IPB

Welcome Guest ( Log In | Register )

4 Pages V  < 1 2 3 4 >  
Closed TopicStart new topic
geology of Gale Crater and Mount Sharp
Astro0
post Jun 30 2014, 10:56 PM
Post #31


Senior Member
****

Group: Admin
Posts: 3108
Joined: 21-December 05
From: Canberra, Australia
Member No.: 615



ADMIN NOTE: All, as noted a few posts earlier, let's keep this discussion ON TOPIC. We're going over OLD ground or sky in this instance. wink.gif
Go to the top of the page
 
+Quote Post
serpens
post Jul 1 2014, 06:09 AM
Post #32


Member
***

Group: Members
Posts: 642
Joined: 17-February 09
Member No.: 4605



The more I look at the "headwaters" of the Mount Sharp channels the more it appears that the channels have been covered by the aeolian deposits that characterise the upper region of the mountain, rather than originating there. The inference is that the channels date from the early period where the crater was infilling and it is only recently (in martian terms) that the less consolidated material has been eroded away to reveal the lithified channels and deltas. An indication of the topography that would enable such channel formation is provided by Endeavour crater which has been overrun by sediment from the NW. If there was surface water flowing in Meridiani today it would possibly flow into the crater, cutting channels in the mound slope similar to those on Mount Sharp, terminating in a lake. Aeolian mountain building process and erosion like those proposed for Gale would then result in topography similar to the Gale channels/deltas, albeit on a much smaller scale.
Attached thumbnail(s)
Attached Image
 
Go to the top of the page
 
+Quote Post
David Palmer
post Jul 1 2014, 09:10 AM
Post #33


Junior Member
**

Group: Members
Posts: 33
Joined: 16-June 14
From: Sweet Home, Oregon
Member No.: 7202



Reply to Serpens:

Your hypothesis (which we can christen the "overland-flow hypothesis") is not plausible, for several reasons:

1) To have such an overland flow which then poured down the northern and western sides of what was to become Mt. Sharp (carving the channels in the process), the eastern/southern portions of Gale Crater would have needed to be filled with sediments to the brim, forming a tableland....but if that were the case, why would the northern/western area of Gale Crater have been sediment-free? (which would have been needed to provide a basin into which the channels dumped their load).

2) Looking at the headwater of the Grand Canyon (seen in the image you pasted above), it is obvious that the channel is beginning at this point, as a juvenile channel that is both shallow and narrow, whereas if the (visible) Grand Canyon were a surviving remnant of what was originally a channel sourced from a great distance, flowing across a tableland (which has since eroded away), then it would have acquired the traits of a mature channel (full or near-full width and depth) LONG before the location of the Grand Canyon's visible headwater.

3) It HAS been suggested by other authors, possibly first by Anderson & Bell, that the Upper Formation was laid down on top of the lower mound AFTER the channels were carved. And this would indeed provide a possible mechanism for protecting the channels and their deltas from erosion and meteor impacts, until such time as these (presumably friable) sediments were stripped away via wind erosion. However, this is not plausible.....the surviving Upper Formation is at least reasonably lithified, as demonstrated by the crisp surface features visible in high-resolution photos of the mountain, including yardangs, ridges, steep topographic gradients such as scarps and cliff-bench layering, impact craters, and boulders in colluvium piles, all of which imply a hardened, indurated substrate (i.e., rock).

If an underlying formation is covered by a later formation that is lithified to a comparable degree (one that is NOT friable and unconsolidated), then the stripping away of the overlying formation can be expected to inflict heavy damage to the lower (older) formation, as there would be no clear dividing line between the formations that would result in highly differential erosion. And if this had happened to the Mt. Sharp channel complex and fans, they would today be a mess, with some portions still obscured by their original sedimentary cover, other portions filled in or covered up by newer (reworked) materials, and still other portions gone forever as a result of erosional cross-cutting or systematic deflation of the landscape, in short a geologic hodge-podge that would require detailed stratigraphic research in order to decipher the original structure (if it even could be deciphered), rather than the channel complex being showcased before us in gleaming, near-mint condition (as it obviously is). And to suggest otherwise would actually involve a violation of the Second Law of Thermodynamics, since erosion is a very highly entropy-producing process, and cannot be expected to cleanly pluck away an overlying formation, almost grain by grain (as if by the Hand of God), without also doing great damage to the underlying formation.

