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 think perhaps everyone needs to take a deep breath and have a nice cup of tea. Colour by definition is a human perception of reflected frequencies and that perception can differ to a degree between individuals. So the human perception of the colours of Mars, after selective frequency transmission and tweaking should best be described as a very good approximation and really is not worthy of this type of argument.

The "artesian hydrant" scenario you refer to would correlate to a spring mound effect and this has been considered previously as a possible influence on the development of Mount Sharp, but is considered a very low probability. For instance Figure 2 of the 2013 paper by Kite et al "Growth and form of the mound in Gale Crater, Mars: Slope-wind enhanced erosion and transport" provides a good comparative illustration of the stratigraphy expected from various influence forming Mount Sharp, including spring mounds. The thing with Gale is that we are looking at an erosional end state and really do not have a clue as to the structure of the crater, or floor depth when some of the features you discuss were formed. But if we consider the lower (seemingly non Aeolian) layers of Mount Sharp in the light of Mr Steno's rules and the apparent structural strength of some of the sedimentary rock observed by Curiosity then at some time there was a lot of material above the current floor that Curiosity is traversing. Despite the exceptional capability of orbital imaging and Curiosity's ground truth , the scope of "hands on" analysis is very limited. This means that even after Curiosity investigates accessible parts of Mount Sharp there will probably be multiple hypotheses alive and well at the end of the day, including possibly some of yours.

You make some good observations and interpretations but perhaps should revisit potential alternative influences. In analysing Gale I think it is necessary to consider it in the context the surrounding region and the somewhat unique North South crater rim height difference due to the position on the dichotomy boundary. There is reasonable evidence that a Mars Ocean existed, possibly a couple of ocean recharges, and that would have implications for partial flooding of Gale from an aquifer.

[David Palmer]

reply to Serpens:
I am very aware of the spring mound hypothesis and discuss it in my essay, and state that it could have contributed to the core of Mt. Sharp, but Rossi et al. envision Mt. Sharp being built of evaporate deposits, and of such activity being confined to the early geothermal phase of Gale Crater, so it is a different hypothesis from mine, where I am claiming that the artesian hydrant is an ongoing phonomenon that was active again fairly recently. And while the northern ocean would indeed have filled Gale Crater, I am claiming (on the basis of the Mt. Sharp channels and their delta deposits) that a deep lake existed in Gale LONG after that ocean had dried up. And the natural interpretation would be that a still-active aquifer occasionally commutes to the surface when conditions are right, the water table of which can be calculated to be well above the half-way point of Mt. Sharp on the basis of the surrounding terrain and the geologically recent Cerberus Fossae outflows.

Dave

[serpens]

Dave, I am answering here rather than by email because I would be interested in the take of a few of the extremely knowledgeable posters on this forum. Note by the way that I said influenced by spring mound effects, not that this is a sole cause. When I suggested looking at a regional context I was considering the topography surrounding Gale, in particular the North and North West which indicates significant erosion and indicates that that Gale was possible once covered to a regional level above the crater rim and then exhumed. If so we have to consider that the channels originating on Mount Sharp could be the end remnants of drainage channels that originated well outside the crater when the crater was filled to a common level. Erosion and exhumation of the crater and Aeolian deposition of the higher section of Mount Sharp would have removed any evidence. The implication of course is that any lake corresponding to the Mt Sharp deltas would have been quite shallow. There are remnant channels all over the area and in generating hypotheses on Gale we have to consider every possibility with respect to the changing regional terrain over many billions of years and the fact that we do not really have a clue as to the actual environment when some of these features formed. Atmospheric pressure, temperature, wind speed or water content. My take is that for a reasonably long period it was one heck of a dynamic environment and the topography of Gale and surrounds was nothing like it is today. There are lots of potential hypothesis for gale and the evidence of a lacustrine environment and I throw the above in simply to point out that every possibility has to be considered.