Cambrian Stromatolite

[TNCollector]

Got the itch to collect and study some stromatolites, so I did some searching and feel that I successfully scratched the itch. I found a section of the Cambrian Copper Ridge dolomite that exposes a plethora of stromatolites of various morphologies. Many of them look as if they are straight out of Shark Bay in Australia, with the characteristic domal structure attached to a thinner holdfast on a hard substrate. Stromatolites are formed over a long period of time in tidal zones by colonies of photosynthetic bacteria and/or algae that form sticky layers that trap sediments and concrete them into layers. The colony then grows over the older, cemented colony and the cycle repeats itself. The process is obviously a lot more complicated than that, but I digress.

 

Stromatolites are the oldest confirmed fossils to have been discovered, with the current oldest ones to be confirmed coming from the Strelley Pool Chert formation in Western Australia, dating back to the early Archaen at approximately 3.4 billion years ago. At that point in time, the Earth's atmosphere was largely devoid of oxygen, primarily being composed of CO2. Over the next several billion years, these stromatolites were largely responsible for oxygenating the atmosphere. They may not look like much, but these bacterial colonies were extremely important to creating Earth's biosphere. After the Cambrian explosion, stromatolites began to become quite rare in the fossil record, with multicelluar organisms feeding on them and disrupting the cementation process. After that point and to this day, stromatolites primarily thrive in extreme environments were the animals that feed on them cannot survive. The stromatolites in the Shark Bay, Australia area live in a hypersaline environment created by a seagrass barrier just off the coast. Unfortunately climate-change induced increases in precipitation are causing floods that reduce the salinity of this location and threaten the survival of the stromatolite colonies. 

 

With that information, enjoy these photos of stromatolites. Cube scale is 2cm on each side

 

Large domal type in the position it would have grown in:

 

Another domal type, almost spherical in shape, composed of multiple separate colonies that appear to have fused together:

 

Another domal type:

 

Cross section of broken laminar piece showing growth layers over an oolitic limestone substrate:

 

A different one, I hope to polish this face:

 

Layers under microscope:

Edited March 21, 2021 by TNCollector

[Tidgy's Dad]

Lovely specimens. 

[Ludwigia]

Are these all from Tennessee?

[FossilNerd]

We don’t see stromatolites very often. Beautiful.   Thanks for sharing! 

[TNCollector]

3 hours ago, Ludwigia said:

Are these all from Tennessee?

Yes they are. Copper Ridge Dolomite. All of the stromatolites are chertified which preserves a lot of the details that are often missing.

[TNCollector]

Got another one to show. I am quite fond of this one. It looks like it literally just came out of Shark Bay! I would like to take some thin slices of these and see if any of the original bacteria are preserved. Stromatolites from some other localities have preserved the bacteria in silica. Reference cube is 2cm on each side.

[Wrangellian]

Missed this til now. Nice ones! I'd hesitate to slice that last one. I don't know what your chances are of finding the actual bacteria preserved. Do you have the means to see them and have you tried other pieces that have preserved bacteria?

I'm thinking of starting a 'Show us your stromatolites' topic, where I will show some of mine (once I get some photos) and invite others to show theirs. (I don't think there is such a topic yet?)

[crabfossilsteve]

Those are very cool and I especially like the one with the oolitic limestone.  I too wouldn't slice that last specimen.  Too nice as is.

[Yoda]

Wow, nice finds 

[MaryLynnRocks]

On 3/20/2021 at 9:08 PM, TNCollector said:

Got the itch to collect and study some stromatolites, so I did some searching and feel that I successfully scratched the itch. I found a section of the Cambrian Copper Ridge dolomite that exposes a plethora of stromatolites of various morphologies. Many of them look as if they are straight out of Shark Bay in Australia, with the characteristic domal structure attached to a thinner holdfast on a hard substrate. Stromatolites are formed over a long period of time in tidal zones by colonies of photosynthetic bacteria and/or algae that form sticky layers that trap sediments and concrete them into layers. The colony then grows over the older, cemented colony and the cycle repeats itself. The process is obviously a lot more complicated than that, but I digress.

