[X] My Assistant

[dburt]

Would someone please tell me where the "Festoons in cliff at Cape St. Mary?" thread went. I wanted to comment, but I can't find it. Was it merged with another discussion?

Yes. Doug moved it over to the "brine splat" thread in Mars, General, because it seemed to be casting doubt on prior interpretations of the intricate cross-bedding in the cliff. Please do comment.

--Don

[CosmicRocker]

Thanks, Doc. Doug does a great job managing this crazy place, but I wouldn't have moved those few comments into the brine splat discussion. I see small scale sedimentary structures in Cape St. Mary, and maybe some festoons.

I've been staying out of that brine splat fray because I would have to post tens of comments, but I have noticed that you are fighting an epic battle there. I don't know where you find the energy, but you do seem to be teaching a few folks that it is not easy to define the geologic environment of rocks that were formed on another planet several billions of years ago.

I'm really having a difficult time fitting the impact surge concept to Meridiani, but I do agree that impact surge deposits should be relatively common in Martian rocks.

[don]

Don - as a graduate of the ASU Geology Dept. (82) and former student of yours it's great to see Arizona State mentioned in the many recent contributions and discussions of mars. With Greeley as my advisor and the likes of Christensen roaming the halls, its hard not to look back and be proud of the accomplishments. I've sat in on a few of your presentations (and posters) over the last few years at meetings such as GSA and its humerous to see how fast you can raise the hackles of some of the MER team members. Your "mine dump" talk in Phily last year for GSA was especially interesting, Grotzinger if a remember correctly had a few "issues" to deal with. The mine dump analogy, while sounding off-beat, is right on in my opinion (but where is the sulfide). If anyone can think "out of the box" its Knauth and yourself, good luck with this idea. Personally, I'm more main stream, but I do have problems explaining the blended salts of Endurance.

[dburt]

I'm struck by the pictures and diagrams that do look similar to what the MERs have seen.
I hadn't fully appreciated that this sort of material existed prior to the MER mission. It
gives the whole base surge theory a kind of predictive quality as opposed to reactive.

The picture on page 292 really struck me. The first I had ever heard of a volcanic "bomb" was
when the one at Home Plate was described. This picture looks like my second exposure to
a "bomb". Strangely though, I don't see specific mention of it in the text.

Thanks for your comment on"reactive" vs. "predictive". Yes, the impact surge hypothesis predicts that spherule-containing, salty, cross-bedded deposits similar to those at Meridiani should be common on Mars, given that impacts (plus wind) have for the past 3.8 billion years or so been the only active geologic processes on Mars that could affect any area at random. In addition there were local major inputs from basaltic volcanism, a process that waned rapidly, but probably continues, brine flow at low elevations (outflow channels), a process that likewise seems to be continuing, at least at a very local scale (=young gullies - we predicted these should be highly enriched in chloride salts in 2002 and 2003), and glaciation (rock glaciers, especially), and perhaps others. More speculatively, if you accept the late heavy bombardment (LHB) scenario, the impact surge hypothesis also predicts that the kilometer or so of sediments beneath Meridiani might contain part or all of the sedimentary history (geologic record) of the near-destruction of a water-rich planet, including a record of impact-derived planet-wide rainstorms or snowstorms, if they occurred. The complex MER team hypothesis predicts little, inasmuch it appears to have been entirely reactive, applied only to that specific area and horizon, and required a sort of localized "Death Dalley Days on Mars" wet, warm scenario. (Of course, strictly speaking, the impact hypothesis was inspired by, and depended on rover images of those same horizons.)

Regarding vocanic bombs and bomb sags - they are highly typical of a certain type of surge deposit, which is perhaps why the bomb sag in the photo wasn't specifically mentioned. This type of "hydrovolcanic" deposit is caused by molten basaltic magma explosively meeting subsurface or surface water, and the volcano involved will usually toss out, via steam explosions, numerous solid blocks and blebs of molten lava (which blebs harden in the air to form a streamlined "bomb") at the same time it is making the surge deposit. If the particles are particularly wet and sticky, owing to an excess of water, the resulting surge deposit forms a distinctive conical "tuff cone," of which Diamond Head in Honolulu, Hawaii, is a fine example (the water involved was sea water). If ground water is less abundant, the steam typically just blows a crater ("maar") in the ground, surrounded by a more diffuse "tuff ring." Kilbourne Hole, New Mexico is a good example of this type of deposit. What puzzles me about the MER team calling "Home Plate" a tuff ring is that there appears to be no associated maar (i.e., no explosion crater) nor any tuff cone either. Also, if you see one bomb sag, you commonly see a dozen others nearby (whereas only one has yet been imaged). The "maar" type of surge deposit is usually quite limited in extent (a few kilometers across) with a rapid decrease in grain size from meter-sized blocks down to sand-sized particles as the distance to the volcano increases. The uniformly fine grain size of the Home Plate surge deposit suggests either that it all formed rather distant (meaning a few km) from the volcano, or it may be a different type of deposit. We suggest, of course, that it might be the erosional remnant of another impact surge deposit, with the single apparent bomb sag representing a hit by a piece of ballistic ejecta from an impact. Hopefully Spirit will last long enough to clear up that mystery, mentioned also in an earlier post.

