To the Cape! (part 2), For real this time! Options

[Stu]

Definitely one of my favourite post-entry views...

[jamescanvin]

Today's offering.



James

[fredk]

Another sol, another spectacular set of pancams - here's one of my favourite views, in 3D:

[peter59]

My favourite views:

http://qt.exploratorium.edu/mars/opportuni...B0P2266L2M1.JPG
http://qt.exploratorium.edu/mars/opportuni...B0P2266R2M1.JPG

Looks like frames from old science fiction movie (Star Trek).

[jamescanvin]

Just one image short of completing the sol 1570/1 bit now. It's becoming an amazing view!

Still this is only half of the total pan taken so far if you include those from sols 1572/3 that are still on the rover.



James

[dilo]

Superb mosaic, James, even with dirt and unfilled rectangle...

Edit: Here I tried to reduce effects of dirt and glare in the half res version:

Attached thumbnail(s)

 

[algorimancer]

http://qt.exploratorium.edu/mars/opportuni...B0P2266R2M1.JPG

The discontinuity between the thick central unit and the lower unit is interesting. Those lower layers seem to be at a significantly different orientation than in the upper.

[Juramike]

The discontinuity between the thick central unit and the lower unit is interesting. Those lower layers seem to be at a significantly different orientation than in the upper.

Very interesting observation! Anyone got a possible explanation?

[nprev]

Mmm...differential weathering? I've seen apparent discontinuities like this in the past on Earth; maybe the prevailing wind path around the two vertically separated regions is just different enough to cause the disparity. (I'm assuming that the whole formation is old, old, old...)

[Juramike]

I'm wondering if we are seeing deposition, tilting of strata, erosion of upper section of tilted strata, then redeposition of upper layers of strata.

That would imply the lower layers are old, AND had an interesting history prior to the deposition of the upper strata.

-Mike

[Phil Stooke]

No - much more likely to be just cross-bedding - i.e. cemented dune sandstones.

Phil

[Juramike]

No - much more likely to be just cross-bedding - i.e. cemented dune sandstones.

Phil

I thought cross bedding had little "wedgie" shapes?

[Bill Harris]

At first glance it looks like truncated cross-beds or an unconformity, which is consistent with the aeolian dune-playa setting. We've seen this at several places in Endurance and Victoria. But if you look closely at the lower beds, you can see a fabric of essentially horizontal beds, morte or less parallel to the upper beds. So I'm thinking that one or the other orientation of the lower bed may be an artifact of aeolian erosion. We need an up-close look. We'll also be able to tell more once Oppy starts taking images out of the flat (shadowed) light.

Of more interest is the open fracture in the upper beds. Is it a solution cavity, or what?

Another example of the x-bedding is in 1P259578369EFF8900P2570L6M1.

--Bill

[Shaka]

Ultimately, these questions all hearken back to the formation of the cape-and-bay crater rim. Why are the bays eroded down the strata at a 20 - 30 degree angle, while the capes are cut down more or less vertically. I can't believe that this is due to a more resistant sediment formation in the capes, neatly interspersed with less resistant strata in the bays. Until somebody lays out a plausible hypothesis for the formation of Victoria's sinuous rim, I don't think this little microcosmic curiosity at the base of one cape can be understood.

[ElkGroveDan]

Why are the bays eroded down the strata at a 20 - 30 degree angle, while the capes are cut down more or less vertically.

Primarily: Capes have greater exposure to the prominent erosion forces - prevailing winds. As a result they are in a less stable vertical condition. The bays are set back and more sheltered from the prevailing winds so they are older and have had time to slump. As an example go dig some holes in your yard, one each month. After a year see what the sides of the holes are like. The newest holes will have the steepest sides, the older holes will have slumped in on themselves.

Secondarily: The capes by virtue of their recessed shape are traps for the heavier particles that the winds are unable to lift from the crater.

This back and forth of capes and bays likely occurs in a manner analogous to a meandering stream. Over the eons the shapes will migrate back and forth as bays fill up and capes are eroded away...and the crater grows ever larger (assuming some external condition doesn't cause it to become filled in by migrating sand dunes or such.)