1 00:00:04,900 --> 00:00:07,700 This is geology B with all of us trumple. 2 00:00:09,300 --> 00:00:13,300 Rivers can seem very ephemeral often changing course or drying 3 00:00:13,300 --> 00:00:17,400 up entirely yet. Some Rivers have persisted for 4 00:00:17,400 --> 00:00:20,700 tens, or even hundreds of millions of years, even 5 00:00:20,700 --> 00:00:24,000 testifying to the breakup of Pangaea, the most recent, 6 00:00:24,000 --> 00:00:28,600 supercontinent about 200 million years ago, on the one hand, 7 00:00:28,700 --> 00:00:32,299 their courses may be determined by tectonic processes, such as 8 00:00:32,299 --> 00:00:36,100 the formation of mountain belts, and on the other, they 9 00:00:36,100 --> 00:00:38,900 themselves can affect tectonic processes bike. 10 00:00:39,100 --> 00:00:43,400 Rating continents scale features such as giant submarine fans. 11 00:00:44,400 --> 00:00:47,400 Martin gambling has spent a lifetime studying rivers and 12 00:00:47,400 --> 00:00:49,300 river sediments around the world. 13 00:00:49,800 --> 00:00:52,500 He is Emeritus professor in the department of Earth and 14 00:00:52,500 --> 00:00:56,700 environmental Sciences at Dalhousie University in Halifax, 15 00:00:56,700 --> 00:01:01,600 Nova Scotia in Canada. This episode is the first of two 16 00:01:01,600 --> 00:01:03,400 of our conversation about rivers. 17 00:01:04,099 --> 00:01:07,300 In this episode, we talk about fluvial deposits in the 18 00:01:07,300 --> 00:01:11,300 geological record and the impact of the breakup of Pangaea on 19 00:01:11,300 --> 00:01:15,400 river systems. In the second episode, we talked 20 00:01:15,400 --> 00:01:18,700 specifically about the history of rivers of Europe and the 21 00:01:18,700 --> 00:01:22,500 Americas as well as the impact of recent ice ages. 22 00:01:23,200 --> 00:01:26,600 We end by considering how humans have changed rivers and their 23 00:01:26,600 --> 00:01:28,700 deposits throughout human history. 24 00:01:29,900 --> 00:01:32,500 Martin giggling, welcome to geology B. 25 00:01:32,800 --> 00:01:35,000 Thanks very much Oliver. It's a great pleasure to talk 26 00:01:35,000 --> 00:01:37,500 with you. How far back into the geological 27 00:01:37,500 --> 00:01:40,000 record, do fluvial deposits. Go. 28 00:01:40,200 --> 00:01:42,600 They go back a surprisingly long way. 29 00:01:42,700 --> 00:01:45,500 The oldest fluvial deposits about which we are really 30 00:01:45,500 --> 00:01:48,600 certain are in the mood is group of southern Africa. 31 00:01:48,900 --> 00:01:53,800 And those date back to about 3.2 billion years and that's a long 32 00:01:53,800 --> 00:01:55,700 way back towards the origin of the earth. 33 00:01:55,700 --> 00:02:00,300 That 4.6 billion the May well be older fluvial Rocks. 34 00:02:00,500 --> 00:02:03,900 But up to now they've been to altered and deformed for anyone 35 00:02:03,900 --> 00:02:07,000 to be certain about. However, it's worth saying that 36 00:02:07,000 --> 00:02:11,100 in rocks of Western Australia, researchers have found Zircon 37 00:02:11,100 --> 00:02:15,100 grains that date back to about four point four billion years 38 00:02:15,300 --> 00:02:19,600 that takes us shortly after the formation of the earth and very 39 00:02:19,600 --> 00:02:22,300 surprisingly. They yield isotopic evidence for 40 00:02:22,300 --> 00:02:25,700 surface temperatures that were very much like those of today 41 00:02:26,100 --> 00:02:29,500 that implies liquid water on the surface of the Earth. 42 00:02:29,700 --> 00:02:33,400 It in turn implies the presence of flowing water and rivers. 43 00:02:33,600 --> 00:02:36,800 So we have to assume that Rivers have been with us since the very 44 00:02:36,800 --> 00:02:39,200 earliest days of planet Earth. Okay. 45 00:02:39,200 --> 00:02:42,700 But with those icons that's quite a complicated chain of 46 00:02:42,700 --> 00:02:46,100 inferences. How do we actually distinguish 47 00:02:46,200 --> 00:02:49,100 an intact fluvial deposits in the geological record? 48 00:02:49,200 --> 00:02:52,900 From other waterborne deposits? Such as those lay down on Lake 49 00:02:52,900 --> 00:02:56,900 beds or on the seashore and those deposited by wind? 50 00:02:57,100 --> 00:02:59,500 Yes you have to get into the details. 51 00:02:59,700 --> 00:03:03,300 The Rock record and the strata. And there were looking at the 52 00:03:03,300 --> 00:03:07,400 organizational architecture as it's called of the strata, as 53 00:03:07,400 --> 00:03:10,700 well as particular sedimentary features and fossils that are 54 00:03:10,700 --> 00:03:12,300 present. And of course, if you're far 55 00:03:12,300 --> 00:03:15,300 back in time, you won't have the fossils to guide you. 56 00:03:15,500 --> 00:03:18,300 And if you've got very deformed or altered rocks, then you're 57 00:03:18,300 --> 00:03:21,600 struggling to make sense of the sedimentary features, but what 58 00:03:21,600 --> 00:03:23,900 you can often see in younger strata. 59 00:03:24,000 --> 00:03:27,200 Its places where River channels, have eroded down into the strata 60 00:03:27,200 --> 00:03:31,000 below and you get surfaces that look very much like Channel 61 00:03:31,000 --> 00:03:33,600 forms filled in with sand and gravel. 62 00:03:33,800 --> 00:03:37,500 What's filling them in is often cross beds laid down on the 63 00:03:37,500 --> 00:03:41,500 Avalanche phases of Ripples and dunes and those allow you to 64 00:03:41,500 --> 00:03:45,400 measure the flow directions at the time, the water was flowing. 