But the layers are not dusty, but sandy, as I explained in my reply.

--HDP Don

MarsIsImportant - Regarding volcanic heat, one of the reasons the MER team rejected volcanism was that there were no signs whatever of any volcanic phenomena anywhere in the vicinity. No volcanism = no volcanic heat for melting. Also, unlike on Earth, volcanism on Mars does not ever appeared to have moved around, owing to the lack of plate tectonics. The main reason why the volcanoes are so big is that volcanism has always stayed in the same place.

Regarding crystalline clays - they seem to occur only in the very oldest, most heavily cratered areas of Mars, and are rare there. They probably have nothing to do with Meridiani itself, which appears to be much younger. They could reflect water melting or condensation that occurred at the height of the late heavy bombardment, or volcanic heating, or a different climate back then. No one knows.

I'm not trying to convince you of anything about Meridiani - just trying to open your eyes to all the possibilities, so that you can make up your own mind, based on the evidence as you understand it. And the berries to me are still pretty round near Victoria, although some of them may have been eroded a bit by the wind (everything else was, that's for sure). They also could have been affected by the Victoria-forming impact itself, during the excavation process. Thanks for the discussion.

--HDP Don

Thanks for answering that far better than I did.

--HDP Don

As some of you know, I don't have nearly the time to devote to thoughtful posts as I used to...but be that as it may, I see in my review of the recent flurry of posts that my name has been called upon for some sedimentological input:

- single grain (or a few grain) layer lamination: the most common occurrences of these in the terrestrial stratigraphic record are due to three processes: 1) Stokes settling, 2) upper stage/critical flow regime streaming, and 3) ballistic/translatent ripple migration. 1) and 2) are subaqueous processes and 3) is aeolian. Stokes settling is simple gravitational fall-out of material suspended in a fluid, with particles sorted by their velocity (generally grain size and density, although drag and grain Reynolds number also are important with non-spherical grains). The results are things like varves, laminated lake clays, and deep-sea oozes, with some amount of grading apparent. Upper stage/critical flow regime streaming occurs when the shear stress at the bed is such that bedforms such as ripples and dunes can not form, but is not exceeding a point at which antidunes or chutes and pools form. A plane, flat "traction carpet" of grains forms, and as velocity wanes, a plane, flat lamination forms before dunes and ripples. There may be low relief (1-2 grains thick) stripes that form down-current due to rollers and stretched-out vortices near the boundary layer. These are expressed as parting lineation in indurated sandstones. These features are common in river, tide, and beach (swashface/foreshore) sandstones, the Tb part of Bouma successions (turbidites), and pyroclastic flows and base-surge deposits. The migration of ballistic or translatent ripples in aeolian regimes produces pinstripe lamination, with alternating finer and coarser grained layers only a grain or two thick. Foreset laminae are generally not present in these types of ripples, and cross lamination is rare in most aeolian deposits. Cross-bedding, on the other hand, is almost always present.

- formation of martian sandstones: siliciclastic sand, of course, forms from breaking up big rocks into smaller ones. Because of the upper size limit of sand (2 mm), most grains in sandstones are either mono-mineralic or are made up of 2 or 3 crystals of different minerals still stuck together by other means (igneous or metamorphic crystallization or sedimentary cementation). Chemical and physical weathering processes on earth can be quite efficient in breaking rocks down to sand and silt size, and the abundance of sandstones and siltstones is related to the distribution of crystal/grain sizes in the parent material. Induration can result from geochemical processes related to the original constituents (pressure solution, dissolution/reprecipitiation, etc.) or post-depositional additions (cement, neomorphic clays, etc.). I guess for me, the larger questions of sandstone formation on Mars are the mechanisms under which sorting to sand-sized material (to a deposit that could be preserved as a sandstone) takes place, and how deep burial (sedimentary basin formation) can occur without an obvious plate tectonic engine driving crustal deformation.

- scour surfaces in aeolian deposits (or their absence): scour surfaces are ubiquitous in aeolian deposits. Stokes surfaces, or supersurfaces, form by regional deflation to a water table. Brookfield surfaces form a hierarchy of bounding migration surfaces of dunes, draas, and larger bedform families. Changes in wind speed, direction, or sand supply can result in regional deflation, and local blow-outs form down-wind of and between dunes at zones of air flow reattachment or impingement.

Don Burt's catastrophist/non-uniformitarian ideas have also made me start to think again about the dynamic nature of Mars climate and paleoclimate. I keep having this nagging suspicion that we have yet to completely comprehend the full impact of Mars precession and obliquity cycles and how they control global volatile distribution (and state). This, plus our generally impact-poor view of surficial processes, makes us ill-prepared to, as Bill Shakespeare once said "figure the nature of the times deceased" on Mars.

The sand on Mars is like fine dust on Earth. Looking with the Micro-Imager, the dust looks sandy. The really fine dust in the high atmosphere is not what I was necessarily referring to. You can see the tracks of the rover dramatically change in appearance during the Dust storm because the wind speed dramatically increases. This allows dust or sand as you say to move and be deposited elsewhere. But really, I should not have to explain this to you. Sometimes I can be the Master of the obvious.:-)

http://qt.exploratorium.edu/mars/opportuni...22P2953M2M1.JPG

http://qt.exploratorium.edu/mars/opportuni...02P2956M2M1.JPG

You are correct. It looks sandy to me too. It looks like its made out of the same stuff. Sorry about that. I sometimes get confused when talking about the dust or rather sand on Mars.

