Victoria Annulus, Discusions about Victoria's Apron Options

[algorimancer]

The microcospic picture taken on scrapped track. It has no spherules but only fine grain -powder- and it is somewhat endurated.

I see 2-3 ratted blueberries, plus 3 distinct horizontal layers. Looks like ratted evaporite to me.

[djellison]

It's soil pushed flat by the mossbauer.

Doug

[glennwsmith]

I hate to keep obsessing about this bit of conchoidally fractured pebble, but Nirgal's superb colorization adds to its interest. A fractured face is visible, while we can just make out the margins of the downward face -- and this would seem to indicate a patina typical of the alluvial (!) chert gravels found in abundance in, among many other places, my home state of Louisiana. So one thesis is that, among the layers disturbed by the impact which created Victoria, is bed of alluvial gravel !?! There are of course other weathering processes which can create patinas, but it is interesting to note the relative freshness of the fractured surface.

[RNeuhaus]

Gleenwsmith: The stone is the original comparing to the rest. It has good edges, a fractured stone after so many years, between thousand millions and millions years. Very strong stone which has withstanded the aeolian and hydro erosion . About the chemical erosion not like to the spherules which is the product of the chemical process ?

I have enclosed a picture. The surface has a very fine grain that leaves the wheels neatly well marked.

http://marsrovers.jpl.nasa.gov/gallery/all...8ZP2575L5M1.JPG

Rodolfo

[glennwsmith]

Rodolfo, I am certainly agreeing with you if you are saying that the fractured stone is the result of different processes than those which resulted in the spherules. And nice picture indicating how spherules are sitting on top of a duricrust. . .

[dvandorn]

I keep wondering if the specific forms we see in the soil right now (the granule size ranges, the organization of the granules into three basic sizes and shapes, color and hardness) can tell us something about the conditions of the impact target at the time of the impact.

Does any of the soil material suggest that the impact target was wet or otherwised volatile-enriched? I'm assuming that at least some of the granules we see are pieces of impact melt, and I suspect the conical "drops" that some have labeled tecktitic are the most likely candidate for being impact melts. Does their shape and size, and the nearly ubiquitous hole in the center, suggest anything about volatiles content of the target? Or about its composition? Do we have to assume that their present shape and distribution is the result of erosional processes, or is there anything of their formation still evident in what we can see?

Unfortunately, the three granule types seem so thoroughly mixed that it will be impossible for Oppy to get a good specific composition of just one of the types... so we'll have to infer composition of the various types from the aggregate Mossbauer and APXS readings we get from it. But I think that, if we could answer some questions about the constituents of this soil, we'd have some further insight into the chemical and climatic history of the region.

-the other Doug

[Bill Harris]

Finally, we got the makin's for L257 images of the current trench and skuff on the ejecta apron.

Doug, I haven't decided about volatiles in the impact target. We'll need to look into Emma Dean and specifically the evaporite chunks with the unusual texture and/or darker tone. Maybe we won't do a drive-by this time...


--Bill

[john_s]

I couldn't resist this comparison:

[glennwsmith]

john s -- sweet!

[CosmicRocker]

That was freakin' brilliant! It is now my wallpaper. It makes me realize that before long we will have bootprints on Mars.

[Aldebaran]

We need a geologist to explain what the deal is with these "holy"rocks. What could be causing such perfect little holes? When I noticed just the one at the upper left, I assumed it was a camera artifact. I have to assume that we are looking at something that disolved out of the rock, or was created when the rock formed.
Any ideas? - [attachment=7236:attachment]Sacramento Bob

I'm not a geologist, but I minored in geology. Others have reported these holes. The best explanation I can find is that the concretions in many cases are associated with a network of dedos-like stalks. When the concretions are worn out of the rock, there is a tendency for these to snap off at the concretion, leaving a small indentation. We have noted the presence of these 'stalks' in several other locations, for example at the feature known as 'Pilbara' by Fram crater on the approach to Endurance. While wind erosion and chemical erosion certainly played a part in producing the stalks, there may be some evidence for a partial network of weakly indurated material within the matrix.