65 00:03:45,700 --> 00:03:48,100 And in the case of river channels, they are 66 00:03:48,100 --> 00:03:51,700 unidirectional, they're all going in One Direction down the 67 00:03:51,700 --> 00:03:54,800 channel, which is strong evidence that these were Fluval 68 00:03:55,100 --> 00:03:58,600 and then you can find things like rain, prints and mud cracks 69 00:03:58,600 --> 00:04:01,000 in the strata. Jinda, Kate that these were 70 00:04:01,000 --> 00:04:05,000 exposures on the terrestrial surface and then in younger 71 00:04:05,000 --> 00:04:07,400 beds, you get terrestrial fossils. 72 00:04:07,500 --> 00:04:12,000 Roots, Woody material, freshwater, fish shells, and 73 00:04:12,000 --> 00:04:16,500 things like, trackways made by giant arthropods, and also by 74 00:04:16,500 --> 00:04:20,100 dinosaurs, of course, so all these lines of evidence can make 75 00:04:20,100 --> 00:04:22,900 you pretty certain that you're dealing with fluvial deposits. 76 00:04:23,100 --> 00:04:26,300 Wouldn't most of those also possibly appear in wind-borne 77 00:04:26,300 --> 00:04:29,200 deposit, or is it that it's unidirectional with rivers. 78 00:04:29,200 --> 00:04:32,300 So, so that rules out win because it couldn't blow this 79 00:04:32,300 --> 00:04:35,400 way and that it can. But you can, of course, get 80 00:04:35,400 --> 00:04:37,900 systematic. Directions of wind flow that 81 00:04:37,900 --> 00:04:41,300 would generate uni-directional crust strata. 82 00:04:41,700 --> 00:04:45,400 But in those cases you wouldn't be seeing the channel basis. 83 00:04:45,500 --> 00:04:50,000 Sometimes with gravel lining the surfaces as a kind of a lag 84 00:04:50,100 --> 00:04:53,700 where the channels eroded in and that's where the architecture of 85 00:04:53,700 --> 00:04:56,900 the strata and their organization come into play. 86 00:04:57,000 --> 00:04:59,500 You would also get mud layers in River Channel. 87 00:04:59,700 --> 00:05:02,900 That you wouldn't be expecting to get in Dune systems, for 88 00:05:02,900 --> 00:05:07,200 example, in that previous episode of geology, B Neil 89 00:05:07,200 --> 00:05:11,200 Davis, Describe the impact on the landscape of the first land 90 00:05:11,200 --> 00:05:14,300 plants during the middle division to the mid devonian. 91 00:05:15,000 --> 00:05:18,400 Can you remind us as to how fluvial deposits changed when 92 00:05:18,400 --> 00:05:20,400 plants? First colonized the land? 93 00:05:20,700 --> 00:05:24,100 Yes, Neil is made a wonderful job of setting the stage for 94 00:05:24,100 --> 00:05:25,700 this. What happened? 95 00:05:25,700 --> 00:05:29,300 When the Earth was greened, the great Green Landscape? 96 00:05:29,600 --> 00:05:32,600 Ellucian. As I think of it, the earliest 97 00:05:32,600 --> 00:05:36,200 land plants in the OR division are represented by spores 98 00:05:36,200 --> 00:05:40,300 microscopic fragments of plants and they came from very small. 99 00:05:40,300 --> 00:05:44,000 Plants with simple unbranched stems and minimal routing 100 00:05:44,000 --> 00:05:46,400 structures. As we move on through the 101 00:05:46,400 --> 00:05:50,600 silurian, they start to become a bit larger complex enough that 102 00:05:50,600 --> 00:05:53,100 you get a bit of a macro fossil record. 103 00:05:53,300 --> 00:05:56,900 And then when you hit the devonian things really take off 104 00:05:56,900 --> 00:06:01,800 large routing systems evolved By the mid devonian and enough 105 00:06:01,800 --> 00:06:06,600 biomass for it to get preserved in the fluvial, record along 106 00:06:06,600 --> 00:06:09,900 with things like peat which indicate that vegetation is 107 00:06:09,900 --> 00:06:14,300 really beginning to build up. Solidly in the case of rivers, 108 00:06:14,300 --> 00:06:17,900 this led to a profound and dramatic increase in the amount 109 00:06:17,900 --> 00:06:22,000 of mud that was preserved in fluvial, deposits and Neil. 110 00:06:22,000 --> 00:06:24,500 And his colleagues are very nicely documented. 111 00:06:24,500 --> 00:06:28,500 This really very dramatic Trend. What the mod implies is the 112 00:06:28,500 --> 00:06:32,100 weathering was Densifying, almost certainly due to the 113 00:06:32,100 --> 00:06:38,000 organic acids and the Carbonic acids associated with plants and 114 00:06:38,000 --> 00:06:42,000 with the drawdown of CO2 from the atmosphere and groundwater 115 00:06:42,000 --> 00:06:45,300 systems. And when you had mud being 116 00:06:45,300 --> 00:06:48,700 produced in Greater abundance, you also had more of it 117 00:06:48,700 --> 00:06:53,000 transported in river systems and then trapped and baffled by the 118 00:06:53,000 --> 00:06:56,300 standing vegetation. And so it tends to build up in 119 00:06:56,300 --> 00:06:59,500 the river Plains and become preserved rather than just 120 00:06:59,600 --> 00:07:03,200 Passing through to our sir is Notions, the mud would have had 121 00:07:03,200 --> 00:07:05,200 the effect of making river, sand. 122 00:07:05,200 --> 00:07:08,900 More cohesive strengthening the the bed of the rivers 123 00:07:08,900 --> 00:07:12,200 strengthening particular the Riverbanks and they would have 124 00:07:12,200 --> 00:07:15,000 become more difficult to erode by flowing water. 