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)
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?
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.
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
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
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...
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.
(Thanks admin )
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.
The operative sentence from the http://marsjournal.org/contents/2010/0004/files/anderson_mars_2010_0004.pdf paper:
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.
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
Add to that the possibility of quite a lot of ice in the original crater fill and you have sublimation as another removal mechanism.
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
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.
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.
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.
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.
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
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.
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.
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?
Here you go. Attached version is 3600 pixels wide (10 pixels per degree) and somewhat compressed. https://planetary.s3.amazonaws.com/assets/images/4-mars/2012/gale_unpolar_crater-rim.jpg 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.
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?
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 http://marsoweb.nas.nasa.gov/landingsites/, there are probably some presentations addressing Martian aqueous chemistry.
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 ?
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.
I've just come across this detailed thermal inertia map. Let's see if the link works:
http://www.nasa.gov/images/content/692124main_Grotzinger-4-pia16159-43_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/multimedia/pia16159.html#
Yes - the full size is here : http://www.nasa.gov/images/content/692127main_Grotzinger-4-pia16159-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 )
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.
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.
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'.
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)
http://www.petergrindrod.net/archives/858
Just what I was looking for, thanks Emily.
I am particularly intrigued by the enclosed depression on the right of Peter's contoured elevation map:
http://petergrindrod.net/wp-content/uploads/2012/08/Gale-GIS-HiRISE-landing-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.
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.
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?
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.
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.
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.
There are contours derived from CTX by Peter Grindrod here:
http://petergrindrod.net/wp-content/uploads/2012/08/Gale-GIS-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.
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 http://www.petergrindrod.net/archives/886, with a bit of an accompanying explanation.
A scaled down example of what's there:
Extremely helpful and much, much appreciated.
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.
A https://gsa.confex.com/gsa/2012AM/finalprogram/abstract_211271.htm 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:
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/msl/workshops/5th_workshop/talks/Tuesday_AM/Anderson_Gale_Traverse_compressed_final_opt.pdf
Greetings,
Ludo.
Ludo, thanks for that--looks like a good inference, based on the caption. Here's a full-res HiRISE detail from the area:
Greetings from Russia
I want to share my observation.
I looked at pictures and noticed that many of the stones are similar to volcanic.
http://www.keepme.ru/upload/images/2012/11/05/c9177f8eb4497c200437d459b4fb5395.jpg
It seems even that lava river.
http://www.keepme.ru/upload/images/2012/11/05/d7cb44164e5852983c3805212e7fb4da.jpg
So close to be a volcano?
This is clearly not Elysium Mons
In the north-west is the mountain, which can be a volcano?
http://www.keepme.ru/upload/images/2012/11/05/f0c8f86801602cae93e913c5b4989614.jpg
It turns out it can be a source of the alluvial fan and inverted (lava?) channels?
http://www.keepme.ru/upload/images/2012/11/05/ca44cdcdb6153cdbf3c6c80897f78d22.jpg
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 http://www.unmannedspaceflight.com/index.php?act=boardrules please.
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.
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
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
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?
My thought involves this element. It looks as a wave or stream consequence.
Are you suggesting that Mt Sharp is just a pile of terminal moraine?
Where is the evidence for the glaciers themselves - the glacial valleys?
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.
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
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.
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.
I think the term you want is 'basement rock' rather than 'bedrock'.
And thank you Ludo.
Make it so
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" .
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.
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.
Okay, I understand totaly 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 . Nevermind . And thanks for the answers.
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.
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.
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?
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.
That's fine for HTIF and HP, but going on Anderson and Bell's map there should be no LTIF at our current location. They have the LTIF mapped to the north of the HTIF while we are to the south of it, hence my query.
http://martianchronicles.files.wordpress.com/2010/09/figure7.jpg
I've been thinking that the landing site was HP, having missed the fan, as you say, to the north. But our confusion is, I think, owing to the inherent complexity:
The distinctions we're talking about are not necessarily visible or even rigorously meaningful. Thermal inertia is a property that can vary from place to place on the basis of any combination of changes in composition or fine-scale morphology in potentially-wicked interaction between the visible surface and the near subsurface. Maybe MSL landed outside the area that Anderson and Bell colored as "fan" on their map, but is nonetheless in an area where the fan material is present, but in combination with other stuff so as to give it a different thermal inertial. In fact, there's no logical disconnect between these labels: "high thermal", "fan unit", "hummocky", and "plains" are potentially overlapping in any combination because they four different kinds of property.
I think MSL missed the region that A&B labeled as being the fan, but may in fact have some of that fan material all around, in some fraction, anyway.
On a very similar theme, I was surprised, having read A&B carefully, how difficult I find it to see the units on Mt. Sharp, which seem apparently in the B&W images taken from orbit, in the images from MSL. There are many possible reasons for this, including the viewing geometry, the image properties (such as gamma), my lack of field geography savvy, etc.
A&B did a good job of imposing some logic and order on Gale, but in both the MSL landing site and the distant views of Mt. Sharp, things seem a little more chaotic up-close.
I was having the same issue you were in seeing the units on Mt. Sharp until I realized that most of the interesting stuff -- the clays and sulfates -- is actually in a trough at the base of Mt. Sharp and mostly not visible from where the rover landed.
Working out some comparisons of the A&B units to images from HiRISE and pointing out locations on the landing site panorama has been on my list of blog entries to write for a long time, but it's a big project and I haven't made much progress yet.
(Replying to JR) All good points. I agree that the views from the ground are taking us into a post-A&B era. But the meeting of three distinct terrain types at Glenelg is most clearly seen in the orbital images so it didn't take Curiosity to show us that.
High thermal inertia is, I think, indicative mainly of a lack of loose cover over the bedrock. In Anderson and Bell that is identified with a particular rock unit, but why would one particular type of rock preferentially remain clear of debris? I think ithe HTI
disribution may be controlled more by the geographical context of the removal process and the ease of removability of whatever material used to cover the bedrock.
EDIT
Emily: good luck with that project - I look forward to seeing the results
In the conclusion section of the abstact for Anderson and Bell III: Mars 5, 76-128, 2010 open access paper,
there is the following sentence -"Some layers in the mound are traceable for >10 km, suggesting that a
spring mound origin is unlikely."
My understanding of that would be that Mt Sharp was not cemented together by underground (upwelling) mineral water flows during,
I guess, - the period when Gale crater was buried in sediment. Because earlier it is said "The rim of Gale Crater is dissected by
fluvial channels, all of which flow into the crater with no obvious outlet." As well as, I guess, that hot springs would be variable in flow,
time and location? After doing some Googling apparently hot spring can create mounds using nothing but precipitated minerals. However;
I don't now how that would relate to the 10 km layers. Would be enough to say that a mound with many layers wasn't created by hot springs?
Or am I completely misunderstanding what the sentence is trying to communicate?
Yep, Mars' surface is primarily basaltic, no doubt. And like the Moon, much of the original crust has been highly brecciated by the Late Heavy Bombardment (the "event" which likely resulted in the Gale impact, among tens of thousands of other impacts of similar size).
Analysis of basalts, where they were emplaced, would give us a nice feel for what was happening in Mars' mantle while the majority of the basaltic eruptions occurred and the basalt was emplaced on the surface. Sort of a snapshot of the mantle during the period(s) of heavy volcanism. However, it is the alterations and re-depositions of that basaltic set of "building blocks" that tell us about the climate and conditions on the surface after the basalts were originally emplaced.
So... Gale is not a good place at all to survey variations in directly emplaced basalt flows. The occasional unaltered chunks of basalt lying on Gale's floor were likely transported from somewhere else (be it a few kilometers to hundreds of kilometers from where a rock might rest right now). It is, however, a wonderful place to look at the history of re-deposition and alteration of rock beds (and even deflation of covering beds), much of which (it seems to me) has to have happened when the alteration, deposition and deflation processes that went on were far more active than they are now.
Since one of the main purposes of Curiosity is to try and characterize those processes (because those processes, once understood, then highly constrain the climate and environment in which they occurred), Gale is a very good place. Precisely because this is a place where we can study the history of those processes and try to understand them.
-the other Doug
I think that rock high thermal inertia is a lava stream, from a volcano about which I wrote http://www.unmannedspaceflight.com/index.php?s=&showtopic=7481&view=findpost&p=194143. Ancient eruption caused a wave of a lava which became HTI. After eruption were weaker and began only water flows from the melted glaciers. So appeared the alluvial fan.
This hypothesis is hasty, but it seems to me logical.
Hope we discover soon.
Replying to stewjack, re: 10 km layer seemingly disproving a spring origin:
I remember encountering this passage for the first time. My interpretation was that a layer which extends 10 km and remains roughly constant in altitude indicates, if sedimentary, a massive reservoir of water filling the crater like a lake, whereas a spring would have a small origin and would not supply adequate water to create a level surface across such a great area. In fact, that seems like a profound understatement, although I suppose that depends entirely on how large the volume of a "spring" may be.
