Fossil or concretion?

[kodpkd]

Found along an old washout in NE Colorado. It's about 3 inches. 

[Fossildude19]

This looks like a nodule or concretion, to me.

[kodpkd]

Probably.   But what sparked my question is the 1/6 inch outside layer, the surface texture and the shape.

Edited December 10, 2021 by kodpkd

[Rockwood]

13 minutes ago, kodpkd said:

Probably.   But what sparked my question is the 1/6 inch outside layer, the surface texture and the shape.

I believe this to be a valid indication of it's being a trace fossil. I have several examples here.

If you too could back the find with more developed structures in additional examples it would definitely strengthen the identification though.

[Rockwood]

My reference. From the Trinity River, Arlington, TX. Eagle Ford Formation.

[kodpkd]

Here is what's strange. Another rock I found last month, has a very similar shape.

[Rockwood]

[abyssunder]

Chert nodule in my thinking..., both.

[abyssunder]

6 hours ago, Rockwood said:

My reference. From the Trinity River, Arlington, TX. Eagle Ford Formation.

It looks that some of them are Rhizocorallium, others Thalassinoides ichnofossils, if I'm not wrong.

Edited December 10, 2021 by abyssunder

[westcoast]

Chert nodules can develop weathering rinds, which is what I think we are seeing, particularly clear in last OP image.