125 00:07:15,100 --> 00:07:19,200 So you start to get more obvious Channel, Banks and channel forms 126 00:07:19,400 --> 00:07:22,600 in The Preserve record through the latest silurian and 127 00:07:22,600 --> 00:07:26,500 devonian, are you suggesting that by the mid devonian, the 128 00:07:26,500 --> 00:07:29,500 modern River had formed and that all the different plants that 129 00:07:29,500 --> 00:07:31,500 Would have had an impact on Rivers. 130 00:07:31,500 --> 00:07:34,900 How that was all sort of, pretty much the way it is today, or 131 00:07:35,500 --> 00:07:39,900 have there been further diversification and have certain 132 00:07:39,900 --> 00:07:41,700 regions of the planet being colonized? 133 00:07:41,700 --> 00:07:44,100 That went really fully colonized by the mid devonian. 134 00:07:44,400 --> 00:07:47,600 The bit devonian was when things really began to take off with a 135 00:07:47,608 --> 00:07:52,000 sense of very large forest trees that were a meter or even a 136 00:07:52,000 --> 00:07:55,900 couple of meters in diameter with very large root systems. 137 00:07:55,900 --> 00:07:59,200 And there have been recent discoveries in Upstate New York. 138 00:07:59,600 --> 00:08:03,400 Boa and elsewhere that have showed very beautifully. 139 00:08:03,400 --> 00:08:06,900 Some of these major Forest systems but that was only really 140 00:08:06,900 --> 00:08:11,200 the start and by the Carboniferous, you're starting 141 00:08:11,200 --> 00:08:15,700 to get early gymnosperm plants, the ancestors of conifers of the 142 00:08:15,707 --> 00:08:20,100 present-day and those were able to penetrate quite deeply down 143 00:08:20,100 --> 00:08:23,900 even into dry land areas. And so you start to stabilize, 144 00:08:23,900 --> 00:08:27,300 not just the Wetland environments, but also 145 00:08:27,300 --> 00:08:31,800 relatively dry open Plains. It's and what's happening is 146 00:08:31,800 --> 00:08:36,400 that Rivers diversify through to about the mid part of the 147 00:08:36,400 --> 00:08:41,100 Carboniferous say, the start of the Pennsylvanian when they are 148 00:08:41,100 --> 00:08:44,400 more or less covering the range of things that we see at the 149 00:08:44,400 --> 00:08:48,100 present day. So, initially we had large sand 150 00:08:48,100 --> 00:08:52,000 bed, River's water typically braided, rivers, with shifting 151 00:08:52,000 --> 00:08:57,100 sandbars, and rather weak Banks, and those progressively move 152 00:08:57,100 --> 00:08:59,400 into being more Meandering, Rivers. 153 00:08:59,700 --> 00:09:03,500 With Muddy Banks, where the and has migrated much more slowly. 154 00:09:03,700 --> 00:09:07,200 You start to get abandoned channels, you start to get 155 00:09:07,200 --> 00:09:13,300 multi-channel anastomosis, river systems Wetlands with black, 156 00:09:13,500 --> 00:09:18,300 organic stained water and the whole range of what we now know 157 00:09:18,300 --> 00:09:22,500 is river systems, today is coming into existence through 158 00:09:22,500 --> 00:09:26,200 that period of time especially with the riparian or Bank 159 00:09:26,200 --> 00:09:29,400 vegetation that makes the whole system so much more intricate 160 00:09:29,500 --> 00:09:34,300 Katyn complex and where life organisms simply began to evolve 161 00:09:34,300 --> 00:09:38,000 at a much more rapid rate in these little niches along the 162 00:09:38,000 --> 00:09:41,000 lines of the river? Corridors was there any 163 00:09:41,000 --> 00:09:43,300 significant impact on the Fluval record? 164 00:09:43,300 --> 00:09:46,700 When the planet started to be covered by large tracts of 165 00:09:46,700 --> 00:09:48,500 tundra open. Grassland? 166 00:09:48,800 --> 00:09:51,400 This was a major change and people are still trying to work 167 00:09:51,400 --> 00:09:55,900 out how much that affected river systems you have the angiosperm 168 00:09:55,900 --> 00:09:59,400 plants flowering plants coming in in the Cretaceous. 169 00:09:59,700 --> 00:10:04,000 They typically greedy of water in many cases and then you have 170 00:10:04,000 --> 00:10:08,200 the grasses coming in, in the, the cenozoic with, they're very 171 00:10:08,200 --> 00:10:11,700 dense, root systems, and the way they bound the flood. 172 00:10:11,700 --> 00:10:15,400 Plain surfaces must have have quite a lot of effect on river 173 00:10:15,400 --> 00:10:17,400 systems. It's just a bit difficult to 174 00:10:17,400 --> 00:10:20,700 figure out how exactly they affected things. 175 00:10:20,900 --> 00:10:25,100 But, along with them, you have the rise of gigantic organisms 176 00:10:25,100 --> 00:10:29,100 like the dinosaurs and the big herds of ungulates. 177 00:10:29,500 --> 00:10:32,600 That you might see in the Serengeti at the present day and 178 00:10:32,600 --> 00:10:35,700 the Buffalo before they were pretty much exterminated in 179 00:10:35,700 --> 00:10:38,900 North America. And those would have trampled 180 00:10:38,900 --> 00:10:43,400 through Riverbanks and in places like hippos do today, they would 181 00:10:43,400 --> 00:10:46,600 have made Trails down to Rivers, which would have allowed rivers 182 00:10:46,600 --> 00:10:49,100 to break out a long low points at times. 183 00:10:49,400 --> 00:10:53,700 And people have even made a case for Dino avulsion so-called 184 00:10:53,700 --> 00:10:56,200 where dinosaurs might have trampled their way through to 185 00:10:56,200 --> 00:11:00,300 the rivers and promoted River breakout, well, Incredible image 186 00:11:00,300 --> 00:11:04,100 of China or a hippo affecting the course of an entire River. 