Need opinions

[Njnewbie]

Found this piece of mudstone at a site that is new to me. Curious to know what could of made these indentations. Any suggestions would be great. Formation is  Lockatong, area is west central New Jersey

 

 

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[caldigger]

That's easy! It's a juvenile rock with acne.

[abyssunder]

That's good !

Maybe the long, narrowing ones are septarian type mud cracks, the little bumps and craters could be result of burrowing organisms trying to reach the surface or digging in the substrate (ichnofossils).

[Wrangellian]

Interesting... I was thinking raindrops but then why are they concentrated in that one spot? Must be some kind of ichno as abyssunder says.

[FossilDudeCO]

I don't know the age of these.

 

But, in some of the mud flats out here in Colorado these similar impressions have been theorized to be gas bubbles.

For a while thought to be raindrops.

The "gas bubbles theory" is explained as air forced up in the thickening, drying mud holes.

Air escapes, bubble pops, small indentation hardens as the mud is too thick to flatten back out, and is covered by the next layer.

 

I can't tell from your photo if these are positives of negatives.

 

Could be either the air bubble trace fossil itself, or the infill from the "bubble hole" 

[sdsnl]

14 minutes ago, FossilDudeCO said:

The "gas bubbles theory" is explained as air forced up in the thickening, drying mud holes.

Where does the air come from? Is it air originally dissolved in the water of the mud, or something else? 

[FossilDudeCO]

 

2 minutes ago, sdsnl said:

Where does the air come from? Is it air originally dissolved in the water of the mud, or something else? 

 

I believe it is just air trapped as water evaporates and dissipates.

In some algae deposits I believe they list them as bubbles formed by CO2 released from the organic material.

Let me see if I can find Martin's paper when I get home.

[sdsnl]

9 minutes ago, FossilDudeCO said:

 

 

I believe it is just air trapped as water evaporates and dissipates.

In some algae deposits I believe they list them as bubbles formed by CO2 released from the organic material.

Let me see if I can find Martin's paper when I get home.

Ah, if it is CO2 I can understand it, possibly the algae is under a little depth and when the gas is produced, simply by density water has to drop? Just like if you blow air through a straw into your hot chocolate, air would be trapped and bubbles would appear at the surface. As a kid I would see how high I could get the bubbles rise in one breath 

[FossilGuy1024]

I did notice some interesting features to some of the indentations. I'd expect bubbles to be simple round divets.

 

 

 

 

 

[Fossildude19]

Trace fossil - maybe something like Psilonichnus?

 

 

[Pemphix]

In algae-laminated habitats, those spots are mostly identified as gas-bubbles as FossilDudeCO already mentioned.

The bigger "stripes" looks like filled mud-cracks as it is typical for the environment.

For example you can find similar pieces in the triassic location Winterswijk (Netherlands) in which it is very common and scientifically well described.

But to tell more, it would be needed to know more about the strata of the find.

In the meantime: +1 for FossilDudeCO.

 

[Njnewbie]

Thanks for all of responses. All the theories seem plausible. Here is some more info that may help. The lockatong formation is part of the Newark supergroup and is upper triassic. The piece I have is a laminated mudstone. The top layer is very thin. The next three layers are about 1/2 inch thick, then changes to a 3/4 in thick sandstone, bottom layer is back to very thin mudstone. There is arthropod or worm trace fossils on the exposed layer as you can see in the lower righthand corner of the pictures. Guess Im gonna have to chip away some layers to see if the indentations continue through the lower layer or are just surface impressions.