Er... ...perhaps we're thinking backwards.

The cliffs may not be the key - perhaps it's the formation of the bays which are strange...


Bob Shaw

Thank you very much, Glenn. Ashamed to say that I haven't had the time to chase this down as promised...been buried under homework & reserve military duty to boot. I'll give it a look.

I'm thinking there were bays in the original vertical cliffs due to an irregular collapse pattern. If you start with bayed cliffs it's easy to see the bays acting as wind tunnels where the cliff edges would be systematically planed off at an angle until the crater fill piled up level with the erosion surface, yielding a smooth bay profile while leaving the top part of the cliffs exposed on the promontories.

Regarding the escalloped bays, whats to prevent the following?

The plains were saturated due to the then-current water table level (or permafrost) at the time of impact, so any crater rim irregularity would be amplified by water erosion as the seepage carried the soft soils down into it, since the amount of seepage would be proportional to the surface area progressively exposed, bays should tend to elongate while capes should stay the same. Since the soils were likely to be much looser back at the time of impact, the bay material was more easily carried downward to fill and flatten the bowl floor, which perhaps didnt have time to develop much of a bathtub ring shoreline with the water that seeped into it before it sublimed away, unless its buried.

This seems simpler a scenario to me than the underground river drainage network scenario. Although Endurance should have similar bays in miniature unless it was created in a period when the soils were signifficantly more dried out, which may not necessarily mean its newer. We'd also expect analogs of this type of process on Earth, any geologists care to set an amateur straight?

The capes have not 'stayed the same' as they were immediately after impact. There are no raised or everted strata even on the capes so they too have expanded outward by collapse, erosion or both (either quickly or slowly), though not as far as the bays.

There is no need for the volatile rich material to have been present right up to the surface at the time of impact. If there was a dry layer on top not fully penetrated by the Endurance impact then Endurance would not be expected to the exhibit the scalloped rim and pronounced vertical cliffs that might plausibly be associated with mass wastage by sublimation of buried volatiles.

That makes a lot of sense to me. Thanks for your concise and convincing input.

with no "drain" at the bottom of Victoria, whats to have caused the scallops? if there was merely a meter or more depth of water when the impact occurred, allowing just enough water to erode the sides this way if the sediments were loose enough, while filling-up the crater but not enough water flow to 'distort it beyond all recognition' this might also suffice..

or maybe not, wouldnt it just make more sense that the scallops have merely developed along radial fractures created during the original impact, allowing greater erosion in these areas? smoothed over and widened by a long history of sandblasting. although id expect some more lasting surface effects trailing out from the crater along these faults, unless they have been erased by these processes, or maybe they have eroded completely out and werent that extensive to begin with.. Endurance might lack these features simply because it didnt have enough energy to create effective fracture patterns in the particular state the sediments were in at the time (mud or meringue) ?

Ah, but Victoria is the anomalous crater, not Endurance. Whatever it is that produced the capes and bays, it must be pretty unusual. I think that rules out the bedrock and the size of the impact, and surely any putative lakes, ponds or puddles of water (or groundwater) would have been present in lots of other places that Meridiani, if they existed. The impact rate would have been much higher that early on, so there'd be a lot more similar examples.

AFAIK there are other cape-and-bay craters, but they're not common. (Actually does anyone have any data on exactly how common/uncommon such features are? Are the preferentially distributed at all - by latitude, or altitude, or bedrock types..? Ah, the million-dollar questions are really flowing tonight ) I don't remember seeing many others except one or two that were posted here on UMSF, and tuits tell me that if they were very common, the throbbing brains of scientific community would have hatched at least a couple of theories (you need at least two, because otherwise how can you have an argument^w discussion?

There are alternatives to the idea of a drain, of course. If VC were volcanic, water would have been evaporating away from the hot rocks over the magma chamber! Personally I think the chances of that being the explanation are slim to zero; but then I just couldn't see any volcanic features at Home Plate, either, until we saw the bomb.

