Sedimentary Geology at Meridiani Planum

[paulanderson]

See also my new thread posted here, with more links including comments from Squyres:<br /><br /><b>The Great Meridiani Debate</b><br />http://uplink.space.com/showflat.php?Cat=&Board=sciastro&Number=410965&page=0&view=collapsed&sb=5&o=0&fpart=<br /><br />The new proposed scenarios used previous MER data, not the updated findings announced recently (re groundwater), according to Squyres, and the MER team is still confident that volcanoes or impacts have been ruled out.<br />

 

[telfrow]

Paul:<br /><br />I just saw that. We apparently posted at exactly the same time. <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>

 

[paulanderson]

Yep, and I'm sure this will provoke a bit of discussion, too, of course...!<br />

 

[JonClarke]

Oh no, not the dreaded brine splat hyothesis!<br /><br />Knauth, Burt, Wohletz are simply wrong, on mutiple counts, IMHO.<br /><br />Base surge deposits are also well known from volcanic deposits. They are characterised by:<br /><br />Scour - present at Meridiani<br /><br />Low angle ripples - poorly developed<br /><br />Reverse dunes - absent<br /><br />Graded beds - no good examples<br /><br />Poor to moderate sorting - Merdiani sediments are moderate to well sorted<br /><br />Large fragments that have dropped into the sediments(bombs) - absent<br /><br />Salt lake sediments are:<br /><br />Moderate to well sorted - present<br /><br />Contain salt minerals - present<br /><br />Show teepee structures - present<br /><br />Can have wave and current ripples - present<br /><br />Can have internal scours - present<br /><br />Show ineternal salt reaction fronts and chemical grading of salt minerals - present<br /><br /><br />So overal the features of the Burns formation are far better explained by the salt lakes than base surges.<br /><br />Some other issues: <br /><br />The brine splat model presumes evaporation to form the brines in the first place. The best way to do this is a lake. You then need an impact into the lake to generate the base surge. So the hypothesis is unnecessary complex without any evidence to support a complex explanation.<br /><br />The different salts are not an issue (and the authors should know this). The salt chemistry seen by the APX (a very blunt tool for this sort of thing is) both integrated over a large area and does not differentiate between salts formed at different time. We know that the Burns formation has a complex diagenetic history - initial formation of salts, partial leaching of those salts, haematite precipitation, and weathering. This is a great way to get a whole host of incomapatible chemistries and mineralogies.<br /><br />Bedding in the Burns formation is cm to 10's of cm thick. An impact might generate a few such horizons in a sedimentary succession. We m <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

There are two papers in Today's issue of Nature looking at relatively dry explanations to the Meridiani sediments.<br /><br />The first is; "Impact origin of sediments at the Opportunity landing site on Mars", by L. Paul Knauth, Donald M. Burt and Kenneth H. Wohletz, Nature 438, 1123-1128<br /><br />Abstract <br /><br />"Mars Exploration Rover Opportunity discovered sediments with layered structures thought to be unique to aqueous deposition and with minerals attributed to evaporation of an acidic salty sea. Remarkable iron-rich spherules were ascribed to later groundwater alteration, and the inferred abundance of water reinforced optimism that Mars was once habitable. The layered structures, however, are not unique to water deposition, and the scenario encounters difficulties<br />in accounting for highly soluble salts admixed with less soluble salts, the lack of clay minerals from acid–rock reactions, high sphericity and near-uniform sizes of the spherules and the absence of a basin boundary. Here we present a simple alternative explanation involving deposition from a ground-hugging turbulent flow of rock fragments, salts, sulphides, brines and ice produced by meteorite impact. Subsequent weathering by intergranular water films can account for all of the features observed without invoking shallow seas, lakes or near-surface aquifers. Layered sequences observed<br />elsewhere on heavily cratered Mars and attributed to wind, water or volcanism may well have formed similarly. If so, the search for past life on Mars should be reassessed accordingly."<br /><br />The other is:<br /><br />"A volcanic environment for bedrock diagenesis at Meridiani Planum on Mars." Thomas M. McCollom and Brian M. Hynek, Nature 438, 1129-1131.<br /><br />Abstract<br /><br />"Exposed bedrocks at Meridiani Planum on Mars display chemical and mineralogical evidence suggesting interaction with liquid water. On the basis of morphological observations as well as high abundances of haematite and sulphate mineral <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[robnissen]

Jon,<br /><br />That was just a tremendous post, concise, interesting, well-written. I, for one, really appreciate your sticking around here. A lot of the scientists that used to post here, have been driven off by the ridiculous drivel that too many spout. (Where have you gone, Joe Dimaggio, er... Alex Blackwell.) I'm so glad you have decided to stick around. I always look forward to your posts, and I look forward to reading many more. <br /><br />Edit: I see you have just posted a second time on this topic. Also interesting, well-written, etc. But I was referring to your first post, I really liked the way how you laid out that the data much better fit a wet history, than a dry history.