[dburt]

Don - as a graduate of the ASU Geology Dept. (82) and former student of yours it's great to see Arizona State mentioned in the many recent contributions and discussions of mars. With Greeley as my advisor and the likes of Christensen roaming the halls, its hard not to look back and be proud of the accomplishments. I've sat in on a few of your presentations (and posters) over the last few years at meetings such as GSA and its humerous to see how fast you can raise the hackles of some of the MER team members. Your "mine dump" talk in Phily last year for GSA was especially interesting, Grotzinger if a remember correctly had a few "issues" to deal with. The mine dump analogy, while sounding off-beat, is right on in my opinion (but where is the sulfide). If anyone can think "out of the box" its Knauth and yourself, good luck with this idea. Personally, I'm more main stream, but I do have problems explaining the blended salts of Endurance.

Other Don - Thanks for the minor vote of confidence. I'm certainly not trying to raise anyone's hackles, just get a word in edgewise with an alternative, more logical, and possibly more useful interpretation of the very same data. Your question "Where are the sulfides?" (to form jarosite) is an excellent one and I'd rank it right up there with Shaka's "Where are the coarse ejecta?" (as you might guess, we've asked ourselves the same questions). Some of the possible answers I've come up with include the following: 1) Mine dump-type damp, oxidative weathering can dispose of most iron sulfides within 50-100 years or less (usually with help from microbes); Mars has had nearly 4 billion years to get rid of sulfides at the surface. 2) Minor sulfides have been found both in Mars-derived meteorites and, I believe I've read, by the Spirit rover. 3) Roger Burns suggested that the sulfides would be magmatically concentrated in massive deposits of Fe,Ni sulfide at the base of lava flows or in magma chambers; impact would shatter or melt or vaporize these, so that survival in the surge deposits would be unlikely. 4) Rather than the little cubes that pyrite (fool's gold, FeS2) leaves on many terrestrial mine dumps, the main sulfide mineral involved on Mars would probably be pyrrhotite-pentlandite or (Fe,Ni)S, which phase generally does not form well-shaped crystals. Weathered-out pyrrhotite blebs in lava might be easy to mistake for gas-bubble type holes in lava. 5) The jarosite reported from Meridiani could previously have been reworked multiple times via multiple impacts, after moist oxidative weathering formed it - so that all signs of its parentage have been lost. 6) Jarosite could also form from oxidized sulfur species (mainly SO2) in the damp impact surge cloud - it need not have a sulfide precursor, except perhaps at the impact site. In presuming sulfide weathering, we were merely following the original "gossan hypothesis" of Roger Burns, as modified for impact. Leave the sulfides out, if you prefer - the impact surge hypothesis does not depend on them.

There! Is that enough sulfide excuses for you?

Regarding my "mine dump" talk at the Geological Society of America Meeting in Philadelphia last fall, the MER team member in question stood up at the end, in front of a large number of witnesses from the Planetary Geology Division, and tried to heckle me, by loudly proclaiming that he and SS had never stated that there was a shallow sea or lake at Meridiani, and that I should "stick to what was published in peer-reviewed literature". I mildly replied that I thought I had. After getting back to Tempe I naturally looked up the original 2004 Science article by Squyres, Grotzinger, et al. and on p. 1714 I found "the area on which these aqueous sedimentary and diagenetic processes operated was at least tens of thousands of square kilometers in size" and "Terrestrial analogs...include...playa lakes and sabkhas adjacent to marginal seaways." If that isn't an extremely strong implication (if not direct statement) of shallow seas or large lakes, I don't know what is. Therefore, one can hardly blame Science reporter Richard Kerr (who at the same meeting had just won the GSA Public Service Award for his excellence and accuracy in science reporting) for inferring only two weeks after the original publication (Science, 2004, p. 2010) that they were talking about "the salty, rippled sediments of a huge shallow sea" when Science Magazine declared this "discovery" to be its 2004 Breakthrough of the Year. Did Grotzinger mean to imply that reporter Kerr and the distinguished editors of Science Magazine were utterly mistaken? If so, he did not correct them. Of course his outburst was irrelevant to the main point of my talk, that no reservoir of liquid sulfuric acid of any kind was likely on a basalt-dominated planet (simply because bases neutralize acids in aqueous solution).

