I believe that Dr. Squires started as a dry Mars advocate, but has gradually shifted position. At Eagle crater he proposed a "fine layers of dust" hypothesis. Several Nasa posts pointed to what I would describe as wildly contorted filamentous and pellicular sediment strands and claimed that it was cross bedding. With more photos, it is now clear (to me) that there is no real cross bedding at Eagle crater. Even these noted deviations from flatness were within very flat lying thin layers. The same is seen over most of Endurance crater. The bedding is very flat lying with one important exception. I have scoured nearly every image in search of cross bedding, and especially cut and fill (or scour) structures that result from channel flow. I though I saw one such large possibility, but it was uncertain. This does not rule out an intermontain playa scenario, which would be dominated by shallow flow structures around its margins, but could lack them more toward the middle.
That one exception was the apparent high angle cross bedding around the base of Burns cliff. I say apparent because it is possible that this is the exposure of a thrust fault from the meteor impact, with the lower layer being a large rotated block. I think it looked a bit too large for that. Alternatively (and no one commented on) the fact that this contact was very flat. It seems to be a substantial erosional discontinuity. The next layer up was flat and extensive, without any other layers filling in any bumps below. If this is not a thrust contact, then it represents a significant change in environment from the high energy - high angle sediment deposition, to an erosional planation interlude, then to low energy deposition. Does this fit a playa model? Only if it is a deeply flooded playa. There are several meters of very flat, very fine layered sediments lying above the contact. None of these layers are significantly disturbed, no channels, no cross bedding over a large visible area. What I think I see is that these layers are not really continuous on the finer scale, but are interleaved. This interleafing seems to show no directional pattern. The basic micro structure of the rock is small strings of pellets (pellicular), a fairly common type for Earth limestones. I believe this implies precipitation, whether biological or mineral. If this precipitation occurred on a drying lake or sea bed, why are the layers not more continuous on the fine scale? These micro layers seem to narrow to be seasonal, but more on the order of daily accumulations. Dry lake bed layers from intermittent floods should be graded (larger particles grading upward to small ones within a given layer), and thicker. I don't completely discount the dry lake possibility, but my favored conclusion is that these are thin mats of material that precipitated at the surface of a body of water, and sank to the bottom, breaking up along the way. This accounts for their exceptional thinness, discontinuity on the small scale, and general (seasonal or geological) uniformity on the large scale.
I disagree with other authors on this thread who stated that the berries and disk-voids do not show deflection of the layers. The better rat hole images distinctly show layers bending around the sides of berries and disks. There are not good examples of layers draping over the tops of these objects and showing glaringly obvious deflection - because none of the layers are all that continuous on the fine scale (this is an important point). I like the posted idea that these disk voids were ice crystals, but the formation of ice lenses would deform the layers. I think this is exactly what is seen.
I think there is no good evidence that the berries formed after the deposition of the sediments. It is just the opposite - nearly every pic showing deflection of micro layers near berries. The berries themselves internally have shown no layering or remnants of matrix texture from any of the many examples. Other examples (Burns) seem to show eroded, misshaped, even cracked berries included in the sediment, further supporting my contention of simultaneous deposition of berries and matrix. My theory is that the berries precipitated along with the filamentous mats as the second principal mineral phase. This allowed for spherical growth, but limited the size range on the upper end. This could have caused the unusually well distributed spatial arrangement, another important and quantifiable parameter that strongly argues against precipitation during diagenesis around some "nuclei". How would the nuclei become so randomly distributed? How would the precipitating solutions not favor more permeable zones, or an upper surface zone? Sure it is possible that the whole formation was flooded completely in a single event, and the berries precipitated later randomly, without appreciable fluid flow, but how likely is that? It is also possible that the berries formed as crystaline spheres that excluded the matrix material. That should have produced a halo of disturbed denser sediment around all sides of the berry, which doesnt seem to be the case. Even if this did occur, it is still a heck of a lot of water to deposit all these layers, and flood the whole formation uniformly. If that much water was present, it only makes sense that seas could be present as well. The formation is extensive laterally and vertically. There are only very gradual changes in the frequency and size of the berries that I have observed so far. This is the main problem for the diagenetic concretion theory. Too bad we did not get to see the high angled beds closer. Were there berries distributed in these layers also? How were they distributed? If these were dunes or river sediments, and the berries formed earlier, then they should have no berries, or a big pile of berries down in the troughs. If the berries formed post deposition, then they could have a uniform distribution, but it seems even more unlikely in that case than in the case of the flat sediments. If the high angled sediments were marine beach front, or reworked subaqueous sediments, then they could have berries throughout. There may be a few pictures that show some of this apparently high angled layer a bit closer. Please inform me if you see any clear evidence for any particular theory. Enjoy Mars, and dive in!