Fossil wood or mineral vein?

[Archie]

Hi everyone,

 

A friend recently found this exposed on some fault breccia that outcrops between a Lower Carboniferous fluviatile sandstone and volcanic neck composed of basalt in my hometown. My friend is convinced the main constituent of the breccia is sandstone but when it is broken into it is full of amygdales containing calcite crystals, and is not made up of grains. His main reason for thinking it is sandstone is the light color, most but not all igneous rocks in this part of Scotland are quite dark, however Ive found basalt containing agates that is almost cream in color nearby. He is also convinced that the object in question is a permineralized tree trunk showing cell structure, while I think it is calcite growth of some kind that has formed along a slichenside. I cant think that Ive ever heard of permineralized plants showing cell structure being preserved in sandstone, I'd be interested to know if anyone else has? Can anyone help put this debate to bed? Any help much appreciated!

 

Best regards

 

Sam

[Tidgy's Dad]

I think you're right. 

look like calcite slickenfibres to me. 

[DPS Ammonite]

It is very odd that some of the fibers are at a right angle to the majority of the fibers. Also, the fibers are very uniform in width. Both features are not common in slickensides. Do not throw out the possibility of plant material; my best guess is plant.

 

What are the fibers made of...calcite, quartz?

[Archie]

This was found nearby to a site famous for permineralized plants in a lava flow (the Kingswood and Pettycur Flora) but they are contained within blocks of limestone caught up in the flow, interestingly some stems do protrude into the basalt surrounding the blocks. I havent heard of any plant material caught up in the basalt that is completely free from limestone at this site though. The fibers appear to be made of calcite, they scratch easily with a pin.

[Tidgy's Dad]

Slickenfibres are often stepped because of irregularites along the fault plane. 

[DPS Ammonite]

Find this publication and you may be able to ID the plant:

https://www.sciencedirect.com/science/article/pii/0034666786900576

 

Availible on Research-gate.

 

 

 

 

Send photo to lead author, Andrew Scott, for an ID. Let us know what you find out.

 

Review of Palaeobotany and Palynology

Volume 48, Issues 1–3, July 1986, Pages 161-180

Studies on a new lower carboniferous flora from kingswood near pettycur, Scotland. I. Preliminary report        by Andrew Scott

 

 

 

@paleoflor

 

[Archie]

I had a read of that paper (cant seem to find a link to it right now) and another published slightly more recently on the Kingswood and Pettycur floras a few weeks back but the figured plant sections they contained were very different looking to this and much smaller unfortunately. My friend and I collected a few blocks of the plant bed with nice stems recently I'm planning to cut, polish and post some pics of soon!   

[Archie]

13 minutes ago, Tidgy's Dad said:

Slickenfibres are often stepped because of irregularites along the fault plane. 

I'm definitely convinced its slickenfibres, I'm not all that knowledgeable about Carboniferous plants so could be totally wrong but I didn't think the plants of this time had woody stems in the true sense of the word wood?

[Rockwood]

Sign me in plant camp. I'm pretty sure I have the textural equivalent in a compression fossil. 

[DPS Ammonite]

1 minute ago, Archie said:

I'm definitely convinced its slickenfibres, I'm not all that knowledgeable about Carboniferous plants so could be totally wrong but I didn't think the plants of this time had woody stems in the true sense of the word wood?

The abstract of the Scott reference mentioned wood with growth rings:

 

“Some gymnospermous stems with pycnoxylic wood and triangular pith also represent new taxa of unknown affinities. The occurrence of growth rings in some woody specimens is noted.”

[Tidgy's Dad]

3 minutes ago, Archie said:

I'm definitely convinced its slickenfibres, I'm not all that knowledgeable about Carboniferous plants so could be totally wrong but I didn't think the plants of this time had woody stems in the true sense of the word wood?

Many of the plants had a woody structure, there were gymnosperms and many pteridophytes had wood of a type. 

But I still think these are slickenfibres. 

[Rockwood]

@Archie, @Tidgy's Dad needs a pan out on the photo. Do we see a fault ?

[Innocentx]

I'm going for plant, in a big way.

[Archie]

2 hours ago, Rockwood said:

@Archie, @Tidgy's Dad needs a pan out on the photo. Do we see a fault ?

It's hard to get a pic from further back, this is a vertical face above a very steep slope. It is in fault breccia though composed of what appears to be igneous rock as evidenced by it containing amygdales. I never took any close up photos of the host rock unfortunately but my friend does have a sample. 

[Archie]

Another friend who was with us that day thought the host rock looked most like rhyolite, he's taken a sample to get ID'd.

[Rockwood]

1 hour ago, Archie said:

It's hard to get a pic from further back, this is a vertical face above a very steep slope.

In that case we may accept personal testimony. No need to add to the mortality rate. Enough people are lost to selfies as it is.  

[paleoflor]

Indeed appears like this could be vegatative. What does it look like in situ when viewed from parallel to the fibrous texture (approximately from bottom end first photo up along the axis of the structure)?

 

 

[Archie]

My friend took all the photos of it, I'll see if he has an end on one or if not get back up to the site and get one in the next few days.

[Carl]

I'm definitely in the wood camp here.

[ynot]

22 hours ago, Archie said:

get back up to the site and get one in the next few days.

I would like to see some close up pictures of the transition zone (edges) and the other structures of the piece in question.

Also, can You outline the areas of the first picture that show the "grain".

Can You see any cellular structures under magnification?

[Archie]

1 hour ago, ynot said:

I would like to see some close up pictures of the transition zone (edges) and the other structures of the piece in question.

Also, can You outline the areas of the first picture that show the "grain".

Can You see any cellular structures under magnification?

My friend has extracted the object along with surrounding matrix so next time I see him I'll get more pics showing the contact between the object and the matrix, he has cut and polished a fragment (at a right angle to the surface shown) and under magnification it is a repeating pattern of rods criss-crossing at perfect right angles, the rods are completely uniform in diameter and all perfectly circular throughout. It has the appearance of wood with growth rings but the "rings" are the horizontal rather than vertical rods. He's able to get pics with his microscope so I'll get some pics of this too.

[Rockwood]

[Archie]

Here's the pic of the cliff face with the area showing the grain texture outlined. 

[Archie]

I'm still waiting to get the pics of the polished section and a close up of the contact between the object and the matrix but heres another couple of pics showing the object in-situ closer up (unfortunately the cliff face is highly weathered) and another couple of pics of the surface under magnification showing the rods, we didnt measure them at the time but from memory they are less than 1mm in diameter.

[Innocentx]

On 1/18/2019 at 12:33 PM, Archie said:

It has the appearance of wood with growth rings but the "rings" are the horizontal rather than vertical rods. 

I find this unexplainable using either theory, slickensides/fibers or wood. 

It may be a type of wrapping growth pattern I or we are unfamiliar with??