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GEOL6379-Applied Biostratigraphy - Video1228040846
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00:00 Uh Yeah. Ok. All right . Good afternoon, everybody. Um
00:16 am going to start today with a bit of a little, a little
00:22 that I didn't do Saturday. I forgotten. Well, we sort of
00:25 out of time and it was at end of everything. So I'm gonna
00:27 one more thing that we talked that didn't talk about Saturday, but I
00:31 it's a good illustration and then I've up with, what is it?
00:38 24 different little scenarios, uh questions , and, and things to,
00:45 discuss and that we're gonna go through those. I think it'll take,
00:49 know, a fair bit of If we get a proper, if
00:52 get good conversation out of these, take us most of the afternoon.
00:56 And the idea is to go over scenarios um that will be similar to
01:03 kind of things I ask on the . These are different, these are
01:07 in, in which I either give AAA particular geologic scenario uh describing the
01:15 gray structure thermo chronology and ask you interpret the geologic history of the,
01:21 the data or I may give you some information about structure photography, thermo
01:31 or I will leave some of that and I will ask uh what uh
01:35 analysis would be appropriate in order to uh answer certain questions. So let's
01:44 with this last bit that I was talk about. Um And I call
01:50 a cautionary tale because it gets why is that doing that? Um
01:57 um it gets to uh it's it's on, let's fix that.
02:07 , I did not. Uh I I could send them to.
02:14 Ok. I can send, I I'll send them. I was just
02:18 unveil them as we go, but guess people would like to see
02:21 So. All right. So I done that. So let me take
02:25 moment to fix that problem. You away, you, you stop
02:49 All right. So I'm going to these. Um Yeah, that's all
03:05 need to do. OK. That's your way. Um Is I will
03:43 that in just a second and post uh this uh a series of slides
03:49 your canvas. I apologize. I to do that. So you get
03:55 in a second but I can go and start talking about this here.
04:05 , I'm gonna fix that too. don't want these transitions. How can
04:09 get rid of that? All OK. Is everything still working as
04:48 should? All right. Um So is a uh a paper um which
04:55 a part of a trio of papers at the uh detrital thermo chronology of
05:01 sequence of rocks in the Himalaya. is a series of rocks called the
05:07 group. Swall group are deposited in in these gray area here. This
05:11 the for and basin of the And um there's a sequence of sandstones
05:17 silt stones that were deposited here and were uh the age was determined by
05:22 mats. So we have an independent sense of their age. And this
05:28 um group mostly of French workers. and Nepali. They looked at geo
05:35 of, of the sandstones here. did, they did uh uh fish
05:39 track dating of the zircons. They fish and track dating of the uh
05:46 and they did Argon 4039 dating of from these sandstones. Um I'm not
05:53 show you the uh I'll show you muscovites just now because that's where I
05:57 they made the mistake. Uh One thing you can find about this work
06:02 that when they did the fish and dating of the appetites, the appetites
06:10 the lower part of the section. here, here's the section they have
06:15 about 4000 m of section in, different places. They have the Kali
06:21 , the Suai Cola and the Tal , three different sections in in Western
06:26 . And they have thousands of meters section. And at the bottom of
06:31 uh Strat graphic sections, the appetite track data was reset younger than the
06:39 of sedimentation. So they were mostly to figure out things about uplift.
06:45 once you start heating up the samples , as I said, you
06:48 you get to, you can only what you can understand about tectonics of
06:52 provenance or you can understand about uh post depositional thermal history. Now,
06:58 for them, they had three different to look at the, the Argon
07:03 and the Muscovite and the fishing track the Zircon were not reset. So
07:08 tells us something about the, the character of uplift before it
07:12 it was eroded. The appetite, tracks were reset or at least partially
07:18 . And so all that tells us , that, that tells us then
07:22 the depth of burial, at least the bottom of these sections uh was
07:26 excess of the temperature required to reset tracks in appetite, which is about
07:34 temperature? Ok. Now, about 100. Yeah. Remember I
07:44 last Saturday that in order for us do well, today, there's not
07:47 be none of this, but I , if you have to, you
07:50 to um good for you. I just, I'm teasing you a
07:55 bit. So we've got a uh so, so what I'm gonna show
07:58 is the results they did for the muscovite dating because this is the Himalayas
08:04 right up there and it's a short of transport. Muscovites are gonna survive
08:09 transport and we're gonna have muscovites as good measure of, of stratigraphy and
08:14 . So, here's what they They looked at what is it,
08:21 , 1011 different Strat intervals in these three stra in these three sections.
08:28 the numbers up here, these red , these numerals represent the number of
08:33 undertaken in each uh in each So you add that all up and
08:40 a pretty big number. It's like or 400. I can't remember.
08:44 , it's a, it's a pretty number. Let's see, that's
08:48 That's maybe I, I don't somebody can add those up, maybe
08:51 500 hundreds of analysis. And they at these data and they thought,
08:59 , this is interesting notice back here , in the middle Maya scene
09:05 we've got evidence for zero age uh . That is and, and this
09:12 , and remember this is Muscovite What's the closure temperature of Argon in
09:22 about 400 degrees? So these things closing to argon loss way far down
09:30 , right? 400 degrees is pretty . That's at least 12 kilometers.
09:38 yet some of these muscovites here in age range, greater than 10 million
09:44 plotting right on this 1 to 1 , the cooling age is equal to
09:47 depositional age. That's, that's evidence really rock and tectonics, right?
09:54 you, because, because these these are muscovite, they didn't come
09:56 of a volcano, they're coming out shifts, the shifts are eroded,
10:00 to the surface and then deposited in fall and basin so fast that we
10:04 tell the difference. That's so that's news. But then they noticed that
10:09 we get younger in this part of Nepal, there seems to be a
10:13 between the minimum zero age and these things. And so they argued that
10:20 represents a slowing down of that tectonic that that back before 10 million years
10:27 , things were rocking it up li he split. But as as as
10:31 progressed, uh that, that that erosive signal was lessened and that's,
10:40 certainly allowed by the data. But you, if you look at these
10:44 here, we can see that it's problematic. I mean,
10:50 this, this this sample here, this interval, they only analyzed 18
10:55 here was only 18 and these was . And so they are making the
11:03 that this gap is significant. But significant can it really be if they
11:10 analyzed 40 grains? Well, you'd expect them if they're there or you'd
11:20 more confidence in their not being having not seen them. But with
11:24 grains only. Um, you that that's, you know, there
11:28 40 there's, there's the actual histogram those agents. It was deposited 2.8
11:35 years ago. And you have you know, nothing much younger than
11:40 , this 10 million year old So they made, they made quite
11:43 bit of hay about that is that gap. No, the pro the
11:47 is N equals 40. And remember you go back to Ramesh uh and
11:53 approach that says that if you only 40 grains, then the detection limit
12:00 which you have a 95% confidence that not, there is only 12%.
12:07 that means the things that we are that we found if they were there
12:13 to represent 12% or more of the , but 12% is getting to be
12:17 pretty big number, right? I , if you're, if you're really
12:20 on saying what is the streams of data? I don't know, 40
12:26 , you know, 12 seems disappointingly . Um And so going back to
12:31 data, you know, look what did, they've analyzed all vision,
12:35 , what was it? What did say? 13 different strata and some
12:38 these, you know, only differ less than a million years along the
12:42 age. It's always going to be case that your, that your analyses
12:47 gonna be limited by how much time have or how much money you
12:51 So you can't just say analyze 1000 every sample. That's just not
12:57 But let's just say whatever this adds to. I seem to remember it
13:00 up to 600. Maybe it I don't know, whatever. Let's
13:03 that end is, we have that time. We have that much
13:07 didn't they, didn't they apportion their in the, in the really smartest
13:15 , I would say no, they've too much stratigraphic coverage and not enough
13:23 . That's, that's being delivered. you had taken say the 43 analysis
13:28 and just did them and made it here, then you'd have some great
13:33 . If we didn't see any here look at these, these, these
13:36 guys here in the same are all , I didn't even put the number
13:39 . But if you would have taken three of these samples and just put
13:43 into one, you'd have 7580 You'd begin to say, well,
13:47 know, we have confidence of what seeing again over here. I
13:51 you know, 48 grains here are the middle of the 8083. If
13:55 have taken their time and money on 48 and put it into over here
13:59 they had, where they got. mean, so I think that this
14:04 poor uh experimental design. Uh and turns out that subsequent work really sort
14:13 uh is it consistent with their notion the tectonic slowing down in this region
14:18 that actually happened? But that doesn't their, their approach of, of
14:23 to figure that out by analyzing only grains in a particular sample, 22
14:28 right next to each other with only , that seems like a waste of
14:32 . Um So that's just the point wanted to make when you're, when
14:36 thinking about, you know, because uh dating sandstones by the minimum depositional
14:43 from a detrital grain, it's very and it's potentially very uh a powerful
14:48 , you know, and you may across a, a AAA Strat gra
14:52 in which your, you know, age control is very poor and you
14:57 wish to decide. Well, we're gonna try this, this
15:00 this detrital dating approach. Don't, commit to this approach if you're just
15:05 analyze 20 grades. Uh because you're gonna have enough confidence to say much
15:11 than you had when you started, got to commit to be able to
15:14 100 grains in, in one So that's the, that's the message
15:20 . Um So that sort of finishes I thought what I meant to do
15:24 Saturday. So before I ca so I've, oh, let me
15:29 So N equals 398. So they 400 grades. Ok. 400.
15:35 right. So I've got a bunch questions now that I've put together that
15:38 can go over one at a But before I go into those,
15:43 , any questions about anything we talked up to this, any,
15:47 any clarifications that you've thought about as looked over your notes, anything,
15:53 work. Ok. Well, like say, then I've got, I've
16:00 25 of these slides that we can on for the rest of the
16:04 And as I say, the more that they deliver the better, but
16:08 we'll start out with this one. and I, I think what I'm
16:11 do is it sort of present each of these to you and then give
16:15 a few minutes to think about it then I'll come back and ask for
16:18 input. Uh So let's start with one. So I've given you some
16:27 , some Argon, 4039 age spectrum I've told you the kind of rock
16:31 is, this is a rite. me what you think you can say
16:38 the history of this ride. and when I say history, you
16:41 , we're gonna be talking about histories general. That can, that,
16:44 includes the formation of the rock. Anything we can say about its uh
16:49 , generally formation will either include rocks form at the surface or below the
16:54 . If they form at the Did they stay at the surface or
16:57 they buried and come back up if were formed below the surface, how
17:01 did they get to the surface and like that? So, um I'll
17:07 you a few minutes to consider this . This is a rite and those
17:10 the data. Um I'll give you minutes to think about it and then
17:14 come back. So prepare, prepare you will uh you know, think
17:19 these as, as, as practice questions. So start start thinking about
17:24 you'd say on a, on on a, a real test question
17:27 then I'll, we'll, we'll have discussion in, in two minutes.
19:51 . The half life of our garden is 269 years. Yeah. So
19:57 way, I'm sorry, what's the ? So 269 A, a stands
20:05 a Adam years. I mean, , what? I'm not sure that's
20:09 really. Oh, the halfway, . Yeah, that's your, so
20:22 not, that, that, that's a key factor of this problem.
20:28 . I think it's been two So we've got, we've got two
20:32 of information to talk about here, ? We've got a Strat democratic bit
20:36 information and then we've got a post thermal history story as well. Do
20:41 not? Who wants to, carry on? I'll try.
20:50 Ok. Ok. Ok. we got a, we got
20:52 we got a, a person from internet so, I can hear
20:55 So we'll start with that and we'll , we'll, you'll carry on
20:58 Go ahead. Um So being that volcanic, I would think that they
21:05 have uh crystallized at about the same and they're not showing that. So
21:12 , let me, let me just just your answer a little bit.
21:15 good. He said that because they're . They should have crystallized at about
21:18 same time. Well, yes, is fine. But what we're,
21:22 you really mean to say is they have the same isotopic age because
21:26 crystallization and these things don't have to the same thing. So I wouldn't
21:30 the word crystallized, but you're on very right track. OK.
21:34 Thank you for that clarification. uh I think then that the biotite
21:39 showing more. So the isotopic But yeah, there was a subsequent
21:45 event afterwards. Uh That was substantial to uh impact the case far,
21:54 has a lower closure temperature than the time. So whether or not burial
22:00 uh what was that? Yeah. , it has to prep, I
22:04 , burial seems the best example we've and so much I like that,
22:08 analysis is pretty good. We've got biotite has a higher closure temperature than
22:14 case bar. So we've got evidence this sample has been buried because it's
22:20 volcanic rock and we know volcanic rock start out at the surface with the
22:25 age, no matter which technique we it by. So the fact that
22:30 two things are different clearly means something happened to this rite rites. You
22:35 , we can make a AAA first on any rite interpretation is that they
22:41 be simple, they went from hot cold very fast and, and all
22:46 agencies be the same. So they're the same. So there's been a
22:51 here. That disturbance makes sense that would be burial. This is
22:55 this is a ST static. This a, it's a layered rock.
22:58 a volcanic rock, but it's a rock like other layered rocks. And
23:01 apparently it's been buried uh since Now, um that was good.
23:09 gonna, did you have anything else add? We were about to say
23:13 ? It was just about. Well, ok. So,
23:19 No, you've slow cooling. But this is this, I mean,
23:24 suppose there could be a component of cooling. But yeah, yeah.
23:35 , I mean, it could be cooling or it could be just a
23:38 uh uh uh episodic reheating and, it could be both, right?
23:44 , I mean, it, an , an episode of burial is gonna
23:47 this sample down to, to make hotter and then if we leave it
23:51 that hot temperature for a while or, or, or on the
23:54 back, I'm assuming that this unless say, so we're gonna assume that
23:57 of these samples are samples that were at the surface of the earth.
24:02 this sample was at the surface Clearly, it was down there somewhere
24:06 the past. And so your slow concern could be realized if you,
24:10 , if as we buried it deep a while and then we took a
24:13 slow time coming back. So it's buried. Um So two questions.