I wonder if that when craters are much smaller than Vic, the cap+bay erosional forces would tend to erase the crater over similar timescales, and if they are much larger than Vic, the same erosional forces tend to create gullies that are much less substantial in relation to the crater's size.

So you'd have to screen out craters larger and or smaller than Vic to really understand its uniqueness.

I think I previously offered a Mars Bar to the first person to identify a blueberry in rock below the ejecta, but I could be wrong. I might have offered that to the first person to identify a festoon. So allow me to suggest that one of the current challenges is to find the "bathtub ring." There is another Mars Bar for that person. I'm not convinced I see it yet, but this raw imagery is hard to use.

While I was thinking about trying to spot blueberries in the bedrock of the capes I remembered the psychedelic false color image of Snout in Eagle crater. It was released early in the mission, and was created with four of the right filters. I never forgot that the file name essentially revealed the ratios used in that composite, so I set out to try the same technique with some of the recent sets of right filter images. Those sets seem to have become more common recently.

The nifty thing about this is the way it distinguishes certain mineralogies, making them appear in very contrasting colors. My first attempts to reproduce such images from the raws were mediocre, but suggestive, since I am kind of dumb about image processing techniques. So I asked slinted, an imagery wizard, for help. As I expected, he said (paraphrased), "Oh, did you mean to do this?" He produced a sweet little image from the raw ratios that was quite similar to that from JPL.

Calibrated luminosities would be best to use for these things, but it appears that the raw rights aren't too bad for qualitative work. This seems to be a useful tool, though the pancam resolution seems to be on the bleeding edge when it comes to spying berries in the cape bedrock.

Attached is an image for comparison of the released left filter color from JPL, their their right filter false color composite, and slinted's version using the raws. Now that I have been mentored, this is relatively easy to do in Photoshop and other software. Click to view attachment

Ok, people, I'm going down with the ship in this thread. The lifeboats are for women and children first, followed by the weak of heart, and then by whomever is quick enough to grab a seat.

I still think the false color images built from the raw right filter ratios are valuable tools in the search for the bathtub ring, otherwise known as the first appearance of these hematite concretions within bedrock that existed prior to Victoria Crater. If I understand it correctly, that place in the stratigraphic column will signify a place where one of this region's water tables existed long ago.

I didn't want to go out on a limb with this, but I'm guessing it is a few meters down. I'm prepared to do anything to save this ship. I expected to at least hear from someone complaining that "you can't do that with raw imagery."

OK Tom,

Do you, or anyone else, know how much of Victoria has been shot with the right filters needed to spot the bathtub ring? A few shots across one of the bays, with the right filters, should tell us if we can spot blueberrys at a distance. If that works, go for a panorama of the far side.

I can hardly wait to see how it turns out.

Steve

Thanks for saving the ship, Steve. It was looking pretty grim there for a while.

We don't have all of the required filters for such a panorama because the concretions are only resolvable in relatively close shots. Thanks to slinted's scripting skills, I have been scanning through all of the available images made with R1, R2, R5, and R7, and then comparing them to what I can see in the left filters. The berries are very evident when they are close enough to emerge from the background noise. Most of these filter sets are targeted subframes that also have a set of visual color filters from the left camera.

So far, I am not certain any of them are really displaying concretions embedded in rock that has not moved very far from it's original location as a result of the impact. There are a lot of them in the closer ejecta blocks. So far, the best guess I have for the ring is from this set from sol 1070 of blocks that seem to have been moved only slightly. The upper parts of the ring are likely to contain fewer berries than the central parts.
Click to view attachment

Don't worry, this thread will be needed, and consulted, for some time yet. I don't often join in because much of the discussion is over my head. My simplistic picture of what's going on is: ejecta over light coloured layer marking the pre-impact surface, and below that essentially horizontal-lying aeolian(?) sediments all the way down as far as we can see. Could you please explain in a non-technical way what, beyond this, you think we are seeing? What hypotheses are you checking out? What can we take as fact from the published interpretations of the regional geology and how much is still open to doubt? That would help me, and perhaps some others, to follow the plot.

