O.K. Time out while everyone has a strong coffee to clear their heads!
There's an awful lot of coffee in Brazil...
O.K. Now, Tesh, can you run that one by us again?

Fair crack of the whip! Tesh meant this one http://qt.exploratorium.edu/mars/opportuni...58P1312L0M1.JPG

Just one of those dried frog pill moments

Further proof of the need for a good photo-mosaic of the floor of Duck Bay.
Don't know whether I'm Artha' or Martha.

Ooops! I really need some coffee.
I'll correct the link in the post. Thanks Aussie for the correct one.

Here's a small animated GIF from 3 of the four links posted. It really needs a proper calibration though!

Click to view attachment

Why 4th Rock, you've discovered CLOUDS ON MARS!!! Better do like the ESA and hold a press conference announcing your discovery.

In the midst of this incredible opportunity afforded by Victoria to look beneath Meridiani's surface, perhaps the most remarkable thing to me is the persistence of this fine layering, as, for example, in the recent rear hazcam view. Think about it! Starting in Eagle Crater, and now several kilometers away in Victoria, and still the same uniform layering, like the pages of an old unabridged dictionary. Somebody look at the Wikipedia entry for "varve" and tell me that that's not what we're seeing . . .

Proper calibration? Looks pretty good to me! Mind letting us in on your flatfielding secrets? Did you just use the average of all the frames in the series to create a flatfielding image?

I'd not heard the word Varve before - but a seasonal climactic pattern tied in with the Athena team's hypothesis for Meridiani makes a lot of sense.

Doug

Varves and their other rhythmic relatives are particularly useful for deciphering geologic sequences, but I don't think they are a valid model for the thin laminations we are seeing here in Meridiani. The sediments here are mostly wind deposited particles left behind by advancing ripples and dunes moved by ancient, day to day, wind activities, along with occasionally local movement caused by flowing water.

Alternatively, I'll admit that many of the aspects of the fine layering observed across Meridiani can be predicted using the dynamics expected to exist within impact surges. I think that is less likely here, but I don't want to revive that debate.

I wouldn't doubt that a seasonal climatic pattern might somehow be embedded in the fine sequences we have been so fortunate to observe through the senses of this amazing rover, but what we see here is surely more complicated than annual pairs of layers.

The earth is covered by hundreds, or thousands of areas where the layers of rock are quite finely laminated, and continuous, across many square kilometers of area. I don't find it so surprising that Mars has layers of rock that appear very similar across some few kilometers.

"The earth is covered by hundreds, or thousands of areas where the layers of rock are quite finely laminated, and continuous, across many square kilometers of area . . ." That's the point! We are talking here about prima facie evidence for sedimentation, ie, WATER!

glennwsmith, regarding your posts 457, 461 and varves: You are going way back to the beginning of Oppy's mission. For a few weeks at Eagle crater the layering was tentatively explained by sedimentation under a body of standing water. The first festoon cross bedding changed minds, taken to indicate that water flow was somehow involved. Another problem with the varve idea is that grains have been identified within the layers that are in the size range of coarse sand. Some dispute that the original deposited grains can still be distinguished but if coarse sand was deposited the particles would probably be too large to remain suspended in standing water long enough to settle out as evenly as the finer particles that typically form varves on Earth.

Kye, you make some good points. How about a process, then, in which a fresh layer of windblown sand/dust is deposited annually and which is then cemented into a permanent layer either by moisture from the atmosphere or by moisture percolating up from below? Obviously, I don't know what I'm talking about here, but simply doing what us amateur UMSF members must do, and that is to look at these pictures and try to understand what we are seeing -- and what we are seeing at Meridiani is predominantly fine, uniform layering. . .

I won't argue with that. That's what makes this robotic, planetary exploration so fun.