24:20 we've, we've got the broad outline what's happening here. We haven't put
24:24 numbers on when any of these things . So, w when did this
24:28 when was this Ry light erupted? by tight Ed, you'd say 90
24:43 . Now, that's true. If reheating event we're just talking about is
24:52 than 300 degrees because we could re could reset the biotite as well,
25:01 ? All we can say for without any other information. Now,
25:04 I gave you a thin section of rock, if I, if I
25:06 you hold this rock in your you could probably tell whether it's been
25:10 to 300 degrees or not. That's , that's a textural thing that would
25:13 , you know, you could, , that's a, that's almost a
25:17 rock, right? So you could tell the difference between a Rol light
25:20 just been down to three or four and a rite that's been down to
25:24 kilometers. Uh But let's say we have any of that. We just
25:27 this. Um So all we can for certain is the biotype that,
25:32 this rite was, it was, was erupted at 90 degrees or
25:38 So this could have been a 200 year old rite which was buried
25:43 and on its way back up, passed through 300 degrees 90 million years
25:48 and then passed through these other temperatures the way back up. Um So
25:56 , so those are two questions, , is the burial which we clearly
26:01 had in this row? Is the ? Was it, was it,
26:05 it remove argon from the case bar or from the case bar and the
26:11 ? What other info, what other data would you like to have to
26:16 that? We got two hypotheses The they both in b burial,
26:22 says it was just buried enough to out some of the f part,
26:25 of the F bar argon. And other one says it's so profoundly deep
26:30 we reset everything. How can we between those two ideas? I have
26:36 question. Go ahead. So is also possible that this could be due
26:43 contact metamorphism? OK. Yeah, mean, it's a, it's a
26:49 event. I haven't given you any geologic context. Um So yes,
26:54 mean, if I, if I to say there are no Pluto in
26:57 region let's just, I mean, it really strictly speaking, all of
27:00 questions I'm asking you would be appropriate of the source of this se subsequent
27:09 . Ok. No, fair This rock's been heated up and that's
27:12 enough because we know that the rite give the same age if, if
27:16 , if they're undisturbed. So, happened. Um, I was speaking
27:21 it in terms of burial just because think that's how we'd like to
27:24 But you're right. It could have , it could have been a reheating
27:27 associated with a Pluto coming up right door. OK. Now, if
27:31 had a, if we had a map of the region, we could
27:34 , you know, say there's the easy peasy. But um in either
27:40 to really nail, you know, still wouldn't know whether that Pluto was
27:43 enough to have reset the biotype or . So, so we still wanna
27:49 this question of was the, was Pluto or the burial, whichever source
27:54 heat you wanna invoke? Was that sufficient to um completely reset the biotite
28:00 is it just teasing some felt some out of the feldspar? What extra
28:04 that's not on this diagram of, something that we've talked about in
28:09 I'm gonna give you time and money go out and get some more
28:12 What is the data you want So to sort this question, Uranium
28:19 uranium leads on. Remember, we just say uranium lead, we got
28:22 pick a mineral to date Zircon. you go. There's probably Zircons in
28:27 rite. And if we could find zircons in this rite and date them
28:32 uranium lead, if, if if it's been, if it's been
28:36 only slightly, we would expect that lead Zirk on age to be
28:41 Right? If it turns out that lead Zircon age is something greater than
28:48 then we'll go to this model in the reheating was really overwhelmingly big
28:57 Everybody understand that questions. So you know, we're, we're putting
29:06 sample in its context. The 1st thing, first context, we
29:11 put a rock like this in is it, we know where it
29:13 , it formed at the surface, cooled rapidly. That's number one,
29:17 can start with, it was at degrees, you know, at its
29:21 temperature. And, but, but because, and, and so
29:25 all, all volcanic rocks, we expect their geo chronology to be straightforward
29:30 always the same. This is not same something happened to it. How
29:34 happened to it is not clear exactly this diagram because it could have been
29:38 minor such that we've got the and let's just now, now I'm
29:42 ask you um the Uranium L Zircon that, that we've just now
29:48 We comes back from the lab and 91 million years. What does that
29:53 us about the total depth of burial this sequence of rocks in which we
29:57 this highlight? It appears that this , like this K Feldspar has had
30:14 lot of its argon taken out of because even at the, even at
30:17 hardest to remove part of the age , we've dropped that from 90 to
30:23 . So we've taken out a fair of the ARGO, but clearly we
30:27 that we haven't gone up to temperatures 300 degrees because that would have reset
30:32 biotite. Remember the uranium lead Zircon that I just made up is 91
30:37 tells us that the thing hasn't been , super, super hot. I
30:42 , not enough, you know, hasn't been heated to past 280
30:48 Can we, can we put anything on it than it was not
30:53 I mean, what's the closure temperature , of, of the, of
30:58 ages that come out of here? . Well, the, the,
31:03 this age would be, would be us something more along the sort of
31:07 50 to 200 time. And this be telling us something more about the
31:11 to 300 time. So, what can say is that, you
31:16 this rock was heated up pretty hot that is probably hotter than certainly hotter
31:22 150 because that's the minimum amount we to get some margon out of a
31:27 bar. Um When did it stop at 150? Well, about 60
31:32 years ago, this basin, let's this is ry light a part of
31:35 basin. This basin cooled to temperatures than 150 about 60 million years
31:44 How hot it got above 150 is something maybe you could do with
31:48 lot more analysis or maybe some more . But we can say for
31:53 by looking at this rock, assuming this ride is interbedded with some
31:57 let's say this sequence of layered rocks the was, it was,
32:02 is about, you know, is . It's about 91 million years old
32:06 we believe our Zircon age to be unmodified and that we're always gonna do
32:12 . So we got a 91 90 year old rock which was buried sometime
32:18 that. The, the, the and subsequent unroofing all took place between
32:27 . So that's a geologic history. could start looking on here. You
32:30 , this rock was buried up, know, past 150 degrees. But
32:36 the tectonics turned around and brought this back up to colder temperatures after at
32:43 60 million years. So you're gonna looking for evidence, you know,
32:49 other, what other things in the region are you gonna be looking
32:52 Are you gonna be looking for faults are active at this time, you're
32:55 be looking for, you know, basins that are being filled during this
33:00 . That's, that's the information you from all that. Everybody happy with
33:05 . Any questions? Well, speak just a bit, please.
33:36 not in not in the simple I've just given you where the biotite
33:39 and the uranium L zircon age, basically the same. So if,
33:44 we, I mean, so, let's start with a simple case,
33:47 , the Zircon age, which is , which is not given here.
33:50 you know, you would want to if you, if you got data
33:53 this and you were somehow still worried the 90 million years isn't the formation
33:57 , you'd say. All right, me a Zircon age. OK.
33:59 couple of weeks happens, come you get the Zircon age, it's
34:03 . So now we can, we , we can confidently interpret that 90
34:08 the age of eruption of that volcanic . Now, if it turns out
34:13 the Zircon age came out to you know, 100 and 10,
34:19 you're gonna have to say that the age of the volcanic rock was 100
34:22 10 and the subsequent reheating was he so profound as to drop that vide
34:27 from its original 110 down to And so in, you know,
34:34 , in the first case, the t in all cases, the,
34:37 time at which Argon becomes retained in b takes about 300 degrees in the
34:42 , in the first case, it's that was the day of the
34:45 right on the more complicated case where eruption was 20 million years before
34:51 Then we've buried this rock, buried very deep, such that we got
34:54 to 300 degrees and then it came to the surface and it, and
34:58 did so as passing through 100 and degrees about 60 million years ago.
35:04 so all of that can then be in any other geologic information you have
35:10 the region, the, the the other Strat gray, all of
35:14 , then all of that has to consistent with the up and down that
35:17 learn about from this rock. There's AAA down and up uh in
35:25 in this store que question. Go . So in that second example where
35:34 Zircon says that it's 100 and 10 and the bio type data that we
35:39 is, is essentially flat. It's staggered like the case bar. Is
35:46 , is that saying that you exhumed or you exhumed it rapidly through the
35:53 type closing temperature and then more slowly the bar temperature. You, you're
35:58 , you're, you're on the right , but it doesn't have to be
36:01 that. It's complicated because the biotype , there's really only one closure temperature
36:06 bio type. And so the, , the, the, the fact
36:10 it's flat is just I draw, drew it flat to make it
36:14 But it's, it's in general, don't get a lot of information about
36:18 rate of cooling through the bio type temperature. We just know when it
36:22 because basically we're saying we are you know, it's just like if
36:27 had a log of say you're driving the highway and you passed, you
36:31 , you passed uh Katie at, know, at, at 145 in
36:36 afternoon. Now, if it, you were passing through Texas, on
36:40 other hand, you'd say I started Beaumont and I finished in El
36:43 And that's gonna give you all sorts information because Texas is much wider than
36:48 . So, um when you have wide zone to talk about the case
36:52 can, then we can say, , this part is the high
36:56 the Beaumont side, this is the temperature, the other side of Texas
37:00 you have a wide range. That's thing. Um So the biotite data
37:05 really allow for cooling rates. It says we passed through 90 passed through
37:12 about 90. That's a, that's smart question. But, but
37:15 it's, it's complicating it more than really needs to be. Ok.
37:19 . No, that makes a lot sense. Thank you. Good,
37:22 . Um All right, let's, , let's see about number the
37:26 So that took us going and we got, we, we all
37:30 , next, next, number All right. This time we're looking
37:37 a granite and we're gonna try and its history on the way up and
37:44 what that might and, and then course, once we understand the history
37:47 that granite, we will, we incorporate that into any, any other
37:53 we have for the region structure Um So let's just consider uh this
38:00 and, and uh what, what can say about it. And so
38:04 give you a couple of minutes to we contemplate those data. All
40:36 let's um let's talk about this Here we are starting with a
40:45 We know where it's where it it started down there somewhere. Not
40:49 the surface like our last example. When did this rock begin? 125
40:58 , you know, uranium lead That's easy. Um Then what happened
41:03 it? It's fairly gradual. I , how well there are, I
41:17 , actually, you know, to, to figure out how
41:19 you know, you might want to drawing little temperature time diagrams here because
41:27 what's the closure, you know, we say crystallization temperature we're talking
41:32 let's say 600 degrees, right? the closure temperature of argon in
41:39 About 500 degrees? No, Yeah, it dropped it dropped at
41:47 100 degrees, perhaps more in 3 years. So that's a, that's
41:54 cooling rate that you can start off . Did that rate get faster?
41:58 the same or go slower on its from Hornblende Closure to biotech closure?
42:05 see. It took, well, dropped 200 degrees in 42 million
42:11 So it's slowed down. Right. then what happened? We went from
42:18 300 degree closure temperature to fishing Appetite is what me, it's fed
42:26 because the clothes, the, the temperature for fishing tracks is about 100
42:32 . So we took 3 million years go 100. So we sped up
42:35 and then we took another 7 million to go, you know, maybe
42:40 30 or 40 degrees. So we've , um, basically, we've got
42:45 time from about 80 to 70 in we have evidence for some fairly rapid
42:51 going on above this, above this . Uh We don't know exactly when
42:56 got to the surface, but it to the surface sometimes after 70
43:01 Um If you were looking for a nearby, filling up with sediment,
43:08 , when would, when would that during what time period? Would
43:12 would the depositional rate in that basin the greatest? What? Mhm.
43:23 the slowest time, isn't it? took? Well, I mean,
43:26 gotta get our calculator here to figure out. What was, let's the
43:32 probably. Well, let's just let ask you this. How, how
43:42 did it, what was the erosion this here? Yeah. Ok.
43:47 out your, we're gonna do a , somebody said, are we gonna
43:50 math here here? We're gonna do little math. So what was the
43:54 rate in this region from 80 to million years ago? Now, erosion
44:03 . First thing we're gonna need to is the cooling rate, right?
44:07 was the cooling rate from 80 to ? That's gonna be uh it's gonna
44:18 200 degrees. It cooled, No, no, excuse me.
44:21 200 yes, 200 from 300 degrees 100 degrees. So that's 200
44:27 And it did so in 3 million , right? So that's 66 degrees
44:34 million years. Um What is that terms of erosion if we assume a
44:42 gradient of 25 degrees C per mi per kilometer? So let me make
44:49 I get our units right. This , that's degree C per Yes
44:56 That 66 Greece C for a million , we're gonna divide that by 25
45:07 C per kilometer. That's gonna give 2.5 kilometers for a million years.
