Swirling lines found in rock

[Caroboneferous]

I've been finding fossils in limestone, sometimes I find fossils in rock that also appears to have these irregular lines interspersed.    They are all shapes and sizes, I’ve attached some pictures.  I am just curious as to what these are.  Carbonized plant material?  Or just inclusions in the rock? 

[Lone Hunter]

Trace fossil trail would be my guess.

[connorp]

They look more like cross sections to me.

[FranzBernhard]

Side views of the specimen would be important.

Franz Bernhard

[Rockwood]

The shapes look like cross sections, but the texture is quite trace fossil like. The two are not mutually exclusive however. 

I wonder if they are lined burrows.

[Caroboneferous]

7 hours ago, Rockwood said:

The shapes look like cross sections, but the texture is quite trace fossil like. The two are not mutually exclusive however. 

I wonder if they are lined burrows.

 

I’ve attached more pictures.   This is, I think, Carboniferous limestone.   This piece actually does have a small shell fossil in it (you can see the pictures).  
 

The shapes make me think of burrows.

[FranzBernhard]

6 minutes ago, Caroboneferous said:

 

Thanks for the extra pics! This one above gives a good impression of the overall distribution of the "dark lines". They look like some shell fragments to me, but the swirly pattern are strange!

Franz Bernhard

[Caroboneferous]

10 hours ago, FranzBernhard said:

Side views of the specimen would be important.

Franz Bernhard

I’ve attached more photos here.   There is actually what looks like a fossil shell in the piece already. 

[Rockwood]

I believe these are nearly all shells and shell fragments seen in various odd section.

[Missourian]

These likely are thalli of calcareous phylloid algae in cross section. There are red and green varieties.

 

In the attached image below, the one on the left is probably Archaeolithophyllum a red alga. The protuberances arrowed in red resemble conceptacles, which are often present on the surface of the blades. The other one, arrowed in green, appears to the the cross section of a cup shaped-thallus, which is more typical of green varieties of calcareous algae.