I agree that the hard limit in size at 5-6 mm is a key observation. Also, it has been observed and discussed on another forum that the size distribution of the berries in or near the crater outcrops, or the berries which are protected from the environment in the craters, exhibit a tail towards small diameters. No Earth analogy of this feature has been proposed. This property is not clearly seen for the berries of the plains, which are generally of smaller diameters, and may have suffered weathering.
Although the implications of this asymmetry is not clear to many of us, I do think that it is not incompatible with a condensation scenario in an impact surge cloud.
Distinctive morphological details have also been discussed : dimps, seams etc.. To me an account of these features in a surge hypothesis seems much more problematic.

denis

Welcome, Denis! Agreed, and esp. since the anomalous small-scale features you cite seem to be much more prevalent on berries that are embedded in sedimentary strata or under the soil (recall those seen in the trenches dug by Oppy early in the mission). If they are condensates rather than accretions, then I am at a loss to explain their symmetry, unless they somehow formed VERY rapidly while airborne or suspended in solution; haven't seen any 'pristine' berries with a flat side, for example.

"Other Don - That's all well and good, but many things are theoretically possible (including little green men, perhaps). Just show me the evidence, please. More to the point, are there any features at Meridiani (or Gusev, or any of those many other salty layered deposits all around the Mars highlands) that CAN'T be accounted for by the impact surge hypothesis?"


HDP Burt

I agree, green men are possible right up there with impact surge- the structure of your debate on impact surge seems to include any and all features can be linked to a surge. If there was a kitchen sink observed in an outcrop I'm sure there is an explanation for it with impact surge. Do salts in a nonequallibrium condition at endurance point directly to impact surge? Of course not. Do hematite spheres? No. What is the evidence for impact surge, just show us the evidence, please! Difficulties or simply holes in the MER theory are not allowed.

"the other Don"

tdemko, Thanks for your reply 154. It is good to get confirmation that single-particle layers do occur in turbidites and base-surge deposits. You seem to have included base-surge among sub-aqueous processes. Do you think of base surge as a sub-aqueous process? I have read some descriptions that make much of the presence of liquid water in creating the surge layers and other sources that do not mention liquid water at all. I resumed my net search on this topic in the last few days and found a 30 year old Wolletz and Sheridan paper that includes a few lines that spell out how the planar beds were thought to form in base-surge:

“Still further from the vent the cloud deflates to the point where inertial flow dominates and void space is generally less than 60%. Here grain collisions set up shear plains along which grains of different sizes seek their respective zones of lowest shear energy and inversely graded planar beds result.”

That reference to shearing layers has been very hard for me to find and confirms the explanation that I have been using. Unlike many layer-forming processes this one involves the simultaneous presence of a stack of unfinished layers all in motion together and interacting. Herr Doctor Burt seems a little bored with these details, but I think that they may be important in changing minds, especially in explaining impact-surge to non-scientists. Surge isn’t a magic cloud that makes layers but it does make layers in a way that is very unfamiliar to most people, that they can't hope to visualize without some help.

Here is the address of that paper. I hope it works. If not, sorry about my bad net skills on a new site and new browser.

http://articles.adsabs.harvard.edu/cgi-bin...p;filetype=.pdf

This statement, if it is a currently accepted postulate for how planar beds are formed during basal surges, is quite well-suited for testing in re the Meridiani deposits.

It predicts that, for each surge event, you should see inversely graded planar beds. In other words, the largest grains should make up the first beds deposited, followed by progressively smaller grains until the uppermost layers are made up of the finest grains. (At least, that's my reading of what "inversely graded" means.)

Has Oppy found such an inverse grading relationship between the beds in the units it has been able to study? Since the theory above uses as a basic theorem that the layering is entirely due to different grain sizes sorting out, there ought to be an observable change in grain sizes from layer to layer. Even if this delta is so small as to be difficult to measure from one layer to another, it ought to have been enough over the depth of the unit observed within Endurance to be able to be quantifiably observed.

So -- here's a direct test of your theory, Herr Doktor. It's even a test on which you can do a little non-rigorous work using the raw JPG images from back during the Endurance campaign (or more rigorous work using the images already released to the PDS). I have to say, I truly think that if anything of this sort had been observed at the time, we would have heard about it... but I'm prepared to be proven wrong on that if you want to try and pursue this proof.

-the other Doug

"Normal" grading is coarsest grain size at the base, finest at the top. Inverse grading is finest grain size at the base, coarsest at the top. Normal grading approximates what you might see from simple gravitational (Stokes) settling.

Aeolian pinstripe lamina are inversely graded due to winnowing of wind ripple crests...fines are trapped in the troughs and the coarser crests bury this material during migration. Debris and turbidity flows that accelerate rather than decelerate during deposition would also be inversely graded.

I threw in the comment about lamination in base-surge deposits as an afterthought. I think that pyroclastic and base-surge flows act differently from both subaqueous and subaerial sediment transport processes. The evolution of hot gases in the flow during transport and deposition make characterizing the hydro/aerodynamics complex and unpredictable, to say the least.