45:21 follow that. So that's 2.5 kilometers million years, which is one very
45:31 . This is why, you there's lots of ways to express erosion
45:35 or sedimentation rates. I really, favor millimeters per year. Sometimes people
45:41 talk about per 1000 years or But the reason I like millimeters per
45:46 is because millimeters per year is exactly same as kilometers per million because there's
45:51 million millimeters in a kilometer. So can so 2.5 kilometers per million
45:57 we some people might be happier calling 2.5 millimeters per year. Remember I
46:03 I told you on Sa last Saturday anything over a millimeter per year is
46:08 very rapid deposition or very rapid So that's pretty fast. Excuse
46:17 I just, I, I went 80 to 77. I I divided
46:21 degrees divided by 3 million years. got 66 degrees C per per million
46:28 , divided that by 25 degrees C kilometer and I got 2.5 kilometers per
46:34 years. Now, let's see. it slow down or speed up in
46:38 subsequent 7 million years we went let's just say we went from 100
46:43 to 70 degrees. Those are sort the nominal numbers we're gonna use for
46:47 other two things. So that's only degrees and it's in 7 million
46:53 So that's four 0.2 degrees C per years. We divide that by 2.5
47:05 excuse me, 25 that's only a of a, of a kilometer per
47:15 here. So we can see that time in which this rock was being
47:20 , fastest was between 8077 really That's a, that's, and
47:25 we, we caught that moment of rapid erosion because we were
47:29 we were able to track it between 22 closure temperatures. If we wanted
47:34 do a better job of understanding that , we, we try and fill
47:37 that gap between 301 100 by doing Zircon uh efficient track or doing Argon
47:47 . But what we can say from is that period from 80 to 77
47:52 was the time of most rapid That's you're gonna look for faults that
47:57 moving at that. At that you're gonna look for basins that are
48:00 up at that time. Everybody follow that. I can't hear you please
48:16 , from here to here. if this is a, if,
48:18 , if, if this time is us when it was 100 °C and
48:23 time is telling us when it was °C. So that's only 30 degrees
48:30 that by 7 million. So you've got five bits of data,
48:37 got a time and a temperature for one. You can then calculate cooling
48:43 and then, and from cooling you can transfer that into erosion
48:46 which is I think how most people of course, transforming from a cooling
48:51 to an erosion rate requires an assumption what the geothermal gradient was. Question
49:03 ? Yeah, that's a good, a good. Now, of
49:07 the, let's just say that the of uranium lead Zircon is 700
49:14 I mean, the problem is it's big number. We don't know exactly
49:17 it is, but we know that know that the rock probably crystallized around
49:20 5700 degrees. So let's just pick degrees. So that's 500 take away
49:26 that, that's 200 degree, 200 in 3 million years. That's the
49:31 fast rate we just picked, Ok. So we got the
49:36 the same cooling rate between 125 and as we did between 8077. Do
49:43 apply the exact same geologic interpretation to time intervals? Clearly, the time
49:50 80 to 77 the rock was cooling because the material was being eroded from
49:56 . You had to have some sort tectonic or climactic event that's unroofing material
50:02 causing this region to cool down. that exactly the same way we'd interpret
50:08 cooling from 125 to 122. I think we would have to do that
50:14 remember at the beginning, when, , when these granites are intruded,
50:19 have to cool down to the temperature the rock surrounding them. And if
50:22 , if this granite was intruded to to temperatures of around 450 degrees or
50:29 degrees. It might take a few years for it to get there,
50:33 not 2030 million years in a million two year or, or to put
50:37 . You know what I'm saying? time it takes to cool to its
50:42 is not a function of some fanta tectonics that's going on. This,
50:47 cooling from the vite age to the age. That's tectonic signal that's erosion
50:53 at the surface because of either faulting happening or because, you know,
50:58 started to rain a lot. But first signal here just just tells us
51:03 the, the depth of intrusion was around 500 degrees. That's not a
51:09 sequence. OK? Any questions from the inter webs? OK.
51:22 go to the next one. What is it? Well, we're,
51:24 moving along pretty well. All This is a straightforward one shouldn't take
51:29 time but, but uh well, it's, it's kind of complicated on
51:33 , but it still shouldn't take much . Tell me potential uh interpretations.
51:38 you, if you wanted to date granite, say you had a fault
51:42 you're interested in dating that timing that and you got a cross cutting granite
51:46 cross cuts the fault. OK. gonna date the fall and those are
51:50 zircons. We get out of uh this granite and we're plotted on
51:53 Concordia diagram what, what, what did the salt move? These are
52:06 data, right? How do we these discordant data on a diagram like
52:11 ? We got, we got two . Yeah, we draw a line
52:21 interestingly that line that we draw might below zero here. And this
52:26 let's say, does this where I'm my cursor look like a good extension
52:31 this line up here to say So if that's the case, when
52:36 the fall? And we're, we're this granite, we're dating this,
52:40 granite in order to help us understand the fault moved if these are the
52:45 , but this granite cross cuts the . When did the fault move
53:06 if this line comes up here and this, how do we interpret
53:17 That's the age. That's what I say. That's, that's the reason
53:20 the reasonable estimate for the crystallization age this rock. So when did the
53:25 move before that? Thank you. . This is not the faulted
53:36 This is the faulted rock. So this was the fault and if this
53:41 the rock that cross cuts our we would say that that fault is
53:45 old fault. It has, it moved since 450. This, what
53:53 you having trouble with the, with extension of this line? Remember,
53:58 got it, we've got uh we've two possibilities on, on Discord
54:03 It can either it, it could up here to some, some upper
54:06 or you can send it down to lower intercept. Um If it's the
54:11 intercept, that if it, if interpret the lower intercept, you're gonna
54:14 that these data are inherited, there's little cores inside there that are
54:18 that are pulling it away from its value. If, if you interpret
54:22 upper intercept, we're gonna say that they're pulling off from its true value
54:26 . Usually as a rule of you won't have a complete span from
54:31 upper intercept to the lower intercept. they're gonna, they're either gonna huddle
54:35 here near the upper or they're gonna down here near the lower. I
54:43 said it was, I just, , no, no, no,
54:45 no fault on this diagram. I this is a rock we are
54:49 So as to better understand the history the fall, this rock intrudes the
54:54 . Oh Yeah, you, you'd very confused if you're, where is
54:58 damn fault on this diagram? there is no fault. I just
55:02 that this rock might help us understand fault motion. If we, if
55:07 were in the field, we see fault. Is this a young fault
55:10 an old fault? You know that may have two periods of faulting in
55:14 region. We may be interested in faulting and, but we're not interested
55:19 in the history of the Paleozoic turns that if this is a rock that
55:23 collected to understand the history of that fault, that fault is an old
55:28 because that fault, it hasn't moved the age of this rock, which
55:32 450. All right. Excuse Yes. Yeah. These are,
55:46 are the millions of years tick marks of years. All right, we've
56:01 a highlight here and we're trying to we, we, we're dating this
56:08 because of its helpfulness in its Strat control. We've got a sequence of
56:13 . Fossils aren't great. We want , we want to uh date this
56:17 and the, the laboratory that dated rite decided to do the single crystal
56:22 . Uh We're analyzing a bunch of , analyzing them whole, whole crystal
56:27 at a time. And then this the distribution of the ages um explain
56:34 distribution and tell me uh what is estimate for the time of, of
56:41 of this rock and therefore the Strat control on this sequence? It's
57:08 it's not homogeneous. I mean, got, I mean, that's
57:11 the, that's, we've got these blips out here. I mean,
57:13 got a bunch of data right here 32 but we got these three guys
57:17 here. Um Do we pay attention these? Are these important? Is
57:23 , does this play a role in interpretation? What's how interpret the,
57:29 eruption age of this rock? Is, it is a time,
57:41 , I guess, uh, I that it, yeah, you do
57:45 to pay attention to those little I think that the age has to
57:50 that blip to the far. Or what? That would be the
57:54 possibility. Um, because I I mean, Fs Far is gonna
58:02 overwritten at 100 and 50 or Well, it certainly would.
58:06 but I mean, if we assume this is a straightforward volcanic rock,
58:11 says he's, he, he, , his, his thought was that
58:14 oldest one is the most important And that's telling us the,
58:17 the age of the rock and all the rest of this stuff has been
58:23 . Um That's possible. Um But mean, if it was overwritten,
58:31 me, if it was, if is an exa if this is a
58:35 that's been reheated, why? OK, you could just have some
58:39 were more prone to be reheating. not the interpretation I'm gonna use here
58:46 , um and again, I'm giving these samples without any real context.
58:50 just say it's from a rite. Let's assume it's from a elite interbedded
58:56 a sequence of un metamorphosed sandstone. want you to try a different
59:04 Taylor and try, you're right to the, the, the ho in
59:19 of these things. If we, mean, I suggested that this one
59:26 not the most important one, if is not the most important one
59:30 what is the most important one over ? Yeah. So if these,
59:38 these guys are important, why are not gonna pay attention to these
59:41 What's going on here? The? , we do. We, I
59:48 , well, I mean, in any volcanic rock we would expect
59:51 all to be the same and yet got a bunch of them that are
59:54 same. And then these three girl out here that are not the
59:59 Why are they not the same? we ignore them at our peril?
60:04 we really want to know the crystallization of this, of this rite,
60:08 eruption age of this rite? What it? Is it 32? Is
60:13 40? Is it 44? Is some 56? Why remember I told
60:19 why it is that we, we this single crystal businesses for problems like
60:26 . The single crystal analysis is and, and you generally do this
60:30 crystal analysis for rites as opposed to kinds of rock because rites are explosive
60:37 . And when that explosion comes you get all of your new crystals
60:41 your magnet chamber, but you might some other stuff, right? What's
60:45 other stuff you're worried about? That's feld bars from the rocks that
60:51 that were broken up. You got explosion before we had that explosion.
60:58 are a bunch of rocks here. . Here's our magnet chamber down here
61:02 then the thing blows up, closets on the ground. Wonderful Strat democratic
61:07 . We're all happy about that. during that eruption, some of this
61:11 in between the magnet chamber and the of the earth gets exploded during the
61:16 . What if some of that stuff a feld from? Because this rock
61:23 formed on the surface? We can that they, that's not a
61:27 These are just old crystals that got up in this young eruption. This
61:32 is 32 million years. The reason analyze these things one at a time
61:38 to not have the influence of these things tossed into the average. If
61:46 have analyzed all, let's, let's say this is 20 crystals and then
61:49 three out here. If we'd have all 23 of these crystals at the
61:53 time, we wouldn't have known anything this. 40 the 44 and the
61:58 they would have just imperceptibly shifted the age from whatever it is 32.1 to
62:06 . And for, for, for or times when you're worried about that
62:14 of 3/10 of a million year you will have moved it to the
62:19 answer and you wouldn't know about So you follow the difference there,
62:29 , I did. Yeah, forgot that one. Thanks. So that's
62:34 reason what that, that we do single crystal, particularly for rites because
62:38 the explosive nature of the, of , of the eruption, it's gonna
62:43 older material in it. And if analyze it all at one time,
62:47 got this problem, we don't have worry about doing this for a granite
62:50 it's not an explosion. The all crystals we get out of a
62:54 we know they all came from the place and the same thing for a
62:57 because basalts are nice and slow and , don't explode, but rites explode
63:02 they can have old stuff that we like. So that's why we do
63:07 this way. And when you see old crystals, you just ignore
63:16 Um This is essentially the same data question number one, but I
63:24 I added something and I changed the type. Think about that for a
64:55 . OK. So this one's different that we now where it started the
64:59 rite started at the surface. This started down there somewhere. Um When
65:05 this rock crystallize nine is a good . I mean, we know the
65:12 temperature of argon and horn blend is, is uh 500 degrees.
65:17 we know this rock was at 500 90 million years ago, was at
65:21 same time as its crystallization. often it is, I mean,
65:26 that crystallized at when the country rock exceeding 500 degrees. Well, it
65:31 happen if we weren't sure if we need, if we, if,
65:34 , if, if, if we wanted to know when the crystallization age
65:38 this rock was, what would we done? Uranium? Like Z,
65:46 , and that's either gonna be 90 older than 90. Right.
65:51 um, what else can we say this rock? It's, it's at
65:55 90 degree, it's at least 90 years old. And then what else
65:58 happened to it? Ok. That's . Ok. Yeah, it took
66:17 , took another 20 million years for rock to cool down to about 300
66:22 and then a, then it cools 300 down to 100 or 150 in
66:28 subsequent another, you know, 15 years. And so again, you've
66:33 three points here, you could be cooling rates between those two points and
66:38 seeing, yeah, was that was that a time when the cooling
66:42 was heating up, uh, speeding or cooling down? And generally,
66:48 know, when we're doing this sort , of information on basement rocks like
66:53 , we're looking for times when when the, when the cooling rate
66:57 because that means that faulting is bringing that rock up fast. Remember
67:02 , I showed those things when we at Mount mckinley where the cooling rate
67:07 whenever we can see for increasing, , cooling rates, that's something that's
67:11 on in the tectonics of the region then can be reflected in other faulting
67:16 it can be reflected in erosion and burial in some basin either nearby or
67:22 away. Um We talked about this last week, so I'm gonna skip
67:28 one. Um So tell me about data from this schist. Again,
67:38 talking about a basement rock but, basement rocks can tell us about basin
67:43 . So what is the basin? does this basement rock tell us about
67:48 , the the tectonics of the the potential filling of basins nearby?
67:57 , let me just get it. me give you a hint. I
67:59 , in general to shift, it's metamorphic rock in general. What,
68:04 kind of rock was a schist before was a shift sedimentary rock pretty clearly
68:17 either a shale or a sandstone. keep that in mind as we carry
68:41 why such a wide range and Uranium Zircon ages from this rock. A
68:47 reign. Thank you. Um we don't reset uranium lead zircons.
68:58 , we'll get to that in a . I wanna know why is there
69:01 a huge range from 1200 to 2400 the Zircon s because it's, it's
69:09 the sedimentary rocks age and it's the . So it came from different parent
69:16 of different ages. Fair enough. the only quibble I'd have there.
69:20 is, it's not necessarily reflecting the rocks age but the provenance material that
69:25 deposited to make this sedimentary rock, ? Yeah. Ok. So with
69:29 in mind, let me ask you the sedimentary rock, the precursor to
69:33 shift, when was it deposited 24 million years ago, I guess 2.4
69:45 years ago or older? How if was deposited 2.4 billion years ago?
69:52 did it get that? No, , no, no, no.
69:55 younger than the 1.2 billion. Very , younger than younger than 1200.
70:01 , we had a sandstone that was sometime since 1200 that, and that
70:07 range in there just says that those the, those are the rock that
70:10 being eroded into that basin some time . And but then then sometime between
70:19 million years ago and 20 million years . Well, what happened? It's
70:28 shift. So it got metamorphosed, ? When did that metamorphism take
70:32 We can't say for sure. But know that the rock was brought up
70:37 temperatures of around three or 400 degrees or 20 million years ago. That's
70:42 this is. Ok. So that these are about the same actually,
70:51 me just, well, no. so, well, no, I'll
70:55 tell you, I didn't, I totally make up this example. This
70:58 a typical kind of bun result you get from rocks in the Himalayas.
