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ngunn
QUOTE (Eyesonmars @ Oct 6 2012, 10:30 PM) *
the almost complete lack of any strong evidence of any standing liquids on Mars at any time in Martian history


I don't think that's quite true. I'm fairly persuaded by the the northern ocean shorelines. But you're right. It is the nature of water on Mars to do its deed and disappear, into space no doubt but also under ground (perhaps not very far).
serpens
QUOTE (Eyesonmars @ Oct 6 2012, 09:08 PM) *
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.


The evidence of long lasting fluvial activity around and in gale would seem to indicate that the pressure and temperature 3 to 4 billion years ago was significantly different to today. From the apparent inverted channels it seems that most recently Gale has gone through a significant deflationary cycle. The topography during the fluvial period may have been quite different to today and some of the effects such as the hollows could be attributable to differential erosion.

The low/high thermal inertia units look like part of the same fan. An alluvial fan that transitioned to an alluvial fan delta when it encountered standing water? Stranger things have happened.
ngunn
QUOTE (serpens @ Oct 7 2012, 04:22 AM) *
The low/high thermal inertia units look like part of the same fan. An alluvial fan that transitioned to an alluvial fan delta when it encountered standing water? Stranger things have happened.


Another interesting idea. smile.gif Does the LTIF/HTIF boundary follow a topgraphic contour, and if so, how big an area does that contour enclose? We will need a more extensive map to answer such questions.

Here's a variation on my 'ice snout' suggestion. In warmer conditions the fan could have terminated in a 'salt snout' rather than an icy one. Flood the whole area at a later epoch and the salt redissolves - another way to form a hollow perhaps. (Would that count as differential erosion?)
Fran Ontanaya
Mmh, is the assumed order of events: 1) the last sulfate layers of Mt Sharp were deposited; 2) Mt Sharp was eroded; 3) The fan was deposited on the new floor of Gale Crater?

In that case the fan would be from an age long after conditions were suitable for the standing acidic water that created Mt Sharp layers, and after a dry period in which all the erosion happened. Maybe the atmosphere was gone already, and they were just seasonal flash streams from molten ice that then sublimated away.
serpens
The filled then excavated crater hypothesis seems a logical explanation for the reasonably thick clay layer exposed at the base of Mount Sharp (neutral pH), beneath the sulphates. The clay layer could be a lacustrine deposition and if so then the fan would possibly have formed at that time, been covered and then excavated. Curiosity will probably be able to clarify with ground truth.
Ondaweb
QUOTE (Eyesonmars @ Oct 6 2012, 04:30 PM) *
Also - as you queried - Where is the water flowing to

That's the question I wanted to ask on this forum also. I'm interested in identifying the lowest point in Gale between here and where we expect to head up to Sharp for two reasons: 1. It may be where some water went as some time in the geological history of Gale and 2. It could/should be the point where we'd expect to find the oldest layers in the stratigraphy of Gale/Sharp. I didn't identify any mention of such a location in the Anderson paper (not that that means it isn't there). It would seem orienting to me to know where that is and what's already know about what's there (for orbital images, spectroscopic studies, etc.)
ngunn
There are contours derived from CTX by Peter Grindrod here:
http://petergrindrod.net/wp-content/upload...CTX-context.png

That shows we are right on the edge of an enclosed depression. I don't know whether it's the deepest in the whole crater, but if water flowed over the alluvial fan today I think it would have nowhere to go except into the hollow we are overlooking now.
pgrindrod
After a few requests, I've made some base maps of Gale and the Bradbury Landing site at a few different zoom levels.

They're all linked over here, with a bit of an accompanying explanation.

A scaled down example of what's there:
Click to view attachment

Hopefully they might be of some use in discussions like those above.
Pete
ngunn
Extremely helpful and much, much appreciated. smile.gif smile.gif smile.gif
Ondaweb
Thanks Pete, very helpful indeed. One of the things I keep wondering about is the much bigger inflow channel (and alluvial fan?) coming in from the southwest crater rim. These maps show there is a very big "sink" at the end of the "fan" (roughly due west of the peak of Sharp), much bigger than the one at Glenelg. It would seem that deposits from that channel would not come into play at Glenelg by my reading, but I'm not sure of that. If the SW channel is the older one, I guess it's possible that it's deposits did reach Glenelg.
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:

QUOTE
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?

Click to view attachment

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
QUOTE (jmknapp @ Oct 15 2012, 08:30 PM) *
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:

Click to view attachment

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 smile.gif

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
QUOTE (Phil Stooke @ Nov 28 2012, 03:37 PM) *
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
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
QUOTE (elakdawalla @ Nov 28 2012, 11:48 AM) *
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
QUOTE (ddan @ Nov 28 2012, 10:12 AM) *
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.

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. smile.gif 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.
Actionman
QUOTE (ngunn @ Nov 28 2012, 03:27 PM) *
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.
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?
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
QUOTE (mcaplinger @ Nov 28 2012, 01:25 PM) *
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
(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
QUOTE (SteveM @ Nov 28 2012, 09:08 PM) *
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.
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
QUOTE (Actionman @ Nov 29 2012, 04:20 PM) *
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
QUOTE (Actionman @ Nov 29 2012, 07:20 PM) *
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
QUOTE (Actionman @ Nov 29 2012, 04:20 PM) *
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.
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
QUOTE
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.
Actionman
And thank you Ludo.