 

Stromatolites are the oldest confirmed fossils to have been discovered, with the current oldest ones to be confirmed coming from the Strelley Pool Chert formation in Western Australia, dating back to the early Archaen at approximately 3.4 billion years ago. At that point in time, the Earth's atmosphere was largely devoid of oxygen, primarily being composed of CO2. Over the next several billion years, these stromatolites were largely responsible for oxygenating the atmosphere. They may not look like much, but these bacterial colonies were extremely important to creating Earth's biosphere. After the Cambrian explosion, stromatolites began to become quite rare in the fossil record, with multicelluar organisms feeding on them and disrupting the cementation process. After that point and to this day, stromatolites primarily thrive in extreme environments were the animals that feed on them cannot survive. The stromatolites in the Shark Bay, Australia area live in a hypersaline environment created by a seagrass barrier just off the coast. Unfortunately climate-change induced increases in precipitation are causing floods that reduce the salinity of this location and threaten the survival of the stromatolite colonies. 

 

With that information, enjoy these photos of stromatolites. Cube scale is 2cm on each side

 

Large domal type in the position it would have grown in:

 

Another domal type, almost spherical in shape, composed of multiple separate colonies that appear to have fused together:

 

Another domal type:

 

Cross section of broken laminar piece showing growth layers over an oolitic limestone substrate:

 

A different one, I hope to polish this face:

 

Layers under microscope:

 

I would love to talk to you, I'm in Straw Plains, TN & recently discovered a huge pile of stromatolite's. A friend of mine owns the property, 4 acres right where Knox, Jefferson & Sevier counties all meet. On my first visit, 3 mths ago, I almost jumped out of the car halfway way up the driveway. As soon as you pull off the road, you're driving over them, they're along the roadside & all over his property. I was told I couldn't have them here but knew there was nothing else they could be. I thought that UT would be interested in coming out but haven't heard back from them. I had reached out to a few of the local rock shops & was able to get Rocky Top rock shop owner, Yvette, to come out last Friday. She came & is positive these are stromatolite's & saw that there are several different formations. I had also come across a bulletin form the Geological Society of America from 1961 about a study that was done in the 50's on an 8 mile area where Jefferson & Sevier counties meet. That's exactly where this property sets, but it technically is inside Knox county. I knew this has to be the zone they mention in that bulletin, they mention the formation having eye's or knot's. I had started a collection of what I also had thought of as eye's a couple weeks before I found that. But it bugged me that this was Knox county, so I dug a little deeper. This area is known as Strawberry Plains, TN or Straw Plains to locals. Knoxville annexed this area back in the 90's, before that this land was Jefferson county. There is a large outcrop that's exposed that has long rows in the ground behind it that are moss covered stromatolite's that are on top of the ground. This place is awesome, it's been left untouched by man. This entire hill is covered in them, top to bottom, anywhere you try to dig here, you'll hit rock. It's a steep hill that didn't have access when he bought it from the county over 20yrs ago. He had to cut a driveway all the way to the top & had 1 heck of a time because it was made up of stromatolite's in places & he bulldozed them into several piles on the property. He hated this rock, had no use for it. I haven't been able to stop rock hounding since I got here. I've got a cool collection too. Problem is, I was only supposed to be here a few weeks. It's been over 3mths now & I've not covered even half of this place. I'd love to get your advice on some of these & a few other thing's I've come across. I've also got alot of what looks to be petrified wood. I was also told I couldn't have that here but the owner of the rock shop agreed with me after seeing them. She's also very curious to find out what the white, bone shaped rock are. They are big & very heavy. I would appreciate any help I can get with this. I've got alot of pics & a few videos I've put in an album on Google photos

https://photos.app.goo.gl/cxoMRvt2rwt8Ho6c9