71:02 is very that everything about this says in including the wide range in Zircon
71:09 , the ages for the muscovite and biotite. And then these 3 million
71:12 old ages down here. What is , what do these two things tell
71:20 ? Close your temperature, efficient track , 100 close your temperature of helium
71:32 . 70 ish 7075. So what says is that what? Yeah.
71:41 we know that this rock was going 100 degrees to 70 degrees so fast
71:46 these two techniques can't tell the This thing was rocketing up to towards
71:50 surface around 3 million years ago. was being metamorphosed around 20 million years
71:56 . That's the time of that, all those mus go by. Oh
71:59 we can say it was at temperatures 300 degrees around 20 million years
72:04 but about 3 million years ago, rocketed to the surface. And so
72:10 would look for sedimentary deposits in this that were thickest in this pliocene
72:18 right? Everybody follow that on the . There any questions? Um Let's
72:31 what time is it? It's we've been doing this for almost
72:34 a little more than an hour. got through one third of our
72:39 That's about right. We got through third of our questions and approximately one
72:42 of our time. So we're doing . Let's do, let's see.
72:47 , let's do this one. And this one is a little complicated and
72:52 we'll take a break and come back carry on with some more of
72:56 So what we've got on this question eight, I've shown you the,
73:03 histogram, the, the probability density for two uh analysis. We've got
73:10 fish and track ages in red and got Zircon uranium lead ages in black
73:17 the, the, the, the probability on the Y axis, the
73:21 on the X axis, the age from 0 to 100 million. I
73:25 you to tell me what happened to sandstone in three different scenarios. One
73:30 one, in which the depositional age know is eocene, say about 50
73:39 . One in which we know the age is miocene, let's say about
73:46 million and one in which we have idea what it was. We'll start
73:52 the first one. Let's imagine the age is 50. What does that
73:57 us? 50 kind of spans the between these two distributions, right?
74:23 Zircon ages are older than 50. appetite ages are younger than 50.
74:29 do we get ages in a sedimentary , younger than the depositional age?
74:43 OK. Well, both of these are, I mean, this is
74:49 in this sandstone. I hold in hand. We've got some Zircons,
74:53 got some quarts, we got some bar, we got some appetite.
74:56 analyzed the Zircons and the appetite be technique. So already there is not
75:01 what I'm after. What, how it just in ge generally speaking,
75:06 is it that you can get any chronologic information? When you date something
75:11 a sandstone, if that's isotopic age obtain, it gives you a younger
75:18 than the, than the accepted Strat age of that sandstone. What does
75:23 tell you? It was reset, appetite was reset around 20 million
75:36 it was reset. You had to in, in general you if,
75:40 you got any, if you got values that are younger than the depositional
75:43 , something had to happen to them when they were deposited at the,
75:47 the time in, in, in , in this, in this
75:50 in the eocene, they had some but it was, you know,
75:53 and they would continue to get So the reason that this is younger
75:57 20 tells us that there's been The fact that we got a pretty
76:01 peak here at 20 suggests that the temperature was obtained or excuse me,
76:07 the maximum temperature that this these rocks reheated and then cooled down to temperatures
76:12 around 100 degrees around 20 million years . That's, that's the and so
76:19 explains the appetite fishing track data. that case, if we, how
76:23 we interpret the Zircon Uranium lead age ? If the depositional age here
76:30 is 50 million, that's just a of provenance, that's telling us what
76:38 of rocks were being eroded 50 million ago to produce these sandstone.
76:42 that they were, we were, were eroding a bunch of rocks that
76:47 cretaceous age zircons in and since I extend this out, older than 100
76:53 can say that that's all there Um What information would you,
77:04 what other information am I not giving here about that? That would be
77:09 in interpreting this, this reheating What information about the appetites? Am
77:16 not telling you about? You? , there's two bits of information we
77:23 to know about fish and track the number of tracks or the density
77:29 the tracks, the length. So , if, if we saw that
77:35 the lengths were all the same, that would, you know,
77:38 all, all 14 millim irons long would tell us that this rock was
77:43 . It could we know certainly the was buried because the appetite fishing track
77:47 are younger than the deposition if, it so they were got buried.
77:52 fast did they come back up through partial and healing zone that would be
77:56 to us by the track length If they are, wi if the
78:02 links have a wide range, then , it came back up slowly.
78:06 the track links have a narrow it came back up quickly. And
78:10 , that tells us something about the in which it was in the,
78:13 , petroleum generation temperature. Right? we can say from the diagram I've
78:17 you today this moment at this moment that we got hot enough, you
78:22 . Yes. The maximum temperature was 100 degrees. If you're, if
78:27 doing this work to evaluate the petroleum , you'd like to know, not
78:32 how hot it got, but how it was there? The fishing tracks
78:36 help you sort that out actually mean fishing track lengths would help you sort
78:40 out. Now, let's change uh the, the, the interpretation
78:46 change the evaluation criteria and say no, no, that's not a
78:52 rock. It's a Miocene rock. can you tell me about the history
78:57 that rock if we have the same ? But we're gonna say that the
79:01 was deposited in the middle of the , say 14 million years ago.
79:09 that change your interpretation of the history the straw? This rock was deposited
79:27 million years ago? And basically all appetite, fishing track ages are older
79:32 that, which is perfectly fine for detrital rock. You know, you're
79:38 some grains, they're old grains, come and they sit in this
79:43 The fact that they are still older the age of deposition tells us.
79:48 about the history of this raw? me put it another way in which
80:08 would this be a better candidate for petroleum system when the rock is
80:12 And when it's my ce mien. , my scene example hasn't been
80:26 Oh, I'm sorry. Yeah, meant you meant the other my
80:32 The es up. Yeah, you mix them up. The eocene example
80:36 a better candidate for a petroleum system it's been reheated. But if this
80:41 was deposited 14 million years ago, really no strong evidence that this rock
80:45 above 100 degrees. In fact, quite a lot of evidence to say
80:50 didn't get above 100 degrees, which that it may not have spent very
80:54 time in the petroleum generation window. by dating this rock, by dating
81:01 low temperature components of this rock and getting anything younger than the, than
81:07 deposition age, we can say this this rock probably wasn't buried, you
81:12 , very deep. Now, in case of the my of the,
81:16 this rock is Miocene, we're gonna the Zircon Uranium lead data exactly the
81:22 because it's older than the depositional Once again, it's just telling us
81:27 the provenance of this rock, these , the the material, the paleo
81:32 that was, that was drawing drawing sediment down to this basin included
81:39 bunch of cretaceous age. Zox that change when we changed the deposition.
81:46 can't remember why I put depositional ages . I guess if we, if
81:51 the depositional age is unknown, we're gonna have to include both of these
81:55 potential uh, interpretations. Uh Not when the, when the dep,
82:00 the, uh, when the depositional is, doesn't allow us to decide
82:06 these rocks have been to 100 degrees not. I guess that's why I
82:11 that in there. Folks see All right. It's 22 26 3
82:24 . Let's take a break and come at 240. Ok. So the
82:35 few slides here um are what do recommend questions and then give you some
82:41 them are straightforward, some, a more complicated. Um But you may
82:46 across uh you know, geologic problems as these, you need to know
82:50 of these many techniques we've talked about the most valuable one. So we
82:56 to know the age of a sequence fossil poor sandstones. We know they're
83:01 and contain some bed night beds. guys know what a bet night
83:07 I used this term once and I it's maybe. Mhm. Well,
83:14 is a, there's a lot of in there but I mean, what
83:19 , what, what is the, is the origin of that bed?
83:27 Yeah, it's volcanic. A bet is a, a highly altered tough
83:34 much its clay now, maybe mo lot of Mount Motor and I or
83:38 clays, but it's a very highly . Uh volcanic unit. So we
83:44 know, we, we know they're , got some bet nights in it
83:49 altered volcanic rock. What do you for figuring out the age of the
83:56 of these sandstones fossils haven't done it us? On, on from,
84:12 , from which from, from the , from the bed nights from something
84:18 . That's it. Ok. You some Iranian led Zircon ages on the
84:22 . What are you gonna learn that ? You're gonna, how many,
84:27 many grains you wanna analyze? Let's with 100. Ok. And,
84:33 when we do this, we're gonna the maximum deposition age, right?
84:39 to be younger than that. that's certainly a way to go.
84:47 , is there another choice? I, I would be before I
84:52 that, I would do something A bed night is a weathered rock
85:01 to be a volcanic rock. But hiding in all that clay? They
85:13 a lot of the bed nights that made up the Strat gray of the
85:18 Basin in, in, in, uh in uh New York, there's
85:22 bunch of, you know, the Catskill Delta coming off the Taconic
85:26 in, in New York. Um of that Strat democratic control is from
85:31 from Zircons in bed kites. These nights are all altered, all of
85:36 felts for all of the, all the biotite that was originally in that
85:41 has been altered. But you don't zircons, right? Zircons are
85:47 So again, this is a, is a generic question, but I
85:51 it up from a real geologic That would be the, the Hali
85:58 strata of, of New York and . Well, particularly New York
86:03 has a lot of Benites in These are, these are distal volcanic
86:07 that came from the volcanic arc in , send off, you know,
86:14 fine grain material that gets, that deposited in the basin and then is
86:19 quickly, probably. And so it a kind of clay rich layer,
86:25 probably in that bed night or some cops. So I would look for
86:29 bet night beds first if it turns that those bed nights didn't have these
86:33 . Then yes, you go to detrital zircons and try and figure out
86:37 maximum deposition age by analyzing as many you had time to analyze. And
86:42 , and then when you're done analyzing 100 or 200 grains, which one
86:46 the most important? One of all those you looked at when you
86:54 when you decide to analyze a bunch zircons from the sandstone, and you've
86:59 100 and 17 grains or 200 which one is the most important one
87:07 those 117 that you just looked at youngest one, right. The only
87:22 we get the maximum depositional age is that the that the rock had to
87:26 deposited sometime after the youngest one of was, was, was laid into
87:31 sandstone, right. The youngest That's why we want to analyze at
87:39 100 of them to give us a that we have found something like the
87:44 group. You know, if we , if we analyze, you
87:50 10 grains, um, you we'll have the youngest one there,
87:54 we don't have great confidence that it's the youngest one we're likely to
87:59 Ok. All right. That's Here's another, what would you
88:03 Question? Same thing. We need know the sequence of some fossil poor
88:09 . We know they were younger than cretaceous, but they were and were
88:13 near a volcanic dark, but no rites have been found. So how
88:20 we figure out the age of this ? This is basically the same question
88:37 before, except I took away your . So if it's the same
89:03 the same answer, yeah, I made it. I, I just
89:09 the difference between nine and 10 is you've got some bed nights here,
89:13 nights are the right choice here. if you don't have a volcanic
89:17 but interbedded rites are not known, you're stuck. You know, remember
89:21 is what I call Plan C. we don't have interbedded rites. We
89:26 have good fossils. We're gonna go Plan C which is to take tridel
89:30 . So I don't think the tral was the best answer for number
89:33 because you've got a volcanic unit. number 10, I disallowed the volcanic
89:38 as a choice. So we go dating to tral minerals. Ok.
89:44 , number 11, we need to the valuate the petroleum potential of a
89:49 that sits 100 m above a narcotic and 50 m below a limestone above
89:56 limestone is a basal. We're not of the age of deposition or the
90:02 thermal history. What do you recommend sort out the geologic history of this
90:07 ? We'd like to know when these were deposited. We'd like to know
90:11 uh maximum temperature or their, their petroleum potential. We give you a
90:18 minutes to think about this. We've , got a narcos, we've got
90:23 basalt, got a limestone, we've a shale, we're interested in the
90:29 . I mean, we're gonna assume the shale is a potential source
90:32 right? So what data would we to gather? We've, we've got
90:39 , we've got a stratigraphy here and thinks that shale has the potential for
90:45 a source rock. How we're gonna that out. We, we don't
90:49 when they were deposited. We don't how hot they got, but I'm
90:54 give you a, we give you months in a budget of $100,000.
91:00 it out. I don't. Who has a suggestion. What are
94:05 important? What are, what are ideas of things we might want to
94:13 fish tracks in where fish we You got, we got different rock
94:19 . We got different minerals. Look fishing tracks is insufficient to start anybody
94:41 . So you could date the That's a good start. The basalt
94:48 , excuse me, Terry, I'm just point out the basalt is the
94:51 to understand of all the units we've in here, right. The basalts
94:55 volcanic rock that we can date and once we got that we'd have
94:59 to hang our stratigraphy on. How we gonna date the basal zircons?
95:05 , wait. Yeah. They don't exist in the salt. Don't really
95:09 zircons in those kinds of rock. . There's some other weird things.
