line:84% two right angles, or at least at a considerable angle. 00:03:15.660 --> 00:03:16.960 align:middle line:90% So you can get different views. 00:03:16.960 --> 00:03:19.280 align:middle line:84% Just on the face, it can be difficult to tell 00:03:19.280 --> 00:03:20.340 align:middle line:90% what's going on. 00:03:20.340 --> 00:03:23.340 align:middle line:84% If you want to try to back out paleoflow directions, 00:03:23.340 --> 00:03:26.320 align:middle line:84% you really need more than one face to look at. 00:03:26.320 --> 00:03:28.880 align:middle line:84% And sometimes we have it, but often we don't. 00:03:28.880 --> 00:03:30.520 align:middle line:90% So let's start with ripples. 00:03:30.520 --> 00:03:33.840 align:middle line:84% I told you all about ripples, ripple bed configurations 00:03:33.840 --> 00:03:36.120 align:middle line:84% and what they look like and how they behave. 00:03:36.120 --> 00:03:39.540 align:middle line:84% And even with a single ripple train, 00:03:39.540 --> 00:03:41.640 align:middle line:84% that's just one train of current ripples, 00:03:41.640 --> 00:03:43.590 align:middle line:84% technically it's cross-stratification, 00:03:43.590 --> 00:03:45.840 align:middle line:84% but typically the ripples are climbing because there's 00:03:45.840 --> 00:03:48.480 align:middle line:84% deposition going on while the ripples are 00:03:48.480 --> 00:03:51.120 align:middle line:90% doing their thing on the bed. 00:03:51.120 --> 00:03:53.100 align:middle line:84% And so that leads us to what's called climbing 00:03:53.100 --> 00:03:55.400 align:middle line:90% bedform cross-stratification. 00:03:55.400 --> 00:03:58.300 align:middle line:84% And I have to tell you a little bit of how bedforms climb. 00:03:58.300 --> 00:04:00.360 align:middle line:84% And we're dealing with unidirectional flow now. 00:04:00.360 --> 00:04:04.580 align:middle line:90% 00:04:04.580 --> 00:04:06.750 align:middle line:84% So here's my favorite terminology. 00:04:06.750 --> 00:04:08.500 align:middle line:84% You won't see this much in the literature. 00:04:08.500 --> 00:04:10.720 align:middle line:84% Erosional-stoss, climbing ripples, 00:04:10.720 --> 00:04:14.980 align:middle line:84% the stoss side is the upstream side and the lee side 00:04:14.980 --> 00:04:16.399 align:middle line:90% is the downstream side. 00:04:16.399 --> 00:04:19.140 align:middle line:84% So erosional stoss, angles climb low 00:04:19.140 --> 00:04:23.100 align:middle line:84% enough so that a given ripple cuts partway 00:04:23.100 --> 00:04:27.700 align:middle line:84% into the next ripple downstream and produces a set of laminae 00:04:27.700 --> 00:04:30.380 align:middle line:84% that's separated from later deposits 00:04:30.380 --> 00:04:31.960 align:middle line:90% by a truncation surface. 00:04:31.960 --> 00:04:34.260 align:middle line:84% But sometimes the angle of climb is large enough 00:04:34.260 --> 00:04:38.560 align:middle line:84% to produce to preserve the entire ripple profile. 00:04:38.560 --> 00:04:40.760 align:middle line:84% And then there are no truncation surfaces, 00:04:40.760 --> 00:04:42.960 align:middle line:84% and you can see the whole thing, which is nice, 00:04:42.960 --> 00:04:46.180 align:middle line:84% but it's not nearly as common as low angle erosional stoss. 00:04:46.180 --> 00:04:50.380 align:middle line:90% Oh, and I should mention that. 00:04:50.380 --> 00:04:52.650 align:middle line:84% In the official terminology, in the literature, 00:04:52.650 --> 00:04:55.330 align:middle line:84% people call it subcritical klein versus supercritical, 00:04:55.330 --> 00:04:56.890 align:middle line:90% but that doesn't tell you much. 00:04:56.890 --> 00:05:01.150 align:middle line:84% So I prefer erosional stoss and depositional stoss. 00:05:01.150 --> 00:05:02.770 align:middle line:90% So let's start out. 00:05:02.770 --> 00:05:04.410 align:middle line:84% But here's a little train of ripples. 00:05:04.410 --> 00:05:06.050 align:middle line:84% And here's one ripple in the train. 00:05:06.050 --> 00:05:10.550 align:middle line:84% We cut the ripple with an imaginary vertical section 00:05:10.550 --> 00:05:12.790 align:middle line:90% parallel to flow. 00:05:12.790 --> 00:05:18.230 align:middle line:84% And do that for a large number of sections, 00:05:18.230 --> 00:05:23.550 align:middle line:84% and all those points where the low point was in the trough 00:05:23.550 --> 00:05:28.310 align:middle line:84% are connected with a rather sinuous, snaky-looking 00:05:28.310 --> 00:05:30.990 align:middle line:84% little surface, connecting all the low points 00:05:30.990 --> 00:05:33.430 align:middle line:84% all along the trough, which varies considerably 00:05:33.430 --> 00:05:35.010 align:middle line:90% in its depth and its shape. 00:05:35.010 --> 00:05:37.852 align:middle line:90% You keep that in mind. 00:05:37.852 --> 00:05:39.310 align:middle line:84% And that leads to what I could call 00:05:39.310 --> 00:05:41.870 align:middle line:84% a cheesewire effect, because cheese wires are straight, 00:05:41.870 --> 00:05:42.970 align:middle line:90% linears. 00:05:42.970 --> 00:05:48.270 align:middle line:84% But this is a snaky cheese wire that moves down with the ripple 00:05:48.270 --> 00:05:55.130 align:middle line:84% and changes its shape as it goes like this, this kind of thing, 00:05:55.130 --> 00:05:57.950 align:middle line:84% and eats into the next ripple downstream. 00:05:57.950 --> 00:06:01.530 align:middle line:84% Every ripple is doing it to every ripple just downstream. 00:06:01.530 --> 00:06:06.850 align:middle line:84% And that gives you the key to what you will get. 00:06:06.850 --> 00:06:10.850 align:middle line:84% Here's an old profile and here's a new later profile. 00:06:10.850 --> 00:06:13.750 align:middle line:84% This is a rotor from the stoss side, and it's deposited. 00:06:13.750 --> 00:06:15.230 align:middle line:90% I mean, this is ho-hum stuff. 00:06:15.230 --> 00:06:16.830 align:middle line:90% I mean, you're aware of that. 00:06:16.830 --> 00:06:20.290 align:middle line:84% But that's what's going on when the ripple climb is low. 00:06:20.290 --> 00:06:23.050 align:middle line:84% So this is the preserved part of the laminae. 00:06:23.050 --> 00:06:26.710 align:middle line:84% This is now eroded completely and gone down that way. 00:06:26.710 --> 00:06:27.650 align:middle line:90% And that's just what-- 00:06:27.650 --> 00:06:30.770 align:middle line:84% every ripple comes along and leaves another set 00:06:30.770 --> 00:06:32.890 align:middle line:90% of what are called four sets. 00:06:32.890 --> 00:06:38.050 align:middle line:84% And in your copies of the PowerPoint, 00:06:38.050 --> 00:06:40.730 align:middle line:84% I wrote it not fourth, but forests. 00:06:40.730 --> 00:06:44.510 align:middle line:84% Forests-- I left out an E. A spell checker won't catch that. 00:06:44.510 --> 00:06:46.290 align:middle line:84% I corrected it on the slide that's 00:06:46.290 --> 00:06:49.840 align:middle line:90% coming along that you have. 00:06:49.840 --> 00:06:52.940 align:middle line:84% I spent a long time making this block diagram once long ago. 00:06:52.940 --> 00:06:57.160 align:middle line:84% Here's a rather garden variety set of sinuous, 00:06:57.160 --> 00:07:01.660 align:middle line:84% crested, and variably deep trough across. 00:07:01.660 --> 00:07:03.360 align:middle line:84% And it's climbing at a fairly low angle. 00:07:03.360 --> 00:07:07.880 align:middle line:84% And we have all these foresets separated by trunking services. 00:07:07.880 --> 00:07:10.700 align:middle line:84% Because remember, I told you how varied ripples are. 00:07:10.700 --> 00:07:11.760 align:middle line:90% They change their shape. 00:07:11.760 --> 00:07:12.960 align:middle line:90% They change their size. 00:07:12.960 --> 00:07:15.220 align:middle line:84% Some of them get formed, others disappear. 00:07:15.220 --> 00:07:18.420 align:middle line:84% And so these are not quite straight, 00:07:18.420 --> 00:07:22.020 align:middle line:84% regular, tabular sets of foresets. 00:07:22.020 --> 00:07:25.300 align:middle line:84% And then if you look at the cross, 00:07:25.300 --> 00:07:28.200 align:middle line:84% vertical cross flow direction sets, 00:07:28.200 --> 00:07:30.100 align:middle line:90% you can see how trophy it is. 00:07:30.100 --> 00:07:36.860 align:middle line:84% You get sets of concave upward laminae separated by one, 00:07:36.860 --> 00:07:39.600 align:middle line:84% or usually two, truncation surfaces. 00:07:39.600 --> 00:07:43.620 align:middle line:84% And we call those truncation cross sets. 00:07:43.620 --> 00:07:45.680 align:middle line:84% And I'll be talking later about what 00:07:45.680 --> 00:07:50.495 align:middle line:84% we see on a stratification parallel section. 00:07:50.495 --> 00:07:51.620 align:middle line:90% But just keep that in mind. 00:07:51.620 --> 00:07:54.455 align:middle line:84% I'll be talking about that when the time comes. 00:07:54.455 --> 00:07:56.080 align:middle line:84% Now, that was for a low angle of climb. 00:07:56.080 --> 00:07:57.400 align:middle line:90% At a high angle of climb-- 00:07:57.400 --> 00:08:01.500 align:middle line:84% Now, I'd like to redo this because it's too regular. 00:08:01.500 --> 00:08:03.660 align:middle line:84% Even though they're climbing at a large angle, 00:08:03.660 --> 00:08:05.300 align:middle line:90% they're still fairly regular. 00:08:05.300 --> 00:08:08.880 align:middle line:84% Although it's clear to me that the higher the angle of climb, 00:08:08.880 --> 00:08:10.460 align:middle line:84% the more regular the ripples are. 00:08:10.460 --> 00:08:12.440 align:middle line:84% And I don't know why that is, but that's 00:08:12.440 --> 00:08:14.500 align:middle line:84% been my experience and the experience of others. 00:08:14.500 --> 00:08:16.400 align:middle line:84% So there are no truncation surfaces-- so 00:08:16.400 --> 00:08:19.120 align:middle line:84% maybe occasionally, when ripples act up and do something 00:08:19.120 --> 00:08:21.940 align:middle line:84% a little bit different from their surroundings. 00:08:21.940 --> 00:08:25.180 align:middle line:84% And this should be a somewhat more sinuous. 00:08:25.180 --> 00:08:27.960 align:middle line:84% But there wouldn't be any truncations in here 00:08:27.960 --> 00:08:30.520 align:middle line:84% for the reasons that I think should be clear to you. 00:08:30.520 --> 00:08:32.380 align:middle line:84% Now, here's my favorite ripple again. 00:08:32.380 --> 00:08:35.299 align:middle line:84% And you can see that this ripple, it's classic. 00:08:35.299 --> 00:08:40.120 align:middle line:84% It has foreset laminae faring out into the trough. 00:08:40.120 --> 00:08:43.140 align:middle line:84% And it has been-- not now-- it has been 00:08:43.140 --> 00:08:44.920 align:middle line:90% eroding, the ripple underneath. 00:08:44.920 --> 00:08:46.800 align:middle line:84% So here are the preserved foresets 00:08:46.800 --> 00:08:48.480 align:middle line:84% underneath the truncation surface. 00:08:48.480 --> 00:08:50.320 align:middle line:84% This is an unusual ripple-- not unusual, 00:08:50.320 --> 00:08:54.020 align:middle line:84% but it's irregular in the sense that early on, when 00:08:54.020 --> 00:09:01.620 align:middle line:84% the crust was here, the upstream side, the stoss side, 00:09:01.620 --> 00:09:02.840 align:middle line:90% was being eroded. 00:09:02.840 --> 00:09:05.500 align:middle line:84% But then more sediment came in somehow, 00:09:05.500 --> 00:09:09.260 align:middle line:84% and now the stoss side is aggrading, rather than cutting 00:09:09.260 --> 00:09:10.800 align:middle line:90% down into the underlying stuff. 00:09:10.800 --> 00:09:12.000 align:middle line:90% So these come and go. 00:09:12.000 --> 00:09:16.860 align:middle line:84% Things change because of the irregularity of the ripples. 00:09:16.860 --> 00:09:18.587 align:middle line:90% Here's a single ripple train. 00:09:18.587 --> 00:09:20.920 align:middle line:84% And maybe I shouldn't have put it in here at this point, 00:09:20.920 --> 00:09:23.840 align:middle line:84% because they don't look like the one I showed first 00:09:23.840 --> 00:09:26.020 align:middle line:84% because they're more nearly symmetrical, 00:09:26.020 --> 00:09:28.000 align:middle line:84% and they do have internal laminae. 