Tube-like objects found on CA beach

[Chilipossum]

Hi all!   I’m hoping to solve a mystery.  I find these objects pretty regularly along the San Mateo coast of Northern California.  I’m not even sure they’re fossils, but the bluffs above the beach are part of the Purisima Formation with plenty of fossils from the late Miocene to early Pleistocene so I thought it would be worth a try.  They look to be made of compacted sand, like a concrete, but laid down in layers, with a more robust top with lines that have some shell-like material. Most pieces I found have this triangular shape that look like they might have formed tubes.  All the pieces I’ve found look like they would have a similar diameter. I’ve never found any smaller.  They’re pretty uniform.  And common.  Since I first noticed them a couple of months ago I find them every time I’m on the beach.  They could be the result of a geologic process, but I’ve asked every beachcomber, zoologist, and marine biologist I can can find and no one can tell me what they are.  

[Oxytropidoceras]

I would identify your finds as fragments of the base

of the trace fossil Teichichnus pescaderoensis that have

been preferentially cemented by calcium carbonate.

I suspect that the base of this fossil burrow was

preferentially cemented because the sand composing

it was more permeable than the surrounding sediment.

Being cemented, the base (floor) of the burrow was

preserved and eroded out as a pebble while the upper 

part (roof) of the burrow was destroyed along with

the enclosing sediment.

 

The laminations are the result of the upward movement

of the base of a burrow and backfilling of its floor as

the animals renovates the burrow.

 

A couple of papers, which I have access to,  are:

 

Stanton, R.J. and Dodd, J.R., 1984. Teichichnus pescaderoensis—

new ichnospecies in the Neogene shelf and slope sediments, 

California. Facies, 11(1), pp.219-227

 

Knaust, D., 2018. The ichnogenus Teichichnus Seilacher, 1955. 

Earth-Science Reviews, 177, pp.386-403.

 

For general information about the Purisima Formation go see:

 

Powell II, C.L., Barron, J.A., Sarna-Wojcicki, A.M., Clark, J.C., 

Perry, F.A., Brabb, E.E. and Fleck, R.J., 2007. Age, stratigraphy, 

and correlations of the Late Neogene Purisima Formation, 

central California coast ranges (No. 1740). Geological Survey (US).

https://pubs.usgs.gov/pp/2007/1740/

https://www.arlis.org/docs/vol1/164589542.pdf

 

Yours,

Paul H.

[ClearLake]

Very interesting objects. I’m not sure what they are either, but they look like some repeated coating/precipitate/evaporite/filling on the inside of a tube/pipe or small bottle or corrugated surface where the original “container” is now gone. But I’m just guessing. 

[Chilipossum]

I was definitely settling on them being fragments from a concrete reinforcement of corrugated culverts, which would explain the uniformity and their presence on the beach, but I would just LOVE if they are indeed Teichichnus pescaderoensis, and will keep digging.  If nothing else I’m thankful this search has led me to this forum.  What a great resource!!

Edited December 8, 2019 by Chilipossum
Edited to include all responses

[Rockwood]

I see sediment balls lining a burrow. Puts me in the ichno fossil camp.

[Carl]

I regularly collected the Purisima back in the early 90s and would also find these occasionally. Having grown up beach combing in the East I had no idea what they were and collected them until I did. I know they turned out to be modern but I can't exactly recall what they were. I seem to remember them being created by the boring clams called piddocks but now I can't find any such thing and can't figure out how or why a piddock would even do this if it already has the ability to bore into rock. All that said, the Purisima fauna is so young and close to the modern fauna it's not impossible that there are also fossil examples on those beaches. I'd send photos to the Santa Cruz Museum of Natural History  and the Monterey Bay Aquarium for an ID. 

[abyssunder]

They might have a good resemblance with Kuphus. Please check the older topics on TFF.