BTW there should be lovely close-up views of the cliffs from the top of 'Hoy'

Well cosmicRocker, your theory has a new boost or ridge.

Most cool is the pictue of Victoria and the suggestion that Opportunity go check out the ridge.

Floyd

Let's not start mixing apples and oranges. Floyd, that straight line of rock on the other side is interesting, and something we have commented on many times since it was first observed, but it may have nothing to do with the bathtub ring of hematite concretions that Steve Squyres mentioned not so long ago. It could be evidence that water once flowed along a pre-existing fracture and caused the rock on either side to become more resistant to erosion, but the bathtub ring is different. The two ideas are linked only because ground water makes it easier to explain both.

I am not proposing any new theory. I am only suggesting that a certain combination of right filters already used by the team can create a false color image that makes the hematite concretions very evident.

I am only guessing about what the researchers are thinking. The people actively doing this research seem to be looking for evidence of places where the ancient water table remained in the same place for a long time. They already have some pretty good evidence, as far as I can tell, of an ancient water table at Endurance. If they can find evidence of the same water table, or a different one at Victoria, it would be useful information, or so I am guessing.

The real hope was to find other changes in the rock layers in the deeper parts of this hole that would be evidence for other pieces of the geologic history on this part of Mars. As ngunn noted, we seem to be seeing the same kinds of rocks all the way to the base of the visible outcrops here. So, it seems to me that the best we can do is make the most of this hole in the ground and look for subtle changes in the stack of rocks we have been looking at since this able little explorer set foot on this planet.

Ancient water tables can appear in different ways. One important way to look for them is with blueberries. The hematite concretions cannot form in dry sediment. If we can find a depth at which the blueberries appear as embedded concretions in bedrock, that is very likely a level that was previously saturated with water.

OMG! This is already too long for anyone to read. To summarize, I am just trying to find a way to make it easier to spot the hematite concretions embedded in rock.

Not too long and very helpful, thanks.

I thought we found it near the base of Verde --
Look to the rightmost base of Verde in this image enhancement by Hortonheardawho


The largest size of the image:
http://www.flickr.com/photo_zoom.gne?id=256610074&size=o

I'm pretty sure there's some depositional variations that we haven't seen quite as clearly in the other Capes. I count three separate divisions here, one at the base, one above that, and then the more massive aeolian section we're familiar with. Now, they indeed COULD be all the same unit, particularly the middle unit, but more on that in a minute. The lowest unit, just looks different. I think there's a stratigraphic equivilent on the other side of the crater, at the "F1" wall, or to the left of Soup Dragon. You can click over to that thread to see my original obsession with that. The closer we get to that F1, the more I think that's probably NOT exactly it, but it's just too hard to tell. The last candidate for this same rock type is near the base of the ramp of "G1", but it's just a scrap.

Now, I'm not convinced you're going to find traces of hematite berries in these rocks, but I'm pretty sure that we're not dealing with just another sub-layer of the aeolian section above. Perhaps a transition to the berry bearing rocks below?

Obviously we won't know enough for several months as Oppy rolls into Victoria and gets some better views, but the base of Cape Verde has the most unique rock types than any other Cape we've seen so far. We've seen at least some view of all the capes all the way around, with the exception of the last of these most northern capes and those images will be coming shortly.

The original rock type of the basal unit seen at Verde might be aeolian but I think it has seen some secondary alteration the rock above has not.

The picture you posted really showed how sparse the blueberries are in Victoria. I had naïvely been hoping that there would be enough blueberries in the bathtub ring that -- even if the individual berries couldn't be resolved, there would be enough to shift the color balance of the areas where they were more abundant.

Your comments and images suggest that's not possible. But then we won't really know until you try.

