These images show the unconformable and in some places rather complex relationship between the upper and lower beds. I look forward to panorama of this series.

I was hoping that Oppy would walk this outcrop but evidently the operators feel it may be safer to not traverse the trough.

Oppy has the IDD deployed; note that the flat rock to the left of te tool cluster has been displaced.

--Bill

http://qt.exploratorium.edu/mars/opportuni...3IP1152L0M1.JPG

I love how adaptable the rover controllers are with the rovers' various ailments. Programming problems, low power in winter, sticky wheels, a broken switch, a fussy spectrometer, and now a broken motor winding. All that, and the rovers just keep going.
Fast forward to sol 1500, when Opportunity is just dragging itself along with its single working wheel and one working instrument. "Keep goin' little feller!"

Well folks. It would appear I somehow managed to confuse the multi-quoter. Sorry about that.


Well a regional dip would be consistent with a prior SS comment that the Oppster has been climbing stratigraphically as we've gone south. At this location I have seen quite a bit of variability in the dips, so I am suspecting local, perhaps on a regional trend. The dips I highlighted may simply be dunes/sandsheets filling paleo-depressions, or maybe a channel filling.



If I haven't already said it, welcome to the forum, neb. I've enjoyed your comments, but I don't know where to look to see the things your are describing. It would sure help some of us if you'd post an annotated image with some of your comments. I'm not sure I see the upper planar unit you mention, nor continuity. There seems to be a fair amount of rubble below the eroded crater rim which Opportunity now faces, and I don't know where you see subsidence.


Ahh, they're taking the high road, since the entrance ramp is nearby. That should be interesting. Like Bill, I was assuming they'd at least zip down the vertical exposure to collect better data from some other areas. Hmm, all I can see in the direction of the ramp, besides easy access to the top, are some possible...nope, I promised myself I wouldn't use the "f" word... It should be an interesting trip across the top though, as long as they take a few photos along the way.

That's my bet.
We should know the answer after tosol evening downlink; there is driving activity planned for sol 747.

The structure here tends to be confusing! From the MOLA data we seem to be climbing topographically, which means we have to be climbing stratigraphically if the beds are flat-lying. My "day job" is working with the Pennsylvanian Pottsville Fm in Alabama, which is a coal-bearing deltaic sequence. It is esssentially flat-lying with a gentle regional dip, but local sedimentary structures can make the local dip anything it wants to be. However, if the underlying "Payson Formation" can be correlated with the "Endurance Fm" this will help nail down the the structure and history of this area. This is our current ace-up-the-sleeve and something we should study as close as possible. I wanted Oppy to stop at the first exposure of the dark bedrock that we saw at "The Four Lane" on the North Erebus Rim but the priority then was to get on with the detour around that monster dune complex. Although forward progress is essential we should not pass up an opportunity to collect data. Although Victoria is an important site, we can't be sure it will be reached and we need to collect what we can when we can.

This current location is a bit troublesome to me: the trough reminds me of underground mine subsidence. It might just be a byproduct of desert winds and sand, but spot is spooky to me.

--Bill

I've just brewed this Flash-based application to calculate Martian horizons for those who are interested.

Andy

Nice tool! Thanks Andy.

Very slick.

Bill:

Yes - my thoughts on this spot are less to do with the detailed stratigraphy, which is of course important, than why the rock that isn't there has decided not to be. There's not much in the way of debris below the outcrop (compare it to the talus slope around HP) which suggests that we're not looking at simply some mass-wasting process. I'm beginning to wonder whether there is a localised faulting process at work, perhaps following the lines of weakness created by (very old) frost polygons.

I hope we get a good look at some of the other outcrops!

Bob Shaw

I think the evaporite rocks and cemented aeolian sandstones simply crumble and blow away after millions of years of weathering, which explains the lack of ejecta blocks on all but the freshest craters. Payson is not the pristine rim of a crater, it's the remnant of an old crater after a billion years or more of weathering, scarp retreat etc. The central bowl of Erebus might be closer to the original crater size.

Phil

Just a thought - the fact that we already have drive direction imaging showing a route up onto the top of Payson suggests that they're not going to hang around here and investigate the front of the outcrop

Doug

Scarp retreat is exactly what I think we're seeing at Mogollon and Payson. It's my belief that the original Erebus was only about twice as large as Endurance, and that it struck into the western side of the bowl of an even older, larger crater (Terra Nova) that had already been mostly filled with dunes, evaporite and sediments. (If Terra Nova had been an unfilled crater at the time of the Erebus impact, I would imagine that you wouldn't see such a pronounced east rim on Erebus, which lies roughly on top of what would have been the deepest portion of Terra Nova.)

Because the evaporite and weakly cemented sandstones are rather friable, scarp retreat ensued rather quickly, and continued even as Erebus' own bowl was filled with sand, sediments and evaporite. It probably continues slowly to this day -- Mogollon and Payson might be moving away from the center of Erebus at the rate of a few centimeters every hundred thousand years or so...

Remember, too, that most evaporites *shrink* a tiny bit as they completely dry out (think of the cracking you see in dried-out lakebeds). This process is complicated if the last stages of dessication involve ice as opposed to liquid water. There would be a tendency for an evaporite "cap" on the crater fill to shrink away from the crater rim a bit, encouraging a final subsidence along the rim line.

I think all of those factors are at work here...

-the other Doug

We should know the answer today at 20:35 GMT (assuming the exploratorium is still working at that time).

From me, too: Goodbye Olympia

Last view of this outcrop shows 3 out of the 4 named bedrock regions. Roosevelt is out of sight.

3 targeted outcrops (447 KB):