00:09:28.000 --> 00:09:30.260 align:middle line:84% You can see vaguely internal laminae. 00:09:30.260 --> 00:09:35.180 align:middle line:84% This is more likely to be oscillatory, oscillation 00:09:35.180 --> 00:09:40.260 align:middle line:84% ripples, starved or semi-starved oscillation ripples, rather than 00:09:40.260 --> 00:09:41.080 align:middle line:90% current ripples. 00:09:41.080 --> 00:09:45.290 align:middle line:84% And we'll be dealing with the differences presently. 00:09:45.290 --> 00:09:49.310 align:middle line:84% Here's a close up of a single ripple in a ripple train. 00:09:49.310 --> 00:09:51.170 align:middle line:90% And there is some asymmetry. 00:09:51.170 --> 00:09:53.890 align:middle line:84% This is more gently sloping than this side. 00:09:53.890 --> 00:09:55.810 align:middle line:84% And you can see the internal lamination. 00:09:55.810 --> 00:09:59.170 align:middle line:84% But again, this is likely to be oscillation ripples. 00:09:59.170 --> 00:10:02.190 align:middle line:84% And I may be arguing-- maybe I'm going to show you this again 00:10:02.190 --> 00:10:04.470 align:middle line:84% when we get to talking about oscillation ripples. 00:10:04.470 --> 00:10:08.170 align:middle line:84% This is more like a train of current ripples. 00:10:08.170 --> 00:10:11.030 align:middle line:84% But there's a tip-off here that maybe it's 00:10:11.030 --> 00:10:13.350 align:middle line:84% oscillation influence, because you see, 00:10:13.350 --> 00:10:16.510 align:middle line:90% the stoss surface is arched. 00:10:16.510 --> 00:10:18.350 align:middle line:84% And that suggests to me they have 00:10:18.350 --> 00:10:22.430 align:middle line:84% an element of being like oscillation ripples. 00:10:22.430 --> 00:10:25.430 align:middle line:84% And toward the end, if I get a chance to get there, 00:10:25.430 --> 00:10:27.550 align:middle line:84% there'll be a section on combined flow 00:10:27.550 --> 00:10:32.350 align:middle line:84% cross-stratification, which is a difficult topic to manage, 00:10:32.350 --> 00:10:34.350 align:middle line:90% and I hope I get there. 00:10:34.350 --> 00:10:37.470 align:middle line:84% Now-- oh, Kristen is not here today. 00:10:37.470 --> 00:10:41.570 align:middle line:84% This is a photo of a plate I have 00:10:41.570 --> 00:10:44.430 align:middle line:84% that was made in modern sediments. 00:10:44.430 --> 00:10:46.410 align:middle line:84% They cut a surface with a machete-- 00:10:46.410 --> 00:10:48.470 align:middle line:84% all sedimentary geologists use a machete. 00:10:48.470 --> 00:10:49.490 align:middle line:90% I own a machete. 00:10:49.490 --> 00:10:54.010 align:middle line:84% And you take an epoxy plate and you put it up against there. 00:10:54.010 --> 00:10:56.370 align:middle line:84% And because the differing permeability 00:10:56.370 --> 00:11:00.470 align:middle line:84% of the various laminae, you get a relief surface. 00:11:00.470 --> 00:11:01.870 align:middle line:90% And this is a photo of it. 00:11:01.870 --> 00:11:05.130 align:middle line:84% All right, so this is classic erosional stoss 00:11:05.130 --> 00:11:06.430 align:middle line:90% cross-stratification. 00:11:06.430 --> 00:11:09.090 align:middle line:84% But it's not entirely so, because here a ripple 00:11:09.090 --> 00:11:12.690 align:middle line:84% got especially vigorous and ended up 00:11:12.690 --> 00:11:14.390 align:middle line:90% with depositional stuff. 00:11:14.390 --> 00:11:15.950 align:middle line:90% But it's mainly erosional stoss. 00:11:15.950 --> 00:11:20.970 align:middle line:84% And we know from where he made this-- 00:11:20.970 --> 00:11:24.050 align:middle line:84% my colleague, Dick Mayall from Mobile Research, 00:11:24.050 --> 00:11:25.430 align:middle line:90% gave me this thing as a gift. 00:11:25.430 --> 00:11:28.970 align:middle line:84% I really, really loved to have it. 00:11:28.970 --> 00:11:31.090 align:middle line:90% This is a flow parallel section. 00:11:31.090 --> 00:11:35.910 align:middle line:84% And we're not showing what it would look like at right angles. 00:11:35.910 --> 00:11:37.920 align:middle line:90% OK, now here's a chunk. 00:11:37.920 --> 00:11:39.880 align:middle line:90% And this is in Kristen's lab. 00:11:39.880 --> 00:11:43.520 align:middle line:84% And I'm showing you one way and then the other way. 00:11:43.520 --> 00:11:45.300 align:middle line:90% And I want you to look at this. 00:11:45.300 --> 00:11:47.440 align:middle line:84% I'll give you maybe almost half a minute here. 00:11:47.440 --> 00:11:48.860 align:middle line:90% Maybe you don't need that long. 00:11:48.860 --> 00:11:51.860 align:middle line:84% You have to tell me which way is up. 00:11:51.860 --> 00:11:54.040 align:middle line:90% Is this upright or upside down? 00:11:54.040 --> 00:11:56.980 align:middle line:90% Is this upright or upside down? 00:11:56.980 --> 00:11:58.340 align:middle line:90% You don't need to tell me now. 00:11:58.340 --> 00:12:00.320 align:middle line:90% We're going to take a vote. 00:12:00.320 --> 00:12:01.880 align:middle line:90% So look at it carefully. 00:12:01.880 --> 00:12:03.520 align:middle line:90% See if you can spot a feature. 00:12:03.520 --> 00:12:04.960 align:middle line:84% And it's a little bit complicated. 00:12:04.960 --> 00:12:07.502 align:middle line:84% Can you spot any feature that would tell you which way is up? 00:12:07.502 --> 00:12:10.220 align:middle line:90% 00:12:10.220 --> 00:12:11.760 align:middle line:90% So let's take a vote. 00:12:11.760 --> 00:12:16.860 align:middle line:84% You can vote-- you can vote the top is up or the bottom is up, 00:12:16.860 --> 00:12:20.140 align:middle line:84% or you don't know, or you can abstain. 00:12:20.140 --> 00:12:25.420 align:middle line:84% How many people that the top shows that it's upright? 00:12:25.420 --> 00:12:28.370 align:middle line:84% How many people the bottom is upright? 00:12:28.370 --> 00:12:30.120 align:middle line:84% One, two, three, four-- almost all of you. 00:12:30.120 --> 00:12:33.740 align:middle line:84% How many people aren't sure, don't know. 00:12:33.740 --> 00:12:37.260 align:middle line:84% OK, this is clearly, when you look at it carefully, 00:12:37.260 --> 00:12:40.200 align:middle line:84% you see a set of four sets tailing off into the trough 00:12:40.200 --> 00:12:42.058 align:middle line:84% and being cut by a truncation surface. 00:12:42.058 --> 00:12:43.600 align:middle line:84% And there are some other places right 00:12:43.600 --> 00:12:47.180 align:middle line:84% in here, which are less obvious here and here and right in here. 00:12:47.180 --> 00:12:48.580 align:middle line:90% But you'll have to look closely. 00:12:48.580 --> 00:12:50.860 align:middle line:84% See, it doesn't jump right out at you. 00:12:50.860 --> 00:12:52.100 align:middle line:90% But you did really well. 00:12:52.100 --> 00:12:56.280 align:middle line:90% 00:12:56.280 --> 00:12:58.380 align:middle line:84% This is a cut through modern sediments. 00:12:58.380 --> 00:13:01.660 align:middle line:84% My valued colleague, senior colleague, John Harms, 00:13:01.660 --> 00:13:04.180 align:middle line:84% one of my mentors early in my career, 00:13:04.180 --> 00:13:08.160 align:middle line:84% cut this through unconsolidated sediment, a view perpendicular 00:13:08.160 --> 00:13:08.980 align:middle line:90% to flow. 00:13:08.980 --> 00:13:10.980 align:middle line:90% And you can see the troughiness. 00:13:10.980 --> 00:13:12.680 align:middle line:90% I like that word, troughiness. 00:13:12.680 --> 00:13:16.500 align:middle line:84% All these little troughy sets here with convex, 00:13:16.500 --> 00:13:20.000 align:middle line:84% concave upward laminae cut by one or two 00:13:20.000 --> 00:13:22.480 align:middle line:84% or sometimes even three truncation surfaces. 00:13:22.480 --> 00:13:25.140 align:middle line:84% In the scale here, these are inches over here. 00:13:25.140 --> 00:13:29.720 align:middle line:84% So you see it's like a few centimeter scale, small scale 00:13:29.720 --> 00:13:31.400 align:middle line:90% trough cross-stratification. 00:13:31.400 --> 00:13:33.020 align:middle line:90% Now, tell me about this. 00:13:33.020 --> 00:13:34.690 align:middle line:90% What do you think about that? 00:13:34.690 --> 00:13:36.970 align:middle line:84% Does that look right to you or not? 00:13:36.970 --> 00:13:39.190 align:middle line:90% I see a shaking head. 00:13:39.190 --> 00:13:43.150 align:middle line:84% OK, well, the next slide shows it in the other way. 00:13:43.150 --> 00:13:46.090 align:middle line:84% And that's clearly small scale trough cross-strat. 00:13:46.090 --> 00:13:48.330 align:middle line:90% So you have to make sure-- 00:13:48.330 --> 00:13:49.612 align:middle line:90% troughiness, I like that word. 00:13:49.612 --> 00:13:51.570 align:middle line:84% I'm not sure how to spell it, and it's probably 00:13:51.570 --> 00:13:54.690 align:middle line:90% not a real word anyway. 00:13:54.690 --> 00:13:58.250 align:middle line:90% OK, so here's some examples-- 00:13:58.250 --> 00:14:03.170 align:middle line:84% erosional stoss, but there's some places where 00:14:03.170 --> 00:14:05.310 align:middle line:90% it's almost depositional stoss. 00:14:05.310 --> 00:14:09.290 align:middle line:84% And the ripple profiles don't quite look like current ripples. 00:14:09.290 --> 00:14:12.430 align:middle line:84% So I'm figuring this may be a combined flow feature. 00:14:12.430 --> 00:14:16.130 align:middle line:84% Maybe there's an oscillation influenced, 00:14:16.130 --> 00:14:17.850 align:middle line:90% largely unidirectional flow. 00:14:17.850 --> 00:14:20.610 align:middle line:84% And you have to look close to guess 00:14:20.610 --> 00:14:23.130 align:middle line:84% whether it's purely unidirectional 00:14:23.130 --> 00:14:24.790 align:middle line:84% or whether it's oscillation influence. 00:14:24.790 --> 00:14:26.310 align:middle line:90% It's often a problem. 00:14:26.310 --> 00:14:28.498 align:middle line:84% A matter of fact, it's a much bigger problem 00:14:28.498 --> 00:14:30.290 align:middle line:84% if you're dealing with-- this is something, 00:14:30.290 --> 00:14:33.430 align:middle line:84% I don't know how this got in here in this particular place. 00:14:33.430 --> 00:14:37.210 align:middle line:84% This is the thing I showed you, except not as nice. 00:14:37.210 --> 00:14:39.130 align:middle line:84% But you see all the troughiness in here. 00:14:39.130 --> 00:14:42.950 align:middle line:84% So it's a face that's largely perpendicular to flow. 00:14:42.950 --> 00:14:45.470 align:middle line:84% It gets a little messier down in here. 00:14:45.470 --> 00:14:47.810 align:middle line:84% I'll talk more about messiness when we get there. 00:14:47.810 --> 00:14:51.110 align:middle line:90% 00:14:51.110 --> 00:14:53.837 align:middle line:84% My wife wanted to put this in the church yard sale. 00:14:53.837 --> 00:14:56.170 align:middle line:84% And it was sitting on the table and looking at it, says, 00:14:56.170 --> 00:14:58.750 align:middle line:84% that's erosional stoss cross-stratification right 00:14:58.750 --> 00:14:59.510 align:middle line:90% there. 00:14:59.510 --> 00:15:00.170 align:middle line:90% We kept it. 00:15:00.170 --> 00:15:02.550 align:middle line:90% We didn't give it up. 00:15:02.550 --> 00:15:06.150 align:middle line:84% I see cross-stratification everywhere. 00:15:06.150 --> 00:15:09.650 align:middle line:84% This is a messier example, a real life kind of example. 00:15:09.650 --> 00:15:11.630 align:middle line:84% But it's clear that there's climbing ripples 00:15:11.630 --> 00:15:13.510 align:middle line:90% and there's ripple drift. 00:15:13.510 --> 00:15:16.430 align:middle line:84% Incidentally, some people use the term ripple 00:15:16.430 --> 00:15:18.650 align:middle line:90% drift cross-stratification. 00:15:18.650 --> 00:15:19.810 align:middle line:90% But I don't like that term. 00:15:19.810 --> 00:15:21.430 align:middle line:90% But it's in the literature. 00:15:21.430 --> 00:15:24.230 align:middle line:90% 00:15:24.230 --> 00:15:26.670 align:middle line:90% This is an interesting slide. 00:15:26.670 --> 00:15:30.840 align:middle line:84% This is a surface in a turbidite that 00:15:30.840 --> 00:15:32.560 align:middle line:90% was deposited with Normanskill. 