Since we only see the edges, I suppose, also that you could have a level visible edge at some distance away from and below the source of the spring (as the edge of, say, Olympus Mons is far away from, but below, the vent, and is nonetheless relatively level), but then Olympus Mons is hardly a "spring."
There are a couple of other reasons why attributing Mount Sharp as a spring mound will not hold water. The lower half of the mound transitions from phyllosillicates to sulphates but the upper half of the mound is a aeolian deposition. So a spring would not explain Mt Sharp. Further, if this was a spring mound then we are considering a huge volume of water - probably enough to fill the crater given the size of Mt Sharp, which would have almost certainly have resulted in a breach of the Northern crater wall. No such breach exists. Well that's my take anyway.
Is there any real evidence that Mt Sharp is anything but a typical central crater peak, albeit with modified surface units due to subsequent environmental variations?
If that's true then the areas of interest are these modifications and the processes that made them, not the mountain's origin.
The peak is too big and other similar size craters nearby don't have them so it's definitely atypical, probably the most extreme example of its kind on Mars.
I'm thinking about the possibility that Gale crater once had a much higher northern rim, at least as high as the top of the horizontal beds on Mt Sharp. If it formed at the edge of a frozen ocean maybe the north rim was largely composed of ice which has gone now.
nprev. I'm with you in that Mount Sharp probably has a central uplift core, but the bulk of the mountain is sedimentary. Have a look at a couple of the complex Lunar craters such as Maunder to get an idea of the relative size of a pretty much pristine central uplift.
The puzzle (and I deliberately avoid the word mystery) is why the sediment ended up as a central mound. I have difficulty accepting the explanation that the crater was overfilled to the height of (or greater than) Mt Sharp and then excavated, despite the credentials and credibility of the proposers. That hypothesis requires that the sediment that must have covered the rest of the crater and the surrounding area was totally removed while that on Mount Sharp was significantly more resistant. I'm backing a shallow crater lake for the phyllosilicates and a vortexing effect for the remainder. I don't have the smarts to model something so complex so take the last as being accompanied by wild guestures from the depths of an armchair.
If I don't say this as smoothly as I might otherwise, please forgive me. The thought racing around my brain delves into areas of physics about which I'm not completely confident.
First, it has struck me that dust devils form more easily on Mars than they do here on Earth. Considering how thin the air is and how cold the overall environment is, you would think there would be more energy available on Earth for such vortex formation than on Mars.
But, I says to myself -- Mars spins around its axis at roughly the same speed as Earth spins about her own axis. But Mars is significantly smaller. Its surface is rather closer to the center of rotation than is ours.
Would this not, based on conservation of angular momentum, mean that the coriolis force would be noticeably stronger on Mars? The spinning skater spins faster and faster as her arms are drawn towards her, and on Mars the difference in rotational speed between me and the spot 10 meters to the north or south is greater than at the same distance on Earth. And, if I understand the coriolis force correctly, it is this difference in rotational speed that drives everything from typhoons to dust devils to the swirl of water running down the drain.
So -- if I'm reading this right and the coriolis force on Mars is noticeably greater than on Earth, encouraging a lot more atmospheric vortex formation, how would this affect simple aeolian erosion patterns on an early Mars with a much thicker atmosphere than now?
Consider that in 6mb air pressure a modern Martian dust devil can pick up and entrain a pretty impressive mass of dust and pebbles. This process keeps much of the Martian surface swept clean of the ubiquitous orange-brown-yellow dust, the darker gray rock beds thus exposed forming the dark markings visible in telescopic images of Mars for more than a century.
How much more erosive would a thicker atmosphere be, if an increased coriolis force makes it tend to form vorteces at every opportunity?
This relates to the previous posts thus -- imagine Gale crater nearly filled with some form of fill. Then imagine a racetrack wind pattern running around inside the crater walls, breaking up into hordes of large dust devils which, due to the thicker air, are able to pick up tons of material and toss it high into the air?
You'd have a pretty dusty atmosphere all the time (which would tend to cool the surface, I imagine), but such a wind pattern might be able to deflate an *awful* lot of material out of a crater in a pretty short time, at least in geologic terms.
Maybe it was such a dust devil breakout phase that deflated a lot of crater fill on Mars?
-the other Doug
^ I tend to wonder if there was a relatively long timescale (like Milankovitch, not seasonal) dust cycle, in which dust was deposited in strata in low energy periods, and excavated by aeolian processes during high solar energy time periods. Throw localized water into the mix, and I wonder if a little water created some inverted channels that were more resistant to the wind erosion that removed the surrounding dust.
It would be interesting with a thicker, dustier atmosphere perhaps also including volcanic ash, whether you could come up with a plausible model for craters being filled with thick dry strata of dust in a period of relatively calm winds, followed by a clearer, windier epoch in which convection and winds undo what was done.
An internal heat source beneath Gale can do more than locally hardening the sediments once formed. It could be the reason they formed in the first place. Imagine a largely frozen Mars with plenty of water in the form of ice or ice-capped seas. Now in Gale Crater picture a geothermally heated lake that is at least sometimes ice-free. The liquid surface acts as an effective dust trap 'quickly' filling the whole thing with horizontal sediments. This avoids the need to bury and exhume a similar pile of sediments on a planet-wide scale.
Fred - thank you.
And Other Doug.....I've never had a visit to the dry deserts of California when I didn't see dust devils. They're very very common here on Earth. Far more common than you think.
I still like the spring mound idea.
The rover is currently seeing a lot of rocks which look spongy and porous. What if there is a thick layer of such rock underlying Gale Crater? In wet, high atmospheric pressure climates these rocks would fill up with water, creating a large aquifer.
Then the atmospheric pressure drops quickly, due to carbon dioxide freezing out at the poles.
The drop in pressure reduces the boiling point of water, and the water in the aquifer starts to boil. The porous beds slope upwards towards the center of the crater, so the warmer less dense fluids migrate in that direction. They erupt from Mt Sharp, leaving behind an evaporite deposit.
The chemistry of the evaporite depends on the chemistry of Martian water and the atmosphere at the time. When the atmosphere was rich in sulfur dioxide, sulphates were formed. More recently, another mineral, maybe carbonates was deposited. Martian winds have eroded Mt Sharp over time, giving the deposits an aeolian appearance.
The lowest clay bearing layers might be old lakebed deposits which were covered and protected from erosion by later materials.
Mt Sharp could be the result of a long history of oscillations in atmospheric pressure which alternately filled an aquifer and then dropped the pressure enough to boil it.
I dunno; sounds like a bit of a reach to me.
Meh; we'll know a LOT more about Gale in a couple of years, certainly enough to constrain these hypotheses based on actual data.
Maybe. But despite Curiosioty's impressive capability compared to the MER she is still pretty much constrained to analysing the immediate surface. Translating findings to the macro environment of the far past may be a bit of an ask.
Didn't say 'solve'; just constrain.
Oh yeah. Gotcha. Duuh - put it down to a senior moment.
As currently conceived, scientific value vis-a-vis the structure of Mt. Sharp is that the most interesting stuff is the oldest materials which are at the bottom. First Curiosity has to get there. Then, as Curiosity ventures higher, it will basically be visiting more recent areas in martian history and perhaps arrive at the same location/era that typified Meridiani - wet but acidic. This is a bit less interesting for several reasons, not least of which that Opportunity already spent years exploring it (with a poorer set of instruments), and that acidic water is in various ways less earthlike and perhaps depleted in other interesting dynamics. Additionally, the structure of Mt. Sharp appears to have much, much thicker layers representing more recent layers, so even given a constant speed of march in terms of terrain, the rate of march into more recent martian history will slow dramatically; in essence, the upper layers appear to be less diverse than the lowest layers.
All of that, is of course based on the best speculation. There's no guarantee that the most interesting single rock on Mars isn't perched high on Mt. Sharp. But rational planning will be based on weighing the expectations with the effort and the risk.
This is all simply to say that when (if we are fortunate enough for all to proceed with success for decades) Curiosity reaches a certain high location on Mt. Sharp, there will probably be a desire to bring it back down, and that will probably be slowed by terrain.
So if I had to place my bets, it'll be that we'll have a wait for the most interesting stuff, then we'll have a long bonanza of peak interest followed by diminishing returns before Curiosity reaches a peak altitude and the decision is made to bring it down to explore the lower altitudes laterally. While layers are emplaced according to chronology, this arrangement is "patchy"; whichever route it takes up, there'll be other units on other paths. Anderson and Bell describe two ascent routes with similar but non-identical attractions. I think we'll have to wait through a relatively boring descent, before a "second coming" when Curiosity gets back down to the layers of primary interest and finds some of the things it missed on the way up.
And of course, this is only an educated guess. The most interesting thing(s) Curiosity finds may come at any time and in any place. That's why it's exploration.
'Relatively boring descent' is relative, of course. The roads to Victoria and Endeavor certainly weren't!