And there is no conceivable mechanism whereby the material that today constitutes the upper mound was lithified, but the outlying materials of the same formation were not (and so could be readily stripped away without substantially damaging the channel complex)....unless, of course, an artesian hydrant were present (as per my essay's main hypothesis) that would provide lithifying water exclusively to the sediments sitting on top of Mt. Sharp (i.e. the upper mound), in which case we also have a ready source for the water carving the channels, and the overland-flow hypothesis becomes redundant.

Dave
Go to the top of the page
 
+Quote Post
Gerald
post Jul 1 2014, 12:26 PM
Post #34


Senior Member
****

Group: Members
Posts: 1817
Joined: 7-December 12
Member No.: 6780



QUOTE (David Palmer @ Jul 1 2014, 11:10 AM) *
And there is no conceivable mechanism whereby the material that today constitutes the upper mound was lithified, but the outlying materials of the same formation were not ...

I admit, that I didn't (yet) read all of your essay. But did you consider an ice cap or permafrost as a possible protective mechanism? This works at least for mountains on Earth. Lower parts tend to melt earlier, hence loose their protective property earlier, and are eroded faster. An ice cap could also explain the canyons, as e.g. fjords in polar regions on Earth.
Then add the - currently I think mainstream - idea of slope winds, which are stronger at the base of the mount, and accelerate erosion further.
The central mount has been higher, even after sedimentation due to the initial impact, this way starting the preferred erosion in the "low-lands".

I don't claim this as the only possible explanation, but just to given an idea that there may be plenty of alternative conceivable mechanisms.

Usually I avoid to discuss about the overall geomorpholgy of Gale, since I think finding "the" correct hypotheses without a huge amount of data and their deep analysis is like a lottery with a couple of tries within millions of possibilities, just think about the largely unknown climate on past Mars, e.g. due to the instability of the rotation axis (obliquity), add volcanism and large impacts. You might win the super-jackpot, but a-priori-chances are low.


About the artesian spring hypothesis: Shouldn't there be obvious cenotes like in the Chicxulub region, due to leaching? And: How did the water manage to get out only at the mount, not at fractures somewhere else (think about the hydrostatic pressure), leaving several smaller mounts in the surroundings?
Go to the top of the page
 
+Quote Post
serpens
post Jul 1 2014, 02:56 PM
Post #35


Member
***

Group: Members
Posts: 642
Joined: 17-February 09
Member No.: 4605



I have a little difficulty with some of the assumptions on which you base your last post David. Taking your numbered points:

(1) Endeavour crater currently reflects the required topography so it is possible that so could Gale at the time the channels were formed.

(2) To my eyes the channel is not pristine and the filled remnant wends towards the top right of the image, disappearing under the (Aeolian?) sediment without narrowing.

(3) The extent of lithification of the various levels of mount Sharp can only be assessed if Curiosity gets up close and personal. But I submit that can assume that the lower (dark) beds will have been saturated (Curiosity's findings, the presence of boxwork and clays and the channels/delta deposits). The overlaying light (Aeolian) deposits evident in the layers above this level would almost certainly have much reduced cementation. So there would seem to be a reasonable probability of a significant difference in erosional vulnerability, particularly in light of the increasingly gentle environment of the past few billion years.