Steve

Here's my idea how the cape-and-bay structure has appeared. The impact that created Victoria created very hot ejecta rays, which fell onto the sedimentary rock and made it harder, in a process similar to making bricks from clay. The rays have been removed by erosion. The strips of hardened rock are still there, but it's impossible to distinguish them from other sedimentary rocks. Those strips slow down erosion of the capes. That's why we have pointy capes and relatively shallow bays.

Floyd : I wish we knew the history of those fractures. Obviously they are of interest to the pros. It would be so interesting to get a closer view through the rover's eyes. Might that encourage them to roam beyond 120 degrees? On Earth, fractures that stand up to erosion are often those that have allowed fluids to flow through them and alter the rock adjacent to the fracture.

Steve: If there are enough berries concentrated in a location, they should appear as you suggest, even if they are too distant to be individually resolved. That's pretty much how concentrations of the loose ones lying on the surface appear, even when individual concretions can't be resolved. I'm happy to see the right filters being used more frequently lately. I don't really understand why they are not shooting the whole place in Rall, though. It would be so sweet to an entire panorama shot with all the right filters.

WindyT: Good point. That section does show signs of secondary alteration. I'm still convinced that those layers are the lower part of the aeolian depositional set that tdemko sketched for us on the first page of this topic. But that section is distinctive in several other ways. There are the textural changes nearby and also the geomorphic differences in the way layers are eroding. It's going to take some work to convince myself, but that part of the section is close to where I was thinking it was. Thanks for reminding me that I need to be looking beyond the mineralogic signatures in IR.

I'm glad to see some life breathed back into this thread! The latest pictures certainly are a nice starting point for additional discussion of the strata exposed in Victoria...we are really starting to see some nice architecture!

I've been a bit scarce here for a few months (lurking, though), but other than the recent press release regarding the alteration around fractures, there hasn't been much new since those first breath-taking views of the first capes visited. I've also been in the middle of a career change (see below) and getting time to write thoughtful posts has been difficult.

I hope we can discuss this more in the coming weeks, but it seems to me that we are now getting some results that pertain directly to the stated main mission of Opportunity in her (partial) circumnavigation of Victoria: to determine the thickness and overall vertical stacking pattern of strata in the exposures in the crater, and to delineate the continuity of strata or facies changes within and between outcrops.

As Tom has mentioned, it seems that the entire section we've seen so far has been characterized by a sedimentary fabric that suggests a depositional origin as large-scale eolian dunes. The large-scale trough cross beds, bed sets, and truncation surfaces suggest that, whatever the original origin of the sediment (reworked evaporite, weathered/altered basalt, etc.), the last thing that moved these particles was wind and they were moving as part of the migration processes of 3D bedforms.

With the data available, I'd suggest that the next areas for interpretion and study could include:

- reconstruction of dune morphology: barchan, parabolic, transverse, longitudinal, etc.; with nice three dimensional exposures like these, this could be possible

- history of landscape aggradation/degradation: the truncation surfaces suggest that the erg/dune field that deposited the Victoria strata was subject to periods of erosion where dunes were planed off and previously deposited strata removed...these could be regional surfaces, associated with changes changes in climate (wind speed, direction, and maybe water table) and sediment supply

Detailed study of eolian strata includes examination at the grain and lamina scale (grain flow, grain fall, and wind-ripple/translatent strata), bed scale (cross bed size, geometry, orientation), and bed set scale (bedding plane and truncation surface geometry). Bed sets in eolian strata are classified in a hierarchy (defined by features called Brookfield surfaces) and the large-scale, regional erosion surfaces I mentioned above are called Stokes surfaces (we constantly remind each other in eolian sedimentology that we stand on the shoulders of giants...). We are likely to be hearing more about these surfaces in the days and weeks ahead because they are becoming increasingly more defined in the images, and they seem to have been a definite post-depositional control on some of the obvious diagenetic features in the strata (as reflected in the colors or textures). If there is interest, I can post some definitions, descriptions, recognition criteria, and key references.

