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The intrusion of magma and some effects on the fossils


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Dimitar
Posted (edited)

Hello guys!

That was outside of my plans to search in such direction, however a small comment started a big discussion about the possibility to have magma melting the rocks and sealing some fossils.  In fact what I was suggesting as simple "melting" seems to be a very complex process or group of processes, that I would suggest to discuss here.

So it was already commented, that magma can't really melt other rocks. The temperature of magma is not high enough and it will cool down .  Still we see many effects of the magma on the rocks and especially on the sediments and fossils.  Here I will try to explain some,  so let try to discuss it in the best scientific way .

 

First of all - we talk for underwater sediments.  Most likely the intrusion of magma happened when there was still water on the surfice.  The main difference between LAVA and MAGMA - these are both the same, however the lava is a magma, that reach the surface and errupt as volcanic activity.  But we don't discuss such lava.  Most of the time we will see some effects of the magma, intruding near the surface .

 

1. First effect of the magma - high temperature.

Because of the high temperature - the sediments where magma is intruding will be heated.  In fact we may not see real melting of these sediments, but because of the high temperature - it will cause these sediments to undergo termal processing which is similar to ceramic production.  The water will evaporate. And the clay will harden into very solid hard matterial. 

 

2. The effect of the pressure  . Because the magma will erupt from the lower layers - it is under high pressure there. If there is way to the survice it will cause volcanic erruption. It the pressure is not high enough or no such way, the molten magma will try to find any  possible space and will fill it.

Together with the high temperature - the magma will burn some organic materials and will fill its space.  So we may see the exact copy / matrix/ of the organic material but filled and formed by the magma.

 

3. Chemical processes.  Some minerals from the magma may reacct with water or dissolve under hither temperature with water and this may create some kind of magmatic liquid -  which would be boiling water with all kind of chemical elements in it.  This water may fill the gaps on the bottom, it will be heavier than the normal water and it may create a layer of sediment.

 

4. The evaporation of water.  This is only for a case if water layer is very low and high temperature from underground to evaporate the water, causing all the sediments to form a solid crust.

 

5. Effects of gases.

 

6.  Cracks - usually the magma will come near the surface through the cracks, so we can see the magma or some products created by magma to fill the cracks in the rocks.   The color of such magma or magmatic liquid substances is usually red-brown or black. 

 

With all the mention here possibilities I will try to provide some examples of rocks and fossils that I found and to give  some explanation, but I should tell that I am not a chemist, I am not geologist. So my explanations are weak.  There should be better explanations by the specialists in this field. 

What is very clear for me:  For  some very specific rocks and fossils - I may suspect or I recognize some effects of the magma .   These are not difficult to recognize.  There are many hints to suggest such magmatic activity .   I fully understand this is a complex problem and I don't have the background to do such scientific research, I would like to share some observations and to discuss with other participants about such effects and fossil affected by magma actions.

 

 

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First , I will give some examples of rocks, affected by the magma. 

 

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Edited by Dimitar
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Dimitar

Here are some examples of rocks modified by magma, which contain fossils:

 

 

 

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Dimitar
Posted (edited)

Few more examples with the fossils.

 

Please note:

1. These are all from the same site. I collected them near the river in a radius of 10 m from each other. 

2. I know there was a volcanic / magma intrusion / event, there was a fault .  This why the river is there now.

3. There is a stable rock in the base it the evidence of such cracks and lava intrusion.

 

4. I have examples of the same type of fossils - just 5 meters on the side - without such magma / thermal / prossessing.  So there is a huge difference in the structure of the fossils with and without such magma effects.

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Edited by Dimitar
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Fossildude19

All of the rocks show here are the result of weathering and erosion, not magma intrusion. :Confused04:  :duh2:  <_<

Heat, pressure, gasses, and chemical changes all occur naturally during fossilization, without magma having been directly involved in the formation of the fossils. 

Your melting fossil hypothesis does not hold water.  :( 

 

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Dimitar
Posted (edited)

The other  site with lot of magma effects is just 2 km asside from the first site that I show earlier. On the second site - there is a lot more magma.  There are still some fossils, but smaller .

Here I am sure you will accept this is magma:

 

 

I also try to show some magma and fossils next to it.  The color of the sediments and rocks around is completely different.  It is just the cracks filled with magma: sills and dikes  - with such brown / black or red-brown color.

 

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Edited by Dimitar
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Dimitar

Because of this site here (the second that I just posted) I know the effects of magma on the fossils nearby.  I've seen such effects on some other places where magma is not directly visible. But most of the time if you find fossils with some effects of the magma - you should be able to find some sills and dikes / unless if such rocks were transported from another place by the river or in another way.

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Dimitar
1 hour ago, Fossildude19 said:

Your melting fossil hypothesis does not hold water. 

