Mystery Holes in Limestone Solved

[DPS Ammonite]

I have found scattered limestone clasts with submillimeter holes in them. I pick them up wondering if they are stromatoporoids, bryozoans, sponges or the like. The holes do not extend into the interior of the rock. 
 

Some of the rocks have lichen and algae growing on them. I finally found a soft dark lichen or algae growing in the holes in the rocks. Let me know if anyone can tell whether the dark spots are lichen or algae.
 

If they are the cause then the rock exhibits bioerosian. Bioerosian was first described by Conrad Neumann in 1966 as “the removal of consolidated mineral or lithic substrate by the direct action of organisms.” The organisms probably secrete acid that dissolves limestone. Algae and lichens were early colonizers of the land. Bioerosian created soil that allowed new forms of life including plants and trees to colonize the land. 

 

Check your limestone rocks for these traces of bioerosian. Theoretical these could become trace fossils if buried for more that 10k years.

Photos show holes in Tertiary limestone with plant fossils that are from 0.2 to 0.4 mm in diameter. Again, if you know what the black organism is let me know. 

https://aslopubs.onlinelibrary.wiley.com/doi/10.4319/lo.1966.11.1.0092

 

OBSERVATIONS ON COASTAL EROSION IN BERMUDA AND MEASUREMENTS OF THE BORING RATE OF THE SPONGE, CLIONA LAMPA  by Conrad Neumann.

 

 

 

[EscarpmentMary]

Good morning! I live on the escarpment here in Ontario Canada. This one of my favourite fossils, I believe personally, and have for many years, that the images I have sent you is the head of an early vertebrae, possibly Devonian. I hypothetically believe he may be a one of brought here by a heavy tide, of a retreating Silurian sea some 400 million years ago. A rock split open revealing him. (I call him Gus, because Gus is us) the outside of the rock has these features on it, could this be the same phenomena you describe in your discussion?

[aplomado]

Weird!

My son picked up a rock the other day completely covered with tiny holes.  It didn't match anything else in the creek.  It is really puzzling.  I even wondered if it was pumice, but I don't think so.  Maybe it is the same?

I will try and post a picture later.

[aplomado]

OK, this is the rock one of my kids picked up in a stream full of cretaceous fossils.  There is a lot of limstone there, but have not seen another stone at that site is this full of holes... any idea of what may be going on here?

[Notidanodon]

14 hours ago, aplomado said:

OK, this is the rock one of my kids picked up in a stream full of cretaceous fossils.  There is a lot of limstone there, but have not seen another stone at that site is this full of holes... any idea of what may be going on here?

I think that’s pumice

[Plax]

lithophagous mollusk (gastrochaenid) borings are a possibility if this is limestone. 

[aplomado]

I did wonder if it might be pumice, but I didn't see similar stone in the area.... (I'm no rock guy though).  It is light, but does not float.

 

There is a lot of limestone around.

I am wondering if it might be mollusk borings as you said, Plax.

 

There is a lot of fossil (lignite) driftwood in the area with shipworm borings.

[DPS Ammonite]

@aplomado It is volcanic scoria or cinder which is denser than pumice and does not float. Being rounded, the rock probably was brought in by a stream. 
https://en.m.wikipedia.org/wiki/Scoria

 

It is not bored because the holes vary too much in size and are too angular in some cases. Basalt and andesite rocks are rarely bored.

Edited July 7, 2020 by DPS Ammonite

[aplomado]

Slag maybe?