1 00:00:04,400 --> 00:00:07,600 This is Geology Bites with Oliver Strimpel. 2 00:00:08,840 --> 00:00:13,400 Most of Earth's salt is dissolved in the oceans, but 3 00:00:13,400 --> 00:00:16,920 there is also a significant amount of solid salt among 4 00:00:16,920 --> 00:00:20,560 continental rocks. And because of their mechanical 5 00:00:20,560 --> 00:00:24,800 properties, salt formations have an outsize effect on the 6 00:00:24,800 --> 00:00:27,720 structure and evolution of the rocks that surround them. 7 00:00:28,360 --> 00:00:32,960 This gives rise to what we call salt tectonics, at first sight, 8 00:00:32,960 --> 00:00:36,720 a rather surprising juxtaposition of a soft, powdery 9 00:00:36,720 --> 00:00:39,640 substance with a word that connotes the larger scale 10 00:00:39,640 --> 00:00:43,560 structure of the crust. Michael Hudeck has been working 11 00:00:43,560 --> 00:00:47,760 on salt tectonics since 1989, when he joined the Production 12 00:00:47,760 --> 00:00:52,040 Research Group at Exxon. He is currently investigating 13 00:00:52,040 --> 00:00:56,320 salt tectonics in regions in which rifting has created salt 14 00:00:56,320 --> 00:01:01,240 basins, such as in Brazil, West Africa and the Gulf of Mexico, 15 00:01:01,960 --> 00:01:05,960 and has Co written a definitive textbook on salt tectonics. 16 00:01:06,840 --> 00:01:10,320 He is a research professor at the Bureau of Economic Geology 17 00:01:10,600 --> 00:01:12,800 at the University of Texas at Austin. 18 00:01:14,000 --> 00:01:16,600 Michael Hudeck, welcome to Geology Bytes. 19 00:01:17,240 --> 00:01:21,160 It's a pleasure to be here. What exactly do we mean by salt 20 00:01:21,160 --> 00:01:24,280 tectonics? Well, I think you have to start 21 00:01:24,280 --> 00:01:27,440 by understanding what we mean by salt, because it's a somewhat 22 00:01:27,440 --> 00:01:30,200 slippery term. What most people mean when they 23 00:01:30,200 --> 00:01:34,200 say the word salt is table salt, which is sodium chloride. 24 00:01:34,200 --> 00:01:38,600 The mineral name for it is halite in the Earth's surface or 25 00:01:38,600 --> 00:01:41,960 in the earth generally. A lot of the world salt is 26 00:01:41,960 --> 00:01:44,880 actually halite, but they're actually a whole bunch of other 27 00:01:44,880 --> 00:01:48,360 minerals that are typically deposited with salt and they 28 00:01:48,360 --> 00:01:52,360 have complicated names of carnalite, tachyhydrides, 29 00:01:52,800 --> 00:01:55,960 silvite and hydride, gypsum and so forth. 30 00:01:56,640 --> 00:02:01,200 So salt is very often in geology used as kind of a catch all term 31 00:02:01,200 --> 00:02:05,000 meaning all of those minerals, but the most important one is 32 00:02:05,000 --> 00:02:09,360 the mineral halite. Now, salt tectonics refers to 33 00:02:09,360 --> 00:02:12,480 the structures that form when this salt starts to flow, 34 00:02:13,000 --> 00:02:16,240 because in geology, salt is a fairly unique mineral. 35 00:02:16,240 --> 00:02:19,240 We think of rock as being a word meaning something hard and 36 00:02:19,240 --> 00:02:22,800 impossible to break. Salt actually is a rock that can 37 00:02:22,800 --> 00:02:27,040 flow at geologic strain rates and under geologic conditions, 38 00:02:27,360 --> 00:02:30,280 and so it's actually one of the weakest rocks on planet Earth. 39 00:02:30,720 --> 00:02:34,000 And salt tectonics refers to the whole set of processes and 40 00:02:34,000 --> 00:02:36,960 structures that are formed when the salt starts to flow. 41 00:02:37,200 --> 00:02:40,360 What sort of size structures are we talking about? 42 00:02:41,000 --> 00:02:47,040 Well, single salt domes are often say 5 to 8 kilometers tall 43 00:02:47,040 --> 00:02:50,200 and can be 10 or 15 kilometers across. 44 00:02:50,600 --> 00:02:53,760 When you start getting a larger composite salt structures that 45 00:02:53,760 --> 00:02:56,400 are made of many salt structures that have sort of flowed 46 00:02:56,400 --> 00:02:59,080 together. The largest ones on earth are 47 00:02:59,080 --> 00:03:03,280 the Angola Salt Nap, which runs for several 100 kilometers in 48 00:03:03,280 --> 00:03:07,600 the deep water offshore Gabon and Angola, and then the Sigsbee 49 00:03:07,600 --> 00:03:10,360 Escarpment in the deep water Gulf of Mexico, which likely 50 00:03:10,360 --> 00:03:13,800 covers several 10s of thousands of square kilometers. 51 00:03:14,200 --> 00:03:17,320 So it's simply enormous structure, bigger than most U.S. 52 00:03:17,320 --> 00:03:20,360 states. Wow, that's absolutely enormous. 