Yes, just that, an average of the four frames. But trust me... a proper flat (with no clouds in it) would give much much contrast ;-)

glennwsmith, You may not know exactly what you are talking about, but your new scenario does incorporate elements of the current rover team hypothesis. I do not properly understand it myself so I can't summarize it. I think that the layering in the top layer of bedrock is explained as an ancient eolian sand sheet, but a high water table and shallow surface flooding are also part of the story. What I don't understand is whether or not the water is part of the explanation of why the layering is so uniform. I have tried to research eolian sand sheets and sabkas but have run out of free online information without ever finding the level of detail that would really help. I have found some photos of sand sheet and sabka sections that show fairly uniform layering but nothing comparable to Meridiani. I think I understand how varves can sometimes be so uniform, planar and extensive but I haven't yet fathomed how the wind would accomplish something similar.

Dunes, ripples, and the like deposit steeply dipping upper laminations and mostly horizontal laminations at their base. Dunes typically advance and leave their tracks when their upper parts are dry, and free to blow about. If the foot of the dune is in the damp sand at the top of the water table, surface tension in the water holds the wet grains together, and preserves the lower laminations.

CosmicRocker, yes, thanks for the plausible mechanism by which irregular dunes can create regular layers . . .

Kye,
Look up adhesion strata. You should find some examples comparable with Meridiani thin layering

Umm. This should not come as news, Aussie, but volcanic (and presumably) impact surge beds are classic examples of adhesion strata too (although they are not usually called that). The grain adhesion is caused by condensation of vaporized water or ice on the particles. This condensation sometimes causes the formation of associated accretionary lapilli in the turbulent cloud. This IS the presently accepted sedimentary environment for the thinly-bedded, salty, easily wind-eroded layers at Home Plate.

-- HDP Don

DBurt. Mais oui. But the query raised by Kye related to how the thin or pinstripe layering at Meridiani could be attributed to aeolian processes. Cosmic Rocker's explanation was excellent and 'adhesion strata' is a good search term to find the illustrations he was looking for.

CosmicRocker re your 467, and Aussie re your 469. Goggle didn't help much with "Adhesion Strata" either I am afraid. I couldn't find a detailed description of the process and the only image I could find shows quite irregular layering.

I may have some idea how water would help to produce fine uniform planar layering in an aeolian environment. How's this?: Sand is removed from an area by wind down to the capillary fringe of the water table where there is enough wet adhesion to prevent further erosion. This sounds like a good start on making planar beds because it would tend to level the area, assuming a level water table and similar soil everywhere. Next a storm deposits an uneven blanket of sand at least sufficient to cover the surface everywhere. Then after a time a stronger storm removes all the sand but a thin new layer that has adhered to the damp surface. Maybe these last two steps could occur together in a single storm, but the event would have to end with all the unbonded sand being removed. Then the cycle repeats to add further layers. What this scenario doesn't explain to my satisfaction is why stacks of several tens of very similar layers have formed. It allows that the aeolian deposition events can be fairly variable as long as each cycle ends with stripping all but a thin layer, but wouldn't the water table have to be rising at the same constant rate between each storm for the layers to be so uniform in thickness? It seems to me that a lot of things would have to work just right and just the same over a very large area to produce the surface bedrock at Meridiani.

I have read of planar layering in sand sheets that is strictly aeolian not related to a high water table. The process involves aeolian sorting and can leave a thin even layer of the largest mobile particles on the surface. Sand sheets also often incorporate sand ripples and granule ripples, and the few images that I have found show less regular and less planar layering than at Meridiani. This is another question that I have: Is there any evidence at all of aeolian rippling among the planar beds of the surface bedrock (the bright band that Oppy is currently examining)?

I searched for "adhesion strata" too, of course, and by far the best reference I found, with lots of photos and diagrams, was a non-technical geological guide to White Sands, NM by S.G. Fryberger here:
http://www2.nature.nps.gov/geology/parks/whsa/geows/
See especially Chapter 5 on interdunes (you may have looked at it already).