I like the idea of acidic weathering being responsible for some of the spongy rocks, but I don't know if the present environment is acidic. The soil at the Phoenix landing site was alkaline, so recent Martian conditions might be more suitable for forming carbonates. I think Glenelg makes most sense if viewed as a big stack of magnesium/iron carbonates with a variety of concretions. For earth examples of a carbonate terrain, see https://www.dmr.nd.gov/ndgs/ndnotes/concretions/concretions.asp .
A result from the Grail mission caught my eye, which was that the crust of the moon is about 12% void to a depth of several km below the surface due to it being fractured by impact. If the ancient Martian crust is similar, then at one time there should have been a huge amount of water in subsurface aquifers. At past Martian surface pressures, hydrothermal is going to mean something different from what is found on earth. At 60mb pressure, water will boil at 36C, so you don't need a lot of volcanic heat to drive a hydrothermal system.
Drop the pressure to 10mb, and water boils at 7C. Previously stable aquifers will boil until they cool below 7C. For a mixture of 90% rock and 10% water, 14% of the water will turn to vapor, if the system starts out at 36C.
An interesting question is what happens if the pressure falls below the triple point pressure of 6mb. If a cup of water starts out at a little above 0C, I think 12% of the water will end up as vapor and the rest will turn to ice.
How much vapor do you get if you start with 1 cubic km of aquifer with a 10% void fraction and turn 10% of the water in the voids to steam over 100 years? That works out to 3kg/s of steam, which should give you a small geyser.
Thanks for sharing the idea of acidic weathering of some of the spongy rocks!
I like the paper 'Concretions and nodules of North Dakota', you pointed to. Several features look rather similar to features near Yellowknife Bay. I had been looking for some paper of that kind, because it may explain the "bubbles" and more.
I can duplicate your calculations, under the given assumptions.
Nevertheless, several things are not quite conclusive to me. Still open is especially: How is the water forced to the mountain top, although there will be needed a hydrostatic pressure of more than 100 bar at the foot of the mountain in porous material? I'd expected a fountaine there, at the foot.
As a non-geologist I wonder if sedimentary rocks can tell MSL anything about their compression history?" Would they have a different signal depending on either a history of being overlain by a couple of kilometers of sediment for a billion years or so OR a more recent formation, and therefore a less deeply buried history. I understand that this entails the assumption of Gale crater being significantly buried.
Edit I did some research and discovered some better terminology, lithification & metamorphism, but can the extent of lithification or metamorphism, due to pressure, be indicated directly or indirectly by MSL. Some of these rocks look pretty weak!
Metamorphim, of course, by CheMin, because metamorphism changes crystal structure. That is well detectable by X-ray diffraction, I'm almost shure.
I cannot give a unique answer to the determination of the degree of lithification, because weathering might make things ambiguous, imho, probably the reason, why some rocks look weak.
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Gladstoner: I'm not sure but I think it's a 'no'. There has to be a special way of accumulating mound sediments - dampness?
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Interesting picture Nicholson Crater of http://spaceinimages.esa.int/Images/2005/07/Colour_nadir_view_of_Nicholson_Crater. Shows that Mount Sharp - not unique formation on Mars.
I linked this blog entry of Emily's previously but it is probably worth repeating to stress the fact that Mount Sharp, while enigmatic, is not an orphan.
http://www.planetary.org/blogs/emily-lakdawalla/2011/3144.html
Thanks for that post serpens. Somehow i had missed that entry in Emily's blog. That huge central dust covered mound in emily's blog brings to mind http://arxiv.org/abs/1205.6840 paper i recently found.
Growth and form of the mound in Gale Crater, Mars: Slope-wind enhanced erosion and transport
Edwin S. Kite, Kevin W. Lewis, Michael P. Lamb. July 2012
The authors propose that slope winds alone might be capable of forming and maintaining these central mounds even under current martian conditions.
One appealing feature of this hypothesis is that it no longer requires the deposition and removal of thousands of cubic kilometers of material and all the related issues. Another thing of note is that it is consistent with the outward dipping mesas and buttes in the lower flanks of Mt. Sharp. ( the larger ones toward the base even look a bit concave to me)
Line 47 of the paper estimates an erosion of 10 to 50 micrometers per year. That means 30 to 150 kilometers of erosion in 3 billion years. So, many things may be possible.
Thanks for the link - as a broad brush approach that katabatic driven deposition makes a lot of sense and this describes the vortexing effect that I previously admitted to not having the smarts to model. But I'’m not sure what effect the model start premise that the crater floor was non-erodible basalt has, since it was more likely erosion susceptible breccia/suevite. Given the clay beds at the lower level of the mound perhaps the start point should be a fluvio-deltaic period. I also wonder what would be the effect on the model if a warmer environment with reasonably high atmospheric pressure was used, which would increase wind energy.
Another possible consideration is whether adiabatic warming could cause temperature overshoot, where the katabatic wind on exit would end up warmer and less dense than the air at the crater floor, providing lift to aid central deposition. Throw into the mix effects like valley exit winds which would reduce erosion of the outer crater floor and the need for pretty extensive sensitivity analysis in the model becomes clear..
Overall this seems a a more satisfying concept than area infill and selective erosion.
So once again we see aeolian processes at work as a major force on Mars. I see a pattern emerging...
--Bill
Yeah, that's a possible scenario although I'm not sure that it is a common outcome in a final crater bowl? But my reservation was more on the effect on the model of a single start point (I assume the initial floor type is of some significance else why mention it in such a short article). Based on the apparent clay beds and the nature of the terrain Curiosity is currently investigating the possibility of initial lacustrine/deltaic sediments would seem worth consideration. Or if there was an inner ring, even a start scenario of a water filled moat between crater wall and inner ring, with mound building internal to the inner ring. Intuitively an inner ring would create some interesting interactions with katabatic winds flowing from the circumference towards the centre.
Sorry if this was discussed already, but there's a http://www.sciencemag.org/content/338/6114/1522.1.summary (subscription required, unfortunately) that talks about the history of Gale according to Kevin Lewis and Edwin Kite.
Yes. I posted a link to their paper a couple days ago. No paywall. Look back a dozen or so posts
That was our submitted version. The in-press version is here: http://gps.caltech.edu/~kite/doc/Kite_et_al_Gale_Mound.pdf
We made several relatively minor changes in response to a useful review by Ryan Anderson, and also ran some 3D simulations as a sanity check on the assumptions in the 1D model.
The fact that the very dark (black) supposedly basaltic sand dunes that partially surround the mound
are completely devoid of red dust has puzzled me. This may help explain it. Assuming the dunes are heavier sand.
Also. The bulk of the mound appears to be shifted north of the crater center. Stronger katabatic winds from the
higher crater rim to the south might explain this. Interestingly the very top of the mound seems to shift back toward the crater center
Very dark to black sand dune structures aren't all that uncommon on Mars. In fact, we've studied one closely -- El Dorado at Gusev.
It would seem that certain Martian wind shadows set up a process that sorts for the grain size of the black sands.
-the other Doug
Indeed, and I had the pleasure of riding a bicycle into a dust devil once (with appropriate safeguards: goggles and kerchief).
Also, I learned when I once saw tumbleweeds appear to be juggled by an invisible giant, dust devils are often there without the dust. We only see them when the cyclone has some dust to grab. Which happens to be common in some places.
Weirdly, the only time I've ever actually seen a dust devil here on Earth was when I was standing watching of one of the big DSN antennas at the Madrid DSCC as it was pointed towards Mars. It looked just like the ones that Spirit saw!
Do we know what these "mini volcanoes" are and how they came about?
From my Sol 137 mosaic. I annotated a few of them with black arrows.
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Yep, these look an awful lot like eroded clasts to me. What fascinates me even more then the bubblies, though, is the overall look of the terrain. I've seen undercut rocks like this many times, in both wet and dry streams here on Earth.
Here is a rather basic question -- the aerial views of this region appear to show alluvial features here. And the ground-based images show what strongly resemble water-cut rock overhangs. However, when we discuss surface rock erosion, it seems like you get Looked At Funny if you speak about the possibility of water erosion, as if suggesting that any close-in surface feature shows any remnant of water erosion just means you don't understand that Mars has been arid for billions of years.
If it looks like water erosion from above and from the surface, don't we have to at least give serious consideration to the possibility that at least some of the terrain we see around us is, in fact, the direct result of flowing water? Perhaps preserved for billions of years, but water-cut nonetheless? Sort of following the logic path of "if it looks like a duck and quacks like a duck, maybe it is a duck."
-the other Doug
p.s. -- I'm visiting family for the holidays, and the only way I really have of following the forum is via my Kindle Fire, and it's a longer process than normal trying to type with the on-screen keyboard, so I won't be posting a huge amount. Great for looking at the pictures, though.
I'm trying to get comfortable with the idea, that the supposed liquid may have been sulfuric acid with solved sulfates, and quartz suspension.
