Is this a fossil? Strange rock found on SF beach

[mooflyrock]

Hello again! I found this rock a while back and have been mystified by it. It looks sort of like a fossil to me, but I don't know what of. Friends have suggested a stromatolite but that doesn't seem quite right.

I found this on a beach in San Francisco, California. Whatever it is, it's been worn down by water.

High res pics are here: https://www.flickr.com/photos/mooflyfoof/albums/72157651000782301

Any ideas? Thanks in advance!

[sseth]

Looks as though you have some fossil coral there. Nice find.

[mooflyrock]

Cool! Thank you!

Coral, of course. That makes a lot of sense.

[DPS Ammonite]

Interesting! Can you tell if the white layered part is quartz or calcite? A knife blade will scratch calcite (possible shell) but not quartz.

What beach did you find it at? Once I know, I'll tell you what rock layers are in the area.

I have never heard of coral fossils from the SF area.

[Peat Burns]

Petrified wood?

[tmaier]

Not petrified wood. It gives that illusion because the parallel lines look a bit like annular rings of a tree, but notice that they are very parallel (not curved like rings), and they are very uniform in spacing (annular tree rings have some variation).

I looks like colonial coral to me. Some non-tabular type.

People sometimes like to give those a wet look by coating them with something (not sure what).

Edited April 26, 2016 by tmaier

[PRK]

Spot on pete

[Peat Burns]

Not petrified wood. It gives that illusion because the parallel lines look a bit like annular rings of a tree, but notice that they are very parallel (not curved like rings), and they are very uniform in spacing (annular tree rings have some variation).

I looks like colonial coral to me. Some non-tabular type.

People sometimes like to give those a wet look by coating them with something (not sure what).

I was thinking radial section, which is linear rather than curved, but I think you're right that it might not be petrified wood. I see in the end view that the structure does not seem consistent with wood structure. Edited April 26, 2016 by Peat Burns

[mooflyrock]

In that first picture it's just wet because I thought it looked better that way. It's dry in the other pics.

I am by no means an expert but having just spent the weekend in Petrified Forest in AZ and seeing a ton of different kinds of petrified wood, this doesn't really look like petrified wood to me. Looks more like coral, based on what I know about what living coral looks like.

Thanks for all the input. Very interesting stuff so far!

Edited April 26, 2016 by mooflyrock

[PRK]

In eastern US most likely coral. But in the west most likely wood. VERY, very small chance it is coral out here

Edited April 26, 2016 by PRK

[Peat Burns]

In that first picture it's just wet because I thought it looked better that way. It's dry in the other pics.

I am by no means an expert but having just spent the weekend in Petrified Forest in AZ and seeing a ton of different kinds of petrified wood, this doesn't really look like petrified wood to me. Looks more like coral, based on what I know about what living coral looks like.

Thanks for all the input. Very interesting stuff so far!

Do you have access to a dissecting microscope or strong hand lens? If so, take a close look at the structure on the end of the rock and see if you can see any cell pattern that might indicate xylem cells.

I looked at that view on your high res pics, and I definitely see microstructure, but it doesn't look quite like xylem cell pattern, but without further magnification, I just can't tell for sure.

Edited April 26, 2016 by Peat Burns

[Herb]

I believe it is wood, not seeing any septae if it is coral

[mooflyrock]

Is it possible it could be a piece of a horn coral fossil? It seems unlikely based on location, but I'm seeing a lot of similarity to the outside structure of horn coral, based on google image search:

http://www.fossilicious.com/horn-coral-fossil-lophophyllidium-proliferum.html

http://wildaboututah.org/fossil-formation/

http://www.nhm.ac.uk/natureplus/thread/5566

http://members.tripod.com/eocene__1/cretaceous_davonian.htm

https://en.wikipedia.org/wiki/Rugosa

I will try to get a closer shot tonight; I have a 10x loupe and maybe that will be enough.

[Peat Burns]

Here are some pics of a particularly well preserved piece of petrified wood in my collection (NOTE: Not all petrified wood will have this kind of preservation where the cell walls are visible...)

Radial Section

Transverse section

Close-up of rings and cells in transverse section

Your images reminded me of a glacial worn horn coral fragment I found over 30 years ago in N. Indiana. It does rather resemble what you have.

Side view

End view

I am not at all familiar with possible source rocks in your area and whether horn coral is a possibility. But it does have some common features... Maybe a fragment of a more geologically recent coral similar to species in the Mussidae or Fungiidae?