Relevant to your question about planar-bedded interdune deposits, I presume that, up to a limit, simple capillarity can cause dry sand sticking to wet sand to itself become moist and adhesive, allowing another sand layer to stick, and so on until a considerable thickness of fine layering is produced. The water table presumably need not be rising at the time (although this would help). What I question, and what I think you are questioning, is where are all the associated facies and structures that should also be present? That is, where are the dunes proper with their long, steep foresets, the sand sheets with their ripples and other irregularities, the salt flat sabkhas, the fluvial and lacustrine deposits? Interdune deposits are typically only a very small proportion of the total section. Even for interdunes, why are there no associated interdune muds, or evaporitic crusts and salt ridges, or large selenite crystals, particularly considering that the original "sand" allegedly consisted of about 30% soluble salts combined with amorphous dust or mud (not the pure quartz or pure gypsum sands present in every terrestrial eolian example). After looking at the pretty pictures of all the above typical features and structures in the above reference, I became even more puzzled.

I guess I agree with CR and Aussie that "adhesion strata" provides a reasonable explanation for the nature of the Meridiani layering. The question then becomes, given two possible independent causes for this adhesion, which one does the preponderance of evidence support? Or are there other possibilities not yet considered?

-- HDP Don

Sigh. I guess I am just a dinosaur at heart because I still find the Mclennan et al arguments in the paper on 'The Provenance and diagenesis of the evaporite-bearing Burns formation' to be the most compelling analysis to date on the provenance of Meridiani.

Dr Burt, Re your 473, Yes, Thanks, I had already read that Fryberger material about White Sands. What I don't understand from your explanation (quoted above) is this: If the process of upward wetting by capillarity and aeolian sand deposition is continuous and takes place during a single storm, why do distinct layers form at all, let alone a stack of similar layers? I think maybe I can guess the answer because I have seen vague references to the process: Each layer consists of a single layer of sand grains sorted to about the same size. The layer thickness is determined by the grain diameter. Is that how the process works? Given this model, do the regular planar beds on top at Meridiani then have to consist of altered single particle layers, because it was the size of those sorted sand grains that determined the thickness of the layers?

They are indeed good arguments and constitute an extremely elegant, erudite, detailed, self-consistent, and largely Earth-centric explanation for the observations made at Endurance Crater. Their main appeal to me as a geologist is that I can easily relate to them, based on my own experience. However, that 2005 EPSL paper neglected evidence available at the time, plus the later rover discovery of similar beds at Home Plate. So ask yourself how well the 2005 and earlier "warm and extremely wet" hypotheses have survived more recent observations, both from oribit and on the ground.

As regards spherules, for example, some quotes from that 2005 paper (p. 106): "The sizes of spherules embedded within the outcrop are rather uniform with a mean diameter of 4.2 mm... The spherules are almost perfectly spherical with aspect ratios averaging 1.06... The vast majority of spherules occur in isolation, but rarely, they form "doublets"... There is no comparison of these with actual concretions (in terms of size, shape, degree of clumping, or spatial distribution), plus no mention of their difficult-to-explain Ni-enrichment and specular (blue-gray) nature. As for origin, they wrote (p. 109): "Four possible origins were considered for the spherules: sedimentary concretions, accretionary sedimentary grains (e.g., pisolith-like), volcanic lapilli and impact glasses." In other words, there was apparently no consideration of the origin that we had suggested (impact-related accretionary lapilli), even though such spherules (rarely forming doublets) have been widely recognized in terrestrial impact deposits, including those from Chicxulub and Sudbury. See my earlier posts.

Kye, regarding your sand sedimentation question, not my field, so I'll let someone else answer before I embarrass myself further.

-- HDP Don

I am definitely out of my comfort zone here and will withdraw with the single observation that I thought the Ni enrichment was pretty much explained and demonstrated by the Western Australian Lake Brown hematite concretions forming in an extremely acidic, low temperature, saline environment over a geologically very short timespan.

