Foss-ilarm - cool weathering, not stromatoporoid

[SteveE]

This post is about a fossil look alike, or to quote my kid, "a foss ilarm".

 

Earlier this year I was scratching my head about stromatolites, stromatoporoids, and algae and coral in general.    It started with finding what I dubbed "the sandwhich rock" (first 3 pics) at a roadcut in Blair County, central Pennsylvania (US).   The outcrop is Mifflintown-Bloomsburg (undivided).   My best guess is this form the Mifflintown part.  

 

 

Friends that know their stuff told me about "honeycomb weathering".   Besides the Wikipedia article, there is more than I ever wanted to know in the Treatise on Geomorphology Volume 4, Weathering and Soils.

 

I returned to the site and took more photos.   This outcrop is on a very busy city highway and just below a freeway overpass.  

I wanted to know if the weathering is just from modern-day exposure, so I poked at the rock layer until I found a piece that was still in place, but loose.   To my surprise, it was olive brown and pitted like this all the way around, even the back side which had not been exposed to wind/sun. 

 

 

I removed that piece and cracked it open.... and was even more surprised to find the inside of the rock is light grey with brachiopods and broken trilobite bits.   it failed the vinegar test (no fizz).     The inside of the rock looked untouched, to my noobie eye.  And that makes me think that all this pitting is from very recent time.

 

 

In my superficial reading, I've seen frequent references to salt as a common factor in weathering.   Even though the backside of the rock was still really pitted (R side of pic with my fingers), there is probably a lot of highway salt that makes it way into the soils and float on the face of the outcrop.   Is it a player?  Beats me, I've gone as far as I can thinking about this.  Except to note my extreme-environment microbiologist wife always likes to say "microbes rule all!!"  

 

 

 

 

[Fossildude19]

Interesting geological "Boxwork" formations.   

 

Wikipedia LINK.

[sTamprockcoin]

Hey Steve,

I live in the same area/ town. I compiled a list of 15+ sites for fossil & mineral collecting in town.  There are many intetesting weathering formations. PM if you're intetested in more info. 

 

[ynot]

12 hours ago, SteveE said:

To my surprise, it was olive brown and pitted like this all the way around, even the back side which had not been exposed to wind/sun. 

Water is known as the great dissolver. It will "wick" through a crack in the bedrock and dissolve the "softer" minerals on the surfaces of said crack The water then carries any dissolved minerals away.

When You look at the fresh break You can see an oxidized (iron) "crust" around the edges (where it was already exposed).

Wind and sun may aid in this type of weathering, but are not necessary for the process.

[SteveE]

9 hours ago, sTamprockcoin said:

Hey Steve,

I live in the same area/ town. I compiled a list of 15+ sites for fossil & mineral collecting in town.  There are many intetesting weathering formations. PM if you're intetested in more info. 

 

Well met, pm sent!

 

[SteveE]

19 hours ago, ynot said:

Darwin said: " Man sprang from monkeys."

Will Rogers said: " Some of them didn't spring far enough."

Funny... and sooOOoooo true.  Thanks for the weathering input.  It would be neat to see this same part of the formation away from any roads, and compare "normal" water exposure to weak brine exposure.

[ynot]

3 hours ago, SteveE said:

compare "normal" water exposure to weak brine exposure.

I doubt that salt would have much effect on the rock, although it does accelerate the oxidation of iron minerals. Salt is a neutral (not acid or base) mineral and would only fill some of the available space the water has to "carry" other minerals away.

[SteveE]

10 hours ago, ynot said:

I doubt that salt would have much effect on the rock, although it does accelerate the oxidation of iron minerals. Salt is a neutral (not acid or base) mineral and would only fill some of the available space the water has to "carry" other minerals away.

A reasonable hypothesis....   I'm not skilled enough to recognize a negative result (definitely recognize the same layer, even though it has no boxwork) but if I find a likely positive (boxwork away from roads that I __think__ is the same layer) I can followup and report that here.   Thanks for your thoughts.