Sea Shell, but How Old?

[Kosmo]

I live at the base of the Rockies (Fountain, CO), where the Western Interior Seaway once was.  I found this shell a couple years ago while exploring a freshly excavated area (for housing development) near my home with my boy.  The soil is a grayish hue, which has me think it might have once been a marshy, swampy area.  The predominant color of the soil in this region is more tan in color, not gray.

It's obviously old, but the question is...how old?  It's in such good condition, I wonder if it's actually a "fossil", as defined by being petrified.  I'm quite novice as far as terms and definitions as such.  So let's say for instance...radio carbon dating revealed this is ancient; i.e., millions of years old and a shell that once lived in the Western North American Interior Seaway.  Is it possible that it's retained its original molecular structure vs. being petrified?

Do/did crustaceans like this live in fresh water lakes?  Could it be just that...that lived in a lake a few hundred or thousand years ago?  Or could it have lived 100 million years ago in the Western Interior Seaway and be as well preserved as it is?    

[westcoast]

This is a marine fossil bivalve, so it is a mollusc not a crustacean  but in any event is likely many millions of years old. Without knowing the geological layer it came from it is difficult to say. It is related to modern scallops.

And yes, some fossils do retain some of the original details from millions of years ago and examining the isotopes in the shells can tell us a lot about the life of the shell, including its age.

 

[Kosmo]

34 minutes ago, westcoast said:

This is a marine fossil bivalve, so it is a mollusc not a crustacean  but in any event is likely many millions of years old. Without knowing the geological layer it came from it is difficult to say. It is related to modern scallops.

And yes, some fossils do retain some of the original details from millions of years ago and examining the isotopes in the shells can tell us a lot about the life of the shell, including its age.

 

Roger on the mollusk (not crustacean).  And of course that's what I was hoping...that it's millions of years old.  But understood isotopic analysis, or whatever technology (didn't know or forgot radio-carbon dating was limited to about 60K years) gives a more solidly founded estimate of its age would be in line...if I was so inclined to have it tested.

On that note, any idea of the cost is for such testing of this kind of sample?  Curious if there are testing labs wannabe/amateur archeologists like myself default to using at a..."reasonable" cost.   

[Fossildude19]

40 minutes ago, Kosmo said:

Roger on the mollusk (not crustacean).  And of course that's what I was hoping...that it's millions of years old.  But understood isotopic analysis, or whatever technology (didn't know or forgot radio-carbon dating was limited to about 60K years) gives a more solidly founded estimate of its age would be in line...if I was so inclined to have it tested.

On that note, any idea of the cost is for such testing of this kind of sample?  Curious if there are testing labs wannabe/amateur archeologists like myself default to using at a..."reasonable" cost.   

 

I doubt it.

It would be an expensive endeavor.

[ynot]

2 hours ago, Kosmo said:

.that it's millions of years old. 

More likely 100s of millions.

Best way to determine is by looking at a geologic map of the area it was found.

[Kosmo]

17 hours ago, ynot said:

More likely 100s of millions.

Best way to determine is by looking at a geologic map of the area it was found.

Okay...I did a few minutes of Googling for geologic maps of my region and while of course I found some, being so novice/naive, I didn't find a source that seemed like it was useful.  Please point me to an online source that'll get the info we'd want.

[ynot]

Try an image search for Colorado geologic maps....

 

Edited May 21 by ynot

[Kosmo]

On the geologic map, found the shell where my mouse arrow is (between the r and i in "Security".  So (Kpu) has it as Pierre Shale, which apparently dates to about 73-70 million years ago.

Honestly, I'm surprised.  I found this site because I thought there was a small chance it was from the western interior seaway, but because of its good condition and not imbedded in hard rock, would've guessed it most likely from a freshwater lake that existed in relatively recent times (hundreds or thousands of years).

 

So this is definitely a first for me (@ 59 y.o.)...and for what it is, kind of exciting.  Recently finding what folks believe is part of an ammonite after looking for maybe 5 minutes has me thinking I got very luck twice (found the bivalve after just a couple minutes of casual searching as well), or this region is rich in such fossils.

Chances are good I'll be back, possibly with a tool or two (rock hammer?) to break open suspect rocks.  Of course I'd ecstatic to find something from a vertebrate...mosasaur or what have you.

P.S.  The scallop is a little guy...about 2.8 cm (hinge to opposing side).

[Kosmo]

1 hour ago, ynot said:

Try an image search for Colorado geologic maps....

 

My first attempt yesterday to find a geologic map was just too brief before getting distracted.  A smidge more concerted effort and I got it...thanks.  

[ynot]

The  Pierre Shale has some very rich sites in North and South Dakotas.

Do a search for  Pierre Shale here on TFF and You will see some fantastic fossils from this formation.

[Mark Kmiecik]

On 5/20/2024 at 7:12 PM, Kosmo said:

On that note, any idea of the cost is for such testing of this kind of sample?

 

Probably thousands of dollars more than what you would want to spend. The simplest way to date the find is to research the types of bedrock of marine origin that exist where you found this fossil. The fossils found in each of the different strata are already well-known. It's simply a matter of putting in the time at your local library and/or online to do the research. Remember that getting there is half the fun! Just be careful. Once you start down that rabbithole there's no coming back.