[X] My Assistant

[djellison]

Looks quite Fram-ish

Doug

[dvandorn]

Looks quite Fram-ish

Doug

Yes, it does, doesn't it?

"Fram-ish" could be better characterized, I think, as "a relatively young, fresh impact crater with blocky inner walls and local blocky ejecta arrayed roughly one crater diameter out from the rim."

I'm fascinated by the erosion patterns being defined by these crater morphologies. Obviously, Viking is an Eagle-sized crater and both seem to have been caused by very similar impacts. Viking, like Fram, has a more extensive exterior ejecta blanket and blocker inner walls -- it seems to be younger and fresher.

The lack of inner blocky walls in older craters is a no-brainer -- mass wasting and slow aeolian deposition means that rubble slides to the bottom and is then covered by wind-blown sediments. But the virtual erasure of the ejecta fields around Eagle-like craters shows just how easily eroded the excavated rock must be. Especially compared to the blueberries that resist erosion. Or even compared to basaltic rocks, like the ones we see at other landing sites -- at Gusev, for instance, the rocks haven't been eroded down to a smooth plain by billions of years of aeolian erosion, like they have at Meridiani.

I think there is a paper to be done, somewhere, on the erosion patterns of the concretion-rich evaporite rocks at Meridiani Planum. You'd almost think that, if aeolian erosion is the only factor in the reduction of the evaporites and subsequent paving of concretion materials, that you would only erode the evaporite down a centimeter or two, until it developed a thin layer of uneroded concretions that would protect it from the winds. Obviously, there has been significantly greater erosion than this, or else Oppy's tracks would be uncovering evaporite subsurface everywhere it went... so the evaporite must have continued to erode after it developed a thin layer of concretion materials.

I'm sure that aeolian dust deposition has something to do with the current state and depth of the regolith, as well -- but if we postulate that the depth of the regolith is primarily due to windborn dust deposition, you have to explain what "gardening" processes result in so many concretions sitting at the surface. And in any event, adding more covering material in the form of windborn dust deposition just reduces the evaporites' exposure to wind erosion even further, and there has to have been a *lot* of evaporite erosion to account for all those loose concretions.

I also have to wonder -- the composition of Meridiani soils and the evaporites are somewhat different, right? The soils seem to be basalt dust/sand (windblown deposition) mixed with concretion elements and *not* an unusually high concentration of the salts and sulphates that make up the evaporites.

So, when the evaporites eroded and left all these concretions littering the landscape -- where did the material go? Is it so thoroughly mixed with the global dust that it's one of the major constituents in the global dust's sulphate and salt content? Or are there large "traps" of eroded evaporite dust lingering somewhere nearby?

Just curious...

-the other Doug

[RedSky]

Looks quite Fram-ish

Doug

Yes, it does, doesn't it?

"Fram-ish" could be better characterized, I think, as "a relatively young, fresh impact crater with blocky inner walls and local blocky ejecta arrayed roughly one crater diameter out from the rim."

I'm fascinated by the erosion patterns being defined by these crater morphologies. Obviously, Viking is an Eagle-sized crater and both seem to have been caused by very similar impacts. Viking, like Fram, has a more extensive exterior ejecta blanket and blocker inner walls -- it seems to be younger and fresher.

The lack of inner blocky walls in older craters is a no-brainer -- mass wasting and slow aeolian deposition means that rubble slides to the bottom and is then covered by wind-blown sediments. But the virtual erasure of the ejecta fields around Eagle-like craters shows just how easily eroded the excavated rock must be. Especially compared to the blueberries that resist erosion. Or even compared to basaltic rocks, like the ones we see at other landing sites -- at Gusev, for instance, the rocks haven't been eroded down to a smooth plain by billions of years of aeolian erosion, like they have at Meridiani.

I think there is a paper to be done, somewhere, on the erosion patterns of the concretion-rich evaporite rocks at Meridiani Planum. You'd almost think that, if aeolian erosion is the only factor in the reduction of the evaporites and subsequent paving of concretion materials, that you would only erode the evaporite down a centimeter or two, until it developed a thin layer of uneroded concretions that would protect it from the winds. Obviously, there has been significantly greater erosion than this, or else Oppy's tracks would be uncovering evaporite subsurface everywhere it went... so the evaporite must have continued to erode after it developed a thin layer of concretion materials.

I'm sure that aeolian dust deposition has something to do with the current state and depth of the regolith, as well -- but if we postulate that the depth of the regolith is primarily due to windborn dust deposition, you have to explain what "gardening" processes result in so many concretions sitting at the surface. And in any event, adding more covering material in the form of windborn dust deposition just reduces the evaporites' exposure to wind erosion even further, and there has to have been a *lot* of evaporite erosion to account for all those loose concretions.

I also have to wonder -- the composition of Meridiani soils and the evaporites are somewhat different, right? The soils seem to be basalt dust/sand (windblown deposition) mixed with concretion elements and *not* an unusually high concentration of the salts and sulphates that make up the evaporites.

So, when the evaporites eroded and left all these concretions littering the landscape -- where did the material go? Is it so thoroughly mixed with the global dust that it's one of the major constituents in the global dust's sulphate and salt content? Or are there large "traps" of eroded evaporite dust lingering somewhere nearby?

Just curious...

-the other Doug

Hi Doug,

Your discussion hits close to a question I've had ever since Oppy left Eagle crater and we saw the whole plain covered with the concretions/Blueberries (BB). It almost seemed in many places like a complete, uniform covering of BBs. My question basically is this: What depth of evaporite would have had to be eroded in order to get that density of surface BBs? There must be some idea as to the BBs occurence density within the evaporate (We've ground into it, microscopically examined it, etc). Think of it this way... if the evaporate were transparent (say, like Jello with, well, blueberries suspended in it) and you could "see" the BBs within... how thick would the layer have to be so that any line of sight into the layer intersects a BB? (almost like Olber's paradox). Thinking back to some of the photos of BB's just on the verge of emerging out of the evaporate... it seems like it would be less than 1 BB per cubic centimeter (BB/cc?). In any event, I would think it would take more than an inch or two of erosion to get the surface BB count seen. ... perhaps several feet... even meters?

That then gets to your issue: where did all that powder go? ... blown away? One would think some salt concentration should be there in the soil. Perhaps once you finally obtain a uniform, protective layer... erosion of the evaporate halts or slows significantly. Once you know the thickness removed to get the observed BB cover, then you can start asking other questions like... how long would that take, etc.

Well, just wanted to pass along a few thoughts.

John/RedSky