Odd deposition surface... biological?

[Wrangellian]

I'd like to put this up for opinions... A thin limy layer interrupting the usual black shales from my usual Upper Cretaceous site (there are bits of the shale still stuck on top here and there). To me it screams of something like a bacterial mat, but I don't know. I can't imagine any non-biological process of formation, but maybe there is one that I haven't considered? The last pic shows an edge to give an idea of the thin lighter-colored layer. These pieces were all from one contiguous surface a couple feet square or so on a chunk of shale - the only one I have found up there so far with this particular pattern, but in other spots at this site and other sites, I have found similar calcareous(?) 'blobs' of all sizes that seem to have something to do with life, sometimes associated with obvious fossils such as Ino- and Sphenoceramus shells (no fossils were evident on this surface, though).

 

[ynot]

Evidence of a change in the environment. Maybe a hurricane went through? Or just a flood?

[Fossildude19]

Microbial matt? 

[Wrangellian]

8 hours ago, ynot said:

Evidence of a change in the environment. Maybe a hurricane went through? Or just a flood?

I think a storm could have deposited the layer in the first place, but how are those bumps formed on top?

[ynot]

1 hour ago, Wrangellian said:

how are those bumps formed on top?

Are they bumps or filled depressions? Are You sure of the ups and downs?

Critter action?

[Wrangellian]

I'm not sure of the ups/downs, but to me it seems far more likely that the limy layer's surface was made up of bumps rather than the corresponding shale layer being covered with pits which the limy layer just happened to settle on: If you can tell by my pics, the entire surface (of the limy layer) has a pebbled look to it. If this is the bottom of the limy layer, the limy stuff must have been made up of various-sized lumps when it was deposited, but this was not in the form of pebbles, as apparently the limy material itself is uniform/graded (fine grained sand, at most).

[supertramp]

It reminds me of the "nodular pattern" someway related to early diagenesis induced by organic matter

https://www.google.it/search?q=calcare+nodulare&source=lnms&tbm=isch&sa=X&ved=0ahUKEwilmLO327jWAhXGJJoKHWaYAPoQ_AUICigB&biw=1280&bih=918#imgdii=w4Tx9L4qFw2aVM:&imgrc=I4PwVc41Q0VfpM:

 

ciao

[ynot]

2 hours ago, Wrangellian said:

. If this is the bottom of the limy layer, the limy stuff must have been made up of various-sized lumps when it was deposited

Could it have been an ash fall that filled divots in the layers of shale?

Have You done a vinegar test to see if it is calcite / limestone?

[Wrangellian]

9 hours ago, supertramp said:

It reminds me of the "nodular pattern" someway related to early diagenesis induced by organic matter

https://www.google.it/search?q=calcare+nodulare&source=lnms&tbm=isch&sa=X&ved=0ahUKEwilmLO327jWAhXGJJoKHWaYAPoQ_AUICigB&biw=1280&bih=918#imgdii=w4Tx9L4qFw2aVM:&imgrc=I4PwVc41Q0VfpM:

 

ciao

It does look similar...

 

9 hours ago, ynot said:

Could it have been an ash fall that filled divots in the layers of shale?

Have You done a vinegar test to see if it is calcite / limestone?

I wondered if any of these layers were volcanic but local experts have told me they think it's just submarine avalanches or storm deposits. That reminds me, @Doctor Mud was going to examine samples I sent him but I don't think he ever did...

I will do a vinegar test and report back.

[Wrangellian]

I do see fizzing with vinegar. I guess that precludes a volcanic origin?

[abyssunder]

I posted in the wrong topic.

 

[Wrangellian]

I've already forgotten, if I saw it.