Hollowed Out Cavities

I know we saw this once before (at Anatolia?), but here is a great stereo pair showing these weird hollowed out features. They seem to occur in one bedding layer/horizon but they definitely occur as separate cavities. Obviously whatever had filled those cavities was a lot easier to erode away than the surrounding rock. But why would the softer material only occur as these discontinuous pods.

These are the source images for the stereo pair:

Sorry about that -- I got my photos mixed up. Here are the source photos:

Left:

Right:

I wonder if they are related to these berry-free crescents from Sol 110. Look at the two large rocks on the right-hand side. Each has a sort of semi-hollow swath of soil (mud??) on the same side, almost like a flow pattern. Any idea?

Cavebugs, berry free cresents? I'll look closer. There are some interesting geological formations.

aldo12xu,

The decomposing hollows, one my favorite features. Sometimes when you look downhill, of this type of decomposing material, You can find the stuff that fell out. That could be a piece in the puzzle.

I you do look, maybe you can let me know what you find. Bounce might have some pieces to.

Mann, I meant the little "clear" patches in the linked image--no berries or anything else adjacent to the same side of two flat rocks. I agree that other hollows have some odd things in them.

It's possible that these might be boudinage structures. These form when a softer layer is sandwhiched between harder layers. If the package is subject to extensional forces, the softer layer gets stretched out, breaks up into sausage-shaped structures and becomes encased in the harder layer.

Here's a good link on boudinage formation:

[link]

Thanks, Aldo, great link. From my reading of it, boundinage structures would require water (or some other liquid) in order to form.

It's the harder layer(s) that fracture into slabs, and the softer that deform around the slabs. Boudinage structures do not require water, though they can form in wet sediments. They just require a difference in plasticity- such as might happen in igneous intrusions or metamorphic rocks. In metamorphic rocks, for example, a series of layers rich in clay and silt might be interfingered with sandy layers. As deformation proceeds, the fine-grained layers are more plastic than the sandy layers. The sandy layers break up into slabs, and the silty layers deform and surround the slabs.

cavebugs, aha. a berry-free zone. Again, the question, why don,t the round berries, roll down and fill these gully areas up? They look to be gathered right above and adjacent, to, but not in.

A most excellent question, Mann. I think we can agree that berry distribution appears to be a much more recent phenomenon than the fracturing of the bedrock. If these zones are "boudinage structures," one would suppose that the fill material dated to the time of the orginal separation into blocks. Yet if that were the case, there is no reason for these patches to be "berry free." Ergo, either they post-date the appearance of berries and somehow appeared in a way that displaced berries to HIGHER ground (most unlikely), OR they are something else entirely, such as recent frost heaves or drainage channels.

Lockwood is right. I had it the wrong way around. Boudinage would give hard material surrounded by soft material. To explain these hollows we need to have soft material surrounded by hard material. The soft material would be eroded away leaving behind the hollows.

So it must be something else other than boudinage......Could it just be vugs that grew bigger by some process, such as ice freezing and thawing within them?

here is some stuff that appears to have fallen out of one of the decomposing hollows.

What do you see?

This is from a hollow a little ways down from the above chunk.

It has the same shaped material, making up its composition. Its like a pile of rotting leaves. I learned a new word yesterday, "squamulose".