I do not wish to start a debate in the wrong place but I strongly disagree with the notion that the HP beds are similar to Meridiani rocks. I support the notion that HP is of volcanic origin and the salts and neighbouring silica rich deposits are a testament to the volcanic past in this area (there may have been contribution from meteorite impacts hence the observed nickel contents). But Meridiani is not = HP.

I do not wish to start a debate in the wrong place but I strongly disagree with the notion that the HP beds are similar to Meridiani rocks. I support the notion that HP is of volcanic origin and the salts and neighbouring silica rich deposits are a testament to the volcanic past in this area (there may have been contribution from meteorite impacts hence the observed nickel contents). But Meridiani is not = HP.

Hello

Have you seen it?


The anaglyph is great (what a pleasure... I've recently switch to mac -a MBP- and I can open all the huge pan of JPL marsrovers mission and scrolling it in easy way).

Exactly, Doc. I recall being challenged over making the same statement.

However (and someone correct me if I'm wrong), I recall reading that the HP rocks were found to be much less friable than the Meridiani rocks, cemented with a much less salty matrix. That data came from the energy required to brush the rocks with the RAT -- and that Spirit's RAT brush made less of a mark into these rocks during brushing than Oppy's RAT does brushing the sulfate rocks at Meridiani.

And, of course, the HP rocks aren't shot throught with concretions (or lapilli, or what-have you) like the Meridiani rocks.

So, IMHO, from various clues I've read about, the HP rocks are quite different, in composition and friability, from the Meridiani rocks.

-the other Doug

More clouds drifting by in sol 1419 and especially 1420 navcams:
http://marsrovers.jpl.nasa.gov/gallery/all...nity_n1420.html

Dr Burt, Re your 476 and my 475, OK, thanks anyway, I guess you are not the person to ask. I should be able to get a clear account of the sand-sheet or sabka explanation of the planar beds from one of the people who have accepted it. How about it, anyone? Is wet sand an essential part of the explanation or would a dry sand-sheet do? Are adhesion strata involved? How exactly do adhesion strata form? What would control the layer thickness in places where there are stacks of a few 10s of very similar layers? How did the upper beds get to be so relentlessly planar? Is there a similarly regular, planar and extensive example of sand-sheet bedding on Earth? I would make a terrible lawyer because I am asking questions without already knowing the answers. Anyone? I will respond skeptically and ask more questions, but please don't let that stop you.

Perhaps, but I didn't hypothesize that they were the same rocks (they are on opposite sides of the planet, after all), merely that they might have formed by the same overall process. Deposits laid down by impacts should mainly reflect the nature of the target, which will differ for different craters, even at a small scale (cf. the reverse stratigraphy made famous by studies at Arizona's Meteor Crater). They should also reflect the distance from the crater, and to a lesser extent, the nature of the impactor. At first glance, in their basic bedding and weathering characteristics, the two groups of rocks look amazingly similar, at least to me (and I taught at ASU's Field Camp, a boot camp for geology students learning to map in mainly sedimentary rocks, for over 20 years, and was in sole charge for the last 5 of those years).

In this regard, I should mention that different layers exposed just at the top of the Meridiani section differ considerably from each other in friabilty, albedo, presence or absence of spherules, and so on. Much has been written (not by me) that these very similar layers must therefore have formed by completely different processes (e.g., wind vs. water flow vs. brine evaporation). To me, the exposed rocks look like they all formed by the same high energy process that resulted in a remarkable preponderance of shallow cross-beds throughout, and little lateral variability. There appears to be very little vertical variability either, compared to that in most terrestrial sedimentary sections I've seen (e.g., exposed in Arizona's Grand Canyon). You probably disagree.

Some people prefer to emphasize very minor differences, others to look for commonalities. Take your pick. Do you want to see the forest or the trees? I guess I'm a forest guy.

