| 00:03 | Yes. Okay. So this map the world shows you the distribution of |
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| 00:10 | warm water carbonate. So in these are the famous areas of modern |
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| 00:15 | marine carbonate deposition. So you can areas around florida, The Bahamas off |
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| 00:20 | yucatan lack of of police in you can see the the area in |
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| 00:28 | Arabian gulf. All right. That setting for modern carbonate ramp deposition. |
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| 00:34 | then of course Southeast Asia and along equator. You see lots of black |
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| 00:38 | . Those are reefs. And the Asia is famous for its uh shell |
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| 00:43 | carbonate platforms with reef deposition. And uh and then you can see |
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| 00:49 | Australia on the north, northwest sorry. And the northeast side, |
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| 00:57 | can see that on the northeast side a great barrier reef. And then |
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| 00:59 | the northwest side there's also shallow water deposition. So, what's the common |
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| 01:04 | here? Well, the red areas define our tropical subtropical belt from the |
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| 01:11 | north to about 30 degrees and from equator south to 30 degrees. And |
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| 01:15 | do we get carbonate deposition in these ? We get it because the water |
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| 01:19 | warm is supersaturated with respect to calcium . It's free of most solicit plastic |
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| 01:26 | . Okay. And that's why you good you have clear water, warm |
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| 01:32 | and those are some of the key for shallow marine carbonate deposition. |
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| 01:37 | And then you'll notice there. The shows cool water carbonate deposition here |
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| 01:42 | And most of the famous cool water deposits are Uh north or south of |
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| 01:49 | latitude. And the famous areas are of New Zealand and Australia, but |
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| 01:55 | notice that some areas off of Western for example, that are in the |
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| 01:59 | belt or subtropical belt. And the for that is because of up welling |
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| 02:04 | the leeward sides of these continents where wind blows offshore, you get up |
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| 02:08 | into the marine water, you get water upwelling along that margin and that's |
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| 02:12 | you can get some carbonate deposition associated cooler water even though you're in a |
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| 02:18 | or subtropical setting. But uh I'm gonna downplay the cold water carbonate |
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| 02:24 | for this segment because in the rock unless you unless you prospect in New |
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| 02:30 | you're not going to find oil and deposits in these so called cool water |
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| 02:34 | . Alright, all right. And the third part of the story is |
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| 02:41 | notice the dark green on this map this is not labelled here. Uh |
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| 02:48 | labeled with the era of the Black . These are the global Torino uses |
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| 02:53 | arena is a plastic foraminifera that lives the upper part of the water |
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| 02:57 | but out in deep water and when dies it contributes to the sediment to |
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| 03:03 | this huge apology carbonate material. This the precursor to the famous chalk deposits |
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| 03:09 | the north sea chalks or the Austin or Eagle furred here in texas. |
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| 03:14 | uh so that's where these accumulate, don't accumulate in shallow water, they |
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| 03:20 | in these deeper water basins. But at the distribution of the dark |
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| 03:24 | It's very patchy in distribution. And reason for that has to do with |
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| 03:28 | saturation state of the ocean and the of the ocean basins. So, |
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| 03:33 | see a lot of dark green and indian ocean and north and southern part |
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| 03:37 | the atlantic oceans in the southern But look at the northern pacific |
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| 03:42 | You don't see a lot of yellow . The yellow means it is devoid |
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| 03:46 | these pelagic uses. All right. not that the organisms don't live |
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| 03:50 | They do live there, but when settle down into the water column, |
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| 03:54 | dissolve out before they ever reached the . And so I'm sure most of |
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| 03:58 | , as an undergraduate heard of the compensation deputy reaganite compensation depth. That's |
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| 04:04 | depth below which all the reaganite or dissolves out and it's relatively shallow in |
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| 04:11 | atlantic. I'm sorry. In the uh it's uh and uh it's controlled |
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| 04:18 | by how much carbon production you have the water column, but also the |
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| 04:22 | of the water because the colder the , the easier it is to dissolve |
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| 04:26 | carbonate as it settles out. And the saturation state is controlled by river |
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| 04:31 | bringing in dissolved carbonate material. So you just don't have a lot of |
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| 04:36 | river systems feeding into the northern pacific . And that's why you don't get |
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| 04:40 | lot of pelagic carbonate is preserved. right. So that's the last I'm |
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| 04:46 | to talk about the Iraq tonight or compensation depth because again, most of |
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| 04:51 | expiration are in basins that are too where this phenomenon would come into |
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| 04:56 | Right? So, uh the now been using the term shallow water and |
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| 05:03 | water. So let me define what mean by shallow water To a carbon |
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| 05:07 | geologist. It generally means water depths than 10 m. Deedee. |
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| 05:14 | And it reflects the relationship shown by cartoon here you see on the left |
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| 05:19 | total carbonate production in blue. Look high it is when your water depths |
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| 05:25 | than 10 m. And then there's dramatic drop off at about 10 |
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| 05:30 | And what does that reflect? it reflects two things. It reflects |
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| 05:33 | fact that as you deepen the light decreases. Most of the organisms that |
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| 05:39 | these skeletal components require light for So as you diminish light penetration, |
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| 05:46 | carbonate productivity decreases. And then what's other thing that happens? The water |
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| 05:51 | colder? Obviously, as you go in cold water again, works against |
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| 05:56 | to precipitate carbonate into a skeleton or sediment. Things like that. So |
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| 06:02 | why we use 10 m is sort the rough cut off between shallow water |
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| 06:07 | relatively deep water. Okay. And . Including the car. Yes. |
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| 06:18 | the virus. Hello, the Sure. I can tell you |
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| 06:24 | Cooperative congress can't from golden after it accumulate below the cal cider or reaganite |
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| 06:33 | depth. That's the depth below which the carbonate is gone. That can |
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| 06:40 | . You could be in a situation some of it dissolves but it's still |
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| 06:44 | on the sea floor. You just reached that calcite compensation depth or reaganite |
|
| 06:49 | depth. Okay. Yeah. It's as the depth below which everything is |
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| 06:57 | . Everything is dissolved out nothing Which is not uncommon today because our |
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| 07:04 | are really deep. But in the record, most of our basins do |
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| 07:08 | explore for? We're not that So usually wouldn't come into play |
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| 07:14 | Okay. So we'll talk about later . We'll talk about the way we |
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| 07:19 | the sediment in shallow marine settings. the breakdown of the skeletal hard parts |
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| 07:25 | organisms live on the sea floor or other organic or inorganic processes that create |
