are these fossils?

no, just patterns.

Hard to say for sure, but they look like patterns to me.

Ceili is right, tho Limestone is made up of fossils and shells

That bottom one looks an awful lot like a 21st century boot tread.

we dont know the scale of the photo so the item could be the cross section of a bivalve shell or some other kind of ancient seafood. OR, it could just be a silt lens that is bent around during the consolidation process as the water is driven out of the wet sediment and converted to a rock.
Ill guess that, based upon the size of the relict pore spaces , the rock is a few cm across .Therefore a cross section of a bivalve shell is most reasonable of a guess.

thank you

wow, I got a red dot. I never got a red dot before. LAst time I answered something somebody reported me.

Although I respect Farmerman's incredible knowledge of Earth's history and upon further review(referee's whistle)...I have to disagree.

The key word in the photo is limestone used as a BUILDING product. Therefore I'm guessing that the photo spans 8 to 12 inches which would make the shape too big for a bi-valve and would indicate some sort of stain caused by acidic etching.

Hers a fossil of a Penicularis from the KAibab ls. Its quite similr to the feature in the opening shots.

The size of the slab has little bearing since various pelecypods from the K to the Miocene were large.( Mercenaria spp. and Crossostrea spp).
We use these cross sectional cuts to help identify the approximate angle of bedding since , statistically,dead shells usually lie with the shell opening downward. ( Its dynamically most stable in a moving current)

The younger the shell fossil, the more chances wed see the linear structures (like growth rings) across the shell.