Edited April 27, 2016 by Peat Burns

[Peat Burns]

Here's another glacial and / or water worn horn coral from N. Indiana (yours could be water eroded, having come from a beach):

Lateral view

[mooflyrock]

Interesting! Can you tell if the white layered part is quartz or calcite? A knife blade will scratch calcite (possible shell) but not quartz.

What beach did you find it at? Once I know, I'll tell you what rock layers are in the area.

I have never heard of coral fossils from the SF area.

It did scratch with a knife, so calcite probably. I PMed you about the beach.

Do you have access to a dissecting microscope or strong hand lens? If so, take a close look at the structure on the end of the rock and see if you can see any cell pattern that might indicate xylem cells.

I looked at that view on your high res pics, and I definitely see microstructure, but it doesn't look quite like xylem cell pattern, but without further magnification, I just can't tell for sure.

I tried to take some more pictures with my 10x loupe but unfortunately I don't think we can see much more than the original pictures. I'm not familiar enough with organic structures to say whether what I'm looking at is xylem or phloem or something else. Here are the high res pics:

https://www.flickr.com/photos/mooflyfoof/26642655376/in/datetaken/

https://www.flickr.com/photos/mooflyfoof/26603518541/in/datetaken/

https://www.flickr.com/photos/mooflyfoof/26063394544/in/datetaken/

https://www.flickr.com/photos/mooflyfoof/26669117235/in/datetaken/

https://www.flickr.com/photos/mooflyfoof/26063395184/in/datetaken/

Here are some pics of a particularly well preserved piece of petrified wood in my collection (NOTE: Not all petrified wood will have this kind of preservation where the cell walls are visible...)

Radial Section

20160426_200816_resized.jpg

Transverse section

20160426_200917_resized.jpg

Close-up of rings and cells in transverse section

20160426_200947_resized.jpg

Your images reminded me of a glacial worn horn coral fragment I found over 30 years ago in N. Indiana. It does rather resemble what you have.

Side view

20160426_201214_resized.jpg

End view

20160426_201223_resized.jpg

I am not at all familiar with possible source rocks in your area and whether horn coral is a possibility. But it does have some common features... Maybe a fragment of a more geologically recent coral similar to species in the Mussidae or Fungiidae?

Interesting - it actually does look somewhat like the petrified wood in these pictures. Superficially it looks like your horn coral pictures but up close I'm not so sure. The black and white striations are all the same level of erosion, as opposed to your horn coral where the black is more eroded than the white. My rock is perfectly smooth. Everyone here is saying coral is very unlikely in my area. (I'm not knowledgable enough yet to be able to say either way.)

Here are some other coral fossils I found on the internet that look similar...

https://www.flickr.com/photos/andrea_scauri/4975246108/

http://paleo.cortland.edu/tutorial/Cnidarians/Cnidarians%20Images/tabulate1.GIF

http://www.geosci.usyd.edu.au/users/prey/FieldTrips/Yass04/Images/Cystiphyllum.jpg

[DPS Ammonite]

Mystery. If the rock was not left by a human or used as ship ballast or road metal it looks most like the cemented marine sandstone with shells and gravel from the Pliocene/Pleistocene Merced Formation that occurs in the area. Some of the clasts in the Merced Formation could have come from the Sierra Nevada or further. I have heard of small singular corals from the Paleocene and Eocene rocks from Oakland, Martinez and Palo Alto. Coral is rare in the Bay area; I have never seen any. I wonder if they layers are actually part of a thick shell such as an oyster.

Edited April 27, 2016 by DPS Ammonite

[Peat Burns]

Mystery. If the rock was not left by a human or used as ship ballast or road metal it looks most like the cemented marine sandstone with shells and gravel from the Pliocene/Pleistocene Merced Formation that occurs in the area. Some of the clasts in the Merced Formation could have come from the Sierra Nevada or further. I have heard of small singular corals from the Paleocene and Eocene rocks from Oakland, Martinez and Palo Alto. Coral is rare in the Bay area; I have never seen any. I wonder if they layers are actually part of a thick shell such as an oyster.