00:15:32.560 --> 00:15:35.480 align:middle line:84% It's a deep basin turbidite-- big, thick stack 00:15:35.480 --> 00:15:39.840 align:middle line:84% of sand, sandstone, shale, interbedded sandstone and shale. 00:15:39.840 --> 00:15:42.340 align:middle line:84% And the ripples are climbing depositionally. 00:15:42.340 --> 00:15:44.680 align:middle line:90% But look at their shapes. 00:15:44.680 --> 00:15:46.640 align:middle line:90% They're very undulatory. 00:15:46.640 --> 00:15:49.240 align:middle line:84% And if I'd looked at that without knowing where 00:15:49.240 --> 00:15:51.400 align:middle line:84% it came from, I'd say, well, that's a combined 00:15:51.400 --> 00:15:53.160 align:middle line:90% flow, a combined flow. 00:15:53.160 --> 00:15:54.140 align:middle line:90% But it isn't. 00:15:54.140 --> 00:15:55.000 align:middle line:90% It's in a turbidite. 00:15:55.000 --> 00:15:56.680 align:middle line:90% And I don't understand it. 00:15:56.680 --> 00:16:02.000 align:middle line:84% So I certainly don't have all the answers. 00:16:02.000 --> 00:16:03.240 align:middle line:90% John Harms gave me this, too. 00:16:03.240 --> 00:16:06.180 align:middle line:84% This is a cut in the Chaco river, New Mexico, 00:16:06.180 --> 00:16:07.200 align:middle line:90% parallel to flow. 00:16:07.200 --> 00:16:08.920 align:middle line:90% There's a sidebar. 00:16:08.920 --> 00:16:11.480 align:middle line:84% And you can see there's lots of climbing ripples. 00:16:11.480 --> 00:16:13.400 align:middle line:84% Down here, they're climbing at a low angle. 00:16:13.400 --> 00:16:15.140 align:middle line:90% And they climb higher or higher. 00:16:15.140 --> 00:16:17.780 align:middle line:84% And there's some kind of hiatus in there. 00:16:17.780 --> 00:16:20.700 align:middle line:84% Then they start to climb again, and they go up to vertical. 00:16:20.700 --> 00:16:22.740 align:middle line:84% And at the top, they're being draped. 00:16:22.740 --> 00:16:25.640 align:middle line:84% The ripples start moving, but sediment is still 00:16:25.640 --> 00:16:26.340 align:middle line:90% showering down. 00:16:26.340 --> 00:16:29.130 align:middle line:90% So you're draping the ripples. 00:16:29.130 --> 00:16:32.510 align:middle line:84% This is maybe one event bed or two event beds. 00:16:32.510 --> 00:16:35.450 align:middle line:84% But things change during the deposition of an event bed. 00:16:35.450 --> 00:16:38.210 align:middle line:84% So you have to look at it layer by layer 00:16:38.210 --> 00:16:41.730 align:middle line:84% to try to make sense of how the flow changed with time. 00:16:41.730 --> 00:16:42.750 align:middle line:90% Here's another example. 00:16:42.750 --> 00:16:45.010 align:middle line:84% This is from glacial Lake Hitchcock. 00:16:45.010 --> 00:16:46.730 align:middle line:84% My valued colleague, Gail Ashley, 00:16:46.730 --> 00:16:50.490 align:middle line:84% took me out and showed me the stuff, a flow parallel 00:16:50.490 --> 00:16:54.450 align:middle line:84% section of erosional source, rock climbers 00:16:54.450 --> 00:16:56.650 align:middle line:84% going into depositional source and then 00:16:56.650 --> 00:17:02.130 align:middle line:84% into drapes, a waning flow kind of situation. 00:17:02.130 --> 00:17:04.349 align:middle line:84% And we got together and made some experiments, 00:17:04.349 --> 00:17:05.450 align:middle line:90% the lab got it-- 00:17:05.450 --> 00:17:08.010 align:middle line:84% paper out of it long ago, in the '70s sometime. 00:17:08.010 --> 00:17:11.250 align:middle line:84% So we started out with a preexisting rippled bed. 00:17:11.250 --> 00:17:13.349 align:middle line:84% And then we were showering sediment. 00:17:13.349 --> 00:17:17.250 align:middle line:84% This was a narrow, long flume, about 5 meters long. 00:17:17.250 --> 00:17:22.130 align:middle line:84% And we set up a shaker apparatus all along above, 00:17:22.130 --> 00:17:24.829 align:middle line:90% which would shake sand in. 00:17:24.829 --> 00:17:26.630 align:middle line:84% And so it would gradually upgrade the bed 00:17:26.630 --> 00:17:28.610 align:middle line:90% while the ripples were working. 00:17:28.610 --> 00:17:30.750 align:middle line:84% And we arranged it so that we gradually 00:17:30.750 --> 00:17:33.890 align:middle line:84% decreased the flow velocity while the sediment was falling 00:17:33.890 --> 00:17:37.110 align:middle line:84% and so just the same way we go from low angle to high angle 00:17:37.110 --> 00:17:38.790 align:middle line:90% to drape. 00:17:38.790 --> 00:17:41.910 align:middle line:84% So you do see that in various places. 00:17:41.910 --> 00:17:47.030 align:middle line:84% We actually did the same by starting out with a rippled bed 00:17:47.030 --> 00:17:51.490 align:middle line:84% at low velocities, draping, going to high angle 00:17:51.490 --> 00:17:54.550 align:middle line:84% climb, low angle climb, back into high climb, 00:17:54.550 --> 00:17:55.730 align:middle line:90% and back into drapes. 00:17:55.730 --> 00:17:58.730 align:middle line:84% It's an almost symmetrical climb. 00:17:58.730 --> 00:18:01.670 align:middle line:84% STUDENT: Climb directly related to the velocity, 00:18:01.670 --> 00:18:02.685 align:middle line:90% the change in angle? 00:18:02.685 --> 00:18:04.310 align:middle line:84% JOHN SOUTHARD: Well, it's a combination 00:18:04.310 --> 00:18:06.510 align:middle line:84% of how fast the ripples are moving 00:18:06.510 --> 00:18:08.710 align:middle line:84% and how fast the bed is degrading. 00:18:08.710 --> 00:18:11.270 align:middle line:84% So look at the ratio of aggradation 00:18:11.270 --> 00:18:13.510 align:middle line:90% to bed form movement. 00:18:13.510 --> 00:18:16.430 align:middle line:84% And the higher, the stronger the faster the flow and the stronger 00:18:16.430 --> 00:18:18.650 align:middle line:84% the ripples are moving for a given aggradation, 00:18:18.650 --> 00:18:23.190 align:middle line:84% the more likely there is to be low angle stratification. 00:18:23.190 --> 00:18:26.330 align:middle line:84% And only when the ripples move slow 00:18:26.330 --> 00:18:28.150 align:middle line:84% relative to the rate of aggradation, 00:18:28.150 --> 00:18:31.130 align:middle line:84% you get a high angle of climb until finally, the ripples start 00:18:31.130 --> 00:18:32.470 align:middle line:90% moving and it's just draped. 00:18:32.470 --> 00:18:33.470 align:middle line:90% Does that make sense? 00:18:33.470 --> 00:18:38.170 align:middle line:90% 00:18:38.170 --> 00:18:39.910 align:middle line:84% This is also from the same place. 00:18:39.910 --> 00:18:42.830 align:middle line:84% But we made a cut, not just a vertical cut parallel to flow, 00:18:42.830 --> 00:18:44.350 align:middle line:90% but we made a horizontal cut. 00:18:44.350 --> 00:18:46.410 align:middle line:84% And you can see there are packets 00:18:46.410 --> 00:18:49.690 align:middle line:84% of laminae, sets of laminae, separated by the truncation 00:18:49.690 --> 00:18:50.470 align:middle line:90% surfaces. 00:18:50.470 --> 00:18:54.730 align:middle line:84% But we're seeing the truncation surfaces from above. 00:18:54.730 --> 00:18:57.850 align:middle line:84% And I'm going to get back to what 00:18:57.850 --> 00:19:01.290 align:middle line:84% these features on that horizontal surface 00:19:01.290 --> 00:19:04.028 align:middle line:90% will show you. 00:19:04.028 --> 00:19:05.570 align:middle line:84% I've looked at a lot of the Moenkopi, 00:19:05.570 --> 00:19:08.530 align:middle line:84% and there's some interesting, really nice section of stuff 00:19:08.530 --> 00:19:13.090 align:middle line:84% in the Moenkopi just north of one of the arms of Lake Mead. 00:19:13.090 --> 00:19:16.210 align:middle line:84% And so that's classic, low angle erosional 00:19:16.210 --> 00:19:20.650 align:middle line:90% stoss cross-stratification. 00:19:20.650 --> 00:19:24.320 align:middle line:84% At a higher angle, there are also erosional stoss mainly, 00:19:24.320 --> 00:19:27.140 align:middle line:90% but there's some arching over. 00:19:27.140 --> 00:19:30.720 align:middle line:84% And that's the kind of thing that we say, 00:19:30.720 --> 00:19:33.380 align:middle line:84% well, might that be a combined flow 00:19:33.380 --> 00:19:35.940 align:middle line:84% with both, maybe unidirectional dominated 00:19:35.940 --> 00:19:38.460 align:middle line:84% and oscillatory oscillation influence. 00:19:38.460 --> 00:19:45.940 align:middle line:84% And the lower the angle of climb, the more ambiguous it is. 00:19:45.940 --> 00:19:49.380 align:middle line:84% The one I just showed you looked clearly like unidirectional flow 00:19:49.380 --> 00:19:50.520 align:middle line:90% cross-stratification. 00:19:50.520 --> 00:19:52.060 align:middle line:84% But maybe the angles climb is such 00:19:52.060 --> 00:19:55.660 align:middle line:84% that you're only depositing the very lowest part 00:19:55.660 --> 00:19:58.380 align:middle line:90% of the foresets. 00:19:58.380 --> 00:20:00.120 align:middle line:84% And you don't see the whole profile. 00:20:00.120 --> 00:20:01.980 align:middle line:84% So you're never can be sure whether you're 00:20:01.980 --> 00:20:04.340 align:middle line:84% dealing with purely unidirectional flow or maybe 00:20:04.340 --> 00:20:05.378 align:middle line:90% oscillation influence. 00:20:05.378 --> 00:20:07.420 align:middle line:84% It's one of those problems you have to live with. 00:20:07.420 --> 00:20:09.545 align:middle line:84% And I've been struggling with that for a long time. 00:20:09.545 --> 00:20:11.220 align:middle line:84% When it gets to this point, they're 00:20:11.220 --> 00:20:13.470 align:middle line:84% clearly climbing depositionally, and you look 00:20:13.470 --> 00:20:14.720 align:middle line:90% at the profiles of the ripple. 00:20:14.720 --> 00:20:18.240 align:middle line:84% It sure looks like they're partly oscillation ripples. 00:20:18.240 --> 00:20:20.230 align:middle line:84% I think you'd agree with me that they 00:20:20.230 --> 00:20:24.790 align:middle line:84% don't look the standard stoss side, a sharp break 00:20:24.790 --> 00:20:30.430 align:middle line:84% at the brink, and then a slip face to form the foresets. 00:20:30.430 --> 00:20:34.750 align:middle line:90% 00:20:34.750 --> 00:20:37.270 align:middle line:84% Here's a case of climb ripples, where the truncation 00:20:37.270 --> 00:20:41.490 align:middle line:84% surfaces are obvious and the foreset lamination is there, 00:20:41.490 --> 00:20:42.730 align:middle line:90% but it's much less obvious. 00:20:42.730 --> 00:20:46.278 align:middle line:84% You have to look closely to see it. 00:20:46.278 --> 00:20:47.570 align:middle line:90% All right, now a ribbon furrow. 00:20:47.570 --> 00:20:49.190 align:middle line:84% Have you ever turned ribbon furrow? 00:20:49.190 --> 00:20:50.250 align:middle line:90% It's a terrible term. 00:20:50.250 --> 00:20:52.710 align:middle line:84% I think it's a terrible-- it doesn't tell you anything. 00:20:52.710 --> 00:21:01.730 align:middle line:84% So we look at a flow parallel, a stratification parallel section. 00:21:01.730 --> 00:21:03.270 align:middle line:90% And I showed this to you. 00:21:03.270 --> 00:21:06.350 align:middle line:84% So when you see this in outcrop, it's 00:21:06.350 --> 00:21:08.310 align:middle line:84% really nice because it tells you the flow 00:21:08.310 --> 00:21:10.190 align:middle line:90% is flowing from left to right. 00:21:10.190 --> 00:21:11.790 align:middle line:84% And those truncation surfaces are just 00:21:11.790 --> 00:21:14.610 align:middle line:84% what you saw when you look at the vertical section. 00:21:14.610 --> 00:21:17.270 align:middle line:84% This is a section through those truncation surfaces. 00:21:17.270 --> 00:21:19.473 align:middle line:84% Now, why are they convex downstream? 00:21:19.473 --> 00:21:20.390 align:middle line:90% Can you think of that? 00:21:20.390 --> 00:21:23.310 align:middle line:84% Can you give me a simple answer for why they're concave, 00:21:23.310 --> 00:21:26.970 align:middle line:90% why they're concave downstream? 00:21:26.970 --> 00:21:29.690 align:middle line:90% Well, I'll tell you why. 00:21:29.690 --> 00:21:31.650 align:middle line:90% A trough is being filled. 00:21:31.650 --> 00:21:34.590 align:middle line:84% And you're filling on the upstream side of the trough, 00:21:34.590 --> 00:21:36.470 align:middle line:90% which is concave downstream. 