It is not that much about melting.  There could be some pressure / melting before the effect of magma, when the clay or sediments are still soft.

The major effect of magma intrusion would be to undergo a heat-treatment (firing) .  We can see the effects of the heat-treatment / similar to ceramics/ on such fossils.

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Posted (edited)

I agree with @Fossildude19, none of your fossils were affected by magma. 

 

If I'm understanding you correctly, yes when magma comes into contact with surrounding rock it does not "melt" the rock. Generally simply raising the temperature is not a very common mode of magma formation; volatile addition at subduction zones (think the Marianas Trench) and lowering the pressure at divergent boundaries (think the Mid-Ocean Ridge) is how most magma is produced. What you're referring to is sort of a real phenomenon, however, called contact metamorphism. You are right that when a pluton comes into contact with country rock it can create a small zone around itself of metamorphosed rock.

 

http://www.geologypage.com/wp-content/uploads/2019/05/Contact-Metamorphism-GeologyPage.jpg

 

However this usually only occurs in close proximity to a pluton, or magma chamber in the plain man's English. In order for your rocks to have been subjected to "magma" as you put it there would need to be evidence of a plutonic body existing nearby, such as granite intrusions. AFAIK there aren't such things. 

 

The deformations in your fossils are caused by what's called chemical weathering:

 

CHEMICAL WEATHERING - YouTube

 

Anything from acid rain to mine drainage into a creek can lead to chemical weathering of rock, which slowly breaks it down and can damage or "weather" rocks and fossils. 

 

Actually...magma at divergent boundaries, which it sounds like you're mostly talking about given the talk of gasses and water, forms as pressure lowers, not raises. It sounds very counterintuitive, but the reason is because of something called the geotherm:

 

http://www.geol.umd.edu/~jmerck/geol100/images/08/decompressionmelt.gif

 

Magma entering the sea at divergent boundaries typically does not "boil" the water, at least to any appreciable degree in the global context. Ocean water at that depth is a lot colder than you might think, cold enough that it can pretty much instantaneously convert liquid magma into solid basalt. 

 

As for cracks and gasses...you're actually partly correct again. Yes, the magma comes up in "cracks," to put it one way. However...the process you're describing, a hydrothermal process, does not typically occur at the surface, and fill the cracks of rocks in the surface. What happens, roughly speaking, is that ocean water sinks into the thin crust near divergent boundaries where they become heated and pick up dissolved metal ions, eventually depositing them in fissures in the rock as the fluid moves away from the magma body. This is how you get a lot of your ore deposits. Of course the actual process is a lot more complex and doesn't occur exactly like that every time, but that's the gist. 

 

Hydrothermal mineral deposit - Wikipedia

 

508px-Origin_of_modern_seafloor_smokers.png

 

 

The water/sea floor around divergent boundaries and black smokers does contain a lot of minerals/ions/"chemicals," and that is one of the reasons they are often home to unique forms of sea life. However, this is not how your fossils lived when they were living creatures (which I want to make clear). Your fossils lived and died in relatively shallow waters, in a tropical sea during Ordovician time around 500-440 million years ago. 

 

 

 

 

 

 

Edit:

 

Regarding your post about the beds of "magma": 1) 2 km is rather far in terms of surface geology - you could be looking in rocks of entirely different age than the ones your fossils are in. This is due to things like disconformities, folds/faults, etc. 2) the beds you're seeing appear to be iron. These were likely NOT formed due to hydrothermal processes at divergent boundaries, like I talked about earlier. Their method of formation is a little more intricate.

 

In layman's terms (and given these are from eastern Canada): after the deposition of your fossils in Ordovician time, those layers were buried under successive layers of rock. During Devonian time you had the Acadian Orogeny and later in the Permian you had the Alleghenian Orogeny, or mountain-building events. During these mountain building events your Ordovician rocks were subjected to folding, fracturing, faulting, etc. due to tectonic forces. Fluids moved into these "cracks" and precipitated iron oxides in veins and layers throughout the host rock. That's pretty simplified, but it's generally what happened. 

 

Again, NOT because of magma coming to the surface at divergent boundaries.   

Edited by EMP
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Oxytropidoceras
Posted (edited)
5 hours ago, Dimitar said:

Here are some examples of rocks modified by magma, which contain fossils:

The reddish brown set of fossils and rocks that are resistant to weathering are iron-stained silicified fossils and rocks that have been replaced by silica. This happens at normal temperatures and pressures. Such silicification is quite common in Paleozoic limestones and dolostones. The silicified fossils and rock stands out in high relief because they are more resistant to dissolution than the surrounding carbonate rock.