I was thinking the same thing. The patterns on the new photos made "shell" come to mind. Here's a pic of a cross section of bivalve shell. Only thing that stumps me on mooflyrock's shell is all the patterns and complex microstructure visible on the end views of her rock.

https://www.google.com/search?q=shell+cross+section&client=ms-android-verizon&prmd=ismvn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiNts2xha7MAhXszoMKHcZ8D68Q_AUIBygB&biw=360&bih=559&dpr=3#tbm=isch&q=bivalve+growth+lines+cross+section&imgrc=UriVzMnmHOETcM%3A

[Boesse]

It's not coral - it's a single plate of a large barnacle from the Plio-Pleistocene Merced Formation. The matrix is a match for the Merced, which is the only pre-Holocene fossiliferous unit anywhere on the northern SF peninsula. Abundant echinoid concretions can be found on the beach, often with the sand dollar Scutellaster oregonensis; barnacles are less common, but in cross section barnacles look like that. There aren't any coral-bearing fossil sites for a long ways away.

[fifbrindacier]

Mystery. If the rock was not left by a human or used as ship ballast or road metal it looks most like the cemented marine sandstone with shells and gravel from the Pliocene/Pleistocene Merced Formation that occurs in the area. Some of the clasts in the Merced Formation could have come from the Sierra Nevada or further. I have heard of small singular corals from the Paleocene and Eocene rocks from Oakland, Martinez and Palo Alto. Coral is rare in the Bay area; I have never seen any. I wonder if they layers are actually part of a thick shell such as an oyster.

I was thinking the same thing. The patterns on the new photos made "shell" come to mind. Here's a pic of a cross section of bivalve shell. Only thing that stumps me on mooflyrock's shell is all the patterns and complex microstructure visible on the end views of her rock.

https://www.google.com/search?q=shell+cross+section&client=ms-android-verizon&prmd=ismvn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiNts2xha7MAhXszoMKHcZ8D68Q_AUIBygB&biw=360&bih=559&dpr=3#tbm=isch&q=bivalve+growth+lines+cross+section&imgrc=UriVzMnmHOETcM%3A

It's not coral - it's a single plate of a large barnacle from the Plio-Pleistocene Merced Formation. The matrix is a match for the Merced, which is the only pre-Holocene fossiliferous unit anywhere on the northern SF peninsula. Abundant echinoid concretions can be found on the beach, often with the sand dollar Scutellaster oregonensis; barnacles are less common, but in cross section barnacles look like that. There aren't any coral-bearing fossil sites for a long ways away.

I share the opinion it is some kind of shell. The idea it could be a kind of barnacle does fit for me, although i am not an expert. I have found photos of fossilized barnacles on the net :

I hope this will help.

Edited April 27, 2016 by fifbrindacier

[Carl]

snarge you, Bobby! I was just poised to post that as I was scrolling down the thread! Well done...

[mooflyrock]

This discussion has gotten incredibly interesting! I totally buy the idea that it's part of a shell of some sort. Sounds like that's much more likely than coral based on the location where I found it. It also would explain how it's sort of cupped around that cement-like material.

Thanks so much, everyone!

[Peat Burns]

It's not coral - it's a single plate of a large barnacle from the Plio-Pleistocene Merced Formation. The matrix is a match for the Merced, which is the only pre-Holocene fossiliferous unit anywhere on the northern SF peninsula. Abundant echinoid concretions can be found on the beach, often with the sand dollar Scutellaster oregonensis; barnacles are less common, but in cross section barnacles look like that. There aren't any coral-bearing fossil sites for a long ways away.

This discussion has gotten incredibly interesting! I totally buy the idea that it's part of a shell of some sort. Sounds like that's much more likely than coral based on the location where I found it. It also would explain how it's sort of cupped around that cement-like material.

Thanks so much, everyone!

Boesse, nice ID! I would have never guessed barnacle.

These kinds of finds are great. Although a worn, broken fragment that many of us might not bring home, it sparked a fascinating volley of thoughts and ideas and resulted in learning something new.

Mooflyrock, thanks for posting it. This was pure "edutainment"

[DPS Ammonite]

I have collected barnacles from the Merced Fm. and I didn't recognize a cross section. Thanks to Boesse for having his "boots on the ground" at that locality. It just goes to show that a good locality description for a fossil often leads to an ID from a local who has visited the site.

Edited April 27, 2016 by DPS Ammonite

[mooflyrock]

I'm glad this provided "edutainment" for all! I certainly learned a lot. I remember when I saw the rock on the ground I had to pick it up because intuitively I knew it just looked "different". I'm glad I did!