53 00:03:20,360 --> 00:03:23,080 I had no idea that we had so much salt. 54 00:03:23,080 --> 00:03:28,200 And where does it all come from? Most salt in the earth comes 55 00:03:28,200 --> 00:03:32,440 from evaporation of seawater. If you think about how much 56 00:03:32,440 --> 00:03:35,160 seawater has to evaporate to make salt, I mean, everybody 57 00:03:35,160 --> 00:03:37,200 knows seawater is salty if you taste it. 58 00:03:37,920 --> 00:03:41,320 If you take 1 kilometer of seawater and evaporate it, you 59 00:03:41,320 --> 00:03:43,920 end up with something like 12 meters of salt. 60 00:03:44,600 --> 00:03:48,880 And so to get salt deposits of one or two or three kilometers 61 00:03:48,880 --> 00:03:52,440 thick, which many of them were, you start having to refill the 62 00:03:52,440 --> 00:03:55,760 basin with water many of times and evaporate all the water and 63 00:03:55,760 --> 00:03:58,080 then refill it again and evaporate all the water. 64 00:03:58,640 --> 00:04:02,240 So you take really just enormous quantities of water. 65 00:04:02,560 --> 00:04:05,760 If you had it all in one place, it would be a column of water 66 00:04:05,760 --> 00:04:09,720 more than 100 kilometers tall to make a lot of the salt basins on 67 00:04:09,720 --> 00:04:12,200 earth. So it takes a while to deposit 68 00:04:12,200 --> 00:04:15,160 it, but it reflects the evaporation of just massive 69 00:04:15,160 --> 00:04:18,640 amounts of seawater. There are some minor salt 70 00:04:18,640 --> 00:04:23,120 deposits that come from evaporation of saline lakes, but 71 00:04:23,120 --> 00:04:26,120 by far the most important one on earth is seawater. 72 00:04:26,360 --> 00:04:30,360 Was the earth endowed with its salt when it was formed? 73 00:04:30,960 --> 00:04:33,640 Well the earth wasn't even endowed with water when it was 74 00:04:33,640 --> 00:04:37,640 formed, so it took a while for the rock cycle to get going and 75 00:04:37,640 --> 00:04:41,560 most of the salt was originally bound up in minerals inside the 76 00:04:41,560 --> 00:04:43,680 earth. And there was a process that 77 00:04:43,680 --> 00:04:47,360 went on for a long time called out gassing, where the early 78 00:04:47,360 --> 00:04:51,240 earth had volcanoes and things spewing various gases into the 79 00:04:51,240 --> 00:04:53,920 air. Which then formed water and 80 00:04:53,920 --> 00:04:58,080 oceans, and the salt was one of the substances that came from 81 00:04:58,080 --> 00:05:01,400 both erosion and out gassing of the original planet. 82 00:05:01,640 --> 00:05:05,760 So it took a while for sort of a stable water cycle and a stable 83 00:05:05,760 --> 00:05:10,840 salt cycle to get going. Do we see evidence of such vast 84 00:05:10,840 --> 00:05:13,880 amounts of salt anywhere else in the solar system? 85 00:05:14,560 --> 00:05:18,080 Well, there has been salt tectonics reported on a whole 86 00:05:18,080 --> 00:05:22,600 variety of different planets. On Mars, on Europa, which is a 87 00:05:22,600 --> 00:05:26,400 moon of Jupiter, on Triton, which is a moon of Neptune. 88 00:05:27,040 --> 00:05:30,560 And it's all done from satellite imagery and saying, oh, that 89 00:05:30,560 --> 00:05:32,440 looks like that could be a salt structure. 90 00:05:32,920 --> 00:05:36,520 So we don't really have direct evidence as in a sample that's 91 00:05:36,520 --> 00:05:41,360 salt, but there are weak things flowing around on other planets, 92 00:05:41,640 --> 00:05:45,040 and they are sometimes inferred to be salt, but we actually 93 00:05:45,040 --> 00:05:48,360 don't know the mineralogy. They could be made of borates or 94 00:05:48,360 --> 00:05:50,360 sulfates. They don't necessarily have to 95 00:05:50,360 --> 00:05:53,240 be sodium chloride, the one we're most most used to. 96 00:05:53,720 --> 00:05:56,280 And in some cases, people think that you have salt like 97 00:05:56,280 --> 00:06:00,640 tectonics going on as a result of ice, frozen water in the 98 00:06:00,640 --> 00:06:03,120 subsurface. What you really need is there's 99 00:06:03,120 --> 00:06:06,800 anything that's weaker than the rocks around it and you can get 100 00:06:06,800 --> 00:06:09,800 salt, like tectonics all over the solar system. 101 00:06:10,160 --> 00:06:14,600 In my introduction I said that salt formations have an outsize 102 00:06:14,600 --> 00:06:18,520 effect on the local structures. Why is that? 103 00:06:18,680 --> 00:06:22,600 And what kind of structures form when salt is involved? 