[X] My Assistant

[ngunn]

This blockbuster article from Emily seems to justify a new discussion topic:
http://www.planetary.org/blogs/emily-lakda...le-of-gale.html

So many thoughts, so many questions, I don't know where to start. What about Gusev? Were those basalts actually sandstones too?

[serpens]

Nice to see the illustrations showing a lake in Gale without Mount Sharp. Personally I feel that a dab of artistic licence to show a higher, less eroded crater rim and ejecta field would have provided a better feel for what it would have looked like. Establishing the time line for the various fluvial/lacustrine artifacts found by Curiosity will be a real challenge. The lower levels of Mount Sharp are a pretty strong indication that at some stage the original lake would have extended over the area of Curiosity's traverse, or alternatively, as the crater filled a bowl shape was retained, confining the lake to the centre of the crater over many millions of years. Mass wasting from an initially high and rugged rim would fit that scenario. The telecon central lake hypothesis for the creation of the lower levels of Mount Sharp, followed by excavation and deposition as proposed by Kite to form the Aeolian upper layers seems a pretty seamless fit although the lithification and evidence of significant water flow on the upper levels provides a good argument that this mountain building occurred when Mars was still experiencing wet cycles.

I am still not entirely comfortable with the early classification of Pahrump Hills as part of the basal layer of mount Sharp, implying it was formed in the original lake. The apparent friability and partly modified basaltic composition would argue against that. Given the position in relation to Mount Sharp a late stage onlap or downlap would seem more logical . The same logic would apply to the Murray Formation.

[Gerald]

... Given the position in relation to Mount Sharp a late stage onlap or downlap would seem more logical. The same logic would apply to the Murray Formation.

It should be possible to discriminate the two hypotheses by their predictions, how the inclination of cross-bedded or deltaic layers are oriented.
They observed (as a key observation) roughly southward oriented inclinations, so it's reasonable to start with testing, whether this will hold during future observations.

Mount Sharp downlap should incline layers away from Mt. Sharp, in general.

Mt. Sharp downlap layers might have been ontop of the base layers, and eroded away (in a mostly aeolian way) by now.