187 00:11:04,200 --> 00:11:08,100 Yes, it's quite remarkable. And you mentioned the tundra 188 00:11:08,100 --> 00:11:11,800 areas and the rise of permafrost, greatly affected 189 00:11:11,800 --> 00:11:14,600 Northern river systems eventually in the ice ages. 190 00:11:14,800 --> 00:11:17,900 And those of course are starting to melt away somewhat at the 191 00:11:17,900 --> 00:11:21,300 present day and you're starting to see modifications of rivers, 192 00:11:21,600 --> 00:11:26,000 as the thermal water begins to erode down into the permafrost. 193 00:11:26,000 --> 00:11:29,700 So that were complex effects related to the glaciations even 194 00:11:30,100 --> 00:11:33,500 in your book. Entitled River Planet, you have 195 00:11:33,500 --> 00:11:37,500 a wonderful chart showing the longevity of modern Rivers. 196 00:11:38,300 --> 00:11:41,100 What exactly do you mean when you talk about the age of a 197 00:11:41,100 --> 00:11:43,700 river, that's a very good question. 198 00:11:43,800 --> 00:11:46,300 Rainwater is always flowing downhill. 199 00:11:46,600 --> 00:11:51,200 So, in reality, the flow Paths of water are always evolving 200 00:11:51,400 --> 00:11:55,700 following tiny gullies, little reels moving together into 201 00:11:55,700 --> 00:12:00,100 larger channels and trying to figure out the age of a It is 202 00:12:00,100 --> 00:12:03,600 really a bit of a chimera it's like trying to say how old a 203 00:12:03,600 --> 00:12:07,700 rainbow is for example, but it's helpful to think of the age of a 204 00:12:07,700 --> 00:12:12,500 river as the length of time that the river Channel or course, has 205 00:12:12,500 --> 00:12:16,700 been following pretty much the line that it has at present, 206 00:12:17,000 --> 00:12:20,500 wouldn't be exactly the same course because channels, migrate 207 00:12:20,500 --> 00:12:24,200 they break out, but the channel belt as a whole would be 208 00:12:24,200 --> 00:12:27,200 occupying within a matter of a few kilometers. 209 00:12:27,200 --> 00:12:31,700 Probably about the same. Mission, that can be very 210 00:12:31,700 --> 00:12:34,700 difficult to, determine you might think it would be obvious, 211 00:12:35,000 --> 00:12:38,100 but sometimes Rivers cease to exist for a while. 212 00:12:38,300 --> 00:12:42,600 Maybe the river plane gets drowned out by the sea or lake 213 00:12:42,700 --> 00:12:46,600 glaciers can overrun it. Lava flows, sand dunes can 214 00:12:46,600 --> 00:12:49,600 invade the area. The river May cease to exist for 215 00:12:49,600 --> 00:12:53,400 a while, but it then may re-establish itself in the same 216 00:12:53,400 --> 00:12:55,700 course. And a good example of this is 217 00:12:55,700 --> 00:12:59,300 the Columbia River in the western us, probably. 218 00:12:59,500 --> 00:13:03,900 Originated about 17 million years ago in the Maya scene as 219 00:13:03,900 --> 00:13:08,500 far as anybody can work it out. But periodically the river was 220 00:13:08,500 --> 00:13:12,000 overrun by lavas and by pyroclastic, flows. 221 00:13:12,300 --> 00:13:15,800 Coming off the Columbia Bassel plateau in the East and the 222 00:13:15,800 --> 00:13:18,600 Cascade Range of volcanoes in the west. 223 00:13:18,600 --> 00:13:22,400 And it seems that the river simply cease to exist in its 224 00:13:22,400 --> 00:13:24,300 organized form for periods of time. 225 00:13:24,400 --> 00:13:27,800 And then it reforged a new course, more or less where it's 226 00:13:27,800 --> 00:13:30,300 been before. So, it gets to be a little 227 00:13:30,300 --> 00:13:33,900 debatable, whether those kind of gaps in the record matter or 228 00:13:33,900 --> 00:13:37,600 not, whether you reset the clock if for a little while, the river 229 00:13:37,600 --> 00:13:41,200 ceases to exist. But in Broad terms, I think we 230 00:13:41,200 --> 00:13:44,000 could say that with minor gaps there were rivers that have been 231 00:13:44,000 --> 00:13:47,600 present for hundreds of millions of years in their courses and 232 00:13:47,600 --> 00:13:50,700 that makes sense. So how old are some of the 233 00:13:50,700 --> 00:13:53,800 oldest Rivers? Broadly, speaking that still run 234 00:13:53,800 --> 00:13:56,900 in their ancestral course has the oldest rivers. 235 00:13:56,900 --> 00:13:59,600 That anybody is really documented running an end That's 236 00:13:59,600 --> 00:14:02,300 true courses. Go back to the Carboniferous 237 00:14:02,500 --> 00:14:06,800 about 300 million years ago by no means back to the beginning 238 00:14:06,800 --> 00:14:09,200 of the earth. The earth is an extremely 239 00:14:09,200 --> 00:14:13,400 dynamic system and rivers have been destroyed in the way that 240 00:14:13,400 --> 00:14:16,800 almost anything else has on Earth over geological time. 241 00:14:17,400 --> 00:14:20,200 But some of the world's oldest rivers, are those of Eastern 242 00:14:20,200 --> 00:14:24,700 Europe, the Volga? The dawn, the Dnieper, they may 243 00:14:24,700 --> 00:14:28,100 be as old as the Carboniferous and they run down into the black 244 00:14:28,100 --> 00:14:30,800 and Caspian Sea. These which are the last 245 00:14:30,800 --> 00:14:34,600 remnants of the tethys ocean death is got squeezed out. 246 00:14:34,600 --> 00:14:39,000 When Africa came up against Europe, Arabia, likewise, and 247 00:14:39,000 --> 00:14:43,200 then India against the southern part of Asia and death is was 248 00:14:43,200 --> 00:14:47,400 eliminated except for these minor Oceanic remnants. 