Nprev (and Denis) - Been taking most of the weekend off from Mars, but have a few minutes now. Just a couple of comments: 1) There are no really comparable deposits on Earth (only volcanic surges, which are real wimps by comparison, and form under vastly different conditions. 2) I suspect that some of the features you describe formed as post-depositional coatings, affected by local bedding - I would only pay attention to the appearance of spherules after any salty coatings have been brushed off by the Rover. Even then, a symmetry (of say a belted waist) is hardly inconsistent with accretion in a cloud. 3) Unlike some people whom I won't name, we don't pretend to have all the answers.

--HDP Don

I disagree with your general philosophy - there were so many inconsistencies and internal contradictions in the MER team theory that we felt compelled to come up an alternative - and this is the best we could do, given our collective backgrounds. Perhaps it's wrong - we almost certainly have some details wrong. I'm open to any and all suggestions for improvement. As for the evidence, it is all around - Mars is drowning in impact craters, of all ages and sizes, hitting any imaginable target composition. It's also drowning in layered sulfate-rich sediments. Both rovers have found almost identical-appearing features in such sediments (including spherules), currently ascribed to completely different causes. If you wish to ignore the hydrosphere (mainly a cryosphere, near the surface) and atmosphere of Mars, and think that impacts on Mars are identical in their affects to those on the Moon (ballistic ejecta only) feel free. Rampart craters, unique to Mars, suggest you would be wrong. If you think that Mars cratering never produced fines, other than a bit of dust and sand on the surface, and that these never were deposited into rocks, other than those deposited by a secondary agent (water or wind or volcanic reworking- never impact surge) feel free. Occam's razor (the simplest explanation consistent with ALL the data, in Einstein's formulation) favors only impact surge, in my admittedly biased opinion. If you think it favors the MER team explanation, or if you reject it as a general philosophy, please explain why.

That's all for now - gotto go eat.

--HDP Don

PS (just ate): Surge is perfectly capable of eroding, transporting, and depositing a kitchen sink (which is more than I can say for the wind); putting it on Mars in the first place might present be a slight problem, though. Outflow channels - no problem moving and depositing it either.

Other Doug - I'm glad Tim Demko has joined this discussion - I hope he feels free to contradict what I say. My impression from when I first learned about inverse grading in volcanic surge deposits nearly 30 years ago was that it was observable mainly in near-vent, coarse-grained deposits consisting of blocks and lapilli of many cm to many mm. In far-out deposits consisting primarily of well-sorted, sand-sized grains you would not expect to see it. No inverse grading has been observed or described from the sandy surge deposits at Home Plate, for example, and yet the MER team is calling them volcanic surge deposits (owing to the presence of a single possible "bomb sag" - there is no volcano apparent, no tear-drop-shaped lava "bombs" have been seen on the surface, and the basaltic bulk composition - and occasional ballistic ejecta sags - are to be expected for practically any impact surge deposit on Mars). So are you suggesting that they are mistaken too? If not, please explain your logic. Thanks for the good ideas, BTW.

--HDP Don

How do you explain the near pure silica deposits found by Spirit? How would that fit in with impact surge?

MarsIsImportant, Re your 165, There is no necessity for impact-surge to explain the concentrated silica found at Gusev. It is a tricky mental exercise, I know, but try to consider the evidence of the layering in isolation from the chemical evidence. A hypothesis should explain all the facts but the facts are always in various degrees of doubt. It is a really solid fact that the layered structure at Meridiani and Homeplate dates from the time when the sediments were laid down. The present chemistry at the surface of these deposits (or near them in the case of the silica) may be the product of processes that have little to do with the original deposition. I don’t think that either theory should have to account for the present-day chemistry at Meridiani or Gusev primarily by invoking ancient processes, because we do not know how old that chemistry is or how deep it goes. Endurance Crater is being considered as if it were a fresh drill core but it has probably been part of the surface weathering environment for hundreds of millions of years. The deepest RAT hole hasn’t even reached through the material that is heated diurnally by the sun. The layered structure of the rock is certainly deep but the chemistry could be that of a weathering rind centimeters to meters thick. There is likely some of the original material present as reaction products but even considerable replacement is possible at the surface, which is all that we have seen. Kilometers of chemically complex dust has settled on these surfaces over Mars history in close contact with even more frost. In high-obliquity periods the surface may be covered with a thin layer of dirty snow that comes and goes annually.

The MERs have added very little to the STRUCTURAL evidence of bulk liquid surface water or near-surface groundwater. There are the ambiguous festoons at Meridiani, and the planar layering believed by the MER team to have resulted from many similar shallow flooding events on very level ground. The evidence of water CHEMISTRY, on the other hand, is overwhelming but the form in which the water acted is unknown as is the time period when the chemicals formed. I think that slow processes involving ice, vapor, adsorbed films, water of hydration and even possibly fleeting liquid capillary water from melting frost, might account for the chemical alterations. Without the chemical evidence, the structural evidence of persistent surface water would be completely unconvincing, even to the MER team I would guess. The two kinds of evidence should be considered separately because they are not equally reliable. The structural evidence of the layering tells us something about the process of deposition at Meridiani and Homeplate. The chemical evidence from the present-day surface may not tell us much at all about the time when the deposits formed.