This initial 2004 "by the seaside" (or lakeside) iteration of the Meridiani hypothesis in Science was by 2005 replaced by the familiar "bouncing aquifer" version in Earth and Planetary Science Letters, in which the unlikely salt mixture had been wind transported from an original vanished playa or sabkha and then various brines conveniently rose in stages from underground, flowed vigorously across the horizontal sandy surface, and sank immediately back out of sight, meanwhile mixing freely, as required, with various other brines underground to make concretions and dissolve larger crystals (or at least that's my possibly faulty understanding of the basics of the current hypothesis, as summarized in my earlier post). Hey, if the initial interpretation was refined as new data became available, why was that something to deny at GSA?

[CosmicRocker]

Ok, I didn't want to get into this debate just yet, but I suppose I was asking for it by posting that relocated comment in the wrong thread. I'll start out by asking "why would the suggestion of festoon cross laminations observed in Cape St. Mary contribute to this argument?" It seems to me that it would be more difficult to explain such small scale sedimentary structures embedded within larger scale sedimentary structures with a surge model. My apologies, if I forgot something discussed earlier.

[MarsIsImportant]

I agree with CosmicRocker.

Although I can see how evidence of Impact surge could be common on Mars, I hardly see it as the only one. IMHO the impact model doesn't fit well with Meridiani--particularly in isolation. There are simply too many signs of both wind and water type erosion and deposition on the these plains. The lack of course material and sulfides cannot be discribed as minor problems. The fact that high rates of oxidation would be required for the surge process to explain what has been observed suggests massive changes in the Marsian environment every bit as complex and messy as anything that the MER team has proposed.

Let's face it. The Marsian environment has changed dramatically. The question is how. IMHO, the fact that massive amounts of water ice have been discovered in the subsurface and polar regions of Mars requires that when the KISS principle is used water in some form or another must have actively participated in the geology of part of the Marsian surface at sometime when the atmosphere was likely much thicker. IMHO, denying the impact of water based processes on early Mars would be a stretch of the imaginiation. There is simply too much of it.

With so many visible impact craters, it is also hard to deny the likely impact of surge processes over large parts of the surface. I just don't think one model alone can explain all the observations...when the evidence to supposrt any one model is marginal at best. All this combined highly suggests that complexity is closer to the truth. So in this case, the KISS principle when properly applied is not nearly as simple as we might want it to be.

[don]

dburt - not that I’m a “brine splat” or “mine dump” groupie or anything like that but I do recall a question you asked following a MER member presentation at GSA in Salt Lake City a few years ago that raised some reflexive hackles. The question you asked was reasonable and the presenter responded quite persuasively with an explanation singing praises for eutectic brines (or something like that). Yet when you responded by the way (I paraphrase) I’m the one that introduced the concept of eutectic brines to mars the presenter realized who you were and immediately became defensive and curt. That moment for me stood out because it became evident (to no surprise) that it’s difficult being outside looking in when it comes to the MER project, if you don’t tow the party line you can be viewed as a non-friendly.

Regarding sulfide - in the recent (2007) Sqyures et al “Pyroclastic Activity at Home Plate in Gusev Crater Mars”, it’s mentioned that the rock “Fuzzy Smith” had a unique MB Fe mineralogy that’s consistent with a Fe sulfide such as pyrite or marcasite (evidently not detected in any other martian rock). Unfortunately the composition or oxidation state of the Fe was not determined and a sulfide confirmation could not be made. An interesting remark nonetheless.

the other don

[Kye Goodwin]

Doctor Burt, Thanks very much for doing this. I have been defending the impact-surge explanation of Meridiani since late 2004 on another Mars forum. I have never been able to find out enough about volcanic surge from references on the net. That big technical paper of Ken Wolletz that you linked here adds much to what I have been able read on the subject but doesn't answer the following question.