104 00:06:23,680 --> 00:06:27,560 Well, if you think about salt flowing in the subsurface and it 105 00:06:27,560 --> 00:06:31,080 moves from point A to point B, and if there are rocks or 106 00:06:31,080 --> 00:06:35,320 sediments over the top of the salt, those rocks above the salt 107 00:06:35,320 --> 00:06:39,400 have to deform and move and go up or down or sideways when the 108 00:06:39,400 --> 00:06:44,640 salt is flowing underneath them. And so a salt basin looks very 109 00:06:44,640 --> 00:06:48,080 different from just a regular basin that does not have salt 110 00:06:48,560 --> 00:06:52,160 because the flow of the salt underground and sometimes up at 111 00:06:52,160 --> 00:06:56,160 the surface has a huge effect on the rocks both above the salt 112 00:06:56,160 --> 00:06:59,640 and to the sides of the salt. So you get styles of structures 113 00:06:59,640 --> 00:07:01,680 that you just don't see anywhere else. 114 00:07:01,800 --> 00:07:07,080 So do we generally see significant salt structures in 115 00:07:07,080 --> 00:07:10,560 any particular plate tectonic setting, for example? 116 00:07:11,120 --> 00:07:15,560 Yeah, plate boundaries. Well, to get salt deposited in 117 00:07:15,560 --> 00:07:19,680 the 1st place, you need to take vast amounts of seawater and you 118 00:07:19,680 --> 00:07:23,320 need to evaporate the seawater. So, for example, there are no 119 00:07:23,320 --> 00:07:27,280 salt basins forming today in the Pacific Ocean because even 120 00:07:27,280 --> 00:07:31,040 though you're evaporating lots and lots of water, that water 121 00:07:31,040 --> 00:07:34,280 gets replaced by flow of water coming in from the Indian Ocean 122 00:07:34,280 --> 00:07:37,640 and from the Atlantic Ocean and from rivers coming in. 123 00:07:37,800 --> 00:07:42,120 So what you need is a lot of water evaporation and coupled 124 00:07:42,120 --> 00:07:45,840 with an isolation of the basin so that you cannot replace the 125 00:07:45,840 --> 00:07:48,880 water that's getting evaporated. And there are some plate 126 00:07:48,880 --> 00:07:52,200 tectonic settings that favor that more than others, in 127 00:07:52,200 --> 00:07:56,080 particular rifting when a continent is splitting apart for 128 00:07:56,080 --> 00:07:59,200 the first time. So you've got Europe and Africa 129 00:07:59,200 --> 00:08:02,120 separating from South America and North America at the birth 130 00:08:02,120 --> 00:08:05,160 of the Atlantic Ocean. Well, initially there's a really 131 00:08:05,160 --> 00:08:09,920 long skinny basin separating the 2 mega continents from each 132 00:08:09,920 --> 00:08:14,440 other as they pull apart. And so that's an ideal situation 133 00:08:14,440 --> 00:08:19,080 for salt to be deposited because there can be a lot of 134 00:08:19,080 --> 00:08:22,040 evaporation in that long skinny basin and it's hard to replace 135 00:08:22,040 --> 00:08:25,400 the water for the water to get in down the axis of that long 136 00:08:25,400 --> 00:08:27,760 basin. So in that case, you had salt 137 00:08:27,760 --> 00:08:31,520 basins forming both in offshore Brazil and offshore West Africa, 138 00:08:32,000 --> 00:08:35,840 and you also had the salt forming in the North Atlantic as 139 00:08:35,840 --> 00:08:38,039 well. Nova Scotia's got salt basins 140 00:08:38,039 --> 00:08:40,440 and so does Morocco, which are a conjugate to each other. 141 00:08:40,440 --> 00:08:42,280 They were originally attached to each other. 142 00:08:42,640 --> 00:08:47,040 So very early in rifting is where you get salt deposition. 143 00:08:47,560 --> 00:08:50,840 Now salt structures, when the salt starts to flow, they 144 00:08:50,840 --> 00:08:53,640 actually sort of have the reverse provenance because it's 145 00:08:53,640 --> 00:08:56,960 when continents collide that this salt, which may have been 146 00:08:56,960 --> 00:09:00,240 perfectly happy to just sit there in the subsurface for long 147 00:09:00,240 --> 00:09:03,360 periods of time, all of a sudden you've got 2 continents ramming 148 00:09:03,360 --> 00:09:05,880 into each other, and any salt that's there wants to get out 149 00:09:05,880 --> 00:09:08,680 any way it can. And so it starts moving all over 150 00:09:08,680 --> 00:09:12,120 the place. So many mountain belts have 151 00:09:12,320 --> 00:09:15,560 large contributions from salt structures in them because the 152 00:09:15,560 --> 00:09:18,360 salt just wasn't happy when the continents started slamming into 153 00:09:18,360 --> 00:09:19,760 each other and it started moving. 154 00:09:19,760 --> 00:09:23,160 Do those structures sometimes make it to the surface? 155 00:09:23,960 --> 00:09:26,400 They do. And in fact, there are some 156 00:09:26,400 --> 00:09:30,320 today in Iran, Iran's undergoing a plate tectonic collision with 157 00:09:30,320 --> 00:09:34,120 Arabia, the Arabian plate, and you've got salt basically 158 00:09:34,120 --> 00:09:37,720 popping out onto the ground surface and flowing sideways as 159 00:09:37,720 --> 00:09:39,760 what are sometimes called salt glaciers. 