[X] My Assistant

[serpens]

Well it looks like mudstone/siltstone/clay - roll on the APXS results. I still think that this is a sedimentary construct resulting from the weathering of the Shoemaker deposit. Given that this weathered material would have encompassed igneous rocks and impact glass couldn't we expect a mixture of clay types, for example montmorillonite-chlorite, potentially layered or veined (crack fill)?

[climber]

Do you remember the time when we didn't know at which side of the planet to look at since two rovers were discovering new things? This time's back

[Bill Harris]

Given that this weathered material would have encompassed igneous rocks and impact glass...

as well as weathered material on the surface redistributed as impact ejecta. This material could have been recycled for aeons, and created under several different climate conditions. Mindbogglingly complex.

--Bill

[ngunn]

Ultimate origin(s) of the material may be too much to expect. We have to work backward from the way it looks now and how it fits into its context. I'd like to try out a rather simplistic hypothesis, namely that it is the remains of a continuous and widespread bed of sediment that formed in situ at some time between the Miyamoto and Endeavour impacts. How would it have responded to the latter? Given its softness and fine texture plus the possibility that it held water, I think it would have squidged and flowed all over the place as the Endeavour rim settled, destroying evidence of its original bedding and occupying cracks in the more resistant rocks. To a first approximation that seems to fit the scene we're looking at.

[Ant103]

Do you remember the time when we didn't know at which side of the planet to look at since two rovers were discovering new things? This time's back

Yes, and what's better : there is TWO generations of rover on Mars. Working. We're living blissed times.

[serpens]

...that it is the remains of a continuous and widespread bed of sediment that formed in situ at some time between the Miyamoto and Endeavour impacts. How would it have responded to the latter? Given its softness and fine texture plus the possibility that it held water, I think it would have squidged and flowed all over the place as the Endeavour rim settled, destroying evidence of its original bedding and occupying cracks in the more resistant rocks......

With all hypotheses I think we need to keep the big picture context in mind. The original impact would possibly have been large enough to create a complex crater. In support of this, the series of interior ridges within the rim to the east could be the remnants of marginal collapse zones. If so, then if CY is indeed part of the outer uplift rim the original surface would have been subject to surface spalling as well as horrendous heat, overpressure and wind scour. I don’t think a sedimentary deposit would survive in the way you suggest and I feel it more likely to be due to post impact weathering.

[ngunn]

We're not looking at the original surface of the interior of the crater but something that has eroded outward a bit from there. What do you think would have happened to previously existing sedimentary layers a little distance out? At least we can say that layering is preserved here - the new spherule layer is still in place and it must have predated the crater. So I think you're wrong (until more evidence turns up). But thanks for responding to my suggestion!

[serpens]

the new spherule layer is still in place and it must have predated the crater.

Not necessarily, that depends on the final determination of the nature of the spherule layer and currently all is conjecture. Emily raised a good point that the crater would have eroded back to some degree, but the hills to the south seem to be remnants of the rim and CY is on the same circumference. So it was likely once internal to the crater rim, which would have been uplift covered by ejecta/suevite.

[ngunn]

I really want to understand what you're saying, but this bit defeats me:

the hills to the south seem to be remnants of the rim and CY is on the same circumference. So it was likely once internal to the crater rim

Anyhow on the 'conjecture' point I totally agree - there are many very different plausible scenarios given the huge depth of geologic time here.

[Stu]

Enhanced view of latest "Whitewater Lake" RAT activity...

[ElkGroveDan]

That's kind of artistic looking.

[Bill Harris]

Not necessarily, that depends on the final determination of the nature of the spherule layer and currently all is conjecture...

At this point any of several puzzle-pieces can easily fit into the spaces allotted. That is why it is necessary to understand the lithologies (and depositional environments) above and below: ie, within the entire section. We're out of the Pottsville (Burns) Formation now, and things are getting more complex. On those two HiRISE images of this area that you and I posted there can be seen accessible outcrops higher and lower iin the section.

Without stratigraphy, geology would have nothing to sit upon; and without geology, geography would have nothing to sit upon. And so it goes...

--Bill

[belleraphon1]

A.J. S. Rayl monthly MER update now available at The Planetary Society Blog...

Mars Exploration Rovers Update: Opportunity Finds Thrill of Newberries on Matijevic Hill
http://www.planetary.org/explore/space-top...newberries.html

Have not had time to read it yet....

Craig

[fredk]

A bit of a bump on 3090 to continue working on Whitewater Lake by the looks of it:
http://qt.exploratorium.edu/mars/opportuni...0M1.JPG?sol3090

[MarkG]

"Mars Exploration Rovers Update: Opportunity Finds Thrill of Newberries on Matijevic Hill"

...a nice convoluted rock and roll pun....