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Hello Forum,

Recently, I acquired the petrified wood specimen (probably maple, Acer sp.) below at a local mineral show. It comes from the Holleywood Ranch in Linn County, Oregon. The broader area, well known for its petrified wood, is often referred to as "Sweet Home", or the Sweet Home Petrified Forest. According to Gregory (1968), the petrified wood is derived from some Miocene age subunit of the Little Butte Volcanic Series (details not entirely clear to me). I really liked the specimen because it shows a structure that I would interpret as the phloem (see this and this website). Though dependent on your definition of the term, this would mean part of the bark is preserved (quite rare, in my experience). Below the photo is an annotated micrograph of the region indicated in the overview. Does my interpretation make sense? Is this really wood (secondary xylem) plus the bark? I would also like to know why the last growth ring(s) of secondary xylem would stick to the bark? I can imagine the latter swelling up and becoming loose as the wood (waterlogged) was underwater for some time, but why not de-bond at the cambium then?

Thanks for your feedback!

Tim

post-2676-0-70758800-1444335273_thumb.jpg

post-2676-0-36557400-1444335286_thumb.jpg (micrograph made as follows)

Searching for green in the dark grey.

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In my opinion, your analysis is readily supported by the visible features: spot on.

This extraordinary preservation may be due in part to the tree having been buried in ash, which dessicated the living layer (phloem) and inhibited bacterial action at the same time. Water-born mineral infiltration after interment would have been a very slow affair, into wood which was under considerable pressure.

It is a beautiful piece!

"There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant

“Try to learn something about everything and everything about something.” - Thomas Henry Huxley

>Paleontology is an evolving science.

>May your wonders never cease!

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If the tree was killed and dried out quickly, the bark would tend to adhere to the wood, rather than coming off cleanly. I speak from personal experience with modern wood: it's easy to strip the bark from a live branch, or a piece of deadwood that has been lying on the forest floor for months. Removing the bark from a branch that has fully dried out is much more difficult, and usually requires scraping with a knife.

Just my 2 cents. I used to do a lot of camping. :D

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Beautiful images, Tim. I love the detail in the micrograph.

The human mind has the ability to believe anything is true.  -  JJ

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In my opinion, your analysis is readily supported by the visible features: spot on.

This extraordinary preservation may be due in part to the tree having been buried in ash, which dessicated the living layer (phloem) and inhibited bacterial action at the same time. Water-born mineral infiltration after interment would have been a very slow affair, into wood which was under considerable pressure.

It is a beautiful piece!

What do you mean exactly by "having been buried in ash"? Hot ash, Pompeii-like? If yes, could you provide a bit more detail as to how fossilisation took place? So far, I imagined the wood would have spent some time underwater, say in a lake or coastal area, before onset of fossilisation (not sure how this would yield this good a preservation though.) Then, at some point in time, volcanic ash rains out onto the body of water, changing its chemistry (by releasing ionic species from the volcanic glass), thus allowing petrification to begin. This allows the log to remain simply underwater for quite some time, during which the bark may have swollen, leading to its debonding (common occurrence in submerged woods, I believe), as seen in the specimen. If I'm not mistaken, some petrified wood with quartz after halite (pseudomorphs) has been found at the Sweet Home Petrified Forest, suggesting the presence of salt water (will have to look for that reference).

Searching for green in the dark grey.

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@ZiggieCie and JohnJ: Thanks!

If the tree was killed and dried out quickly, the bark would tend to adhere to the wood, rather than coming off cleanly. I speak from personal experience with modern wood: it's easy to strip the bark from a live branch, or a piece of deadwood that has been lying on the forest floor for months. Removing the bark from a branch that has fully dried out is much more difficult, and usually requires scraping with a knife.

Just my 2 cents. I used to do a lot of camping. :D

This is quite interesting! Would the heat of the ash not damage/burn the bark? For maple its only a couple mm thick... Clearly, I need to read up more on the locality.

Searching for green in the dark grey.

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I don't think that ash fall was "Pompeii hot", as none of the petrified wood there shows signs of charring, but being buried in dry ash is going to be a different environment from being buried in water-born sediment.

"There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant

“Try to learn something about everything and everything about something.” - Thomas Henry Huxley

>Paleontology is an evolving science.

>May your wonders never cease!

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I don't think that ash fall was "Pompeii hot", as none of the petrified wood there shows signs of charring, but being buried in dry ash is going to be a different environment from being buried in water-born sediment.

Okay, yes, that makes sense. Thanks for the additional feedback. Some petrified wood shows dessication features (mostly evident as mineral-filled veins), but I didn't know any from Sweet Home, that's why I asked. It is often quite difficult to find information on the fossilisation conditions...

P.S. Haven't found the paper on the quartz-after-halite-bearing wood yet, but I did find a photo of it.

Searching for green in the dark grey.

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The question of why it de-bonded within the xylem is certainly intriguing.

Looking at your photo, I notice there is very little sign of damage to the tree. There are a couple of tiny cracks on the edge, especially at the bottom, which are probably dessication features.

I wonder if there was a point of damage elsewhere on the tree that allowed a fungal infection to colonize the xylem? Usually, loose bark will separate at the cambium, so there must have been something unusual going on here to create a layer of weakness. I know that a hard impact can cause wood to delaminate, but I'd expect that to strip the bark off first.

Lightning can also have odd effects on a tree, but that would leave other marks. I once saw a large oak tree that had been killed by lightning--the tree still had all of the leaves attached (dried out and dangling), and the trunk had several vertical splits with chips of wood sticking out! The lightning had traveled down the center of the tree and killed it instantly with a steam explosion. I've also seen trees with a scar along the trunk where a strip of bark was damaged, with one dead branch and the rest of the tree still alive and growing. I don't think that's what happened here.

I'd ask a dendrologist what might cause this kind of delamination without removing the bark. :D

Good luck!

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Fungal attack is an interesting thought! Not sure how I should test such an hypothesis, though... (so yes, let's ask a dendrologist!)

The photographs below show a second piece of petrified wood (something conifer-like) with preserved bark material. This specimen comes from the Upper Jurassic (appreciably older than the previous specimen) of the Morrison Formation, famous for its Hermanophyton wood (found at East McElmo Creek near Cortez, Collorado). Note the phloem with large sieve tubes, visible on the periphery of the specimen (clearer in the micrograph). It's quite remarkable that the bark preserved so well, considering the not-so-great preservation of the xylem in this stem.

post-2676-0-95045900-1444501714_thumb.jpg

post-2676-0-38852800-1444501716_thumb.jpg (EDIT: scale bar corresponds with 4 mm, not 2 mm)

Anyone else have examples of petrified wood with preserved bark? I'd like to see!

Searching for green in the dark grey.

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