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Geomorphology of Cape York and Solander Point, Examining Opportunity's destination at Endeavour Crater
CosmicRocker
post Oct 23 2011, 02:51 AM
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smile.gif Many thanks, anonymous Mod. smile.gif


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CosmicRocker
post Oct 25 2011, 03:15 AM
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I'd like to follow up on my earlier observation about possible blueberries (hematite concretions) in pancam images from sol 2748 on Cape York. It had been suggested that if a residuum of such concretions would be found on top of the very different geologic bedrock of Cape York, it might mean that the cape had previously been buried by the blueberry containing sulfate sandstone that covers Meridiani Planum.

Since the target was imaged with a full set of infrared filters, we can make a false color image based on pancam right filter ratios that has successfully identified hematite in the past. In such false color images hematite typically appears in shades of yellow or orange. Some of us briefly discussed this image processing in another part of the forum.

Getting to the bottom line, the processed image showed plenty of hematite in the ground Opportunity is driving over. There were numerous spherical hematite concretions as well as angular fragments of hematite visible in the image. The question now becomes, How did this hematite arrive on top of Cape York? It seems to me that there are three alternatives:

1: It dropped down onto the basement rocks as a lag deposit as overlying sulfate sands were eroded away.
2: The concretions and fragments were transported to their current location by wind or water currents from the surrounding plains.
3: They were thrown onto the cape by meteorite impacts on the plains.

I think it may be difficult to distinguish among the alternatives. Are there other alternatives that I missed? I would have liked to provide a thumbnail link to the above image, but I still have not figured out how to do that without uploading the whole file again.


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ngunn
post Oct 25 2011, 09:29 AM
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QUOTE (CosmicRocker @ Oct 25 2011, 04:15 AM) *
Are there other alternatives that I missed?


4: Condensation lapilli (distinct from your no. 3, I think)

Disclaimer: doesn't mean I believe this, just that if we're brainstorming upon finding the things in an unepected location nothing should be dismissed.
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Bill Harris
post Oct 25 2011, 06:00 PM
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I see angular and rounded pebbles with a "hematite signature" but not to the extent that I can call them "blueberries". We've not seen these rounded pebbles in-situ, nor broken in x-section, so I can say that they are blue, but can't say berries.

And, as Nigel suggests, they may be lapilli. One characteristic of this region of Mars is the abundance of various Iron (III) oxides and hydroxides. And we don't have much experieces locally with hematites as impact melts.

The western slope of CY is so shallow that some "onlap encroachment" is indeed possible, especially at this highly-eroded point on the Endeavour rim. So a blueberry or two wouldn't be earthshaking. Those clasts do simply _look_ rounded, and not necessarily blueberrish. So the jury will be out til we get more mineralogical data.

--Bill



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CosmicRocker
post Oct 26 2011, 04:35 AM
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I understand what you are saying, Bill. It would be nice to see these pebbles on the surface rather than embedded in the soil, and a x-section would be the icing on the cake. A wheel scuff to dig a few of them up would help a lot. However, I don't think it is such a stretch to imagine that the most obviously round ones are truly spherical and not simply pebbles rounded by erosion. If you can imagine that, and accept the evidence that these things are indeed hematite, it is simpler to assume the spherical pieces of hematite are the same ones we've been seeing all these many years through Opportunity's eyes, rather than assuming some other origin for them.

This is really an interesting soil image. The abundant, angular pieces of hematite are very curious. We have rarely seen gravel composed mostly of hematite and with a large population of angular fragments. It looks like a bimodally sorted size distribution and perhaps a bimodal shape distribution as well. I'm not sure what that means, but it could possibly be evidence of a very different transportation mechanism than we have normally observed for the hematite fragments. If I had to guess, I'd suspect a higher energy environment.


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brellis
post Oct 26 2011, 07:16 AM
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Over the years, there have been many discussions of "shorelines" as theoretical possibilities or dry analogs.

Could we be for the first time approaching an actual ancient shoreline? How would that confirmation happen?
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