There are two articles in the most recent issue of Icarus that we all might take a look at that might influence our interpretation of curiosity's current environs. Using the latest spectroscopic parameters for CO2 as well as a detailed cloud microphysics parameterization the authors make the case for an extremely cold ancient Mars in which the periodic collapse of the atmosphere might occur even with up to 7 bars of CO2. Imagine what might happen at the base of a Co2 glacier say 100 meters or greater in thickness if a modest amount of geothermal heating lifts the base temperature to 224K.
Im on a ski trip doing this on my iphone so pardon my brevity and for not posting links
The "missing links" to the articles about early Mars climate:
http://arxiv.org/abs/1210.4216
http://arxiv.org/pdf/1210.4216v1.pdf
http://www.sciencedirect.com/science/article/pii/S0019103512004290
EDIT: For the Hesperian, I think, one should take into account the acidity of water. Sulfuric acid may decrease the freezing point of water.
Is the outcome of this a re-run of Nick Hoffman's white mars hypothesis? He made a good hypothetical case, but the physical and geochemical indications garnered by Opportunity over the years present compelling evidence for long lasting liquid groundwater with periodic surface exposure. As far as Curiosity's current environment is concerned I'm in the Other Doug's camp with respect to the fluvial provenance of this area. But keeping an open mind, the cementing agent in the sediment (and what appears to be significant variations in lithification) will provide a good indication of the environment in which it formed.
I'm very sceptical of models of what climate "should" have been for early Mars. Similar models completely fail to explain the undisputed evidence for widespread liquid water, and modern-type fluvial erosion, on Hadean earth. There's a bug in our understanding of that time.
I share your scepticism. Given the track record of climate modellers on Earth where outcomes do not reflect predictions despite the ability to empirically measure input constants and variables, it is difficult to accept at face value the output of models directed billions of years into the past for an alien planet where many of the inputs must, of necessity, be guestimates.
It's more than that. Climate models for the contemporary earth are quite good, unless we're talking about regional details not particularly relevant to an analysis of the global Mars climate. Heck, the models seem to do a pretty good job back through the entire Phanerozoic; they even can go beyond that and describe the "Snowball Earth".
But those same models can't handle the Hadean - specifically, the existence of sufficient quantities of liquid water to support modern-type sedimentary processes and/or the generation of felsic crust - based upon best estimates of insolation at that time, without some pretty improbable assumptions. And if they can't describe Earth, it's hard to imagine why they'd get Mars right. We're missing a piece of the puzzle.
Pure climate models will be insufficient for a description of early telluric planets, I think. They should be extended e.g. by gravitational shrinkage heat, radioactive decay heat, impact heat, chemical reaction heat like serpentinization to become more appropriate, imho.
Somebody has access to the full text? Interestingly about what it.
http://www.sciencemag.org/content/338/6114/1522.1.summary
This is essentially a news article, so I'm wondering why it's behind a paywall. No matter, I have access through my university. In essence: the researchers say that since the mound's sediment layers are inclined 2-4 degrees from the horizontal (according to MRO observations), as well as the fact that none of the eroded beds reaches the crater wall, the mound is not a remnant of a sediment layer (from an old lake, say) that completely filled Gale.
Instead, they say it was primarily aeolian processes building up an enormous pile of dust. Intense winds from solar heating and air movement could have propelled its' creation from essentially nothing. Water may have been involved at some point, but only marginally.
I hope this helps.
Yes, thanks, for an explanation.
Inclination might be a result of erosion and creeping, or a result of preferred sedimentation near the mound. Indications for clay minerals in the lower layers of Mt. Sharp still have to be explained. High D/H ratio and a high level of chemically bound water (Rocknest soil) indicate a water-rich past (Noachian) of Mars. The conglomerate finding at Curiosity's landing site strongly indicates a water-rich period. A layer in Yellowknife Bay looks much like containing bound water from the Hesperian (to be confirmed). The crater rim probably is younger as Mt. Sharp, this was assumed before. Science is an adventure; I don't feel any damper.
And don't forget the fairly extensive "box works".
The clay at the base of the mound has been identified as nontronite, indicating a wet, neutral pH environment when it formed. When Curiosity gets to the trough we should get an idea of how the smectite bearing layer formed but the extensive indications of water inflow from the rim and on the floor make a shallow lake a real possibility. Smectites consume acidity and the rate of mineral dissolution increases as the pH falls, the end product being amorphous silica. So the survival of the smectites indicates that they were protected from acid waters during the sulphate period. From Ryan Anderson and James Bell's analysis, what they term as the light toned ridge material sandwiches the nontronite layer. I guess that if it was a smectite dissolution product that would have been identifiable so it must have been impermeable.
The katabatic / slope winds hypothesis makes a lot of sense, particularly for the upper mound, but the early history seems fluvial.
One thing I would want to check is the direction of the tilt and how that relates to the long-term changes in Mars' shape due to, say, the construction of the Tharsis volcanic complex. The MESSENGER team has shown how lava-filled craters near Mercury's pole now have tilted floors that must once have been horizontal, due to tectonic activity. My own work on Venus dealt with the same thing, measuring current topography of lava surfaces that you assume started out as flat in order to get at ancient tectonics. I'm sure the same could happen on Mars. We certainly know Mars' shape has changed in the past, and it's been suggested that the entire crust has reoriented (true polar wander). I'd love to see if the tilting observed here is consistent with geophysical work on Mars' tectonics -- or inconsistent, which would be just as interesting.
If "true polar wander" did occur in the past that means GALE crater could have been at a higher latitude when some of these fluvial features were created. Are there any constraints on this imposed by the formation of the tharsis bulge ( which wants to be on the equator i assume)? Do we even know if Gale and/or its fluvial geomorphology formed before, during, or after Tharsis?
Since Edwin Kite's article generated this discussion it is interesting that he (and others) also wrote a paper on true polar wander a few years ago.
http://www-eaps.mit.edu/faculty/perron/files/Kite09.pdf
Several of the rocks near the border of Yellowknife Bay look to me like creeping.
Seasonal temperature cycling might lead to a creeping of the top layer in the direction of the net force, if the top layer consists of material sufficiently different from the layer below.
Might it be, that slope winds exert a force to the top-layer rocks strong enough to result in a net movement towards the crater rim?
An annual creeping of 1mm will be sufficient to exceed aeolian abrasion (0.01 to 0.05 mm per year estimated) twenty- to one hundredfold.
A rough sample calculation, assuming one creeping step per (Earth) year, i.e. two per Marsian year, a difference of the linear thermal expansion coefficients of the two layers of 10 ppm per Kelvin, a seasonal temperature difference of 20 Kelvin, and a length of a rock fragment of five meters yields
0.00001/K x 20 K x 5000mm x 0.5 = 0.5 mm
annual creeping. (Factor one half, because I have to look at the center of the rock.)
For small and thin rocks, even diurnal creeping may occur.
This may touch only tangentially on the case of Gale, but I was struck recently upon learning that a 100 km lunar crater, Icarus, also has a central peak that is higher than its rim. Because, obviously, the Moon lacks many of the mechanisms that act on Mars, it offers a far narrower set of possible explanations. In fact, I'm not sure if anyone has explained the case of Icarus. I see a citation of one article I can't read without disbursing some cash:
http://www.sciencedirect.com/science/article/pii/0019103573900237
That said, it is certain that Mt. Sharp has undergone a lot of phenomena that could not be shared between the two cases, but it's interesting to note the lunar case when trying to piece together the logic of Mt. Sharp.
Save your cash! There's nothing in that paper about the crater Icarus - it was published in the journal Icarus! (is that where a search led you astray?) There is also absolutely nothing in that paper about any central peak higher than the rim of its crater. LOLA data will allow this topic to be explored much better than any past studies have done.
Phil
Sorry, Gerald, what you're describing makes no physical sense, and multiplying a couple of numbers together doesn't make it any more sensible. I encourage you to read a physical geology textbook and then ideally a geophysics textbook -- or take some classes -- before trying to do quantitative geophysics. I like both Press & Siever (Earth) and Monroe & Wicander (Physical Geology) as introductory texts, though my textbooks are aging now and there may be better ones out there.
As Phil has said before this forum is better at image processing than geology.
Thanks for the tip, Phil. Actually, it was not an errant search, but a comment online by the author of the article who cited it in reference to that crater, but the relevance he inferred to the case of the crater Icarus may have been largely (or entirely) overstated. There may be no scholarly work at all on the case of the lunar crater Icarus.
Thanks Emily, for the hints to appropriate literature! It's difficult to find literature, that is not based on conditions observed on Earth.
I looked for investigations of soil creeping on Earth in the web, before I wrote the post. Unfortunately on Earth there is almost always water involved, which leads to additional expansion and shrinking by binding and releasing water to rock containing clay minerals, so that those processes may lead to an estimated soil creeping of about 1cm per year, less than solifluction, so it is mostly negligible on Earth. This may not be obvious for Mars. Therefore I redid the calculations based purely on temperature cycling. Normally such creeping occurs on slightly inclined layers or even within a layer. So the creeping will per se be a valid physical process. The question to me is, whether the thin atmosphere of Mars can exert a net force.
