The Real Ejecta of Endurance Crater?

I have been looking at these clusters of darker projecting rocks unevenly distributed around the rim of Beagle Crater, for example:

Have a look at Horton's excellent panorama of Beagle Crater to see more in context.

The concentrations of darker projecting rubble at Beagle resemble these mysterious mounds of disorganized blocks sticking out of the walls of Endurance Crater:

I think that these mounds at Endurance are the real ejecta of the original impact crater. The material above the ejecta is a later impact surge deposit that covered Meridiani, filling all smaller craters and adding a few meters of new material to the surface of the plains. I have been wondering if the exhumation of Endurance has proceeded to a level below the older, pre-surge surface. This ejecta buried part way up the wall suggests that exhumation has reached down into the original impact crater.

Sorry, here is that image of Endurance:

Kye: I disagree with you about the rubble piles in Endurance. I think they are more likely ledges ,similar to the one you now see, that have broken off and fallen down the slope of the crater and disintergrated.

I mentioned in an earlier thread that I thought the pile of dark rubble on the wall of Beagle that you refer to is the remains of older basaltic material ejected from VC , covered by later, thin, evaporite beds and then exposed by the Beagle impact.

As we approach VC and rise up in the section,we should see more of its basaltic ejecta and if lucky may see some places where the more recent beds have covered it.

If I am correct the piles of dark rubble we just passed may be VC ejecta that were never covered by later beds or have been exhumed by post VC erosion.

Ben, We may have a little in common. You suggest that there may be material that is more basaltic under the bright top layer of the plains. I have been wondering about the two kinds of rock in the ejecta of Beagle. It is not known just how erosion works on Mars, but it seems likely that some of the blocks excavated from Beagle are more resistant to erosion than others and end up standing above the surface. It seems that all the blocks, dark and protruding, or bright and flush with the soil are layered, and must have been emplaced close to where they are by the Beagle impact.

I have been playing with an idea about how these two kinds of blocks originated. I imagine that not far below the surface at Meridiani there may be material that consists of unaltered basalt clasts frozen in a matrix of ice. This material was excavated from the crust by a distant impact and deposited here in fine layers by the associated wet impact surge. Nearer the surface the ice matrix has been slowly replaced by sulphates that originate in airfall dust and are concentrated downward into the rock, by a process similar to that which is apparently concentrating sulphates downward in the soil at Gusev.

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Perhaps the Beagle impact penetrated into the underlying material that still had a high ice content. This would be imperfectly mixed with blocks from the surface layer that had already been transformed from clasts in ice into sulphate cemented conglomerate by weathering. In my scenario it would be the surface materials that are most resistant. The deeper materials would consist of blocks of dirty ice and would begin to fall apart by sublimation, now exposed to the daily sun at the surface. This process would quickly slow down as the solid materials collected on the surface and insulated the remaining ice. At some point the ice would be stable enough to begin the much slower process of replacment by sulphates which normally takes place just below the surface. The initial thermal deterioration of the icy conglomerates would tend to reduce the ejecta pile to a smoother surface quite effectively, but the material that had been transformed to sulphate before the impact would not be affected and end up standing high.

Kye: On some things we agree and others I just don't see enough evidence to more than speculate.

I believe the upper layers of the Meridiani bedded unit are more resistant than beds below. Ejected chunks of these beds rest at odd angles, generally above the surface , where they have been more resistant to erosion.
Near the crater is a jumble of bedded ejecta that have been eroded flat and show bedding surfaces exposed at various angles.
I attribute their flat surface to erosion of chunks of the softer lower beds.

Surrounding this zone are the slightly elevated rays of chaotic material which extend out onto the undisturbed flat lying beds typical of the general area. Scattered larger chunks of ejected material rest on these flat undisturbed beds.

You may be right about thermal and chemical processes that were also ongoing but I need more evidence.

Ben, I am definitely speculating. We should be speculating because scientists can't, at least not freely in public.

There is something strange about the those resistant blocks standing high on a fairly smooth surface that is made up of soil and "softer" "planed-off" blocks. The projecting blocks don't seem to have protected the adjacent surface from erosion. If the erosion were by wind-driven sand scour we might expect to see rough yardangs or wind tails of softer blocks downwind of the projecting blocks. As usual I suspect that some other sort of erosion is involved.