 

For a discussion of silicification of fossils go see either 1. Butts, S.H., 2014. Silicification. The Paleontological Society Papers, 20, pp.15-34. (has link to PDF file) or 2. PDF file from Peabody Museum

 

For pictures of similar iron-stained, silicified fossils weathering out of limestone go see the pictures at the bottom of the web page, Devonian and Pennsylvanian Fossils in the Martin and Naco Limestones Coral Locality at Tonto Creek, in Arizona Fossil Adventures by Chris and Dawn Shur.

 

In a couple of pictures, there grayish fossils are slightly more resistant than the surrounding matrix. I suspect that in their case, this is because they are composed of crystalline calcite, which is slightly more resistant than the surrounding fine-grained limestone to weathering.

 

Yours,

 

Paul H.

Edited by Oxytropidoceras
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Dimitar

The places I describe are exactly on the line of the fault. This fauld is described by T. H. CLARK and he provides a map with detailed explanation of all the processes. (MONTREAL AREA LAVAL AND LACHINE MAP-AREAS)

Initially I used the term "melted by lava" as a simple way to describe some observations , but as we see there is no real melting and it was not lava, but magma under the surfice. In addition the process of chemical transformation may happened many millions of yeas after these fossil layers were already formed.

4 hours ago, Dimitar said:

20210602_153511.jpg

I want to use this picture as what we see like "melting", but it is not melting.  It is chemical transformation. Heat-treatment (firing) is also a chemical process.  So we have many consecutive chemical and physical processes one after another until we get what we see on the picture above.

The shell above the plane (surface) should be the same as below the surface. But as we see - these are not the same.  That means - there was a heavy water which formed the gray sediments below.  On top of this layer - there was another layer, another chemical solution that kept the red-brown color. The shells of the fossils served as boundary , or they were filled with some of these chemical sollutions and become part of the lower or upper level. 

 

Melting is a physical process,  where the atomic or molecular structure doesn't change.  

Solvation is a chemical process, the structure of the material would change during the solvation. 

 

What we see on the picture is chemical process (not melting) .

If it was just a water to go from liquid to solid state or to gaz - it would be a physical process.  But we have more complex structures and it goes through many chemical transformations. So using "melting" as description was incorrect.  Solvation would be a lot more appropriate term.

 

I have no doubt about connection of these processes with magma, but as it has been said , this may happened 300 million years after the fossils were formed.  There could be huge time difference between fossil formation and fossil transformation where some magma activity was involved. 

As we search for fossils - when we find some rock or fossil - understanding such effect of the chemical processes and magma /or high temperature/ helps to understand part of the picture. 

 

 

 

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Oxytropidoceras

A paper that describes how fossils and associated limestone are replaced by red-colored chert is:

 

Loope, D.B. and Watkins, D.K., 1989. Pennsylvanian fossils replaced by red chert; early oxidation of pyritic precursors. Journal of Sedimentary Research, 59(3), pp.375-386.

 

PDF file in CiteSeer

 

Another paper is:

 

Butts, S.H. and Briggs, D.E., 2011. Silicification through time. In Taphonomy (pp. 411-434). Springer, Dordrecht.

 

Researchgate PDF file web page

 

Yours,

 

Paul H.

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Dimitar
Posted (edited)
51 minutes ago, Oxytropidoceras said:

The reddish brown set of fossils and rocks that are resistant to weathering are iron-stained silicified fossils and rocks that have been replaced by silica. This happens at normal temperatures and pressures. Such silicification is quite common in Paleozoic limestones and dolostones. The silicified fossils and rock stands out in high relief because they are more resistant to dissolution than the surrounding carbonate rock.

 

Edited:  you may ignore this ( we wrote at the same time)  .

Thanks for your explanation.  So if these reddish-brown color is caused by  iron-stained silicified - may we suspect the source of such iron + silicates to be in the cracks or connected to magma? 

The main issue is:  we have the same layers, we have the same fossils on the same site.  However near the crack - we see such colour, such transformed fossils.  Just 2-3 or 5 meters aside - we see the normal fossils without any transformation. 

If all the fossils on the field were the same type, the same color - it would be  easy.  But when we see a crack in the rocks and all the fossils around it are modified by some chemicals - it is logical that this crack was the source of some chemicals or minerals .

 

If it was just a crack - filled with water, or silicates or salt - we see different colors.  I've seen such cracks filled with white cristals, or structure similar to glass.  So that is very possible too.  But if the minerals come from above - they will crate a layer.  When the minerals come from below, from the Earth - then these will affect the fossils near the crack only.  

 

In my case here - the cracks were filled with something that looked like magma. And I have examples also of rocks formed by such magma. Black /green granites. Not much, but there are some.  So I am sure the magma was not far from the surface, but how exactly - no idea.  It penetrated through some cracks , however most of the effects from such magma could come as water solution with some minerals  or metals. 

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Dimitar

Thanks a lot @Oxytropidoceras and @EMP

 

I will need to spend some time and look at the provided links and materials which seems to be very interesting. 

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