This MI image shows an example of such a stalk protruding from a spherule.

http://marsrovers.jpl.nasa.gov/gallery/all...00P2959M2M1.JPG

Please view the above as a half-baked suggestion rather than a fully baked hypothesis I'm just thinking aloud.

Bill Harris, I like your explanation of 'tektites' for at least some of the pebble-like fragments we have seen amongst the desert pavement. I'm not sure if that's a cut and dried explanation without more data, but it stands to reason that there must be 'tektites' present on Mars somewhere.

[CosmicRocker]

I've gone over all of the recent MIs and I can't find anything I'd call a tektite. If someone would post a picture identifying one of the suspected critters, I'd appreciate it.

Regarding that berry with the central hole, it's not the first one we've seen on this long trek. That one seems to be one of the occasional concretions that we've come across that has been cleaved in half and abraded. I would interpret the hole as the place where the concretion's center was more friable, so the material was easily eroded away. That is not an uncommon phenomenon in earthbound concretions. The one with the dimple might be the same thing as the first.

The third hole identified is in a clast (fragment) that doesn't resemble a concretion at all. There seems to be several sub-populations of fragments of different origins on the surface here. Among those that are not obviously concretions, some have noticeable porosity. But I must admit that the MI posted by SacramentoBob showing three different, tiny clasts with neat round holes is intriguing. ...just thinking out loud here... I wish I could tie them all together with a pretty pretty pink ribbon, but I can't.

[Aldebaran]

Regarding that berry with the central hole, it's not the first one we've seen on this long trek. That one seems to be one of the occasional concretions that we've come across that has been cleaved in half and abraded. I would interpret the hole as the place where the concretion's center was more friable, so the material was easily eroded away. That is not an uncommon phenomenon in earthbound concretions. The one with the dimple might be the same thing as the first.

I've also noticed a disproportionate number of concretions that have split in half.

If we accept that the concretions formed within the evaporite matrix as per the terrestrial analogy, I'd expect to find fine planar inclusions of evaporite within the concretion itself. We've discussed the possibility of changes in hydration states with diurnal temperature fluctuations. Intuitively, any such inclusions would tend to undergo a net increase in volume with an increase in hydration state and this would act as a wedge, exerting internal pressure on the 'berry' causing it to split in the plane of the original strata.

Do you think that's a credible mechanism?

[Bill Harris]

"Tektites" or "impact lapilli" are the best name I can come up with. Unlike earthly tekties they are neither appear glassy nor aerodynamic (for the most part) and unlike earthly lapilli they are't volcanic. They are the basaltic basal unit melted by the impact, assuming a near-spherical shape in the thin atmosphere and falling onto the ejecta blanket. I think the observation of the larger-sized spherules in this locale is important. Look at the L257's taken at this stop, the larger spherules tend to have a color similar to the basaltic cobbles, while the smaller spherules have a slightly different color. I see we have new Pancams of this crater and the distinctive light-toned rocks, so perhaps this will not be a drive-by sighting. Although we'd like to get to the photo-ops at Victoria, we need to do some science at this stop. Understanding erosional-depositional processes on Mars is the key to understanding the geomorph.

I agree with the idea that the holes in the berries are related to the stalks we've seen. And I wonder if some of the berries are not hollow or have a "softer" internal composition (related to Aldebaran's "planar inclusions"). I'm thinking that we see more broken berries here because of the impact. When the evaporite was catastrophically fractured and pulverized by the impact some of the berries were broken along the fracture lines, whereas with slower weathering processes the evaporite matrix breaks around the berries.

By way of earthly analogy, take a look at the attached...

--Bill

[Bill Harris]

Here are the latest color Pancams from the current stop, maybe these are next targets. Interesting rocks, we'll discuss later. I need to go fly...

--Bill