geology of Gale Crater and Mount Sharp Options

[David Palmer]

The idea that the Lower Formation of Mt. Sharp is of lacustrine origin (lakebed sediments) has rather fallen out of favor recently, but I just finished my essay on Mars, "An Interpretation of the Geology of Gale Crater & Mount Sharp, with Implications for the History & Habitability of Mars," which I have spent over one year researching and writing, and the primary thrust of this paper is to offer a fresh defense of the lacustrine model, incorporating some fairly original ideas on my part. I'm not a professional scientist, but this is a labor of love that springs from a near-lifelong interest in Mars (since I was a young boy in the 1960s). And I'm trying to publicize it prior to Curiosity reaching Mt. Sharp, as that will be a test of my theories, and I'm hoping to get some recognition if I'm right. So here's the link for all interested readers: http://galecratergeology1.tumblr.com/post/...le-crater-mount

[serpens]

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.

[David Palmer]

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

[Gerald]

...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.

[David Palmer]

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

[Gerald]

Picking out a couple of statements:

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.

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.

...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.

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.

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.

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.)