-- HDP Don

"Relentlessly planar" -- yes! That is what is what has been jumping out at us from these photos!

Aussie, I presume you are referring to this meeting abstract:
http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3175.pdf
I suggest you reread it. If you think those few red to brown, lumpy, rounded, quartz-filled concretions, which range in size from 2 mm to 40 mm are a good match for the uniformly sized (4 mm), uniformly distributed, perfectly spherical, blue-gray specular (high temperature shiny) martian spherules, you are entitled to your opinion. If you think those lake beds, like Meridiani, contain no muds or large salt crystals or lateral zoning, and are everywhere cross-bedded, you are wrong, according to the abstract.

Nickel: In crystals, nickel prefers to substitute for magnesium (in igneous rocks, most commonly in olivine). That is, it will partition from a fluid into a magnesium-bearing phase. Nickel, unlike iron, cannot be oxidized in aqueous solution. It can nevertheless end up in hematite if it has nowhere else to go (as in the evaporating Australian lake or in pure quartz sandstones, neither of which contain magnesium phases), or, apparently, if temperatures are high, conditions are highly oxidizing, and disequilibrium rules (as in a surge cloud). The Meridiani beds, unlike the Australian lake, are full of soluble magnesium sulfates (reportedly up to about 30%). If they were ever soaked in a brine, any nickel present should have partitioned into the magnesium salt, not into crystalline hematite. Can you find any example of nickel preferring crystalline hematite to a magnesium phase in the presence of water? I've looked through all the literature on nickel laterites (a type of ore deposit formed by intense weathering), and I certainly can't.

Australian acid lakes in general: Despite claims to the contrary, probably not a good analog for Mars. Billions of years of acid rains have leached Western Australia soils of virtually all alkalies and alkaline earth elements, other than a few attached to salts. I understand that the soil is therefore terrible for agriculture without heavy external applications of fertilizer. Owing to the lack of alkaline earth elements to neutralize them, acids (presumed to be produced by sulfide weathering) can therefore persist in some lakes. Mars is just the opposite - chock full of alkaline earth elements, especially magnesium, in the common rock basalt. The dominant sand seems to consist mostly of basalt particles (probably mostly produced by impact fragmentation). I defy you to make a persistent acid lake or acid groundwaters in such an environment, no matter what the original source of acid. Roger Burns and I both proposed local oxidation of sulfides as a reasonable source for acid (as for Australian lakes), although my model added impact cratering. Burns long ago recogized that the only way for acids to persist on Mars was for them to be either frozen or preserved in acid salts like jarosite. That is, no liquid water (other than moisture) and no acid brine. I agree.

Thanks for mentioning that reference. I hadn't looked at it recently.

-- HDP Don

Planar bedding is fine, but for it to be everywhere cross-bedded in addition is the truly puzzling feature. This indicates that erosion (scouring) was going on at the same time as deposition, and implies an unusually energetic environment for such fine sediments. Boom! Whoosh! does it for me, especially in view of the ubiquitous cratering. Do you have a better suggestion?

-- HDP Don

Dburt, rather than offering [another] theory of my own -- and at the risk of having our current colloquy on layering moved to a thread of its own -- let me rather try to take a closer look at your theory. As I understand it, you and some of your colleagues believe that each meteor strike/crater formation event ends up (without going into the intermediate details) leaving a layer of dust over a very large area, which collectively now form the strata we are seeing. Assuming that this understanding is basically correct, here is my big reservation: why are the layers so seemingly uniform in thickness? Wouldn't a big meteor strike/crater formation event (or one closer in) leave a [much] thicker layer of dust, and vice versa? It is largely this reservation which leads me, and I suppose others, to think of some uniform, annual process. The Meridiani subsurface is not only "relentlessly planar", but the planes themselves are "relentlessly uniform" . . .

