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ngunn
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?


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Eyesonmars
I'm a little confused about the layers on Mt. Sharp. Could one of you geology types set me straight?

a) the thinking is that the mound is a remnant of the vast sediment that once filled gale crater
correct?

cool.gif If so, wouldn't most if not all of the sedimentary layers be flat since no tectonic activity has occured?

Perhaps it is a trick of perspective but all of the layers I can see in the buttes and mesas below the discontinuity are uniformily tilted up toward Mt. Sharp.
So I'm wondering if the layers have nothing to do with the original deposition but are an artifact of more recent aeolian erosion.



Ondaweb
QUOTE (ngunn @ Sep 26 2012, 05:22 PM) *
How about 'Geomorphology of Gale Crater'?


I like that idea. I, too, have some questions perhaps better posted there.
Phil Stooke
Sediment settling out of a fluid onto a flat surface might make horizontal layers, but other situations can make tilted layers from the start. In particular, if the surface is already tilted and you start depositing layers of wind-born material (sand, volcanic ash etc.) on it, each layer could follow the slope of the ground underneath it for quite a while until upper layers became more level.

Another possiblity - layers form fairly horizontally over uneven topography. Then over time they gradually compact under their own weight, but more so in areas of deeper sediment fill ("differential compaction"), resulting in deformed layers.

So we can't just assume layers would be horizontal.

Phil

dvandorn
One rim of Gale Crater is quite a bit higher above mean than the other, right? Even though it appears to be a regular ringwall kind of structure, not breached nor significantly out of circular. It could be that much of Mt. Sharp was deposited in horizontal layers and the overall ground mass below the entire crater could have tilted before the deflation that exposed the central mound and revealed the horizons we now see as the floor. The entire subsurface table tilting would account for the different heights of the rim between north and south.

As to what could have caused the entire subsurface below Gale to tilt -- well, the Tharsis bulge was responsible for enormous deformations of the crust. Also, if this area of Mars ever went through extensive glaciations, the entire subsurface could have been pushed down by the weight of the glaciers during the deposition of Mt. Sharp's layers, and has since recovered its original elevation and orientation via isostatic rebound.

Finally, if the material that supposedly infilled the entire crater (and has since been deflated) was emplaced by a rapidly moving force, such as the rush of waters or repeated pyroclastic flows from the same vent area, well, that material could have piled up on the far wall and filled back from there. If the force emplacing the materials was consistently from the same vector, you would get layers that are tilted in a sort of compromise between the gravity vector and the emplacement vector.

In other words, there are a lot of ways on Mars that you can get tilted and discontinuous rock beds, you don't have to assume tectonic processes.

-the other Doug
Explorer1
Could we figure out a ballpark estimate for the size of the original impactor that formed Gale, or is it too degraded?
There's online simulators but they're for Earth impacts only...
serpens
Great idea ngunn.

To appreciate the variations in layering we need to take into account the sheer size of this crater (some 18,000 square kilometres) and the necessary presence of a central uplift which could possibly be a factor in Mt Sharp resisting erosion. Seemingly lots of water early on with aeolian deposition/erosion subsequently. Being on the slope at the edge of the dichotomy there would have been a gravitational gradient towards the north. Couple this with cycles of depositition, variable lithification and differential erosion over billions of years and as impied by dvandorn and Phil, flat layers without variation rather than uneven layering would be the eyebrow raiser.
ngunn
(Thanks admin smile.gif)

I have been wondering about the 'high thermal inertia' region that is now in front of us. It looks like it has been somehow scoured clean of loose material. Noting also that it is located ahead of the margin of a presumed alluvial fan, I have been wondering if that 'fan' could actually be the remains of a long-outrun avalanche that formed very rapidly, sending a powerful shock wave ahead of it that blasted the soil off this area.
jmknapp
The operative sentence from the Anderson/Bell paper:

QUOTE
Despite interest in Gale Crater as a potential landing site, the origin of the mound remains enigmatic.
ngunn
Also in that paper (pp107-8) is discussion of the low-thermal-inertia/high-thermal-inertia fan formations and the nature of the boundary between them. We are approaching the margin of the HTIF Glenelg. We'll soon have some new data to match against the proposed interpretation.
Chmee
Great idea for this thread.
Since there is no obvious outlet along the rim wall for water / glaciers etc to have eroded the crater bed to, I lean in favor of the theory that the floor of the crater actually dropped, instead of eroding away (with some later minor depositing which smoothed the floor out). Since Mt Sharp sat atop the old central peak of the original crater, it did not sink like the rest of the crater floor. My two and one-half cents rolleyes.gif
djellison
QUOTE (Chmee @ Sep 27 2012, 01:25 PM) *
Since there is no obvious outlet along the rim wall for water / glaciers etc to have eroded the crater bed to,


