Paolo's Plunge, First dip into Victoria Options

[CosmicRocker]

I see festoons in the "work volume." They are most evident in the top pancam. I wonder if Opportunity will find itself pretty much at the same stratigraphic level as at Endurance and Erebus.

[dburt]

I see festoons in the "work volume." They are most evident in the top pancam. I wonder if Opportunity will find itself pretty much at the same stratigraphic level as at Endurance and Erebus.

I politely disagree, so far. Looking at that photo (from post 116) I see mainly bedding planes intersecting irregular topography, as viewed from above. Look at the right branch of the Y-shaped notch about 40% down from the top, 60% to the right, for example, or the right side of the large notch cutting the top left. Cross-bedding and minor bedding irregularities (waviness) make it tricky to see what's going on, I agree, but so far no festoon- or trough-type cross beds are evident, to me at least.

-- HDP Don

[CosmicRocker]

Doctor Burt: I agree that bedding planes intersecting irregular erosional surfaces can often display deceptive appearances. Hopefully I am not making such a mistake. The features I was referring to are not as convincing as the Erebus nested festoons at the rock called "Overgaard," but they look like troughs to me. I wasn't certain from your described locations which features you were referring to. In my attached image I have yellow arrows pointing to the troughs I think you won't have to squint too hard to see.

From the PDT site, I see that this set of images was called "workvolume_column." It's apparently the beginning of the measured stratigraphic column.

[jamescanvin]

From the PDT site, I see that this set of images was called "workvolume_column." It's apparently the beginning of the measured stratigraphic column.

My take on it was that 'column' refered to the two frames being one above each other, i.e in one column.

[dburt]

Doctor Burt: I agree that bedding planes intersecting irregular erosional surfaces can often display deceptive appearances. Hopefully I am not making such a mistake. The features I was referring to are not as convincing as the Erebus nested festoons at the rock called "Overgaard," but they look like troughs to me. I wasn't certain from your described locations which features you were referring to. In my attached image I have yellow arrows pointing to the troughs I think you won't have to squint too hard to see.

CR - Inasmuch as Overgaard was Knauth's type example of "normal cross-beds and convex/concave rounded surfaces viewed from above mistaken for festoons" (what a beginning geological mapper might call "sub-horizontal contacts V-ing upstream"), we'll probably have to agree to disagree about that example being "convincing" (I was further convinced that Knauth was right after looking at Overgaard in 3D via a stereo imaging set-up called "GEOWALL"). Clearly, all of the "smile-shaped features" in the lower part of the Overgaard rock photo, referred to in the NASA caption that you linked to, are pointing up cracks in the rock (are V-ing upstream, in other words - and sorry if you lack the geological mapping background to understand my jargon) and thus the "smiles" are optical illusions created by the downward-pointing angle of the Pancam. In any case, thanks for posting the attachment with arrows. Your arrows appear to to point to what I referred to in my original post as "bedding irregularities" - waviness without cross-bedding (i.e., no cross-cutting relations as in real "festoons"). Again, feel free to disagree - the images aren't all that great.

I guess the important point is that real trough-shaped cross-beds ("festoons"), as well as wavy bedding surfaces (what your arrows appear to indicate), can occur in either water-flow or surge-flow rocks, so we probably need to find another, less ambiguous, method of testing whether or not liquid water ever sheet-flowed across the salty horizontal surface of Meridiani.

-- HDP Don

[CosmicRocker]

James: You may very well be correct about the image set name, but from my point of view I am expecting them to also begin characterizing the local geologic section, or column.

Doctor Burt: As you suggest, I think we should agree to disagree on this, mainly because neither of us wants to rekindle the great debate. If you'd like, we can continue via email. I am actually a serious fan of the impact surge hypothesis as a theoretical concept for early Martian processes. I am just not convinced it fully explains Meridiani observations.

Inasmuch as the V-ing upstream concept is normally introduced in Geol. 101, it is a well embedded concept for me. I've been a geologist for about 35 years. I've studied Overgaard in 3D anaglyphs, and although its surface does have topographic expression, I think one would be hard-pressed to explain Overgaard's train of nested troughs simply as subhorizontal contacts V-ing upstream. I'll attach an anaglyph of Overgaard for others who may want to look at it in 3D.

