Posted on 03/27/2004 7:35:06 AM PST by Bush Cheney
"Mazatzal" Rock on Crater Rim NASA's Spirit took this navigation camera image of the 2-meter-wide (6.6-foot-wide) rock called "Mazatzal" on sol 76, March 21, 2004. Scientists intend to aggressively analyze this target with Spirit's microscopic imager, Mössbauer spectrometer and alpha particle X-ray spectrometer before brushing and "digging in" with the rock abrasion tool on upcoming sols Mazatzal stood out to scientists because of its large size, light tone and sugary surface texture. It is the largest rock the team has seen at the rim of the crater informally named "Bonneville." It is lighter-toned than previous rock targets Adirondack and Humphrey. Its scalloped pattern may be a result of wind sculpting, a very slow process in which wind-transported silt and sand abrade the rocks surface, creating depressions. This leads scientists to believe that Mazatzal may have been exposed to the wind in this location for an extremely long time. The name "Mazatzal" comes from a mountain range and rock formation that was deposited around 1.2 billion years ago in the Four Peaks area of Arizona. Image credit: NASA/JPL |
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I'll be back.
Cogitator - could you pass this along to you Geology Photo of the week ping list?
Thanks, CR
The fact that we have the whole range of angularity makes me suspect that the rounded grains are abraded. I still don't have a handle on scale, however.
And why do you think that there is no evidence of fluid flow around the larger grains in several of the photos, especially the one in the upper right corner? I pulled out my old copies of Reineck & Singh and Blatt, Middleton & Murray and found noting even remotely similar. Are we not looking at sediments? If so, is it so quiescent that there is no apparent turbulence wake or wake vortices?
But looking at the pictures, it appeared that the blueberries were falling out of the rocks, which would definitely point to the concretion identity. First thing that came to mind as a terrestrial analogue is oolites (click on this to see the full-size pic):
This next picture is of oolitic sand from Great Salt Lake, which is a decent analogue to the environment described at the Opportunity site:
From this Web site:
Oolitic sand at Stansbury Island, Tooele County
This page has some ugly-looking hematite concretions:
And this is a good article about the identity of the blueberries:
'Blueberries' Reveal Only Part of the Mars Water Story
This was posted before the press release that showed the stratigraphic layers interpreted as formed in shallow water.
Regarding your last question, and drawing on experience from when I visited Great Salt Lake one time: what they're talking about is a surface brine region. The water is going to be much denser (more saline), and the sediments are initially going to be "goopy" thick oozes that only over time will turn into rock. So though you can get layering as successive wet/dry cycles, this isn't a very active flow environment where you'd see evidence of water movement.
My field experience is somewhat limited to the American Southwest, particularly the deserts and mountains of California, Nevada, and Arizona. So my observations are made with those parochial biases. (I have very little experience with carbonates, for instance.) However, I think some of the "desert pavements" I have seen bear a striking resemblance to Martian pictures.
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