160 00:09:40,160 --> 00:09:43,120 You actually get salt flowing down the sides of mountains. 161 00:09:43,520 --> 00:09:45,800 And if you actually go on Google Earth, you can find them. 162 00:09:45,800 --> 00:09:49,680 They're very spectacular. Now, Iran's a nice place to see 163 00:09:49,680 --> 00:09:52,920 those because it's a desert, because as you can imagine, or 164 00:09:52,920 --> 00:09:56,480 large parts of Iran are desert anyway, as you can imagine, the 165 00:09:56,480 --> 00:09:59,240 more it's raining, the more the salt tends to get dissolved just 166 00:09:59,240 --> 00:10:00,920 the minute it comes up to the surface. 167 00:10:01,240 --> 00:10:04,040 But to get those things preserved, you need a way not to 168 00:10:04,040 --> 00:10:06,560 have them all dissolved. And a desert's a great place to 169 00:10:06,560 --> 00:10:09,720 do that. So where do we see evidence of 170 00:10:09,720 --> 00:10:14,240 salt tectonics today? Well, salt is active in a whole 171 00:10:14,240 --> 00:10:16,960 bunch of basins, many of them offshore. 172 00:10:17,120 --> 00:10:22,000 So unless you have some sort of echo sounding of the sea floor 173 00:10:22,000 --> 00:10:23,720 or seismic data to look underneath. 174 00:10:23,720 --> 00:10:26,520 But the Gulf of Mexico, both the northern and southern parts of 175 00:10:26,520 --> 00:10:31,040 the Gulf of Mexico, offshore US and offshore Mexico are just 176 00:10:31,080 --> 00:10:32,960 riddled with active salt tectonics. 177 00:10:32,960 --> 00:10:35,720 Salt is flowing all over the place in those basins. 178 00:10:35,720 --> 00:10:38,800 The same is true in offshore West Africa and Gabon and 179 00:10:38,800 --> 00:10:40,920 Angola. The same is true in offshore 180 00:10:40,920 --> 00:10:43,320 Brazil. You've got active salt 181 00:10:43,320 --> 00:10:45,200 structures happening in the North Sea. 182 00:10:45,520 --> 00:10:50,400 So most active salt provinces are actually marine and so the 183 00:10:50,400 --> 00:10:53,000 main people that know about them are people who look in marine 184 00:10:53,000 --> 00:10:55,880 areas, which could be researchers doing hydrography, 185 00:10:55,880 --> 00:10:59,160 but mostly oil and gas companies who are looking for the oil and 186 00:10:59,160 --> 00:11:02,320 gas that is very often associated with salt structures. 187 00:11:02,680 --> 00:11:05,720 So you mentioned the compressive environment. 188 00:11:06,640 --> 00:11:10,480 What happens to the salt then if it doesn't come to the surface? 189 00:11:10,480 --> 00:11:13,200 Do you get domes, diapers forming? 190 00:11:13,200 --> 00:11:16,080 And is that a collapse of the material above it? 191 00:11:16,840 --> 00:11:21,320 Well when you squeeze salt it a really wants to get to the 192 00:11:21,320 --> 00:11:23,520 surface of any kind of way it can. 193 00:11:24,160 --> 00:11:26,680 But if it can't get up to the surface normally it will 194 00:11:26,680 --> 00:11:30,160 accumulate into large bulges which form anticlines and Dome 195 00:11:30,160 --> 00:11:33,440 the rocks over the top and between the domes. 196 00:11:33,440 --> 00:11:35,680 They're what are called synclines, the low area where 197 00:11:35,680 --> 00:11:38,720 the salt flowed out of. But if there are any 198 00:11:38,720 --> 00:11:42,120 pre-existing salt domes that were there before the shortening 199 00:11:42,120 --> 00:11:45,440 started, it's like kind of holding a banana in your hand 200 00:11:45,440 --> 00:11:48,760 and squeezing the banana and the just liquid banana comes 201 00:11:48,760 --> 00:11:51,800 shooting out the top because you're squeezing it shut. 202 00:11:52,280 --> 00:11:55,000 And so that's what happens to any pre-existing domes is they 203 00:11:55,000 --> 00:11:58,920 typically pinch shut or close to shut and the salt goes squirting 204 00:11:58,920 --> 00:12:02,080 out the top. So it can form a variety of 205 00:12:02,080 --> 00:12:05,160 different structures. It's also a very good lubricant 206 00:12:05,160 --> 00:12:09,040 because it's so weak and so if there is a salt layer someplace, 207 00:12:09,280 --> 00:12:11,880 rocks like to slide along salt layers. 208 00:12:11,880 --> 00:12:15,400 So that's another big factor in both compressional environments 209 00:12:15,400 --> 00:12:18,160 actually and extensional ones is salt as a lubricant. 210 00:12:18,360 --> 00:12:20,880 And how does that manifest in the local structures when you 211 00:12:20,880 --> 00:12:24,720 have that sliding movement? Well, when you have that, rocks 212 00:12:24,720 --> 00:12:29,040 can move 10s of kilometers sideways, and so there are 213 00:12:29,040 --> 00:12:31,560 extensional structures in the area where the rocks are pulling 214 00:12:31,560 --> 00:12:33,160 away. It's sort of like the top end of 215 00:12:33,160 --> 00:12:36,400 a landslide and down at the bottom that the down dip end of 216 00:12:36,400 --> 00:12:38,280 the landslide. There are shortening structures, 217 00:12:38,280 --> 00:12:40,760 thrust faults, folds, and so forth. 