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| 07:30 | sediment that accumulates in shallow water. so one of the things that I'm |
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| 07:38 | hopefully give you an appreciation for with discussion next weekend when we get into |
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| 07:42 | carbonate environments is that uh, many these carbonate environments have the potential to |
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| 07:51 | a great volume of sediment forgiven unit time. And that's what this diagram |
|
| 07:57 | trying to show here. So the bars that you see here, our |
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| 08:02 | of sedimentation, you can see one per 1000 years or 10 m per |
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| 08:06 | years. You see tidal flats, lights, reefs, and, and |
|
| 08:12 | that are associated with the reefs. it's really important to appreciate this for |
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| 08:17 | reasons. First of all, most these sediments are accumulating in the same |
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| 08:21 | which they initially formed. Okay, unlike classics, we don't erode from |
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| 08:26 | environment re deposit somewhere else. We do that, but it's not as |
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| 08:30 | as just being in an environment and producing and preserving the sediment in that |
|
| 08:36 | . Okay. And what that means that, sorry? What that means |
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| 08:43 | that uh, you compare these rates sedimentation as you can see how they |
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| 08:47 | outpaced long term subsidence. So that they're gonna do what through time, |
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| 08:52 | gonna shallow up. Right. We about carbonate systems showing up through |
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| 08:56 | And that's because of this relationship And even some of these carbonates systems |
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| 09:01 | outpace are rising sea levels that we during different geological time periods. And |
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| 09:10 | they can easily outpaced these rising sea , which again allows them to shallow |
|
| 09:14 | or to even build up above sea to make an island or or something |
|
| 09:19 | that. Okay, so when you back to the rock record and you |
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| 09:22 | at these ancient platform systems and we're to talk about the bomb a platform |
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| 09:28 | later in this segment, the bahama complex started to develop arguably during the |
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| 09:35 | Jurassic, but certainly in the early and it's now 5 to 6 kilometer |
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| 09:40 | package of shallow marine carbonate deposits So, when you see that, |
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| 09:46 | really not hard to appreciate why that because of the high rates of sedimentation |
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| 09:52 | , whether a number of these environments make up these carbonate platforms. |
|
| 09:57 | and that really should be the takeaway for from this, from this |
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| 10:04 | Okay, so let's talk about the , distinctive aspects that differentiate carbonate rocks |
|
| 10:09 | solicit plastic deposits. The first is basil origin. The second is this |
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| 10:15 | dependence on organic activity. The 3rd is this high susceptibility to post oppositional |
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| 10:22 | . And then the last part is complex poor geometry that often comes along |
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| 10:27 | the dye genesis of these carbonates compared a simple sandstone system. Okay, |
|
| 10:34 | let me take each of these points break them down a little bit more |
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| 10:37 | and everything that I talk about in lecture, I will repeat again in |
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| 10:42 | detail when we get into more just focused discussions about these different aspects of |
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| 10:49 | or die genesis. Okay, so do we mean by inter basin |
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| 10:54 | We mean that most carbonate sediments are at, We're close to the point |
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| 10:58 | final deposition. Okay, They're going be sensitive to what we call fizzy |
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| 11:03 | setting, Sea level change and the and chemical processes that operate in that |
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| 11:09 | of deposition. And I'll let me fizz a graphic setting. That's a |
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| 11:15 | region that is influenced by both global local effects. And uh let me |
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| 11:24 | it at that for right now because gonna come back and explain that much |
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| 11:26 | detail later. But but there is global aspect of fizzy graphic setting, |
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| 11:31 | is where did you sit relative to equator. Right. That controls whether |
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| 11:35 | tropical, subtropical or temperate and then a local control and that's the bottom |
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| 11:42 | that ties back to the two in models that I just mentioned, the |
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| 11:46 | margin platform versus the carbonate ramp. . And then you're going to see |
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| 11:53 | these carbonates not only control their own environment that they modify. They strongly |
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| 11:58 | their neighboring environments. In the classical , that as a carbonate reefs, |
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| 12:03 | reef is building up like this as builds up as it shallows up the |
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| 12:07 | character, the reef changes because the change responding to changes in water depth |
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| 12:12 | energy. But as it shallows up sea level, it modifies circulation behind |
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| 12:17 | in the back briefly again. So this process response response. No process |
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| 12:24 | feedback mechanism that comes into play when talking about some of these carbonate |
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| 12:29 | Okay. And you get that you that, I think to some degree |
|
| 12:33 | classics, to write a barrier island an effect obviously on the back barrier |
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| 12:38 | . Right? As it builds up this builds up to sea level. |
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| 12:42 | , so to drive this relationship we have the simple cartoon here that |
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| 12:47 | a shallow water carbonate platform That we've now as being less than 10 m |
|
| 12:52 | water depth, dropping off into a deeper basin. And I have not |
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| 13:00 | the term basin because there is no definition of a carbonate basin. There's |
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| 13:04 | specific water depth that we put onto . All right, so, you're |
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| 13:09 | see some carbonate basins are like we today in the Caribbean where there are |
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| 13:13 | m deep. Other basins, like going to show you from the Arabian |
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| 13:17 | , 80 m Steve. So, a relative term. Okay, and |
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| 13:21 | how we use it in carbonates. , we're talking about a carbon base |
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| 13:25 | we're not talking about gulf of Mexico depths where you're talking about thousands of |
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| 13:29 | of water. Okay, And when look at your shallow water carbonate |
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| 13:34 | you look at the top of this all along the top of the |
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| 13:37 | In shallow water, you're producing different of carbonate sediment based on the influence |
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| 13:43 | water depth and circulation of seawater salinity alkalinity and things like that. And |
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| 13:50 | of these sediments are accumulating essentially the environment which they initially formed. So |
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| 13:55 | the concept of inter basin origin. , that doesn't mean you can't move |
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| 14:01 | from one area to another, you do that by major storms or hurricanes |
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| 14:04 | typhoons. All right, so a storm or hurricane can take material from |
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| 14:09 | shallow subtitle and throw it up on adjacent land mass. That's how we |
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| 14:14 | a carbonate titles. Lab. We really should call the storm |
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| 14:19 | but in the literature we call them flats. Tidal currents usually don't have |
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| 14:23 | to do with deposition. It's the deposition that brings the sediment from A |
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| 14:29 | feet or five ft of water and that sentiment up on the adjacent land |
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| 14:33 | . Okay, sometimes it goes the way the storm pushes material from shallow |
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| 14:39 | off into deeper water. So in , we will get deep water |
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| 14:43 | liked urbanites, debris flows, grain . Okay. Like you're doing |
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| 14:49 | but mostly most of the time it's a bomb a sequence or anything like |