Kye that was a good reasoned response. That fact is that we don't know all the circumstances in which this near surface water chemistry took place. We don't know for sure (not 100%) whether this was a very local occurrence or evidence of water chemistry in bulk. But the mere fact that we found this evidence within a few kilometers from the landing site suggests that it is rather common on the surface of Mars.

It certainly does not rule out impact surge as an explaination; but it certainly is not helpful to that hypothesis either. It proves that additional processes have altered parts of the surface since these layers were laid down. It certainly gives me confidence in what the MER team has suggested as the explanation at Meridiani too, simply by implication.

Yes, much of the MER team's evidence for their hypothesis is circumstantial. Yet, the circumstantial evidence keeps building. To rule out impact surge or confirm it, we need a prediction that can be tested by the rovers. I know science is not exactly a court of law; but many people are convicted upon mere circumstantial evidence. If the circumstantial evidence has substantial weight, then chances of error become very low. When circumstantial evidence is backed up by empirical evidence, it becomes very strong of a case indeed! In my eyes, the evidence of some sort of water chemistry occurring on or near the surface combined with the circumstantial found so far makes the case almost conclusive. At this point, I see no reason to doubt the MER teams's conclusions.

In my opinion, the impact surge or brine splat hypothesis maybe a contributing factor to the complexity of the geology on Mars. I don't doubt that, given the enormous number of visible craters on the surface. I do doubt the impact surge hypothesis as an explanation of the evidence found at Meridiani so far. Although very thin deposits would be possible with an impact surge, many are not that thin. In fact, we should have already seen evidence of some thick layers at Meridiani, if the impact surge explanation was even plausible. At this point even if we find thick layers laid down much deeper, it still will not rule out the current MER team consensus. It will only place constraints upon time frames for the various processes involved.

Kye - Thanks for your thoughtful and philosophical reply to this post. Let me try to answer it much more directly (although I may have already stated this in a previous post): As far as I can tell from the images, the silica-rich rocks are loose pieces sitting on top of the surge deposits, along with various chunks of highly vesicular (gas bubble-filled) and totally non-vesicular (bubble-free) rock. Therefore they need have nothing to do with the surge deposits. They and the other loose surface rocks most likely are random pieces of impact ejecta, of unknown ages, from unknown sources. The silica-rich rock presumably indicates some sort of hydrothermal activity, but whether associated with water (or ice) interacting with a volcano or associated with water/ice interaction with impact melt, would be impossible to say. The silica-rich rock, as another conceptual possibility, might have formed at low temperature by silicate rock reaction with sulfuric acid formed during sulfide weathering (my mine dump model), as a result of acid leaching of the more basic constituents (MgO, CaO, etc.). Again, not necessarily anything to do with the surge process. If a hydrothermal system had interacted with the surge deposits themselves, they would all most likely have been turned almost instantly into clay-rich goo, owing to their highly reactive and porous and permeable nature. Good question - I hope this was a good answer.

--HDP Don

Yes, that was a good answer Professor Burt. But much of these silica deposits are in the form of sand. So they cannot be ejecta pieces. A few silica rocks indeed have been found and could correspond to what you just stated. But the sand or dust like 90% pure silica require a longer term water based solution in my eyes.

I supposed it could simply be local because of hydrothermal activity; but that is similar to what the MER team has stated.

Your answer was helpful however. Thank you.

This thread seems to be decaying into the same non-specific objections by just a few people. Does this mean that everyone else reading this agrees with the reasonableness impact surge hypothesis, in light of Occam's Razor? In hopes of providing some fresh material for discussion, I attach, from March 2006, a detailed critique by Squyres et al. of our original 2005 Nature paper, and our point-by-point attempted rebuttal of that criticism. After sending the critique and our response out to two reviewers, Nature decided not to publish it (although they did publish a critique of the competing volcanic surge model). I therefore feel justified in "publishing" it here, as an attachment. This is particularly so because the Squyres critique (but never our response) was for a long time published on the Cornell website, here: http://www.astro.cornell.edu/~banfield/nature2.pdf (link since removed), without giving us any ability to respond. Also, the MER team has repeatedly used these highly dubious points (e.g. the spurious idea that Fe/Ni ratios in iron meteorites must match those in the spherules) in allegedly "refuting" the impact surge hypothesis in publications, even though, IMHO, we demonstrated these objections to be utterly without merit well over a year ago. Note: be aware that this pdf file (short and hopefully not too technical) is a time capsule from over a year ago. Our insights have evolved since then, in part owing to my past several weeks of highly useful discussions here.

One example of an insight not mentioned in the file is the simple fact that all the Meridiani spherules consist uniquely of the high temperature form of hematite - the blue/gray or "specular" (shiny) form. This, the main reason why Oppy landed in Meridiani, appears to provide unambiguous evidence against the low-temperature concretion hypothesis of the MER team. Although this point was as plain as the nose on my face, looking through my own eyes, I didn't see it for years, until I had discussed things on this forum (a form of mirror). Thanks.

Please enjoy or feel free to mock.