If the creeping as a valid process looks questionable, I may describe the mechanics behind that. In literature it is mostly sketched very briefly, because it's rather easy.
The idea of soil creeping on Mars is not quite new, see http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1190.pdf
Thanks JRehling, thanks Phil, thanks Emily, thanks drz1111 for your assessments, and for being honest!
The idea is either too brilliant, or nonsensical, probably the second.
I'll return to image processing.
EDIT: Luckily, I came across the literature, where I originally found an explanation of soil creeping, including quantitative estimates:
David John Briggs, Peter Smithson: "Fundamentals of Physical Geography", p. 325.
Just in case, someone is interested.
Speculating about processes on other planets is a better way to spend your time than many others. I do it a lot and in the case of Mars I know I'm 'getting warm' when one or more of the real geologists here responds. There have on many occasions been good geological discussions on this forum even if it isn't what we're best at.
On another tack: crowd sourcing is becoming fashionable in science, mainly for searching through large data sets. I think it can apply also to ideas if similar filtering processes are employed. This forum is perhaps a precursor for what could be done more generally. In the meantime the admins have to keep judging their interventions. It's hard work done for free and I respect them greatly for it.
My favourite LPSC abstract (so far, I'm still reading) : http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CDIQFjAA&url=http%3A%2F%2Fwww.lpi.usra.edu%2Fmeetings%2Flpsc2013%2Fpdf%2F1322.pdf&ei=kUgMUZGcPKWx0AXnvICYCA&usg=AFQjCNFazWO9F0iCs1_YVuTC9aAZh11iQQ&bvm=bv.41867550,d.d2k&cad=rja
In lieu of movement towards Mt. Sharp, here's an attempt at what a scene might look like from an aerial view when the rover gets there (anaglyph):
Can this inconclusive blue green spotty pattern on CRISM where Curiosity has found carbonates be extrapolated to what is seen higher on Mount Sharp, past the blue and magenta sulfates (as seen here: http://www.planetary.org/multimedia/space-images/mars/crism-map-of-gale-crater.html)? It would be something if under the dust it was all phylosillicates, except for a sulfates apron.
Suffering from a mild case of cabin fever from being stuck inside due to dreadful weather I thought I would resurrect this thread to throw out a few ideas on the dating of Gale. pdf attachment for brevity of post.
Re 3: Reliably tracking back the orbits of the planets of our solar system more than about 0.5 billion years isn't currently feasible, afaik. Adding the excentricity of Mars' orbit, I don't see convincing evidence for the implicite assumption, that the Martian orbit has been 3.7 billion years ago where it is today.
So, I'd think that there is sufficient space to play with resonances and close encounters with other planets, which may or may not still be present in our solar system. Some planets/planetesimals might have been ejected from the solar system, swallowed by the Sun or the gas giants, or fused to today's planets.
Over long time scales close encounters with other stars might have disturbed the orbits of our planets, too.
The faint sun hypothesis is a hypothesis, and despite theoretical evidence, data are lacking. The activity of stars can vary.
And radiogenic heat has generally been considerably higher in the young solar system than today; so we get the Martian interior as a source of heat.
There is of course still quite some uncertainty about the composition and density of the early Martian atmosphere, as well as of its albedo.
Hence I agree, that an early warm Mars is a mystery, but not because there is a lack of possible solutions, but because there are too many solutions.
Therefore I'd take it as valid to assume surface temperatures as inferred from geology, no matter for which particular physical reason.
@Gerald: I recently came across another very interesting possible explanation for the faint young sun paradox. In his "Lectures on physics", Feynman discussed the possibility that the gravitational constant G had changed over time. It turns out that the luminosity of the Sun is strongly affected by changes in G, with the luminosity proportional to G to the sixth power. Feynman points out that this would have made the ancient earth far too warm. However Feynman wrote that in 1962, which was a few years before the faint young sun paradox was identified. It turns out that a warmer earth is just what we need.
I did some digging around on the internet and it appears the current observational constraints on G can't rule out the possibility of G changing by enough to solve the faint young Sun paradox. So the idea that G has always been constant is really an assumption.
From the GSA meeting abstracts:
"LONG-LIVED DEEP LAKES IN EARLY MARS: SEDIMENTOLOGICAL EVIDENCE FROM THE CURIOSITY ROVER AT GALE CRATER"
"... the Striated and the Murray formations represent a subaqueous fan in a large lake, estimated to be 1 - 3 km deep. Fining-upward layers of the Striated formation are coarse-grained turbidites deposited on the proximal part of the fan by sediments delivered by floods through the northern rim of the crater. The Murray formation formed on the distal part of the fan and extended into the center of the lake in waters so deep that bottom sediments were unaffected by wave actions, lake-level fluctuations, and storm activities....."
"The rhythmic nature of layering indicates a regulated flow of flood waters into the lake, possibly controlled by changes in climate. The most likely forcing mechanism was variations in obliquity. Floods occurred during hothouse periods when the Martian climate was warmer than Present. The lake became saline at least to gypsum saturation during subsequent cold and/or dry climate of icehouse intervals and precipitated sulfate-rich nodules in the Murray formation. "
My comment: This was a deep lake. Other abstracts indicate that it likely lasted for millions of years.
"TESTING A MECHANICAL MODEL OF FRACTURE FORMATION BY COMPACTION-RELATED BURIAL IN GALE CRATER, MARS; IMPLICATIONS FOR THE ORIGIN OF AEOLIS MONS"
"These results imply that formation of these fractures [in the Murray and Stimson rocks] requires at least one significant burial event in the evolution of Mt. Sharp, providing key insight into the geologic history of Gale crater. "
My comment: After the lake dried up, sand dunes formed which later became the Stimson formation. Then the crater filled in and the pressure fractured the rocks.
"DIAGENESIS ALONG FRACTURES IN AN EOLIAN SANDSTONE, GALE CRATER, MARS"
" The mineralogy and geochemistry of the altered sandstone suggest a complicated history with several (many?) episodes of aqueous alteration under a variety of environmental conditions (e.g., acidic, alkaline). "
My comment: More water flowed through the fractures and altered the rocks.
"MINERALOGY OF MUDSTONE AT GALE CRATER, MARS: EVIDENCE FOR DYNAMIC LACUSTRINE ENVIRONMENTS"
" At the time of writing, CheMin has analyzed 14 samples, seven of which were drilled from lacustrine deposits. The mineralogy from CheMin, combined with in-situ geochemical measurements and sedimentological observations, suggest an evolution in the lake waters through time, including changes in pH and salinity and transitions between oxic and anoxic conditions. "
My comment: The mention of "oxic conditions" is interesting. Anoxic conditions are not surprising on a planet with a CO2 atmosphere. However, what produced the oxic conditions? Where did the oxygen come from?
Re your comment on "TESTING A MECHANICAL MODEL.....". The Stimson Murray interface is an erosional unconformity covered by an fragile aeolian dune deposit that does not seem to demonstrate any significant compaction or lithification. Rather than being an early construct buried by crater infill the Stimson deposit was potentially laid down following the erosion of the crater infill with a large contribution from landslips from a degrading Mount Sharp. In other words the Murray formation is an erosional endstate for the mudrock (mudstone/siltstone because it is hard to tell the difference) lacustrine Murray formation and the easily eroded sandstone of the Stimpson is a late feature (in Mount Sharp erosional terms) .
@serpens....Yes, I was wondering about that when I wrote the post. I thought Stimson was supposed to be young, but the abstract didn't read that way. I went back this morning and took another look at it, and the authors do seem to be arguing that the cracking in Stimson was produced by burial in the same way that the cracking in Murray was produced. It seems to me that that would only be possible if Stimson is old.
The authors by the way are Watkins, Grotzinger and Avouac at Caltech.
"TESTING A MECHANICAL MODEL OF FRACTURE FORMATION BY COMPACTION-RELATED BURIAL IN GALE CRATER, MARS; IMPLICATIONS FOR THE ORIGIN OF AEOLIS MONS"
" Large fractures which exhibit complex banding structures with distinct chemical trends (e.g. halos) are primarily found in the Stimson formation, but do extend into the Murray formation in one location. Smaller, sulfate-filled fractures are most prevalent in the Murray but are also associated with haloed fractures in the Stimson."
The Watkins, Grotzinger and Avouac paper in no way precludes the probability that the Stimpson was laid down subsequent to a significant burial and then exhumation of the crater. The extension of minor fractures into the Stimpson with limited examples of larger fractures can be readily explained through reactivation.
A possible scenario would be that the initial fractures in the Murray formation occurred as a kilometres thick overburden was removed through erosion and pore water was released. Subsequent deposition of the Stimpson material would have provided a compression force on the Murray formation, albeit at a comparatively minor level. The catastrophic channel outflow events, combined with a surge in volcanic activity would have provided sufficient acidic water through groundwater recharge and limited precipitation to replenish pore water to a degree, as well as (poorly) lithify the Stimpson. Subsequent erosion of the Stimpson would have caused a change in pore pressure in the underlying Murray sequence which could cause the pre-existing fractures to propagate up into the overlying Stimpson rock. This propagation could be assisted by pore water at the fracture tip causing chemical weakening of the overlying rock. Fracture propagation would have been restricted by the limited availability of acidic pore water due to the minor compression unloading.