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| 14:54 | . It is just a simple grain or debris flows. That oftentimes just |
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| 15:00 | one on top of the other sometimes create greater thicknesses. Okay, All |
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| 15:05 | . So in the literature, people about carbonates being born not made. |
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| 15:10 | basically what they're saying is carbonates have central basin origin. They basically accumulating |
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| 15:16 | same setting where they initially formed, is good because that means we can |
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| 15:21 | at the attributes of the sediments and out something about the deposition environment and |
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| 15:26 | to extend the trend when we're trying map trends in the subsurface, |
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| 15:30 | Yeah. Alright. To illustrate that a photograph taken from one of the |
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| 15:37 | shuttle flights um looking down on the eastern portion of the great bahama Bank |
|
| 15:46 | . So mentally you have to look the left 150 km. That's where |
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| 15:51 | city of Miami would be. so we're about 27, north of |
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| 15:56 | equator when a subtropical setting. And can see in this photograph the lighter |
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| 16:03 | colored water. This is the shallow carbonate platform area. Where are we |
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| 16:09 | shallow water carbonate deposition? The black that you see here that runs sort |
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| 16:15 | north to south is an older Pleistocene called the Luther island. And the |
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| 16:21 | is built up to about 200 ft present a sea level. It formed |
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| 16:26 | during a different sea level stand. was five day m higher Than it |
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| 16:31 | today, back about 120,000 years Okay. And then sea level dropped |
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| 16:37 | everything got exposed to verily to be into the present day limestone. And |
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| 16:44 | you see the darker blue surrounding this Where the 20 km bar is. |
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| 16:49 | called Exuma Sound. That's a deep and payment that cuts into the |
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| 16:53 | It's 2000 m deep in the axis that in payment. Okay. And |
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| 16:59 | off to the right is the open ocean and it's even deeper as 4000 |
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| 17:05 | just a couple of miles off of island to the right. Okay, |
|
| 17:11 | just look at the area here that outlining with my pointer, you can |
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| 17:15 | changes in the color of the sediments the sea floor, right along the |
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| 17:19 | margin. Here is one style of . And then what do you see |
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| 17:23 | , a long linear belt of this material. This turns out to be |
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| 17:28 | energy bulajic sand deposition driven by strong current agitation. And then when the |
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| 17:34 | currents weighing you stop making the woods you transform into a quieter water, |
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| 17:41 | muddy carbonate environment. Further inboard on platform. Okay, so you can |
|
| 17:46 | this out which is what I did my master's thesis many, many moons |
|
| 17:51 | . And you can see this pattern here. A type of coral and |
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| 17:58 | Calgary's algae contributing sediment along the margin , it's not a reef. |
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| 18:06 | It's a rocky bottom with scattered coral algal growth producing the thin veneer of |
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| 18:11 | sediment. So we typically call this sand and then behind it and yellow |
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| 18:15 | black is the you allergic sand belt then a changed orange and green reflects |
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| 18:20 | low energy, slightly deeper water setting the sand body system. Uh The |
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| 18:26 | should be uh talented fecal pellets created burrowing organisms right with a muddy |
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| 18:34 | but more fecal pellets than mud. it's a what we call a political |
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| 18:40 | . And then the green would be polluted line muds that occur in the |
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| 18:43 | restricted part. Okay, so what happening here, we're changing the environmental |
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| 18:50 | as we move from the high energy margin to the low energy platform |
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| 18:55 | And we see these belts of deposition correspondent lee and you see how they |
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| 19:00 | up parallel to the platform margin. . In the bulk of the sediments |
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| 19:04 | each of these environments stays fixed in in those particular deposition environments. That's |
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| 19:10 | concept of international origin. All right , it doesn't mean you can't move |
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| 19:15 | from the top of the Luther bank say Exuma sound. You can do |
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| 19:21 | Back in the mid 1980s. UU group from the University of Miami went |
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| 19:26 | to Exuma Sound and they dropped these piston cores into the basin. They |
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| 19:32 | these piston cores into 2000 m of and they penetrated through the whole scene |
|
| 19:37 | the upper part of the unconsolidated And what do they recover? |
|
| 19:42 | they recovered mostly deep water, pelagic deposition related to global giants. |
|
| 19:47 | That's because that's where they live. sometimes they would encounter a few inches |
|
| 19:53 | maybe half a foot of bulajic Well, you'll exam doesn't form in |
|
| 19:58 | m of water. Right. Wood wood stands for him in shallow |
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| 20:03 | persistently agitated shallow water. And so implication is that periodically storm shed? |
|
| 20:09 | is from these platforms into that deeper setting. Okay. But the bulk |
|
| 20:14 | this material up on the platform stays in place. That's the concept of |
|
| 20:19 | origin. Okay, the second point this high dependence on organic activity. |
|
| 20:29 | you've all looked at, I'm sure samples as part of your undergraduate training |
|
| 20:35 | most lines phones are made up of recognisable remains of the skeletal hard parts |
|
| 20:40 | these organisms. Right? And the the pieces, the easier it is |
|
| 20:43 | recognize what contributed that material. But course the stuff can be broken down |
|
| 20:49 | the sea floor, uh by crunchers stingrays and sharks in the finer grained |
|
| 20:56 | , or can be broken down by activity on the sea floor in the |
|
| 21:00 | grade material. And so it's always the rock record of challenge, trying |
|
| 21:04 | recognize some of the smaller scale fragments where they come from. Right. |
|
| 21:09 | you do see the recognizable organic remains these organisms that contribute to the |
|
| 21:15 | The second point was that the little parallel bio faces. You just saw |
|
| 21:19 | illustrating the previous map. Right? little faces, Those belts of different |
|
| 21:24 | of deposition parallel the margin because the contributing to those environments. Also paralleled |
|
| 21:32 | distribution parallel the platform margin. All , and then you're going to learn |
|
| 21:36 | the next lecture. The grain formation is often related to organic activity. |
|
| 21:42 | reworking is very common in carbonates, as it is in some solicit plastic |
|
| 21:48 | . And then the diabetic patterns that see in carbonates often reflect the mineralogy |
|
| 21:54 | the constituents that contributed to the So, when I take you through |
|
| 21:58 | grain types in our next to I'm going to make you aware of |
|
| 22:01 | . What we think are the starting ease, Right. Are they cal |
|
| 22:05 | ? Are there a genetic that makes big difference in terms of the way |
|
| 22:10 | sediments later respond to die genesis? whether we generate any secondary porosity in |
|
| 22:16 | carbonates or not. Okay, so me let me take this slide and |
|
| 22:22 | on this in more detail. here's an underwater photograph of a modern |
|
| 22:27 | from the caribbean. What's the organic here? Well, it's obviously the |
|
| 22:31 | and make up this reef. These corals are fast growing corals that |
|
| 22:36 | 16-18 cm a year. I the girl like weeds underwater, |
|
| 22:41 | All right. And they'll continue to until what until a big storm comes |
|
| 22:47 | and knocks them over. Right. , the big scale hurricanes will knock |
|
| 22:51 | reefs over. And and you'll see of this later in our discussion uh |
|
| 22:56 | know, in a couple of Alright. Uh So, it's pretty |
|
| 23:00 | in a reef. What the organic . Right? It's the it's the |
|
| 23:04 | and you know, not all reefs made up of wall to wall |
|
| 23:08 | you living coral, I don't know any of you have ever snorkeled on |
|
| 23:12 | modern reef or not. But you very quickly that there are a lot |
|
| 23:16 | open areas between where the corals grow there's a lot of sedimentation occurring in |
|
| 23:21 | areas that are occupied by other kinds organisms producing settlement. So when you |
|
| 23:26 | at any modern setting, like this from the great barrier reef in |
|
| 23:32 | the zone of active reef growth is the re front. So that underwater |
|
| 23:36 | would be associated with this part of reef on the right And it's relatively |
|
| 23:42 | at any one point in time. only one or 200 m across. |
|
| 23:47 | right. But when it gets decimated major storm activity, what do those |
|