In the Mer team Science publications of Dec 2004 single-particle layers were identified in the strata of Eagle Crater. I think that these were explained as an aeolian phenomenon affected by moisture. I have never been certain of this, but in some images of layered surge exposures that I have seen, it appears that single-particle layers are fairly common. I have never read anything that explicitly confirms this. Are single-particle layers a feature, maybe even a distinctive feature, of surge lamination?

[centsworth_II]

...it’s mentioned that the rock “Fuzzy Smith” had a unique MB Fe mineralogy that’s consistent with
a Fe sulfide such as pyrite or marcasite (evidently not detected in any other martian rock)....

I remember that Steve Squyres expressed an interest in going back to Fuzzy Smith
when Spirit got back to Home Plate after the winter. But he specifically referred to
high silica content as the reason. This was before the discovery of "silica valley" so
I wonder if they would still make a point of going back.

[dvandorn]

I was just thumbing through Squyres' "Roving Mars" again recently, and ran across something that I had thought I remembered.

For quite a good time (several weeks), Steve himself kept holding on to the notion that the layered rocks in the walls of Eagle crater were some type of welded tuff. As I understand it, Don is basically proposing that these rocks are, in fact, a form of welded tuff.

The vugs and especially the formation of concretions within the rock layers (as opposed to disturbing or displacing the rock layers) were the factors that changed Squyres' mind. That and the fact that the blueberries were of rather different composition (i.e., hematitic) than the rock in which they were embedded; the question that begs an answer is why *any* basal surge (volcanic or impact) would deposit simultaneously two populations of materials, each very different from the other. The compositional differences were sort of the nail in the coffin as far as Squyres was concerned.

Don, I don't think I've yet seen you address the question of why the blueberries would be so well distributed within the fine suplhate-rich layers and yet be of such different composition from them if these rocks were laid down by the same surge process. Wouldn't the mixing that occurs within the surge cloud, and the tendency for items of like mass to travel like distances (and of unlike mass to travel unlike distances) tend to sort out the gravels from the fines? An atmosphere would only tend to accentuate such sorting, I would think.

I just don't think we're seeing the kind of sorting one would expect between the heavy hematite-rich ferrous gravel and the sulphate-rich salt fines.

Also, how does the impact surge theory account for the apparent "feeder" formations into blueberries still in place -- small stalks of blueberry-like material leading in random directions from many of the in-place berries? These make sense if you picture the berries as concretions, formed by water flow within microfractures in the salty rocks. I don't have a feel for any inherent process in a surge that would account for them.

-the other Doug

[dburt]

Ok, I didn't want to get into this debate just yet, but I suppose I was asking for it by posting that relocated comment in the wrong thread. I'll start out by asking "why would the suggestion of festoon cross laminations observed in Cape St. Mary contribute to this argument?" It seems to me that it would be more difficult to explain such small scale sedimentary structures embedded within larger scale sedimentary structures with a surge model. My apologies, if I forgot something discussed earlier.

CosmicRocker - Thanks for joining this discussion. Well, so far 3 people, including you, have chimed in agreeing with me that those look like "festoons" in the middle of the Cape St. Mary cliff, and none have disagreed, so apparently I wasn't, in my highly biased way, just seeing things. It has been claimed by a certain member of the MER team that these are an unambiguous record of little current ripples (like tiny sand dunes) that uniquely indicate water that was locally flowing vigorously ankle- to waist-deep across the flat surface of Meridiani. We have begged to disagree about the significance of these features, and even about their actual presence. Most look much more like a topographic artifact, caused by the downward viewing angle, as discussed in a previous post: Imagine yourself standing behind a person wearing horizontally striped trousers, and looking down at their posterior - you will see perfect "festoons" every time - UU.

The MER team, as far as I am aware, has been stating for the past 6 months or so that the cross-bedding in the Victoria cliffs uniquely indicates a record of aeolian (wind) deposition. Do you possibly see a consistency problem with having "festoons" in the middle? Does it in general sound reasonable to you that water (a sort of miracle brine) came gushing out of the ground, flowed ankle-deep to waist-deep across a level sandy interdune playa (an oasis among the dunes in the desert), leaving local little current ripples and absolutely no other record, and then sank back into that same reservoir? Can you explain why this artesian water flowing across water-saturated sand didn't simply form a braided stream deposit (dozens of tiny channels branching and rejoining as they flow leisurely across a plain), which is what 99.9999% of terrestrial streams would do under the same circumstances? Sorry for answering a single good question from you with so many more from me, but then I hope the answers to my questions are obvious.