Why must it have been water? The theories I have seen suggest wind.
ngunn
Add to that the possibility of quite a lot of ice in the original crater fill and you have sublimation as another removal mechanism.
Eyesonmars
Also note that Curiosity is sitting on or very near the lowest spot on the planet (outside of Hellas).
How did it get that way ? There are far larger craters along the global dichotomy. I suspect that the uniqueness of Mt. Sharp and the fact that it is immediately adjacent to this global low spot ... is not a coincidence
serpens
QUOTE (Eyesonmars @ Sep 27 2012, 10:16 PM) *
I suspect that the uniqueness of Mt. Sharp and the fact that it is immediately adjacent to this global low spot ... is not a coincidence


Not unique. Emily did a rather nice presentation on this.

http://www.planetary.org/blogs/emily-lakda.../2011/3144.html
Don1
Anybody like the idea of a mud volcano for Mt Sharp? Looking at the way the upper layers are tilted, it looks like something came out of the top and flowed down the flanks. In fact I think I recall reading something about a hydrothermal spring as an origin theory for the mound.

Somebody asked about the size of the impactor that made the crater. Gale is about the same size as Chicxulub, which is linked to the extinction of the dinosaurs, and is said to have been made by a 6 mile diameter asteroid.
xflare
What kind of theories and ideas are floating around to possibly explain the composition and origin of the Glenelg/high thermal emission region? It seems to be right at the base of the Alluvial fan. Perhaps it's where that water pooled into a small lake.
ngunn
See the discussion I referred to in post 10 for starters, plus the MSL team's conclusion that the fan extends to the landing site, i.e. beyond the margin of HTIF.
Eyesonmars
QUOTE (serpens @ Sep 28 2012, 05:10 AM) *
Not unique. Emily did a rather nice presentation on this.

http://www.planetary.org/blogs/emily-lakda.../2011/3144.html


I based my comment on many hours of using the VERY cool app "Mars Globe" by M. Howard and brought to my attention by E. Lakdawalla. It is a must have app on the iPad. (everyone I show it to is fascinated by it)
While I do see quite a few craters with what might be central sedimentary mounds. Most of them could also be remnant central peaks and are much smaller compared to their craters than Mt. Sharp.
Art Martin
I'm having a hard time reconciling from the newly released pictures where exactly Glenelg is in them. When I look at the overhead route updates it appears the rover is moving East (I'm assuming North is to the top of the image) along the base of Mt Sharp with Glenelg further to the East. Logic says that if we're facing Glenelg and targeting it in the images, Mt Sharp should be to the left and yet all the images being returned are looking to the left of Mt Sharp or at its left-most flanks. Could someone show an overhead route map that includes where Mt. Sharp is in context of our journeys and what direction these latest images are pointing.
ngunn
QUOTE (Art Martin @ Sep 28 2012, 09:01 PM) *
Could someone show an overhead route map that includes where Mt. Sharp is in context of our journeys and what direction these latest images are pointing.


Here:
http://www.unmannedspaceflight.com/index.p...st&p=192020
Phil Stooke
Art, Mt Sharp runs all around the south horizon from due east to south to southwest. It's really big! The pics ngunn linked to show that well.

Phil
elakdawalla
I made this two days ago -- it's an un-polar projection (if that makes sense) of the CTX image of Gale, centered on Curiosity's landing site. The bottom edge of the image is Curiosity's location (the "pole," if you will); the top edge is about 18 kilometers away. Everything along the same horizontal line in this image is at the same distance from the rover. Due south is in the center of the image; due north is at the edges.

The sand dunes skirting the mountain occupy about 160 degrees of Curiosity's point of view, which means you'll see the mountain on your right if you're looking east, on your left if you're looking west, and in front of you if you're looking south; the only time the mountain wouldn't be in your field of view is if you're looking north.
Art Martin
Thanks, so much clearer now. I just had no idea of the scale of things before. The link from ngunn put things into perspective and spun me around the right direction. Amazing image Emily, thanks. The lines showing our travels wouldn't even show up on your picture other than maybe a pixel. Ok back to lurking in amazement.
ngunn
QUOTE (elakdawalla @ Sep 28 2012, 09:08 PM) *
un-polar projection (if that makes sense)


I really like these. James Canvin used them effectively to identify horizon features seen by Opportunity and he calls them 'inverse polars'. I think that's a good term for them. Any chance of extending yours to include the crater rim?
elakdawalla
That is precisely what I was using it for. Don't know when I'll get to finish this, so here's a preliminary version, featuring a touch of Phil-O-Vision.

