Two Odd Features In Tully Limestone

[Mediospirifer]

A couple of weeks ago, during a brief January thaw, I collected several pounds of Tully limestone from a local creekbed. When I went to clean the mud off, I found that some pieces had an odd, bumpy texture that I'm not familiar with, and other pieces had a black coating that looked like a coat of paint. Except that I've never found paint inside a rock before!

Here's one of the textured pieces:

Top:

Top showing edge detail:

One side:

Bottom:

I'll post another side and a different piece in the next post.

[Mediospirifer]

Here's the front side of the previous piece:

Here are some photos of the second textured piece:

Top:

Front:

Side:

More rocks to come!

[Mediospirifer]

Here's a piece showing the black layer. Note the area in the middle when a little bit of peeling is visible:

And the bottom of the same piece:

One more post to come!

[Mediospirifer]

This is a piece that looked like it had a layer of the black coating through it. The rock was thin enough that I was able to break it along the layer, and the black coating did indeed go all of the way through.

Here's the broken edges of the two (unequal) halves:

And here's the top of both pieces in close to their original relative positions:

I'll be interested to hear what these might be!

[painshill]

Parts of the Tully Limestone incorporate thin sheets of encrustation within the sedimentology which also exhibit features resembling shrinkage cracks. I think they're now generally accepted to be silty biofilms of a stromatolitic nature from algae and micro-organisms in areas that represented shallow intertidal lagoon environments or terrestrial-to-marine transition zones. I wonder if that's what you have there?

[Shamalama]

At first glance I want to say speleothem but if it didn't come from a cave then maybe not.

The black film I think is called a "Styolite" which form as pressure forces solutions through micro fractures in a rock. Often the black stuff is Bitumen which is a naturally occurring form of Petroleum. This webpage explains it better than I can.

[MarleysGh0st]

We had a January thaw?

I'd like to get out to my collecting spot, again, but I'm not going to shovel snow and risk frostbite to do it.

[painshill]

At first glance I want to say speleothem but if it didn't come from a cave then maybe not.

The black film I think is called a "Styolite" which form as pressure forces solutions through micro fractures in a rock. Often the black stuff is Bitumen which is a naturally occurring form of Petroleum. This webpage explains it better than I can.

Hadn't thought of that. Black films of that type are also known as "bitumenous partings". If you can flake a small piece off it, put a flame to it on the end of a penknife blade. If it's bitumenous you'll soon know from the odour and the smoke.

[Mediospirifer]

At first glance I want to say speleothem but if it didn't come from a cave then maybe not.

The black film I think is called a "Styolite" which form as pressure forces solutions through micro fractures in a rock. Often the black stuff is Bitumen which is a naturally occurring form of Petroleum. This webpage explains it better than I can.

Hadn't thought of that. Black films of that type are also known as "bitumenous partings". If you can flake a small piece off it, put a flame to it on the end of a penknife blade. If it's bitumenous you'll soon know from the odour and the smoke.

Interesting. I'll have to try that. There are certainly bits that I could flake off.

I should also mention that I collected the pieces as a potential micromatrix. I have a handful of small pieces soaking in vinegar, including a couple with the black layer. When I last drained the vinegar and probed at the black layer with a needle, it had softened a bit. I can easily imagine it to be a petroleum material.

We had a January thaw?

I'd like to get out to my collecting spot, again, but I'm not going to shovel snow and risk frostbite to do it.

OK, it wasn't much of a thaw, but we did have 3 or 4 days in the upper 30s. That was enough to melt most of the snow. I think it was around 40^o when I went to look at the site I was thinking of, and saw that the creekbed was (partly) reachable and dry. I wasn't going to do any slope climbing, though, so most of the site wasn't reachable. And the water the rocks were sitting in was FREEZING!

I didn't stay long, just enough to collect what was loose and easily reachable. Above freezing or not, it was still cold!

[norm52]

looks like a "fish scale" from an armored fish, they could be quite large. [actually, plate]

[Mediospirifer]

looks like a "fish scale" from an armored fish, they could be quite large. [actually, plate]

That did occur to me, but I don't know what to look for to confirm or disprove it. How thick would a plate be? Some broken edges seem to show an indistinct layer that's a little redder that the rest of the matrix, others don't.

It's either a new fossil for me, or a really weird weathering pattern. I'm not sure what to look for to tell which.

When the weather warms up again, I plan to go back to the site where I found it. I'll have to see if there's any more of it around.