The answer to your question is, no, I seen no problem with a huge variety of features, ranging from dune-like to ripple-like, occurring in a single cliff face that exposes surge deposits. The extreme turbulence (violence even) and rapidly changing conditions (including stickiness of particles) allow for far more variety than would be expected in a simple blowing-wind- or flowing-water deposit. The Victoria cliff exposures and their intricate, inconsistent bedding patterns therefore strike me as typical surge deposits.

Those so-called festoons are the only evidence ever cited for flowing water on this part of Mars. IMHO (as mentioned in an earlier thread), it's as unlikely to have such flowing water on a horizontal surface is it is was to have a puddle at a 20 degree inclination on Burns Cliff (as discussed prior to my participation here).

In deference to the other Don who started posting here before me, I'll henceforth refer to myself as

--HDP (for Herr Doktor Professor) Don

[tdemko]

Like Tom, I've been lurking as this excellent discussion has progressed, but I now have to comment on what Don/"HDP" wrote in his last post regarding "festoons". As I've mentioned before, I never use this term, and it really has been out of fashion in clastic sedimentology for quite a while. We have better terms that more exactly speak to the scale and geometry of cross bedding and cross lamination.

What I see in the images in question of Cape St. Mary, at this distance, are large (meter) scale trough cross beds bounded by truncation surfaces. Other views of the other capes have also shown evidence of deflation or other more regional truncation.

What I interpret as having been called "festoons" in the past are either current or oscillation ripple cross lamination that is on the centimeter scale. Without better exposures that show more dimensions of these features, it will be difficult to definitively interpret their origin. The key features that I would like to examine would point to angle of climb, preferred current direction, foreset asymmetry etc. The clotty, recrystallized nature of the rocks in close-up photos of these features also makes "remote sensing" difficult.

Don Burt has provided some good references on the theory and some of the sedimentological features of base surge deposits, which include both cross lamination and cross bedding. However, bedforms are bedforms, no matter what the fluids and particles may be (channeled scablands to mud puddles). Allen's seminal work on the signal importance of flow separation phenomena on bedforms and resultant cross stratification is required reading for any and all interested parties, and Dave Rubin's visualizations are also very educational.

I am looking forward to even higher resolution close-ups of the Victoria cliff faces. If we start seeing grain-flow tongues and grain-fall drapes at the toesets of the large-scale trough foresets, an aeolian interpretation will certainly be preferred.

[dburt]

There are simply too many signs of both wind and water type erosion and deposition on the these plains. The lack of course material and sulfides cannot be discribed as minor problems. The fact that high rates of oxidation would be required for the surge process to explain what has been observed suggests massive changes in the Marsian environment every bit as complex and messy as anything that the MER team has proposed.

Let's face it. The Marsian environment has changed dramatically. The question is how. IMHO, the fact that massive amounts of water ice have been discovered in the subsurface and polar regions of Mars requires that when the KISS principle is used water in some form or another must have actively participated in the geology of part of the Marsian surface at sometime when the atmosphere was likely much thicker. IMHO, denying the impact of water based processes on early Mars would be a stretch of the imaginiation. There is simply too much of it.

With so many visible impact craters, it is also hard to deny the likely impact of surge processes over large parts of the surface. I just don't think one model alone can explain all the observations...when the evidence to supposrt any one model is marginal at best. All this combined highly suggests that complexity is closer to the truth. So in this case, the KISS principle when properly applied is not nearly as simple as we might want it to be.

MarsIsImportant - Thanks for chiming in. You haven't asked a specific question, which makes me uncertain how to respond. Perhaps I'll blather a bit, like you. First, as I stated at the very beginning of this thread, please don't confuse me with Nick Hoffman and his "white Mars" scenario. As far as I'm concerned, you can have all the wind and water and climate change you like on Mars. Just be aware that surge deposits, in their considerable variety, can mimic nearly perfectly a huge variety of features generally described as being typical of (or even unique to) wind or water. Also be aware that, since the end of heavy bombardment (late or not), Mars scientists overwhelmingly agree that the dominant Martian climate has been very similar to that which we see today (with perhaps short excursions variously attributed to obliquity variations, underground brine outflow, volcanism, or impacts). The Meridiani "oasis" thus appears to be something of an anomaly, which is why it interests so many people. (Its high-temperature or "gray" hematite signature was an anomaly from orbit, which is why Oppy landed there.)

