Geomorphology of Gale Crater, Rock on! |
Geomorphology of Gale Crater, Rock on! |
Sep 26 2012, 10:22 PM
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#1
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
I'd like a discussion thread about the geology detatched from the time limits of current MSL threads. We had a 'Geomorphology of Cape York' thread that attracted a lot of interesting posts. How about 'Geomorphology of Gale Crater'? I have one or two ideas but many more questions, and I'd like to post them in a longer-running thread away from the day to day imaging discussion. Any other takers?
For starters, does anybody have a contour map of this place like the one at Meridiani with 5m intervals? ADMIN: You have your wishes fulfilled on UMSF (sometimes) |
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Nov 28 2012, 04:48 PM
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#2
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Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
One feature very common to Gale crater, both its floor and on the central mound, is "inverted topography," where there is something that looks like a stream valley (with dendritic tributary or distributary features), except that it stands higher than the surrounding terrain, rather than lower. That is generally interpreted to mean that there once was a valley, whose fill was, for whatever reason, more resistant to erosion than the material into which it carved. The fact that it stands high now tells you that the whole surrounding landscape has been deflated, eroded away, since the last time there was significant fluvial activity here.
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Nov 28 2012, 05:12 PM
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#3
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Newbie Group: Members Posts: 7 Joined: 18-September 12 Member No.: 6655 |
the whole surrounding landscape has been deflated, eroded away, since the last time there was significant fluvial activity here. One thing that I don't quite understand is where did all the eroded surface go? Does it have places where it accumulates preferentially? How many meters of surface can we expect to be removed in 2-3 billion years? At some point the erosion stops because the landscape is already covered with sand, so there must be some upper and lower limits to this phenomenon. |
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Nov 28 2012, 06:25 PM
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#4
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
One thing that I don't quite understand is where did all the eroded surface go? Good question. I don't think anyone knows yet. From Malin and Edgett, "Sedimentary rocks of early Mars", Science, 2000, http://www.sciencemag.org/content/290/5498...&siteid=sci (italics mine) QUOTE Not only is evidence of the depositional processes not apparent, neither, in most cases, are the processes that exposed and eroded the layered and massive units (with the obvious exceptions of faulting in the Valles Marineris and the presence of yardangs that imply wind erosion). For example, Henry Crater contains 10,000 km3 of material in an isolated mound within the crater. This material is layered and stands nearly as high as the crater rim. This observation implies that some process or processes have removed 15,000 km3 of material from Henry Crater. Notwithstanding recognition of morphologies that suggest an apparent sequence illustrating removal of material from impact craters, the actual processes are unknown. The implication is that most of the exposure and erosion of the layered units must have occurred some time far in the martian past, when transport out of the craters (again, with no obvious transport pathways) could have occurred via processes not acting on the planet today. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Nov 28 2012, 08:08 PM
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#5
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Member Group: Members Posts: 267 Joined: 5-February 06 Member No.: 675 |
The uniformitarian in me gets nervous when I read an appeal to "processes not acting on the planet today".
But as a historian of science, what do I know. Steve |
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Nov 29 2012, 09:13 PM
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#6
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Senior Member Group: Members Posts: 1057 Joined: 17-February 09 Member No.: 4605 |
The uniformitarian in me gets nervous when I read an appeal to "processes not acting on the planet today". That seems a bit harsh. There are pretty clear indications that early Mars was a very energetic environment, predominantly aeolian with at least episodic fluvial periods. Living as we do in a corrosive and energetic erosional environment I guess that most of us have difficulty really understanding just how benign present day Mars is, or the immense amount of time that has elapsed since that more energetic environment. The statement ’processes not acting on the planet today’ seems appropriate given the current lack of any significant mechanical or chemical erosion. There is pretty clear evidence of massive erosional/depositional cycles across ancient Mars. I think all agree that the Gale central mound is sedimentary (possibly with a remnant central uplift core) and most of this material would have come from somewhere else. The deposition appears to have taken an extended time since the changes as we go up the mound could potentially map the changing depositional environment. Heresy perhaps but the ESA definitions of the Martian eras actually seem to make more sense (intuitively at least) than the traditional nomenclature. http://www.esa.int/esaCP/SEM117OFGLE_index_0.html Despite the remnant fluvial valleys and inverted channels, the lack of transport pathways out of the crater indicates that fluvial influences would not seem to have been significant in the excavation process. Aeolian seems the culprit. I could imagine the crater partially filled by deposited materiel and I wonder if a vortexing effect around the rim could have actually moved material from rimward to the central area resulting in the moat around the mound. That would account for some of the eroded material. Where did the rest go? Mars wide, Arabia Terra and Meridiani alone account for hundreds of thousands of cubic kilometres of sedimentary material and there are probably a lot of sedimentary traps across the surface of Mars. I guess a lot ended up in the Northern plains. |
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