In reading this, please keep in mind the profound ancient-ness of these landforms.
"The mention of "oxic conditions" is interesting. Anoxic conditions are not surprising on a planet with a CO2 atmosphere. However, what produced the oxic conditions? Where did the oxygen come from?"
There is actually an abiotic mechanism for producing appreciable amounts of oxygen photochemically in a cold glacial/interglacial environment. UV light will produce small quantities of hydrogen peroxide which will be stable enough at low temperatures to be stored in ice. When an interglacial arrives and the ice melts the hydrogen peroxide decomposes into water and oxygen.
Probably photodissociation of CO2 and H2O. This recent release by JPL provides some substantiation.
http://www.jpl.nasa.gov/news/news.php?feature=6544
Yes. The process has actually been rather extensively discussed in the literature in connection with Archaean/Proterozoic glaciations ("Snowball Earth") since there is evidence for oxic conditions immediately after the glaciations. And hydrogen peroxide is actually found in measurable amounts in snow in Antarctica. Incidentally the quantity deposited increases in early summer when ozone is low.
http://rstb.royalsocietypublishing.org/content/363/1504/2755
http://www.pnas.org/content/103/50/18896
https://www.academia.edu/15042568/Production_of_hydrogen_peroxide_in_the_atmosphere_of_a_Snowball_Earth_and_the_origin_of_oxygenic_photosynthesis
http://web.gps.caltech.edu/~jkirschvink/pdfs/RaubKirschvink08DeglaciationOxidationReviewAndModel.pdf
Hematite? (aka Squyers' blueberries)
After the exhaustive work to identify the provenance of Opportunity's berries there is a tendency to consider small spherical objects seen on Mars as concretions. This particular example is isolated so if it is a concretion then transport was involved. However we cannot rule out other causes such as an impact artefact, molten material with a reasonably high ferric component that assumed a spherical shape and cooled in flight, possibly quenched by fall into water. Note Greg Malone's post #810, page 54 on 22 December.
We have to climb around another hundred metres of Murray formation mudstone and sixty metres or more above that to the hematite ridge. Nicolas Steno's principle of lateral continuity holds that this strata would have originally covered Curiosity's current position, requiring significant water influence over a long period of time. As an aside, the more I look at the hematite ridge the more I wonder whether it could be an inverted bed of what was a reasonably well oxidised stream.
Simply brilliant stuff!
To add to the mix of ideas about dessicated mudcracks is the notion of syneresis, believed to have possibly been active at some sites investigated in Gale -- where differential salinity in interstitial water causes lower salinity water (I believe) to migrate out of the muds being replaced by denser higher salinity water, creating cracks that are somewhat similar to dessication cracks... all the while the entire environment being saturated with subsurface water... i.e. not a 'drying out' or dessication.
Basically a closed system I expect. One needs to pull back a bit to see the big picture. Aeolis Serpens to the NE of Gale is an inverted river complex over 500 kilometres long that spans a period somewhere between 1 to 20 million years with evidence of varying water and sediment supply and occasional desiccation. It would have terminated at the northern ocean and this would imply a shoreline to the north of Gale. Groundwater at Gale could reasonable be expected to reflect the level of the Northern ocean, creating a lake, while impact tsunami could also have overflowed the northern crater wall.
The problem is that empirical data from the rovers and orbiters prove an early warm wet Mars with a complex hydrological cycle spanning millions of years. No model of plausible environments can explain this. But Curiosity has a long way to climb and hopefully more clues will be found to help complete the jigsaw.
Sulphates on Earth require oxygen to form either by volcanic eruptions or the action of sulphate reducing bacteria. Deposits of iron pyrite have been attributed to rising levels of atmospheric oxygen. Varying sulphur isotopes have been regarded as biosignitures.
What do findings of sulphates, gypsum, manganese oxide and haematite on Mars tell us about climatic condition's with regard to atmospheric and water oxygen levels? Is Curiosity rover equipped to measure isotope ratios?
SAM has the capability to conduct isotopic analysis of the lighter elements. You have a few misconceptions in that sulphate reducing bacteria uses sulphates as an energy source, producing sulphides. Iron pyrite forms in a reducing, not a oxidising environment and on Mars probably formed through melt separation during magma crystallisation.
With respect to your question on what rover and orbital findings indicate about previous environments, these have been the subject of a huge number of erudite papers and articles by acknowledged experts in their fields and address the dramatically different environments encountered by the landers and rovers. A good search engine and some careful culling to separate the grain from the chaff will provide you with your answers and attempting to paraphrase these would take up immense space and justifiably draw the wrath of the overworked moderators.
Julius, I agree with what Serpens said, but to try to save you a bit of trouble, let me summarize (with some trepidation) what you are likely to find in an exhaustive literature search. In short, sulfates don't tell you a great deal about environments. Yes, they are oxygen-bearing, but so are virtually all the other minerals that make up planetary crusts, such as silicates and carbonates. Sulfates require a tad more oxygen than most, to avoid forming sulfides instead, but not much more. There are igneous and hydrothermal sulfates as well as sulfides, so sulfates are not unique to a particular environment (at least on Earth). Some elements (e.g., calcium) form sulfates more easily than others (e.g., iron), but you didn't ask about that.
Manganese oxides and hematite on the surface of Mars probably don't tell you a great deal either, because the surface of Mars is believed to be locally far more oxidizing than the inside, owing to the influence of solar ultraviolet light, not from an oxygen-rich atmosphere (as on Earth). It doesn't take a great deal of oxygen to form either type of oxide. Finding manganese or iron oxides inside a rock can tell you that it or its ingredients were formerly exposed to sunlight at the paleo-surface, and presumably to some moisture (to assist their growth), but nothing more.
I won't address sulfur isotopes, because there is no data and they are not my area of expertise.
The consensus up to now seems to have been that sulphate minerals tend to rest on top of more ancient clay minerals and has been interpreted as reflecting a climatic change on Mars from neutral water environment to a time when the planets water turned acidic indicating a drier environment. The finding of jarosite at Pahrump hills and lack of clay minerals sandwiched if you like between abundant clay containing Yellowknife bay rocks and abundant clays found in Murray buttes would seem to contradict this . Any thoughts about this?
My first thought about the silica enrichment has been a process connected to the hematite enrichment at Vera Rubin ridge, kind of leaching and precipitation cycle. But there are lots of gaps, of course, and those two layers could have formed independently. I don't see an immediate connection to the overlying sulfate layer thus far.
One may also conclude, that we are going to learn more about the details of Martian history, but our understanding of the long-term geological structure doesn't need to be challenged.
Julius, I think that Curiosity will need to get up close and personal with the clay bearing trough before they can assess how and when it was formed. In their brilliant Geological mapping and characterisation of Gale as a potential landing site, Anderson and Bell depicted the clay as a thin bedding plane with a segment exposed by the trough and that characterisation has carried forward. As I understand it the clay signature seems to indicate smectites. The overlying hydrated sulphates would likely have formed in an acidic environment and smectites are pretty good at consuming acidity with the end product being amorphous silica. So if the smectites had been exposed to the acidic waters during sulphate deposition, wouldn't hydrated silica and kaolinite have been detected, unless the clay had been covered by an impervious layer? An alternative is that the clay was formed following deposition of the sulphates as a function of erosion of the sulphate and formation of the fan. Could this clay be a localised deposit formed from pooled water that had leached Mg from the higher sulphate deposits? Both the hematite ridge and the clay trough are going to tell interesting stories.
QUOTE (HSchirmer @ Nov 8 2018, 05:06 PM
...Given the elevation of Gale crater, and recent northern-ocean papers, is there any way to differentiate whether Gale was lacrustine or perhaps an interior estuary?
All evidence to date implies lacustrine. Dichotomy elevation differences aside, the northern crater rim is heavily degraded compared to the northern rim and the area directly north of Gale is somewhat atypical compared to adjoining topography. it is possible that it was overtopped by lake water or by catastrophic events such as impact driven tsunami although there is no evidence of such. The rim is above the elevation assessed for proposed shorelines for the northern ocean(s).
Hmm, reminds me of the Newark Basin paradox- a 2-mile deep deposit of shallow water mudstone interbedded with fanglomerates and sandstones. (It is a paradox because with a 2-mile deep basin [~about the average depth of the Atlantic or Pacific] you'd expect to start with deep water sediments which get shallower as you fill in the basin over time. Instead, the Newark basin was shallow during the entire time that 2 miles of sediment were deposited.)
I thought the Newark basin was the result of a slow graben process? As the land sank the rate was matched by shallow lake deposition.