Our impact interpretation for the Meridiani (and Home Plate and, tentatively, other salty cross-bedded) deposits implies that they need not indicate either wind or water. No one argues that the soluble salts indicate water (a brine) in the past - the only argument is over when in the past. The impact hypothesis argues that the salts could be considerably older than the deposits in which they are found. After we had pointed out that the unlikely Meridiani mixture of salts that were both soluble and insoluble, and acidic and neutral was incompatible with a simple evaporation (playa or sabkha - marine salt flat) model, the MER team modified their model to include wind transport and mixing of older salts. (Then one of them, in what could be perceived as an attempt to heckle or intimidate me, vehemently denied having done so, in front of the entire Planetary Geology Division of GSA - as brought up by an eyewitness yesterday. A year earlier SS had argued to reporters that our Nature paper was worthless because we weren't aware of - and therefore didn't address - the latest changes to their model. Whom to believe? Did they make changes to their model or not?)

I won't argue with you that Mars is complex. Occam's Razor (or the K.I.S.S. principle) is useful only in deciding among competing hypotheses (preferably physical ones involving neither biology nor biochemistry), not as a general description of natural processes. You seem to be accusing me of misusing it. I don't think I am. Nevertheless, I'll freely admit that my personal prejudice is that Mars geology is probably considerably simpler than Earth geology (and more complex than lunar geology). The problem is that we all wear terrestrial "blinders" and cannot always recognize the stark, beautiful simplicity of Mars when we see it.

--HDP Don

[dburt]

dburt - not that I’m a “brine splat” or “mine dump” groupie or anything like that but I do recall a question you asked following a MER member presentation at GSA in Salt Lake City a few years ago that raised some reflexive hackles. The question you asked was reasonable and the presenter responded quite persuasively with an explanation singing praises for eutectic brines (or something like that). Yet when you responded by the way (I paraphrase) I’m the one that introduced the concept of eutectic brines to mars the presenter realized who you were and immediately became defensive and curt. That moment for me stood out because it became evident (to no surprise) that it’s difficult being outside looking in when it comes to the MER project, if you don’t tow the party line you can be viewed as a non-friendly.
the other don

Other don - Thanks for the exact reference to the Spirit reporting of sulfides. It sounds like you were lucky enough also to be an eyewitness to my very first scientific encounter with the MER team member you mentioned in your last post, only a year earlier. After his GSA talk (which dealt with the team's new "vanished playa" modification to its earlier "playa" model - so I was quite aware of this modification well before its publication in Earth and Planetary Science Letters, contrary to claims made afterwards by SS) I asked the speaker, quite reasonably I thought, why the possibility of brine freezing was apparently excluded from consideration, given that Mars is such a cold planet (i.e., why the "Death Valley/Persian Gulf Days on Mars" story, instead of, say, making analogs of the permanently frozen, highly saline lakes of the Antarctic Dry Valleys). He replied, as I recall, that "because the brines are eutectic, we don't need to worry about them ever freezing". I was astonished nearly speechless by this statement, inasmuch as, 1) as I blurted out, Knauth and I had co-authored the 2002 Icarus paper "Eutectic brines on Mars..." which seemed to freak him out a little - at that time we had never met, and 2) he didn't seem to have the least idea how eutectic brines actually form. As I explained to him and SS in a later e-mail, by definition, the only way to make a eutectic brine is by freezing (or melting) - it is the last tiny little bit of brine left after fractional crystallization of all the solids, including ice and various salts (hey Ma, can you tell who'd been teaching igneous and metamorphic petrology for the previous several years? ). For the record, no reference to "eutectic brines" has ever afterwards found its way into the Meridiani literature, not even in meeting abstracts or talks.

Sorry about telling that story (no Ma, really ). You gave me the obvious opening, and I couldn't resist. The utter misapplication of the term "eutectic" (I think he meant to say "all-salt saturated" or some such) certainly didn't inspire confidence in his infallibility as a sedimentologic super-authority. Nevertheless, rather than dissecting personalities (to which I'm as vulnerable as the next person), I'd really much rather keep this thread devoted to a semi-scientific dissection of that horrible, awful impact surge hypothesis, if you don't mind. As a starter question, are there any observed features of Meridiani that CAN'T be explained by that horrible, awful impact surge hypothesis?

BTW, Phoenix is supposed to get up to 116 F (47 C) tomorrow, for the holiday. Does that sound a lot like Mars to anyone?

--HDP Don