--HDP Don

Um, to what sand or dust of 90% pure silica are you referring? All I recall seeing in images are broken rocks (some of them quite tiny pieces, but no more than you would expect from breaking a weak piece of impact ejecta as it landed or grinding it under the rover wheels). None of the high-silica rock seems to be "in place." Thanks (and all for now).

--HDP Don

...Very interesting arguments Professor. Many of the issues brought up in the attachment have been discussed already, sometimes at length. It does give us a better idea of why you seem frustrated. Some of your counter-arguments are good.

I still have not changed my mind. But this discussion may be useful.

I must point out that silence does not indicate affirmation. Despite the common rumor among salesmen, many people simple don't want to argue. That does not mean that the customer actually agrees; they just don't want to create confrontation.

http://marsrovers.jpl.nasa.gov/gallery/pre...39_L257F_br.jpg

Sorry but there is no way that the rover could possibly crush these deposits to such fine grains. There are image examples where the rover has crushed some silica rocks. They don't resemble this at all.

Um, again (I came back online). Are those really silica rocks? They sure look like crushed subsurface sulfate efflorescences to me - something that Spirit has been seeing more and more of since it broke its wheel. Please don't confuse high-albedo soft sulfates with high-albedo hard silicates. (Or is it I who am confused?) Thanks.

--HDP Don

http://marsrovers.jpl.nasa.gov/gallery/pre.../20070628a.html

It is clearly marked as fine grained silica. This was the biggest and best discovery of the entire mission and it was very recent. I am correct.

Thanks for your kind comments. I am not asking you to change your mind - only open it.

As someone who has been teaching for a while, I am well aware that a class full of sleeping students does not indicate that they all agree with me. Sometimes I have to give them a quiz to wake them up. Inasmuch as you seem to have appointed yourself spokesman for the sleepers, how would you, for example, explain 1) the high-temperature (blue/gray) hematite in the blueberries, if they are actual low temperature sedimentary concretions, not to mention 2) why they are strictly size limited to 5 mm diameter, unlike actual concretions, 3) why they are not shaped like actual concretions, being generally perfect spheres, 4) why they never clump together like actual concretions (just the odd doublet or triplet of small spherules, explainable by natural stickiness and growth in a cloud), 5) why their distribution is apparently never controlled by fluid migration paths, inasmuch as fluid migration and mixing is how actual concretions form, 6) why they are characteristically nickel-enriched (keeping in mind the arguments in our Nature rebuttal), or 7) why similar appearing (albeit smaller) spherules are locally abundant at and near Home Plate, if that outcrop has an entirely different origin? Take as much time as you need, and feel free to work in groups. This is a take-home exam for the entire class. Good luck.

--HDP Don

You are quite correct about the quote (and my impression about sulfates, based on the image alone, was apparently wrong). I am still apparently correct that it is a loose soil, of unknown origin, sitting on top of whatever rocks lie underneath. If future investigations show that it is part of an outcrop, and not just an orphaned bit of soil, then its parentage will have possible genetic significance. Otherwise it's just another Mars mystery. But defininitely score one for your team.

--HDP Don

Well, I cannot speak for those who sleep. However, let me again state that the limited and consistent size of the spherules is your best argument--that in the absence of any known nearby volcanic source. That has bothered me from the beginning of the mission.

I cannot really explain it. My mind has been open all along.

Knowing how big some of the volcanoes on Mars are, I wonder whether the less gravity would allow surge clouds to travel much further than expected. But I cannot explain the distribution of the berries either. It doesn't seem to make sense--whether it is volcanic surge, impact surge, or concretions. I think there is a missing major piece of evidence that opportunity needs to find. Whether it will ever find such a piece of evidence is hard to say. Spirit did not find the silica until very recently, and only because of a broken wheel. Maybe Opportunity needs to lose a wheel in a place that it can dig deep too. I don't know where that could possibly be. Perhaps when it is inside Victoria.

Absence of objection doesn't mean evidence of support.

Doug

Well, I for one find all this very interesting, even though my lack of relevant knowledge means I'm a million miles away from actually holding an opinion.

Sadly, however, I note that we are now 'students' who have been given 'homework' and even for the brighter ones an occasional 'mark' !!! This is an excellent strategy for deterring rather than encouraging intelligent comment. Why oh why do you do it, dburt?

HDP Don,

One fact is missing from your class exam . As I mentioned earlier, we have shown on another forum that the size distribution of the berries is asymmetric, with a left-sided excess of particles. This has been consistently obtained for both MI and Pancam observations (*). I consider now this feature as correlated to the hard upper limit in size.
In your opinion, does the impact cloud condensation hypothesis, where the dropplet growth may be limited by gravity, fit with these observations ? I am anxious to get you comment on this particular point. Thanks.

denis

(*)
http://geocities.com/rlewis6/Spherule_Database.htm
http://www.geocities.com/jnelson351/statistics_paper.html
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1001.pdf

I was infamous for dozing off during lectures, but this one has kept my attention very well. To switch metaphors I think the brine splat hypothesis has gone the full 15 rounds and come out of its corner fighting every time. Certainly its true that it has been unfairly dismissed in some quarters. I would still say my gut reaction (and very possibly my earth bound predjudices) tell me that to account for several billion years of surface evolution with only one process is stretching even the best idea, but I can't find any specific objection. My gut, which is very talkative today because my brain knows little about either geology or chemistry, also finds the idea of a mars which is cold and slightly damp for a long time easier to digest than one which was recently warm and very wet. So congratulations Herr Professor, I'd say impact surge is a convincing alternative. I hope you can find time to post on some of the other discussions. I'd be very interested to hear your opinions on the features and processes of Titan for instance.

