Purisima Formation (3-7 Ma), Santa Cruz, CA: One piece doesn’t match the rest

[Slow_BS]

Hi there, 

 

I have a collection of Santa Cruz, CA shell hash, from the Purisima Formation. It’s pretty much all non-mineralized  mollusks, I think. 

 

I received a new piece that seems to be from the same formation (it was a gift from the heir of the original collector who lived in Monterey - the other side of the bay from the formation). The fossiliferous pieces inside this one have a totally different structure - much more of a radial/flakey look. I circled it in red in the first picture, and it’s the only rock in pics 3-6. 
 

I’d love to here if anyone has any thoughts on whether the new piece is Purisima, and what the white portions may have been.
 

Thanks for reading!

[Fossildude19]

Lots of fossil bryozoans in cross section.

Looks like the same matrix as the other fossils. (Cross sections of bivalve shells. )

[DPS Ammonite]

Looks like branching bryozoans to me too.  @Boesse

[Slow_BS]

Big thanks to both the commenters. That looks pretty good to me. I’ve shared the pics with the local natural history museum, since they offer a lot of info on the formation, and I’ll let you know if they respond / see any conflicts with the bryozoan ID. Thanks again!

[siteseer]

Bryozoans are known from the Purisima.  The piece you showed could be just from a different bed.

[Oxytropidoceras]

Some pertinent papers about the Purisima Formation are:

 

Boessenecker, R.W., 2011. Comparative taphonomy and taphofacies 

analysis of marine vertebrates of the Neogene Purisima Formation, 

Central California (Masters thesis, Montana State University-

Bozeman, College of Letters & Science).

https://scholarworks.montana.edu/xmlui/handle/1/940

 

Boessenecker, R.W., Perry, F.A. and Schmitt, J.G., 2014. Comparative 

taphonomy, taphofacies, and bonebeds of the Mio-Pliocene 

Purisima Formation, Central California: strong physical control 

on marine vertebrate preservation in shallow marine settings. 

PLoS One, 9(3), p.e91419. (open access)

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0091419

 

Norris, R.D., 1986. Taphonomic gradients in shelf fossil assemblages: 

Pliocene Purisima Formation, California. Palaios, pp.256-270.

 

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

Perry, F.A., Age, Stratigraphy, and Correlations of the Late Neogene 

Purisima Formation, Central California Coast Ranges. US Geological 

Survey Professional Paper 1740: 1–32.

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

 

Yours,

 

Paul H.

[siteseer]

Hmmm, I think we should try to find this Boessenecker person.  F.A. Perry knows a thing or two about the Purisima as well.  Years ago (maybe before Bobby was born), he wrote a cool little guide to invertebrate fossils from it.

[DPS Ammonite]

6 minutes ago, siteseer said:

Hmmm, I think we should try to find this Boessenecker person.  F.A. Perry knows a thing or two about the Purisima as well.  Years ago (maybe before Bobby was born), he wrote a cool little guide to invertebrate fossils from it.

Robert (Bobby) Boessenecker is a Forum member: @Boesse

Edited October 8, 2021 by DPS Ammonite

[siteseer]

28 minutes ago, DPS Ammonite said:

Robert (Bobby) Boessenecker is a Forum member: @Boesse

 

Yeah, I know.  I was making a joke.  Years ago, he showed me a couple of his secret California localities.  I'm not sure I remember exactly where they are now so his secrets are safe.

[Slow_BS]

I’m petty amazed that this place has an expert(s) on my random local formation. Awesome stuff. Thanks again!
 

If there’s anyone you know who would be particularly interested in large chunks of Carmel Valley, CA bivalve fossils, feel free to tag them too. I found a cool 65 pound rock full recently. Not really an ID question, but it’s close by so I figured I’d mention it. 

[DPS Ammonite]

24 minutes ago, siteseer said:

 

Yeah, I know.  I was making a joke.  Years ago, he showed me a couple of his secret California localities.  I'm not sure I remember exactly where they are now so his secrets are safe.

Were you part of or do you remember this San Francisco Bay Paleontology Society run by Bobby? I heard about the fossils in Daly City from Bobby.

 

 

[Boesse]

I have *never* seen branching bryozoans in the Purisima Formation, let alone a concretion full of them like this. Color me extremely skeptical that this is local. I'd believe it if it were found in situ.

[DPS Ammonite]

On 10/5/2021 at 6:19 PM, Slow_BS said:

from the heir of the original collector who lived in Monterey -

 

I see now that the formation of this rock with branching bryozoans is unknown. The Temblor is possible; don’t know if bryozoans have been found in it.

[siteseer]

12 hours ago, DPS Ammonite said:

Were you part of or do you remember this San Francisco Bay Paleontology Society run by Bobby? I heard about the fossils in Daly City from Bobby.

 

 

 

No, I had heard of it.  I remember a site near an outdoor mall in Daly City.  I think it has since been further developed or landscaped. 

 

[Slow_BS]

Hi,

 

I’m sorry if I buried the part about the unknown origin. My understanding is that the original collector didn’t travel too widely, and it probably originated not too far from central California - medium confidence level. 
 

I would love to hear if anyone has any other thoughts on where branching bryozoans may have been found in this sort of matrix. 
 

I’ll say I got one opinion that it was a weird calcite deposit, and not bryozoans. It doesn’t sound likely but figured I’d mention it. 
 

Thanks again for everyone’s input. It’s really gratifying to try to better ID my pieces. 

 

-Slowly But Surely