00:21:36.470 --> 00:21:41.410 align:middle line:84% So the laminae that are making-- doing the filling-- 00:21:41.410 --> 00:21:44.130 align:middle line:90% are all concave downstream. 00:21:44.130 --> 00:21:45.530 align:middle line:90% So you make the cut. 00:21:45.530 --> 00:21:47.770 align:middle line:84% You see these concave downstream laminae. 00:21:47.770 --> 00:21:49.750 align:middle line:84% And that gives you the paleoflow direction. 00:21:49.750 --> 00:21:54.170 align:middle line:84% It's nice to have, but it's a terrible term. 00:21:54.170 --> 00:21:56.430 align:middle line:84% This is that same slide I just showed you. 00:21:56.430 --> 00:21:59.050 align:middle line:84% And you can see on the flow parallel 00:21:59.050 --> 00:22:00.713 align:middle line:84% section, the horizontal section, you 00:22:00.713 --> 00:22:02.630 align:middle line:84% can see the flow is definitely going that way. 00:22:02.630 --> 00:22:06.910 align:middle line:84% Of course, you already knew that from the vertical section. 00:22:06.910 --> 00:22:09.250 align:middle line:84% But sometimes, all you see is the horizontal section. 00:22:09.250 --> 00:22:10.470 align:middle line:90% And then you really know. 00:22:10.470 --> 00:22:13.010 align:middle line:90% 00:22:13.010 --> 00:22:17.510 align:middle line:84% Here's another example I forget where I took this picture. 00:22:17.510 --> 00:22:21.690 align:middle line:84% This one I took in Sochi in Russia at a tea plantation. 00:22:21.690 --> 00:22:22.910 align:middle line:90% They had paving stones. 00:22:22.910 --> 00:22:25.590 align:middle line:84% And I forgot about the tea and just got down and looked 00:22:25.590 --> 00:22:29.292 align:middle line:90% at them, looked at the rocks. 00:22:29.292 --> 00:22:30.750 align:middle line:84% But it happens on large scale, too. 00:22:30.750 --> 00:22:33.170 align:middle line:84% Now, we're going to talk about dune cross-stratification. 00:22:33.170 --> 00:22:37.030 align:middle line:84% Here's a horizontal surface through large scale dune 00:22:37.030 --> 00:22:38.590 align:middle line:90% cross-stratification. 00:22:38.590 --> 00:22:41.590 align:middle line:84% Here's a set of these curving laminae and another set 00:22:41.590 --> 00:22:43.210 align:middle line:90% with curving laminae this way. 00:22:43.210 --> 00:22:45.790 align:middle line:84% And the flow is like in this way somehow. 00:22:45.790 --> 00:22:48.770 align:middle line:84% So it's not as common to see as with small scale, 00:22:48.770 --> 00:22:53.430 align:middle line:84% because you need a big outcrop, a nice big outcrop, to see that. 00:22:53.430 --> 00:22:59.630 align:middle line:84% So dune cross-stratification-- same kind of diagram. 00:22:59.630 --> 00:23:02.250 align:middle line:84% Remember that at low flow velocities, 00:23:02.250 --> 00:23:04.400 align:middle line:84% dunes tend to be two-dimensional. 00:23:04.400 --> 00:23:06.150 align:middle line:84% They look the same at every cross section. 00:23:06.150 --> 00:23:08.192 align:middle line:84% And at high velocity, it's the three-dimensional. 00:23:08.192 --> 00:23:11.770 align:middle line:84% This is-- I drew this, and it's really too regular. 00:23:11.770 --> 00:23:14.880 align:middle line:84% But you can see you have these sets of foresets, 00:23:14.880 --> 00:23:17.460 align:middle line:90% which are less irregular. 00:23:17.460 --> 00:23:19.840 align:middle line:84% I think I can say less irregular than in the three 00:23:19.840 --> 00:23:21.160 align:middle line:90% dimensional case. 00:23:21.160 --> 00:23:23.000 align:middle line:90% And again, you see. 00:23:23.000 --> 00:23:28.700 align:middle line:84% I probably should have made these more sinuous, 00:23:28.700 --> 00:23:30.220 align:middle line:90% but it gives you the idea. 00:23:30.220 --> 00:23:33.340 align:middle line:84% But there's also another one of the three dimensional ripples. 00:23:33.340 --> 00:23:35.020 align:middle line:90% It's more likely than dunes. 00:23:35.020 --> 00:23:38.240 align:middle line:84% It's more likely to see 3D dunes and their structures than 2D 00:23:38.240 --> 00:23:38.740 align:middle line:90% dunes. 00:23:38.740 --> 00:23:41.560 align:middle line:84% And again, this is pretty much like what 00:23:41.560 --> 00:23:44.460 align:middle line:84% you see for ripple-- climbing ripple cross-stratification. 00:23:44.460 --> 00:23:46.240 align:middle line:90% But it's dunes, much larger. 00:23:46.240 --> 00:23:50.560 align:middle line:84% And you often see dunes, small dunes on the large dunes. 00:23:50.560 --> 00:23:53.180 align:middle line:84% If there's enough surface there and the velocity is right, 00:23:53.180 --> 00:23:54.840 align:middle line:84% it'll make dunes anywhere, including 00:23:54.840 --> 00:23:56.420 align:middle line:90% on the backs of large dunes. 00:23:56.420 --> 00:23:59.160 align:middle line:90% 00:23:59.160 --> 00:24:02.800 align:middle line:84% That's Paul Heller, Marianne Amarto, and my former student, 00:24:02.800 --> 00:24:05.120 align:middle line:84% Chris Paola, with a block that just happened 00:24:05.120 --> 00:24:07.240 align:middle line:84% to be lying there with two faces almost 00:24:07.240 --> 00:24:08.920 align:middle line:90% at right angles to each other. 00:24:08.920 --> 00:24:11.600 align:middle line:90% And I was a photographer. 00:24:11.600 --> 00:24:13.440 align:middle line:90% And so this is detail. 00:24:13.440 --> 00:24:17.060 align:middle line:84% So one side shows pretty good flow parallel 00:24:17.060 --> 00:24:19.520 align:middle line:84% or nearly full parallel cross-stratification. 00:24:19.520 --> 00:24:23.000 align:middle line:84% The other side is sort of trophy, but somewhat irregular. 00:24:23.000 --> 00:24:24.780 align:middle line:84% And I'm thinking-- just think about, 00:24:24.780 --> 00:24:26.300 align:middle line:90% what's the direction of flow? 00:24:26.300 --> 00:24:28.640 align:middle line:84% And I think, it's not straight into the board. 00:24:28.640 --> 00:24:32.100 align:middle line:84% It's probably something like this, 00:24:32.100 --> 00:24:35.580 align:middle line:84% to produce that kind of surface on both sides. 00:24:35.580 --> 00:24:42.980 align:middle line:84% Here's a close-up of a similar view of large scale trough 00:24:42.980 --> 00:24:46.580 align:middle line:84% cross-stratification, but erosional stoss, flow 00:24:46.580 --> 00:24:48.520 align:middle line:90% from right to left, obviously. 00:24:48.520 --> 00:24:50.560 align:middle line:90% And that's just 6 inches there. 00:24:50.560 --> 00:24:55.980 align:middle line:90% 00:24:55.980 --> 00:24:57.560 align:middle line:90% But how about erosion? 00:24:57.560 --> 00:25:01.020 align:middle line:84% How about depositional stoss, climbing dunes? 00:25:01.020 --> 00:25:03.495 align:middle line:84% I have seen it twice in my long life. 00:25:03.495 --> 00:25:05.120 align:middle line:84% I'm going to show you one picture here. 00:25:05.120 --> 00:25:06.995 align:middle line:84% It's very uncommon, because you don't usually 00:25:06.995 --> 00:25:12.070 align:middle line:84% get a situation, strong flow and dunes, but a very high rate 00:25:12.070 --> 00:25:13.390 align:middle line:90% of aggradation. 00:25:13.390 --> 00:25:15.090 align:middle line:90% And I'll show you a slide. 00:25:15.090 --> 00:25:19.060 align:middle line:84% This is from the Brushy Canyon in Delaware Mountains. 00:25:19.060 --> 00:25:20.810 align:middle line:84% And you can see, it's not a great picture, 00:25:20.810 --> 00:25:22.310 align:middle line:90% but it's the best one I have. 00:25:22.310 --> 00:25:26.490 align:middle line:84% You can see this dune shape like this, arching over. 00:25:26.490 --> 00:25:28.050 align:middle line:90% And this is-- that's a lens cap. 00:25:28.050 --> 00:25:29.870 align:middle line:90% So it's pretty good size. 00:25:29.870 --> 00:25:32.450 align:middle line:84% I think there's a turbidite basin. 00:25:32.450 --> 00:25:35.830 align:middle line:84% I think there was a pre-existing hollow, good sized hollow, 00:25:35.830 --> 00:25:38.550 align:middle line:90% which got filled during-- 00:25:38.550 --> 00:25:41.350 align:middle line:84% the ripples were still moving in there, but the rate of climb, 00:25:41.350 --> 00:25:45.190 align:middle line:84% because the accumulation of sediment in the depression, 00:25:45.190 --> 00:25:48.510 align:middle line:84% was high enough to make a depositional stoss-- very 00:25:48.510 --> 00:25:49.990 align:middle line:90% uncommon. 00:25:49.990 --> 00:25:51.010 align:middle line:90% This is a nice cut. 00:25:51.010 --> 00:25:53.358 align:middle line:84% We did this in the Arkansas River, the flow. 00:25:53.358 --> 00:25:54.650 align:middle line:90% And we knew the flow direction. 00:25:54.650 --> 00:25:55.710 align:middle line:90% It was a sidebar. 00:25:55.710 --> 00:25:56.590 align:middle line:90% It's this way. 00:25:56.590 --> 00:25:59.750 align:middle line:84% And you see the standard erosional stoss, large scale 00:25:59.750 --> 00:26:07.510 align:middle line:84% erosional stoss, and the flow perpendicular troughiness 00:26:07.510 --> 00:26:10.400 align:middle line:90% of the dunes. 00:26:10.400 --> 00:26:15.040 align:middle line:84% This is a close-up of that last slide. 00:26:15.040 --> 00:26:18.800 align:middle line:84% It's just a classic kind of trough cross-stratification. 00:26:18.800 --> 00:26:20.560 align:middle line:84% And there's even a detail of the detail 00:26:20.560 --> 00:26:22.760 align:middle line:84% if you want to see what it really looks like. 00:26:22.760 --> 00:26:26.820 align:middle line:84% And I won't go into it, but I always like that photo. 00:26:26.820 --> 00:26:30.320 align:middle line:84% And here's some stuff in the ancient 00:26:30.320 --> 00:26:34.000 align:middle line:84% that's clearly trough cross-stratification, 00:26:34.000 --> 00:26:38.000 align:middle line:84% but not always easily perceivable. 00:26:38.000 --> 00:26:39.220 align:middle line:90% Now, the Nubian Sandstone. 00:26:39.220 --> 00:26:40.720 align:middle line:84% I don't know much about it, but it's 00:26:40.720 --> 00:26:43.180 align:middle line:84% known to be a subaqueous deposit. 00:26:43.180 --> 00:26:44.600 align:middle line:90% It's marine sandstone. 00:26:44.600 --> 00:26:46.040 align:middle line:90% And look at these sets. 00:26:46.040 --> 00:26:49.640 align:middle line:84% They could be called planar tabular sets, 00:26:49.640 --> 00:26:53.760 align:middle line:84% but with regular foresets, erosional foresets. 00:26:53.760 --> 00:26:59.840 align:middle line:84% And I'm guessing that was made by relatively low velocity 2D 00:26:59.840 --> 00:27:02.420 align:middle line:84% dunes, rather than 3D irregular dunes, 00:27:02.420 --> 00:27:08.380 align:middle line:84% which would produce a lot of variability in set settings. 00:27:08.380 --> 00:27:11.540 align:middle line:84% I like this because you get of the two little sets 00:27:11.540 --> 00:27:13.360 align:middle line:84% with stratification this way and this side, 00:27:13.360 --> 00:27:15.360 align:middle line:84% and although you can't see it well on this side. 00:27:15.360 --> 00:27:16.320 align:middle line:90% So it's coming right out. 00:27:16.320 --> 00:27:17.760 align:middle line:84% The flow is coming right out at you. 00:27:17.760 --> 00:27:18.927 align:middle line:90% Does that make sense to you? 00:27:18.927 --> 00:27:22.460 align:middle line:90% 00:27:22.460 --> 00:27:26.380 align:middle line:84% I took this close-up to show how the foreset laminae come down 00:27:26.380 --> 00:27:29.880 align:middle line:84% and flare out into the trough very nicely. 00:27:29.880 --> 00:27:33.060 align:middle line:84% And, of course, there's erosion there at that surface. 00:27:33.060 --> 00:27:35.940 align:middle line:90% That's pretty large-scale. 00:27:35.940 --> 00:27:39.240 align:middle line:90% Another example, pretty classic. 00:27:39.240 --> 00:27:42.300 align:middle line:90% 00:27:42.300 --> 00:27:44.100 align:middle line:90% Now, look at this. 00:27:44.100 --> 00:27:48.860 align:middle line:84% And you should see by now that looks fishy, right? 00:27:48.860 --> 00:27:50.220 align:middle line:90% This was a block. 00:27:50.220 --> 00:27:51.320 align:middle line:90% And you turn upside down. 00:27:51.320 --> 00:27:52.380 align:middle line:90% Now it looks right. 