95:16 , bli. Yeah. Yeah. . Ok. That's, that's
95:20 I'm glad you caught on, on . But it would be an excellent
95:23 to go. They're, they're kind weird and they're not. I
95:26 if you could find a bli and in a, in a basalt,
95:29 be terrific. Suppose you didn't have much patience to go looking for
95:34 Is there another way to date it ? So, uh Argo,
95:40 we could try the Argon 4039 We, I showed you some examples
95:44 how that had been successful. dating the basalt, I think is
95:48 good idea. It gives us it , it, it, um
95:52 it, it, it gives us sense of, of some part of
95:54 stratigraphy. So that would tell you know, are we looking
95:58 you know, rocks that are 10 years old, 100 million years
96:01 whatever. That's a good start. But since that Basalt lives at the
96:07 of our stratigraphy, it only gives a sort of maximum, uh only
96:13 us a capping age for that. doesn't tell us about the uh other
96:18 we want to hear is to evaluate petroleum potential. If you thought more
96:22 your fishing track, suggestion problem with is that the shale is so fine
96:35 . There's probably not. I what again, what minerals are we
96:40 be evaluating if we do fishing track or you could also do Zircon appetites
96:51 probably best for this petroleum potential example of its closure temperature shales. The
96:58 shales is the rock we're interested Unfortunately, shales are super fine grained
97:03 they probably don't have very many appetites so and, but your app your
97:13 appetite idea is a good one. can we find appetites in these
97:18 Can, can't we just do it the basalt? And that'll give us
97:22 sense of relative. Well, it tell us that it would tell us
97:28 the thermal history of the basalt, the basalt could have come after all
97:32 this stuff. We're looking at the basalts on the top of our
97:34 gray, we wanna look, we understand the thermal history of the
97:40 And there's this, you know, , there could be an un conformity
97:44 the, that there, there basically an un conformity between the basalt and
97:48 limestone. Below and below that, a shale and below that, there's
97:52 narcos from the sandstone from the, the Arcos, I think that's probably
98:05 way to go. It's, and again, I'm making up real
98:08 examples where, you know, you , well, let's just, let's
98:10 do the appetite in the shale. not a thing. It's a great
98:14 , but real rocks don't, don't give us that. And the basalt
98:18 , we talked about all the ways we can do the basalt, but
98:21 salt being on the top of the doesn't tell us very much about the
98:25 history of the lot. So we're date if we look at fishing tracks
98:29 our in appetites in the Arco. that's perfectly reasonable to expect appetites in
98:35 Arcos, right? An Arco is that we are eroding of a nearby
98:40 source and it's close by, the are gonna be fine. So there's
98:45 appetites in that Arcos that's 100 m our potential source rock. So the
98:53 . So the Arcos has gotten a bit hotter than the, than the
98:57 than the, than the shale but the best we can do.
99:02 I would look for appetite fishing track perhaps appetite helium dating from rocking that
99:10 . And then we're gonna try to our geothermal gradient to say,
99:13 well, I mean, 100 m really not that much. So whatever
99:17 history we can figure out for the , we can just cut and paste
99:21 onto the shell and decide whether or that is a uh promising thermal
99:29 Um That would tell us the timing that. But we, and we
99:33 also know well, if and the age of the basalt would also be
99:39 . So I would date the basalt give us a sort of top end
99:42 for this photography. And then I date appetites from the Arcos uh
99:47 by both methods, helium and, F and track. Be sure
99:51 to, to be sure to marking uh fish and track lengths when we
99:55 that. And that would help us a sense for how deeply buried,
100:00 for how long it was buried that is. And that would be very
100:05 in the evaluation of our petroleum I I have a question. Go
100:13 . So mm for the appetites and sandstone, why? And I'm,
100:22 probably just having trouble wrapping my head this at the moment. But
100:27 why couldn't that just be a reflection the provenance material? It most certainly
100:33 be. And if it was a if it was a reflection of the
100:37 material, then of course, we evaluate the petroleum system potential as being
100:42 low. Now, the, the , I guess you're pointing out is
100:46 , if we don't know the depositional of the, our coast, how
100:49 we gonna evaluate that good point? least we know that it's, the
100:54 age is older than whatever we get that basalt that you saw that we
100:58 date. So, I mean, , you're bringing up a good point
101:04 that we still haven't definitively answered the of the, the, the,
101:08 Arcos. But suppose we could do lead dating on the zircons in that
101:15 do the maximum depositional age business where analyze a 200 of those grains,
101:20 haven't been reset by whatever depositional happenings going on. So if we dated
101:26 200 Zircon grains by Iranian lead, could help, that could help us
101:30 a better understanding of the depositional then we do the fish and tracks
101:34 the appetite. That'll help us understand the appetites are telling us about provenance
101:39 you just suggested Taylor or whether it's us about post depositional thermal history.
101:51 . So, I mean, you're you that the question he just
101:54 up there is just, you essential to every one of these
101:58 When we're looking at the uh thermo data from a sedimentary basin, we
102:03 one or the other. You can learn about the provenance, which is
102:08 very useful, very helpful turning telling about tectonics in the provenance, telling
102:12 about paleo geography, that's all valuable in, in developing a, a
102:17 of what the uh what the entire looked like that's good or if the
102:24 . But if the rock got buried , all that information gets thrown away
102:28 we're, now we're telling us about , the, the post depositional thermal
102:33 . But as I just suggested in example, what if we did 22
102:37 things that have very different thermal The Irani L Zircon is always telling
102:42 about the provenance and potentially the depositional , the fishing tracks have the potential
102:48 tell us about the post deposition of history. So I think we did
102:53 one. OK. Can I move ? We need to know the depositional
103:00 of unit B? What do you ? And, and, and let's
103:16 this, but we've, we've we, we, what do we
103:20 ? What do we do when we have a short amount of time and
103:23 ? Now, when we have lots time and lots of money, we're
103:25 gonna analyze the hell out of, ? But, but I mean to
103:32 it will bring us some information. if we're in a big hurry,
103:35 don't have a lot of money. the number one choice here. Excuse
103:50 ? Or gone on. What? . What mineral, I mean,
104:07 , well, oh, yeah, whatever mineral exists in this rock,
104:14 pota, the potassium minerals that we're be looking for, we look for
104:18 Bar and by basically, or some rye lights have horn blend in
104:22 that's not very pa. Um, , so that'd be one way.
104:26 . Um, that might give us , that, that'll give us
104:31 a, um, a minimum age the sandstone, right? The sandstone
104:34 older than that. Um, but it's a, if it's a
104:38 if it's a fairly conformable contact, mean, obviously it's not conformable,
104:43 time there's gotta be some time but if there's a small amount of
104:47 missing, then that's a good way go. Um, dating the ry
104:51 by argon dating. That'll probably Um, suppose the ar suppose that
104:57 call up the Argon lab and they , oh, we had a,
105:00 had a fire in the lab last . We can't work on your sample
105:03 a year. What else would you besides call another Argon lab? All
105:12 labs are shut down for the next months. Uranium lead on zircons,
105:35 lead on zircons from the rite. , that'd probably be my first choice
105:40 . I mean, the argon is . Uh, but the zircons are
105:43 always a better choice because they they'll withstand any sort of alteration or
105:49 . Uh, so that would be first choice, you know, but
105:52 course, you know, you have make these choices on, you
105:54 suppose, suppose that this was not nice outcrop study, you know,
105:59 you can go, you drive the up and bring back £100 of every
106:03 you're interested in. Suppose we have photography, but it's only known from
106:08 , only known from core. that's when finding a zircon becomes a
106:12 much difficult, more problem. Zircons found in rites but not in,
106:16 in a, you know, not a shot glass full of rite.
106:21 probably not enough Zircon today but in shot glass full, you know,
106:25 few cubic centimeters of rite, there's a few f spots or, or
106:30 . So, depending on the size the sample you have access to.
106:33 you can drive, you can drive pickup truck up to your outcrop,
106:36 you can bring back enough rock to Zircon it. But if this is
106:40 a drill core, you know, only got, you know, small
106:44 of rock. So it's only say ry light, it's only, you
106:46 , 20 centimeters thick and you only , you know, a broken bit
106:50 core from that. It's only you know, four inches across.
106:54 you're lucky, uh Zircons might not your first choice. Um Is there
107:00 other thing you would do to this to help to this, to this
107:02 in this Strat gray that I've shown any other thing to help sort out
107:08 depositional edge of the sandstone so far dated the rite and that tells us
107:13 the sandstone will be older than Can we do anything else? Anything
107:25 can do with the granite? We do everything that we did to the
107:37 to the granite, right? The composition. And there's probably even better
107:41 minerals in the granite. Of all things we could do to the
107:46 which one's gonna help us understand the the best. Is it the same
107:55 the rite the Uranium Lead Turk on ? No, it's not because we're
108:22 in learning when the sandstone was the the granite obviously made it to
108:26 surface, then the shale was then the sandstone was deposited. So
108:31 like the little bit of information that us best. When did the
108:35 When was the granite exposed at the ? Not when it was crystallized.
108:39 could have been a billion years How are we gonna figure out when
108:44 granite was brought to the surface? track, appetite, fishing track.
108:56 be a good choice. Uh Appetite would be a good choice. All
109:00 those techniques that give us really low . That's gonna be when that granite
109:04 brought near the surface, the sandstone gonna be younger than that,
109:11 Assuming that this whole sequence hasn't been buried once once again. But if
109:16 just assume this is a pretty straightforward , granite was granite was formed down
109:21 , brought to the surface eroded, shale was deposited on top of
109:25 the sandstone was deposited on that top that. The Rite was deposited on
109:29 of that, the sandstone age is be somewhere between the uranium lead Zircon
109:34 of the rite and the uranium helium of the appetite from the granite.
109:43 two ages ought to bracket the age that sandstone. Wait, I
109:53 Why did you use uranium helium? it has the lowest closure temperature of
109:58 of them? Ok. That's gonna you the best estimate for, you
110:04 , that still doesn't tell you the that the granite re breached the surface
110:08 it's still, that still was when granite was at 70 degrees. But
110:12 another kilometer up from when it was 100 degrees. And why were you
110:17 about when the granite was? Because , because dating the rite in this
110:23 only tells us that the sandstone must older than that, how much older
110:26 can't say for certain. So if can get it from the other
110:29 that would be nice. So I to know something. The granite is
110:33 only dateable rock that's older than the . We can't do anything with the
110:37 , I'm afraid. So we're gonna the granite and, but we don't
110:40 to date, we wanna know when granite was close to the surface because
110:45 the sandstone can't be deposited until the is deposited and the shale can't be
110:50 until the granite is at the Follow that. Got it. Got
110:55 . Ok. Yeah. So that's , that's why in this example,
110:58 leaning towards those systems that have the closure temperature that don't start ta talking
111:04 us until they are quite near the . In the case of uranium helium
111:11 , that could be as low as degrees, maybe only, you
111:16 two kilometers. It's not at the but it's two kilometers and that's,
111:20 as good as we're gonna get. so that age is gonna be older
111:26 the sandstone, then we can date rite and that's gonna be younger than
111:30 sandstone. Everybody. Happy. All right. As I recall,
111:42 is a complicated one. I want to take a few minutes with this
111:47 and maybe draw out some, some time uh graphs for each of the
111:54 , you know, draw, draw your uh your photography and then figure
111:59 the temperature time graphs. Um And that we've, let's see. Uh
112:04 , yeah. Temperature time histories are here. Get a little temperature versus
112:09 graph and plot the granite, plot conglomerate. Well, plot whatever you
112:14 about when these rocks were at different assume, let's see. Do
112:18 what assumptions do we have? You're assume that the, uh,
112:22 that there's no, that there's, obviously a un conformity between unit A
112:28 B. Um, I've left unit off of there for some reason.
112:34 don't know why. Um So just at those units try and work out
112:41 temperature time, significant points and then the entirety of that sequence.
112:47 it's complicated. You gotta read through and, and, and figure these
112:53 . So I'm gonna give you a minutes to work on that. This
112:56 a, this is one of this , this is the, this is
112:58 challenging question. OK. Are are we making any headway with
118:40 I think the key here is to by, by showing what's the,
118:45 the thermal history of the granite that a, that tells us something about
118:50 bottom of this section. You the rock is at least 450 million
118:57 old. The horn blend is OK. It's even older. The
119:04 feldspar tells us that it, what's 380 tells us what it was probably
119:09 below 200 degrees by 380. sitting on top of that granite is
119:17 conglomerate with granite class. And in class, we found a zircon and
119:22 uranium helium age for the zircon is million. That's pretty close to the
119:32 million we got for the case And that so uranium helium zircon has
119:39 closure temperature. That's what about 100 50 ish unless it's really damaged.
119:47 I would say that unit B came from the gran, you know,
119:50 is not uncommon to have a conglomerate full of plast from the material just
119:54 it. Right. The thermo chronology the class is consistent with that.
120:01 on top of that, we have sandstone, it's got a helium appetite
120:07 of 90 million, significantly younger. on top of that, we've got
120:15 highlight with the uranium lead Zircon It's nearly old 358 million. Is
120:23 a problem here? We've got a on the top of the sequence gives
120:27 older age than the rock below It's not a problem when you look
120:35 what kind of ages they are, right light sits on top of that
120:40 the uranium lead 358. Under what will the Iranian led jerk on HB
120:54 . Bit of a trick question. what conditions will the uranium L jerk
121:00 HP reset. Well, OK. other words, almost no conditions.
121:09 , it ain't gonna be reset under conditions will the uranium helium appetite age
121:17 reset? The closure temperature of Yeah. 70 fiveish. OK.
121:36 if the highlights 385 but the sandstone below it is 90 by, by
121:42 age what does that tell us about entirety of this sequence? I like
122:02 way you're moving your hands around. makes sense. That's what you need
122:05 do. What was it? The, what? The summit?
122:21 possible. But we won't learn that the fact that we've dated it by
122:24 different methods here. That's not what asking you to think. The highlight
122:33 the simplest interpretation of everything we've got . Rites are easy to interpret and
122:38 Lead Jon is easy to interpret. highlight was erupted at 3858.
122:45 that's easy. So all of the beneath it are older than that,
122:53 ? So how do we get a ? That's unit D, it's older
122:56 unit D and yet it has a helium age of 90 million. The
123:03 sequence was what was, was, re was reheated. We take that
123:08 down, the whole thing was at surface at 358. Then we bury
123:16 such that these s the sandstone, appetites in the sandstone are reheated and
123:21 their helium and start retaining their helium again at 90 million. So then
123:29 , this uh this Pennsylvanian sequence was in the Cretaceous reheated. And
123:40 that's the main, that's, that's main answer here. Well, let
123:45 see. Pennsylvania, you've got this was crystallized around 4 64 50.
123:52 was then erupt, then it it was brought to the surface by
123:58 . Because the because the granitic class we are assuming there in this rock
124:03 from this rock, those granitic class uranium helium zircon agents of 360.
124:09 between 4 63 60 this rock was to the surface. Then at 358
124:18 2 million years later, the top was deposited. So that means in
124:22 that, that sandstone was deposited, sandstone followed on from the conglomerate.
