I'm quoting here a question that Bruce Moomaw asked over on Alex's Planetary Sciences group, and repeating my "answer" here. I'd like to offer this as a starting point for discussion amongst the audience here, especially those who've spent time playing on the beach and in streams, looking at ripples and bedforms.

How good are our Earth analogues and instincts when we deal with Mars?

When is an observation "evidence" and when is it "interpretation"?

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--- In planetary_sciences@yahoogroups.com, "Bruce Moomaw" <rmoomaw@s...> wrote:
> We have now learned that "Pyrrho", one rock on Endurance crater's edge observed with a Microscopic Imager mosaic by MER-B, has what's described as a "braided ripple" pattern. What's the significance of this? Does it increase the probability that the sediment layers were laid down (or at least modified) here by flowing water, rather than by wind?

Well Bruce, that's pretty much the $64,000 question, isn't it.

The issue is a complex one. We're looking at a fragmented exposure of weathered rocks, which are outside our normal experience, and with remote handling and sensing tools that aren't ideal.

On Earth, you'd get on your mule or 4wd and find a better exposure where things are more obvious, but we don't have that option so let's go carefully through the evidence:-

We see complex contorted features in the bedding. Sometimes they're ripple-like, sometimes cross-bedded, sometimes a wavy undulose sort of stacked ripple or loose folding of the beds. In the case of Pyrrho, the most significant feature that I would point to is that there is a diagonal band of distorted bedding running across the rock, like a slump fold (on Earth, a sign that soft, unconsolidated sediments began to slump into a nearby depression and got folded in the process. On earth, sediments need to be wet for this to happen.

That doesn't mean that the sediments were laid down in water, neccesarily. I still think the Sabkha model has a lot going for it, especially since we can explain broad areas of sulphate deposits without a confining basin, and also explain some of the layered crater mounds that rise above the crater rim (they're aquous/sulphate "volcanoes" or "geysers", IMO).

I'm working on an overall analysis of the deposits but it's not finished yet. Suffice it to say that "braided ripples" are not, to my knowledge, a standard geologic term, nor disgnostic of any particular process or environment. I think it's just an ad-hoc description that the MER scientists have picked to describe what they see.

Ayway, continue to take things with a pinch of salt, and watch for conflicting observations and interpretations. You'll notice that the MER team is a little less sure about their shallow warm pond than they were at Eagle Crater...