Cepholopods and concretions of the Britton Formation

[Nimravis]

Kim you did it again, you are my favorite Fossil Forum trip reporter. You reports always take us along for the hunt and ice cream- LOL. Thanks for taking the time to be so detailed, though it does not help when I am having a typical night of not being able to sleep, like tonight. 

 

P.S.  Great finds and love the pics.

[bone2stone]

Kim,

It stands to reason that there should be some crab material coming from that place.

Everything you have posted, is found in the same deposits as the crabbies. 

I know they are difficult to see. 

BTW: That particular rock is extremely difficult to clean off. No magic solution that I know of.

           There will be times when you find one of the concretions that cleans easily, but that does not occur often.

 

PS, I bet you were tired by the time you got home.

[KimTexan]

19 hours ago, Innocentx said:

Nice bit of nacre on that last baculite.

Do you know when nacre becomes ammolite or how you make the distinction between the two?

Most of my cepholopods are dull, but I found a few fragments that had the mother of pearl look to them and only 3 fagments of them that I think have bits of ammolite on them.

 

9 hours ago, bone2stone said:

Kim,

It stands to reason that there should be some crab material coming from that place.

PS, I bet you were tired by the time you got home.

You must not haven’t stumbled across my concretion post. I did find crabs, but didn’t realize it for several days until I was rinsing off all that I had collected. I think I may have found 7-8, but I’m only certain 4 or so of them are crabs.

I gave one of the uncertain ones to @Heteromorph when I saw him at the DPS meeting along with a number of other fossils. Unbeknownst to me it happened to be his birthday.

I’ll get to posting that in my next segment. I will post a lot more photos of all the stuff I found too. I just haven’t had time to take pics of everything yet. Also when I get ready to take pics I end up wanting to prep one or another some more before taking pics. Then I end up not taking pics. I’ll get there. I may never finish all the prep work though.

 

Regarding being tired, I was not tired. I was excited to have found the ammonite. 

Plus this site is a walk in the park compared to some of my trips to the NSR. I have not had to extract anything either. Some sites I’ve been to I’ve spend a long time hammering trying to extract something. Hammering with a sledge hammer is exhausting for me.

Also, the fossils are fairly small so far. So no carrying out multipul 10-20+ lbs ammonites. Although, I have heard of people finding skeletons in the formation. I’m sure that would wear me out trying to haul out.

[Kane]

7 minutes ago, KimTexan said:

Do you know when nacre becomes ammolite or how you make the distinction between the two?

Most of my cepholopods are dull, but I found a few fragments that had the mother of pearl look to them and only 3 fagments of them that I think have bits of ammolite on them.

 

 

From my understanding, ammolite occurs in Cretaceous ammonites along the Rocky Mountain stretch, and that it is almost synonymous with nacre insofar as both contain aragonite. I'm not sure if that same nacre on baculites is associated with ammolite as it is with ammonites. I know there can be some slight variations in the mineral composition... And on that note, I tag @ynot!  

[DPS Ammonite]

Ammolite is a trade name for fossilized nacre. Here is a great article on Ammolite that defines it as:

 

"Ammolite is vivid iridescent fossilized ammonite shell (aragonite) that thus far has been obtained from only two ammonite species (Placenticeras meeki and P. intercalare), and only from those found in the Bearpaw Formation of southern Alberta, Canada."

 

 

BTW, the nacre from the Britton Formation needs to have a protective coating put on it beacause it is very fragile and flakes off easily. I used spray acrylic clear coating from the hardware store. Butvar, PVA  etc. dissolved in the proper solvent might be better.

[ynot]

1 hour ago, Kane said:

From my understanding, ammolite occurs in Cretaceous ammonites along the Rocky Mountain stretch, and that it is almost synonymous with nacre insofar as both contain aragonite. I'm not sure if that same nacre on baculites is associated with ammolite as it is with ammonites. I know there can be some slight variations in the mineral composition... And on that note, I tag @ynot!  

All I know is ammolite is a trade name for cephalopod shell that has an iridescent sheen to it,

There are several locations that have "ammolite" type iridescents other than the original location in British Columbia.

[KimTexan]

I’m not sure exactly what distinguishes the nacre from ammolite. From what I have read the color is a result of the aragonite 

 

@Kane I found this with regards to the nacre in different mollusks

This is from the wiki page for nacre

“The form of nacre varies from group to group. In bivalves, the nacre layer is formed of single crystals in a hexagonal close packing. In gastropods, crystals are twinned, and in cephalopods, they are pseudohexagonal monocrystals, which are often twinned.