Painstaking analysis of Curiosity's findings by the resident experts will narrow the field but as I mentioned previously, there will probably be a number of hypotheses as to the formation of Gale alive and well at the end of the mission. Consider how long it took to get a handle on Opportunity's small area of Meridiani. Anyway, as you are aware I threw the "overland-flow hypothesis" as you termed it in purely to point out that there are alternatives to an extremely high pressure aquifer to explain the Mount Sharp channel features. But it is merely wild arm waving from the depth of an armchair and not worth argument.
Go to the top of the page
 
+Quote Post
David Palmer
post Jul 1 2014, 09:33 PM
Post #36


Junior Member
**

Group: Members
Posts: 33
Joined: 16-June 14
From: Sweet Home, Oregon
Member No.: 7202



Reply to Serpens:

Actually, I WANT "argumentation" over my hypotheses....my model needs to be roundly criticized, it needs to go through the wringer....its not just there to sit and look pretty.....and I figure that by this time next year, it will have been proven right or wrong. It's put forth as a serious scientific hypothesis, which means it is something that needs to be tested....Emily (elakdawalla) doesn't seem to understand exactly what I am trying to accomplish here....just because I am an amateur scientist, and this is a hobby of mine, doesn't mean I also can't be attempting serious science, and attempting to get the notice of professional planetary scientists. And sure, I'm going out on a limb by presenting my ideas, but there's a void to be filled, because no one else has a coherent, all-encompassing model to present. And although Gerald wishes to wait till there is more data in, I figure that the prize is to be had by the person who jumps into the fray and is the first to come up with a model that holds water (no pun intended), even before the so called "experts."

I'm having to get back to work now, but later today I'll make specific replies (concerning geology) to you and Gerald.

Dave
Go to the top of the page
 
+Quote Post
ngunn
post Jul 1 2014, 10:09 PM
Post #37


Senior Member
****

Group: Members
Posts: 3429
Joined: 4-November 05
From: North Wales
Member No.: 542



QUOTE (David Palmer @ Jul 1 2014, 10:33 PM) *
Reply to Serpens:

Actually, I WANT "argumentation" over my hypotheses.

just because I am an amateur scientist, and this is a hobby of mine, doesn't mean I also can't be attempting serious science,


This is indeed a place where engagement with non-professional contributions have resulted in fruitful discussions, and I hope that's what will happen here. To encourage that you need to bend a bit with incoming comment, accept that learning is a two-way process and so forth.

I'm an interested follower of the thread. I do think Aeolis Mons is bizarre and takes a bit of explaining.
Go to the top of the page
 
+Quote Post
Gerald
post Jul 1 2014, 11:12 PM
Post #38


Senior Member
****

Group: Members
Posts: 1817
Joined: 7-December 12
Member No.: 6780



QUOTE (David Palmer @ Jul 1 2014, 11:33 PM) *
...just because I am an amateur scientist, doesn't mean I also can't be attempting serious science, and attempting to get the notice of professional planetary scientists.

If you persue this idea seriously, I'd suggest first to duplicate Kite et al's simulations, as an exercise.
Then model your ideas, and run similar simulations. Compare the results of the simulations with each other, and with available data.
Describe your model and simulation runs in a way, that other scientists can duplicate your results, usually as a paper. Show, that the results of your model fit better to the empirical data than results of other models.
Go to the top of the page
 
+Quote Post
David Palmer
post Jul 2 2014, 07:43 AM
Post #39


Junior Member
**

Group: Members
Posts: 33
Joined: 16-June 14
From: Sweet Home, Oregon
Member No.: 7202



Reply to Gerald:

It is beyond my means to do a computer simulation or mathematical modeling of SWEET, however that is not a requirement. If I can show that Kite's SWEET hypothesis is logically incoherent or in conflict with empirical data, that is all that's needed. And in fact, my essay was originally motivated by reading the SWEET hypothesis and finding it anything but "sweet."

In my essay, I point out MANY insoluble problems with SWEET, and here is an example: it proposes that wind-entrained sediment drops when it encounters the "stagnant air" in the center of Gale (building up a mound), however the Upper Formation consists of cross-bedded dune deposits, which require strong horizontal surface winds to form....and not only is this incompatible with SWEET's aeolian model, but it would cause the sediment to cascade down the side of Mt. Sharp, and the upper mound never be able to form (the only model that makes sense is that the entire crater was filled with extended horizontal sediments, and there was a dune field on top of those sediments).

