Ask a Geologist

[Orogeny]

Thanks for proving my point. Now, if you've got a question about geosciences that you'd like to have answered, I'll be happy to answer it.

 

[Naraoia]

I'm a carbonate stratigrapher and salt tectonicist. I study the strata deposited adjacent to passive salt diapirs in an effort to understand how diapirs develop, and how diapir growth influences local sedimentation patterns. Nothing nerdy goin' on over here!

My first question: which genius invented that word?

It brings to mind cute baby tapirs in nappies.

(If anyone finds me a picture of that, you get imaginary cookies! )

On a more, erm, geological note, and since plate tectonics came up earlier - what the heck is going on with plate tectonics (or lack thereof) and Venus?

 

[RickG]

So the Holocene Extinction and the Neolithic Revolution has nothing to do with Science?

They have everything to do with science and nothing to do with the bible.

 

[juvenissun]

Based on your 'logic sequence', you've absolutely no idea how ooids form. Read this webpage, then revise your sequence.

So there will be no more input from me. Too bad.

Thanks for the nice image. I like it.

 

[juvenissun]

So the quartz crystal forms somewhere, but the ooids were not yet formed? And this doesn't make the quartz allochthonous? Was the quartz crystal forming "authigenically" suspended in the void of space and the ooids later formed around it?

I thought the words "authigenic" and "allochtonous" had some meaning in geology. Was I mistaken?



So the authigenic quartz (which is actually in relation to the ooids allochthonous, not authigenic) is corroded?



Just a few.



Maybe it's just for a book report in junior high school geology class. You know, junior high school geology? Like when you cited a jr high geology class for your definition of "mountain" here?

I bet he's going to be doing some re-writes after reading your posts, Juvenissun.

Get to it, Orogeny!

I like to answer your questions. But I guess it won't do any good anyway. If you like to know, ask me again.

 

[Orogeny]

My first question: which genius invented that word?
It brings to mind cute baby tapirs in nappies.

(If anyone finds me a picture of that, you get imaginary cookies! )

Apparently it was derived from the Greek word diapeirein, meaning to pierce, since salt diapirs were originally thought to have forcibly intruded into overlying strata due to buoyancy and/or geopressuring. We now know that these forces generally do not initiate salt diapirism, although they may play a part once diapirism has commenced. Buoyancy and geopressuring may, however play an important roll in mud diapirism.

Thick layers of evaporites (salt) and overpressured or water-rich shales and muds behave like fluids over geologic time scales, so they 'flow' under pressure differentials. One way to accomplish this is by uneven sediment loading (such as a delta complex prograding over one side of a salt sheet), which presses down on the underling salt, squeezing it out laterally as you would squeeze the toothpaste out of a toothpaste tube resting on your bathroom counter. Inhomogeneities in sediment dispersal and absolute strength of the salt layer cause the salt to squeeze out of some areas faster than others. This results in depressions that then catch even more sediment, creating a feedback loop. As this happens, the areas with less sediment actually begin to be forced upward as salt is displaced from the drpressions and into the highs. The salt highs, given enough time, evolve from salt domes or 'pillows' and linear salt-cored anticlines into tall (relative to their width) diapirs. This diagrams illustrates this evolution (showing the salt only, with no sediment around the diapirs), with early stages in the foreground:

Diapirism may also be initiated by tectonic compression or extension, where the salt and/or mud react to the tectonic pressure by rise buoyantly into weaknesses such as faults.

The most heavily studied diapiric province is the Gulf of Mexico, where the Mississippi River delta is prograding over the Louann Salt Sheet and squeezing it out into the Gulf. In this image, you can see Louisiana to the north, the shelf edge (essentially the edge of thickest continental sediments) the salt sheet (bumpy bits, with the highs-warm colors-representing the diapirs), and the boundary labeled 'Sigsbee Escarpment' representing the leading edge of the advancing salt sheet:

ETA this image, which I described but did not include!

For anybody who's ever been to the Moab, Utah area, the Paradox Basin is a salt province, with the town of Moab actually sitting on top of a deflated salt wall (Moab is the green dot labeled 'M':

Wow that map's big. Sorry if I just killed your formatting, people.

Here's a picture of the Onion Creek diapir in the Paradox basin, the white bits being the diapir (mostly gypsum and dolomite at this point), and the red bits being the sediments surrounding the diapir:

I enjoy dealing with diapirism because it adds a rather counterintuitive element to tectonics- you have to think about 'fluid' motion. It's an extra variable that can have a lot of unexpected consequences.


