Algae or graptolite or what?

[CZ Wang]

I check this website from time to time and always learn something new. I am a bedrock geologist for many years - although I had a good training in paleontology, I still have to work hard to try to figure out a fossil. I recently and currently map rocks in northern Maine. The pictures show below are from a recently discovered greenbed basin (probably aged middle-late Early Devonian and deposited in a continental or sea-land transitional environment). My question is what are the dark-colored pieces? They don't look like burrows because they don't occur across layers. They don't look like tracks because they occur as separate pieces. They are not plant fossils. They appear like graptolites but I can hardly see any theca. Are they algae? Or what? Any help would be much appreciated.

Edited July 26, 2021 by CZ Wang

[Rockwood]

I call them trace fossils. Maine is littered with them.

[westcoast]

Agree with Rockwood; trace fossils. I think you dismissed burrows too quickly. Burrows can be largely horizontal too and don't always appear 'across layers'.

[CZ Wang]

Thanks to Rockwood and Westcoast! Westcoast is right that burrows can be also horizontal. I have seen lots of burrows and the same formation where these fossils occur does have burrows but they are typical burrows. These guys are not - they may be some special burrows if they have to be burrows. A veteran paleontologist with expertise in graptolite thinks they may be graptolite, but among many I have seen, I have never seen any theca or other features that can confirm they are graptolite.

[Rockwood]

45 minutes ago, CZ Wang said:

Thanks to Rockwood and Westcoast! Westcoast is right that burrows can be also horizontal. I have seen lots of burrows and the same formation where these fossils occur does have burrows but they are typical burrows. These guys are not - they may be some special burrows if they have to be burrows. A veteran paleontologist with expertise in graptolite thinks they may be graptolite, but among many I have seen, I have never seen any theca or other features that can confirm they are graptolite.

I've collected graptolites in a matrix with similar appearance from Aroostook county. I see a slight similarity to the texture often seen in these traces, but the size and form is quite different from my experience. You have to take into account the fact that virtually all Maine rocks are at least slightly metamorphosed. Grain size can be deceptive. (Ya right, I'm telling a geologist ) . 

At a little quarry near Rockwood they are exposed as a centimeters thick layer in places. It's been scrambled by tectonics and explosives though.

[Rockwood]

The curator of this little museum in Greenville graciously let me use a display in progress to photograph an example. I think it's most likely from the Tomhegan formation.

[Tidgy's Dad]

I'm pretty sure they aren't graptolites if this is Devonian. 

They don't look like bits of dendroids and the only graptoloids to make it into the Lower Devonian were spiral forms, I think. 

Burrows is my guess as well. 

[CZ Wang]

I agree with "Tidgy's Dad". Thanks for your comment. I have seen a lot of them but never noticed anything like theca. The host rocks are either sandstone or siltstone.