As far as a mathematical modeling or simulation of my hypothesis, all that is needed is a determination that there is (or was) a net hydraulic head at the location I propose (6,000 feet below datum), and indeed this is/was the case, thanks to the low elevation of Gale, and the high surrounding terrain. And in fact, there probably still is, considering that there was an outflow at Cerberus Fossae (likely from the same aquifer) several million years ago that is estimated to have had a nearly 3-mile-high effective hydraulic head (according to James Head, et al....again, no pun intended). And if the Martian aquifer is still that active, it was certainly FAR more than adequate to fill Gale Crater in the distant past. Hence, bye-bye SWEET (although I do agree with a number of aspects of the wind regime they model, as I explain in my essay, and attribute the erosional deflation of the outlying parts of the crater fill of Gale to those winds).

Concerning your earlier posting: the channels of Mt. Sharp are NOT fjords, those are U-shaped glacial valleys that have moraines at their end, whereas the channels are obviously water-carved, and have deltas at their end. And because of the lack of available watershed area and the lack of a dendritic tributary system, the obvious interpretation is that they were spring-fed.

Also, an ice cover could not have protected the channels and deltas from wind erosion and meteor impacts, as conditions over the last few billion years have been generally far too dry to allow surface ice at this location (it's only been present during high obliquities).

Concerning your suggestion that there should be "cenotes" in Gale Crater if there was an aquifer like I am proposing: cenotes normally form in karst terrain with a limestone basement, where water flow through fractures widens those fractures further (due to the high solubility of carbonates), until sink holes or related features develop (and such a basement was present at Chicxulub). But with a basaltic basement, as in Gale, things are the opposite: the minerals in basalt are relatively insoluble, and in response to weathering in the presence of water, they swell to form clays and so will tend to fill fracures. PLUS, almost the entire region, especially the floor of Gale, is covered by fine-grained (frequently clay-rich) sediments, which are a very effective aquiclude, and would serve to contain an aquifer and allow it to build up high pressures.

My suggestion is that the only area in the local terrain that still has fractures commuting from the surface to the deep aquifer, and thus the only location where water could exit, would be the (largely buried) central peak and its associated megabreccia field (and in fact, as indicated by Schwenzer et al, on the east/southeast side of Mt. Sharp they do show spectroscopic clay signatures at approximately the same elevation as the headwaters of the channels on the west side of the mountain, suggesting seepage from fractures, and which provides additional support for my artesian hydrant hypothesis).

Dave
Go to the top of the page
 
+Quote Post
Gerald
post Jul 2 2014, 12:12 PM
Post #40


Senior Member
****

Group: Members
Posts: 1817
Joined: 7-December 12
Member No.: 6780



Picking out a couple of statements:
QUOTE (David Palmer @ Jul 2 2014, 09:43 AM) *
It is beyond my means to do a computer simulation or mathematical modeling of SWEET, however that is not a requirement.

This would have been a way to become accepted by professionals.
QUOTE (David Palmer @ Jul 2 2014, 09:43 AM) *
If I can show that Kite's SWEET hypothesis is logically incoherent

Computer simulations are a good way to reduce that risk drastically, since simulations use to refuse running, if inconsistent.
QUOTE (David Palmer @ Jul 2 2014, 09:43 AM) *
...it proposes that wind-entrained sediment drops when it encounters the "stagnant air" in the center of Gale (building up a mound), however the Upper Formation consists of cross-bedded dune deposits, which require strong horizontal surface winds to form

A net deposition is sufficient for the growth of the mound, supported by humidity. Low humidity levels may be sufficient to form thin crusts supported by hygroscopic salts like almost ubiquitious perchlorates. The crusts reduce erosion for settled strata, be it horizontally-layered or dune fields.


QUOTE (David Palmer @ Jul 2 2014, 09:43 AM) *
the channels of Mt. Sharp are NOT fjords, those are U-shaped glacial valleys that have moraines at their end, whereas the channels are obviously water-carved, and have deltas at their end. And because of the lack of available watershed area and the lack of a dendritic tributary system, the obvious interpretation is that they were spring-fed.