Although diapirism typically refers to the above cases, magma bodies that intrude into overlying country rock may be referred to as 'igneous diapirs'.

On a more, erm, geological note, and since plate tectonics came up earlier - what the heck is going on with plate tectonics (or lack thereof) and Venus?

I'm not an astrogeologist by any stretch of the imagination, but my understanding of the issue is that surface temperatures are so hot that there has been significant crystal fractionation (alluded to in an earlier post) in the crust, making the lithosphere much more buoyant than the mantle. This buoyancy inhibits subduction, which requires crustal rocks (on earth, old, cold oceanic basalts) approaching the densities of the upper mantle. I haven't any sources for this, just heard it in a lecture a while back. I'm happy to look into it for ya, but right now I'm going to go have some dinner.

 

[Orogeny]

So there will be no more input from me. Too bad.

Look, I'm not discouraging you from participating in the conversation. Just don't come in here acting like you're Hutton's gift to geology and insult me on your first post. I've given ample evidence that my petrographic description is spot on, and you've waved it off for (apparently) no reason. You've shown a serious misunderstanding of ooid formation and the lithification process. These are basic mistakes, Juve. I'm glad to discuss geology with you, but I'm not going to tolerate being insulted; certainly not when the person doing the insulting states that a diagenetic feature can occur BEFORE the deposition of the rock's framework grains.

Thanks for the nice image. I like it.

Thank you. I've really enjoyed studying that system.

 

[thaumaturgy]

I like to answer your questions. But I guess it won't do any good anyway. If you like to know, ask me again.

Juvenissun, don't flatter yourself. You would be highly unlikely to be able to answer any geologic questions I have, but on those occasions when I have dared ask you about the points you've made you've said the following, and I quote:

It is VERY EASY to explain that what you said above does not apply to the situation of a global flood. But I am NOT going to tell you why this time. Why should I educate you if you do not appreciate anything I have said? I have posted many idea along this thread. However, to you, it seemed I have said nothing. If so, why should I continue?

You are confused on who you are in this forum. I am not obligated to explain anything to you. In fact, until you touched the very point, I am not going to explain anything to you. Demand me to give evidence on what I said is an useless effort. When I feel I should give you some, I will. Otherwise, if you don't like what I said, very simple, don't respond.

It is VERY EASY to explain that what you said above does not apply to the situation of a global flood. But I am NOT going to tell you why this time. Why should I educate you if you do not appreciate anything I have said? I have posted many idea along this thread. However, to you, it seemed I have said nothing. If so, why should I continue?

 

[thaumaturgy]

So there will be no more input from me. Too bad.

Thanks for the nice image. I like it.

CLASSIC Juvie! Excellent!

Next time, take your own advice,juvie and HUMBLE YOURSELF.

 

[thaumaturgy]

So the Holocene Extinction and the Neolithic Revolution has nothing to do with Science?

Ummmm, what?

Can you count the grains of sand?

Yes. It's just a matter of whether I can count them all.

 

[thaumaturgy]

My first question: which genius invented that word?

At least he isn't a mineralogist studying cummingtonite

On a more, erm, geological note, and since plate tectonics came up earlier - what the heck is going on with plate tectonics (or lack thereof) and Venus?

What I've heard is that the surface of Venus is remarkably young (based on impact crater counts) which leads some astrogeologists to think that perhaps the planet's crust has at one time broken up and experienced massive "flood basalts" (planetary wide versions of the flood basalts like you see in Washington state) and essentially re-paved the planet (LINKY)

I think this is still being debated.

 

[Orogeny]

At least he isn't a mineralogist studying cummingtonite

I giggle every time I see that word. SO immature.

What I've heard is that the surface of Venus is remarkably young (based on impact crater counts) which leads some astrogeologists to think that perhaps the planet's crust has at one time broken up and experienced massive "flood basalts" (planetary wide versions of the flood basalts like you see in Washington state) and essentially re-paved the planet (LINKY)

Cool.

 

[razeontherock]

I dunno what and asthmatic camel runs like, but you reminded me of this clip and I laughed and laughed.

Girl vs. Camel (in race!) - YouTube

Somehow a used car salesman that could sell a car that runs like a spastic camel, just doesn't have quite as good a ring to it ...