Getting back to the title of this thread, I am speculating that the real ejecta of Endurance is visible in these projecting mounds of blocky material that form an intermittent stratum on the crater wall in this image:

I have been looking at these mounds since Edgett's contention that Endurance is buried and exhumed sent me back to Endurance a few months ago. I agree that they could be debris fallen from an undermined layer above, but to me they look more like they are sticking through the smoother material of the crater wall. They are not shaped like talus piles. Why has the descent been checked while still on a steep slope? Seeing similar piles around Beagle made me look at these again.

I have another reason why I now think that this is more likely to be the buried ejecta of Endurance. I finally got a copy of the Burt, Knauth and Wolletz paper from Nature that came out late last year. Unfourtunately it is not free on the web. These authors explain the Meridiani deposit as impact surge layering. I had never had a clear idea of the likely depth of one of these deposits from a single surge, but according to the paper the depth we see above my putative ejecta is about right. Big impacts should cover very large areas with just one to a few meters of material. I wanted to explain all of the Endurance layering with a single event but now it looks like two or more impacts are probably responsible for the Endurance exposures.

I was having trouble when imagining a deeper surge because deep burial of Endurance would not leave the buried rim ejecta showing as a rise at the surface. For example, if Endurance had ejecta piles a meter or two deep then even as little as 10 meters of deposition would likely conceal the raised rim at the new surface. Now I am happier. Not only do Edgett and the Brinesplatters seem to be consistent but the buried ejecta itself has turned up in about the right place.

It realy does look as if the evaporite material flowed right up, and over the crater rim, and over the darker rocks.

FMR Why can't I reply to his thread without my comments being erased after a few lines. I have tried a half dozen times.

Ben, can you be more specific? What do you mean by "comments being erased after a few lines"? Do you get any error messages? Does the comment appear to post correctly, but then you only see a part of your message? I can see 3 replies from you in this thread -- the ones shown above, and they appear to complete. Are you referring to other attempts? If you have difficulty posting the specifics to this thread, please email mark at marsroverblog.com and be sure to include mars rover in the subject.

I just wanted to say regardless who is right. You two are sharing a great debate.

Mark: I am typing along in the comments box and suddenly the next letter (particularly t ) doesn't appear and then the enire text disappears.

Could it be my computer?

Kye, I think the mounds are ledge debris that has fallen and become imbedded in the soft talus slope because they are not horizontal as they should be if they were an ejecta layer.

They also have no visible bedding bounding them on the top or bottom and there is no mound below the remaining ledge which hasn't broken off yet.

Ben, that does sound like it might be your computer. Have you tried other sites with forms or other threads?

That does seem strange indeed. I will keep thinking about it, but right now I don't think anything on the site could be causing something like that.

Mark: I am a 2 finger typist and my daughter watched me and apparently I have a dangling finger that screws it up.
Will try to do better. Thanks for your help.

I think the 'darker rocks' are a function of the light on rock surfaces. The flat bedding plane fragments exhibit 'white' surfaces with greater light reflectance. The angular materials, where blocks are not showing bedding surfaces, show darker colours because they are sections through the rocks and present irregular surfaces.
Hort, is this nonsense? Frequently rock outcrops present different colours depending on the surface exposed. Can you test this?

Newboy, I think that what you are saying in 14 is right. The rocks that stick up will present some shadowed surfaces to the viewer and the broken edges of the layers might show a rougher and therefore less bright surface than the horizontal rock surfaces showing just one layer. I still think that I see overall inherently darker rocks sticking up even considering the confounding effects.

Horton and I have been around this topic before and he suggested that the difference I see is a lighting effect. Rigourous testing could be done given NASA'S 3D capabilities to factor out the angles of sunlight and view and arrive at intrinsic surface brightness.

Its a reasonable notion that the projecting rocks in Beagle's ejecta might be a different color than the "flush" rocks. The projecting rocks might be more erosion resistant because they are a slightly different material also differing in color. The projecting rocks might be a different color because sticking up exposes them to a different weathering environment that darkens their color. I know that we have usually seen very bright rock coatings on the pre-brush surface of outcrops. I don't think that any projecting layered rocks have been targeted for IDD work.

Sometimes when just reading this forum, the text runs of to the right forever. Gotta scroll and scroll. A few hours later all of the text is within the screen. Mystery to me.

John, can you be more specific? What browser are you using? Which threads (specifically) require scrolling?

I use Firefox browser. Does not matter what thread, and only happens occasionally. Two days ago, I had to scroll, yestereday and today it is fine. Puter stays on, settings the same.