Alternatively, melting ice caps washed away parts of the moraines and formed deltas, most remnants of the moraines wheathered physically and were transported away by slope winds, some remnants may still be there and accessible for investigation by MSL. No need for a tributary system, and if it has been present, most of it would have been eroded by now.
QUOTE (David Palmer @ Jul 2 2014, 09:43 AM) *
Also, an ice cover could not have protected the channels and deltas from wind erosion and meteor impacts, as conditions over the last few billion years have been generally far too dry to allow surface ice at this location (it's only been present during high obliquities).

It could, since it allowed for cementation and lithification, reducing erosion in the dry phases, when not covered by softer layers.
QUOTE (David Palmer @ Jul 2 2014, 09:43 AM) *
cenotes normally form in karst terrain with a limestone basement, where water flow through fractures widens those fractures further (due to the high solubility of carbonates)...

They can also form in a calcium sulfate-rich settings (on Earth: gypsum karst, e.g. in gypsum Keuper (upper Triassic) regions); hydrated calcium sulfates have been found in relevant amounts at Gale.
After an impact the underground is heavily fractured, not just at the central peak (see e.g. p.7 of this paper).

(I probably won't continue the discussion, since my priorities are somewhere else, but I'll read possible replies.)
Go to the top of the page
 
+Quote Post
David Palmer
post Jul 2 2014, 01:59 PM
Post #41


Junior Member
**

Group: Members
Posts: 33
Joined: 16-June 14
From: Sweet Home, Oregon
Member No.: 7202



Reply to Gerald (my comments are in upper case): Admin Edit: Upper case is considered 'shouting'. Please either use "quotes" or as has been done in this case, italicise comments.

G: A net deposition is sufficient for the growth of the mound, supported by humidity. Low humidity levels may be sufficient to form thin crusts supported by hygroscopic salts like almost ubiquitious perchlorates. The crusts reduce erosion for settled strata, be it horizontally-layered or dune fields.

My point was that dunes shouldn't have even formed on Mt. Sharp, given the SWEET hypothesis.....because there shouldn't have been horizontal winds, and dunes only form on a near-horizontal surface, not the top of a mountain.

G: Alternatively, melting ice caps washed away parts of the moraines and formed deltas, most remnants of the moraines weathered physically and were transported away by slope winds, some remnants may still be there and accessible for investigation by MSL. No need for a tributary system, and if it has been present, most of it would have been eroded by now.

For such a small watershed, the flow rate produced by ice melt in such a cold environment would have been insufficient to transport the up-to-ten-meter-wide boulders we see in the channel fill.

[i]G: It (ice cover) could (have protected the channels), since it allowed for cementation and lithification, reducing erosion in the dry phases, when not covered by softer layers.

Lithification would not have protected the surface against meteor impacts, which are almost absent in the foothills of Mt. Sharp.

G:
(Cenotes) can also form in a calcium sulfate-rich settings (on Earth: e.g. in gypsum Keuper (upper Triassic) regions); hydrated calcium sulfates have been found in relevant amounts at Gale. After an impact the underground is heavily fractured, not just at the central peak

But the basement under the calcium-sulphate-containing surface sediments is what is important here, that is what lies between the surface layers and the aquifer....and on Mars it is almost always basalt...and in the floor of Gale Crater, there would have been an impact melt lake, which then cooled and solidified and formed cracks, but sedimentary deposition of fine-grained clay-rich materials in such a sump, together with authigenic clay production, could be expected to fill those cracks and form an aquiclude in the crater floor (forcing the water to exit the only fractures left open for it, even though that represents a higher elevation).
Go to the top of the page
 
+Quote Post
serpens
post Jul 2 2014, 02:52 PM
Post #42


Member
***

Group: Members
Posts: 642
Joined: 17-February 09
Member No.: 4605



ngunn provides some sage advice above. I commend it to both of you.

Kite's model is reasonably simple, but he clearly states that it was designed that way to investigate a concept. Shortcomings include assuming a non erodible crater floor, failing to consider the effect of a previous lacustrine environment and the overlooking the potential effects of valley exit winds or possible adiabatic warming of katabatic wind that on exit would end up warmer and less dense than the air at the crater floor, providing lift to aid central deposition. We also do not have a clue about the air density during the formation period. But I would assume that a degree of sensitivity analysis was employed and the model certainly fulfilled its intended purpose. While Dave presents a number of arguments against the concept these are based on assumptions and unsubstantiated statements, depending on qualitative reasoning (I think this therefore it is so).