It'd be easy to make a version extending to the rim. How many pixels wide would be useful? Is 3600 enough? 7200?
fthurber
QUOTE (elakdawalla @ Sep 28 2012, 06:17 PM) *
That is precisely what I was using it for. Don't know when I'll get to finish this, so here's a preliminary version, featuring a touch of Phil-O-Vision.

It'd be easy to make a version extending to the rim. How many pixels wide would be useful? Is 3600 enough? 7200?


WOW! Nice job. BTW, the dragon's teeth at the bottom of the sulfate layer look like nunateks, but, of course, they are not. I assume that the vertical scale in the bottom picture is exaggerated, right?
elakdawalla
Here you go. Attached version is 3600 pixels wide (10 pixels per degree) and somewhat compressed. Here is a less-compressed 7200 wide version. The original data for this one was at about 55 meters per pixel, so it's of lower quality in the near field, but it's fine at the distance of the crater rim.
atomoid
QUOTE (Eyesonmars @ Sep 27 2012, 02:16 PM) *
Also note that Curiosity is sitting on or very near the lowest spot on the planet (outside of Hellas). ...

i'd always thought Hellas was an ancient ancient impact resulting in a sort of unsuspecting ocean basin much later, though i don't know if theres much evidence of that.
Makes me wonder on how much Gale's similarly lower elevation affected atmospheric pressure back during that thicker warmer atmosphere? im curious what models might suggest as far as atmospheric pressure at Gale vs the mean elevation during that time and if it makes sense to expect that to have much impact on making a Gale lake more habitable.
Or the processional inclination at the time might have kept the Gale interior iced over with Vostok-style lake beneath but probably heated by plenty of geothermal activity. how much glaciation and erosion of the crater walls would be expected under that scenario and if extensive, could evidence of that type have been erased by now.
ok, too many stray hairs, i wont even get started on Mt Sharp, its all too enigmatic..
dvandorn
QUOTE (atomoid @ Sep 28 2012, 08:34 PM) *
i'd always thought Hellas was an ancient ancient impact resulting in a sort of unsuspecting ocean basin much later, though i don't know if theres much evidence of that.

I used to think along those lines, too. But the orbiters (especially Odyssey) have seen almost no indication of hydrogen in Hellas -- i.e., no indication of subsurface ice or even strongly hydrated materials.

Instead of harboring water in the past, these results tend to indicate that Hellas has never seen much water at all. I think that's likely why it has never been considered as an attractive landing site, even though it is such a low spot that the atmospheric pressure there is higher at the surface than just about anywhere else on Mars.

Hellas would be a wonderful landing site if you're looking to examine Martian mantle materials, because it is certainly deep enough to have exhumed mantle rocks. Geologically speaking, it's very attractive. But since the main interest in Mars is (and, I think, always has been) the investigation of water, habitability and life, the geologic questions that drove the exploration and analysis of the Moon are taking a back seat to the water- and life-seekers when it comes to Mars.

-the other Doug
fthurber
QUOTE (dvandorn @ Sep 28 2012, 10:36 PM) *
Instead of harboring water in the past, these results tend to indicate that Hellas has never seen much water at all. I think that's likely why it has never been considered as an attractive landing site, even though it is such a low spot that the atmospheric pressure there is higher at the surface than just about anywhere else on Mars.


Hi Doug

Was Hellas was thought to have some glacial formations? Maybe the ice is covered so deep by rock debris and dust that it cannot be picked up by the spectrometer. However my source is Wikipedia so that may be wrong. http://en.wikipedia.org/wiki/Hellas_Planit...sible_glaciers/ Supposedly MROs radar sounder saw it.

drz1111
A question about redox and sedimentary paleoenvironments on Mars:

One of the things I've been thinking about the last few days is that my instincts w/r/t paleoenvironments is all wrong when it comes to Mars.

Take "hottah" - when I saw that, I immediately thought "oh, its cool as hell, but I see why they didn't stop there - fluvial conglomerates are notoriously poor environments to preserve organics".

But that's wrong, or rather, potentially wrong, on Mars, isn't it? It's true on earth in post-proterozoic rocks b/c the atmosphere is oxic and sediment deposited in well-mixed water will lead to oxidized organics, most likely through biologic activity.

But who-the-hell-knows what the Mars atmosphere was like when those conglomerates were deposited? Wouldn't it be more likely that the conglomerates were deposited in a reducing environment, like those auriferous precambrian conglomerates in south africa? Is that necessarily a bad environment for preservation of organics?