PS: For those interested, I've resigned my position as a professor and have gone back to the oil and gas industry as an exploration geologist. I am keeping my university web pages up, at least for a little while, since the department has graciously allowed me to continue on in an adjunct position. As long as the funds allow, my email and web pages should keep working.
--
Tim

Does this meant that You will be moving Tim? There can't be much scope for oil exploration up there on the Precambrian shield.

That was really interesting, Tim. I had to Google a few of your terms first. I had never heard of Brookfield and Stokes surfaces, but now I think I know what they are. I've seen these surfaces on earth and now Mars, but didn't know they had names.

Regarding your "If there is interest" question, we're all ears if you have the time.

Tim,
There is definitely interest in Hawaii (and I'm sure elsewhere)! We'll need guidelines to help us sort out the wacky environs of Home Plate too.

Although recent oil prices have not completely ruled that out, you are correct. Thanks for reminding me...profile updated!

...all roads lead to Houston for petroleum geologists these days...

...that's almost exactly how I looked when I first saw today's crop of pancams from Oppy...check it out: http://marsrovers.jpl.nasa.gov/gallery/all...nity_p1091.html

Notice this image in particular (the background, near the top). I'm lost here; this looks like a ridge, but I'm sure that it's another bay. Why does it look higher, and also check out the relatively large rocks sitting nearby?

Got a new swear jar...<clink!!!!>

As somebody said, the largest concentration of geologists in the world lives in a place where there isn't a decent rock within a hundred miles.

That "ridge" is Guam, aka the "dock" - see the route map. Those rocks are only cms across, notice Oppy's wheel tracks at upper left for scale.

Gotcha now...thanks! I wasn't sure if those were tracks or not. Truly an awesome vista, though...

I've got a college buddy in Alberta...

Now, that was simply cruel, even if true. The poor fellow will discover enough reasons to be disappointed with Houston as soon as the climate and traffic sets in.

One of my esteemed professors taught me that sand and mud should be considered as rocks, and even that water is a rock. I would call him a purist, but how can one argue with that?

If this previously landlocked allocthon misses his earlier PreCambrian roots, he can do what some desperate geologists do. Look to the building stones for satisfaction.
http://www.google.com/search?q=geologic%20...+building+stone
AFAIK, no one has written such a guide for Houston.

Question: How do you tell which building on a campus houses the geology department, without reading a map or looking at signs?

Answer: It's the one with really big FLR's (Funny Looking Rocks) lined up along the sidewalks leading up to it's doors.

In the latest view looking back at Cape Desire you can see, in the shadowed part, what looks like an abrupt change of tone - darker below, lighter above. However this doesn't follow the horizontal texture changes that I presume are bedding layers but seems to cut across them at an angle, rising towards the tip of the cape. I don't know if this is something interesting or just a trick of the light. If someone were to post a brightened version of the shadowed part it would be a lot easier to make out.

Your wish is my command!

Click to view attachment

Thanks! Well, it does look as if it's really there, however I wouldn't dare to venture an interpretation.

ngunn -

Thanks for pointing this out. I'll add a couple more observations. The lighter toned layer lies between the lower cross-bedded stratum and the upper brecciated layer. I think I can see stratification within the lighter toned layer that is similar to the stratification in the lower darker layer. The upper part of the lighter toned layer has been broken by numerous vertical and horizontal fractures.

Forgive me for stating the obvious, but, for me, beginning with the obvious helps me to frame the questions.

What I thought I was seeing were stratification features passing through the light/dark boundary. What you suggest is inherently more likely. In that case it would be the light/dark boundary which is actually horizontal (as elsewhere all round Victoria) and the cross-bedding below is confusing the perspective to make it appear otherwise. However looking at the image again I can't make my first impressions go away entirely. Of course the MER team know the truth since they have their 3D terrain model, and maybe if this were something special we'd have heard. Then again it is a holiday . .

