[X] My Assistant

[dvandorn]

I've been looking at some of the more recent Spirit images, and I'm seeing some really impressive layering at several different scales.

First off, there's these rocks (about one-fourth of the way from the top of the frame, one on the far right side and one on the far left side):

http://marsrovers.jpl.nasa.gov/gallery/all...00P2373L2M1.JPG

These rocks show fine layering. The one on the left side shows them perhaps a little more clearly, but the one on the right side is larger and shows more layers (though less distinctly). I can't tell the rock sizes conclusively from the context of the image, but the layers in these rocks appear to be very thin. They remind me of the layering in the Meridiani rocks.

We haven't seen this kind of layering, indicative of sedimentary rocks, much at all elsewhere in Gusev. I find this exciting. It's very definitely a different type of rock than we've seen down on the plains at Gusev.

Then there's this scene:

http://marsrovers.jpl.nasa.gov/gallery/all...00P2372L2M1.JPG

Not how there are coherent layers in the mid-field rocks that predominantly carry over from rock to rock. It's as if most of the rocks have been exposed and weathered out of the material making up the hill, showing that the hill itself was laid down in relatively thin layers and then eroded away. Yeah, some of the rocks have tumbled down to their current locations, but a lot of them seem to show in-situ, thin bedrock layers.

Finally, there's this scene:

http://marsrovers.jpl.nasa.gov/gallery/all...00P2373L5M1.JPG

It clearly shows the larger-scale layering of outcrops made up of rock layers several feet thick. If the rocks making up the larger outcrops are similar to the layered rocks seen in the above images, then we seem to be looking at the successive laying of similar-composition rocks with much finer layering within them.

I suppose we could be looking at wind-laid layers... but the fine layering in the rocks looks a LOT like the fine layering in the evaporite rocks at Meridiani. Any bets we find out the Hills were originally laid down as water-laden sediments?

Doug
dvandorn@NOSPAM.mn.rr.com

[aldo12xu]

The finely layered, darker rock with concretions (bottom centre of your photo in the previous post) could be similar to the Layered Unit that Oppourtunity is investigating right now. The one rock they already analysed from there was determined to be a sandstone with a basaltic composition. It also had concretions.

http://marsrovers.jpl.nasa.gov/newsroom/pr.../20040517a.html

The other rock (top centre) seems to be lighter in colour and not only has concretions, but it also has concretions attached to stems.

If these are ejecta blocks and not outcrop, the source might be within the Columbia Hills, in what some have called the Ultreya Abyss. Ultreya is a cave-like opening that contains one or two light coloured layers that might represent an evaporite sequence. The white layers are underlain by well stratified darker sediments. I posted some close-up stereo views of Ultreya on my website below (just scroll down a bit):

http://www.tobescene.com/Mars.html