| 23:52 | or typhoons do they throw this material up onto the reef? They create |
|
| 23:57 | wide rubble flat that we call the flat. That can be 10-20 times |
|
| 24:03 | than the reef front. Okay. when you if you were to go |
|
| 24:08 | at some of these deposits in the , you would see the re flat |
|
| 24:13 | made up of the coarser grain. recognisable fragments of the corals, but |
|
| 24:18 | lot of the coral materials broken down an even finer scale sand material like |
|
| 24:24 | see uh just north of my foot . All right. All right. |
|
| 24:30 | then the reef system is pretty obvious the organic influences. But you go |
|
| 24:34 | other carbon environments. And here's a underwater. Looking down on the sea |
|
| 24:40 | . This is c egress. And seagrass is not unique to the |
|
| 24:45 | sea grasses go all the way back the lower cretaceous. All right. |
|
| 24:50 | been able to document sea grasses yet the paleozoic, but certainly common all |
|
| 24:55 | the Mesozoic and tertiary. And so the role? What's the subtle role |
|
| 25:01 | seagrass? Well, first thing cigarettes is it is a baffler. |
|
| 25:06 | It grows these light obviously and it on the sea floor and it traps |
|
| 25:11 | suspended material, putting a suspension by storms or the occasional hurricane. So |
|
| 25:17 | actually can build topography through time. can actually build what we call mounds |
|
| 25:23 | on the sea floor and that actually of these mountains turned out to be |
|
| 25:28 | in the rock record. All And then the second thing is it |
|
| 25:32 | an effective route network. And so that's accumulated in the setting is going |
|
| 25:37 | be better preserved because it's very difficult erode these sea grass banks. |
|
| 25:42 | Once they take place very, very to ride them, It takes base |
|
| 25:47 | a category four or 5 hurricane to them up. Okay. And then |
|
| 25:52 | the third important important influence of It's a substrate for other carbonate |
|
| 25:59 | Okay. And if you look at you look at the sea grass blades |
|
| 26:03 | close, you see all kinds of on the sea grass. You see |
|
| 26:09 | crusty looking material here that has sort a light pink color. That's actually |
|
| 26:14 | in crusty in red algae. That's carbonate related material. All |
|
| 26:19 | so, that's living on the grass . Then, you see these little |
|
| 26:24 | features here. Those are little cal worm tubes. So, it's a |
|
| 26:29 | that secretes a little worm like It lives in. It filter |
|
| 26:33 | but it attaches to the grass And then you get things like bright |
|
| 26:38 | , you get things like benthic You could gaster pods that graze on |
|
| 26:43 | seagrass. Okay, and why is important? That's important because the grass |
|
| 26:49 | only lift each grass blade. Let start over. Each plant Proceed four |
|
| 26:55 | . Alright. And each blade only 15 days. So every 60 |
|
| 27:01 | whatever is living on Those blades becomes of the seven. Right? As |
|
| 27:05 | blades die. And what happens to organic material of the blade? It |
|
| 27:10 | disintegrates. Right, get oxidized in water column, and it disintegrates. |
|
| 27:15 | are you left with? You're left all this carbon material that wouldn't be |
|
| 27:20 | if the sea grass blades weren't there begin with. Okay, so that's |
|
| 27:24 | much more subtle organic influence on carbonate then, of course, in |
|
| 27:31 | we get borrowing activity. These volcano features, you see here underwater are |
|
| 27:37 | uh mounds of excreted sediment produced by shrimp. The borrowing shrimp look like |
|
| 27:46 | . They're about the scale of This or 3". Okay. That's as |
|
| 27:52 | as they are. But look at tails. They're separated. The tales |
|
| 27:56 | adapted to digging. All right. so what do these shrimp do they |
|
| 28:01 | ? They're deep escalating borrowers. They down like this. They put outside |
|
| 28:06 | at one level, they go to level. They put outside chambers like |
|
| 28:10 | . Okay. And when they encounter screen material, they don't try to |
|
| 28:14 | it out to the top to make volcano man, they packed the side |
|
| 28:18 | with the shell material. What do push out the top? The lightweight |
|
| 28:22 | pellets that they produce? Okay, what are they shrimp doing? They |
|
| 28:28 | first of all destroying any primary Right? And then secondly, they're |
|
| 28:33 | oxygenated water into the sediment. So doing what They're oxidizing organic material. |
|
| 28:39 | destroying the potential for that rock or to be a source rock. |
|
| 28:44 | so when we talk about carbonate source later, you'll see that all the |
|
| 28:48 | class carbonate source rocks are associated with settings where you didn't have anything living |
|
| 28:54 | the sea floor, right? Including burrowing organisms. And these are the |
|
| 29:01 | pellets. So if you sample the of one of those borough mounds and |
|
| 29:05 | it back and to the lab and run it through as if this is |
|
| 29:10 | you would get. These are what call the hardened fecal pellets there, |
|
| 29:15 | he cemented after deposition on the sea . These are the ones that better |
|
| 29:20 | in the sediment. Okay. And can see from the millimeter scale here |
|
| 29:24 | of them have a short diameter less one millimeter. And they all have |
|
| 29:29 | unique ovoid to live soil shape. , so these are called fecal pellets |
|
| 29:34 | the modern environments. That's another influence organic activity on the sea floor. |
|
| 29:42 | organic influence perhaps a little bit more is activity related to boring organisms. |
|
| 29:50 | by boring, we're not talking about and personality. We're talking about physical |
|
| 29:57 | where an organism takes bores into hard . Okay. And how does it |
|
| 30:03 | that? It either does that by creating a hole or by excreting acid |
|
| 30:10 | dissolve the carbon a material or doing . Okay, so all of the |
|
| 30:14 | you see here in this coral were by various boring organisms. This is |
|
| 30:19 | boring Wallace where the militia was still . You see these little features like |
|
| 30:26 | . He's open galleries. These are by boring sponges. And then you |
|
| 30:31 | these linear holes like this. These created either by boring worms for boring |
|
| 30:38 | . Okay, so what are they ? Well, first thing they're doing |
|
| 30:42 | they're creating ferocity. Right? That's they want to live right there creating |
|
| 30:46 | habitat where they can live. But importantly, they're taking a bigger piece |
|
| 30:50 | coral and they're breaking it down into sand silt sized or mud size |
|
| 30:56 | And this is the way we break down on the sea floor. |
|
| 30:59 | This is why our lime stones are made up of these huge shells. |
|
| 31:04 | ? There all stuff that gets broken either by sharks and stingrays or by |
|
| 31:09 | macro boring organisms. All right. you can see the slide here, |
|
| 31:14 | rate that these organisms produce sediment, boring sponge, for example, can |
|
| 31:19 | up to 20 kg of sediment per . I mean, that's incredible when |
|
| 31:24 | think about it. All right. , we'll build on this relationship when |
|
| 31:29 | when we talk about some of the carbonate environments. And then two slides |
|
| 31:35 | basically differentiate carbonates from classics in terms their the dye genetic potential. It's |
|
| 31:41 | carbonates. The thing that scares a of companies from chasing carbonate reservoirs is |
|
| 31:47 | productive prediction. Right. And they're concerned about predicting ferocity because they know |
|
| 31:54 | systems are much more reactive than a . Simple sandstone. Uh, |
|
| 31:59 | right, courts doesn't react very And even, you know, feldspar |
|
| 32:05 | , but certainly not to the degree certainly don't get the degree of dissolution |
|
| 32:09 | we get in these carbonate systems. so the post deposition, all these |
|
| 32:16 | are very susceptible. Post oppositional highly reactive system. I'm sure you've |
|
| 32:21 | put to loot hydrochloric acid on a . You see it fizz, |
|
| 32:25 | That's a reflection of its higher So it has a higher solid solid |
|
| 32:30 | than courts. But even within the of carbonate mineralogy, right? A |
|
| 32:35 | calcite, dolomite, those minerals have stability relationships too. And that's one |
|
| 32:41 | the drivers. We're going to talk tomorrow for die genesis for both for |
|
| 32:45 | stones and dollar stones. All And then what's another important control is |
|
| 32:49 | size of the particles. Right. you want to dissolve something in |
|
| 32:53 | what do you do you make it her grand. Right. You powder |
|
| 32:57 | . So final Grand carbonate reacts much quickly than coarser grained carbonate material. |
|
| 33:02 | an important control on solid ability Right. And what's interesting about these |
|
| 33:08 | systems, whether it's more low energy carbonate system or high energy carbonate. |
|
| 33:13 | reef. Most of these systems start with relatively high porosity and permeability is |
|
| 33:18 | the sea floor. Which means that off the bat, if you bring |
|
| 33:21 | right kind of fluid through that rocker , you can start to modify |
|
| 33:26 | Die genetically. Even on the sea , you can't do that in the |
|
| 33:30 | of classics. Right? Nothing happens in the world of plastics. On |
|
| 33:34 | sea floor. Everything is driven by burial. Okay, so early die |
|
| 33:39 | is very important in carbonates. Not at all in a classic system. |
|
| 33:46 | as a result, we end up carbonate ferocity. That's much more complex |
|
| 33:50 | terms of its geometry and genesis compared sand stones, we have a mixture |
|
| 33:55 | what we call pre deposition of That's the ferocity associated. But the |
|
| 34:00 | fossils of the organisms lived on the floor. Right? And then we |
|
| 34:06 | other environmental processes that control the texture the sediment and the texture obviously has |
|
| 34:12 | impact on the starting processing permeability. . But that's just what happens on |
|
| 34:17 | sea floor. Then we have to concerned what happens when you take those |
|
| 34:21 | and you start to progressively bury Well, that's the world of die |
|
| 34:25 | . And this is what creates the of trying to predict process ahead of |
|
| 34:29 | drill bit. But we'll try to some sense out of this tomorrow. |
|
| 34:33 | we get into more detailed discussion about diet genesis. All right, So |
|
| 34:38 | me just show you a couple of to illustrate some of these relationships and |
|
| 34:42 | I'll build on this in much more tomorrow. The first slide here is |
|
| 34:48 | underwater photograph taken on that white sand system that I showed you in the |
|
| 34:52 | photograph. So you're looking down about , 20 ft of water. And |
|
| 34:58 | what do you see on the sea ? You see some ripple dualistic sands |
|
| 35:02 | here on the bottom left side. most of the bottom here looks like |
|
| 35:06 | rocky outcrop. Yes, yeah. it is because what's happening here, |
|