Brine splat stuff stays in this thread however.

Doug

I don't know if anyone has yet referenced the "Not a base surge" section at the end of
one of the MER papers presented at the Seventh International Conference on Mars.
I'm happy to see these issues formally addressed by the MER team. I see the arguments
as being in three categories:

1) "Regional geological context... no evidence for age-appropriate impacts of
sufficient size."

2) The berries: a) "Fe/Ni levels are inconsistent with such an impact origin."
b) "...spherules are dispersed across all strata, even at obvious erosional
surfaces..."

3) "Stratification styles" that "are most consistent with low velocity, subcritical
flows, characteristic of fluvial and eolian transport.

I have a hard time fitting the stratification models in my head, so I settle on
the berry distribution argument as the one I best understand.


HDP Burt, tell me where my reasoning is faulty here:

If there are layers, with erosional discontinuities in between, and the
distribution of berries across the layers and across the discontinuities
is even, what is the best explanation? That various base surge events
just happened to contain the same distribution of berries, or that the
berries formed after the layers were in place? I think the simplest
explanation is the second.

I think the berries forming after the layers were laid down is the simplest explanation too.

The more I think about it, the possibility exists that the missing clumped berries that Professor Burt asks about might actually exist. Opportunity may simply not have found a good example yet. If Meridiani is primarily a current aeolian erosion area, then most clumps near the surface might have been dispersed already. So the only realistic way to find these clumps is to dig.

The other problem is the apparent limit in size of the berries. Some quick change must have stop the process that created them. Perhaps the condition that created them was marginal at best. So the quick change didn't need to be as drastic and quick as it sounds. Perhaps in other areas of Meridiani there are much larger berries. We won't know until we visit those areas.

Edit: I know that Spirit has found some clumped berry like feactures in certain rocks. It was long time ago and it would take some time to dig the images out. But they are there. Gusev is not Meridiani. But Like I said previously...we still might not have found good examples of them at Meridiani yet.

I was looking thru Opportunities Micro-Imager files to find before and after images of the magnets on the rover. I found something very interesting that relates to the discussion of spherules.

They have been looking for the clumped masses of concretions that we have assumed were missing in this discussion. The MER team must have known that the spherules was their weakest point in the hypothesis. I now believe they have found good evidence of these missing clumped masses. I've found more than doublets and triplets in the files. I suddenly noticed that some of the larger spherules were actually composed of many many smaller spherules glued together!!! I was surprised to see that many clumped together. I have not gone through all the files yet. But I believe they have found plenty of evidence to provide the 'smoking gun' for their wet Meridiani theory. The MER team seems to be ready to provide the empirical evidence they needed.

Edit: Look in the May 2007 files for the Micro-Imager to see what I'm talking about. There are a LOT of images.

Dr. Burt,
One big difference between Earth and Mars is the presence of life here. Maybe the Martian concretions are how they would grow on a lifeless world, but here the growth is more irregular due to bacterial contamination in the water or sand? Perhaps in a lifeless environment concretions do not form as readily as here on Earth, so the volumetric density is not as high preventing conglomerations, and the growth is more even allowing for spherules instead of flattened discs?

http://www.daviddarling.info/encyclopedia/E/endolith.html

I guess that option doesn't reduce the number of "dead grandmothers", but it does open up some possibilities.

Has anyone tried creating concretions? I found a semi-crankish site on the web that said nobody has, but the tinfoil-hattery was everywhere (concretions and blueberries are formed by electric discharge!). It would be interesting to try to create concretions with well water (with appropriate added salts) and dune sand vs distilled water and sterilized sand.

Do we know how long the it takes concretions to form?

I hope you start you own thread as you mentioned.
This thread should just be for questions and comments
to Dr. Burt.

Only to provoke a response from you and Doug, and thanks to both of you for yours. Also, to misquote Arne in T2 again, "Of course. I'm a professorator." - I've been programmed, after 35 years. I can't help that. I just hope no extra grandmothers die during the quiz (if you followed the beginnings of this thread).

--HDP Don

Denis - Great question, and of course I am utterly unqualified to answer it. Luckily, my co-author Ken Wohletz filled with the gap (what else are co-authors for?) with an e-mail containing the following quote:

I did a sequential fragmentation/transport analysis on the referenced
data. To my surprise, the distribution of berry sizes is almost perfectly
described by an SFT distribution with a mode at -2.22 phi and
dispersion value of 0.39. Dispersion values greater than zero generally
indicate aggregation (rather than fragmentation); thus my results suggest
that his observations perfectly support an accretionary hypothesis.