00:27:52.380 --> 00:27:57.220 align:middle line:84% So it's easy to spot when you attune your eye to it. 00:27:57.220 --> 00:27:58.537 align:middle line:90% I just-- I'll mention this. 00:27:58.537 --> 00:28:00.620 align:middle line:84% One thing that's nice to know would be, how do you 00:28:00.620 --> 00:28:01.880 align:middle line:90% get the bedform height? 00:28:01.880 --> 00:28:03.620 align:middle line:84% How do you back out the bedform height 00:28:03.620 --> 00:28:05.840 align:middle line:84% from what you see in the cross-stratification? 00:28:05.840 --> 00:28:07.620 align:middle line:84% And it seems like a difficult problem. 00:28:07.620 --> 00:28:10.270 align:middle line:84% But my former student, Chris Paola, 00:28:10.270 --> 00:28:12.520 align:middle line:84% and his colleague in the math department at University 00:28:12.520 --> 00:28:16.080 align:middle line:84% of Minnesota wrote a paper back, quite some time ago, 00:28:16.080 --> 00:28:19.680 align:middle line:84% developing the idea that the average set thickness is only 00:28:19.680 --> 00:28:22.460 align:middle line:84% slightly less than the average bedform height 00:28:22.460 --> 00:28:24.720 align:middle line:84% and not very sensitive to the angle of climb. 00:28:24.720 --> 00:28:25.740 align:middle line:90% And I read the paper. 00:28:25.740 --> 00:28:26.900 align:middle line:90% I can be convinced by it. 00:28:26.900 --> 00:28:27.900 align:middle line:90% But that's nice to know. 00:28:27.900 --> 00:28:29.720 align:middle line:84% You can back out the size of the bedform 00:28:29.720 --> 00:28:31.820 align:middle line:84% just by looking at the cross-stratification, 00:28:31.820 --> 00:28:33.600 align:middle line:84% no matter what the angle of climb is. 00:28:33.600 --> 00:28:36.540 align:middle line:84% Well, how about backing out flow depth from cross tread? 00:28:36.540 --> 00:28:37.620 align:middle line:90% How do you do that? 00:28:37.620 --> 00:28:39.480 align:middle line:84% Well, for ripples, you can't do it 00:28:39.480 --> 00:28:42.960 align:middle line:84% because, as I mentioned to you in the last presentation, 00:28:42.960 --> 00:28:46.720 align:middle line:84% the size of ripples is almost independent of flow depth 00:28:46.720 --> 00:28:48.640 align:middle line:84% unless the flow is really shallow 00:28:48.640 --> 00:28:51.480 align:middle line:90% and make for little ripples. 00:28:51.480 --> 00:28:52.820 align:middle line:90% They do vary with grain size. 00:28:52.820 --> 00:28:55.760 align:middle line:84% I think I mentioned they're somewhat longer spacing 00:28:55.760 --> 00:28:57.340 align:middle line:90% for coarser grain sizes. 00:28:57.340 --> 00:29:00.280 align:middle line:84% But with dunes, there's general agreement 00:29:00.280 --> 00:29:02.740 align:middle line:84% that if you look at the ratio of flow depth to dune height, 00:29:02.740 --> 00:29:07.310 align:middle line:84% it's around 7, which makes us-- if they're at equilibrium. 00:29:07.310 --> 00:29:09.750 align:middle line:84% And so that gives you a handle on how deep the flow was 00:29:09.750 --> 00:29:12.490 align:middle line:84% when you see the dune height, which you would see 00:29:12.490 --> 00:29:14.570 align:middle line:90% from the cross stratification. 00:29:14.570 --> 00:29:16.790 align:middle line:90% I mean, that's-- backing out. 00:29:16.790 --> 00:29:18.370 align:middle line:84% Now, I'm not going to say anything 00:29:18.370 --> 00:29:19.870 align:middle line:84% about antidune cross-stratification. 00:29:19.870 --> 00:29:21.770 align:middle line:90% I don't have any photographs. 00:29:21.770 --> 00:29:26.010 align:middle line:84% But it's reported in the literature, and it does happen. 00:29:26.010 --> 00:29:30.470 align:middle line:84% Here's a case-- here's a flow, supercritical flow. 00:29:30.470 --> 00:29:33.450 align:middle line:84% And the waves are moving, are migrating 00:29:33.450 --> 00:29:35.250 align:middle line:90% upstream, not downstream. 00:29:35.250 --> 00:29:40.490 align:middle line:84% And the bed geometry is going along with the upstream, 00:29:40.490 --> 00:29:41.690 align:middle line:90% moving antidunes. 00:29:41.690 --> 00:29:47.130 align:middle line:84% And you're leaving foresets going upstream. 00:29:47.130 --> 00:29:48.670 align:middle line:84% Then eventually, the waves break. 00:29:48.670 --> 00:29:51.250 align:middle line:84% This gets messed up, and it doesn't preserve them 00:29:51.250 --> 00:29:51.990 align:middle line:90% all that well. 00:29:51.990 --> 00:29:55.470 align:middle line:84% And I've never gotten a photograph of one, 00:29:55.470 --> 00:29:59.410 align:middle line:90% so I can't help you with that. 00:29:59.410 --> 00:30:01.220 align:middle line:90% You often see this at the beach. 00:30:01.220 --> 00:30:04.580 align:middle line:84% A small stream flows across the beach to the water. 00:30:04.580 --> 00:30:08.920 align:middle line:84% And it's high Froude number flow, fast flow, shallow depth. 00:30:08.920 --> 00:30:10.318 align:middle line:84% And you get these standing waves. 00:30:10.318 --> 00:30:11.860 align:middle line:84% Sometimes they're standing, sometimes 00:30:11.860 --> 00:30:13.340 align:middle line:90% they're migrating upstream. 00:30:13.340 --> 00:30:16.140 align:middle line:84% And they break, and then they reform. 00:30:16.140 --> 00:30:17.700 align:middle line:90% Those are antidunes. 00:30:17.700 --> 00:30:20.360 align:middle line:84% They're not a major part of the stratigraphic record. 00:30:20.360 --> 00:30:22.900 align:middle line:84% So now we have to talk about oscillatory flow features. 00:30:22.900 --> 00:30:25.540 align:middle line:84% So remember this-- there's UM, that's 00:30:25.540 --> 00:30:28.020 align:middle line:84% the maximum velocity during an oscillation, 00:30:28.020 --> 00:30:31.260 align:middle line:84% period T of the oscillation, and D0, 00:30:31.260 --> 00:30:33.520 align:middle line:84% which is the orbital diameter, how far it moves. 00:30:33.520 --> 00:30:36.980 align:middle line:84% And only two of those are independent of each other. 00:30:36.980 --> 00:30:39.060 align:middle line:84% The third depends on the other two. 00:30:39.060 --> 00:30:42.580 align:middle line:84% And so we did this with bed configurations. 00:30:42.580 --> 00:30:45.940 align:middle line:84% And sometimes you see a vertical climb. 00:30:45.940 --> 00:30:48.900 align:middle line:84% You'd think it'd be very common, but it isn't common at all. 00:30:48.900 --> 00:30:54.260 align:middle line:84% I've seen it just a few times in my field observations. 00:30:54.260 --> 00:30:54.940 align:middle line:90% Why? 00:30:54.940 --> 00:30:55.580 align:middle line:90% Why not? 00:30:55.580 --> 00:30:57.120 align:middle line:90% I can think of two reasons. 00:30:57.120 --> 00:31:00.080 align:middle line:84% You think about reasons why, even 00:31:00.080 --> 00:31:01.980 align:middle line:90% in purely unidirectional flow-- 00:31:01.980 --> 00:31:03.920 align:middle line:84% Do you remember I told you that, because 00:31:03.920 --> 00:31:07.620 align:middle line:84% of the asymmetry of the oscillation, fast and strong, 00:31:07.620 --> 00:31:11.060 align:middle line:84% one way, slow and weak the other way to make an oscillation? 00:31:11.060 --> 00:31:13.800 align:middle line:84% So the sediment transport rate and shoaling waves 00:31:13.800 --> 00:31:15.240 align:middle line:90% is toward the beach. 00:31:15.240 --> 00:31:18.400 align:middle line:84% And so that could cause the ripples to climb 00:31:18.400 --> 00:31:23.160 align:middle line:90% at some non-vertical angle. 00:31:23.160 --> 00:31:26.575 align:middle line:90% And that's very common. 00:31:26.575 --> 00:31:28.200 align:middle line:84% The other is, of course, you can always 00:31:28.200 --> 00:31:30.218 align:middle line:84% have a slight unidirectional flow component. 00:31:30.218 --> 00:31:31.760 align:middle line:84% And how would you tell the difference 00:31:31.760 --> 00:31:34.218 align:middle line:90% between the one and the other? 00:31:34.218 --> 00:31:34.760 align:middle line:90% I don't know. 00:31:34.760 --> 00:31:37.440 align:middle line:84% Maybe other things about the section 00:31:37.440 --> 00:31:39.620 align:middle line:84% might be able to tip you off on that. 00:31:39.620 --> 00:31:41.600 align:middle line:84% But it's not an easy thing to deal with. 00:31:41.600 --> 00:31:43.020 align:middle line:90% I showed you this before. 00:31:43.020 --> 00:31:46.240 align:middle line:84% This is from the Wappinger Cambrian in New York, 00:31:46.240 --> 00:31:48.360 align:middle line:90% in the Hudson Valley. 00:31:48.360 --> 00:31:51.540 align:middle line:84% And it's pretty clear they're oscillation ripples. 00:31:51.540 --> 00:31:54.240 align:middle line:84% But they're moving because you can see the laminae inside them. 00:31:54.240 --> 00:31:57.940 align:middle line:84% Almost symmetrical, but they're shifting. 00:31:57.940 --> 00:32:00.400 align:middle line:84% Another example, close-up, the same kind of thing. 00:32:00.400 --> 00:32:03.860 align:middle line:84% We can be pretty sure they're oscillation ripples. 00:32:03.860 --> 00:32:05.740 align:middle line:84% This is one of the few places I've ever 00:32:05.740 --> 00:32:09.260 align:middle line:84% seen where the ripples really are climbing vertically 00:32:09.260 --> 00:32:10.580 align:middle line:90% for a long distance. 00:32:10.580 --> 00:32:12.420 align:middle line:84% Now, it's not a matter of draping, 00:32:12.420 --> 00:32:15.100 align:middle line:84% because if they were draped, they'd die out much more rapidly 00:32:15.100 --> 00:32:15.760 align:middle line:90% upward. 00:32:15.760 --> 00:32:17.820 align:middle line:84% So these really are, whatever the environment 00:32:17.820 --> 00:32:21.020 align:middle line:84% is, whatever the oscillatory environment is, they're 00:32:21.020 --> 00:32:23.740 align:middle line:90% climbing almost vertically. 00:32:23.740 --> 00:32:25.820 align:middle line:90% But I've seldom seen that. 00:32:25.820 --> 00:32:28.820 align:middle line:84% Here's another example from the Ferron in Utah. 00:32:28.820 --> 00:32:31.100 align:middle line:84% And they're climbing at a pretty steep angle, 00:32:31.100 --> 00:32:34.007 align:middle line:90% but that's very uncommon. 00:32:34.007 --> 00:32:35.840 align:middle line:84% It's more common to see something like this. 00:32:35.840 --> 00:32:37.660 align:middle line:84% They're clearly oscillation ripples. 00:32:37.660 --> 00:32:41.020 align:middle line:90% They're depositional stoss. 00:32:41.020 --> 00:32:46.020 align:middle line:84% And in this case, their angle of climb 00:32:46.020 --> 00:32:49.540 align:middle line:84% suggests that it's because it's combined flow, rather than 00:32:49.540 --> 00:32:53.700 align:middle line:90% a purely unidirectional flow. 00:32:53.700 --> 00:32:55.710 align:middle line:84% This is one of my favorite photographs. 00:32:55.710 --> 00:32:59.230 align:middle line:90% It's also from the Moenkopi. 00:32:59.230 --> 00:33:01.050 align:middle line:84% So there they are, climbing, climbing, 00:33:01.050 --> 00:33:04.630 align:middle line:84% climbing, for a long distance throughout this deposition 00:33:04.630 --> 00:33:05.250 align:middle line:90% of the bed. 00:33:05.250 --> 00:33:07.750 align:middle line:84% Flow conditions stayed pretty much the same for a long time, 00:33:07.750 --> 00:33:08.610 align:middle line:90% in that case. 00:33:08.610 --> 00:33:11.310 align:middle line:90% 00:33:11.310 --> 00:33:13.830 align:middle line:84% I showed you this already, and I mentioned to you 00:33:13.830 --> 00:33:16.930 align:middle line:84% that it looks fishy to be current ripples. 00:33:16.930 --> 00:33:24.670 align:middle line:84% And I'm pretty sure that's it's either oscillation influenced, 00:33:24.670 --> 00:33:27.750 align:middle line:84% as well as unidirectional influence 00:33:27.750 --> 00:33:32.750 align:middle line:90% at a medium angle of climb. 00:33:32.750 --> 00:33:34.510 align:middle line:90% That's a close-up. 00:33:34.510 --> 00:33:38.692 align:middle line:84% So you can see exactly what I'm talking about. 00:33:38.692 --> 00:33:40.150 align:middle line:84% I think I showed you this, too, now 00:33:40.150 --> 00:33:41.750 align:middle line:84% that we're coming to unidirectional 00:33:41.750 --> 00:33:43.190 align:middle line:90% versus oscillatory. 