| 35:12 | of the olympic stand is being cemented place to create this hard ground |
|
| 35:17 | So this is an example of early genesis on the sea floor where right |
|
| 35:22 | some of the sands are being cemented a reaganite. It is precipitating out |
|
| 35:26 | the marine water column. So this called marine sanitation. And the byproduct |
|
| 35:32 | what we call a marine hard which is this stock cropping material you |
|
| 35:37 | on the sea floor. Okay. then if you look at this in |
|
| 35:41 | section, you can see the nature these cements. All right there they |
|
| 35:47 | . All the way around the zoo which are magnetic and the cement sarl |
|
| 35:54 | uh because of the way they don't to a certain type of stain. |
|
| 35:59 | know there are magnetic and uh this material that literally starts to precipitate within |
|
| 36:05 | few months or a few years on sea floor. And then is that |
|
| 36:09 | ground develops? You keep adding more more cement as you pass seawater through |
|
| 36:14 | hard ground. Okay, so that's example of uh essentially Cindy positional marine |
|
| 36:21 | . Now sometimes our carbonates and we'll stick with the simple analytic stand |
|
| 36:26 | Sometimes I carbonates get exposed severely to water. Either regionally sea level drops |
|
| 36:32 | a low standard sea level or we an island up above sea level to |
|
| 36:36 | it to rainfall. Well, what to a magnetic goods a reaganite doesn't |
|
| 36:42 | to be exposed to fresh water so quickly dissolves. Okay. And so |
|
| 36:47 | what happened here in the Jurassic. former Reagan ecowas were exposed to fresh |
|
| 36:53 | . They dissolved out to create what secondary molding ferocity. But what happens |
|
| 36:59 | that dissolved carbonate? It goes back the system and re saturates and re |
|
| 37:05 | as a more stable form of low calcite. Low magnesium calcite is stable |
|
| 37:10 | fresh water Oregon. It's not So here's an example of what we |
|
| 37:15 | Parisian version controlled by the starting meteorology by exposure to fresh water. And |
|
| 37:23 | of course, sometimes rus sands never any marine sedimentation, any exposure to |
|
| 37:28 | water. They just get progressively Well, this is a common |
|
| 37:32 | right? They end up being not by exposure to fresh water, |
|
| 37:37 | they get dissolved because of pressure. is pressure solution. All right. |
|
| 37:42 | all heard of the term skylight? this is this is like a style |
|
| 37:46 | but it's called grain to grain. . Train wherever the grains touch, |
|
| 37:49 | dissolve and inter penetrate into each other of the extreme pressure. Okay. |
|
| 37:56 | we'll talk about this in more detail . And then sometimes after these uh |
|
| 38:03 | example, the zoo it sands have buried into the realm of virtual |
|
| 38:07 | You can see the grains are future later. If there's still some permeability |
|
| 38:12 | those brain stones, you bring the kind of fluid through. You can |
|
| 38:15 | this is all some of those they're not a magnetic anymore. They've |
|
| 38:19 | been stabilized to cal side, but they're seeing a fluid that is aggressive |
|
| 38:24 | to dissolve even the cal citic material that grain. And this is what |
|
| 38:29 | call barrel dissolution. So all the Hugh that you see here in the |
|
| 38:34 | , it is secondary micro porosity created burial dissolution. Barrel dissolution just means |
|
| 38:40 | occurs after the onset of the pressure . And we'll talk about how deep |
|
| 38:46 | have to be for that tomorrow. right. But roughly a 1000 m |
|
| 38:51 | , but it could be a lot than that. All right. |
|
| 38:55 | you see there are all these different for di genesis that affects reservoir |
|
| 39:00 | And this is what we need to about. And then apply to our |
|
| 39:03 | type discussion toward the end of the . This is just limestone die |
|
| 39:09 | We haven't even talked about Dolomites. , right. So, there are |
|
| 39:13 | number of major reservoirs around the world produced from these dola stones. And |
|
| 39:18 | we'll try to make sense out of decolonization process tomorrow afternoon and try to |
|
| 39:25 | about the different pathways for making reservoir and dramatized lime stones. Okay, |
|
| 39:33 | . All right. So, to of summarize these are the questions that |
|
| 39:37 | going to try to answer over the several weekends, give you a feel |
|
| 39:41 | where carbonate systems form, both in and deep water. Talk about the |
|
| 39:46 | controls on these carbonates systems. What their their occurrence and distribution. Right |
|
| 39:52 | each faces type. And again, way we're using the term faces. |
|
| 39:57 | a rock that reflects an environment of . All right. So platform margin |
|
| 40:03 | reef is a faces type. The flat as they face this time grain |
|
| 40:08 | is not faces. Pakistan does not . You want to associate a position |
|
| 40:14 | these depositions profiles when we use this faces. Okay, everybody understand. |
|
| 40:20 | for each faces, we're gonna first with the modern we're going to talk |
|
| 40:24 | the size and shape or geometry. talking about distribution Environmental Association. We're |
|
| 40:30 | going to talk about what controls the starting porosity and permeability. And then |
|
| 40:36 | going to happen. We're going to about what happens these carbon assistance when |
|
| 40:39 | get progressively buried. And then one we need to answer is to these |
|
| 40:45 | systems. Some of these carbonates systems organic material in quantity suitable enough to |
|
| 40:51 | a source rock. And when I in this business Back in the |
|
| 40:57 | nobody thought carbonates can be a source . But now they're world class source |
|
| 41:01 | all over the place. And so answer to that question obviously is is |
|
| 41:05 | . Okay. And then what are conventional unconventional carbonate play types? I'll |
|
| 41:11 | what I mean by conventional unconventional when get there. But I do think |
|
| 41:15 | is some predictability here with respect to fizz a graphic setting and with respect |
|
| 41:19 | geological age. And so I'll share you my classification scheme for trying to |
|
| 41:26 | about where these carbonate playtime's exist. if you're in the cretaceous and you're |
|
| 41:31 | at a platform to base in what kind of plays could you develop |
|
| 41:37 | that deposition profile? Okay, that's I want you to start thinking about |
|
| 41:42 | appreciate toward the end of the Yeah. Okay. So you're gonna |
|
| 41:47 | this when I when we start our about carbonate plays, you're going to |
|
| 41:52 | this slide again. Every play obviously a in a relationship between reservoir, |
|
| 41:59 | nearby source rock doesn't have to be could be a shale source rock. |
|
| 42:04 | need a ceiling faces. Right? be carbonate or could be shale. |
|
| 42:09 | . And then you need a trapping . And so historically most of our |
|
| 42:14 | or what we call combination traps have structural and strata graphic component. But |
|
| 42:21 | going to find more and more strata traps as we use three D seismic |
|
| 42:26 | , more and more in industry. we are finding more strata. Graphic |
|
| 42:30 | . All right. So they're going become more and more common now that's |
|
| 42:34 | play type. Right, Made up these three elements source rock. |
|
| 42:38 | seal faces. This is what we to talk about for each of those |
|
| 42:43 | before we get to our discussion about place to understand the big scale controls |
|
| 42:48 | deposition all faces and digest history on play type elements. And then how |
|
| 42:54 | these control? Well, they're controlled things like barrel history and the poor |
|
| 42:58 | chemistry that comes with progressive burial. controlled on a bigger scale by fizzy |
|
| 43:02 | setting geological age relative sea level changes things like that. Okay, so |
|
| 43:09 | come back and talk about put this together. Later when we talk about |
|
| 43:13 | play types for the next several sessions get together this is what I'm going |
|
| 43:18 | be talking about. Right? The of deposition, influence of die genesis |
|
| 43:23 | some of the big scale controls that into play to drive each of those |
|
| 43:29 | . Okay, now I need to a couple more comments here and then |
|
| 43:33 | we'll break we'll take our break. minute break. Um I want to |
|
| 43:39 | sure you understand that the four different that we're gonna be talking about for |
|
| 43:43 | segment. All right. Ah Calcium is broken out into three mineral |
|
| 43:51 | A Reaganite. Hi matt calcite. high magnesium calcite. So we just |
|
| 43:57 | the community we just say hi Mag and then lo mein calcite. |
|
| 44:02 | so what's the difference between these The difference is a reaganite is a |
|
| 44:09 | mineral With a specific gravity of So it's very dense crystal lattice. |
|
| 44:16 | inner crystalline spaces are the inner I even think of the right word to |
|
| 44:24 | this. But the space between the irons is so tiny that the only |
|
| 44:29 | you can easily substitute in a reaganite the calcium is straining. Okay. |
|
| 44:35 | sometimes you can substitute up to 10,000 astronomy. Um and some of the |
|
| 44:40 | to make a modern day corals for . Right now calcite as you see |
|
| 44:46 | a hexagonal system is still calcium carbonate a different crystal structure. Hexagonal is |
|
| 44:51 | little bit more open structure. So actually easier to substitute cat irons like |
|
| 44:58 | and iron and manganese. Okay. when you substitute anywhere from 4 to |
|
| 45:05 | magnesium for the calcium, cat And you do it in a random |
|
| 45:10 | . This is what we call high calcite. Okay. So if you |
|
| 45:15 | to the modern today, if you go back to Luther bank and you |
|
| 45:19 | a sample of the settlement off the floor and you come back to the |
|
| 45:23 | and you run it through the X diffraction machine. What is the sediment |
|
| 45:27 | be comprised of mineral, logically mostly reaganite and I made calcite because that's |
|
| 45:33 | the organisms form initially in their skeleton that's what the U. S. |
|
| 45:37 | made up of a reaganite. Right physical chemical precipitation. Those minerals are |
|
| 45:43 | very happy in seawater, normal But what happens when you take those |
|
| 45:47 | minerals out of seawater, they very stabilize through digestive processes to what we |
|
| 45:54 | Loma calcite. So Lomax calcite is a hexagonal mineral. But now what |
|
| 46:00 | ? You lose the magnesium, you out most of the magnesium. Just |
|
| 46:04 | just eliminate it. You only have or two, Sometimes 4% magnesium. |
|
| 46:11 | by definition low mag cal side is less than for percent magnesium randomly distributing |
|
| 46:19 | callously lattice. So you go back the rock record while most lime stones |
|
| 46:23 | made up of lome account site, may have started out having a lot |
|
| 46:28 | a reaganite or a lot of time cal side. But now there are |
|
| 46:32 | down into a more stable form of medical side. Okay. And that's |
|