249 00:14:47,600 --> 00:14:51,300 And in that part of Eastern Europe, the deformation has been 250 00:14:51,300 --> 00:14:56,100 south of the black and Caspian seas in turkey and the Caucasus. 251 00:14:56,400 --> 00:15:00,600 And so, the rivers further north have not yet been Disrupted by 252 00:15:00,600 --> 00:15:03,400 the rise of mountains to the South that affect them. 253 00:15:03,600 --> 00:15:07,800 And so in course of time they marry very well reverse their 254 00:15:07,800 --> 00:15:11,500 directions to flow north, as other of us have done, but they 255 00:15:11,500 --> 00:15:14,500 haven't done that yet. So they're still in ancestral 256 00:15:14,500 --> 00:15:17,700 courses quite remarkably or broadly within them. 257 00:15:18,200 --> 00:15:21,600 And if you want an example in North America, there were Rivers 258 00:15:21,600 --> 00:15:24,800 Running along the line of the modern Mississippi, west of the 259 00:15:24,800 --> 00:15:29,000 Appalachians back into the Carboniferous about 300 million 260 00:15:29,000 --> 00:15:29,800 years. Ago. 261 00:15:30,100 --> 00:15:33,200 And this is a case where the Mississippi for a while in the 262 00:15:33,200 --> 00:15:38,000 Triassic and Jurassic ceased to be in its present position, due 263 00:15:38,000 --> 00:15:42,400 to faulty activity Marine flooding, but it's been running 264 00:15:42,400 --> 00:15:45,700 along its present line down to the Gulf of Mexico since the 265 00:15:45,700 --> 00:15:50,100 Jurassic a lot of these courses take us back to the time when we 266 00:15:50,100 --> 00:15:54,500 had the supercontinent Pangaea. Wouldn't the subsequent breakup 267 00:15:54,500 --> 00:15:57,600 of Pangaea have completely altered the drainage patterns 268 00:15:57,600 --> 00:16:00,800 and therefore, the courses of the rivers, Yes, certainly. 269 00:16:00,800 --> 00:16:05,000 So the breakup of Pangaea into smaller continents that drifted 270 00:16:05,000 --> 00:16:08,600 apart had profound effects on, virtually all of the world's 271 00:16:08,600 --> 00:16:12,700 Rivers, when Pangaea was in existence, there were rivers of 272 00:16:12,700 --> 00:16:15,700 immense length. Some of them probably longer 273 00:16:15,700 --> 00:16:18,800 than any in existence, today, they would have flowed out of 274 00:16:18,800 --> 00:16:23,100 Mountain chains like the Appalachians in the eastern US 275 00:16:23,400 --> 00:16:27,700 and the risk and Mountain chains Europe and those were equivalent 276 00:16:27,700 --> 00:16:31,300 in scale to the modern and he's So we have to envisage, Rivers, 277 00:16:31,300 --> 00:16:35,000 probably on the scale of the Amazon at time's running out 278 00:16:35,000 --> 00:16:38,800 cross the adjoining Plains. And in the case of the southern 279 00:16:38,800 --> 00:16:43,000 continents gondwanaland, there's evidence from age dates from 280 00:16:43,000 --> 00:16:45,300 again. Zircon grains that there were 281 00:16:45,300 --> 00:16:48,900 very large rivers that flowed out of Antarctica which was not 282 00:16:48,900 --> 00:16:53,600 at that time under ice and they flowed out across Australia into 283 00:16:53,600 --> 00:16:56,400 the Sydney Basin. For example, on the New South 284 00:16:56,400 --> 00:17:01,200 Wales coast and then out into the sea, some part of India and 285 00:17:01,200 --> 00:17:04,400 these continents, of course, and a thousands of kilometers apart. 286 00:17:04,400 --> 00:17:07,800 But at that time, they were part of single very large river 287 00:17:07,800 --> 00:17:11,800 systems that ran through. But once Pangaea began to break 288 00:17:11,800 --> 00:17:15,400 up, all of those systems were dismembered to begin to change. 289 00:17:15,500 --> 00:17:18,700 That's fascinating. So can we track a particular 290 00:17:18,700 --> 00:17:22,700 river that used to be contiguous that now has been separated by 291 00:17:22,700 --> 00:17:25,400 thousands of miles of ocean? I mean, do we look at fossils or 292 00:17:25,400 --> 00:17:28,400 is it all the detrital zircons? How can we do that matching or 293 00:17:28,400 --> 00:17:31,700 is that even possible? It's very difficult and there 294 00:17:31,700 --> 00:17:36,200 aren't many cases where anybody has made a very precise match. 295 00:17:36,200 --> 00:17:38,900 These are not for the most part rivers that exists of the 296 00:17:38,900 --> 00:17:42,500 present day so they're not rivers with names in other words 297 00:17:42,500 --> 00:17:47,000 that we apply to actual flowing water in the case of the, the 298 00:17:47,000 --> 00:17:51,100 Sydney Basin in Australia. It's the grains that give you 299 00:17:51,100 --> 00:17:56,300 the age signature of an eroding Upland in Antarctica and the, 300 00:17:56,300 --> 00:17:59,200 the Sydney Basin has the Triassic. 301 00:17:59,400 --> 00:18:01,800 Rocks of the Hawkesbury sandstone. 302 00:18:02,000 --> 00:18:06,400 A very very big brahmaputra scale or nearly that scale of 303 00:18:06,400 --> 00:18:09,500 river system. It's flowing in across a full 304 00:18:09,500 --> 00:18:14,000 belt out into the what was the ocean at that time and it has 305 00:18:14,000 --> 00:18:18,600 been matched to the highlands in Antarctica, but it's very 306 00:18:18,600 --> 00:18:21,600 difficult to actually track it all the way back there. 307 00:18:22,000 --> 00:18:25,100 There are gaps the erosion and so on and so forth. 