Personally I don't see that concepts such as Aeolian slope wind formation, crater infill, "overland-flow", airfall (volcanic ash draping), surge deposits and springs are in any way mutually exclusive . It would seem that the lower dark beds of Gale were laid down in a neutral pH saturated environment where probably Mount Sharp merely consisted of a central uplift. Above that is a sulphate/clay mix which could imply an interface between basalt buffered ground /lake water and acidic inflow with the sulphates domination with height. The amount of material would seem to point to infill. If Curiosity makes it to the delta above the entry point then the pH of the deposit may provide an indication as to whether it came from a nearby basalt buffered ground water spring or whether it was acidic surface flow.

The higher reaches of Mount Sharp seem to have both massive layers and also cross beds with indications of deposition/erosion cycles and a number of deposition events with various material. My take for what it is worth is that Mount Sharp was formed through a combination of mechanisms over a long time. Mount Sharp is not so much an enigma as a jigsaw puzzle.

All possibilities remain in play. Edit. Inflow requires a transportation medium. Aeolian transportation results in cross beds. There are also massive beds in the upper level where air fall deposition is the most likely cause. The reduced impact evidence in the foothills would seem pretty compelling evidence to me that the area was buried and then exhumed.
Go to the top of the page
 
+Quote Post
mcaplinger
post Jul 2 2014, 03:13 PM
Post #43


Senior Member
****

Group: Members
Posts: 1574
Joined: 13-September 05
Member No.: 497



QUOTE (David Palmer @ Jul 1 2014, 02:33 PM) *
...I figure that by this time next year, it will have been proven right or wrong... the prize is to be had by the person who jumps into the fray and is the first to come up with a model that holds water (no pun intended), even before the so called "experts."

What is the test for your hypothesis that you expect to be resolved in a year?

BTW, referring to the scientific community as "so-called experts" is a sure way to have your work dismissed.


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
Go to the top of the page
 
+Quote Post
David Palmer
post Jul 2 2014, 03:29 PM
Post #44


Junior Member
**

Group: Members
Posts: 33
Joined: 16-June 14
From: Sweet Home, Oregon
Member No.: 7202



QUOTE (mcaplinger @ Jul 2 2014, 07:13 AM) *
What is the test for your hypothesis that you expect to be resolved in a year?


1. Particle size distribution, minerology, and bedding characteristics of the Lower Formation should all indicate lacustrine, not aeolian, deposition,
2. The channel fill of what I am referring to as the "Northern Channel" should show a very young cosmic-ray exposure age (several million years),
3. The minerology and isotopic ratios of the channel fill should reflect a groundwater origin, rather than surface precipitation (I am expecting a high salt content....and a bias towards heavy isotopes in the bound water, as compared with atmospheric moisture or frost or snow).
Go to the top of the page
 
+Quote Post
Gerald
post Jul 2 2014, 05:30 PM
Post #45


Senior Member
****

Group: Members
Posts: 1817
Joined: 7-December 12
Member No.: 6780



QUOTE (David Palmer @ Jul 2 2014, 05:29 PM) *
3. ...I am expecting a a bias towards heavy isotopes in the bound water...

Didn't you actually mean a bias towards light isotopes? That's what I would expect for an old aquifier.

Item 1 could be explained by lakes, ruling out Kite's simplified purely aeolean model, although not the concept;
item 2 could have been caused by rapid recent erosion.
Item 3 appears to be more specific to your main hypothesis of an ancient aquifier, although there may be some ambiguity with a hypothesis of an early formation of the channel filling material, or just old buried ice as kind of a local aquifier.

In which way is the test specific to the (high-pressure) artesian spring hypothesis? Or which additional tests could provide unambiguous evidence?
Go to the top of the page
 
+Quote Post

4 Pages V  < 1 2 3 4 >
Closed TopicStart new topic

 



RSS Lo-Fi Version Time is now: 28th June 2017 - 10:37 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.