00:33:43.190 --> 00:33:48.270 align:middle line:84% I'm guessing that's in between oscillatory unidirectional 00:33:48.270 --> 00:33:49.090 align:middle line:90% influence. 00:33:49.090 --> 00:33:50.670 align:middle line:90% That's my guess. 00:33:50.670 --> 00:33:53.880 align:middle line:84% But I can't pin it down particularly, either. 00:33:53.880 --> 00:33:59.840 align:middle line:84% All right, now, I'm dealing with how 00:33:59.840 --> 00:34:02.280 align:middle line:84% you can tell between unidirectional flow, 00:34:02.280 --> 00:34:05.720 align:middle line:84% depositional source, climbing ripple, and combined flow 00:34:05.720 --> 00:34:07.840 align:middle line:84% climbing ripples without erosion. 00:34:07.840 --> 00:34:10.800 align:middle line:84% And the only thing I can think of is try to look at the profile 00:34:10.800 --> 00:34:13.480 align:middle line:84% and see whether it looks like unidirectional flow ripples 00:34:13.480 --> 00:34:15.020 align:middle line:90% or oscillatory flow ripples. 00:34:15.020 --> 00:34:20.179 align:middle line:84% And when you have deposition in the stoss, on the stoss, 00:34:20.179 --> 00:34:24.120 align:middle line:84% as well as in the lee, you can do that. 00:34:24.120 --> 00:34:27.679 align:middle line:84% But it's not all that common to be able to do that. 00:34:27.679 --> 00:34:32.105 align:middle line:84% So is this combined flow, or is it unidirectional flow? 00:34:32.105 --> 00:34:33.480 align:middle line:84% And you look at it, and from what 00:34:33.480 --> 00:34:35.219 align:middle line:84% I've said, oh, that's unidirectional-- 00:34:35.219 --> 00:34:37.040 align:middle line:84% that's unidirectional flow climbing 00:34:37.040 --> 00:34:38.540 align:middle line:90% ripple cross-stratification. 00:34:38.540 --> 00:34:40.479 align:middle line:84% But from what I've just said, you 00:34:40.479 --> 00:34:43.800 align:middle line:84% have the suspicion that maybe it's combined flow. 00:34:43.800 --> 00:34:45.760 align:middle line:84% And I don't see any way of telling. 00:34:45.760 --> 00:34:48.420 align:middle line:84% And yet, combined flow features must be pretty common, 00:34:48.420 --> 00:34:51.340 align:middle line:84% which I'm going to talk about soon if I have the time. 00:34:51.340 --> 00:34:56.460 align:middle line:84% Here's another example from the Moenkopi, same problem. 00:34:56.460 --> 00:34:59.000 align:middle line:84% It's nice to think that it's always unidirectional flow, 00:34:59.000 --> 00:35:00.480 align:middle line:84% but it doesn't have to be that way. 00:35:00.480 --> 00:35:03.540 align:middle line:90% 00:35:03.540 --> 00:35:06.860 align:middle line:84% And the other thing is, we see climbing oscillatory flow 00:35:06.860 --> 00:35:07.420 align:middle line:90% bedforms. 00:35:07.420 --> 00:35:11.500 align:middle line:84% And they're usually on a small scale, not on a large scale. 00:35:11.500 --> 00:35:13.820 align:middle line:84% And I'm going to get to that presently when we talk 00:35:13.820 --> 00:35:18.740 align:middle line:90% about combined flow features. 00:35:18.740 --> 00:35:22.460 align:middle line:84% So I'm going to repeat a slide that I 00:35:22.460 --> 00:35:28.020 align:middle line:84% showed last time, a graph, a diagram, that you may remember. 00:35:28.020 --> 00:35:32.600 align:middle line:84% And it's orbital velocity versus oscillation period. 00:35:32.600 --> 00:35:34.480 align:middle line:84% And you can see that in the lower left, 00:35:34.480 --> 00:35:42.100 align:middle line:90% this is for weak flows. 00:35:42.100 --> 00:35:44.247 align:middle line:84% The ripples are small, and they're 00:35:44.247 --> 00:35:46.080 align:middle line:84% three-dimensional-- they're two-dimensional. 00:35:46.080 --> 00:35:48.420 align:middle line:84% But above this line, they become larger, 00:35:48.420 --> 00:35:50.230 align:middle line:84% and they become three-dimensional. 00:35:50.230 --> 00:35:54.830 align:middle line:84% Now, so it's down in here that we usually see these small scale 00:35:54.830 --> 00:35:55.770 align:middle line:90% oscillation ripples. 00:35:55.770 --> 00:35:57.030 align:middle line:90% And they're understandable. 00:35:57.030 --> 00:36:02.030 align:middle line:84% But this is-- it's not exactly terra incognita, 00:36:02.030 --> 00:36:03.550 align:middle line:90% but it's close to it. 00:36:03.550 --> 00:36:06.005 align:middle line:84% And we know the bedforms exist because they've 00:36:06.005 --> 00:36:07.630 align:middle line:84% been observed in many flume experiments 00:36:07.630 --> 00:36:09.330 align:middle line:84% and in some natural environments. 00:36:09.330 --> 00:36:11.070 align:middle line:84% And we know they're three-dimensional. 00:36:11.070 --> 00:36:13.930 align:middle line:84% So what kind of stratification do they present? 00:36:13.930 --> 00:36:16.550 align:middle line:90% 00:36:16.550 --> 00:36:18.910 align:middle line:84% That's where we get the hummocky cross-stratification. 00:36:18.910 --> 00:36:24.350 align:middle line:84% This is a term that's been around since the 1970s. 00:36:24.350 --> 00:36:26.110 align:middle line:84% It's a kind of medium scale to large scale 00:36:26.110 --> 00:36:28.430 align:middle line:84% cross-stratification, which I think, 00:36:28.430 --> 00:36:29.990 align:middle line:84% and I think most people think, it's 00:36:29.990 --> 00:36:32.850 align:middle line:84% produced by oscillatory bedforms during aggregation. 00:36:32.850 --> 00:36:35.150 align:middle line:84% But they're large in a three-dimensional. 00:36:35.150 --> 00:36:39.270 align:middle line:90% 00:36:39.270 --> 00:36:43.470 align:middle line:84% Aggradation in the presence of 3D large oscillation ripples 00:36:43.470 --> 00:36:47.050 align:middle line:84% and what we're dealing with here. 00:36:47.050 --> 00:36:49.410 align:middle line:84% It's been controversial, but the general belief 00:36:49.410 --> 00:36:52.670 align:middle line:84% is it's purely oscillation-dominant flow. 00:36:52.670 --> 00:36:55.750 align:middle line:84% I showed you my favorite outcrop last time. 00:36:55.750 --> 00:36:59.690 align:middle line:84% Remember that 45 degree dipping bedding surface, 00:36:59.690 --> 00:37:02.330 align:middle line:84% where the hummocky-- where the hummocks and swales arranged 00:37:02.330 --> 00:37:02.950 align:middle line:90% around it. 00:37:02.950 --> 00:37:04.350 align:middle line:90% And they're all very isotropic. 00:37:04.350 --> 00:37:06.370 align:middle line:84% They're not moving in one direction or another. 00:37:06.370 --> 00:37:08.890 align:middle line:90% And so we know that happens. 00:37:08.890 --> 00:37:11.050 align:middle line:84% It was a purely oscillatory flow produced 00:37:11.050 --> 00:37:14.210 align:middle line:84% these large, three-dimensional hummocky valley bed 00:37:14.210 --> 00:37:15.570 align:middle line:90% configurations. 00:37:15.570 --> 00:37:19.130 align:middle line:84% And I wish that I had gone around the corner 00:37:19.130 --> 00:37:22.610 align:middle line:84% and taken a picture of the section through that bed. 00:37:22.610 --> 00:37:24.470 align:middle line:84% We saw only the top surface of it. 00:37:24.470 --> 00:37:28.030 align:middle line:84% And it was classic, medium-scale hummocky cross-stratification. 00:37:28.030 --> 00:37:30.410 align:middle line:84% So that tips me off that maybe everything 00:37:30.410 --> 00:37:34.130 align:middle line:90% we're talking about across-- 00:37:34.130 --> 00:37:36.890 align:middle line:84% everything we're talking about, oscillatory flow 00:37:36.890 --> 00:37:40.970 align:middle line:84% cross-stratification, involves large 3D bedforms aggrading 00:37:40.970 --> 00:37:42.150 align:middle line:90% in various ways. 00:37:42.150 --> 00:37:43.910 align:middle line:84% And I'm going to go through some slides. 00:37:43.910 --> 00:37:47.340 align:middle line:84% I might not get to combine flow features right now. 00:37:47.340 --> 00:37:51.340 align:middle line:90% 00:37:51.340 --> 00:37:55.540 align:middle line:84% Irregular shifting, but isotropic shifting. 00:37:55.540 --> 00:37:58.220 align:middle line:84% Now, there's a term swaly cross-stratification. 00:37:58.220 --> 00:38:00.120 align:middle line:84% They usually spell it with an E in there, 00:38:00.120 --> 00:38:02.140 align:middle line:84% and I don't like that, because it's like shaly. 00:38:02.140 --> 00:38:05.340 align:middle line:84% We spell chailey without the E. But anyway-- 00:38:05.340 --> 00:38:07.060 align:middle line:84% and they think of it as something else, 00:38:07.060 --> 00:38:08.520 align:middle line:90% SCS instead of HDS. 00:38:08.520 --> 00:38:12.140 align:middle line:84% To me, there's a gradation between SCS and HCS 00:38:12.140 --> 00:38:14.300 align:middle line:84% depending on the rate of aggradation 00:38:14.300 --> 00:38:16.440 align:middle line:84% relative to the shifting of the bedforms. 00:38:16.440 --> 00:38:18.140 align:middle line:84% If the rate of aggradation is slow 00:38:18.140 --> 00:38:19.940 align:middle line:84% and they're acting that way, you're 00:38:19.940 --> 00:38:22.020 align:middle line:84% going to see lots of trough fillings 00:38:22.020 --> 00:38:23.980 align:middle line:84% and very little by way of swales. 00:38:23.980 --> 00:38:25.960 align:middle line:84% But for a higher rate of aggradation, 00:38:25.960 --> 00:38:28.440 align:middle line:84% you're going to see not just erosion in the troughs, 00:38:28.440 --> 00:38:32.840 align:middle line:84% but you also see deposition over the crest of the swales. 00:38:32.840 --> 00:38:34.800 align:middle line:84% This is the classic block diagram. 00:38:34.800 --> 00:38:39.140 align:middle line:84% We gave a short course way back in 1975, John Harms was the one. 00:38:39.140 --> 00:38:40.760 align:middle line:90% He originated this term. 00:38:40.760 --> 00:38:44.720 align:middle line:84% He was the first to perceive that it's a distinctive style 00:38:44.720 --> 00:38:46.300 align:middle line:90% of cross-stratification. 00:38:46.300 --> 00:38:48.240 align:middle line:84% And he thought about how it would happen. 00:38:48.240 --> 00:38:52.040 align:middle line:84% And in later years, he would say, 00:38:52.040 --> 00:38:55.400 align:middle line:84% there are people nowadays who make their careers out of HCS. 00:38:55.400 --> 00:38:57.280 align:middle line:84% But he was the one who started it. 00:38:57.280 --> 00:39:01.280 align:middle line:84% It's an illustration of that there's a saying, 00:39:01.280 --> 00:39:03.280 align:middle line:84% I wouldn't have believed it if I hadn't seen it. 00:39:03.280 --> 00:39:05.405 align:middle line:84% You can reverse it and say, I wouldn't have seen it 00:39:05.405 --> 00:39:06.680 align:middle line:90% if I hadn't believed it. 00:39:06.680 --> 00:39:08.560 align:middle line:84% Everybody was seeing HCS, but they never 00:39:08.560 --> 00:39:11.920 align:middle line:84% gave any particular credence or significance to it 00:39:11.920 --> 00:39:14.240 align:middle line:84% until somebody, Harms, came along and realized 00:39:14.240 --> 00:39:16.980 align:middle line:84% this is a very specific kind of depositional model. 00:39:16.980 --> 00:39:18.580 align:middle line:90% So that's what HDS is now. 00:39:18.580 --> 00:39:21.720 align:middle line:84% And everybody is seeing it, whereas nobody saw it before. 00:39:21.720 --> 00:39:24.160 align:middle line:84% And one of the prime characteristics 00:39:24.160 --> 00:39:27.840 align:middle line:84% is you have places where conformable laminae end up 00:39:27.840 --> 00:39:30.640 align:middle line:84% going into a truncation surface and then maybe back 00:39:30.640 --> 00:39:31.860 align:middle line:90% out into conformity. 00:39:31.860 --> 00:39:32.760 align:middle line:90% That's if you see-- 00:39:32.760 --> 00:39:37.090 align:middle line:84% that's a tip off that we're dealing with HCS. 00:39:37.090 --> 00:39:38.340 align:middle line:90% That's what I just showed you. 00:39:38.340 --> 00:39:41.000 align:middle line:84% But also, we see places where hummocks 00:39:41.000 --> 00:39:43.140 align:middle line:84% turn into swales during deposition 00:39:43.140 --> 00:39:45.340 align:middle line:84% and where swales turn into hummocks. 00:39:45.340 --> 00:39:46.720 align:middle line:90% I got that right-- yeah, right. 00:39:46.720 --> 00:39:48.040 align:middle line:90% That's very characteristic. 