| 46:38 | related to die genesis. And we'll about more detail tomorrow. And then |
|
| 46:42 | this unique mineral called dolomite, Which explain in more detail tomorrow. Dolomite |
|
| 46:47 | definition has 50% calcium, 50% Now randomly just not randomly distributed |
|
| 46:55 | Now, it's alternating plains of calcium magnesium. Cat Island separated by planes |
|
| 47:01 | the carbonate and irons. Okay, an ordering to the distribution of the |
|
| 47:06 | and calcium. All right. That's unique mineral called dolomite. All |
|
| 47:11 | And we'll obviously talk about that later what happens to a lot of lime |
|
| 47:16 | in the rock record? They get to dolomite. And we need to |
|
| 47:21 | about that. And we will tomorrow . Okay. And then I want |
|
| 47:28 | to appreciate this diagram which has been in the literature for or modified versions |
|
| 47:33 | it have been around literature for for long time here. Well over 20 |
|
| 47:40 | . And you can see this concept calcite a reaganite sees, right? |
|
| 47:46 | there's a slide behind this that I'm over. That explains party and Stanley's |
|
| 47:51 | about why you go from the Reagan seize to calcite sees they basically related |
|
| 47:57 | sea floor spreading right? The reaction seawater with the bath salts modifies the |
|
| 48:04 | and calcium ratio seawater. Obviously when have a lot of magnesium in the |
|
| 48:09 | column, that favors times where you a reaganite or high mag calcite |
|
| 48:16 | And when you don't obviously you get calcite precipitation. So you can see |
|
| 48:22 | people have broken the south. This of calcite, a reaganite sees through |
|
| 48:26 | time. I don't have a problem this. I just want you to |
|
| 48:31 | that if you're in a calcite, that doesn't mean everything is going to |
|
| 48:35 | cal siddiq. And if you're in rag and I'd see everything can be |
|
| 48:38 | magnetic. All right. Sometimes you make a reaganite season accounts organized cement |
|
| 48:44 | a so called cal side. See you can have a regular, you |
|
| 48:48 | have regulated organisms living in a for , the upper upper paleozoic, |
|
| 48:56 | Times of Yeah propellers. OIC. you're still in supposedly a calcified |
|
| 49:02 | right. Some organisms can do whatever darn Well please by physical physical chemically |
|
| 49:10 | a reaganite or high, make calcified in a so called calcite C. |
|
| 49:16 | , So take this with a grain salt. Use it, you |
|
| 49:19 | to sort of guide you, but get the impression that if you're in |
|
| 49:23 | calcite, see everything was cal Okay, that's not the case. |
|
| 49:27 | right. And then let me introduce to the trade wind belts here. |
|
| 49:34 | is a relatively new concept. uh, this is why this is |
|
| 49:42 | representation of why I said fizzy graphic at a global scale is so |
|
| 49:48 | All right. So the global scale where does your environment deposition sit relative |
|
| 49:55 | the equator? So where is the today? It's right here. |
|
| 50:01 | Runs through southern africa, northern part South America. And you can see |
|
| 50:07 | broken out the white color belts 5° on either side of the equator |
|
| 50:14 | what is called the Doldrums. That's the sailors term. Right? |
|
| 50:21 | you're an ocean going sailor, you want to sail in the doldrums because |
|
| 50:25 | wind doesn't blow. Okay. So you're 5° on either side of the |
|
| 50:30 | , there's no persistent trade wind All right. And then what happens |
|
| 50:35 | you go from 5° To 30° north south of the equator. You go |
|
| 50:41 | a tropical to subtropical belt that is by easterly trade winds. Okay, |
|
| 50:48 | the strong easterly trade winds only operate five degrees to about 22 degrees north |
|
| 50:55 | south of the equator From 22 to , it's the more gentle easterly trade |
|
| 51:01 | . Okay. And then what happens you go north or south of |
|
| 51:05 | You get into the western lease? . And that's into your temperate water |
|
| 51:11 | . All right. Cool water Now, what do we mean by |
|
| 51:15 | trade winds? We don't mean that winds just blow out of the eastern |
|
| 51:19 | . The winds can come from the . They can come from the |
|
| 51:22 | They can come from the southeast that vary from year to year. That |
|
| 51:27 | vary during the year. Okay. this is very, very important concept |
|
| 51:34 | you will not find in the older Prior to the I'd say the mid |
|
| 51:41 | . Okay. Nobody knew about trade because nobody had worked in modern setting |
|
| 51:46 | we had strong trade wind influences. . But we've worked one in the |
|
| 51:51 | Bahamas now, and I'm going to that information with you and I'm sure |
|
| 51:54 | you all the application that comes along this and it's something that needs to |
|
| 51:58 | factored into any evaluation in the rock . If you were influenced by easterly |
|
| 52:05 | winds right from 5° north or south the equator to 30° north and |
|
| 52:11 | I'll come back and build on this and I'll show you the modern responses |
|
| 52:16 | the trade winds. And I'll show the application of the trade wind influences |
|
| 52:20 | actually, to carbonate place and Okay, so when you go back |
|
| 52:25 | the rock record, we have all published maps now that show you the |
|
| 52:29 | geography that exist for different geological time . And this is one for the |
|
| 52:35 | cretaceous. And here's the gulf of . Right? Which we're going to |
|
| 52:40 | quite a bit about because there's a of cretaceous and Jurassic oil and gas |
|
| 52:44 | around the periphery of this ancestral gulf Mexico basin. Well, what does |
|
| 52:50 | map suggests? We set where where we sit? Paleo geographically? There's |
|
| 52:56 | equator And we're about what? 15° of the equator based on relationships |
|
| 53:02 | That puts us in the heart of strong easterly trade wind belt. That |
|
| 53:07 | the area's off of the florida would been leeward to those strong winds. |
|
| 53:13 | means areas like Mexico would have been into the winds. It would have |
|
| 53:17 | windward facing. Okay, these are things. You need to think |
|
| 53:22 | All right. And so we can these maps to guide us to sort |
|
| 53:26 | think about where we're at. I never take these maps specifically and say |
|
| 53:33 | I'm right here, I'm in the subtropical setting. I would try to |
|
| 53:41 | the geology to prove these relationships. , and I'm going to show you |
|
| 53:44 | we do that during this segment. . Mhm. All right. And |
|
| 53:50 | , um Okay, I'm a rock . I look at, I have |
|
| 53:56 | at tons of core. I've looked literally tens of thousands of thin sections |
|
| 54:00 | my career. And you're gonna see lot of thin section data here because |
|
| 54:04 | carbonates we have to get to the section level in order to confirm face |
|
| 54:09 | relationships and understand die genesis and reservoir . So, historically, what is |
|
| 54:17 | way people have looked at a thin ? They looked at it with they |
|
| 54:21 | the thin section on the microscope. you see here, like coming up |
|
| 54:25 | the thin sections called plane polarized You cross the nickels on either side |
|
| 54:30 | the light goes up in one that's called cross Nichols. Cross Nichols |
|
| 54:35 | what gives you the colours to the . Right. That's called by |
|
| 54:39 | And that's what we historically used to court screen from a feldspar grain from |
|
| 54:46 | uh carbonate piece of carbon, a . Okay, but Back in the |
|
| 54:53 | 80s, as you see here, stumbled on a technique called fluorescent |
|
| 54:58 | where you generate this high intense blue light, you reflected on the thin |
|
| 55:03 | . And that allows you to see fabric. And if you spike your |
|
| 55:09 | with the fluorescent died to see micro and these carbonates that you can't see |
|
| 55:15 | the normal thin section views. And then I'll show you pictures of |
|
| 55:20 | as we go along. And so you see photographs in your notes where |
|
| 55:25 | a scale bar and it says That was shot with fluorescent microscopy. |
|
| 55:30 | . And then a few years I stumbled on this simple white paper |
|
| 55:34 | where you put a piece of white paper on your thin set on your |
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| 55:39 | the and the microscope stage and you light up from underneath. I call |
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| 55:45 | diffused plane polarized light. The simple that you've seen the literature is white |
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| 55:50 | technique. And what does this What does this technique do allows you |
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| 55:55 | see the blue microprocessor t easily without the fluorescent its attachment. And then |
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| 56:02 | also allows you see really grain fabric highly altered lime stones or dullest stones |
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| 56:06 | you can't see with any of these techniques. So, you see pictures |
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| 56:10 | this. I just want you to you see the acronyms your P. |
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| 56:14 | . F M X N. And you'll see these on the photographs of |
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| 56:19 | thin section pictures that I have in power points. Okay. That I'll |
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| 56:24 | from. And I just want you know how this was shot. All |
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| 56:28 | . And then the last slide, , the President a composition of of |
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| 56:34 | seawater. Uh you can see the proportion of the obviously a lot of |
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| 56:40 | and sodium, but I want you appreciate there's a lot of magnesium and |
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| 56:43 | a seawater. The magnesium comes into when we're trying to talk about how |
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| 56:48 | make early form dolomite? A lot the early form Dolomites are coming from |
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| 56:53 | modified seawater. Okay. And then want you to appreciate that we're going |
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| 56:59 | use this term open marine to characterize of these environments of deposition. What |
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| 57:04 | that term mean? It means normal , which today is 35 parts per |
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| 57:09 | . So, when we talk about inferred open marine environment back in the |
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| 57:13 | record, we're implying similar relationship to we have today, Which means 35 |
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| 57:20 | per 1000 salinity and good exchanges seawater that environment. Okay, yeah. |