218 00:12:41,080 --> 00:12:45,120 So if you take 2 margins, 2 continental margins, one of 219 00:12:45,120 --> 00:12:48,840 which has salt and one doesn't, and you crunch them both in the 220 00:12:48,880 --> 00:12:52,600 same plate collision, the one without salt is certainly going 221 00:12:52,600 --> 00:12:54,760 to be deformed. But the style is not going to be 222 00:12:54,760 --> 00:12:58,040 nearly as complicated as what you see when there is salt 223 00:12:58,040 --> 00:13:00,360 present. Salt just makes everything 224 00:13:00,360 --> 00:13:03,720 pretty much go nuts. Has the presence of large salt 225 00:13:03,720 --> 00:13:08,200 structures had a significant effect on the way Earth's global 226 00:13:08,320 --> 00:13:12,320 plate tectonics takes place? The presence or absence of large 227 00:13:12,320 --> 00:13:16,840 salt structures really has no influence at all on the overall 228 00:13:16,840 --> 00:13:18,600 pattern of global plate tectonics. 229 00:13:18,600 --> 00:13:21,200 The plates that we're going to collide, collide anyway. 230 00:13:21,200 --> 00:13:23,280 The rates don't particularly change. 231 00:13:23,560 --> 00:13:27,520 However, what you do get is a very significant modification in 232 00:13:27,520 --> 00:13:30,240 the structural styles that you see now. 233 00:13:30,240 --> 00:13:34,080 The structural styles of a plate collision zone in the absence of 234 00:13:34,080 --> 00:13:36,600 salt structures have been extensively studied and are 235 00:13:36,600 --> 00:13:39,880 really very well known. Classic examples include the 236 00:13:39,880 --> 00:13:44,280 Canadian Rockies and many other fold and thrust belts around the 237 00:13:44,280 --> 00:13:46,400 world. Now when you have salt 238 00:13:46,400 --> 00:13:50,280 structures that are present, the whole structural pattern of the 239 00:13:50,280 --> 00:13:54,440 collision zone changes because the first thing that happens in 240 00:13:54,440 --> 00:13:58,480 a collision zone that involves pre-existing salt structures is 241 00:13:58,480 --> 00:14:00,880 that the salt structures are the first things to activate. 242 00:14:00,880 --> 00:14:03,560 And so the pattern that results depends on the pattern of the 243 00:14:03,560 --> 00:14:06,280 salt structures. And you get patterns that are 244 00:14:06,280 --> 00:14:10,520 completely unlike the normal fold and thrust belts that form 245 00:14:10,520 --> 00:14:15,640 in margins without salt. So in the 1950s, sixties, 70s, 246 00:14:15,640 --> 00:14:20,200 even into the 80s, you had geologists who are unknowingly 247 00:14:20,200 --> 00:14:24,360 mapping collision zones that involved salt and trying to 248 00:14:24,360 --> 00:14:27,560 interpret them with standard fold and thrust belt ideas. 249 00:14:27,560 --> 00:14:29,800 And they would be tying themselves into all kinds of 250 00:14:29,800 --> 00:14:33,760 knots because they're actually were salt structures there that 251 00:14:33,760 --> 00:14:37,280 were confusing everything and it just wasn't a normal fold and 252 00:14:37,280 --> 00:14:39,040 thrust belt. And the geologists would have 253 00:14:39,040 --> 00:14:43,280 all kinds of problems trying to make a salt involved margin that 254 00:14:43,280 --> 00:14:46,760 was involved in a collision as if the salt was not present. 255 00:14:47,560 --> 00:14:52,240 So starting in the late 1980s and into the 1990s, geologists 256 00:14:52,240 --> 00:14:55,360 began to understand the huge influence that salt tectonics 257 00:14:55,360 --> 00:14:58,720 could have on continental collision zone. 258 00:14:59,040 --> 00:15:02,080 There's been a pattern ever since then, one after another, 259 00:15:02,360 --> 00:15:06,360 of looking at collisional belts and identifying where the salt 260 00:15:06,360 --> 00:15:10,480 had actually been present and actually reinterpreting all of 261 00:15:10,480 --> 00:15:13,280 these margins in a new way with the recognition that they 262 00:15:13,280 --> 00:15:18,440 involved salt tectonics. So is there an overall control 263 00:15:18,440 --> 00:15:21,080 of salt tectonics on global plate tectonics? 