Horton
I confess I am having a real trouble understanding your point(s) in reply 41. You seem to be saying that the crater predates the evaporitic sediments, that the evaporites formed in the crater, which was formed a lake.
This does not make sense of the data.
First, the "ripples" have the morphology and scale of sand dunes formed by wind. They don't form this size in lakes.
Second, the same evaporitic sediments are found in the walls of Fram, Eagle, and Endurance craters. As far as we can tell from MER images, they also occur in the walls of other craters as well, and are exposed in the etched terrain. The eavporite sediments are older than the craters. As we have seen in both Endurance and Eagle (Fram is probably too degraded) the fact that sediments dip away from the crater in all the walls, the dip rapidly approach horizontal with distance away from the crater, and the radial faults and fractures all point to this. It is logically impossible for a crater to be older than the material in which it forms. It is like saying a bullet hole is older than the glass it has passed through.
Third, who has said the evaporite beds are vertical? Sediments are laid down horizontally. The evaporitic sediments at Meridiani are still horizontal, apart from some local dip caused by impact craters.
Fourth, while increasing evporite content down the crater walls is consitwent with a salt pattern formed by a lake in the crater, it is also consistent with a range of other causes, including a change in composition in the host succession.
Fifth, there is no evidence of drape that I can see. I do see lots of fractured blocks that have been beveled to the same level. I also see surface crusts of cemented material. But this does not mean that the evaporite sediments have been draped over the crater. Quite the contrary, it is eactly what you would expect from weathering and erosion of a crater in such seidments in a hyper arid environment.
Sixth, manganese nodules? They contain manganese for a start, these concrtions don't. Then they form in areas of essentially zero sedimentation, whereas Meridiani was a site of active sedimentation. Als they form only on the surface-water interface, the Meridiani concretions have formed at depth after deposition. This does not mean to say they are without value as analogues, they do after all provide yet another example of spheroidal concretions. But that is about as far as it goes.
Cheers
Jon