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| 57:29 | Questions or comments before we take our minute break. All right, I'm |
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| 57:37 | to pause. We're going to start the the different grain types will start |
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| 57:47 | with the non skeletal grain types. are not carbon particles derived directly from |
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| 57:52 | breakdown of the skeletal hard parts of . But many of these grains are |
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| 57:57 | by uh Oftentimes influenced by organic And so we want to talk about |
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| 58:04 | and then we'll come back and talk the skull of particles as our last |
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| 58:08 | this afternoon. And again, the here is to introduce you to the |
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| 58:14 | green types, how we recognize how we think they form and then |
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| 58:19 | importantly, talk about their environmental Right? So, if we find |
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| 58:23 | new it in the settlement, we a uh fecal pellet or uh even |
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| 58:29 | mud in the sediment? What does tell us about the deposition environment or |
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| 58:33 | does it help us to better interpret deposition environment? So that's the whole |
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| 58:39 | . But to go through this, gonna overwhelm you with all this |
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| 58:42 | So be patient as we work through . And I'll try to apply this |
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| 58:47 | . When we get into our discussion modern carbonate environments. So this is |
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| 58:52 | standard list of carbonate, not scalable . By convention. Everybody lists. |
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| 58:57 | mud is one of the components, though lime mud, which is very |
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| 59:01 | grained carbon material can be sourced from skeletal or non skeletal material. By |
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| 59:07 | , we listed as a non scalable type and lime mud in the modern |
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| 59:13 | unconsolidated. Right. If you were walk through a muddy environment, you |
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| 59:16 | up to your ankles or knees in muddy sediment. But when it gets |
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| 59:21 | in the rock record, we don't the term line mud. We use |
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| 59:24 | term Mick. Right, Mick, , is an acronym for micro crystalline |
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| 59:29 | and reflects this transformation from a muddy textured material to a hard |
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| 59:36 | Okay, and then the rest of grain types are listed here are all |
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| 59:40 | sized grain types, all greater than a half microns in size. Many |
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| 59:46 | these hundreds of microns two millimeter and the first would be composite |
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| 59:51 | So there are three types of composite . So one grain made up of |
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| 59:55 | particles. Inter class lumps and lift class, I'll explain these in detail |
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| 60:00 | a minute and then fecal pellets. already been introduced to this a little |
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| 60:05 | . I'll build on this relationship in minute. And then I want to |
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| 60:10 | you to another group called altar grains some of these sand sized grains that |
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| 60:14 | see on the sea floor were formed some sort of marine di genetic alteration |
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| 60:20 | the sea floor. And whether we them P. Lloyd's or crypto crystalline |
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| 60:24 | depends on uh the shape of the . All right, so it's been |
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| 60:29 | critic fabric a very fine um a fabric if it's ovoid shaped, they're |
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| 60:34 | P Lloyd's. If they're regularly they're called crypto crystalline grains and then |
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| 60:39 | coda grains would be you, it's acolytes. And then pies lights. |
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| 60:44 | , so okay, let's work our through this. We'll start first with |
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| 60:49 | origins of lime mud. And these illustrate potentially the different uh pathways for |
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| 60:56 | fine grained carbon a material that we line mud. Now you need to |
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| 61:02 | that people that have worked modern carbonate going back to the mid-1950s, What |
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| 61:07 | would do is take a sieve out the field, right, 125 micron |
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| 61:12 | sieve and they would they'd washed their through that. Anything that came through |
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| 61:17 | sieve, they called lime mud. anything less under 25 microns was described |
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| 61:21 | mud. Anything coarser grain was obviously carbonate sand. And that was the |
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| 61:27 | off that everybody used and still uses . Right. So we can compare |
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| 61:30 | area to another area. But what my mud? My mud is material |
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| 61:35 | so fine grain That you can't see individual components. You can't see with |
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| 61:40 | eyeball. You can't see with the lands. You can't see with a |
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| 61:44 | microscope, you can't even see it a thin section. Okay, so |
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| 61:49 | , we're talking about material that is microns in size. All the way |
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| 61:53 | to sub micron sized material. Where see it? You would need a |
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| 61:57 | electron microscope to do that. so that's really what we should when |
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| 62:03 | played this to the rock record, really what we should use the |
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| 62:07 | Cut off anything less than 20 or microns in size. But I just |
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| 62:11 | you to know that every everybody in modern, including myself, We all |
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| 62:17 | use 125 micron. As size ranges cut off between fine grained mud and |
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| 62:23 | sand. All right now, what the ways to make this fine grained |
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| 62:28 | a material? We know in the , that one common way is disintegration |
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| 62:32 | calculus algae. A few percent of cal curious algae or modern green |
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| 62:39 | Are cal Correas, which means when alive on the sea floor they precipitate |
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| 62:45 | their tissue. Tiny needles of a And by tiny, we're talking about |
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| 62:49 | raggedy needles that might be 10 or microns in length, one or 2 |
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| 62:55 | across for scale. Okay. And they die, they're organic material |
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| 63:01 | And what do they release the environment deposition? The tiny needles of a |
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| 63:05 | . So that's a contributor to lime . Again, why is that |
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| 63:11 | It's important because these plants only live a few months, then they are |
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| 63:15 | by another plan. So the rapid allows you to account for a lot |
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| 63:20 | the slime mud in some of these environments. In fact, the breakdown |
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| 63:25 | calculus algae, for example, easily for all the lime mud we see |
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| 63:30 | in florida Bay off of the Everglades south florida. Okay, What's another |
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| 63:37 | another way is by by erosion of substrates? I mentioned, the macro |
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| 63:42 | and what they do to bigger pieces coral and shells. Right? Some |
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| 63:46 | the material they break down is silty size material, but this boring activity |
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| 63:52 | on a finer scale. There are boring algae and fungi that take an |
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| 63:58 | sand sized grains. The scale there is 20 microns, and what |
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| 64:03 | they do to the grain they bore that individual sand sized grain they're creating |
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| 64:09 | to live in. But in creating whole they're releasing mud sized carbonate material |
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| 64:14 | the environment of deposition. All Very, very common process, but |
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| 64:19 | very difficult process to quantify. You quantify what the macro brewers produce. |
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| 64:26 | ? And you do that in the in an aquarium and see how much |
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| 64:29 | they produce. But you can't do to the micro borough. So nobody |