Which leads me to my next point, color. When you look at some of the finely-bedded outcrops that the pictures are showing, they're clearly darker and, more importantly, greyer than the overlying rocks (e.g. compared to the hottah, which seems to be a light tan). Earth-instincts; that's a shale or shale-like rock, deposited in an anoxic environment.

But why would that be so on Mars? I guess EVERY lacustrine-type depositional environment on Mars could be anoxic, but, that's not consistent with where Mars eventually evolves to and what MER observed. Redox is all a big mystery, right? We don't know the chemsistry, and one thing that seems likely is that the biologicially mediated redox chemistry that you see in sediments in Earth is unlikely to apply there. And do our usual Earth-honed instincts about color & redox state of the paleoenvironment hold true?

And, to sum it all up, to the extent we don't know much about any of the above, how the heck do we know where to look for preserved organics?
elakdawalla
Re: Hottah, that's a good question, and there were a lot of talks at landing site selection meetings about what kinds of rocks were good for preserving organics. Grotz's emphasis through the last three rounds of meetings was preservation, preservation, preservation. High-energy environments like mountain streams are not good places. Fine sediment settling in deltaic environments are good, which was why Eberswalde was the other favored landing site. So you're probably right, Hottah was cool but not the paleo-environment they were looking for. Glenelg has better potential.

Mars doesn't have an oxygen atmosphere but it does have strong oxidizers acting at the surface, so some of the chemistry is analagous. That goes out of my depth though. Check the landing site selection meeting website, there are probably some presentations addressing Martian aqueous chemistry.
Eyesonmars
The area Curiosity has been traversing has quite a few small, mostly ghostly, circular features ( looking at the route map). Assuming they are impact related - are they primary or secondary impacts ? Do they date from the time of creation of the deposit or have they been created after/during erosion exposed the surface. I'm surprised at how dense they area. Our eventual target area, the phyllosilicate area, also has these craters in abundance. They seem to have a maximum size cutoff.
What do they tell us ?
drz1111
QUOTE (elakdawalla @ Oct 1 2012, 03:03 PM) *
Re: Hottah, that's a good question, and there were a lot of talks at landing site selection meetings about what kinds of rocks were good for preserving organics. Grotz's emphasis through the last three rounds of meetings was preservation, preservation, preservation. High-energy environments like mountain streams are not good places. Fine sediment settling in deltaic environments are good, which was why Eberswalde was the other favored landing site. So you're probably right, Hottah was cool but not the paleo-environment they were looking for. Glenelg has better potential.

Mars doesn't have an oxygen atmosphere but it does have strong oxidizers acting at the surface, so some of the chemistry is analagous. That goes out of my depth though. Check the landing site selection meeting website, there are probably some presentations addressing Martian aqueous chemistry.



Mars has strong oxidizers acting at the surface now. IIRC, however, the redox chemistry is thought to have been totally different back when clays may-or-may not have been being deposited. I would presume in a higher-Ph surface environment, most sedimentary settings would be reducing - like Precambrian earth.
ngunn
Eyesonmars: Interesting question. Here's an off-the shelf response based on the conventional story about impact crater counts and age of surfaces. No big craters means a spell of significant deposition or erosion since heavy bombardment ceased. Many small craters means little net deposition or erosion for a very long time after the reworking of the surface that erased the big ones.

This being Mars you'd have to add that these little craters must have formed into a relatively dry surface since the little impactors couldn't have penetrated a significant thickness of water or ice.

Like you, I think the peculiar density of craters here, just above the Glenelg boundary, is significant. It could signify the exposure of an ancient surface neither mantled (as at Bradbury Landing) nor scoured away (Glenelg high thermal inertia unit). I note its similarity to the third type of terrain to the SE of Glenelg.
Eyesonmars
QUOTE (ngunn @ Oct 1 2012, 09:31 PM) *
Like you, I think the peculiar density of craters here, just above the Glenelg boundary, is significant. It could signify the exposure of an ancient surface neither mantled (as at Bradbury Landing) nor scoured away (Glenelg high thermal inertia unit). I note its similarity to the third type of terrain to the SE of Glenelg.