00:39:48.040 --> 00:39:50.040 align:middle line:84% And I can show you some photos pretty soon. 00:39:50.040 --> 00:39:50.920 align:middle line:90% Let's ignore this. 00:39:50.920 --> 00:39:53.980 align:middle line:84% This was an attempt on my part, some years ago, 00:39:53.980 --> 00:39:58.980 align:middle line:84% to organize everything about HCS and other oscillatory 00:39:58.980 --> 00:40:00.660 align:middle line:90% flow, large scale bedforms. 00:40:00.660 --> 00:40:03.420 align:middle line:84% It doesn't quite work, because I can't draw the sketch as well. 00:40:03.420 --> 00:40:05.867 align:middle line:84% And I invite you to look at it if you want to look at it. 00:40:05.867 --> 00:40:07.200 align:middle line:90% So let's get on to other things. 00:40:07.200 --> 00:40:10.860 align:middle line:84% OK, here's the swale going to a hummock. 00:40:10.860 --> 00:40:12.820 align:middle line:90% It happens. 00:40:12.820 --> 00:40:17.980 align:middle line:84% Here's a hummock growing from a flat surface, planar surface. 00:40:17.980 --> 00:40:23.580 align:middle line:84% Here's a nice, big, broad hummock all by itself. 00:40:23.580 --> 00:40:25.440 align:middle line:84% Here's a swale going into planar. 00:40:25.440 --> 00:40:29.260 align:middle line:90% 00:40:29.260 --> 00:40:34.340 align:middle line:84% Here's a hummock going into a swale with the same kind 00:40:34.340 --> 00:40:37.500 align:middle line:84% of thing-- from conformable to truncation 00:40:37.500 --> 00:40:39.270 align:middle line:90% to conformable over there. 00:40:39.270 --> 00:40:40.690 align:middle line:90% That's another tip off. 00:40:40.690 --> 00:40:43.847 align:middle line:84% When you see that kind of thing, you must be dealing with HCS. 00:40:43.847 --> 00:40:45.430 align:middle line:84% There's a hummock going into-- there's 00:40:45.430 --> 00:40:49.190 align:middle line:90% a swale going into a hummock. 00:40:49.190 --> 00:40:53.950 align:middle line:84% And a hummock going into a swale with erosion, 00:40:53.950 --> 00:40:56.250 align:middle line:84% trailing off into conformity over that way. 00:40:56.250 --> 00:40:57.370 align:middle line:90% That's very common. 00:40:57.370 --> 00:41:00.510 align:middle line:90% 00:41:00.510 --> 00:41:02.470 align:middle line:84% I carried this out of the Wood Canyon 00:41:02.470 --> 00:41:06.130 align:middle line:84% Formation in the Southern end of the Nopah range once. 00:41:06.130 --> 00:41:07.990 align:middle line:90% And it's not that big. 00:41:07.990 --> 00:41:09.790 align:middle line:84% It was heavy, but I could carry it out. 00:41:09.790 --> 00:41:12.350 align:middle line:84% It shows medium scale, hummocky swale 00:41:12.350 --> 00:41:14.052 align:middle line:90% topography on the bed surface. 00:41:14.052 --> 00:41:15.510 align:middle line:84% This is from the Wood Canyon, right 00:41:15.510 --> 00:41:17.870 align:middle line:84% at the precambrian-cambrian boundary. 00:41:17.870 --> 00:41:20.330 align:middle line:84% And although you can't see it very well in this picture, 00:41:20.330 --> 00:41:23.830 align:middle line:84% it shows medium scale hummocky cross-stratification. 00:41:23.830 --> 00:41:26.312 align:middle line:84% I was going to bring it, but I can't find it. 00:41:26.312 --> 00:41:28.270 align:middle line:84% It's somewhere around the house or in the barn, 00:41:28.270 --> 00:41:29.490 align:middle line:90% and I couldn't find it. 00:41:29.490 --> 00:41:32.750 align:middle line:84% But it's one of my prized possessions. 00:41:32.750 --> 00:41:36.290 align:middle line:84% Here's a better view of the cross-stratification, 00:41:36.290 --> 00:41:40.960 align:middle line:84% which looked like medium-scale cross-stratification. 00:41:40.960 --> 00:41:43.520 align:middle line:84% This is the classic John Harms photo 00:41:43.520 --> 00:41:44.860 align:middle line:90% when he developed the concept. 00:41:44.860 --> 00:41:47.580 align:middle line:84% He showed this photo in the short course we gave. 00:41:47.580 --> 00:41:50.280 align:middle line:90% 00:41:50.280 --> 00:41:51.860 align:middle line:90% This is very characteristic. 00:41:51.860 --> 00:41:55.040 align:middle line:84% You can see truncation surfaces going into conformity 00:41:55.040 --> 00:41:58.815 align:middle line:84% and being overtopped by another hummock. 00:41:58.815 --> 00:41:59.940 align:middle line:90% This is pretty large-scale. 00:41:59.940 --> 00:42:00.982 align:middle line:90% I mean, this is 6-inches. 00:42:00.982 --> 00:42:03.800 align:middle line:84% So this is, like, this is meter plus 00:42:03.800 --> 00:42:07.400 align:middle line:90% scale we're dealing with here. 00:42:07.400 --> 00:42:09.960 align:middle line:84% Same kind of thing-- look at this, conformability 00:42:09.960 --> 00:42:13.760 align:middle line:84% into truncation and then back into conformity over here 00:42:13.760 --> 00:42:15.760 align:middle line:84% because of the way those hummocks and swales are 00:42:15.760 --> 00:42:17.180 align:middle line:90% interacting with one another. 00:42:17.180 --> 00:42:20.920 align:middle line:90% 00:42:20.920 --> 00:42:23.800 align:middle line:84% A swale overtopped by a hummock and another hummock 00:42:23.800 --> 00:42:29.740 align:middle line:84% on top with that same erosion surface, truncation going on. 00:42:29.740 --> 00:42:33.160 align:middle line:90% 00:42:33.160 --> 00:42:36.260 align:middle line:90% Even more classic HCS-- 00:42:36.260 --> 00:42:39.460 align:middle line:84% conformability into truncation, and probably back 00:42:39.460 --> 00:42:41.700 align:middle line:90% to conformability over there. 00:42:41.700 --> 00:42:43.780 align:middle line:84% When you see that, that's a tip-off. 00:42:43.780 --> 00:42:47.180 align:middle line:84% This is from the Johnnie formation in the Nopah range 00:42:47.180 --> 00:42:48.300 align:middle line:90% in California. 00:42:48.300 --> 00:42:51.120 align:middle line:84% And a lot of indistinct planar lamination, 00:42:51.120 --> 00:42:52.800 align:middle line:84% but then it got hummocky and swaley. 00:42:52.800 --> 00:42:55.100 align:middle line:84% But then it stopped over top, I guess 00:42:55.100 --> 00:42:57.480 align:middle line:84% I should say, by planar lamination again. 00:42:57.480 --> 00:43:00.180 align:middle line:84% As the current velocity changes, as the water 00:43:00.180 --> 00:43:04.740 align:middle line:84% flow velocity changes, you can go from one to the other. 00:43:04.740 --> 00:43:08.200 align:middle line:84% This is more like what they call swaley cross-stratification. 00:43:08.200 --> 00:43:11.960 align:middle line:84% You see a fair number of hummocky-looking features, 00:43:11.960 --> 00:43:13.220 align:middle line:90% shallow features. 00:43:13.220 --> 00:43:15.840 align:middle line:84% And it doesn't look much like what I just showed you, 00:43:15.840 --> 00:43:17.860 align:middle line:84% because I think the aggradation rate is low 00:43:17.860 --> 00:43:21.100 align:middle line:84% relative to how fast these things are shifting around. 00:43:21.100 --> 00:43:24.100 align:middle line:84% That's my that's my colleague, Roger Walker, explaining 00:43:24.100 --> 00:43:30.660 align:middle line:84% swaley cross-stratification to a bunch of students long ago. 00:43:30.660 --> 00:43:33.670 align:middle line:84% And I guess this is HCS, too, on a small scale-- very 00:43:33.670 --> 00:43:35.530 align:middle line:90% small scale, medium scale. 00:43:35.530 --> 00:43:38.430 align:middle line:90% 00:43:38.430 --> 00:43:41.310 align:middle line:84% Look at that big hummock, same kind 00:43:41.310 --> 00:43:46.412 align:middle line:84% of features going on there that we've seen before close up. 00:43:46.412 --> 00:43:48.870 align:middle line:84% This is interesting, because there's pretty deep scour over 00:43:48.870 --> 00:43:50.690 align:middle line:90% here that truncated this stuff. 00:43:50.690 --> 00:43:56.270 align:middle line:84% And it got overtopped by this and goes to conformity again. 00:43:56.270 --> 00:43:57.630 align:middle line:90% And I tell you-- 00:43:57.630 --> 00:44:01.450 align:middle line:84% I've told you some things about combined-flow stratification, 00:44:01.450 --> 00:44:03.420 align:middle line:84% but I want to just show you a couple of slides. 00:44:03.420 --> 00:44:04.670 align:middle line:90% You can look at them yourself. 00:44:04.670 --> 00:44:05.770 align:middle line:90% You've seen this before. 00:44:05.770 --> 00:44:09.030 align:middle line:84% This is from Simon Dumas' experiments 00:44:09.030 --> 00:44:11.270 align:middle line:84% over in the laboratory in building N9. 00:44:11.270 --> 00:44:13.630 align:middle line:90% And these lines are fakey. 00:44:13.630 --> 00:44:16.190 align:middle line:84% These are all gradational-- symmetric small, 00:44:16.190 --> 00:44:19.470 align:middle line:84% symmetric large, asymmetric small, asymmetric large. 00:44:19.470 --> 00:44:21.870 align:middle line:84% And so this is purely oscillatory. 00:44:21.870 --> 00:44:23.250 align:middle line:90% That's purely unidirectional. 00:44:23.250 --> 00:44:26.530 align:middle line:84% And look at this broad range of possibilities in between. 00:44:26.530 --> 00:44:27.870 align:middle line:90% It's a jungle. 00:44:27.870 --> 00:44:29.590 align:middle line:84% I mean, in Grotzinger's terminology, 00:44:29.590 --> 00:44:32.550 align:middle line:90% the dog's breakfast. 00:44:32.550 --> 00:44:37.210 align:middle line:84% And we don't know as much about combined poststratification 00:44:37.210 --> 00:44:40.930 align:middle line:84% as with the more classical unidirectional flow 00:44:40.930 --> 00:44:43.250 align:middle line:84% and oscillatory flow classification. 00:44:43.250 --> 00:44:45.490 align:middle line:90% Progress has been slow. 00:44:45.490 --> 00:44:48.170 align:middle line:84% Unless I missed some very recent papers, 00:44:48.170 --> 00:44:52.530 align:middle line:84% Nobody has really come to grips with the whole systematics 00:44:52.530 --> 00:44:55.290 align:middle line:90% of these intermediate features. 00:44:55.290 --> 00:44:57.170 align:middle line:84% But they must be important out there, 00:44:57.170 --> 00:45:00.370 align:middle line:84% because it can't always be purely unidirectional, purely 00:45:00.370 --> 00:45:00.870 align:middle line:90% oscillatory. 00:45:00.870 --> 00:45:02.290 align:middle line:90% There must be combinations. 00:45:02.290 --> 00:45:05.150 align:middle line:84% And as I told you when we dealt with bed configuration, 00:45:05.150 --> 00:45:07.050 align:middle line:84% combined flow bed configurations, 00:45:07.050 --> 00:45:08.672 align:middle line:84% there's a wide range of possibilities. 00:45:08.672 --> 00:45:10.130 align:middle line:84% And when they're grades, it's going 00:45:10.130 --> 00:45:12.630 align:middle line:84% to produce a wide range of cross stratification. 00:45:12.630 --> 00:45:14.050 align:middle line:84% And we've only begun to understand 00:45:14.050 --> 00:45:15.970 align:middle line:84% how we recognize where we would be 00:45:15.970 --> 00:45:19.050 align:middle line:84% in this vast sea of possibilities. 00:45:19.050 --> 00:45:21.410 align:middle line:84% And I think that's probably about all I have. 00:45:21.410 --> 00:45:26.470 align:middle line:90% This is from Simon Dumas' paper. 00:45:26.470 --> 00:45:32.710 align:middle line:84% And you can see this-- concentrate on small scale bed 00:45:32.710 --> 00:45:37.770 align:middle line:84% forms with mainly oscillatory, but partly unidirectional. 00:45:37.770 --> 00:45:39.412 align:middle line:84% And it's a very three-dimensional. 00:45:39.412 --> 00:45:40.870 align:middle line:84% And when they agrade, they're going 00:45:40.870 --> 00:45:42.995 align:middle line:84% to leave a particular kind of cross-stratification. 00:45:42.995 --> 00:45:46.210 align:middle line:84% And I'm not sure what it's going to look like, frankly. 00:45:46.210 --> 00:45:51.550 align:middle line:90% 00:45:51.550 --> 00:45:53.550 align:middle line:84% All right, this is going to be the last slide 00:45:53.550 --> 00:45:56.950 align:middle line:84% here, a bunch of things to say about how 00:45:56.950 --> 00:45:59.110 align:middle line:90% you make interpretations. 00:45:59.110 --> 00:46:01.230 align:middle line:84% Now, if you have vertical climb, asymmetric, you 00:46:01.230 --> 00:46:03.750 align:middle line:84% know it's oscillatory flow right. 