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| 64:33 | for sure exactly how much one micro algae produces in terms of mud sized |
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| 64:39 | . But when you look at any section of modern sediments riddled with these |
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| 64:43 | Boren's, you know that they contribute lot of fine grain carbonate material. |
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| 64:48 | right, So that's a very common . And then on the lower left |
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| 64:53 | of mobile carbonate sediments. When you active agitation of sediment being moved by |
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| 65:00 | wind wave agitation or tidal currents, ? The grains, sands are |
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| 65:04 | they're moving back and forth, You're get grain to grain abrasion and that's |
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| 65:09 | break off bits and pieces of carbon material. Again, very difficult to |
|
| 65:13 | , but it certainly happens because if if you snorkel on any modern |
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| 65:19 | high energy sand body system, whether skeletal or analytic, where there's a |
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| 65:24 | of rippling of the sediment right on shallow part of that sand body, |
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| 65:28 | water has sort of a cloudy color it. When you get off of |
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| 65:32 | sand body system, the water is clear. So clearly you're breaking off |
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| 65:36 | and pieces of material. Again, difficult to quantify. And then uh |
|
| 65:43 | is sort of tongue in cheek. I put in fish, there are |
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| 65:46 | tropical fish that actually seem to precipitate in their guts. Carbonate mud biologists |
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| 65:53 | they probably use it to help them digestion. Of course, every time |
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| 65:57 | fish dies is going to contribute a bit of carbonate mud to the |
|
| 66:02 | Again, this is more tongue in than anything. But well, what |
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| 66:08 | do is they break off bits and of coral and stuff like that and |
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| 66:11 | produce sand sized material and then they that and they pass it through their |
|
| 66:17 | and they kick it out. You've seen it if you snorkel on the |
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| 66:20 | , we saw parrotfish basically pooping out sized material. Right? That's what |
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| 66:25 | do. Right? So they feed the dead coral, they're eating the |
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| 66:29 | of bacteria that lives on the dead . The last mechanism here, direct |
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| 66:35 | from sea water. This is the controversial mechanism. This was proposed back |
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| 66:41 | the late 18 Uh 1890, I . So, it's well over 100 |
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| 66:46 | old. The concept is that in parts of the water column the water |
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| 66:51 | so supersaturated that precipitates tiny bits and of barragan. I'd material to create |
|
| 66:59 | mud maybe. Yeah. So a of controversy. I have a hard |
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| 67:05 | with this model because most of the only occurs supposed precipitation occurs in the |
|
| 67:12 | water settings, not the high energy . Right? You all you all |
|
| 67:18 | chemistry 101, right. And you uh something out of water. |
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| 67:25 | what did you have to do to water? And you had to supersaturated |
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| 67:29 | then you had to have something on to precipitate had to be warm enough |
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| 67:34 | precipitation. And then what was the thing? You had to have the |
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| 67:37 | rod and have agitation. If you have those four things operating together, |
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| 67:41 | didn't get precipitation out of that Okay, yet here people are asking |
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| 67:46 | to believe that you precipitate this material in these quiet water settings. |
|
| 67:53 | well, address this in a But these are the these are the |
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| 67:57 | are the four ways that people have that you can create lime mud in |
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| 68:03 | modern carbonate environments. Okay, so a here's an air photograph from part |
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| 68:10 | great bahama Bank. Uh this would west of Luther bank that I showed |
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| 68:15 | in the shuttle photograph. And what looking at here is a inner part |
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| 68:20 | the carbonate platform. This is stand water here. So it's two or |
|
| 68:24 | ft of water depth here and you see these white areas in the water |
|
| 68:28 | . These are what are called Whiting's these are what the geochemist argue or |
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| 68:33 | of instantaneous precipitation of lime mud out the water column. Right? They |
|
| 68:37 | stick their ph meter in this water they look, it's it's prime for |
|
| 68:42 | . All these carbonate environments are prime precipitation. That's that's unique. Two |
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| 68:48 | subtropical settings that don't have a lot classic or fresh water influx. |
|
| 68:53 | so it's not waiting. The other explanation of whiting is, and you |
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| 68:59 | have heard this is it's fine grained stirred up by by bottom feeding |
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| 69:05 | Right? And once you put this and suspension, it stays in the |
|
| 69:10 | column for days or weeks and it drawn off, drawn out like this |
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| 69:14 | title exchange to give you the patterns see in this air photograph here. |
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| 69:19 | that's the other explanation, but it's limited to these quiet water inter platform |
|
| 69:28 | , right situation, stagnant water and fact the salinity goes up a little |
|
| 69:38 | . Uh, the organism, the of organisms decreases because it's a little |
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| 69:42 | more restricted. It's just the opposite the kind of setting you'd want to |
|
| 69:46 | precipitation. So if you go out the margin of this platform where you've |
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| 69:50 | good reefs or sand development, you see any whiting's developed their only in |
|
| 69:55 | mormon critic low energy, quiet water . In fact, you know, |
|
| 70:00 | you I don't know if any of have ever bone fish, right? |
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| 70:02 | you go to the caribbean, to fish. Where do the guides take |
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| 70:06 | ? They take you to the winnings the bone fish put their snouts. |
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| 70:10 | fish are about this big. they their snouts in the sediment to |
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| 70:14 | they stir up this mud and the stays in suspension for days and |
|
| 70:18 | We know this. Okay. There's a white shark adapted to the |
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| 70:24 | You think the shark is tracking the of instantaneous precipitation where he's tracking the |
|
| 70:30 | fish? Yeah, No, I so personally, I have a hard |
|
| 70:34 | with this being instantaneous precipitation and further it was a setting for precipitation, |
|
| 70:40 | to see precipitation in and on the sediment and you don't see that. |
|
| 70:45 | , But you get that out on reef. Sand. High energy sand |
|
| 70:49 | where you don't have weddings. But this is the controversy. I |
|
| 70:55 | , I've got I've got good friends colleagues who still think this is these |
|
| 70:58 | zones of instantaneous precipitation. Right. supposed there's dust but not carbonate |
|
| 71:13 | That's cloud sit rows. So it yeah, that's happening today. Coming |
|
| 71:21 | the Sahara. Yes, you don't usually create carbonate dust from the exposed |
|
| 71:29 | stones. All right. You're talking the less glacial till and stuff like |
|
| 71:38 | . That's glacial till created by the grinding Iraq. There is dust coming |
|
| 71:44 | the Sarah desert today that blows all way across the atlantic into these carbonate |
|
| 71:50 | . Okay. And that's been proven monitoring stations all the way across the |
|
| 71:56 | and then they captured the dust on caribbean islands. Mhm. Right. |
|
| 72:03 | good. Just now it dissolves the , cement it up. And if |
|
| 72:14 | want to erode it, you've got do it by some other process. |
|
| 72:18 | . Okay, correct. That's what refer to as cursed. Okay. |
|
| 72:29 | . So that's all I want to about Whiting's. I mean, you |
|
| 72:34 | and you've got all the handouts that give you have tons of references to |
|
| 72:40 | to these slides and everything I'm talking . So you can always go chase |
|
| 72:44 | of these references down. Uh She a little bit more detail but uh |
|
| 72:48 | think pretty clearly one of the common in these modern settings is first of |
|
| 72:53 | disintegration of the calculus algae. This a typical mud producing algae. That's |
|
| 72:57 | common all through the shallow parts of caribbean. Uh It's called the |
|
| 73:02 | As And you see the scale The plants only about this big It |
|
| 73:07 | this whole fast the seven water interfaces here. Uh It's in the |
|
| 73:12 | What precipitates these tiny Oregon i But because the plan only list for |
|
| 73:17 | few months and then dies, that's you can contribute or add a lot |
|
| 73:22 | the syringe and needle mud to these of deposition. And people have done |
|
| 73:27 | crop studies to show that in some that I mentioned florida bay, that |
|
| 73:31 | can account for all the lime Just by this mechanism alone. |
|
| 73:36 | forget the by erosion. Forget the to grain abrasion. Just by this |
|
| 73:40 | alone, you can create all the |
|
