Possible Oyster Fragment?

[Lostintheforest]

Hi all,

First time posting in this forum, I was out visiting Lake Castaic in southern california yesterday and among many interesting finds along the shore, i found this (see picture). to me it looks like a fossilized osyter shell, or at least the base end of one. but if so, it would mean this oyster was quite huge.. just have one photo at the moment, but hopefully some of you with a discerning eye can help me identify this find. the area had a lot of sandstone and clay deposits. Thanks for the help y'all.

[Auspex]

That would have been a massive shell for sure! At first glance, I thought of petrified wood, but in detail I can tell it is shelly material.

Welcome to the Forum, BTW

[Lostintheforest]

Thanks for the reply (and welcome)! The thin and fine layers do initially strike me as shelly, but again the size (and lack of a complete specimen) are making me question whether it actually is. More supporting evidence for the oyster hypothesis is that in the same immediate area i noticed what was almost certainly a full oyster fossil embedded in a solid piece of sandstone. the floor was also littered with reletively large fragments of what looked like more shelly material (although the fragments were so fragmented that it was difficult to gather what general shape the material had when whole. I will take more detailed photographs when i get home tonight, hopefully more photos will help with identification.

[Lostintheforest]

here are a few more photos from different angles. anyone?

[Lostintheforest]

[squali]

sandstone with contact metamorphisis?

[Lostintheforest]

hmmmm my background in geology is still quite weak so I can't really agree or disagree with your guess (but thank you for your post!). any other folks out there know more about geology and can tell if this looks more like a natural geologic formation or a fossilized organism? I have been collecting rocks for most of my life, and have not found one that looked as distinct as this one, but it is certainly possible this some kind of sandstone/metamorphic rock. keep em commin!!

[squali]

It's a tough one. To me some pics do look like weathered shell and some look like weathered banded chert.

It is an interesting find.

[Lostintheforest]

After looking up other photos of banded chert, i can certainly see the similarities with this specimen. however the area in which i found it seemed to be otherwise devoid of larger chunks of banded chert. for the most part it was sandstone, mudstone and clay (was found near castaic lake california). I had noticed another odd looking specimen embedded in a solid piece of sandstone that very much resembled a full oyster shell. That combined with the preliminary research i did which seemed to suggest the area was covered by a shallow (pacific) ocean around 6 mya is what put the oyster shell idea in my head. i might have to go back to the area and do a more thourough survey of the surrounding geology. I also found several clear crystals in the same area. they are very transparent and resemble pure quartz, however they are much softer than quartz and can be scratched with a coin. again my familiarity with geology is amateur at best, but after doing a little bit of research i've come up with the possibility that the crystals could be a form of calcite.

[Ludwigia]

Although I can only judge through photos, I'm nevertheless relatively convinced that you've got part of a very large oyster there.

[fossilpicker]

It looks like part of a large oyster to me. The Yuha Basin, in the desert near Ocotillo, CA has a vast area of fossilized oyster shells. Years ago, you could have found dinner plate-sized ones there. While you usually won't find complete ones now, you can still find pieces of large ones. And calcite crystals are commonly found in proximity to the shells.

[Lostintheforest]

Thanks for all the thoughts/replies everyone! Seems like my suspicions are shared by others, and what I found is indeed (likely) a piece of a large oyster. Feels good to have some confirmation on this case. So glad i found this forum, everyone on here seems very knowedglable, passionate, and pleasant, love it!

fossilpicker-

Oysters the size of dinner plates?! boy howdy that would be quite a find! gotta make a trip out to The Yuha Basin sometime. Any tips on other good fossil finding spots near the l.a. area?

Also, do you happen to know if the correlation with the calcite and fossil oysters has to do with the fact that oyster shells are primarily made of calcium carbonate?

[fossilpicker]

Lostintheforest-

Years ago, one could find large ones out there. We're talking a long time ago, though - 50's, 60's. As I said, anything that was on or close to the surface has already been taken home by someone. However, I'm sure there must be some big'uns still buried out there. For more info, just Google "yuha basin oyster beds" and you'll come up with a lot of reading material.

I don't get up to LA so much, I mainly head east (from San Diego). Again, Google is your best friend for info. Just type in "fossil hunting los angeles ca" or "collecting fossils in california" and you'll be amazed at the quantity of info you'll find.

There may be some correlation between the calcite and the shells, but we also find a lot of calcite with other fossils, and even inside of geodes. It's possible the calcite was present in solution while the fossils were being transformed? Just a guess...

Jean

[fossilpicker]

I forgot to mention - there's an article starting on page 4 (six, if you count the cover and page inside it) of the May 1940 issue of Desert Magazine. You can download it (no hoops to jump through!) at http://mydesertmagazine-1940-May.pdf. Actually, in the article, they said they found shells up to 8" in diameter - so a small dinnerplate, lol! I love those old Desert Magazines!!! Jean

[CastaicDave]

I can confirm that there is a fossil oyster bed in Castaic Lake, we pulled a few full shells out over the years but have kept the location a secret. I just curious how old these would be? When was Calif. under water?