Nacre is composed of hexagonal platelets of aragonite (a form of calcium carbonate) 10–20 µm wide and 0.5 µm thick arranged in a continuous parallel lamina.^[2] These layers are separated by sheets of organic matrix composed of elastic biopolymers (such as chitin, lustrin and silk-like proteins). This mixture of brittle platelets and the thin layers of elastic biopolymers makes the material strong and resilient, with a Young's modulus of 70 GPa(when dry).^[3] Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which inhibits transverse crack propagation. This structure, at multiple length sizes, greatly increases its toughness, making it almost as strong as silicon.

Nacre appears iridescent because the thickness of the aragonite platelets is close to the wavelength of visible light. These structures interfere constructively and destructively with different wavelengths of light at different viewing angles, creating structural colours.

The crystallographic c-axis points approximately perpendicular to the shell wall, but the direction of the other axes varies between groups. Adjacent tablets have been shown to have dramatically different c-axis orientation, generally randomly oriented within ~20° of vertical.^[4][5] In bivalves and cephalopods, the b-axis points in the direction of shell growth, whereas in the monoplacophora it is the a-axis that is this way inclined.^[6] The interlocking of bricks of nacre has large impact on both the deformation mechanism as well as its toughness.^[7] In addition, the mineral–organic interface results in enhanced resilience and strength of the organic interlayers.”

The nacre page had a lot more info than this. It was quite a lengthy page.

 

This is from the wiki page for ammolite

”

An iridescent opal-like play of color is shown in fine specimens, mostly in shades of green and red; all the spectral colors are possible, however. The iridescence is due to the microstructure of the aragonite: unlike most other gems, whose colors come from light absorption, the iridescent color of ammolite comes from interference with the light that rebounds from stacked layers of thin platelets that make up the aragonite. The thicker the layers, the more reds and greens are produced; the thinner the layers, the more blues and violets predominate. Reds and greens are the most commonly seen colors, owing to the greater fragility of the finer layers responsible for the blues. When freshly quarried, these colors are not especially dramatic; the material requires polishing and possibly other treatments in order to reveal the colors' full potential.

The ammolite itself is actually a very thin sheet, ca. 0.5–0.8 millimeters (0.02–0.03 inches) in thickness. Rarely is ammolite without its matrix, which is typically a grey to brown shale, chalky clay, or limestone. So-called "frost shattering" is common; exposed to the elements and compressed by sediments, the thin ammolite tends to crack and flake; prolonged exposure to sunlight can also lead to bleaching. The cracking results in a tessellated appearance, sometimes described as a "dragon skin" or "stained glass window" pattern. Ammolite mined from deeper deposits may be entirely smooth or with a rippled surface.”

 

There is a lot of interesting stuff in there that I found very enlightening.  Like the comment about the aragonite plate arrangement inhibiting transverse cracks. That would explain in part why we find so many fossil shells and likely ammonites.

 

I’m not sure all that I read completely answered my question. The ammolite page basically said ammolite was fossilized nacre. One distinction I saw was that “Nacre is composed of hexagonal platelets of aragonite (a form of calcium carbonate) 10–20 µm wide and 0.5 µm thick arranged in a continuous parallel lamina” whereas the ammolite was said to be 0.5-0.8 mm thick. But one is talking about the ammolite thickness itself and the other is just the thickness of the aragonite plates in general not nacre as a whole.

 

I do see a fair amount of aragonite out in the field in addition to calcite, but I can’t always tell which is which unless it is in the classic free form growth with the thin needle/hair thin crystals vs the crystals on the rocks in the one pic.

[Innocentx]

4 hours ago, KimTexan said:

Nacre appears iridescent because the thickness of the aragonite platelets is close to the wavelength of visible light.

Extreme eye candy.

[dalmayshun]

always enjoy your trip reports. I understand the heat stroke thing with your daughter...three years ago I got hit, and now have little tolerance for heat...drinking lots, LOTS of water is a bit helpful to me, besides having friends who fossil hunt and watch out for me...they sometimes catch me before I begin to feel aweful...they say I start looking pale, and tell me to drink. 

[Plantguy]

Nice fossil finds and some plants to go--yeah! Great report. Continued hunting success! Regards, Chris