Geomorphology of Gale Crater, Rock on! Options

[jmknapp]

A paper from the MSL team to be delivered at the Geological Society of America conference in Charlotte next month talks about an area on Mt Sharp containing "boxwork" structures:

Boxwork structures are mapped in a distinctive sedimentary layer exposed on Mount Sharp in shallow depressions about 700 m above Curiosity’s landing ellipse in Gale Crater. This layer, exposed over about 1 km², is characterized by penetrative fracture networks expressed as ridges and separated by shallow depressions (2-10 m diameter) that are filled with dark windblown sand. Ridges are light-toned, averaging 4-5 m in width and sometimes marked by a thin dark strip (0-1.5 m across) in the center of the ridge. These are interpreted as large-scale boxwork structures, formed when saturated groundwater flowed through the fractured host rock and crystals precipitated within fractures and pores in the host rock, making the fractures more resistant to weathering than unaltered host rock. After weathering, the fracture fills stand as topographically higher rims around eroded host rock.

Curious to know where that is on the HiRISE imagery. Might it be this area in the large (what appears to be) outflow channel?



Other ideas?

[Stellingwerff]

Hi Joe,

I think you are slightly too high up the mount. I believe they are talking about the polygonal structures as shown on page 30 of: http://marsoweb.nas.nasa.gov/landingsites/...d_final_opt.pdf

Greetings,
Ludo.

[CosmicRocker]

A paper from the MSL team to be delivered at the Geological Society of America conference in Charlotte next month talks about an area on Mt Sharp containing "boxwork" structures: ...

Those large scale boxwork stuctures may be the most spectacular geomorphic features Curiosity images on this mission. I can only hope that Curiosity will send us some amazing pics as she carefully traverses the area.

[jmknapp]

Ludo, thanks for that--looks like a good inference, based on the caption. Here's a full-res HiRISE detail from the area:



I'd imagine that rover driver skills would be taxed to get into that maze of twisty passages.

CosmicRocker--beyond amazing pictures, the other instruments could probably feast on the crystalline minerals formed in the cracks.

[Zelenyikot]

Greetings from Russia

I want to share my observation.

I looked at pictures and noticed that many of the stones are similar to volcanic.



It seems even that lava river.


So close to be a volcano?
This is clearly not Elysium Mons
In the north-west is the mountain, which can be a volcano?


It turns out it can be a source of the alluvial fan and inverted (lava?) channels?

[acastillo]

Hi, my first post.

The problem with a volcanic interpretation of these landforms is the conglomerates already discovered. Conglomerates only form in alluvial environments, where water has flowed and rounded the cobbles. I agree that some of the rocks look like volcanic in nature, but the closeup images taking with the MARDI they show no mineral grains. This means the grains are smaller, at least on the surface, than the resolving power of MARDI, which is pretty small. The only volcanic rocks that I have seen with no visible grains is volcanic glass. Since volcanic glass is not stable, at least on Earth, it should have devitrified by now, and show some crystallization of the rock.

Of course reality is probably a mix of both alluvial processes and volcanic process were involved with the formations we see today. Which makes this area probably the more exciting spot explored on Mars so far, sorry opportunity.

Mod: Excessive quoting removed. Read rule 3.5 please.

[dvandorn]

You can see it an awful lot better in the Navcam anaglyph on page 2 of this thread. It's difficult to do geomorphology from Hazcam anaglyphs because the field of view is so limited. That hummock is just part of the edge of a much wider resistant layer that forms a major terrace all around the depression.

Well... the one end of the depression that is obvious in the most recent pans that have been assembled, here, looks rather circular. Anything that describes a partial or complete circle on Mars, with its higher impact rate than we are accustomed to on Earth, could be the remnants of an impact crater. The flow lines etched into the rock working into the depression could just be the result of eons of aeolian modification.

However -- and this is a big however -- the overall morphology of the region is indicative of alluvial activity, i.e., modification from flowing water. So, even though the edge of this depression is circular and may still represent the remnants of an impact crater, with the clues to alluvial action we can see in the aerial images, it looks to me that the initial modification of the terrain is more likely from water flowing and then ponding in the topographic low point of the depression. Multiple episodes of flash flooding, or continuous drainage from the central mound, could have resulted in the patterns we see.

In any event, the original forces that carved the topography here at Glenelg has since been modified by many, many eons of aeolian erosion since the last of the flowing water was seen here.

-the other Doug

Reason for edit: Link to the main thread

[elakdawalla]

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.

[ddan]

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.

[Phil Stooke]

At some point if the debris breaks down into sufficiently small particles it can be removed from the vicinity, even lifted out of Gale crater completely. So it might not remain in this area to choke off further erosion.


We had a small move, slightly backwards and to the left, so a rock slab that was immediately adjacent to the left front wheel is now slightly further away and right of center where the arm can work on it. Following common practice in the past I expect it backed up a bit, turned, moved forwards again to the desired location, and turned to face the rock. It's hardly enough of a move to warrant updating the route map just yet.

Phil

[mcaplinger]

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)

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.

[SteveM]

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

[ngunn]

It's a great phrase isn't it? Get's you out of any problem - except that it doesn't. With its 'impossible' central mound Gale crater is the perfect place to seek real answers to that big Martian mystery.

Meanwhile at Glenelg we have a smaller mystery but one whose resolution should also prove enlightening. Why did the removal process, whatever it was, selectively target the outer margin of an alluvial fan?

[Zelenyikot]

My thought involves this element. It looks as a wave or stream consequence.

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[Guest_Actionman_*]

With its 'impossible' central mound Gale crater is the perfact place to seek real answers to that big Martian mystery.

I would think that would be a good reason not to to go here... which in all honesty means i should have a theory/hypothesis but I don't see the word "glacial" mused much.
Here it goes: Rock slipping inward to the center from a thick ice glacier.

Some of these rock seem to show frost heave to me.