264 00:15:21,080 --> 00:15:24,120 No, there's not. But does it change the style of 265 00:15:24,120 --> 00:15:28,040 what happens in plate tectonics? Yes, it does, very much. 266 00:15:28,320 --> 00:15:32,240 And one of the big advances in structural geology in the last 267 00:15:32,240 --> 00:15:35,880 30 or 40 years has been the recognition that you really have 268 00:15:35,880 --> 00:15:39,240 to know if salt structures are present or not in order to 269 00:15:39,240 --> 00:15:43,320 correctly interpret the margin. Some of the places that you 270 00:15:43,320 --> 00:15:48,080 mentioned are also centers of oil production, that's true. 271 00:15:48,200 --> 00:15:51,680 Is there a connection between salt tectonics and the formation 272 00:15:51,680 --> 00:15:55,280 of hydrocarbon reserves? There are for a couple of 273 00:15:55,280 --> 00:15:58,600 reasons. One is to get hydrocarbons, oil 274 00:15:58,600 --> 00:16:01,000 and gas, you need what's called a source rock. 275 00:16:01,400 --> 00:16:06,000 And a source rock is generally a very organic rich shale in most 276 00:16:06,000 --> 00:16:07,600 cases doesn't have to be a shale. 277 00:16:08,360 --> 00:16:10,400 So you need a very organic rich shale. 278 00:16:10,400 --> 00:16:12,640 Well, so how do you get an organic rich shale? 279 00:16:12,960 --> 00:16:16,440 So most basins have little microscopic creatures or bigger 280 00:16:16,440 --> 00:16:19,960 creatures dying all the time and they accumulate at the bottom. 281 00:16:19,960 --> 00:16:23,560 But there are all sorts of organisms that eat organic 282 00:16:23,560 --> 00:16:27,200 matter, little bugs both at the surface and in the subsurface. 283 00:16:28,120 --> 00:16:30,720 And so you need an environment in which those bugs are not 284 00:16:30,720 --> 00:16:34,120 active for some reason. You preserve the organic matter 285 00:16:34,120 --> 00:16:36,800 better. And the kind of hyper saline or 286 00:16:36,800 --> 00:16:41,480 very salt rich environments in which salt is deposited are also 287 00:16:41,480 --> 00:16:45,360 very hostile to the organisms that eat organic matter. 288 00:16:45,360 --> 00:16:48,000 They can't survive in hyper saline environments. 289 00:16:48,480 --> 00:16:51,920 So if you've got an environment that is either making salt or 290 00:16:51,920 --> 00:16:55,400 has recently made salt and is still very hyper saline, the 291 00:16:55,400 --> 00:16:58,880 organic matter that dies very often is preserved. 292 00:16:58,920 --> 00:17:01,280 There's nothing at the bottom to eat it because the water is too 293 00:17:01,280 --> 00:17:05,119 salty. So one factor is that salt 294 00:17:05,240 --> 00:17:08,680 basins tend to have very good source rocks associated with the 295 00:17:08,680 --> 00:17:11,040 salt. And then there's the factor that 296 00:17:11,040 --> 00:17:13,640 all this movement of salt that I've been talking about, the 297 00:17:13,640 --> 00:17:17,359 flow of salt in salt tectonics, tends to make a lot of big 298 00:17:17,359 --> 00:17:21,079 structures, big anticlines. And many of those structures 299 00:17:21,079 --> 00:17:24,839 trap hydrocarbons, you know, an anticline, which is a big Dome 300 00:17:24,839 --> 00:17:28,000 of sediments coming up. Well, hydrocarbons tend to be 301 00:17:28,000 --> 00:17:30,320 lighter than water, so they migrate up to the top of the 302 00:17:30,320 --> 00:17:33,480 Dome and they're trapped there. And so oil companies come and 303 00:17:33,480 --> 00:17:36,360 they drill the top of the anticline and produce the oil 304 00:17:36,360 --> 00:17:38,320 and gas. So it's an environment very rich 305 00:17:38,320 --> 00:17:42,880 in traps for oil and gas. And then the last thing is that 306 00:17:42,880 --> 00:17:46,720 salt is itself a very good seal for hydrocarbons. 307 00:17:47,240 --> 00:17:51,680 And by a seal we mean that if the oil or gas is trapped under 308 00:17:51,680 --> 00:17:54,600 the salt, it's very difficult for them to leak through the 309 00:17:54,600 --> 00:17:57,320 salt. It makes a good sort of trap 310 00:17:57,320 --> 00:18:00,560 over the top and if for some reason you do manage to 311 00:18:00,560 --> 00:18:05,000 fracture, the salt itself heals because it re crystallizes very 312 00:18:05,000 --> 00:18:07,160 easily. So if you somehow managed to 313 00:18:07,160 --> 00:18:09,640 disrupt the seal, it heals itself. 