[X] My Assistant

[djellison]

New SS Update - "December 23, 2005

Things have been going well at Gusev. We've spent most of the past week looking at a rock right next to Comanche that we call Comanche Spur. Like everything we've seen since we've descended off of Haskin Ridge, Comanche Spur has undergone very little alteration and has a lot of olivine in it. But the composition is different from what we saw at Seminole and Algonquin, so we seem to have yet another rock type at Gusev.

With the Comanche campaign wrapping up, it was decision time... Allegeny Ridge or El Dorado? We had a long meeting about that at mid-week, and the consensus decision was to head for El Dorado. We should begin the drive on about Sol 704, and we're hoping it will go quickly. Expect Spirit to do a lot of driving and (except at El Dorado) not much IDD work in the weeks ahead...."

704 is Boxing Day

What do you think - El Dorado for New Year with a nice 6 x 3 pancam postcard....go on Jim, you know you want to


Doug

[Bill Harris]

am not a geologist; but, the sharp El Dorado boundry demarkation and elevation bothers me. This looks to me more like a deposit from the weathering of a large central mass "crumbling" and flowing down and outward.

I am, and the morphology of this spot is bothersome. I can believe in wind deposition, but the boundary is remarkably sharp, and the material is being deposited on a slope and seems to be moving downslope. I'm leaning more and more in the direction of the source of dark sand being at the head of the slope.

"I think that the answer will be complex. Is this area the result of selective winnowing or deposition of the dark sand because of a unique wind pattern caused by orographic effects, or is it caused because the source material for the sand is _at_ this location, or both? We need MIs of the sand, and minerology."

Looking at the first MIs of the dark sand today, my first impression is that it looks very similar to the last MIs Spirit did at the dark rock at Comanche Spur. Are deeply weathered and crumbling outcrops of this material present at El Dorado, with the dark sand winnowed and concentrated by unique aeolian conditions?

This is indeed an odd area.

--Bill

[dvandorn]

...Are deeply weathered and crumbling outcrops of this material present at El Dorado, with the dark sand winnowed and concentrated by unique aeolian conditions?

I posted this idea quite a while back, somewhere in the many, many posts I've made at this forum. I fear it would take hours for me to try and fine it, so I'll just re-state it.

I had been looking at the orbital imagery and commented that I thought I saw a series of bench-like outcrops along the side of the hill that seemed to border the upslope side of the dark-material field. It looked to me like the benches could be the source of the dark material, since they seemed to be just as dark as the rest of the field. I was arguing that this seemed to be unique material -- much, much darker and less red than everything around it (which, we now see, it surely is).

I proposed that the dark beds could be the eroded remnants of a layer of lacustrine materials, uplfted at the base of the hills. And I thought that made what has now been named El Dorado a prime target for investigation.

I may be wrong about the lacustrine origin, but I'm surely glad we're checking it out! I would also hope that a mini-TES from this spot would be able to characterize the outctops we *do* see at the far extent of the dark sand field as either the source of the dark sand, or definitely *not* its source.

In any event, we need a decent shot at the mineralogy here, to constrain any assumptions on the origin of these sands. Until we get that, this discussion is pretty much in the energetic-arm-waving phase.

However it comes out, this is a very exciting process!

-the other Doug