308 00:18:25,200 --> 00:18:28,800 So it's these kinds of lines of evidence of B circumstantial 309 00:18:29,100 --> 00:18:31,700 that We build those stories. But I think some of those are 310 00:18:31,700 --> 00:18:34,600 the most fascinating stories that you could pick up a river 311 00:18:34,600 --> 00:18:37,600 in one continent, and potentially find its 312 00:18:37,600 --> 00:18:41,600 continuation in another continent 5,000 kilometers away. 313 00:18:41,900 --> 00:18:44,000 I think there's going to be a lot more coming through on that 314 00:18:44,000 --> 00:18:46,400 kind of thing in the future. Yeah it's amazing. 315 00:18:46,400 --> 00:18:49,400 And can you go even further? You said earlier that fluvial 316 00:18:49,400 --> 00:18:51,900 deposits were characterized by being unidirectional. 317 00:18:52,200 --> 00:18:55,300 So can you infer the direction of current flow and say okay? 318 00:18:55,300 --> 00:18:57,200 Well Upstream there. There must have been a mountain 319 00:18:57,200 --> 00:18:58,600 belt at that time. Yes. 320 00:18:58,800 --> 00:19:03,000 A lot of This comes from where the fluvial deposits are located 321 00:19:03,000 --> 00:19:06,700 and their flow directions. While people refer to, as paleo 322 00:19:06,700 --> 00:19:09,600 current flow, the flow directions of the ancient 323 00:19:09,600 --> 00:19:11,600 currents. And if you go on the field, you 324 00:19:11,600 --> 00:19:16,600 can measure tens, or hundreds of cross bed, directions and figure 325 00:19:16,600 --> 00:19:18,400 out which way the flows will going. 326 00:19:18,500 --> 00:19:21,600 And you can begin to build up patterns regionally afloat. 327 00:19:21,600 --> 00:19:25,000 Our actions did any major rivers actually survive the breakup of 328 00:19:25,000 --> 00:19:26,800 Pangaea. Oh, do we have a whole fresh lot 329 00:19:26,800 --> 00:19:29,800 of rivers? After that happened, the Quite a 330 00:19:29,800 --> 00:19:34,600 lot of rivers that are relics There Are Places on some of the 331 00:19:34,600 --> 00:19:39,100 plateau lands in Africa, and in parts of Asia are up on the 332 00:19:39,100 --> 00:19:42,700 Tibetan Plateau. Where there are Remnant River 333 00:19:42,700 --> 00:19:46,500 patterns, people have mapped them, they appear on satellite 334 00:19:46,500 --> 00:19:50,700 images and they've been inferred to represent remnants of the 335 00:19:50,700 --> 00:19:54,700 original pangaean drainage, but they're not now connected to 336 00:19:54,700 --> 00:19:57,500 active systems. They've been broken through and 337 00:19:57,500 --> 00:20:01,400 so they seem to be virtually all that we've got in the way of the 338 00:20:01,400 --> 00:20:04,000 original drainage, except for those Rivers. 339 00:20:04,000 --> 00:20:07,100 We talked about particularly like those of Eastern Europe, 340 00:20:07,200 --> 00:20:10,100 which haven't yet had the effects of mountain building 341 00:20:10,100 --> 00:20:14,500 from collisions where some Rivers born, as a direct result 342 00:20:14,500 --> 00:20:17,200 of the breakup of Pangaea. Yes, they were. 343 00:20:17,400 --> 00:20:21,300 When you have a supercontinent like Pangaea heat begins to 344 00:20:21,308 --> 00:20:26,100 accumulate underneath it and you start to get doming mantle 345 00:20:26,100 --> 00:20:29,200 plumes, volcanic activity that begins. 346 00:20:29,400 --> 00:20:35,500 To generate domes Rifts of various sorts and these began to 347 00:20:35,500 --> 00:20:37,800 affect virtually. All the continents, in different 348 00:20:37,800 --> 00:20:43,200 ways, you have things like the Kuru plume and the Parana plume 349 00:20:43,400 --> 00:20:46,700 across southern Africa and South America. 350 00:20:47,000 --> 00:20:50,800 These domed up the crust and there's evidence from paleo flow 351 00:20:50,800 --> 00:20:55,400 directions, that the rivers were radiating in places from those 352 00:20:55,400 --> 00:20:59,800 very large domes and then in particular, once the Continents 353 00:20:59,800 --> 00:21:03,800 began to separate new Rifts formed, which divided them 354 00:21:04,100 --> 00:21:07,900 widening into oceans. And because the roofs were 355 00:21:07,900 --> 00:21:12,600 relatively low elevation, they drew in the river systems and 356 00:21:12,600 --> 00:21:15,400 generated and tie a new drainage networks. 357 00:21:15,600 --> 00:21:17,600 And this is the case with the Niger. 358 00:21:17,900 --> 00:21:21,600 Also, with the Rhine very recently and in the case of the 359 00:21:21,600 --> 00:21:25,500 big rivers of Peninsular India, many of which occupy Cretaceous 360 00:21:25,500 --> 00:21:30,000 Rifts, and you would think that. Then once a continent is Away, 361 00:21:30,200 --> 00:21:33,700 nothing much would happen. But in point of fact, continents 362 00:21:33,700 --> 00:21:37,100 are drifting over thousands of kilometers of mantle, which is 363 00:21:37,100 --> 00:21:41,400 not uniform, it varies in it, density in its temperature to 364 00:21:41,400 --> 00:21:44,300 other properties. And as the continents move 365 00:21:44,300 --> 00:21:48,300 slowly across at a few centimeters a year, they rise, 366 00:21:48,300 --> 00:21:53,200 they fall they tilt up and over and normal is in the mantle 367 00:21:53,200 --> 00:21:55,200 below. And this is what's called 368 00:21:55,200 --> 00:21:58,700 Dynamic, topography, link to the mantle properties. 