One More Bland Blob For Your Opinion

[Wrangellian]

I suppose these are boring to most people but they have piqued my interest as of late, when I started noticing how many of them there are and how consistent their form. It appears as a trough-shaped thing made of carbonate, lighter than the surrounding black shales.

These shales (Haslam Fm, Upper Cret.) are full of odd blobs and lumps and tube-shaped things that I have always ignored, assuming they were non-fossil, but they don't seem to work as burrows or concretions either, and considering the possibility of calcareous algae and the like, I started to wonder. (Do burrows ever have a U-shaped cross-section, and why would they have a lighter, calcareous appearance?)

This one is not the best example, I need to pick up more when I see them, but hopefully you can see what I'm looking at.

There are some lumpy, grainy shapes as well:

Possibly a (sideways) U-shaped cross-section on the end here too but it is faint.

Lots of variety of shapes aside from the usual roundish concretions, many nondescript but some recurring patterns among them such as the above. They all have a calcareous/carbonate composition (I assume from the lighter color).

Any opinions? Biogenic or not? What would account for the formation of this long trough shape in particular? I will make a point of picking up more/better samples and add them here.

[Missourian]

'Boring' can be fertile ground for discovery.

Have you seen the half-tubes in situ? It'd be interesting the see them in context.

[Wrangellian]

'Boring' can be fertile ground for discovery.

Have you seen the half-tubes in situ? It'd be interesting the see them in context.

That's what I was thinking! But it seems you and I are rare in that regard.....

I need to take more in situ pics - I will do that next time I'm up there. I am usually too busy digging fossils..

I did take a pic of this piece, containing numerous blobs, but the matrix is also hard unlike the usual shale, so maybe it's not as representative of the above items but may be related:

Note my shoe for scale (all I had at the moment!)

[Missourian]

That's what I was thinking! But it seems you and I are rare in that regard.....

It's not so much that. It's that most people are unaware that some things aren't boring.

[Missourian]

Hmmm... Perhaps:

1. Sedimentation.
2. Burrowing.
3. Very early diagenesis, including oxidation.
4. More sedimentation that fills burrows.

The tube-like structures could be 'diagenetic rinds' around the burrows.

[Wrangellian]

It's not so much that. It's that most people are unaware that some things aren't boring.

That's what I mean, and what I thought you meant!

[Wrangellian]

Hmmm... Perhaps:

1. Sedimentation.

2. Burrowing.

3. Very early diagenesis, including oxidation.

4. More sedimentation that fills burrows.

The tube-like structures could be 'diagenetic rinds' around the burrows.

Certainly there is oxidation around these blobs, but what would account for the blobs themselves? There could be a variety of things happening up there I guess. I have an odd burrow-looking thing from the Chemainus site which seems to have such a rind as you describe. I'll post pics of it too when I get them done.

Also I have things that look like microbial mats or some such growth, from both sites, which I may have posted elsewhere but will post here too. Stay tuned...

[Missourian]

but what would account for the blobs themselves?

What's the lithology of the bed above (if present)?

I'm picturing something like this:

[Wrangellian]

You could be right, I need to take a closer look at it next time, but I found it loose where it sits and have not seen any bed that it could have come from - more likely a large concretion type of thing in the shale than a distinct bed. Here are a couple in-situ shots of the sort of concretions this site is full of -the one in 2nd shot is comparable in size to the one with the blobs:

[Wrangellian]

Had a chance to get up the mtn again today.. Didn't see everything I'd like to take pics of up there but got a few. I'll start with a chunk I collected earlier with bivalves in it - what I am interested in here is all the blobs and branches the bivalves are surrounded by. Whatever these things were seem to have been the bivalves' habitat. Hope this pics show well enough..

They are not simple concretions.. but they don't seem to be trace fossils either. There is little to no consistency, they seem to vary between the two... branches, blobs, and anything in between.

Edited June 5, 2014 by Wrangellian

[Wrangellian]

A couple chunks full of these limy looking blobs:

Not much in the way of texture/detail in any of it to show, but one piece in there seems to have something fibrous (closest thing I have found before is bone)..

[Wrangellian]

Now today for the first time I noticed these little discs:

Keys and fingers for scale.

I am not sure if they are related to the above items. These all occurred in one little area and I am not sure if I have seen them anywhere else. As you can see they are little disc-shaped things with a slickensides-type texture, at different orientations in the rock. Some of the ones that have been broken seem to show a thin 'wafer' core surrounded by the limy material as you can see in one pic.

My first thought was they might be related to those pseudofossils recently posted elsewhere from the Triassic of Australia.. but I don't know. Any ideas on any of this?

Edited June 5, 2014 by Wrangellian

[Wrangellian]

First one annotated:

Loose ones at top - numerous cross-sectioned ones embedded in one chunk below.

Slickensides texture (negative examples):

Edited June 5, 2014 by Wrangellian

[Plax]

A couple chunks full of these limy looking blobs:

DSC_0254 shr.jpg DSC_0255 shr.jpg DSC_0257 shr.jpg

Not much in the way of texture/detail in any of it to show, but one piece in there seems to have something fibrous (closest thing I have found before is bone)..

reminds me of the crab bearing concretions in the island creek member of the Peedee. Dark colored silt with light gray concretions. These are often burrow shaped or just amorphous blobs or masses. They come in varying degrees of hardness from hammer ringing to crumble at a touch. Most have nothing at all in them. Some are accompanied by long straightish darker cylinders running through them usually along an edge.