First of all, Meridiani is not "relentlessly planar." Much of it is quite planar, but there are just as many examples of cross bedding and/or cross lamination in these capes and bays. We've seen that mix everywhere between Eagle Crater and Victoria. Do we need to post more panoramas showing the angular layers?

Honestly, I think an impact surge is a legitimate model, still worthy of consideration. But I also think dunes migrating across an area where the water table is rising, and leaving behind toe-set laminations, is another simple explanation for the planar laminations. I think there are other aeolian models that could explain what we see.

Don (and others) theory of Meridiani etc. has been discussed to death and beyond in its own thread. http://www.unmannedspaceflight.com/index.php?showtopic=4308 which has now been closed, as it was going around and around in cirlces and getting nowhere. There's >40,000 words of Don's thoughts in there - enjoy.

Doug

Better now than never...
Click to view attachment

Very good as always Dilo another "Little Prince" picture
Roy F

Agree completely. As a professor, I am accustomed to answering the same questions multiple times (as evidenced by that long, repetitive thread), but bandwidth here is limited, as is my uncommited time, so please verify that your question hasn't already been answered (as the latest bedding question has) before posing it. Also, for the sake of caution, please leave any strong emotional attachments to the rules of Earth at the door, and assume (until demonstrated otherwise) that Mars plays by its own. Finally, never confuse models with observations. Thanks.

-- HDP Don

Here is a good summary of the aeolian playa explanation of Meridiani by Grotzinger and all from LPSC 2006. (Brian pointed me to it on the other Mars blog, Thanks Brian.)

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2254.pdf

It answers many of my questions. Yes, the presence of water is an essential part of the model. Layering has been created by several different processes: Aeolian dune formation, dry aeolian sand-sheet formation, wet aeolian sand sheet deposition, surface water flow, and surface water flooding. Lake Eyre, Australia is the closest Earth analog.

And here is the 2007 version of the same paper very little changed but with a rebuttal to impact-surge included:

http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3292.pdf

Maybe I "get" Occam's Razor at a "gut" level that most others do not. Having some practical experience of the world helps. I am not a scientist, just a curious spectator whose first motivation is to understand what we have discovered at Meridiani. I found a satisfying simple explanation within a few weeks of taking an interest, unfortunately I'm almost tempted to say, because it has been a long frustrating wait for mainstream Mars science to catch up. I predict that when the wet aeolian model goes it will take the whole Earth-centric approach to Mars with it. I hope I won't have to wait for a whole generation of Mars scientists to pass before serious progress can be made.

general comment - the need to claim mars operates by its own set of rule is greatly exaggerated. The ability of the MER landing team to get the rovers down in one piece was truly remarkable and this could not have been done without a very good understanding of the rules they were playing within. Winds, reflectivity, thermophysical properties, atmospheric density, temperature variations, etc etc., brilliant work by that group. You need a new set of rules only if you can demonstrate the old ones don’t apply, and I think we have demonstrated many times that the physical rules of earth do apply to mars.

"the other don"

Amen, brother!

OD - With all due respect, and I assume you actually realize this, we're not talking about the straightforward rules of physics and chemistry, or the unsurpassed engineering (and a certain amount of marvelous luck) that went into the landings and subsequent rover explorations. We're talking about rather subtle geological features with multiple possible interpretations, and the challenging detective work needed to eliminate possibilities. For this type of detective work, an open mind is a prerequisite; groupthink, unwarranted assumptions, and preconceived notions are the enemy. (If you don't believe me, imagine yourself wrongly accused of a crime, or perhaps about to be lynched.)

-- HDP Don

Other don, Mars engineering has been successful because it is based on the present Mars. I wish that Mars science could have the same starting point instead of assuming that almost everything we see was created during a brief early Earth-like period.

The results of analysis of Meridiani data are not based on the assumption that there was an earlier warmer, wetter Mars with a reasonably thick atmosphere. Rather the proposition that such an environment existed flows from the scientific evidence.