369 00:21:59,000 --> 00:22:02,300 And Of course, rivers are very, very sensitive to Elevation and 370 00:22:02,300 --> 00:22:05,500 to gradient. And so you have good examples, 371 00:22:05,600 --> 00:22:09,700 for example, in Africa, which is currently very high in the 372 00:22:09,700 --> 00:22:13,000 southern areas. Its, anomalously high, a super 373 00:22:13,000 --> 00:22:17,600 swell as people have called it. And this is affected the history 374 00:22:17,600 --> 00:22:21,100 of the Zambezi Limpopo and orange Rivers, which have 375 00:22:21,100 --> 00:22:25,400 altered their courses and directions to correspond to the 376 00:22:25,500 --> 00:22:28,500 elevation of southern Africa as fascinating. 377 00:22:28,500 --> 00:22:31,700 We actually did Analia podcast with Karina left guard 378 00:22:31,700 --> 00:22:33,900 Barcelona. You talked about Dynamic 379 00:22:33,900 --> 00:22:36,600 topography and another one with Becky flowers, which included 380 00:22:36,600 --> 00:22:39,700 some discussion specifically about South Africa, and what we 381 00:22:39,700 --> 00:22:42,100 can tell about the effect of dynamic topography there. 382 00:22:42,700 --> 00:22:46,200 So the ongoing Collision of India with Asia that started 383 00:22:46,200 --> 00:22:49,800 about 50 million years ago, must have had a dramatic effect on 384 00:22:49,800 --> 00:22:52,900 the river systems there. Yes, this is one of the big 385 00:22:52,900 --> 00:22:56,900 stories of river modification through the breakup of Pangaea 386 00:22:57,000 --> 00:23:00,400 and it's absolutely fascinating. India is Is drifting northwards 387 00:23:00,400 --> 00:23:04,500 are quite a rapid rate. Separated intern from Australia, 388 00:23:04,500 --> 00:23:09,900 Antarctica Africa, elsewhere. And by, about 60 million years 389 00:23:09,900 --> 00:23:12,300 ago. In the paleocene, India is 390 00:23:12,300 --> 00:23:16,000 approaching the Southern Shores of Asia. 391 00:23:16,200 --> 00:23:20,600 The tethys ocean is narrowing down to a narrow sea way and 392 00:23:20,600 --> 00:23:23,900 then you have the start of collision and everything 393 00:23:23,900 --> 00:23:26,600 changes. In fact, there are not many 394 00:23:26,600 --> 00:23:30,700 rivers in this part of Asia. It go back more than about 20 395 00:23:30,700 --> 00:23:34,100 million years and there are constant changes of Direction 396 00:23:34,108 --> 00:23:39,000 and River capture tributary systems that affect them. 397 00:23:39,000 --> 00:23:42,600 All, and if you think of Himalaya and the Tibetan 398 00:23:42,600 --> 00:23:46,000 Plateau, there were Rivers radiating out in all directions, 399 00:23:46,000 --> 00:23:50,300 it's called the water tower of Asia, and the thrust sheets are 400 00:23:50,300 --> 00:23:54,100 continuing to move southwards and indeed, India has pushed 401 00:23:54,100 --> 00:23:57,900 probably a couple of thousand kilometers into the body of 402 00:23:57,900 --> 00:23:59,200 Asia. Why wouldn't it? 403 00:23:59,300 --> 00:24:03,200 It have an enormous effects and the kind of effects go a bit 404 00:24:03,200 --> 00:24:06,000 like this. Probably the oldest river in the 405 00:24:06,000 --> 00:24:10,600 system is still the Indus which actually runs along the line of 406 00:24:10,600 --> 00:24:14,400 the collision westwards and then cuts through the Himalaya. 407 00:24:14,600 --> 00:24:19,700 That's the Western sin taxes where Asia curls around the edge 408 00:24:19,700 --> 00:24:23,400 of India, as it indented into the continent. 409 00:24:23,600 --> 00:24:27,300 And so, it curls around and runs down into the Arabian. 410 00:24:27,300 --> 00:24:32,900 Sea and initially, The Ganges occupied the for Land Based on 411 00:24:32,900 --> 00:24:37,500 so-called, on the south side of the Himalayas running westwards 412 00:24:37,500 --> 00:24:40,300 into the Indus. So it was initially in in 413 00:24:40,300 --> 00:24:43,400 distributary, and then, as India, move progressively, 414 00:24:43,400 --> 00:24:48,100 northwards an old body of rock in the ravely, Hills, South of 415 00:24:48,100 --> 00:24:53,700 Delhi began to impinge on the river basins, and separated them 416 00:24:53,700 --> 00:24:57,800 off into two catchments. And the Ganges was diverted 417 00:24:57,800 --> 00:25:02,400 eastwards about 15 million years ago in the Maya scene along, its 418 00:25:02,400 --> 00:25:05,300 present, line down to the Bay of Bengal. 419 00:25:06,500 --> 00:25:10,500 Also up in the Himalaya flowing, eastwards on the line of 420 00:25:10,500 --> 00:25:15,200 collision was the yarlung tsangpo river and that initially 421 00:25:15,400 --> 00:25:19,200 flowed on into the Irrawaddy and out through my admire. 422 00:25:19,600 --> 00:25:23,100 And that is known because of fish populations that are 423 00:25:23,100 --> 00:25:25,800 relatively similar in the two rivers but don't match 424 00:25:25,800 --> 00:25:30,100 elsewhere. But the brahmaputra Steep 425 00:25:30,200 --> 00:25:33,900 eroding head words into the Himalaya cut through and 426 00:25:33,900 --> 00:25:38,000 captured the line of the song power of 18 million years ago 427 00:25:38,300 --> 00:25:40,700 and brought it down into the Bay of Bengal. 428 00:25:40,900 --> 00:25:45,000 Those are massive changes in river and drainage systems and 429 00:25:45,000 --> 00:25:47,400 give us time and there will be more to come. 430 00:25:47,700 --> 00:25:52,200 Because there are several Rivers like the Aaron and the Gann doc 431 00:25:52,400 --> 00:25:55,700 that actually cut through the Himalayas and are now within 432 00:25:55,700 --> 00:25:59,100 Striking Distance of capturing parts of the yelling. 