124:29 of that happened between, you that conglomerate was brought to the surface
124:33 360. The uh or excuse the class in that conglomerate were brought
124:38 the surface around 360. Then some was deposited. Then at 358 the
124:46 was erupted and covered the whole But then we know something else happened
124:52 the sandstone has helium ages that are younger than everything else. So that's
124:58 that whole sequence got buried during the . And then it was brought back
125:03 , passed through, passed through 75 90 million years ago. We've got
125:08 paleozoic sequence of rocks were buried in mesozoic, brought back up to the
125:14 around 90. Does everybody see how got through that? I should just
125:24 out, but let's take a moment talk about your test next week.
125:27 didn't, I didn't appreciate until just other day that I've been,
125:31 I've taught in this accelerated master's A lot of times this might be
125:36 10th time I've done this for a like you all in, all the
125:40 times everybody comes to this room to the test. As I understand that
125:45 not the case. This time, are some people out in the world
125:48 just will get the, get the emailed to them that's gonna change how
125:54 , I take the test. I I'm just gonna email. So I've
125:57 what I'm gonna do is I'm gonna you a test and I'm gonna give
125:59 like two days to finish it, is not really to your benefit,
126:05 ? Because a test that's open ended that, I'm gonna grade it
126:11 Uh but it gives you plenty of to think of it. Look it
126:14 for your notes. You know, I'm not gonna, I'm not gonna
126:17 the standard that I often use as , the standard of the uh of
126:21 pilot, you know, on the , you want your pilot to not
126:24 to be, look at stuff but you want him to know
126:26 right? I'm not gonna use that for you guys. You know,
126:30 , I always, I, I show the uh there's a scene from
126:33 13, you know the movie Apollo when this stuff happens and they,
126:37 call down to Houston to say, do we need to do? And
126:40 show this picture of all these guys slide rules, figuring it out the
126:43 and they all tell them the I always use that as an example
126:46 people, those guys with the slide really did their homework. They knew
126:49 the end they knew how to They, I'm not gonna apply that
126:53 to you guys because you're not all be here in the same room.
126:57 is the kind of question I can you that requires you to think
127:02 requires you to know all the things , and write it down. And
127:05 you, you know, if I you a day to answer that
127:07 I'm fine. But this is the of question I'm gonna give you,
127:11 gonna give you a variety of It's gonna involve you. It's probably
127:14 involve an up and a down. got rocks that are easy to interpret
127:19 they're volcanic rocks we've got and so so forth. So you should be
127:26 with this. Um If everybody, know, I went through this
127:30 you should be, you know, , who is, who is there
127:34 question you can ask me about this that makes you feel better because this
127:38 a good, this is a good question. Why don't we?
127:44 I'm gonna, let's see. it's 325. We got another hour
127:49 20 minutes to go here. Um we'll come back to this one and
127:55 take a break. In a few minutes. We've been going for little
127:59 an hour. We, we, , let's look at a couple,
128:02 look at it. What's wrong Let's look at this one. Um
128:06 is a similar question. Let's see we got here. We got a
128:11 with some information and a sandstone sits top of that and then a rite
128:17 on top of that. Let's We've got, so this is a
128:23 question. Uh I can tell. right. So think of this question
128:30 the same way. Is this, this also, you know, the
128:35 question we had evidence for the basement up to the surface being covered by
128:40 , being, being buried, coming up. Do we see the same
128:44 here? Or is this a, this a simpler example? More complicated
128:49 ? We've got basement rocks. We've a schist, we got some sandstones
128:52 rites on top of that. Is the sequence of rocks that is did
128:57 schist obviously, there's an un conformity the sandstone and the schist.
129:02 how profound is that in conformity? And where was this sandstone uh buried
129:11 subsequent to its original deposition? Um This, this bit of
131:39 the Iranian led Zircon age from the tells us that we've got some old
131:43 that were in the original sedimentary That's about all we can say
131:48 Next, we've got a bunch of information. Muscovite and biotite give this
131:53 54 60. Um That may you know, when this rock was
132:00 , the helium Zircon age is So this shift was getting pretty close
132:04 the surface or at least to temperatures 100 and 50 degrees or so.
132:09 about 300 sandstone above d give very information about the thermal history,
132:19 Because what do we got there is uranium lead zircons. Uranium Led Zirk
132:24 never tell us about the post depositional history, but tell us about the
132:30 . We get no information about the depositional thermal history from that sandstone because
132:34 didn't date anything but that. So that tells us, however is that
132:39 age of deposition of the sandstone has be less than 325. Well,
132:46 good because it better damn well be , less than 300 right? Because
132:51 , the, the shift below has cooling age of 300. It
132:54 it was near the surface at The sandstone has to be less than
132:59 . So this didn't tell us anything the age of deposition, either we
133:03 knew the age deposition was less than . All this means is that
133:07 the zircons that were being deposited sometime 300 didn't include any grains that were
133:14 than 325. So in terms of of deposition or post depositional thermal
133:23 those zircons from that sandstone. They do us any help at all.
133:30 tell us about the provenance and they us that some of these zircons,
133:34 mean, it, it, it us, look at that, that
133:36 2450 some of those zircons may have from the shift. Um But that's
133:43 we can tell. And then we a rite that sits on top of
133:47 that and it has an age of uh that's younger than the 300.
133:56 And so what we have here is shift that came to the surface sometime
134:00 300. And these other two rocks were, that were deposited sometime,
134:05 with the top rock here would was deposited at three, at 250
134:09 other rock was deposited somewhere between 302 . And you know, this is
134:15 , is a bit of a tricky in which in which if I'm asking
134:19 about the history of the sandstone, its provenance, we don't know anything
134:25 than it's between 2 5300. you know, all that Uranium Lead
134:30 ages tells us nothing about depositional age this instance because we already knew it
134:35 less than 300. And it tells nothing about post depositional thermal history because
134:40 never tells us about the post depositional history. When we're talking about Uranium
134:45 Circuit Uranium Lead circus are not gonna reset unless you, you know,
134:51 the rock and these are sandstones, not melting. All right, let's
135:00 another one and then we'll take a . So, what have we got
135:08 ? We've got a granite with some here on top of that, we've
135:14 a CRE Triassic sandstone and on top that, we've got a Cretaceous
135:21 We've got a granite that's got an old 1750 uranium L Zircon
135:28 The biotite in that granite is old , 1400 and the appetite fishing track
135:34 is 500. So the uptight fish age is telling us what the last
135:40 that granite was at 100 degrees. The Triassic sandstone, well, we
135:53 is deposited at the surface. So granite was at the surface in the
136:00 . What happened to this granite during paleo got two points. You
136:15 I can, you can tell me this granite was at 500 then in
136:19 tri acid, right? That, constrains what happened during, in between
136:35 happened in this granite, it has have stayed colder than 100 degrees,
136:42 ? Because this fishing track age is , 500 million. So between the
136:49 this rock cooled to 100 degrees and Triassic, it was never, it
136:53 somewhere between surface temperature and 100 This rock has been near the surface
136:58 all that time because it was, was clearly at the surface in the
137:06 . But because the fish and track is old, it's 500. I
137:11 , since 500 this rock has I mean, you know, we
137:15 know exactly, but it was never hot. And then the sandstone
137:20 top of this gives, it gives appetite helium age, which is got
137:24 lowest closure temperature of 40 million Now, we could say that that's
137:33 tral or provenance age in which all tells us is that the Cretaceous sandstone
137:39 deposited after 40 million. Or we interpret that Cretaceous sandstone, appetite helium
137:47 as being a reset age. In case, the Cretaceous sandstone would have
137:53 be greater than 75 degrees. But fish and track in the granite with
137:59 was still can't be more than 100 . So that's a narrow window between
138:06 . I mean, if, if Triassic sandstone is, it would,
138:11 would be helpful to know the thickness this Triassic sandstone. How far apart
138:15 this Cretaceous sandstone from this, from Proterozoic granite? Uh So there's
138:23 there's a, there's a, there's variety of information you might like to
138:27 more about how far apart. You , if these things are close
138:30 That's, that's very odd because this was at 70 degrees, 40 million
138:36 ago, but this rock's never been degrees for 500 million years. It
138:40 doable. But, you know, a, there's a ST Strat graphic
138:44 of information we don't know there. without the co unit C really kind
138:52 makes this a harder problem if you forget unit C, it's an easy
138:56 . The uh the granite has been the surface for all of the paleozoic
139:01 , and part of the mezzo and , you know, that's valuable
139:06 When you're trying to put together a geography of a region, there were
139:10 , there were no important basins that been filled and, and ripped off
139:14 , this rock was always at the . What, what was option one
139:24 for unit C that the detrital Yeah, that could be, it
139:29 be, it could be that those are, are completely unset and just
139:34 us about the provenance of this where know the, the material that
139:37 that was shed into the Cretaceous basin helium s that were 40 million.
139:43 that would, in that way, would interpret the Cretaceous sandstone.
139:46 wait a second. No, no. Hey, we've got
139:48 This, we know the rock I'm, I'm, I'm, I'm
139:51 that the Cretaceous sandstone tells us when were, when we were deposited.
139:56 rocks were deposited in the Cretaceous but helium appetite helium ages are 40
140:02 There has to be a resetting I, I totally forgot to read
140:07 Cretaceous there. Thank you, I missed that. The Cretaceous sandstone
140:13 he helium ages of 40 million. that means that this is a narrow
140:17 in which we have, we, teased out a little helium out of
140:21 Cretaceous sandstone, but we haven't drawn the fishing tracks from the granite.
140:28 that's a narrow, that's a narrow range that tells us that these rocks
140:32 to 80 degrees but not 100 It's actually a kind of, as
140:40 , as I look at this that's a very unusual geologic situation.
140:46 write a better test question than this . This one's hard. OK.
140:57 Since we're, since we're doing interpret the history of things, we'll
141:00 one more like this and then we'll a break and then the next questions
141:04 a little different. Once again, got a basement rock and two sandstones
141:09 sit on top of it here, got the Cretaceous and Triassic sandstones,
141:13 I've given you different data this A granite this time has a Zircon
141:17 of 350 Argon biotite age of 350 an appetite efficient track age of 200
141:26 years. On top of that sits Triassic sandstone on top of that sits
141:33 Cretaceous sandstone with appetite helium ages as as, as high as 200 but
141:39 low as 100. Start with this fishing track age of 200. What
141:58 that tell us about the history of granite? Right? It was
142:10 it, got close to the surface 200. Um, well, actually
142:19 know that. Yeah, it it was close to the surface road
142:21 . It was at a, it at a temperature of 100 degrees 200
142:25 years ago. Um, when did Triassic happen? Not that old be
142:45 , 252. And it ended at 212. Right? You don't have
142:50 there? I think it's 212 is end of the Triassic. That's the
142:55 Jurassic boundary. Uh So this Triassic Triassic is over at 212. I'm
143:03 sure somebody can tell me I'm Um Let's say it, it's
143:09 That means that the fish and track of this granite is younger than the
143:15 that overlies it gs A says the ends at 201.30201. All right.
143:30 two still 200 is still younger than . Thank you for looking that
143:37 I was, I don't know I thought it was 212,
143:40 Really? All right. Either. , that's fine. We'll, we'll
143:43 with 201. So the fish and age of the granite is younger than
143:49 youngest possible time that the Jurassic sandstone be deposited. And of course Triassic
143:58 don't have to be deposited on the day of the Triassic. No,
144:08 , no, no, this is . The, the granite was,
144:12 crystallized back here at 350. so I, yeah, I wouldn't
144:17 that the reason that this fish and , um, when, when we
144:21 these, when my, when I you a Strat gra sequence like
144:26 I'm looking for reheating because of If I, if we, if
144:30 , if, if there's an intrusion be had, I'll tell you about
144:34 because, I mean, I want guys to think in terms of photography
144:37 basins and that sort of thing bringing bringing in the odd granite just is
144:42 easy, right? I mean, , and then, and then we
144:45 , we turned the dial. So , let's, let's think in terms
144:47 basins. Mhm. Um So what tells us is that the,
144:55 and then notice the Cretaceous sandstone, has ages that go from 200 to
145:01 . Those are all Cretaceous. Cretaceous started at what one Taylor?
145:08 did the Cretaceous begin? You, on the, you're on the web
145:13 ? Uh Cretaceous again. 1 45 40. OK. So 45 41
145:21 . So we've got, so we've some, some, some, some
145:26 , some grains that are older than in here. Um So some of
145:31 grains in this Cretaceous sandstone are older Cretaceous. They are, in fact
145:35 same age as these guys down So I would look at this and
145:40 say clearly this Triassic sandstone there and this granite were buried such that
145:50 fishing tracks in the granite became younger the the sandstone above it. And
145:57 probably was the result of the burial this other sandstone on top of the
146:01 business, this thing, this thing this hotter, made this hotter the
146:06 ages here are about 200. Uh they get too young, you
146:10 So are these are, does this tell us about provenance or depositional
146:16 Uh It's hard to say, but we can say is that this Triassic
146:22 was insufficient to, to, to the barrier, the, the reheating
146:26 we see here because it was deposited that value. And so Triassic
146:38 it would, wouldn't really allow you get just by itself this age.
146:44 the whole thing, the, the, the, the sandstone,
146:46 granite was buried by a Triassic but the ages then are yet younger
146:52 that. So that would probably be result of burial by the, by
146:57 , by the succeeding unit. Um got about an hour's worth of stuff
147:08 . And so we've got 345. let's take a, what do you
147:14 to take? 10 minutes? Just sort of chill out. We'll,
147:18 start again at 355 and then we go and look at these last few
147:24 that'll take us to pretty much the of our day. So again,
147:33 the next few examples I have here various Strat graphic examples with questions.