314 00:18:10,520 --> 00:18:13,840 So because there's good source rocks, because it makes lots of 315 00:18:13,840 --> 00:18:16,880 traps and because it's a very good top seal. 316 00:18:16,880 --> 00:18:20,000 For example, most of the salt on the Arabian platform or at least 317 00:18:20,000 --> 00:18:23,280 a large part of the salt on the Arabian platform, which is why 318 00:18:23,280 --> 00:18:27,280 Saudis Dr. Mercedes-Benz around is sealed underneath salt. 319 00:18:27,480 --> 00:18:30,200 And in this case, it's not halite, the mineral, it's 320 00:18:30,200 --> 00:18:33,320 actually anhydride is the principal top seal over a lot of 321 00:18:33,320 --> 00:18:37,640 the Arabian platform, another salt, but still illustrates the 322 00:18:37,640 --> 00:18:40,960 prospect that salt makes a very good top seal for oil and gas. 323 00:18:41,520 --> 00:18:44,680 In Saudi Arabia in particular, and the Middle East perhaps more 324 00:18:44,800 --> 00:18:48,640 generally, the oil is very close to the surface, isn't it? 325 00:18:48,640 --> 00:18:51,800 Is that because you're looking at the top of one of these 326 00:18:52,200 --> 00:18:54,120 domes? No. 327 00:18:54,120 --> 00:18:57,600 The oil reservoirs in Saudi Arabia are actually much more 328 00:18:57,600 --> 00:19:00,560 widely distributed than in any single salt structure. 329 00:19:01,000 --> 00:19:05,000 And in fact, in most cases, the oil is actually not in one of 330 00:19:05,000 --> 00:19:08,320 those anticlines. It's in another type of trap 331 00:19:08,320 --> 00:19:10,240 entirely. And the main function of the 332 00:19:10,240 --> 00:19:14,000 salt on the Arabian platform is actually as a top seal, not in 333 00:19:14,000 --> 00:19:15,760 making the structures themselves. 334 00:19:16,000 --> 00:19:18,920 To stop it sort of leaking out into the surrounding rocks. 335 00:19:19,040 --> 00:19:20,960 Yes, to stop it from leaking away. 336 00:19:20,960 --> 00:19:23,640 Exactly. Salt has been a valuable 337 00:19:23,640 --> 00:19:27,520 commodity for much of human history, and it has many uses 338 00:19:27,520 --> 00:19:31,560 even today. What are those uses, and do we 339 00:19:31,560 --> 00:19:34,200 get our salt by mining the salt structures we've been 340 00:19:34,200 --> 00:19:36,680 discussing? Well, for many years we did. 341 00:19:36,920 --> 00:19:39,640 We don't generally anymore get our salt from mining. 342 00:19:39,640 --> 00:19:43,080 So going back into the Neolithic, the principal uses of 343 00:19:43,080 --> 00:19:47,360 salt were for food preservation. It was used in tanning hides, 344 00:19:47,360 --> 00:19:50,120 and it also had some medicinal uses as well. 345 00:19:50,600 --> 00:19:55,280 And so for that reason, a lot of early Neolithic settlements were 346 00:19:55,280 --> 00:19:59,360 located around sources of salt, and they're big archaeological 347 00:19:59,360 --> 00:20:03,040 sites going back many thousands of years around some of these. 348 00:20:03,360 --> 00:20:06,640 Some of these were salt springs where the groundwater just had 349 00:20:06,640 --> 00:20:10,040 salt dissolved in it, and the people took the salt and heated 350 00:20:10,040 --> 00:20:12,080 it up in a pan and got the salt out of that. 351 00:20:12,360 --> 00:20:15,800 In other cases, the salt was exposed at the surface and you 352 00:20:15,800 --> 00:20:18,480 had Neolithic miners going in and mining it. 353 00:20:19,160 --> 00:20:23,440 You can go look up the Salt Men of Iran online if you want to. 354 00:20:23,800 --> 00:20:26,840 A series of miners got trapped in cave insurance in some of 355 00:20:26,840 --> 00:20:30,400 these salt mines. And because salt is very good at 356 00:20:30,400 --> 00:20:33,840 preserving things, they basically got pickled inside the 357 00:20:33,840 --> 00:20:35,600 salt. They died and were buried by 358 00:20:35,600 --> 00:20:38,080 salt and were more recently extracted. 359 00:20:38,080 --> 00:20:41,440 And there's some museums in Iran that have these, you know, heads 360 00:20:41,440 --> 00:20:44,320 of Neolithic miners preserved in them. 361 00:20:44,320 --> 00:20:47,320 So it's sort of a ghoulish, but it does illustrate very well 362 00:20:47,320 --> 00:20:50,280 exactly why salt was so valuable because things are preserved 363 00:20:50,280 --> 00:20:52,000 very well when they're packed in salt. 364 00:20:52,880 --> 00:20:57,000 So these days, up until I'd say 50 years ago, the most common 365 00:20:57,000 --> 00:20:58,760 way to get salt was by mining it. 366 00:20:59,240 --> 00:21:01,560 And so there were many salt mines around the world. 367 00:21:02,000 --> 00:21:06,160 These days, at least in the United States and Europe, most 368 00:21:06,160 --> 00:21:09,280 salt is made in factories by chemical reactions. 369 00:21:09,480 --> 00:21:12,560 It's not naturally occurring salt, although there are still 370 00:21:12,560 --> 00:21:14,640 parts of the world in which salt is mined. 371 00:21:15,200 --> 00:21:17,560 But in most of the industrialized world, it's 372 00:21:17,560 --> 00:21:21,240 actually made in factories. What about evaporation pans in 373 00:21:21,240 --> 00:21:23,200 shallow seas or even in the Dead Sea? 374 00:21:23,560 --> 00:21:27,880 Yes, those still exist, and in many places where there were no 375 00:21:27,880 --> 00:21:33,680 naturally occurring salt basins, again, Neolithic or Middle Ages, 376 00:21:34,240 --> 00:21:37,520 miners evaporated seawater one way or another, even in climates 377 00:21:37,520 --> 00:21:39,240 where you wouldn't think that was possible. 