Continuing into Glenelg, Leaving Rocknest behind, sols 102-166 (Nov 18 2012-Jan 23, 2013) Options

[nprev]

To steal a phrase from Stu & the UK: Absolutely gob-smacking!!!

Geological question: Given that at least a portion of this area is thought to be an alluvial fan, how much small-scale compositional diversity would be expected?

I would think that the only significant sorting would be by weight, but there seem to be contrasting deposits of material (to say nothing of large rocks) randomly distributed.

Does this provide any indication as to the length of time that the purported hydrological drainage was active, or provide any other parameters/constraints? (The extremes are one-time flood or long-term flowing water).

[fredk]

On the above pans from Ant & Cargo, we can see whitish stones on the right hand side.

Maybe we're seeing specular reflection of sunlight, like we saw in this image?

Thanks for the superb mosaics, guys! This view is really something - I like how the increased tau gives us a sense of the immense distances in a view like this one:
http://mars.jpl.nasa.gov/msl-raw-images/ms...8000E1_DXXX.jpg

[ngunn]

Geological question: Given that at least a portion of this area is thought to be an alluvial fan, how much small-scale compositional diversity would be expected?

With luck we'll get the real answers soon when these rocks 'speak' for themselves. This may be our last chance to indulge in some wild Glenelg guesswork from the back seat. So for those who enjoy such things here goes . .

The well organised horizontal strata exposed around the Glenelg basin don't look to me like fan deposits, either slow or fast, but more like lacustrine sediments probably much more ancient than the fan. The fan-forming process whether slow, fast (or a complicated combination of the two involving both ice and liquid water) seems to have resulted in net removal of regolith here. Greater exposure of older, well consolidated bedrock is consistent with the observed high thermal inertia. Where's all the regolith gone? Well, there's what looks like a substantial pile of it over at the far end of the basin (leftmost third or so of the latest panoramas).

[stewjack]

These blue/grey rocks toward the top of the image look like they were formed by something sticky and viscous - or maybe it's just a weird and strange erosion pattern.

I am not a geologist but my working assumption is that these are not simply an example of erosion causing weird shapes, but rocks that erode weirdly due, at least partially, to something varied about their physical nature. I seem to remember a few examples of this in some MER images.

Warning: This is all from memory.
1. Not long after Opportunity left Eagle crater, I remember an image of a rock with "blueberry" tipped "fingers." It was just a common Meridiani sedimentary rock with "blueberries," that had been ejected from a recent small crater. One solution mentioned was that wind blowing primarily from one direction eroded much of the rock that was not shielded by the more resistant "blueberries" - leaving behind "fingers."

2, As Spirit started up Husband hill there were images of what could be described as hollowed-out rocks. This was explainable as a soft rock that had a very hard crust form on it's exterior, and allowing the interior rock to erode away.

3. In the interior basin around Home Plate Spirit imaged some rocks that looked, a little, like loosely woven metallic scrub pads!!! Can you provide a possible explaination if I give you a hint? There appeared to be a number Pumice stones lying nearby on the surface.

About these recent rocks - Not a Clue!

[EdTruthan]

Wowsers! Another complete HALF of the MC100 Sol107 mosaic just arrived, showing splendid detail of the entire foreground. One frame (0107MR0682055000E1_DXXX) is still AWOL but here's the rest so far...

Click thumb for Half Resolution version (8333x4680px 11MB):


Full Resolution version (16666x9360px 32MB) is here: Sol107-MC100-East-Looking-Mosaic-16666x9360px.zip.

The blocks at center right seem to be the same ubiquitously distributed material that Phil's Sea Lions are made of. Almost every instance of this formation as seen in previous panoramas seems to readily split into blocks. To my eye this formation seems to overlay and form outcrops across much of the area.

[Phil Stooke]

My take on the geology - the alluvial fan north of the ellipse is just the last of many episodic alluvial and slump deposits that have covered the crater floor. I would think of the unconsolidated gravelly sediments we see in the cratered unit and the hilly unit as being earlier alluvial deposits, and the layered and fractured material as an older unit, either lacustrine as already suggested or maybe layers of cemented volcanic ash and/or aeolian deposits.

Phil

[ngunn]

Phil that's exactly the overall picture I had in mind. To explain the basin I would only add one thing to your 'episodic alluvial and slump deposits'; one of two things in fact.
Either A: episodic scouring events, interleaved with and overlapped by the fan deposits
or B: emplacement of a special type of deposit more than usually susceptible to subsequent removal by sublimation and/or wind erosion.

Of course it could be C: something I haven't thought of.

About the layered rocks in the basin: I agree, not necessarily lacustrine but flat lying, well consolidated and almost certainly old.

[Eyesonmars]

On the way to Glenelg we passed a couple of spots where rounded pebbles were eroding out of a formation. Such as here as noted by xflare

Talking of pebbles - Sol 52

http://mars.jpl.nasa.gov/msl-raw-images/ms...0000E1_DXXX.jpg

I have searched the foreground and midground images since then, including the most recent, and am a little surprised not to see any more "pebbles". ( at least not to my eye). Has anyone else spotted any?
I suppose this is consistant with Phil's interpretation.
Any comments?

[xflare]

My take on the geology - the alluvial fan north of the ellipse is just the last of many episodic alluvial and slump deposits that have covered the crater floor. I would think of the unconsolidated gravelly sediments we see in the cratered unit and the hilly unit as being earlier alluvial deposits, and the layered and fractured material as an older unit, either lacustrine as already suggested or maybe layers of cemented volcanic ash and/or aeolian deposits.

Phil

A lot of these rocks look a bit like Pumice.

http://mars.jpl.nasa.gov/msl-raw-images/ms...8000E1_DXXX.jpg

[Ant103]

Mastcam100 panoramic updated (see my previous post).

And it's only 56° FOV

[Cargo Cult]

I really should have become a geologist. There's so much detail...

Nice work, all!



(I've posted my final version here - two giant-sized versions to choose from. 'Huge', and 'About the same mass as Mars itself'.)

[SFJCody]

I'm sort of reminded of the textures that Spirit saw at Home Plate.

[Don1]

I really like the idea of these rocks being layers of alluvial fan and layers of lakebed sediments. If the atmospheric pressure varied, then when it was low, water would evaporate quickly and alluvial fan would be formed. When it was high, then water would hang around and form a lake.

I think that Glenelg may be just what it looks like. A dried up lake bed with a fairly obvious shoreline. We know that there is a river system feeding into this area so that seems like a straight forward interpretation.

Looking at the pictures of the porous, sponge like rocks I remembered I'd seen something like that before in a book on peak oil. It looks like reservoir rock, which is the sponge that holds the oil in an oil field. Good reservoir rock is often made of carbonates. Some of the rocks look to be harder and more cohesive than others, so that started me thinking about the possibilities of dolomite for the slab like stuff. And of course the conglomerate looked like earth concrete, which is just aggregate held together by calcium carbonate. The bottom line is that I like the idea of carbonates for a lot of the rocks here at Glenelg.

[brellis]

Thinking of Death Valley, one might wonder if there was a long period of flash floods in an otherwise dry area?

[iMPREPREX]

I was a little impatient in waiting for image #55 from the Sol 107 MastCam 100 pano, so I blew up the thumbnail and got it in. And I Gigapaned it if anyone is interested.

http://gigapan.com/gigapans/118975

I also got rid of most of those hot pixels in the sky.

Very cool stuff. But I'm sure you all know that!

Small preview:

Attached thumbnail(s)