[X] My Assistant

[djellison]

http://www.unmannedspaceflight.com/doug_im...aving_larry.jpg (476kb)

Larry is the outcropping to the right - Methuselah is the layered rock on the left.

As an interesting point to judge distances - assuming zero slip the marks made by the hold-down-brackets on the wheel tread are 80cm apart - or about 2ft 7inches

Doug

[dvandorn]

Good discussion.  Let me jump in here.  There are a few things I would like to bring up. 

1) Gusev has a number of compression faults that are generally aligned north-south and perpendicular to the direction to the tharis bulge.  In fact the tharis bulge is ringed by compression faults in all directions.  This is most likely due to the relaxing of the bulge.  Picture a cone on a desk.  As you push down on the cone, the sides either have to compress or they split.  It seems that tharis is doing both.  And it seems to have occured as far out as Gusev.

Further, this could have been active before the lava flows embayed the hills.  Thus the hills could easily be formed by thrust faulting.

2) Sedimentary rocks can form at an angle.  These rocks need not have tilted at all.  Air born ash falling on a hill side or the rim of a crater will have angled layers.  Think of snow falling in the mountains.

3) On the point of active volcanism, it is posible that Mars has seen it's last eruption.  However, some very good studies have pegged the ages of lava flows in the tharis and elisium region at less than a million years old.  This means that the last flows occured in the last 0.025 percent of the planets age.  It is highly unlikely that we would get there and miss the volcanic age of Mars by just a tad.  It is more likely that there is still molten magma in the mantle and that future reruptions will occure.

In re your point 1) -- really? I'm not disputing, certainly, I've just never seen compressional stress features when I've looked at all the various images of Gusev and its surrounding region. I would assume the features we're talking about look, at the surface, like low ridges as opposed to graben?

On point 2), yeah, sedimentary rock does form at angles (people *do* need to remember that sedimentary rock forms in all sorts of ways, and water deposition is only one of those ways). I just think that Gusev's features, taken at a gross level, really do suggest that it was a lake at some point in the past, and applying Occam's Razor, it's simply more likely that layered sediments were water-deposited. But, of course, we'll be able to tell a lot better when we've gotten a really good look at the rocks in this outcrop.

And on point 3), I'm also of the opinion that we haven't seen the last of Martian volcanism. After all, we really don't have a complete understanding of the process of core/mantle cooling in rocky planets. And as for Marsquakes, we also have to remember that the Tharsis bulge may yet be in the active process of deformation as it settles, which can drive quake activity. And billions of tons of dry ice get deposited on, and removed from, alternate poles every Martian year, which has to have *some* impact on the overall flexing of the Martian crust.

About the only thing I would think is pretty certain about Martian crust/mantle interactions is that there seems to be no sign, whatsoever, that active plate tectonics are happening on the planet currently. Other than that, I think the door is wide open for most other processes.

-the other Doug

[Guest_Edward Schmitz_*]

In re your point 1) -- really?  I'm not disputing, certainly, I've just never seen compressional stress features when I've looked at all the various images of Gusev and its surrounding region.  I would assume the features we're talking about look, at the surface, like low ridges as opposed to graben?

-the other Doug

Here is a great example of a thrust fault in Gusev. It seems quite posible that the hills are the result of thrust faulting and later embayment by lava flows. The hills have more than a passing resemblance to the thrust fault hills in the other image. That would be consistant with layers being sedimentary and the angle that they now sit at. But they could easily be ash fall on the hill after it was thrust / embayed. The plains are volcanic (we know that) so why not ash fall as well.

Lots of senarios are open. That's what makes this exporation. It is really exciting. So far, the hills have been quite difficult to interpret. I wouldn't be surprised if this doesn't clear up the mistery.

Thrust Fault
http://themis-data.asu.edu/img/V06798003.html

Colubia Hills
http://themis-data.asu.edu/img/V00881003.html

[Guest_Edward Schmitz_*]

I was just noticing in this image of the Columbia Hills (http://themis-data.asu.edu/img/V00881003.html) that the fault at the top of the image seems to be embayed by the same flow as the hills. It almost looks like the hills are an extension of that fault. Perhaps if they had landed 15 kilometers to the north, they would have found the sediments they were looking for.

[Bill Harris]

Here is a great example of a thrust fault in Gusev.

Interesting food for thought. I've thought of "wrinkle ridges" like that as simply basalt flow fronts and the Columbia Hills as an eroded, flooded crater.

We need SeismoBots over there...

--Bill

[djellison]

We need netlander

Doug

[dvandorn]

In re your point 1) -- really?  I'm not disputing, certainly, I've just never seen compressional stress features when I've looked at all the various images of Gusev and its surrounding region.  I would assume the features we're talking about look, at the surface, like low ridges as opposed to graben?

