Geomorphology of Gale Crater, Rock on! Options

[djellison]

Are you suggesting that Mt Sharp is just a pile of terminal moraine?

Where is the evidence for the glaciers themselves - the glacial valleys?

[Guest_Actionman_*]

yes, maybe
glacial cone/funnel

Some evidence would be that much of the surface rocks the larger ones we see has little or no impact signatures like they would have landed on snow or ice. Flat sediment slabs we're seeing right now don't have many rocks on them, sled off.

[Phil Stooke]

There is plenty of evidence for glaciers elsewhere on Mars, but none here. Let's try to keep the focus of this forum on the images, that's where it really shines.

Phil

[Chmee]

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)

(ddan @ Nov 28 2012, 10:12 AM) *
One thing that I don't quite understand is where did all the eroded surface go?

Well, I can think of 2 methods:

1. Ice / Glaciers - After Gale formed, water entered the crater, creating a lake, which then froze over with the central mount sticking out. Sediment accumulated over the ice in layers (and the central peek), essentially filling the crater 'to to the brim'. Later, perhaps as the Martian atmosphere lost most of it's density (or the polar tilt moved Gale from polar region to equatorial) the ice sublimed away, sinking the floor down, but maintaining the central peek.

2. Fractured/Soft Material - When Gale formed, the rock under the crater floor had less strength then the central peek. The crater filled up with sediment over time, again near the rim of the crater. However, over the eons, all that weight compressed the original material in the crater floor, in effect sinking or slumping the floor away from the rim and central peek.

Just my 2 cents!

[serpens]

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.

[Guest_Actionman_*]

It's a cinch we're not going to be finding bedrock, NASA came here looking for bedrock.. didn't they.
Bedrock should be at the bottom of a deep crater, shouldn't it.
We would like to fine something solid some place.
No bedrock on lake affect... if the area is below the frost line.

[djellison]

It's a cinch we're not going to be finding bedrock

I don't think bedrock means what you think it means.

The definition I've found
"solid rock underlying loose deposits such as soil or alluvium."

We have clearly already seen that at Gale crater - from the surface and from orbit.

[centsworth_II]

It's a cinch we're not going to be finding bedrock....

Gale crater is easily old enough for bedrock to have formed in it from once loose material that filled the crater. I think the mission is not to discover material from the surface that existed before the impact that formed Gale Crater. I think the mission is to learn the deposition history of the material that later filled the crater. That history is preserved in bedrock that formed long after the crater's creation and which now lies exposed in Mount Sharp and the area around it that Curiosity is currently exploring.

[elakdawalla]

It's a cinch we're not going to be finding bedrock,

I'm sorry to have to say it, but this sentence proves that you just don't know what you are talking about. I suggest you stop talking about geology, and just listen instead. You could really learn a lot here.

I don't want to have to add a rule to section 2 that tells people not to post if they don't know what they are talking about. I feel that that should be obvious.

[Guest_Actionman_*]

I'm sorry elakda for making it sound too you like i'm talking about the Flintstones.

Bedrock on Mars as far as I know, now you correct me if I'm wrong: basalt.
Not to be confused will the surface photos of conglomerate and limestone sediment slabs we see.

We see chucks of basalt everywhere BUT what we don't see is the primal intact basalt global covering if there is one. Basalt like all the surface basalt littering the surface indicates there should be basalt in the floor a deep crater it should be revealed or even to have been blasted clean through.
Bedrock is not compressed sediment. At lest not the type of bedrock I was talking about.
NASA will be drilling for subsurface basalt NMHO.

[ngunn]

I think the term you want is 'basement rock' rather than 'bedrock'.

[Stellingwerff]

We see chucks of basalt everywhere BUT what we don't see is the primal intact basalt global covering if there is one.

If you refer to the Anderson and Bell paper on this subject: http://marsjournal.org/contents/2010/0004/...s_2010_0004.pdf,
you'll find on page 122 a very nice graph showing exactly why we don't see the basalt yet. It's close, but MSL will need to drive towards the mount to find an exposed trough all the way down to the basalt unit. (In many places the dark dunes are actually covering the basalt floor, instead of on the sediment layers, see image 34a on page 109)

Greetings,
Ludo.

[Guest_Actionman_*]

And thank you Ludo.

Make it so

[centsworth_II]

...Bedrock is not compressed sediment. At lest not the type of bedrock I was talking about.
NASA will be drilling for subsurface basalt....

This mission is specifically designed to study the compressed sediments of Mount Sharp and the surrounding area. Not to look for subsurface basalt. The drill goes no deeper than a couple inches. The landing site was chosen because of the deep layered stack of compressed sediments that could be seen in Mount Sharp, not because of any sub-surface basalt.

Edit: Here is a short description of why MSL went to Gale Crater. Notice, no mention of basalt.

[djellison]

NASA will be drilling for subsurface basalt

They will not. I was right - you don't know what bedrock means.

I'm going to repeat Emily's excellent words from earlier... this sentence proves that you just don't know what you are talking about. I suggest you stop talking about geology, and just listen instead. You could really learn a lot here.