I suspect that this would represent the maximum fill with your suggested high ocean level, with the northern rim less degraded and above water level. Occasional tsunami drain back cutting the few possible channel like features but who knows. Certainly the mount would not exist at this time and the central uplift would be the sole feature within the lake. There is some evidence from tsunami features that the proposed first ocean was not iced over although the second, shallower ocean was.
Theory - Gale Crater was a bay when the Arabia Ocean filled the northern lowlands of Mars.
Reaching way back to discussions about the thickness of sediment deposits in Gale-
The basal/basalt misinterpretation was explained, in fact done to death in pages 7 to 9 of this thread. Let's not resurrect it.
The accelerometer analysis by Lewis et al is innovative although I am not certain that their conclusion on the extent of overburden considers all the variables. I do not question their methodology or measurement results. However I do note that during the ascent of Mount Sharp the Murray formation has consisted primarily of mudstone with some sandstone lenses. Depositional muds have high porosity (up to 65- 70%) due to the nature of the particles and electrostatically bound water and compaction of such in Mars' low gravity takes significant overburden. Given the thickness of the mudstone significant pore fluids may have been retained, retarding compaction and retaining density indicative of shallower depth than was the case.
As referenced in an https://www.sciencenews.org/article/nasa-curiosity-mars-rover-weighed-mountain-its-climbing accelerometer-based gravity readings suggest:
"...the rock beneath Curiosity's wheels is less dense than its mineral composition led them to expect. It's "more like the density of soil than a fully cemented rock," Lewis says. That means the crater must never have completely filled with rock — the upper layers would have crushed the lower ones — and supports the windblown sands theory for how Mount Sharp formed...
...suggests there were two different periods of mountain-building in Gale Crater, one that laid down lake sediments and a drier one that built Mount Sharp's peak. Curiosity might find the transition point as it keeps climbing...
...measurements suggest that the rocks beneath Curiosity are riddled with holes. “But the rover doesn’t see any holes,” Kite says. Either the pores are too small for Curiosity to see, less than 10 micrometers wide, “or there’s something unusual about the rocks right at the surface where Curiosity is driving.”..."
Assuming an accelerometer measurement wouldn't be able to discriminate between holes/pores at surface vs subsurface... so seems simpler that the subsurface pore fluids desiccating could lead to mineral solidification of their environs preventing the sedimentary compaction due to pore collapse could help explain away some of the missing mass?
The hardness of the Jura and upper Pettegrove Point members combined with CRISM results indicate that they are well cemented with iron oxide, primarily hematite. This localised and comparatively shallow phenomena most likely occurred post lithification and the erosion resistant upper surface of the ridge is indeed different to the underlying Murray formation. Mudstone is a bit of an anomaly where compaction is concerned because the platy particles compact at surfaces rather than points, significantly reducing porosity. But this reduction means that the remaining pore water is retained despite increases in load, so bulk density is not necessarily an accurate yardstick to measure load (overburden).
Just in case anyone missed it, Emily provided an update on Curiosity's investigations including the intriguing Rock Hall drill initial results. http://www.planetary.org/blogs/emily-lakdawalla/2019/curiosity-update-sols-2257-2312.html with a link to the LSPC abstract. https://www.hou.usra.edu/meetings/lpsc2019/pdf/1127.pdf
Sheer conjecture, but the decreasing phyllosilicates and increasing amorphous with elevation at VRR combined with the identification of akaganeite would seem to strengthen the case for volcanic outgassing providing precipitation, acid snow perhaps including dissolved HCl. Subsequent melting and interaction with groundwater would provide ferrous and chloride ions in acidic conditions.
Curious if a new theory about the Pathfinder site might be relevant for Curiosity...
The Pathfinder landing site may have been shaped by water overflowing from Mar's northern ocean into a depression.
HSchirmer, could I perhaps suggest that you may like to post images as thumbnails, it would make your posts easier to read.
It is now clear that Vera Rubin Ridge was laid down as part of the Murray formation and the erosion resistance is a product of post deposition diagenetic/alteration episodes. The comparative hematite, phyllosilicate, amorphous and opal CT proportions with elevation combined with the identification of akaganeite is indicative of low pH fluids infiltrating from above. The likely formation candidates from the options proposed to date are a springline during the Mount Sharpe erosion process or a much earlier, low energy stream after the lake dried.
It is pretty clear that clay rich Glen Torridon is not associated with the Murray formation, is possibly cemented with clay and does not seem to have undergone significant compaction. I retain the belief that this formed following the erosion of the Murray formation on both sides of the resistant ridge, and is potentially a function of the formation of the fan. Basalt buffered water and sediment originating in upper Mount Sharp pooling in the hollow between ridge and mount. In the absence of tidal influences the rhythmic laminations or “bundling” could well reflect a shallow lake with annual ice cover. During winter dust collects on the ice and on thawing settles to form the thin laminations. During summer ice on the mount melts and a thicker layer of sediment is deposited.
Or it could be something completely different which the experts, having actual data to work with will advise in due course.
Already received that admonition from a Mod.
Curious,
In addition, acidic waters rapidly neutralize in basaltic systems due to weathering reactions. Groundwater flowing up from below would need to interact with a far greater volume of rock than water coming from above, so it is less likely to contain strongly acidic fluids. There would have been a very clear acidic alteration signature in the underlying stratigraphy associated with the level of alteration seen at VRR if it were groundwater.
There is no indication that the northern ocean interacted directly with Gale crater and in any case it would be highly unlikely to be salty at its maximum extent. But jccwrt's point is germane regarding acidic alteration signatures in the underlying sedimentary Murray formation. All data indicates top down infiltration.
We know that Vera Rubin Ridge is part of the Murray formation and it would be safe to assume that the lake and hence the Murray formation extended to the central uplift, at a height pretty much commensurate with the top of VRR. So the problem is when and how did acidic water interact with a discrete , long and thin section of the formation. One critical data point we do not have and unfortunately cannot get is the length of the altered section because quite limited cover would hide the signature from orbit. Increased length would imply a stream because even the length of the visible portion would be unusual for a springline.
The proportional change in phyllosilicate and amorphous content is just one indicator of what influenced VRR. Once again taking a generalist approach, based on the evidence the groundwater within the Murray formation would have had a reasonably neutral pH (6-7) and low Eh voltage. This would provide for a stable, high level ferrous solution. Now if this groundwater mixed with precipitation from volcanic activity, say acid snow melt the following would take place.
4Fe++ + O2 + 4H+ ------> 4Fe+++ + 2H2O
There is then a pathway to hematite through Ferric Oxide Trihydrate to Goethite or even direct to hematite if the pH of the mixed solution, mitigated by the phyllosilicate consumption of acidity, is around 5.
Top down infiltration really is the only process that fits.
I'm not sure we can entirely discount a contribution from acidic groundwater traveling along a fault - especially since Gale Crater seems to host some diverse evidence of igneous activity (float rocks from an igneous suite on the northwest rim, K-rich sedimentary layers apparently derived from a different source region, a possible(?) exposed intrusion at Ireson Hill [my memory is fuzzy on this one, I remember an LPSC talk in 2018 talking about finding a new kind of igneous float rock there] and tridymite detections). In addition we do see extensive alteration haloes in places in the Murray which are also suggestive of acidic groundwater.
That said, I'm not sure that points to a bottom-up process - a regional/global groundwater system should be at or neutral pH given the sheer volume of rock it needs to travel through, so it would need to be something local to Gale Crater. I'd wager that for the most part even the local groundwater was neutral. There's a hydrofractured interval in the Murray that suggests considerable groundwater content at some point in the crater's history, and these don't appear to be associated with much alteration.
So I think it comes down to the existence of an acidic brine reservoir, the existence of which is difficult to prove. Offhand I could think of a couple of tests: 1) check for highly altered rocks in Ellipse Edge Crater and Slagnos Crater ejecta, 2) do a geochemical balance to see how much acid you need to reach equilibrium with the surrounding rocks and still remain acidic (or failing that, how long an acidic solution would last before neutralizing).
And even if you have a pathway, you also need a mechanism to get a dense brine moving towards the surface - a brine pool has persisted in Chesapeake Bay so long precisely because it is dense and hard to dislodge.
I think on the balance, a top-down alteration pattern is a more convenient explanation. We're not stratigraphically far below a sequence of rocks containing abundant evidence for a more acidic environment, and we also saw evidence for surface conditions starting to slide towards more water-limited and oxidizing conditions on the approach to VRR. Something weird happening along a redox interface within the lake or some sort of alteration process that managed to proceed deeper along a fault-line seems more likely to me.
In such well informed company I have nothing to add except to say how much I am appreciating the quality of this discussion, not only for the insights shared but for the the clarity and accessible language of the posts. Anyone following could not fail to have their imagination stirred about past and present geological processes on Mars. It's a perfect example of the best that happens on this forum, alongside the image work.
Perhaps Gale crater was, for perhaps half-a-million-years, like the Dallol hydrothermal field?
Hot basalt mixing with marine sediments can generate some REALLY nasty water.