Congratulations on the career adjustment, Tim. A dozen years ago I considered a change from regulatory to industry with a relocation to Arizona, but since I was so close to retirement here, I decided to stay on instread of starting the clock again. I still have some options open...

The traverse around Victoria is proving to be as wonderful as I assumed it would. We are starting to see some interesting lateral and vertical changes in the lithologies. I'm looking forward to examining the paleo-surface of Meridiani as it existed at the formation of Victoria, as well as the linear features at the SE quadrant of the crater.

--Bill

ngunn: That looks like one of those truncation surfaces delineating sets of overlapping dunes and related bedforms that Tim described a few messages back. Imagine a sea of wind-blown sand with dunes and ripples migrating with the wind. If water appears in the environment it could complicate things a bit, but maybe not too much. Sometimes parts of pre-existing dunes are left behind, to be buried by a later arriving dune. These wind-blown shapes (bedforms) often have a finer internal structure that gives us additional clues to the environment they were formed in, their shapes, and the direction of the fluid that is moving the particles.

There might be a couple of other less prominent truncation surfaces in this outcrop, too. Mapping out all of these surfaces and correlating them is the tricky part.

Bill: Good to see you again.

The trouble with that is that the tone change seems to intersect the strata. I accept this could be an optical illusion, but if its not there must be two separate processes here - one depositional and one post-depositional.

FWIW, a similar pancam mosaic pointed at Cape Desire is planned to be taken tomorrow (sol 1095) but this time in color (L257) and from a slightly different position for long-baseline stereo purposes. It might be useful here.

Yes that's good news. For clarification here is what I think I'm seeing. I don't know how to annotate posted images so a verbal description will have to do. Towards the right end of the cliff there is a pair of horizontal-looking dark bands in the light zone aboult half way between the top surface and the light/dark boundary. These could be continuous with two similar bands that appear near the end of the cape a little below that boundary.

This what you were refering to?
Click to view attachment
The overhang on the right continues onto the cape where Oppy is sitting. I wonder if there is any signs of the change in shading on the other side of cape Desire or if this feature is only on this side.

I'm not sure. but I think these (noted in blue) might be the dark horizons that appear to cross cut the boundary. It's unclear because the possible intersection occurs at the large fracture.

Yes, that's the one. And to find the 'strata' that I think this line [/i]may[i] cross start from the extremity of the overhanging nose on the cape, go almost horizontally to intersect the red line near those isolated sunny patches then continue in the same direction across the lighter-toned region. I've looked at the other side of the cape and I can't see anything similar there. There the light layer seems to sit quite tidily on top of the darker stuff. This makes me suspect an optical illusion - an anaglyph should clear that up.

Edit; Gray, that's right, thank you. Now everyone knows it takes me 9 minutes to type a post!

Glad we were seeing the same thing.
I'm not convinced that horizon in question does cross-cut the boundary but it does deserve a look.

Real geologists, get ready to chuckle at the naive babblings of an amateur.

To me the blue line appears to be parallel to the original strata. The red line in question appears to clearly cut across the original planes. Equally remarkable about the red line is that it defines a smoothed-looking overhang.

I'm proposing that the red line marks a fault plane. The rock above the plane slid in a direction approximately towards the camera some time ago. Originally there was a very sharp overhang, but it's since eroded from the wind. Of course the fault plane must be dipping towards the camera.

Notice what looks like another fault parallel to the red one, here marked in yellow:
Click to view attachment
The yellow fault clearly runs diagonally across the original strata.

If you look at Cape Desire from above, I think this picture makes sense. Desire is a very narrow cape, and it actually looks steeper on the eastern face, as if the upper section had slid roughly eastwards. Also, this slippage event may have caused the feature Guam. In this hirise image I've indicated the direction of slip with white arrows. The actual feature in question, red line on previous image, is just visible as a faint broken white line at the tips of the white arrows:
Click to view attachment

Interesting, fredk, but I think I can see the horizon indicated by the blue line continuing through your yellow line as well.