First, a few words about Endurance... it features several spots along the inner wall where scalloped edges of the rim have fallen into "slump blocks" halfway down the wall, right? We've seen several of them in the pans of Endurance.

We also see some terraces along the rim which display undersapping of soil beneath what are obviously five to ten foot thick layers of evaporite rock.

The rim has been degrading over millions of years, as underlying soil has been eroded away and layers of evaporite rock have come sliding into the crater's inner walls.

Now, look at an image of the Keratepe entrance path to Endurance:

http://marsrovers.jpl.nasa.gov/gallery/pre...rive-B150R1.jpg

Note how the edge of the primary contact between apparently evaporite rock and what lies below seems to scallop into the crater, rather than follow the curve of the crater itself. In other words, if the rim of the crater defines a concave curve, the edge of this layering unit seems to define a convex curve.

And there seems to be this little raised rimlet of exposed evaporite-appearing rocks right at the edge of this convexly-curved bedding.

It looks to me for all the world like Opportunity is traveling along the edge of a ledge that collapsed into the crater. Instead of looking at really, really deep layering of the underlying units, all of the evaporites in view look to me like they're shattered remnants of an evaporite "terrace" unit that collapsed into the crater a while back. So, instead of a beautifully layed-out series of in-place bedrock layers, we may well be looking at the partially-coherent, partially-jumbled talus of an infall of a layer that seems to be about five to ten feet thick at other points along the rim wall, but here is spread out by its slump to cover forty or fifty linear feet, all told.

Does anyone see what I'm seeing here?

Doug
dvandorn ((New Address To Be Announced))

</center>Dvandorn,

I was discussing this at another forum, and thought I'd share this with you:

The original meteorite that caused Endurance Crater was probably only about 1 metre in diameter.

The original crater was probably a simple crater, perhaps around 70-90 metres diameter. Underlying strata was pushed outwards and upwards causing plastic deformation of upper strata to form an uplifted circular rim.

Subsequent to the initial impact, a (partial) annular downfaulted zone, or graben feature developed along the concentric fault lines along the rim. This feature resulted in the surface strata slumping around the edge of the crater. The surface strata can be seen on the crater walls at an angle of between 20 and 40 degrees to the surface plane.

It's unusual for a graben feature of this type to form in such a small crater, but the bedrock is clearly quite friable in places.

There are many examples of such downfaulted crater structures on Earth.

I think we're dealing here with some very friable material that contains large proportions of soluble salts such as magnesium sulfate, and not so soluble minerals such as jarosite.

I get the impression that the top layer is largely oriented in a similar direction, with one or two obvious exceptions. It tells us something about the seismic event that accompanied the impact. Look at the cracks between the surface rocks - They just seem too narrow for an ejecta bed. The most likely solution I think is that they are the original strata, but just jostled around a bit by the impact.

I also believe that topography has a fair bit to do with the flat surface. If we have a rock that sticks up, it will be preferentially eroded.

The downfaulting if that's what it was, must have been quite unique to result in the structure we see today. What's strange is that the "pavers" are all virtually undisturbed on the crater walls.

That fact leads me to think that the subsequent process was slow and gentle. If it was a rapid process, the rocks would have ended up in a much greater mess.

So I'm thinking in terms of an upwelling of brine and some kind of chemical erosion/ ion substitution(?) that gradually ate away the lower levels.

Why did it leave the upper levels intact? Possibly the ground water level was too low for that.

I don't have all the answers, and the above is just a working hypothesis. If you can fill the gaps or come up with an alternative, go right ahead.