147:39 we'll start with this one. We've basalt Arco highlight sandstone. Um I'm
147:45 an un conformity between the Arco and rite. Presumably there is no one
147:49 conformity in the other uh context. put this in here a few years
147:56 when I first learned about, do know that, you know when
147:59 what tyrannosaurus rex tells you about Vy rex is actually an index fossil prenos
148:08 rex was only found in the Maastricht the very last part of the
148:15 So all those stories you see you know, tyrannosaurus rex did not
148:20 until the protasis was almost over. if you find the T rex,
148:25 know, you're in the Merican, is, I don't know how much
148:28 guys know about the Peras Mesrine is very end of persis, the very
148:34 one. So already we were asking , what's the depositional age of the
148:39 ? What can we say immediately? , how old the Arcos is based
148:43 this data here? Based on our understanding of tyrannosaurus rex. Well,
149:01 older than, well, yeah, than 66 right? Because I
149:08 a T rex could have been, have, could have died on,
149:11 know, as many T rexes did T rex could have died on the
149:15 day of the Cretaceous. So it's than 66 but we could do better
149:21 that. We've got some, we've a little bit of a budget here
149:25 do some isotopic dating shoot. Did say younger? Well, that was
149:30 mistake. Yes. Older than It's older than 66. Uh,
149:39 , not necessarily older than 71. mitri I think goes from 71 to
149:44 but we can't say for sure it's than 71 because this truck, this
149:49 rex could have died as many T did on the last day of the
149:55 . All right. So we know older than 66. What? Now
149:58 we've got that out of the What can we do to help us
150:03 the depositional age of the ARCOS? we're in a big hurry. We
150:25 know how old the green rock How can we figure out the age
150:28 the, out of the three, particular, the, the blue one
150:34 could date to the basalt and the light pretty easily with Uranium Zircon.
150:41 Well, you, you, you wrapped up two things at once
150:44 . Which, which is you how are you gonna date the
150:50 Uh with Zircon? Uh Jeez, keep doing that. I mean,
150:56 , you've got the right, you've the right instinct to always go to
150:59 L Zircon. But basalt is one the few examples where that's probably not
151:02 best choice, right. So, , you have to use argon,
151:06 argon or bed or some other, know, you might even do a
151:10 strontium Isac on a basalt. But , any of those, any of
151:15 ways might be? Ok. Um , yeah. Ok. That'll,
151:20 give us an, a maximum age the basalt. What else? Um
151:25 that the, is, is that agree? That's the first thing we
151:28 do if we were in a big , if time is critical and we
151:32 to know this Arcos age the best can straight away. Would you date
151:35 basalt by Argon? Is that your choice? It's certainly a choice.
151:43 me? Right. But, I , is it the, I
151:47 we've got a lot of choices here date that we've talked about a lot
151:50 minerals. We've talked a lot of . Many of those are applicable to
151:54 , narcosis and basalts. If you have, you know, a very
151:59 amount of time and perhaps not, lot of money on this project
152:03 is Argon on themselves. The first you would do, you're shaking your
152:07 . What would you do? it's, it's not, it
152:13 Well, I mean, I remember you're working at, you know,
152:17 or Exxon you don't really care about, care about the money.
152:21 can call up an Argon lab and , would you, would you be
152:24 to put this at the front of line? We'll pay an extra
152:28 The Argon lab would say great, know, Exxon would say, where
152:32 that? $5000 go? So, , it's not much more expensive,
152:36 it is a, it does have potential time consuming. If it's treated
152:39 a regular sample, it might take months. Whereas a Zircon, you
152:47 , if you, if you can a zircon out of a rock,
152:49 can send it to somebody's lab and prob it, it, I
152:53 if you did it here, you a, for example, and then
152:55 the laser hitting, you know, can actually take that in maybe a
153:00 . Um So with all that in is two months, you know,
153:10 months for the argon is what it probably take two weeks for the B
153:17 . Uh, but we can't do , which is the best choice on
153:24 right light. Yeah, biggest problem that is that there's an un conformity
153:29 . So we know that there's time . So it might not be the
153:32 . I mean, it's certainly gonna it, but by, but by
153:36 that there's an un conformity there, know that the, the bracketing age
153:40 the Basalt might be closer to the than the, than the riot,
153:43 would guess. Although the, the , you know, I don't
153:48 I mean, I, they're both . I mean, if,
153:52 if, if I was grading a and you made a good case for
153:55 or the other, I'd be, be generous. But you'd have to
153:58 why. That's a good choice. , what if, what if
154:03 what would you do if time and is of no concern? You do
154:08 Argonne on the, on the, salt and then, well, you
154:13 the two things we just talked Would you do anything else? There's
154:19 method for determining the age of the that we haven't talked about yet?
154:25 . Well, on what material appetite where Arcos? Well, that's either
154:35 tell us about the age of the or the depth to which it's been
154:44 . I mean, but we have about dating sandstones by, uh,
154:48 you try to date it right? a bunch of zer 117 of
154:54 Perhaps that's probably the most time That's, that's probably what I was
155:00 at when I made up this About time. You'd have to analyze
155:04 grains. Although I, I, know, the time is really not
155:08 big deal because I mean, I , I have told you that with
155:12 nice automated systems, we could do grains in a day. So it's
155:16 just a matter of, of, know, you've got to choose your
155:20 of priorities, I would say probably my, in my opinion, the
155:24 dating of the basalts probably number then maybe the detrital dating of the
155:30 the, the zircons by uranium lead the Arcos might be number two and
155:35 uranium lead dating of the rite might number three. All of those
155:40 better be older than 66. let me just add that.
156:01 let's add another question to 18. , how do we evaluate the Arcos
156:13 a part of a petroleum system? it, I guess? Mm.
156:32 , we would learn, it's, max, we learn something about its
156:35 burial. The fishing tracks would say or not it got to above fishing
156:39 in appetite would tell, would tell whether that unit got to above 100
156:43 or not. Um If you were , you know, interested, you
156:48 do both the fish and track age the helium age from the appetite that
156:53 you a real good sense about its history in the oil window starting at
156:59 50 degrees and going up to about and 20 degrees. That's basically the
157:03 temperature range that's gonna be producing most and gas. Gotta be above 50
157:11 get above 150. So those are , those are your friends when you're
157:18 that? Um All right, here's question. We've got this uh same
157:36 . We got a Narcos sits on of a granite this time and we
157:41 that it's got a sandstone with What does that tell us about the
157:45 of this stuff? Guys, you learn about trilobites? Yeah,
157:51 the trilobites, there are some Most trilobites are early pale Lazor.
157:55 are a few trilobites that are late Zoric. All trites went extinct at
158:00 end of the permit. So these , these are pre mesozoic rocks.
158:13 did that? Arcos de deposited? see. Two, two avenues of
158:33 potential here. That's one way. , you just date a bunch of
158:57 , we assume there's gonna be some in this sandstone. That's, that's
159:02 . So, date a bunch of ones. And then when you're,
159:06 you're done dating 200 zircons, which the most important one, the youngest
159:14 , your, your Arcos has to younger than the youngest Circon you
159:28 So that's, that would be probably best way to, for looking at
159:32 in the Arcos. Um Is that question? What else? I
159:50 So that's one way. Is there else that would help us towards an
159:54 here on this, on this section approached, we've got it on conformity
160:04 , right? So that Arcos was at the surface on top of that
160:14 . Suppose the, suppose the, , suppose the zircons that we dated
160:18 this Arcos were all pre Cameron, were all like 1000 million years
160:31 All that tells us is that our is less than 1000 right? If
160:37 was the case, would you would, would that be something you'd
160:41 comfortable with? I mean, it, it, it's less than
160:46 . Um, but it's overlain by sandstones with trilobites. Unless, unless
160:52 bunch of time is missing between that and that sandstone. This Arcos is
160:58 a lot younger than 1000. I mean, I'm, I've showed
161:02 an nonconformity here. I've not shown what I mean, if I don't
161:06 it un conformity here, we we can assume that there's not a
161:09 of time missing between the Arcos and trites, which means that the,
161:14 Arcos is somewhere, the Arcos is , right? Well, I suppose
161:21 could be precambrian if, well, I mean, it can't be
161:27 really if, if, if these are Cambrian trilobites, then this Arcos
161:32 only be the latest precambrian at the , right? So this this and
161:38 course, if these trial adviser Mississippi then of course, we got
161:43 this rock gets much younger. Um with those concerns in mind,
161:50 the, the, the, the led Zircon agents of the s of
161:53 , of the zircons, they turned to be somewhere between 1 billion and
161:58 billion. Is there anything else we do that might help us? Because
162:03 didn't seem to help us very What about this one? What about
162:13 granite? Remember what was it this was, let me go back to
162:24 this, remember this, remember this , what did we do for the
162:30 here? Why do we? Yeah, because we're after the sandstone
162:44 , and this would be, and we were trying to find when the
162:48 got close to the surface. That's same problem we have here. Uh
162:53 have uh here, right? We know when that Arcos was in contact
162:59 that granite was at the surface. it happened. If the, if
163:04 , if the detrital icons in the are not helpful, we're gonna try
163:08 work at it from the other When did the granite get near the
163:13 ? Um Now, of course, granite could have been sitting at the
163:18 for a very long time. Suppose got a, we suppose we got
163:22 fishing track, uh, appetite age the granite of uh, 600 million
163:32 . All that, that would tell that, that there are coaches younger
163:37 600 right? And that would mean the Arcos was, was somewhere between
163:43 45 which maybe the, you but of course, if the
163:47 the granite could have given us more more tight information. If that granite
163:51 come to the surface until sometime in paleozoic, that's gonna narrow it right
163:56 and tell us, you know, arc, we, we already know
163:59 upper bound of this Arcos is the of the paleozoic. So the,
164:06 detrital Zircon in the Arcos or the temperature cooling age of the granite are
164:15 be helped, are gonna help us put a bottom end or an old
164:19 on this. The, the young is, is the range of the
164:23 bits. The bottom end, the old end is gonna be those
164:27 two things. And this may be example in which you don't,
164:32 you know, you may not, , narrow it down a lot.
164:44 . Yeah, that's gonna tell us assuming that this whole system wasn't then
164:48 again in the Mesozoic. Uh That's tell us when the granite got
164:53 when it, and you know, gonna help. We know that this
164:57 was deposited at the surface because it's set of entry rock. And that
165:02 that the, that, that un that, that, that, that
165:06 was covered at the time the Arcos deposited, we know what temperature that
165:11 place at, but we don't know what time. So if we can
165:16 the granite temperature, we, we figure out a granite temperature time point
165:21 a temperature not much hotter than the at which the Ghose was deposited.
165:28 the, that's the logic there. . Um Well, we've, we've
165:40 , we've been over this. that whole question is really done.
165:45 . What I guess this is the half isn't gonna take as long as
165:49 thought. But anyway, this is one. This is one I made
165:51 today as a matter of fact. this is not, this is a
165:55 one. Imagine that we have this democratic situation. We've got a granite
166:06 by quartzite and a shale. And that thing that all of that is
166:11 overlain by a Narcos. And we've a sample of the granite as shown
166:18 . Sample number one has been sampled and we get those, that bit
166:23 information there. Uranium lead, Zircon , 43 9 vite, appetite fission
166:29 appetite helium. So, what we'd to know is the age of those
166:37 rocks, the quartzite in the And, you know, we'd like
166:42 evaluate the shale as a potential source . So what extra information would
166:51 the uh be looking into to sort out? We've got, we,
166:58 know, we've got those four rocks work with. You're, you're allowed
167:03 take any reasonable mineral combination for any those rocks and apply any of the
167:08 we've talked about, you've got six and, and a half a million
167:28 . OK. And so how would do that? I mean,
167:31 that's, that's basically the question you're , I've asked you how to get
167:34 edge of the chords there. you're gonna say we're gonna get the
167:36 of chords there now. Good. we're gonna do the, we're gonna
167:42 the 117 grains. Yeah, it's a bad start. So we're gonna
167:48 the youngest. We're gonna date a of those, um, suppose that
167:54 , uh, let's see, I'm , so, so that's good.
167:58 gonna see if I can throw make it difficult for us.
168:02 now, we've, we've, we've taken a sample of the quartzite
168:06 we've sent it to a Zircon lab they've analyzed it and they get a
168:12 of ages for that, uh, of between. Let me think what
168:18 sense between, uh, let's say the zircons in that quartzite are 500
168:29 years old. Does that help us all? They're 500 million years old
168:53 they probably come from. Yeah, the same age. They were probably
169:02 shed right off into this local, know, right at the edge of
169:06 granite there. So, unfortunately, already knew that the rock was younger
169:11 500 million years old. I I'm, I'm, I'm,
169:18 I'm purposely trying to frustrate you here this is how it really works.
169:22 I got, I got, I how I'll do this and then the
169:24 come back and go. That wasn't lot of help. Um So because
169:31 quartzite was apparently uh locally sourced, , that's unreasonable. If I called
169:39 an art post that then it would been locally sourced. Let me,
169:42 me give you more reasonable answer. say, uh let's see, I
169:46 this, I made this example up . So I, I don't have
169:49 the, all the ins and outs my head here. Let's see if
169:53 , uh, suppose the range of was between. Well, let,
170:07 , let's start with what we we know that the courts before
170:11 Ok. Yeah, before we start new stuff, let's write down what
170:17 know already without any, you you have no budget. You just
170:22 to look at what's there and figure out. How, what, what
170:25 you say? For sure about the aon. I this stuff, you
170:40 certainly say it's younger than 500 because the Uranium L Zirk age. What
170:45 those other ages? We can probably it's younger than 275 right? If
170:49 when the, if that's, if when the granite got near the
170:52 then the, the quartz air night deposited on top of that so that
170:56 sandstone and the shale are probably younger 275. Um But it turns out
171:06 the zircons from that sense in, the quartz aite came exclusively from the
171:13 there. So that didn't help. there something of what could we do
171:18 the, what could we do in Arcos? It, we are close
171:29 yeah, there's no conformity. I , there's gonna be some time missing
171:32 . That's a problem. But, , but again, you know,
171:36 , you can't look, you, are, remember we're geologists here,
171:40 not engineers, we don't get to the problem. We're stuck with
171:44 Ok. And so don't say, , those are non conformity. What's
171:49 point? But that's not the way look at it. Ok. This
171:54 , geologists have to deal with this all the time. You know,
171:57 gonna deal with our conformity. We're deal with the fact that,
172:00 there's time missing there. And it out that this particular granite was sourced
172:05 , this particular sandstone was sourced from sandstone from the granite right next
172:10 But if we dated the uranium led Cots in the Arcos, and let's
172:14 that Arcos came from a different source it gives ages between uh between 502
172:21 million years. Well, that means the Arcos is younger than 200 million
172:29 . Right? Actually, let's, , let's, let's let me,
172:40 , I'm making this up as I along. But let's say though that
172:43 , the rang in ages from the were from or from 200 to
172:49 Now, that doesn't help us. we know is that the sand that
172:52 Arcos is less than 200. Uh know that the quartzite is less than
173:04 um without fossils or without, without volcanic rock, we're kind of
173:16 Uh But we can answer the second , maybe even easier than the first
173:23 it down. The exact time of might not be quite as valuable to
173:27 as determining whether the whole thing well, shoot, let me,
173:36 know these rocks are less than So in order for this to be
173:46 petroleum system, it has to have buried below 100 degrees since 275 because
173:57 couldn't have been done so earlier than . So if we looked at the
174:02 bars or the fish or the appetites , in these purple rocks, if
174:09 ages are all older than 275 it's a petroleum system younger than 275.