Make it so
centsworth_II
QUOTE (Actionman @ Nov 30 2012, 07:13 AM) *
...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
QUOTE (Actionman @ Nov 30 2012, 04:13 AM) *
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.
Ant103
Can I ask something ? Not very important, but for me it is. Modifiy the thread from "Geomorphology" to "Areomorphology". As "Geo" came frome "Gaia", the Earth in Greek mythology, so as "Areo" from "Arès", Mars in Greek mythology. But I will understand that's not necessary for the quality of this thread. After all, we use specific word to qualify a day on Mars like "sol" wink.gif.
ElkGroveDan
Not a good idea. The science of geology is what is being discussed here. If you drop one Greek root then you have to drop them all and it starts to sounds like nonsense.
Actionman
In this GIF from the above Mr. Anderson and James F. Bell paper they illustrate their view of the basal layer with the possibility of some of which maybe exposed. The examination of any of this is mandatory NMHO. More over I don't think it will be visible. Out of sight out of mind, apparently.


djellison
QUOTE (Ant103 @ Nov 30 2012, 09:46 AM) *
Can I ask something ? Not very important, but for me it is. Modifiy the thread from "Geomorphology" to "Areomorphology".


What would you call Phobos geology. Deimos. Venus. Europa. Dione. Our own Moon. Titan. Nix. Hydra. Tempel 1. Itokawa. There are hundreds and thousands of worlds out there for us to explore, study and understand - and the science we will be practicing is geology / geomorphology / geochemistry etc etc.

Having a different word for the same scientific discipline just because it's a different place is nonsensical.

Ant103
Okay, I understand totaly smile.gif I was just asking. It's funny because in french, when you land a probe onto a surface, we use the word "Atterrissage", with the root "Terre" aka Earth in english. And I'm against using word like "Amarsissage" when you land something on Mars. So then, yeah, I think I was a little too bit enthousiast wink.gif. Nevermind smile.gif. And thanks for the answers.
djellison
QUOTE (Actionman @ Nov 30 2012, 09:54 AM) *
they illustrate their view of the basal layer with the possibility of some of which maybe exposed. The examination of any of this is mandatory NMHO. More over I don't think it will be visible. Out of sight out of mind, apparently.


You know that Basal and Basalt are not the same thing, right?

Not visible? They've already seen it (and attempted to characterise it) from orbit!

From Page 105-106 of their paper ( for those unfamiliar - it's available here - http://www.marsjournal.org/contents/2010/0004/ )
"Light-toned basal unit
The light-toned basal unit is distinguished from the crater floor units by a sharp drop of ~10 m (Figure 34a). The light-toned basal unit has a CTX albedo of up to 0.20, and is primarily composed of fractured rock that in some locations has a subtle texture suggestive of layering (Figure 39b). It has a moderate thermal inertia ranging from roughly 500-540 J m-2 K-1 s-1/2. Mesas of mound- skirting unit are common on top of the light-toned basal unit (Figure 34b), and much of the basal unit is covered by dark-toned mafic dunes. The light-toned basal unit slopes upward in a series of poorly-defined fractured, light-toned layers to form the northwestern side of the light-toned ridge unit (Figure 36a).
Dark-toned basal unit
The dark-toned basal unit (Figure 39) has a higher thermal inertia (~780 J m-2 K-1 s-1/2) than the light-toned basal unit. It has an albedo of 0.15-0.16 and occurs to the southwest of the landing ellipse and the light-toned basal unit. The transition between the light and dark-toned basal units (Figure 40) is sharp and the dark-toned basal unit appears to be topographically lower than the light-toned basal unit. This suggests that it is either stratigraphically lower or that the dark-toned unit is younger and fills a depression that had been eroded into the light-toned basal unit."


Plus - the paper goes on explicitly define a location to visit to help in characterizing it is an important stop on any MSL traverse.

Actionman
Basal and basalt are important distinctions both of which are said to scattered on the surface.
Any intact strata should be checked for type. That's all I'm saying.

And no, basal strata in large thick strata placements are not visible from space here at Gale Crater.
djellison
You can not scatter 'basal' on the surface. Basal is a descriptor derived from location. The basal unit is the bottom unit. It's not a type of material - it's a placement.

The basal unit IS visible from space. How do you think they mapped it and characterized it from orbit. Read the paper. Heck - just read the description I cited above.
ngunn
With the Anderson and Bell diagram easily to hand could somebody clarify for me which geologic unit we actually landed on? Bradbury Landing is located beyond the outer margin of the HTIF yet the rocks on the traverse have been identified as fan deposits. So did we land on a detached portion of LTIF? A patch of MSU?
djellison
We're (I think) in the area where the HP, HTIF and LTIF all meet - that three way junction at Glenelg. I'm guessing we landed on LTIF. Broken up fan deposites with lots of sand/fines etc would show up as low TI I would expect ( which is what we've seen) The brighter material to the N/E of us is the HTIF I believe. When we head south, we'll be on HP.
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