-the other Doug

Here is a great example of a thrust fault in Gusev. It seems quite posible that the hills are the result of thrust faulting and later embayment by lava flows. The hills have more than a passing resemblance to the thrust fault hills in the other image. That would be consistant with layers being sedimentary and the angle that they now sit at. But they could easily be ash fall on the hill after it was thrust / embayed. The plains are volcanic (we know that) so why not ash fall as well.

Lots of senarios are open. That's what makes this exporation. It is really exciting. So far, the hills have been quite difficult to interpret. I wouldn't be surprised if this doesn't clear up the mistery.

Thrust Fault
http://themis-data.asu.edu/img/V06798003.html

Colubia Hills
http://themis-data.asu.edu/img/V00881003.html

Interesting... it always looked to me like these thrust faults were very similar to the wrinkle ridges on the lunar maria, and that, as such, they were a result of the (relatively) heavy lavas compressing under their own weight. In other words, that they were an artifact of the lava fill and not pre-existing of them.

But yes, I do see the orientation of the north-south trending faults, and in fact the one main fault line does extend beyond Gusev into the non-lava-filled ancient cratered terrain to the north.

I stand corrected... *smile*...

-the other Doug

[dvandorn]

We need netlander

Doug

I'll second that.

-the other Doug

[TheChemist]

Exploratorium is still dead, but at last JPL updated its site, and the first pancams from Sol465 have been uploaded.

http://marsrovers.jpl.nasa.gov/gallery/all/spirit_p465.html

[arccos]

Uuuh. This looks pretty Opportunity-like to me!

[dvandorn]

It looks like fine-grained sedimentary rock that's not *quite* as finely layered as the evaporite at Meridiani. It doesn't seem to show much in the way of concretions, concretion pits, or vugs (though you'd probably have to RAT some of the rock to really see if it had vugs).

If it's ashfall- or aeolioan-deposition sandstone, the layers look pretty thin... but not so thin as to completely preclude either.

However -- and this is a big however -- is it just me, or is there cross-bedding present in a lot of the layering in that rock? I see a lot of the layers forming into little crescents, just like in the rocks at Meridiani.

If that *is* cross-bedding, I'd bet that these are liquid-deposition sedimentary rocks.

In any event, the minerology investigations are going to be *very* interesting on this one... *grin*...

-the other Doug

[tty]

Cross-bedding is actually more typical of aeolian deposits than waterlaid ones, though they do occur in the latter if there were currents along the bottom.

[Tman]

It could be a deposit by a single event. And what we see now is only weathered by wind that forms such layer-like appearance. Anyway the composition seems to be aggregated.

[glennwsmith]

Gentlemen,

It seems that interest in the stratigraphy of the Larry's Lookout/Methusaleh area is heating up.

I refer to an article just posted at www.universetoday.com (excerpt included):

HAS SPIRIT FOUND BEDROCK IN COLUMBIA HILLS?

http://www.universetoday.com/am/publish/sp...ia.html?2642005

"Crumpler says they are seeing evidence of finely bedded materials in the rocks, with very fine laminations that signify bedded, sediment-like materials. 'This all indicates that we’re not just looking at volcanic rocks or old broken up rocks, but there is some sort of organized layering,' he said. 'We’re going to do a full scale campaign to try to understand all of these things.' Although the MER science team still has a plethora of unanswered questions about this area of the Columbia Hills, from the evidence so far, water is likely to be at least part of the final equation."

I am not sure of the protocol here, but I am going to post this same item to the "Spirit/Blueberries" topic.

Glenn

[Guest_Edward Schmitz_*]

It could be a deposit by a single event. And what we see now is only weathered by wind that forms such layer-like appearance. Anyway the composition seems to be aggregated.

Without actual layers, there is no way that the wind can etch pseudo layers. There has to be hardness differences to allow uneven erosion to occur. If there are hardness differences that are aligned along parallel planes, then you have layers by definition.

[john_s]

Without actual layers, there is no way that the wind can etch pseudo layers.  There has to be hardness differences to allow uneven erosion to occur.  If there are hardness differences that are aligned along parallel planes, then you have layers by definition.

True, except that if you have a rock with random variations in hardness, e.g. a volcanic ash containing various-sized chunks of broken-up rock, and you then erode it by wind, you'll get aligned tails of protected soft material extending downwind behind the hard chunks, giving the impression of layering. I think this is at least part of what's happening at Methuselah, as in this area. There are probably real layers too, but I think the wind erosion helps make the layers look finer-scale than they really are, particularly as the wind happens to be roughly parallel to the bedding.