174:20 we could give a sense for, , for when it, when it
174:24 at its well without a, without Strat democratic tie, it's gonna be
174:29 . But we can get a sense suppose we had fish and track ages
174:33 were, let's do it easy. we had fish and track ages in
174:39 courts in the, in the Arcos were uh 25 million years.
174:46 no, not in the Arcos. the quartz aite in the sandstone.
174:50 have appetite fisher track ages that are million years old. That means this
174:56 thing was buried recently. Oh, , we can't do that. We
175:02 do that because of this. Because this, this whole thing. This
175:07 , this, this basically, I think I made a good,
175:12 good question. It took me a to figure out why there's no chance
175:16 there's oil in that shell. The helium. Appetite ages of the granite
175:22 this granite has been cold since So this, this rock, this
175:30 hasn't been above, hasn't been above degrees since 275 which means all of
175:38 rocks have been colder than that since . So we know these rocks are
175:47 than 275 and they probably wouldn't have very deeply ever during that time.
176:00 I guess that's the answer to the which I made up at lunchtime
176:14 Uh We got a couple. So we ever uh come up with a
176:21 way then to age the purple No. OK. It's difficult.
176:27 mean, I mean, we I mean, iiii I frustrated it
176:31 having some bad data come back. best way to date. The all
176:35 those sedimentary rocks is to with detrital , uranium led dating of detrital
176:42 Um And so whatever that gives you , that's the best way. There's
176:46 other valuable way to do it. would do it for the quartzite,
176:49 do it for the arcos and we take what we can get, we
176:52 that they're younger than 275. Uh could get more information from, from
176:57 Uu Uranium lead uh data of the . But what we can take say
177:03 sure is that granite never got hotter , than 100 degrees since 275 would
177:10 none of the rocks above it got than that as well. OK,
177:18 . All right. Uh We're almost . Let's see. This is a
177:24 question. Although it's less complicated by . We've got an albion Arcos
177:30 I'm always picking Arcos is just to sure that it's, it's reasonable that
177:34 have all our good minerals. If a pure 100% port sandstone, we
177:39 get appetites and, and albion, guys know when albion is, that's
177:48 middle of the Cretaceous about 100 and million years. This, this should
178:03 pretty straightforward to you guys. By , we've asked this question over and
178:06 again. I'm just asking this without geologic context. We've got three systems
178:16 we, that we've illustrated are possible , in understanding the maximum temperature burial
178:23 sedimentary rocks, fishing tracks in appetite even in zira, we could do
178:32 in those two rock, two And I showed you an example on
178:37 of where you could, you could at the argon in the feldspar.
178:42 it got hot enough. If it really hot, then the argon is
178:45 tell you information that the fish attracts the helium don't. So that's a
178:55 question. You sh you ought to , you ought to be ready to
178:57 this easy because this is, this no geologic context. There's no comparison
179:01 faults or folds or others to take . But I probably won't ask you
179:07 a simple question. I'm gonna ask questions that ask you to try and
179:11 it in, in, in the of, of other stratigraphy. Um
179:18 , you know, maybe there's a I haven't shown you example.
179:20 I have, you know, I shown you examples of false but I
179:24 ouch. Um Are we done? , here's another one. So there's
179:41 , there's your observations. We've got granite overlain by Triassic strata with
179:48 with those, with those values of data. What can you say about
179:53 history of this place? Basically the of these two rocks, granite and
180:02 sandstones. Mhm Well, remember that doesn't necessarily tell us about the
180:33 It just tells us about the time a granite could be formed anywhere in
180:37 crust. Remember that high temperature, mean, this is it good,
180:44 . The, the high, the page we get out of the granite
180:48 us when it began, but it really tell us about where because it
180:53 have started 20 kilometers below the surface three kilometers. It's the second bit
180:58 information that tells us more about So just that little bit.
181:07 No, no. Excuse me. of these data of the data.
181:09 this stuff here. This is this is, oh shoot, I
181:14 , I didn't write that sentence very . With the following isotopic data.
181:19 referring these, this, these are from the granite, the Triassic sandstones
181:24 on top of this granite. All the data here is from the
181:28 The sandstone we know is Triassic from . Use that information. I'll
181:34 I'll read uh Yeah, that, sentence gave you a sense that maybe
181:39 , those data were from the I didn't mean it that way.
181:41 apologize. So we got two Brandon has Zircon bide and fish and
181:48 in it. The Jurassic rock has fossils in it. So, what
181:58 you say? Well, it was 100 degrees since 500 degree.
182:05 it's been, since this granite has no hotter than 100 degrees since 500
182:10 years ago. And then it was by this Triassic sandstone is this Triassic
182:17 a good candidate for a petroleum No, why not? Right.
182:27 it sits on top of this That's been less than 100 since 500
182:31 . So it's never been hot. , although we don't have direct information
182:36 the sandstone, we know that the that sits beneath it has been
182:41 the entirety of the Fanner Zone. so every rock that sits on top
182:45 it would be even colder. that's not a good candidate for petroleum
182:50 because it's probably not been very Um, let's see. I put
183:02 in here one year when I did difference though. Oh, well,
183:11 , let's play around with this one only Isotope geochemistry. How can we
183:16 understand the source area of the Wilcox . Wilcox formation is a eocene
183:23 I think it's, it's this it's this here. I wanna know
183:41 much as I can about where the came, the Wilcox formation or where
183:46 material came when the Wilcox formation. we're gonna, and of course,
183:50 probably got thin sections, we've got gray, but now we've,
183:55 we're, we're really spending all our dollars because it's the end of the
184:00 , we can't have, we can't it on something. What ice
184:05 uh information would you like to do learn to learn more about the source
184:10 of the Wilcox formation. This is , not a very, it's not
184:26 very constrained problem. I mean, , I've made it sound more,
184:30 made it sound harder because I gave a particular stratigraphic name. I could
184:37 this unit X. The same I mean, uh this happens to
184:45 an Eocene or excuse me. is an Eocene deposit. But I
184:49 think that the answer wouldn't change very if it was older or younger.
184:54 are the key ways in which we provenance? Do the zircons using uranium
185:10 , Zirk on uranium lead would be first thing. But if you were
185:13 to just go crazy, you would all of the things we talked
185:16 You could, you could date the bars, you could date. I
185:19 , there's probably felt, I don't , are felt bars in the Wilcox
185:22 , maybe not. But let's assume are some felt bars. Let's assume
185:26 are some appetites that we would It's quite a reasonable assumption to assume
185:31 are zircons and with those zircons, will take those zircons three different
185:37 Right. That'll really tell us about source area. I mean,
185:42 and indeed what it would be nice maybe to double date or triple
185:46 Some of these zircons, we can a zircon by fish and track and
185:50 laid it by uranium lead. So can know that the not we can
185:53 , not just that this zircon came a place where the, where that
185:57 a billion year old, you crystallization age, but it also has
186:02 certain fission track age or a certain age. So double dating, triple
186:08 of ma of zircons is a thing you can do. And if you're
186:13 to, you know, spend some and money, you can really add
186:17 to that uranium l provenance information, know, you're gonna get a,
186:20 gonna get a histogram shows that there's old ones and some young ones and
186:25 medium ones, but maybe some of , some of those billion year old
186:30 say have a billion year old uranium age, but they have a,
186:33 have a billion year old uh fish track age. Whereas some of the
186:38 year old, uh Zircon. Uranium ages have a 20 million year
186:43 uh, fish and track age. we then we'd be looking for billion
186:47 old granites that only popped up to surface yesterday. So this would be
186:53 example of where double or triple um, would add a lot
186:59 a lot of nuance, a lot character to your, um, to
187:04 uranium lead data, which, which to, which really ought to be
187:07 first answer to most questions, Uranium Zircon. Yes. Uh so,
187:15 , and, and this gets back the question of, of when
187:18 when you're, when you're evaluating lag when we're interested in the tectonics of
187:24 region. And we're comparing the, cool, the, the,
187:27 the, the, the isotopic say we're doing a bunch of fish
187:30 track dating on Zircons and we do bunch of fish and track dates
187:35 and a lot of those fish and ages are the same age as the
187:39 deposit. Let's say it's eocene. is an exciting bit of tectonic
187:46 Unless those grains were popped off in volcano. How do we figure out
187:53 they are exciting tectonic information or less volcanic information? Remember what we can
188:07 about volcanic rocks in terms of but it doesn't matter what, how
188:11 date them, we should get the answer. Single great date, the
188:25 brains date them how, um, the, uh um, I'm forgetting
188:38 on the right track. Well, , that's just a, that's a
188:42 that it doesn't matter how we, , a laser might be involved.
188:46 worry about that. Ok. you're not gonna date a Zircon by
188:56 Taylor. You're close to it. are you gonna say? How are
188:58 gonna date these zircons? I Ok. So I know this
189:10 we're, we're just about done What we're trying to say is how
189:13 we figure out if a grain is volcanic grain, a volcanic grain will
189:18 the same no matter how you date . And the good news is we're
189:22 , we have three ways we can zircons and we can do that on
189:24 same grain. So a volcanic Zircon have a uranium lead age and a
189:30 and trek age that are the right? That's how you can tell
189:34 volcano. Either that or it's just unbelievable amount of erosion. So we're
189:38 gonna assume that when we get two that are the same, we get
189:41 single grain that gives us two ages vary in closure temperature by hundreds and
189:47 of degrees. The only way we get them to have the same age
189:51 if they cooled on the same And the only way that happens is
189:56 that cooling occurred when they were shot into the air, right? That's
190:00 volcano, it cools off, hits ground, cools off. It's
190:06 We can then later on go back interrogate an individual individual zircon grain that
190:11 grain. You know, and we say by, we did the fish
190:15 track age, the fish and track is the same age as the Strat
190:19 . That's potentially exciting. Oh, tectonics going on someplace rapid super duper
190:24 or it's just the volcano popping up tell the difference by double dating these
190:32 . And if the fission track age the uranium helium age are the
190:35 that's probably a volcanic rock, volcanic . If they're different. Well,
190:40 , then they did, they didn't all at one time and then we're
190:43 at a tectonic signal. Um That like we've come to the end of
190:53 2224 slides. Um I would suggest over these 24 slides again and making
191:01 that you understand what we talked about . Um I'm gonna make up a
191:08 that's gonna have questions a lot like . I'm gonna give you sometimes complicated
191:16 of information. The, the way sort through that is to draw a
191:20 time diagram for the various units. you will have lots of information for
191:25 unit, but less information for a above or below it. But if
191:29 above or below it, you need , you need it, you
191:32 it should always be hotter or colder the, the, the unit for
191:36 you have lots of information. Um so with that various information, then
191:43 could start to, you know, in whatever geologic context you were
191:47 There's an un conformity here, there's , there's a fault here or
191:52 I'm telling you, there's a cert with that information. Then you can
191:56 about the, the, the history the overall region starting with far
192:01 as far back as you can Might be, you know, if
192:03 got a, you've got a for example, you can go back
192:06 the protolith of that shift was a and that zircons are in there.
192:11 mean, tell me everything you Sometimes that's, that's very brief.
192:15 it's very, it's a whole Uh But that's what I'm looking for
192:20 geologic interpretations. I'll try to, try to mostly keep it in the
192:25 of some basin context, but not single time because does it mean people
192:31 study basins need to understand about the that are next to those faces?
192:36 sometimes there'll be more mountain questions, there'll be more basin questions. I'll
192:41 to relate the two when I Um I may also ask you questions
192:49 sort of ask you um you broadly speaking with for what age rocks
192:54 this technique good for? Is there , is there any time which we
192:57 not want to try and use you if we've got a, we've got
193:00 precambrian rock. Is this technique Or if we've got a rock that's
193:04 million years old, is this technique ? So, just have a sense
193:07 what the rage ranges are basically. age ranges are pretty wide.
193:14 what I'm gonna do is come up a test and I'm gonna email it
193:18 everybody on Wednesday and then I want to email it back to me by
193:31 p.m. on Thursday. So you'll have , I don't know, 28 hours
193:42 so to do the test. But , yeah, that's what I'll
193:50 So that'll be, I mean, my plan. Unless I, unless
193:55 hear some complaints about that, that , I'm gonna give everybody. So
193:58 be, I don't know half a questions. Um, and I'll give
194:03 data like I've given you day to and, uh, I'll ask you
194:08 , uh, tell me a story . You have any questions you can
194:24 me between now and then. otherwise I guess that's it. I
194:37 a quick question, please. We have class tomorrow. We do
194:43 Ok, thank you. This is ? Ok. Bye
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