Your point about no clay is interesting. I had not thought about it, but, I have not heard any mention of clay minerals there. I draw a parallel from that to the apparent stability of olivine on Mars. No degradation of olivine and related mafic minerals = no clay.

As to the mudcracks, well with all those hydrated minerals present - these should shrink and recrystalize drastically if they actually dried out, so clay is not needed for cracking. It looks like this may have happened to some of the chunks of rock in Endurance crater. Thus, I would more favor the efflorescence variation of your model where things just dont dry out, that there is constant wicking of moisture. The current soil surface shows signs of efflorescence in the almost pervasive "labrinthine" texture (with many hollow, or "hopper" crystals and much branching). This resembles crystals that form rapidly under wet conditions with capillary flow, not subaqueously. This could have occurred more extensively in the past, before the Meridiana plain was exhumed, and cut off from the higher (water) source region. Also in support of your efflorescence deposition model, most of the rock seems to be very porous, I mean on a smaller scale than the "big" arcuate voids. This is a problem for my deep sea model, which should have a more compact rock- but it is kind of hard to tell without more magnification. One big problem for the efflorescence model is that the harder layers within the sediments, the ones that stick out upon erosion, should form a completely continuous surface. These denser layers could have formed in the drier climate cycle periods, as you suggest, but they should form a complete continuous surface. What is seen, IMO, is that these layers never extend very far, and often interfinger with each other, and also bend out of the horizontal in many cases. These layers often seem bubbly or beaded, reniform, but not cracked. These textures usually form under complete submersion. I do agree that overall, many of these rocks look like spring deposited tufa, a model I continue to seriously consider.

Inherent in my marine origin model, though I may not have stated it, is I believe that Mars was very tectonically active early on. Meridianna may have been uplifted, even multiple times. I would guess a smaller planet like Mars, with lighter and less rigid elemental composition than Earth, would have had a higher temperature gradient initially from core to surface, thus driving a greater degree of tectonism, but of shorter duration. Some areas I have seen in the North (enigmatic ground?) look like chocolate swirl ice cream. This implies deep tectonic folding followed by near complete planation. There are other., different deposits that seem to be on top of this. Thus, I believe there is complex tectonic history - so there does not need to be any obvious signs of or current morphology of a basin for Meridianna sediments to have formed in a basin.

I saw a better wide shot of the angled layers below Burns cliff and saw that I was wrong and it looks clearly like there is good cross bedding within that particular unit. Lenses of sediment are visible, but within the unit they are not very high angle. My guess is still that these are not aeolian, but aqueous, and that the one high angle contact at the cliff base is an erosional discontinuity.

I thought you might say something about the "rain." I just seems unlikely to me that there could be significant water around without having rain at times. The efflorescence/wicking model needs a steady source of moisture for 2 million years providing the near saturated salt solution (but not in excess), and it needs a volume of solution at least 3 times greater than the volume of the evaporite sediments. An aquifer would not provide such a steady source for so long, unless it was cyclically replenished itself. This could be seasonal melting of an ice cap, or rain.

One significant point I did not make earlier is the lack of frost patterns in the sediment layers. If these were deposited subareal in a cold environment, there should be some marks from small ice crystals, or from frost wedging, etc. These don't seem to be present, though I have seen frost crystal marks (small needle shaped and radiating voids) in the dust coating boulders at the Spirit location. The common voids at Meridianna are generally lense shaped, but these shapes are a long shot to be explained as ice lenses, IMO. For one thing, a great many of them are convex/concave lenses, not bi-convex. This is hard to explain for an ice crystal-or for any crystal for that matter. An important point is that they have very little or no order to their orientation. Ice wedges or ice crystals should have some marked orientation to the temperature gradient or bedding direction. Other crystal types forming diagenetically should have some orientation to the stress field or solution flow direction. These seem to have formed concurrently to the rest of the sediment. There really aren't that many minerals that are more soluble than epsomite, though there are a few and acid could be a factor. If these were from crystals, how come they are all about in the same size range over such a large vertical and lateral extent? Has anyone put a metric to that? This is a really big problem for the Nasa theory on these, IMO. How could these voids all get dissolved out, all over the place, (and are never seen still filled) while the super soluble Epsomite host rock retains its very fine bedding structure, and shows no signs of internal dissolution in any examples I am aware of. My (non mainstream) best guess is that these are the remains of blobs of jelly, not necessarily biological, but possibly a scum that formed at the water surface to a characteristic size before sinking. Tar balls, maybe? At any rate, I see a strong parallel in relationships between the spheres and voids. Both have random orientation, a very limited size range, and a typical (to monotypical) morphology. I think there is evidence that both were deposited along with the host rock, which also contains a third "precipitated" component - the bedding "plates", I believe. A fourth possible component is the stem like linear pieces occasionally seen. There is a lot to these rocks that needs explaining. Interesting times!