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]

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)

 

[David Palmer]

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

[Gerald]

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?