 

[razeontherock]

Man would that be some SWEET skiing! I'd think geologists would be into that; the main place I go is an extinct volcano, which should be just oodles of fun for you, right?

Anyway, I have (what seems to me) a really off the wall question. About a year ago I came across a book on a (rare) lunch break. I picked it up thinking it was a ski magazine, and only after a while confirmed it was a college geography textbook. The first page I opened it up to just happened to discuss global magnetic pole shift, and it presented many aspects of this as fact:

we'll have one very soon, based on weakening magnetic field in certain places including the Indian Ocean, (I'm sure they were a bit more specific than that, I just don't remember those details) which has always preceded every other pole shift. Those bolded words really struck me as odd, and I read that part at least 3x to make sure I got it right. (There were other reasons cited too, but this is the one that struck me, and also the main one that predicted a time frame)

How in the world could anybody know something like that?

Continuing on they admitted to not knowing the mechanism of pole shift, and presented the theory that maybe your diagram of core / mantle /crust isn't accurate, but there could be unknown space around the core. I didn't find any explanation of how or why the mantle would "float" above this, but they went on to theorize this would facilitate pole shift, and they gave a minimum / maximum range of time it might take to complete.

Does any of this sound as ridiculous to you as it does to me, or could any of these ideas have merit?

 

[Tiberius]

Anyway, I have (what seems to me) a really off the wall question. About a year ago I came across a book on a (rare) lunch break. I picked it up thinking it was a ski magazine, and only after a while confirmed it was a college geography textbook. The first page I opened it up to just happened to discuss global magnetic pole shift, and it presented many aspects of this as fact:

we'll have one very soon, based on weakening magnetic field in certain places including the Indian Ocean, (I'm sure they were a bit more specific than that, I just don't remember those details) which has always preceded every other pole shift. Those bolded words really struck me as odd, and I read that part at least 3x to make sure I got it right. (There were other reasons cited too, but this is the one that struck me, and also the main one that predicted a time frame)

How in the world could anybody know something like that?

I believe the answer to this is...

In the mid ocean ridges, new rock is being formed as the molten rock oozes up from deeper. As it comes to the surface, it cools.

There are crystals in these rocks that act like miniature magnets, and they are aligned to the earth's magnetic field at the time they solidify (after they solidify, teh crystals obviously can't move). We can compare the arrangement of the crystals in the rocks and get an idea of what the earth's magnetic field was like at the time the rocks solidified.

 

[Assyrian]

I can understand how layers of salt could be formed in a dried up lake bed, but shouldn't the salt dissolved when the next layer of sediment is being laid down? Or are layers above salt always wind borne?

 

[TemperateSeaIsland]

How common is it to find fossilized coral in limestone in Britain? I'm sure I found some while digging up the garden.

 

[juvenissun]

I can understand how layers of salt could be formed in a dried up lake bed, but shouldn't the salt dissolved when the next layer of sediment is being laid down? Or are layers above salt always wind borne?

So, it dissolved again. But it will precipitate again too. Through this cycle, the total amount of salt increased. There will be one day, the new water can not dissolved all the old salt any more ...

This is one of the possibilities.

Another one: the new water is not likely to be all water. It will come with sediments and the sediments will lay upon the old salt immediately. Could you imaging what would happen after that? Yes, some old salt will not get dissolved.

 

[Jazer]

Thanks for proving my point. Now, if you've got a question about geosciences that you'd like to have answered, I'll be happy to answer it.

Of course the big question has to do with age. Now to be sure you have unrelated ways to verify the age of the earth. For example we have the receding rate of the moon. We have things like Niagara Falls where we know the erosion rate and we can see how much erosion there is, so we can determine age from that. Still they change this stuff all the time. They just recently changed the age they think the universe is. One thing it all comes down to is an assumption of what is consistent. We do not know for sure that it is all that consistent. So how do we know we can depend on you to give us the right time frame for the various geological ages?

 

[Jazer]

I can understand how layers of salt could be formed in a dried up lake bed, but shouldn't the salt dissolved when the next layer of sediment is being laid down? Or are layers above salt always wind borne?

Nature cleans itself, but sometime man puts pollution out there faster then the envirment can deal with it. There is a lot of salt in layers under the great lakes. Back when they were salt water the salt just settled to the bottom.