It's all pig-Latin to me, but that definitely sounds like a yes for accretion. Contact him for more details. In a later message he added the following general words of wisdom:

I seem to get that one of the problems readers have with the impact surge
hypothesis is that thousands of layers of similar thickness seen in
Meridiani suggest thousands of surges all depositing similar layers. It is
very important to get across the idea that a single surge may wax and wane
hundreds of times at any single location during its runout, resulting in
deposition of numerous layers. This phenomenon comes from the breakdown of a
shock wave into a train of hundreds of waves because of shock reflections
off of the substrate, off of internal density contrast surfaces, and off of
each other. Think of thunder and how the sounds rolls, cracks, and rumbles
all from one lightning stroke moving through air of different density,
temperature, and moisture content. The flow regime in a surge is a response
to a pressure gradient, and that pressure gradient is analogous to a sound
wave. So just like thunder, some surges can be loud and short lived, while
others can be prolonged starting with a crack but followed by numerous
booms.

So yup, that's why we all need co-authors.

--HDP Don

Marsbug - Thanks for waking up, and thanks even more for the compliment. As for being profound about Titan, I'm already partly faking it here (as you may have noticed), so consider it unlikely unless I stick strictly to P-chem aspects (and even then you'd have to provide me with the relevant phase diagrams).

--HDP Don

Thank you Professor,

You finally addressed my biggest problem with the surge idea. You showed how it is not necessarily a problem at all.

If the surge made so many thin layers, then how would we distinguish between it and the wet Meridiani model?

It seems that Dr. Burt and his co-author are having some success in changing minds. I wish that more Unmanned Spaceflight readers would tell us where they stand.

Centsworth - Congratulations on doing independent research. I believe you're the first to mention that particular long meeting abstract (which appears to be the first ever to acknowledge the prevalent Meridiani interpretation as "a model"). Regarding your item 1) I seriously doubt this, inasmuch as relative age is assigned solely by superposition (what's on top of what) and the assumption of original horizontality. These assumptions work rather well for "wimpy" deposits deposited by wind and water (or for ballistic ejecta on the Moon). A large impact surge could completely cover low spots such as craters, giving them an apparently young crater count age, yet completely scour even slightly earlier deposits off the nearby heavily cratered highlands (as stated in a previous post to you), giving them an anomalously ancient apparent age relative to the nearby lowlands. Also, I imagine he is basing his size statement on 1) the wrong assumption that the Meridiani exposures had to result from a single large distant impact and 2) the conventional wrong assumption that impact deposits only reach about 2 crater diameters out. Models are only as powerful as the assumptions that feed them (classically known as "GIGO" - garbage in, garbage out). That's why I prefer stick with observations, where possible.

Regarding 2a), as stated in previous posts, even if the spherules are oxidized iron condensates (which we mentioned in 2005 as only one possibility among many), we regard their assumption that the Fe/Ni ratio in vapor-condensed accreted spherules has to match that in Fe-Ni meteorites as completely mistaken and misleading (see our unpublished Nature critique refutal attached to my post 170 above) - there is no conceivable reason why there should be a match. More to the point, despite special pleading to the contrary (see, e.g., abstract 3231 at the same meeting), they cannot explain why water-deposited hematite, containing only Fe3+, should be at all enriched in Ni2+, given that Ni2+ at Meridiani had so many other favorable crystalline sites to go to, such as the Mg2+ sites in Mg-sulfates or silicates. Look up, e.g., the terrestrial literature on the mineralogy of Ni-laterites (as I believe I mentioned in a previous post). This concept is called "partitioning" and in those terms, Ni2+ is "incompatible" in hematite (should never be enriched). Remember, you're talking about a couple of my supposed fields of expertise here (no co-author needed).

Regarding 2b), as stated in multiple previous posts, I regard the observed pattern of distribution of spherules at Meridiani as a far stonger argument AGAINST the concretion hypothesis than it is for it. Perhaps the author in question should do some more field work in the Page and Navajo sandstones (as I have been doing for the past 3 years), inasmuch as he has made these his favorite Meridiani analogs (apparently based largely on published articles). Actual hematitic concretions there, other than being round, little resemble his model - e.g., they're commonly concentrated and clumped at erosional surfaces. Let me know if you'd like photographic documentation.

Regarding 3) the "stratification styles" such as so-called "festoons" that are allegedly unique to wind and water - haven't we already beaten that one near to death in previous posts? (I'd be happy to try to put it out of its misery, but only if specifically requested).

Regarding the allegedly even distribution of berries - certainly not true at the large scale, and at the small scale I remain satisfied by my prior analogy of injecting them with sand into a turbulent jet exhaust (little reason to separate, and every reason to mix). Keep in mind that once berries are formed, later impacts could further distribute and mix them across an even wider area and thicker stratigraphic interval (as must have occurred at Victoria Crater, prior to wind erosion). If wind ever concentrated them as a lag at the surface, as today seen at Victoria, later surges could scour and mix them in with the rest of the particles. Of course, at the extreme far end of the surge run out, as things calmed down, they might well be concentrated as a lag along bedding planes, but even that seems not strictly to be required (as in a perfect condensation dump-out, for example). One shouldn't confuse what is sometimes seen in wimpy little volcanic surges with what might be expected big he-manly impact surges (with apologies to Arne and SNL). All you Ph.D. clastic sedimentologists, please feel free to contradict me - like any professor, I sometimes make this stuff up as I go along...

