[X] My Assistant

[vikingmars]

Bravo Ant 103 : this is a nice and great mosaic !
Funny thing : we did our processings at the same time !
This is my careful processing and own interpretation of colours there and the "fin" ridge looks really grey (NOT blue) in its most interesting part...
A very unusual geological formation indeed... Enjoy !

[ngunn]

At Santa Maria Oppy also encountered blue, burple and light-toned rocks of "unknown affinities" that, unfortunately, we did not have time to examine closely.

I supect that this basal unit is the pre-Endeavour surface, highly weathered and comprised of a mish-mash of various impactites, ejectites and other residual units. This may well be the source of the holy-grail phyllosilicates

Every word of your post sounds eminently plausible to me. It's a long shot but I wonder if we saw any of the older low-iron spherules at Santa Maria but passed over them as 'ordinary' Meridiani blueberries at the time?

Once we get to know these older rocks in detail through exploring Endeavour we may even find that we saw the odd fragment around Victoria.

[fredk]

Did I dream this, or was there some mention of a phyllosilicate detection (CRISM I guess) on the unexplored side of Victoria, after we had left?

[ngunn]

Maybe you're thinking of this? http://www.google.co.uk/url?sa=t&rct=j...yaQ&cad=rja

[ngunn]

Following up on an earlier comment:

"fine-grained material with unknown affinitities". What intrigues me is the pattern of fractures.

Perhaps this mud-like stuff is wet (or icy) when buried and only dries out where exposed.

[fredk]

Maybe you're thinking of this?

That's it, thanks. So not phyllosilicates.

[serpens]

Sometimes we need to remind ourselves of the scale of this feature.


Taking a step back, Ant's superb stitch provides some perspective although I do prefer Viking Mar's color treatment. But my xmas wish list would include a climb to the top of CY from here to check out the nature of the intervening outcrops and hopefully connect a few dots. Are the spherules in this apparent mudstone/siltstone concretions as opposed to the apparent impact generated layer? The distribution does seem to make this possible. If they are is tdemko right that these are attributable to the Burnes formation groundwater event, or does their composition indicate something else?

[Bill Harris]

Perhaps this mud-like stuff is wet (or icy) when buried and only dries out where exposed.

Here, near the equator, solid or liquid water is not likely. The rock looks like mud/plaster because of the way it's eroded.

But my xmas wish list would include a climb to the top of CY from here to check out the nature of the intervening outcrops and hopefully connect a few dots.

Exactly, Serpens. This geologic column starts down at the bench and can be investigated all the way to the hilltop (and beyond). We need more puzzle-pieces, and these pieces are not always big spectacular outcrops.

Take a look at the color HiRISE image I posted the other day to see what can be seen onthe way up:
http://www.unmannedspaceflight.com/index.p...st&id=28072

--Bill

[serpens]

Right. Gotcha. Step back a bit further.

The sediment (mudstone or whatever) seems to be localised and follows the contour - pooled against the impact spherule layer?

Oooh - those perpendicular (unloading joints?) are just over there and that old crater just to the NW could maybe perhaps provide a roadcut. Let someone else break an unimportant distance record - I like this place.

[ngunn]

That's it, thanks. So not phyllosilicates.

No, but its colour and lustre I guess makes kieserite a candidate for Bill's 'anomalous' Santa Maria stuff. It could be a marker for the layer where the two different rock chemistries meet. If so, it should be present here at Endeavour too.

Bill - no water or ice at the equator even, say, 10 or 20m down? Do we know this?

[marsophile]

A very unusual geological formation indeed... Enjoy !

In looking at your excellent and evocative rendering, I can't help imagining that an impact sheared off the entire top of the Fin formation. Nah, it can't be!

[Bill Harris]

Bill - no water or ice at the equator even, say, 10 or 20m down? Do we know this?

I'm presuming. <shrug> We really won't know til we drill the area, right? At or near the surface, no. At depth, possibly. Get heat from the thermal gradient, pressure from the depth of water and voila, liquid water. Mineralized, nasty by terrestrial standards, but water nonetheless.

Let me change that nay to a definite maybe?

--Bill

[serpens]

No, but its colour and lustre I guess makes kieserite a candidate for Bill's 'anomalous' Santa Maria stuff. .....Bill - no water or ice at the equator even, say, 10 or 20m down? Do we know this?

Well kieserite is pretty unstable and is a good indicator that there has been no water since exposure from any source. Was any kieserite identified near the smectite signature on CY? Bill's yellow could be kieserite, but then again nontronite is yellowish. From ngunn's link there are polyhydrated sulphates around CY. Anyone have any idea what the hydration state is thought to be and were they Mg or Ca?

But the purplish tinge to Bills anomalous stuff is another thing and could be as simple as a Basaltic breccia precursor, anoxic environment with little if any initial organic carbon. Agatha Christie mysteries are a doddle compared to this place..

[Guest_Oersted_*]

And yes the news about these spherules hit ScienceDaily now also.
So it's not just us on this forum who think this is noteworthy.

Definitely hit the big news:
http://cosmiclog.nbcnews.com/_news/2012/09...an-mystery?lite

[ngunn]

To continue discussion of the fine-grained 'mud floor':

Perhaps this mud-like stuff is wet (or icy) when buried and only dries out where exposed.

Let me change that nay to a definite maybe?

Almost 6 years ago I proposed this scenario: The Victoria impact fluidises an ice-rich layer buried, say 100-200 metres below the surface. Some of this material drains out from under the crater rim and collects as a temporary lake in the centre of the crater. The crater rim collapses in an irregular pattern into the void created, forming the cliffs and bays we see now.

At the time there was no evidence for an under-layer beneath Victoria, let alone one with the right properties and at the right depth, so unsurprisingly the idea got no support here and we moved on. Now, though, I think this fine-grained unit is a potential candidate for the stuff that fluidised. Dry materials can fluidise when shocked, but it happens a whole lot easier if there's even a little water present. (It also helps with clay-making.)

If the fine-grained unit was patchy to start with (not unreasonable in a "mish-mash of various impactites, ejectites and other residual units") sapping would also have been irregularly distributed, possibly determining the outlines of the capes and bays of Victoria and her similarly endowed twin some kilometres to the south.

Did somebody mention arm-waving?