433 00:25:59,200 --> 00:26:02,100 Tsangpo system. They may eventually diverged 434 00:26:02,100 --> 00:26:06,400 flow down into the Ganges and out to the Bay of Bengal by 435 00:26:06,400 --> 00:26:08,700 different route. It's really fascinating. 436 00:26:08,700 --> 00:26:11,800 Wow, it's incredible. Meanwhile, down in Peninsula 437 00:26:11,800 --> 00:26:13,700 India. The rivers have not yet been 438 00:26:13,700 --> 00:26:17,500 affected and you get a big Rivers still lying within 439 00:26:17,500 --> 00:26:21,100 Jurassic and Cretaceous Rifts as they have been since The 440 00:26:21,100 --> 00:26:24,200 Break-Up when India separated from other continents. 441 00:26:24,400 --> 00:26:27,900 But as time passes and we're talking millions of years, 442 00:26:28,100 --> 00:26:31,700 they're going to come closer. Closer to the mountain front and 443 00:26:31,700 --> 00:26:34,900 will thrust front. And so as time passes, they are 444 00:26:34,900 --> 00:26:38,800 going to be modified drawn under with subduction, they're going 445 00:26:38,800 --> 00:26:42,200 to become tributaries to other systems or whatever. 446 00:26:42,300 --> 00:26:44,300 So there's a lot more still to come. 447 00:26:45,100 --> 00:26:49,900 And when we go further east into a share the big rivers of the 448 00:26:49,900 --> 00:26:53,900 Yangtze, the Mekong, the salween All Began life, as little 449 00:26:53,900 --> 00:26:57,400 Coastal, rivers, on the edge of the rising to bat and they then 450 00:26:57,400 --> 00:27:01,100 eroded head word. Started to capture the Red 451 00:27:01,100 --> 00:27:04,000 River, which may have been the biggest drainage system. 452 00:27:04,300 --> 00:27:06,600 It's thought that the middle part of the Yangtze was, 453 00:27:06,600 --> 00:27:09,900 originally a tributary of the Red River but reversed, its 454 00:27:09,900 --> 00:27:14,700 course, cut the 3, Gorges in the miocene probably and then was 455 00:27:14,700 --> 00:27:17,800 locked into place. So there's been a jockeying of 456 00:27:17,800 --> 00:27:22,300 rivers, all very close together as the tectonics of the Himalaya 457 00:27:22,400 --> 00:27:25,700 and Tibetan plateau of squeeze them, modified them, 458 00:27:25,700 --> 00:27:29,100 structurally, change them. And these changes are still 459 00:27:29,300 --> 00:27:32,200 Ongoing one thing that really struck me, as you were giving, 460 00:27:32,200 --> 00:27:34,800 all these examples is how you can have a river. 461 00:27:34,800 --> 00:27:40,000 Course that can be relatively unchanged for geological time, 462 00:27:40,100 --> 00:27:44,200 then it can get more or less in a geological blink of an eye 463 00:27:44,500 --> 00:27:48,100 captured by another River and then flow to somewhere 464 00:27:48,100 --> 00:27:50,600 completely different on the planet essentially. 465 00:27:51,000 --> 00:27:52,300 Yes. Yes. 466 00:27:52,300 --> 00:27:55,200 And you can get rivers that are captured and then diverted 467 00:27:55,200 --> 00:27:59,000 literally from one ocean into another for example, something. 468 00:27:59,200 --> 00:28:02,900 Thousands of kilometers apart in the case of the Yangtze Mekong 469 00:28:02,900 --> 00:28:07,300 and salween, they actually all run in a series of Gorges within 470 00:28:07,300 --> 00:28:09,300 about 100 kilometers of each other. 471 00:28:09,600 --> 00:28:13,100 And they all end up, diverging in two completely different 472 00:28:13,100 --> 00:28:15,500 oceans. They've been likened to a bundle 473 00:28:15,500 --> 00:28:19,500 of javelins in the hands of Zeus Arrangement pictures where you 474 00:28:19,500 --> 00:28:23,900 have the javelins held by Zeus but their tips are radiating out 475 00:28:23,900 --> 00:28:27,100 in different directions. Good example of this, by the 476 00:28:27,100 --> 00:28:31,700 way, is the Niger in Western Africa, which just began in a 477 00:28:31,708 --> 00:28:36,300 rift and was quite small. And then it took over an inland 478 00:28:36,300 --> 00:28:38,600 drainage very suddenly to the west. 479 00:28:38,900 --> 00:28:43,200 And then it went further west when a river that was running 480 00:28:43,200 --> 00:28:46,500 out into the Sahara. Got blocked by sand dunes and 481 00:28:46,500 --> 00:28:49,500 diverted into the upper part of the Niger. 482 00:28:49,500 --> 00:28:53,400 So very, suddenly you had a river that rises very close to 483 00:28:53,400 --> 00:28:56,800 the coast runs. North swings round in the Big 484 00:28:56,800 --> 00:29:00,400 Bend at Timbuktu. And then Runs for some 4,000 485 00:29:00,400 --> 00:29:04,000 kilometers and runs into the Atlantic on down the coast in 486 00:29:04,000 --> 00:29:06,600 the original position. Absolutely fascinating. 487 00:29:07,100 --> 00:29:10,100 The continuation of my conversation with Martin Giblin 488 00:29:10,400 --> 00:29:14,400 is in the next episode of geology B will be talking about 489 00:29:14,400 --> 00:29:17,800 the rivers of Europe and the Americas as well as the impact 490 00:29:17,800 --> 00:29:20,700 of the ice ages and humans on River courses. 491 00:29:30,800 --> 00:29:34,000 For more about geology b, as well as pictures and 492 00:29:34,000 --> 00:29:38,500 illustrations, that support this podcast, go to geology B.com.