Regarding their hematitic composition (thanks for not bringing that up again too ), my co-author Ken Wohletz today shared these general words of wisdom:

It is not uncommon that volcanic accretionary lapilli vary in composition
with the matrix in which they finally reside; the reason being that they
have sampled a different portion of the ejecta plume than what is mainly
represented in the surge. Lapilli can form high in the atmosphere, fall out
into a moving surge, and experience horizontal transport before being
deposited. The "sampling" process involved with accretionary lapilli is
complex and depends a lot on electrostatic potentials that are in turn
compositionally dependent. Thus it is entirely possible that accretionary
lapilli can grow by preferentially accreting particles of a specific
composition. These results are covered by an experimental study done by
Schumacher a number of years ago.

More or less equal to what I randomly made up in response to previous posts, but in much fancier words. Ain't co-authors wonderful?

BTW, the morning session of this upcoming Friday the 13th in Pasadena seems to have some the most relevant MER presentations - sorry I won't be there. Perhaps some of you who will be can comment afterwards, or I can comment on some more of the abstracts. Apologies to the rest, this is all I have time for now.

--HDP Don

Here's a final one before I go home (before the subject gets completely lost in the crowd).

As regards Ken's pig-Latin in my post 198 about berry size distributions, here's some more pig-Latin from him in a subsequent e-mail:

I stand by my analysis but cannot vouch for the
quality of the data used. In fact in all my years of applying SFT to natural
samples, I have not seen one so perfectly explained by SFT than these
blueberry sizes.

The fact that the distribution is perfectly unimodal is eye-catching; most
natural samples demonstrate some degree of polymodality caused by mixing of
fragmentation and/or transport processes. The fact that the distribution
dispersion value (gamma includes sorting, skewness, and kurtosis) is
positive strongly supports an aggregation process (smaller particles
sticking together to form larger ones tends to make a distribution more
peaked with a decreased fine tail).

An aggregation origin predicts a rather limited size range, with a mode
giving a hydrodynamic equivalent for turbulent suspension in a multiphase
fluid. If one observes average blueberry size of 4 to 5 mm over a wide
range, then one might suggest that the bulk Reynolds number in surges was
fairly constant, a situation possibly coming from runout over a surface of
fairly constant surface roughness and elevation. Other hypotheses from surge
theory can also be tested. One I like is the self-limiting process of
deposition, which tends to keep Re steady in some surge runouts.

Hey, I didn't even make that one up out of whole cloth first (I couldn't even if I tried). All I can say is it sounds like the original poster should contact him ASAP about possibly writing a paper together...

Whatever happens, remember, you read it here first!

--HDP Don

My mind has not changed, just because I ceded one point of contention. The professor did not change his mind when he ceded one to me earlier. I never expected him to change his mind about his surge hypothesis. I also anticipated his response of the possibility of erosion of an ejecta piece in the area of home plate as an explanation for the silica sand found recently.

Just because something is deemed possible in one particular respect does not mean it is probable. It only adds a small amount of credibility to an alternative argument. It simply raised the scenario from the realm of impossibility in my mind to one of possible but unlikely. I'm sure the Professor feels the same way about his concession to my point. Yet, such concessions are expected, else this issue would not be given the room for argument on this forum.

A straw poll (and given the nature of forum software, such things are easily done ) of the two main rock formation theories would be an interesting thing. I think it's only fair to give HDP's hypothesis more airing time, and then we could do a poll to see which camp people fall down on.

Doug

Yes, Professor you have addressed the topic before. But you concentrated on how features observed coincided with those predicted by your surge hypothesis. That seems to make your scenario somewhat possible in those respects (I'm temporarily discounting objections for other reasons). But those same characteristics of those features also coincide with the MER team's explanation. Differences in interpretation of the same features cannot distinguish between the two competing theories.

What I'm looking for are distinguishing characteristics of your explanation that would not be present given the MER team's wet Meridiani scenario...or vice versa. This would offer a test to determine which hypothesis is more probable. A predicted distinguishing feature that can be observed would turn this argument away from a 'he said she said' like confrontation.

dBurt – back to the sulfates: You’ve stated often that you have a problem with the latest MER scenario that: “requires maintenance of a highly acidic aquifer in rocks containing basaltic materials” (unpublished response to response Knauth, Burt and Wohletz). You feel the neutralization capacity of the basalt wouldn’t allow this imbalance. You reference Zolotov 2005 to support of your point. However in a recent abstract of Zolotov (Lunar and Planetary Science 2007) the point is made that “acid weathering on early mars probably player a larger role……”. Apparently he doesn’t have a problem with longer duration acidic conditions. As you have pointed out by the presence of neutral salts, neutralization eventually occurs, but after what period of acidity? He also discusses the role of large impacts as a cause of acid weathering. Another abstract by Benison et al (Seventh Int. Conf on Mars) discusses the geochem and mineralogy of mars and makes a good case for extended acidic conditions even in the presence of mafic rocks. Do I hear the sound of rock hammers chipping away at this once solid foundation ?

"the other don"

HDP Don re#190,195

Thanks so much for your input. Looks like our questions encounter a resonator with Dr Wohletz . I would like to know to which data on berries sizes he is refering to. I will try to figure out what is the significance of his SFT distribution parameters (phi, dispersion), as compared to our more conventional ones (mean, skewness). What impress me is his statement for a signature of an accretion scenario.

denis