Turritella concretion - possible to ID locality?

[farahad]

Hello,

I purchased this specimen a few months ago at an estate sale.  No label, no information.  The fossil has been split lengthwise, polished, and the interior void space looks to have been filled with a sort of yellowish epoxy.   Each half measures approx. 4.75 cm long x 2.5 cm across.  Original depth before cutting looks to have been around 2.5 cm.  I believe it is a Turritella, in a distinctive layered, calcareous concretion.

I was able to find a photo of an almost identical specimen on a college professor's website, but I was unable to get additional information after following up: the specimen isn't in their collection and the professor who took the photo has since retired -- and supposedly liked to take photos of odd specimens at the Tucson Gem and Mineral Show [direct link to image]:

http://skywalker.cochise.edu/wellerr/fossil/gastropod/6fssl-gastropod-turritella2.jpg

I think I've seen similar specimens before, but can't recall where...  Does anyone know where this piece might be from?  I'm hoping the concretion is distinctive enough to be identifiable...

 

Thanks
 

[Al Dente]

Here’s a similar one from this webpage-http://geoweb.uwyo.edu/geol2100/Lecture27_NonSkeletalAllochems.pdf

The layered concretion was formed by algae coating the gastropod. They are called “oncolites”

 

[RJB]

Really cool!!!

 

RB

[farahad]

Thank you!!!  I spent a good few hours trying to track this down, can't imagine how you found that.  I know oncolites, but didn't realize they could form around things like this.