Pure conjecture here: If this dense crater network is an ancient feature that has been exhumed recently can we infer that the atmosphere must have been quite thin at this time? As I understand it there is a relationship between minimum crater size and mass of an atmosphere. IF so, and ( another IF) the cratered surface dates to roughly the time of the next surface below - our alluvial fan/stream bed - does this fact influence our interpretation of what we assume (almost certainly) is the water carved/deposited features in front of us ??
ngunn
I've just come across this detailed thermal inertia map. Let's see if the link works:
http://www.nasa.gov/images/content/692124m...-43_946-710.jpg

EDIT Well it sort of worked, but it leaves out the caption and the link to the bigger version. I'll have another go . .
http://www.nasa.gov/mission_pages/msl/mult.../pia16159.html#

smile.gif
djellison
Yes - the full size is here : http://www.nasa.gov/images/content/692127m...9-full_full.jpg

I find the NASA HQ websites very hard to navigate so I tend to use the photojournal where you'll find it also

http://photojournal.jpl.nasa.gov/catalog/PIA16159

(PS Base map from Fred Calef, annotation by me )
ngunn
Brilliant! Thanks Doug. While you're on the line, can you point us to a contour map of this place (my quest in post 1)? We're in an enclosed basin and since ancient liquid water is in play I'd like to get a sense of which direction is down and where the bottom is.
djellison
Contour - no - but there is this - http://photojournal.jpl.nasa.gov/jpeg/PIA16158.jpg
You could have found it by going to the first page under 'Mars' on the photojournal.
ngunn
That's good, and there's also this:
http://blogs.esa.int/mex/2012/08/03/gale-crater-in-3d/

However they're not really at the level of detail required to help us 'on the ground'.
Eyesonmars
True. But even at 100 meters/pixel you can just make out the channel where it enters Gale crater and the upper portions of the alluvial fan.
(we are looking southwest so the channel enters from the far right)
elakdawalla
Peter Grindrod has a good blog entry on this topic.
ngunn
Just what I was looking for, thanks Emily.
ngunn
I am particularly intrigued by the enclosed depression on the right of Peter's contoured elevation map:

http://petergrindrod.net/wp-content/upload...g-site-topo.png

The depression coincides exactly with the outer margin of the high thermal inertia fan (HTIF). I'm also curious about where the substantial quantity of flowing water that formed the fan was actually flowing to. I'm toying with the idea that it spread out and froze in place, forming over time a substantial ice deposit. I don't know the proper name for such a thing so for now I'm calling it an 'ice snout'. Maybe all of the HTIF is a marker for the former extent of the ice snout. Sublimation of volatiles is widely invoked to explain hollows. Here we appear to have a hollow and a ready supply of volatile material at some time in the past. There are what look like polygonal markings on the bottom of the depression. Where have we seen that before? I can't wait to get down there.
Eyesonmars
QUOTE (ngunn @ Oct 6 2012, 10:30 AM) *
I am particularly intrigued by the enclosed depression on the right of Peter's contoured elevation map:

http://petergrindrod.net/wp-content/upload...g-site-topo.png

Sublimation of volatiles is widely invoked to explain hollows.

Hmm - The peculiarity of the craterlet density in the unit covering the area SE of Glenelg has been mentioned earlier in this thread. Notice the complete saturation and fairly uniform size of these little hollows in the eastern part of this unit.
Could this unit be a remnant of a sediment saturated outflow that was deposited more or less all at once ?? Assuming the slurry is near the triple point pressure of H20, small variations in conditions within the slurry could result in explosive boiling one place while a few meters away the slurry is still liquid. At the same time it is rapidly freezing on its surface so that the little craterlets that are left behind as the vapor bubble breaks the surface are flash frozen in place. IF the slurry is thick enough the craterlets might still be discernible as the remaining H20 slowly sublimates away and the remaining dry deposit settles.
(this is somewhat consistent with your "ice snout" idea)
ngunn
It's fun to look at those craterlets and imagine the kind of one-off event you describe, although I'm having difficulty with the idea of individual bubbles of the required size. There's a long timespan and a wide range for climate parameters (including, crucially, the total mass of the atmosphere) available as possible conditions for the processes that formed this landcape so it's open season for imaginative suggestions, I think.

EDIT: I've looked again and the crater sizes go right down there: too small for impacts under any kind of atmosphere. Interesting.
Eyesonmars
I agree. It is great fun to try to imagine processes that are beyond our earth biased experiences.
Over on the "Temperature and Pressure" topic I've been making trouble with the goal of perhaps gaining some insight into the subject of this thread.

It is hard to imagine how water might behave around the triple point on a large scale in a low g environment since it is beyond our earthly experience. But small changes can have major phase consequences. In addition, in the low Martian gravity I would imagine the bubbles would grow larger than on earth .... true?
Eyesonmars
Also - as you queried - Where is the water flowing to

I've always been struck by the apparent contradiction between the ubiquitous, planet-wide evidence of flowing liquids on Mars but the almost complete lack of any strong evidence of any standing liquids on Mars at any time in Martian history. Mars is trying to tell us something.
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