378 00:21:39,800 --> 00:21:42,200 I mean England for example, which isn't a tropical 379 00:21:42,200 --> 00:21:44,240 environment, and you wouldn't think you could do that. 380 00:21:44,240 --> 00:21:49,920 In England a witch was a salt working from usually water 381 00:21:49,920 --> 00:21:51,640 evaporation. So any English city with the 382 00:21:51,640 --> 00:21:55,440 word witch in it, Norwich and so forth was originally a salt 383 00:21:55,440 --> 00:21:58,760 working. Salt was also used as a form of 384 00:21:58,760 --> 00:22:00,720 currency in antiquity, wasn't it? 385 00:22:01,200 --> 00:22:04,520 It was the rumor that Roman soldiers were sometimes paid in 386 00:22:04,520 --> 00:22:08,360 salt is correct. And in fact the Roman word Sal, 387 00:22:09,000 --> 00:22:11,680 which meant salt, was the root of our word salary. 388 00:22:12,000 --> 00:22:13,640 Was somebody being worth their salt? 389 00:22:13,640 --> 00:22:16,000 I mean it actually. They were on occasion paid 390 00:22:16,000 --> 00:22:18,800 directly in salt. It was that valuable. 391 00:22:19,160 --> 00:22:22,520 And in other times wars were fought over access to salt 392 00:22:22,960 --> 00:22:25,960 because it was so critical for civilization, especially food 393 00:22:25,960 --> 00:22:29,680 preservation. In lots of Europe cod there were 394 00:22:29,680 --> 00:22:34,120 wars over COD and salt to pickle the COD or preserve the COD 395 00:22:34,640 --> 00:22:36,520 fought in especially northern Europe. 396 00:22:37,400 --> 00:22:38,960 What are you working on at the moment? 397 00:22:39,360 --> 00:22:41,080 I've been working on a couple of things. 398 00:22:41,080 --> 00:22:44,800 One of them is some of the salt tectonics going on in the very 399 00:22:44,800 --> 00:22:48,640 deep water part of the Nile Delta and offshore Egypt. 400 00:22:48,640 --> 00:22:50,760 It's actually far enough out in the Mediterranean that it's 401 00:22:50,760 --> 00:22:53,280 offshore Cyprus. You've passed from Egyptian 402 00:22:53,280 --> 00:22:57,840 waters to Cypriot waters. And in that area the salt has 403 00:22:57,840 --> 00:23:00,720 been flowing downhill under the weight of the Nile Delta. 404 00:23:01,280 --> 00:23:04,600 And it's actually ramming up against a big basement high 405 00:23:04,600 --> 00:23:06,760 that's out in the middle of the Mediterranean called the 406 00:23:06,760 --> 00:23:10,360 Eratosthenes Seamount. And it making all kinds of 407 00:23:10,360 --> 00:23:12,880 really interesting structures that are visible on seismic 408 00:23:12,880 --> 00:23:15,280 data. And so we're working on a big 3D 409 00:23:15,280 --> 00:23:18,000 seismic cube to try to understand what's going on. 410 00:23:18,480 --> 00:23:21,160 And there have been some recent oil and gas discoveries in that 411 00:23:21,160 --> 00:23:24,640 area, which is why oil companies are interested in the research 412 00:23:24,640 --> 00:23:27,280 and are helping to support us financially to do it. 413 00:23:27,840 --> 00:23:33,040 So the salt structures might be indicative of the presence of 414 00:23:33,040 --> 00:23:36,600 oil. Not directly, but the oil and 415 00:23:36,600 --> 00:23:39,800 gas is certainly associated with salt structures and you need to 416 00:23:39,800 --> 00:23:43,200 be able to correctly interpret the salt structures in order to 417 00:23:43,200 --> 00:23:47,040 find the oil and gas because salt structures, because they 418 00:23:47,040 --> 00:23:50,440 are so complicated when you look at them for the first time on 419 00:23:50,440 --> 00:23:54,880 seismic data, many interpreters, the first response is go, what's 420 00:23:54,880 --> 00:23:56,720 that? You know, it looks terrible. 421 00:23:57,400 --> 00:24:01,200 And so we sort of try to provide techniques for understanding 422 00:24:01,200 --> 00:24:03,760 what's going on and being able to interpret it. 423 00:24:03,760 --> 00:24:06,520 So you can say, oh, I get it, that's what this is, which means 424 00:24:06,520 --> 00:24:08,360 the oil and gas would be over here. 425 00:24:08,800 --> 00:24:11,800 And so it's not so much that the oil and gas is directly 426 00:24:11,800 --> 00:24:15,800 reservoir inside the salt or caused by the salt, but you need 427 00:24:15,800 --> 00:24:18,280 to be able to interpret the salt structures to find it. 428 00:24:19,400 --> 00:24:21,520 Michael Hudeck, thank you very much. 429 00:24:21,880 --> 00:24:25,240 It's been a pleasure, Oliver. 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