Admitedly, the recent "work volume" images really aren't the greatest, and the features I am pointing to are not well defined. But I really think there is more going on there than wavy or irregular bedding. I think I see cross-cutting relationships. Let's just see what we see as the exploration unfolds. Some MIs would help. Supposedly the plan is to travel some tens of meters along this contact. We should get a better feel for what the depositional environment was as we extend our explorations laterally.


The thing that really freaks me out when looking at these rocks is the realization that I have never seen such mildly altered sedimentary rocks that are so old, let alone from another planet. We all really do need to keep an eye on our blinders.

[jamescanvin]

Oppy moved again tosol (1305). Here is what is in front of us at the new site.



The right side of this image is the same patch of ground as at the top-left of my sol 1302 image, near where CR was pointing to interesting stuff.

James

[Tesheiner]

It looks like this will be the first place to be "sniffed" with the IDD.

[CosmicRocker]

In the previous set of pancams it appeared that we might be seeing some patchy occurances of mini-blueberries. These latest pancams show them more convincingly. If so, this would be the top of the hypothetical, blueberry bathtub ring that was expected. The last time we saw this potential geochemical contact was when the berries became very small and eventually disappeared, near or shortly after Erebus, as Opportunity was climbing the section toward "Hell of a View."

[jvandriel]

The panoramic view taken on Sol 1302

with the R0 Navcam.

jvandriel

[jvandriel]

Another view taken on Sol 1305

with the R0 Navcam.

jvandriel

[climber]

Must be a lot easier to Rat than the "Pot of Gold" back at the base of Columbia Hills

[dburt]

... I think one would be hard-pressed to explain Overgaard's train of nested troughs simply as subhorizontal contacts V-ing upstream. I'll attach an anaglyph of Overgaard for others who may want to look at it in 3D.
...The thing that really freaks me out when looking at these rocks is the realization that I have never seen such mildly altered sedimentary rocks that are so old, let alone from another planet. We all really do need to keep an eye on our blinders.

Tom - Thanks for the nice anaglyph of Overgaard. When I look at it, I clearly see the topographic irregularities (notches) I referred to in the lower part of the rock - yielding the "smile-shaped features" referred to in the original NASA caption, but only because Pancam views things from 5 feet up (i.e., they are a topographic artifact of the angle of view). Perhaps we agree there. The "nested troughs" area in the upper right part of the rock is a lot trickier because (1) it contains an actual cross-bed (a normal one) rather than simple horizontal planar beds and (2) the edges of some beds are broken off, making bed continuity difficult to follow across notches. Still, the large notch at the far upper right, and the bedding contouring into and around it, is clearly visible, and the other beds likewise can be followed with considerable mental effort. So we continue to agree to disagree.

Regarding your closing comment, "mildly altered" is probably the key phase, especially considering how salty and old these rocks are. To me that very freshness indicates that they have never seen liquid water for any extended period of time, if at all, in contrast to the extant hypothesis of multiple episodes of acid groundwater immersion and even surficial water flow. To my predjudiced eye they look remarkably like some fresh volcanic surge deposits do on Earth, including the very "toothy" or "ashy-looking" edges of the exposed beds (as seen in the excellent panorama of James Canvin's post #127). They sure don't look like any variety of terrestrial sandstone or evaporite I've ever seen (and I think we can agree on that).

Here for your amusement are some actual current ripples in fluvial sand from the Grand Canyon (2003 rafting trip).

Probably not directly comparable, because they seem to have formed in an eddy next to the cliff, but certainly not artifacts of the viewing angle (which was from the side, because unlike the Pancam, I can bend down ). BTW, I took that photo in May, 2003, before I had ever even heard of "festoons". I rafted down the Canyon again last July (Knauth organizes trips every year), and looked for similar flow features along the shoreline, but river levels were just too high (twice the normal discharge owing to lots of flash flooding below the dam at Lake Powell). Made for exciting rapids though!

-- HDP Don

[climber]

Stu,

It appears that Oppy sent a postcard for you :
http://qt.exploratorium.edu/mars/opportuni...JZP2363L5M1.JPG

[climber]

Nasa release : http://www.jpl.nasa.gov/news/news.cfm?release=2007-109
So Oppy is tilted 25° and has experienced "only" 10% slipage.
Reading back "Roving Mars" they says that, before entering Endurance, they were confortable up to a little more than 30°. Does somebody know if they ever tried more than that and how far they think they can go with the angle of the slope?
Something else that I don't know is : how much they've tried with a position of the rover perpendicular to the slope which seams to me how Oppy's positioned at this time.