Given the height of the Gale crater central peak the development of a peak ring is unlikely since this is predicated on the collapse of the central peak.
There is clear evidence that the sedimentary formations investigated by Curiosity since landing predominantly reflect fluvial lacustrine environments and the accessible 300 metre odd thickness of the Murray formation was laid down over some considerable time in a reasonably deep, neutral pH lake. We do not know just how deep the Murray formation extends; or indeed if it is actually the basal layer of Mount Sharp or whether beneath it is a sedimentary formation reflecting the environment you describe. Certainly the veins and halos indicate that there have been extensive hydraulic fracturing and deposition incidents, primarily alkaline but in the lower levels acidic on occasion.
The clear transition from the phyllosilicate bearing Murray formation to the sulphate bearing layers represents a change in the local environment from water dominated to arid, acidic conditions. But there is clear evidence of significant water, both surface features and groundwater well into the Mount Sharp erosion period. For example hydraulic fractures extend across the contact between the Murray formation and the much later, aeolian Stimson.
The thing I think we all struggle with is the timescale represented by the sedimentary layers of Mount Sharp and the subsequent erosional end state of Gale crater. On Earth we have only fragments of the Eoarchean crust which date to the time of the Gale impact. The evidence of long standing surface water on Mars presents a real challenge to the traditional view of the early solar system.
Hypothesis - Vera Rubin Ridge's odd chemistry is the result of the ridge's location above the inner ring of Gale crater; hydrothermal activity concentrates at crater peaks and rings, so the ring is associated with mineral deposits. Water flowing down through sediments leached minerals into the overlying strata which alter the overburden to create the erosion-resistant Vera Rubin Ridge.
Here's a thought- Ahuna Mons on Ceres seems to the result of mud burping up from an underground chamber.
On Earth it would be a reasonably simple matter to confirm or deny your hypothesis of Vera Rubin Ridge being an artefact of a peak ring. However while the visual and analytical data from Curiosity is frankly stunning, it is also extremely limited with respect to the footprint investigated and the fact that such investigation is skin (or at least drill) deep. Regardless any hypothesis, by definition, should reflect the available empirical data. This data reflects a transition to a more acidic influence with elevation. If the ridge were the result of covering a peak ring then the influence would be evident across the entire ridge slope. As far as Mount Sharp being a mud volcano is concerned, this was a hypothesis put forward very early on but was dismissed based on the evidence.
Jccwrt’s 12 June comment regarding tridymite detection jogged my memory with respect to the detection of not insignificant amounts of opal CT in the Highfield drill sample. Presumably caused by diagenesis under burial of amorphous silica Opal A to the micro-crystalline SiO2 polymorphs cristobalite and tridymite. I wonder if estimation of the transition depth for Opal A to Opal CT under Mars gravity could give a wet finger estimate of the overburden.
I don't think that a pseudo Langmuir circulation effect has any relevance to the Murray formation or indeed to the sum of data and analysis covering Curiosity's traverse.
[Edit] Apologies if that comment seems terse but concepts must at least bear some relation to the features. Stack, Grotzinger, Gupta, Edgar et al. "Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation" assessed Pahrump hills to be deposits from hyperpycnal flow (turbidity currents) attributed to rivers from the rim plunging into the lake. Hyperpycnal plumes can travel significant distances before dropping entrained sediment loads so this does not constrain the size of the lake, but it does mean that it lasted a very long time
Let me take a step back-
I've been thinking about some great ideas from earlier parts of this discussion-
Immediately following the Gale impact there would have been a lava pool on the crater floor and intense hydrothermal activity. But the final crater floor is well below the current floor and a consideration is how long it took for at least a kilometre of sediment to build up. Certainly by the time the Pahrump Hills sediment was deposited hydrothermal influences do not seem to have been significant. All indications are that this deposition was traction controlled in deep, neutral pH water.
During the 7 years since the inception of this thread Curiosity has revealed important information, not the least of which is the evidence of a fluvial / lacustrine mudstone dominated environment across the transit. Kimberly revealed a delta that would have defined the edge of a lake at that point in time. This is some 60 metres below Pahrump hills and 350 metres below the top of the ridge. By the time the sediments were deposited at the level of the ridge the lake must have covered most of the crater. Impact heat and associated hydrothermal activity may have lasted a couple of hundred thousand years. The Crater Lake would have had to have lasted closer to a million. Though an apples and watermelon comparison, Lake Malawi sediment cores dating back a million years were taken at a depth of around 300 metres.
The introduction of the paper you link indicates that the authors believed that the lower section of Mount Sharp (the Murray formation) was Aeolian, formed from erosion of sediments identified during Curiosity’s transit and evidence of surface inflow to Gale occurred following the formation of Mount Sharp. However we now have empirical evidence that deposition at least to the level of Vera Rubin Ridge was lacustrine.
Over a few billion years erosion has removed much evidence but my wet fingered guess would be that evidence of inflow dates to the Murray formation lake and any later inflow following the formation of Mount Sharp involved reactivation. The fan dates from this period and we are going to get a good look at it. Any concept or hypothesis should reflect current data.
To put the depth of sediment and the size of the lake in context, unless Mr Steno got it wrong the sediment would have been deposited across this view to at least the same level at the crater rim. Water level would have been higher.
Maybe it's worth noting that we see absolutely no sign of any former shoreline on the rim mountain range. Of course being steeply sloping we would expect plenty of erosion there in the meantime, but viewing now on a level with it one might think that some features could have lined up.
In their supplementary materials for their paper "deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars", Grotzinger, Gupta, Malin et al provided the results of topographic analysis of Gale and the power law relations for the calculated “fresh” final crater conditions. They estimate the rim horizontal back stepping distance through erosion to be 4.8 km. That is a heck of a lot of material. How much of this occurred before the lake filled and how much after it dried is unknown but given the amount transferred to form Mount Sharp, erosive conditions after the lake dried must have been pretty severe, removing evidence that might have been visible from a distance.
Some interesting and thought provoking abstracts from the Ninth International Conference on Mars.
https://www.hou.usra.edu/meetings/ninthmars2019/pdf/ninthmars2019_program.htm
I found the abstracts from sessions on Tuesday covering Geology and Geochemistry of Gale and the Glaciers, Oceans, Rivers, Lakes of particular interest with respect to this thread. Reading these abstracts and also back through the thread which covers 7 years I am struck by the extent to which Curiosity's ground truth has altered and refined the perceptions of Gale crater's history. With the MER and MSL, NASA/JPL have established a baseline for value for money.
I'd expect most of the new science results were shown at LPSC back in March. The Mars conference is more about reviewing the last several years of science and getting a community sense of the directions that Mars research is going. It's more of a "here's the big picture and problems we need to address" conference rather than a "here's what we found this year" conference.
Exactly.
This open source paper appears to address some of the early questions in this thread, well at least for the Vera Rubin Ridge...
"Regional Structural Orientation of the Mount Sharp Group Revealed by In Situ Dip Measurements and Stratigraphic Correlations on the Vera Rubin Ridge"
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JE006298
Thanks for that link. The conclusion that "the possibility that VRR members are distinguished primarily by diagenetic processes that did not follow strata boundaries" seems to be supported by Chemin results (link below). The difference between Grey Jura and Red Jura with significant akaganeite in Rock Hall would seem to indicate a localised concentration of chloride rich acidic fluid within the Jura member.
https://www.hou.usra.edu/meetings/lpsc2020/pdf/1601.pdf
Curiosity Rover Finds Clues to Chilly Ancient Mars Buried in Rocks (NASA Goddard News Release) https://www.nasa.gov/feature/goddard/2020/nasa-s-curiosity-rover-finds-clues-to-chilly-ancient-mars-buried-in-rocks
Associated paper (pay-walled) https://www.nature.com/articles/s41550-019-0990-x
I don't feel there is any contradiction with the Gale crater sediment requiring millions to tens of millions of years to form in warm, humid conditions and some of the carbonates within that sediment possibly being formed in icy conditions. For the last 3 million years or so Earth has experience cyclical glaciation with shorter, warm and humid interglacials, initially on a 41 kyr cycle and then, for currently unknown reasons, switching to a 100kyr period. Even during interglacials there are significant temperature variations. It would probably be more surprising if there were no indications of temperature variability.
An interesting abstract from LPSC 2021 which includes possible flooding of Gale by breaches in the Northern crater rim.
https://www.hou.usra.edu/meetings/lpsc2021/pdf/1605.pdf
Not sure it’s the right section…
From lake to river, open access paper from Gwénaël Caravaca : https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE007093
Another possible indication of a northern ocean with implications for potential flooding of Gale crater.
https://www.psu.edu/news/research/story/traces-ancient-ocean-discovered-mars/
Trying to make sense of the geologic context of the various units...
A major angular unconformity can be discerned by the truncation of the bench-forming sandstone (red). The Greenheugh Pediment sandstone (green) appears to be the basal unit of the overlying sequence:
Possible northward extension of the Marker horizon (lavender):
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