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Exploring Mt Sharp - The Dunes - Part 2: Naukluft Plateau, Sites 53-54, Sols 1274-1352, March 7-May 27 2016
Gerald
post May 30 2016, 04:39 PM
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Thus far, I didn't see foldings typical for tectonic activity.
So, I'm sceptical, that tectonics plays a major role for mound formation at Gale.
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serpens
post May 31 2016, 07:35 AM
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I don't think that Gale crater should be considered in isolation from the surrounding terrain, particularly the massive, heavily eroded sedimentary deposits of Aeolis Planum or the increasing evidence for a long lasting ocean. The thing is that despite lots of erudite specialists presenting diverse hypotheses we still don't really have a self consistent theory with respect to Gale. Why the changes in lithology in such a narrow stratigraphic column? Why is the erosion of the northern rim so much greater than the South? Statements in papers that this is attributed to being on the dichotomy just dodge the problem. There was a lot of surface water at Gale. Where did it all come from? Gale continues to present challenges.
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elakdawalla
post May 31 2016, 03:19 PM
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With a long westward drive on sol 1353 to finish the drive off the Plateau, away from the Stimson, and on to the Murray, it's time for a new thread.


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Phil Stooke
post May 31 2016, 03:54 PM
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"Why is the erosion of the northern rim so much greater than the South? Statements in papers that this is attributed to being on the dichotomy just dodge the problem."

I don't agree with this. I don't see any evidence for more erosion of the northern rim. The crater formed on a slope (the dichotomy) so its northern rim formed in the lowlands and its southern rim formed in the highlands. That is not dodging the problem.

Compare it with Sinus Iridum on the Moon. Its northwest rim is on a highland area. Its southeastern rim is deep in the old Imbrium crater, and from the first day it existed it was much lower. The Imbrium basalts flooded the lower parts. Some people still talk about a massive fault lowering the inner part of the rim but there is absolutely no evidence for a fault. We can see countless small craters formed on the sloping rims of older craters all over the solar system, it's not a rare thing.

Phil



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serpens
post May 31 2016, 11:43 PM
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Figure S9 in the linked attachment provides a compelling profile of the crater from south to north. The northern rim has most definitely experienced significantly more erosion than the southern. If you haven't seen this previously the supplementary data is as illuminating as the primary paper by Grotzinger et al.

http://web.gps.caltech.edu/~wfischer/pubs/...retal2015SM.pdf

This erosion pattern is also evident in Robert Sharp crater, just to the West of Gale and of similar size, where the northern rim is completely degraded.







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jccwrt
post Jun 3 2016, 10:33 PM
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Here's a red-cyan anaglyph of some of the exposed bedrock on the south edge of Fracture Town from Sol 1348. Lots of depth in this image!


Southern Edge of Fracture Town - Sol 1348 by Justin Cowart, on Flickr
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Phil Stooke
post Jun 10 2016, 12:50 PM
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" Figure S9 in the linked attachment provides a compelling profile of the crater from south to north. The northern rim has most definitely experienced significantly more erosion than the southern. If you haven't seen this previously the supplementary data is as illuminating as the primary paper by Grotzinger et al. "

I only just noticed this post by Serpens. The profile can be interpreted in different ways. It's true that the rim seems less elevated than its surroundings on the northern side than the southern side, but is this due to erosion or partial burial? As for Robert Sharp, the entire crater has been buried almost completely and is being exhumed, leaving many remnant massifs inside the crater. The characteristic mix of deposition and erosion which shapes the dichotomy and adjacent plains has acted within the crater, including its northeastern wall, which always was topographically lower.

Basically I would say Robert Sharp is older than the dichotomy (or at least the arrival of the dichotomy in this area as it cut back into the highlands) and was affected by it. Gale is younger than the dichotomy and more influenced by formation on a slope and partial burial by northern plains material and whatever formed the upper unit of Mt. Sharp.

It would be good to see where that profile was measured!

Phil


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serpens
post Jun 11 2016, 12:30 AM
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The North south profile crosses the central peak (exposed central uplift peak?) which I guess pretty well defines where the profile was measured. With respect to the northern rim there is consensus across numerous papers and technical notes dating back as far as the 1990s that unlike the southern rim, the northern rim and adjacent ejecta blanket are heavily eroded.
I fully agree with your point that Robert Sharp is an exhumed crater and certainly the Eastern rim of Robert Sharp remains buried. But the northern rim is entirely degraded. I have trouble with your concept that Robert Sharp is older than the dichotomy, but since there is no real consensus on how the dichotomy formed I guess that under a tectonic scenario it could be possible.
I guess I am suffering from the Julius Sumner Miller "Why is it so" syndrome with respect to Gale because under current Mars models what Opportunity is finding at Gale should not exist. Anyhow, probably the wrong thread for a discussion of this type.
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Sean
post Jan 5 2017, 02:52 AM
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Sol 1302 ML



Extended sky, exposure pass, noise fixes & minor edge patches.




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