[Wrangellian]

Yes that description sounds similar. Usually a concretion forms around something, but what can account for these? I have not noticed any crabs or anything in them, but then I don't bother to break them (most seem like they're on the hammer-ringing side...) and those that are already broken show nothing. If there is anything in there, like these bivalves, they are not necessarily at the center of a concretion - sometimes on the side of one. I also find ball concretions that look like a worm went all thru it to eat whatever ultimately caused the thing's formation. I should add some pics of those (stay tuned).

[Plax]

will try to get some pics of mine for reference over the weekend

[Auspex]

Concretions often accrete around an organic nucleus (bacteria play a big role), but the nucleus is not always preserved.

[Plax]

here's the concretions in outcrop, note the ICM pinches out to the right of the photo

[Plax]

and some more pics

[Missourian]

I think many (if not most.... or all?) concretions are, for all intents an purposes, the rock lithification process 'frozen' in time. That is, cementation begins at various nucleii and spreads out along bedding planes. Eventually, the concretions would merge into continuous beds. In many cases, though, the rock is compacted before the process completes. I came to this conclusion when observing beds in the upper Winterset Limestone:

http://www.thefossilforum.com/index.php?/topic/25424-backyard-trip/?p=322745

In some spots, the sediment is fissile to blocky shale. In others, there are continuous, wavy beds of micritic limestone. In the outcrop shown above, the concretions had grown quite large but stopped before they merged. Particularly interesting is the distorted beds and burrow here:

Features marked in color, with concretions in magenta, bedding planes in yellow, and burrow in green:

These features nicely display the thickness of the sediment before and after compaction. So basically this shows that these concretions formed early in the whole process. Exceptional preservation of fossils in rare cases is another indicator.

In your case, the concretions could have formed around a fossil, along one side of a burrow, or in various spots for no obvious reason. It comes down to the conditions being favorable for crystal growth.

Edited June 6, 2014 by Missourian

[Wrangellian]

Thanks all..

So the limy-looking composition in a concretion is just a crystallization or some other form of chemical alteration of the material that's already there? Otherwise, where does the limy 'cement' material come from when the surrounding rock is black shale?

[Missourian]

So the limy-looking composition in a concretion is just a crystallization or some other form of chemical alteration of the material that's already there? Otherwise, where does the limy 'cement' material come from when the surrounding rock is black shale?

Possibly from the dissolution of calcareous shells or from migrating groundwater (or both).

[Wrangellian]

Would the sea have been acidic enough to dissolve a lot of shells during the Late Santonian, does anyone know? Or is this more or less a constant thing even today? The larger shells at this site like ammonites display some dissolution in their upper sides that were exposed above the sediment they came to rest on, but otherwise shells are well preserved and complete (if crushed). That's a whole other question I guess. Otherwise I'm not sure where all that calcium would have come from, but I suppose the groundwater thing makes sense as long as there is a source of dissolved calcium, but I may be way out of my league here..

What would you make of the trough-shaped 'burrows' (better pics yet to come) - would they be 'concretized' burrows that collapsed sometime during compaction?

[Missourian]

There has been a tremendous amount of shell destruction through the ages. Otherwise, imagine how many fossils there would be if all were preserved.

I don't think the pH of seawater would have much of an effect in most cases. (Edit: Dissolution can occur if the shells fall below the aragonite compensation depth (ACD), which would have been a couple kilometers or so. Your deposit may have been that deep).

Mechanical and biologic processes can do a lot more damage. Once buried, the shells can be bioeroded or dissolved before compaction, which could end up leaving no trace of their existence. This could be a source of CaCO3 in intrapore water.

In the case of the ammonites, the better preservation on the bottom sides could have had something to do with some process at the shell-sediment contact (microbes perhaps?, which is how the Ediacaran biota may have been preserved. Edit: Shells below the ACD could have been dissolved on top, at least).

In the groundwater environment, aragonitic shells are less stable than calcitic ones. You may have noticed that certain fossils (forams, echinoderms, bryozoans, brachiopods) are often better preserved than others (mollusks), even in the same deposit. The ammonites are still there, but they likely had been completely dissolved and replaced with calcite.

I still have no clue what could have produced the troughed things. There are various process that could have interplayed that can be difficult to sort out.

And no, you're not out of your league. You've come this far already. Anything remaining is just details. Anyway, struggling to understand it all is so much of the fun.

Edited June 10, 2014 by Missourian

[Wrangellian]

Sometimes I just want the answers given to me but I guess they only come from a back-an-forth discussion with other members... Until then I have had my own theories, not based on much I suppose..

There are no forams, bryos, etc. here - just Uintacrinus, some unID'd echinoids, a rare brach, but mostly mollusks: ammos, bivalves, snails, scaphs. And plant material. Aside from the ammos which have their topsides missing, in specific localized spots I find empty cavities where anything from bivalves to echinoids have been dissolved out, apparently after lithification, and thus far I have supposed this to be due to the tectonic activity involving hydrothermal action that occurred in this area during the Paleogene. There is usually an oily sheen and a fissile nature to the rock where this occurred. Where it has not occurred, the fossils that remain are well preserved other than those missing ammonite topsides. I have not noticed any half-dissolved shells that could not be accounted for by the groundwater theory, in my mind, but I could be wrong.

I'd really like to know what could account for those 'forests' of concretions, of various irregular shapes, all tightly packed together. I have seen no widespread layers of these that would imply an environment/chemical conditions favorable to their formation all over - just localized clumps of them as you see above. Maybe biological communites of something - seaweed/algae perhaps, with burrowing organisms and those bivalves mingling in here and there? That chunk with the bivalves in particular tells me there was something about that spot that the bivalves liked which also produced those smaller concretiony lumps around them.