00:46:03.750 --> 00:46:07.010 align:middle line:84% If you have depositional stoss climb of asymmetrical ripples, 00:46:07.010 --> 00:46:08.510 align:middle line:84% you have to look at the ripple shape 00:46:08.510 --> 00:46:11.070 align:middle line:84% and try to back out, whether it's combined 00:46:11.070 --> 00:46:14.943 align:middle line:90% flow or unidirectional flow. 00:46:14.943 --> 00:46:17.110 align:middle line:84% STUDENT: Does that have to do with [INAUDIBLE], when 00:46:17.110 --> 00:46:19.490 align:middle line:84% you say look at shape, do you mean concavity? 00:46:19.490 --> 00:46:23.270 align:middle line:84% JOHN SOUTHARD: Well, the shape of the ripple 00:46:23.270 --> 00:46:25.570 align:middle line:84% that you can see in the structure, 00:46:25.570 --> 00:46:27.310 align:middle line:84% to some-- you can always see that. 00:46:27.310 --> 00:46:29.260 align:middle line:84% At low angles of climb, you don't know that. 00:46:29.260 --> 00:46:31.400 align:middle line:84% And I think that's mentioned here. 00:46:31.400 --> 00:46:35.240 align:middle line:84% When it's erosional stoss, very asymmetrical ripples. 00:46:35.240 --> 00:46:38.340 align:middle line:84% It's probably unidirectional flow, 00:46:38.340 --> 00:46:40.140 align:middle line:84% but it may be not purely oscillatory, 00:46:40.140 --> 00:46:41.680 align:middle line:90% a unidirectional flow. 00:46:41.680 --> 00:46:45.320 align:middle line:84% Isotropic HCS, on a good sized scale, 00:46:45.320 --> 00:46:47.640 align:middle line:84% it's almost certainly oscillatory flow. 00:46:47.640 --> 00:46:49.300 align:middle line:90% I've convinced myself of that. 00:46:49.300 --> 00:46:51.940 align:middle line:84% I think the general feeling is the truth. 00:46:51.940 --> 00:46:56.100 align:middle line:84% If it's anisotropic HCS-- well, you see that sometimes. 00:46:56.100 --> 00:46:58.480 align:middle line:84% But I haven't seen it very often. 00:46:58.480 --> 00:47:03.240 align:middle line:84% And that must be influenced by unidirectional flow. 00:47:03.240 --> 00:47:05.320 align:middle line:84% If you see large scale trough stratification-- 00:47:05.320 --> 00:47:06.960 align:middle line:90% and I showed a lot of it-- 00:47:06.960 --> 00:47:10.120 align:middle line:84% we assume, when we look at it, it's unidirectional flow. 00:47:10.120 --> 00:47:12.240 align:middle line:84% But it may be unidirectional flow 00:47:12.240 --> 00:47:13.980 align:middle line:90% with an oscillation influence. 00:47:13.980 --> 00:47:16.500 align:middle line:84% And we can't back out the oscillation influence. 00:47:16.500 --> 00:47:20.760 align:middle line:84% It's one of those things that become difficult to manage. 00:47:20.760 --> 00:47:24.280 align:middle line:84% And now there's a spectral gap that I mentioned last time. 00:47:24.280 --> 00:47:27.400 align:middle line:84% Ripples are always about 10, 15 centimeters, 00:47:27.400 --> 00:47:28.680 align:middle line:90% thereabouts-- maybe 20. 00:47:28.680 --> 00:47:31.500 align:middle line:84% And dunes seldom get below a meter or half 00:47:31.500 --> 00:47:34.780 align:middle line:84% meter at the least, unless the flows are really shallow. 00:47:34.780 --> 00:47:42.220 align:middle line:84% And so if we see cross-stratification 00:47:42.220 --> 00:47:45.660 align:middle line:84% that looks like it's scales in that spectral gap, 00:47:45.660 --> 00:47:50.380 align:middle line:84% we almost can conclude that it's oscillatory flow because you 00:47:50.380 --> 00:47:52.460 align:middle line:84% don't make oscillatory flow ripples 00:47:52.460 --> 00:47:56.700 align:middle line:84% in that spectrum, unidirectional flow ripples in that gap. 00:47:56.700 --> 00:47:58.500 align:middle line:90% So I'm going to quit there. 00:47:58.500 --> 00:48:02.340 align:middle line:84% I had a few comments about the fact 00:48:02.340 --> 00:48:06.780 align:middle line:84% that many beds, a single event, don't have uniform conditions 00:48:06.780 --> 00:48:07.400 align:middle line:90% throughout. 00:48:07.400 --> 00:48:08.780 align:middle line:90% I showed you some. 00:48:08.780 --> 00:48:11.180 align:middle line:84% It can start slow and go fast and start slow, 00:48:11.180 --> 00:48:12.200 align:middle line:90% or the other way around. 00:48:12.200 --> 00:48:16.980 align:middle line:84% And I had just a few slides that aren't particularly needed 00:48:16.980 --> 00:48:18.060 align:middle line:90% at this point. 00:48:18.060 --> 00:48:20.320 align:middle line:84% So that's my pitch on cross-stratification. 00:48:20.320 --> 00:48:22.460 align:middle line:84% I've been a fan of cross-stratification since I was 00:48:22.460 --> 00:48:27.230 align:middle line:84% a grad student in 1960, early 1960s. 00:48:27.230 --> 00:48:31.910 align:middle line:84% And it wasn't all that well-understood at that time. 00:48:31.910 --> 00:48:34.750 align:middle line:84% It wasn't totally mysterious, but people 00:48:34.750 --> 00:48:36.668 align:middle line:84% have made a lot of progress up to now 00:48:36.668 --> 00:48:38.210 align:middle line:84% in interpreting cross-stratification. 00:48:38.210 --> 00:48:40.790 align:middle line:84% And I've tried to cover the ground rules, 00:48:40.790 --> 00:48:43.110 align:middle line:90% cover the ground on that. 00:48:43.110 --> 00:48:46.830 align:middle line:90% So that's my pitch. 00:48:46.830 --> 00:48:48.750 align:middle line:90% [? Lyle. ?] 00:48:48.750 --> 00:48:51.230 align:middle line:84% STUDENT: You showed a bunch of different sizes of Hummocky 00:48:51.230 --> 00:48:52.510 align:middle line:90% Cross-stratification, HCS. 00:48:52.510 --> 00:48:58.070 align:middle line:84% What's the significance of the size of HCS? 00:48:58.070 --> 00:48:59.450 align:middle line:84% JOHN SOUTHARD: In presentation 3, 00:48:59.450 --> 00:49:04.030 align:middle line:84% I showed you my favorite outcrop with a meter scale HCS. 00:49:04.030 --> 00:49:06.810 align:middle line:84% And I showed you another slide-- it wasn't a good one, 00:49:06.810 --> 00:49:10.350 align:middle line:84% but it's the only one I had-- of three, 00:49:10.350 --> 00:49:15.270 align:middle line:84% four decimeter scale, which must be common. 00:49:15.270 --> 00:49:19.730 align:middle line:84% If the larger scale is common and the smaller scale is common, 00:49:19.730 --> 00:49:21.760 align:middle line:84% the intermediate scale must be common, too, 00:49:21.760 --> 00:49:23.840 align:middle line:84% judging from the various experiments 00:49:23.840 --> 00:49:26.020 align:middle line:84% of the kind that Simon Dumas did and others. 00:49:26.020 --> 00:49:28.103 align:middle line:84% There are a couple of others' really good studies. 00:49:28.103 --> 00:49:31.520 align:middle line:84% And I don't know how to deal with that. 00:49:31.520 --> 00:49:34.000 align:middle line:84% STUDENT: Does it have to do with wave period? 00:49:34.000 --> 00:49:37.222 align:middle line:90% Or what's controlling the-- 00:49:37.222 --> 00:49:39.180 align:middle line:84% JOHN SOUTHARD: Well, you remember I mentioned-- 00:49:39.180 --> 00:49:43.480 align:middle line:84% I mentioned along the way, and I showed you this dimensionless 3D 00:49:43.480 --> 00:49:48.920 align:middle line:84% diagram of oscillatory flow features and the fact that when 00:49:48.920 --> 00:49:52.360 align:middle line:84% you make lab experiments, you could fill any of that whole 3D 00:49:52.360 --> 00:49:54.000 align:middle line:90% diagram with points. 00:49:54.000 --> 00:49:56.020 align:middle line:84% But when you're dealing with real waves, 00:49:56.020 --> 00:49:59.120 align:middle line:84% there are certain constraints on how the waves themselves work 00:49:59.120 --> 00:50:03.720 align:middle line:84% that only some subset of space in that 3D diagram can be 00:50:03.720 --> 00:50:07.920 align:middle line:84% occupied by natural flow oscillatory features. 00:50:07.920 --> 00:50:10.840 align:middle line:84% I tried to make that point, and it's generally 00:50:10.840 --> 00:50:12.600 align:middle line:90% agreed that would be the case. 00:50:12.600 --> 00:50:14.507 align:middle line:84% So is that relevant to your question? 00:50:14.507 --> 00:50:15.340 align:middle line:90% STUDENT: I think so. 00:50:15.340 --> 00:50:17.140 align:middle line:90% Yeah, I don't know. 00:50:17.140 --> 00:50:22.580 align:middle line:84% I think people, HCS is commonly used as a storm [INAUDIBLE] 00:50:22.580 --> 00:50:25.000 align:middle line:84% JOHN SOUTHARD: Yes, What else-- what else could it be? 00:50:25.000 --> 00:50:26.000 align:middle line:90% That's how I look at it. 00:50:26.000 --> 00:50:28.083 align:middle line:84% STUDENT: And I'm just wondering if there's further 00:50:28.083 --> 00:50:30.440 align:middle line:84% you can go based on the measuring the size, 00:50:30.440 --> 00:50:31.682 align:middle line:90% like anything you can learn. 00:50:31.682 --> 00:50:33.140 align:middle line:84% JOHN SOUTHARD: Well, I did show you 00:50:33.140 --> 00:50:36.100 align:middle line:84% a medium scale one, my favorite little piece there. 00:50:36.100 --> 00:50:38.120 align:middle line:84% And so I haven't seen many like that. 00:50:38.120 --> 00:50:41.000 align:middle line:84% And I don't know why it's scarce compared to the larger scale. 00:50:41.000 --> 00:50:41.820 align:middle line:90% I don't know that. 00:50:41.820 --> 00:50:43.740 align:middle line:84% There's some reason for that, and I haven't 00:50:43.740 --> 00:50:45.380 align:middle line:90% come to grips with that. 00:50:45.380 --> 00:50:48.540 align:middle line:84% But that's all I can say about it. 00:50:48.540 --> 00:50:50.900 align:middle line:90% Other questions, comments? 00:50:50.900 --> 00:50:53.420 align:middle line:84% Thanks for staying to the bitter end. 00:50:53.420 --> 00:50:55.420 align:middle line:84% STUDENT: Could you mention what that reference-- 00:50:55.420 --> 00:50:57.080 align:middle line:90% you had that reference for the-- 00:50:57.080 --> 00:51:00.760 align:middle line:84% I didn't quite write it down-- for the average set thickness. 00:51:00.760 --> 00:51:03.980 align:middle line:84% JOHN SOUTHARD: Yes, OK, Paola and Borgman-- 00:51:03.980 --> 00:51:08.780 align:middle line:84% well, you have the PowerPoint, don't you? 00:51:08.780 --> 00:51:09.940 align:middle line:90% And you can-- 00:51:09.940 --> 00:51:11.300 align:middle line:90% I don't know the reference. 00:51:11.300 --> 00:51:11.940 align:middle line:90% We can go back. 00:51:11.940 --> 00:51:13.480 align:middle line:90% It was 1990 something. 00:51:13.480 --> 00:51:14.260 align:middle line:90% I don't remember. 00:51:14.260 --> 00:51:17.220 align:middle line:84% STUDENT: Because Bill Arnot told me that-- 00:51:17.220 --> 00:51:18.810 align:middle line:90% I was on a field trip with him. 00:51:18.810 --> 00:51:23.692 align:middle line:84% He said he always assumes one third of the bed thickness is-- 00:51:23.692 --> 00:51:26.150 align:middle line:84% JOHN SOUTHARD: Well, they seem to think that it pretty much 00:51:26.150 --> 00:51:28.410 align:middle line:90% scaled with the set thickness. 00:51:28.410 --> 00:51:30.290 align:middle line:90% But read the paper. 00:51:30.290 --> 00:51:31.430 align:middle line:90% I read it once. 00:51:31.430 --> 00:51:34.430 align:middle line:84% I have to confess it was only once. 00:51:34.430 --> 00:51:36.630 align:middle line:90% And it seemed reasonable to me. 00:51:36.630 --> 00:51:39.490 align:middle line:84% Bill Arnot is another close younger colleague of mine. 00:51:39.490 --> 00:51:40.570 align:middle line:90% I was on his thesis-- 00:51:40.570 --> 00:51:42.570 align:middle line:84% I was examiner on his thesis committee. 00:51:42.570 --> 00:51:44.450 align:middle line:84% Went to Edmonton for his defense. 00:51:44.450 --> 00:51:46.170 align:middle line:90% And then after, we drove down. 00:51:46.170 --> 00:51:49.173 align:middle line:84% We were 400 some miles to his field area in Montana, 00:51:49.173 --> 00:51:50.590 align:middle line:84% had a great time for a whole week. 00:51:50.590 --> 00:51:52.570 align:middle line:84% So we've been a close colleague ever since. 00:51:52.570 --> 00:51:55.550 align:middle line:84% He and Paul Meyer are my closest younger colleagues. 00:51:55.550 --> 00:51:58.740 align:middle line:90% OK, so that's it. 00:51:58.740 --> 00:52:17.000 align:middle line:90%