 

[telfrow]

I"ll second that. That's the reason I posted the articles in Jon's thread. <img src="/images/icons/wink.gif" /><br /><br />Thanks for the insights, Jon. <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>

 

[JonClarke]

The fact that people find it interesting is one reason I post here <img src="/images/icons/smile.gif" />. I am debating whether to submit a letter to Nature on this, but I suspect I will have to stand in line.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[silylene old]

Interesting ! <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[paulanderson]

I had linked to those already in the other thread also (linked previously), but good to see the abstracts copied here too. I appreciate your input on all this as usual, and personally I am still on the side of MER / Squyres.<br /><br />I've also posted comments from Squyres in the other thread, for anyone who hasn't seen them yet (in Space.com article) and, as we could guess of course, he is in complete disagreement...!<br />

 

[jatslo]

I have issues with the shallow water hypothesis.<br /><br />[1] Elevation of detected layers suggests to me depth.<br /><br />[2] Geological signatures of rather large ice burgs, that when one does the research, less than 7% of a burg is visible above the surface of the water. Some of the ice burg's, if in fact, are humongous. We are talking hundreds maybe thousands of feet deep when constructing topography that is relative to these obvious geological features. For instance, Ice burg's the size of New York; do the math. <img src="/images/icons/smile.gif" /><br /><br />[3] Need I say more?

 

[bonzelite]

many structures could be due to lightning strikes. vallis marineris could be a gigantic electrical scar. as it really in no way resembles a water-carved structure if you really study it. throughout mars, too, many crooked rille patterns that look like dried, narrowly cut, water channels follow electrical machining patterns. <br /><br />it's nonetheless interesting that they are going with an impact idea for myriad structure creation. it sort of fits, actually, in a certain way. the planet is scarred heavily with impacts of all ages, particularly in the southern hemisphere. <br /><br />i still believe in episodic, albeit very brief, sort of outflow spray events. as well, Hartmann's book very quickly establishes Mars as a planet with EXTENSIVE subsurface ice throughout the entire planet, a sort of super-tundra planet. with the ice in Mars' case being much farther down, then being very near the surface to surface level at higher latitudes near the poles. <br /><br />in a manner of speaking, he goes into tectonic-like activity of massive subsurface ice sheets. <br /><br />get the book!<br /><br />

 

[JonClarke]

The parable of the blind sages and the elephant is very apropros here! the picture is complex and we know very little. <br /><br /><br />Despite by scoern above there is value in these two papers I do like the fact that Knauth et al. point out problems with the popular extreme acidity interpretation. I am not comfortable with this either. I think they are right in saying that these rocks have seen a lot of water and the basaltic source has been completely reacted, in such cases you would expect the acidity to be greatly reduced. I also like how McCollom and Hynek observe that jJarosite is not in equilibrium with any of the salt assemblages modelled. they suggest that it is the product of later weathering, something I have suspected on simple gut feeling (jarosite has been reported from weathering rinds in the Antarctic)<br /><br />Mind you, there is a certain irony in these two papers. The pyroclastic experts (Knauth et al.) postulate an impact origin, it is hydrochemical experts (McCollom and Hynek) who postulate a volcanic origin.<br /><br />It is probably worth trying to separate out the various issues in this immensely complex unit.<br /><br />1. The origin of the sediments - every agrees at this stage that these are highly altered basaltic sands and silts.<br /><br />2. The nature and timing of the alteration. Did it happen before, during or after fragmentation, transport and sedimentation? I think this is still open although I think most papers lean towards after.<br /><br />3. The nature of the transporting and depositing process - wind, water, volcanic surge, impact surge? As a sedimentologist i would go to wind and water in lakes and dunes, although I would not rule out the possibiliy of some pyroclastic and even impact deposits.<br /><br />3. The wetness of the depositing environment - wet, damp, or dry? I would go with the Squyrfes team and stay it was mostly wet.<br /><br />4. The nature of subsurface alteration - there is clearly been a lot of this, but <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

What do you mean by the elevation of the deposits?<br /><br />What is the evidence for icebergs?<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[jatslo]

Topography maps show buried ice burgs or sheets, and shorelines several hundred feet high, but I risk looking lie RCH, if I post PICS that have multitudes of perceptions. <img src="/images/icons/smile.gif" /> Oh, there are also tell tale signs of rather large glacier activities and possible buried ice. Is this an appropriate thread to discuss topography as it relates to sea levels? I now realize you are talking of a local event, whereas I am talking about Mars in general. <img src="/images/icons/cool.gif" />

 

[centsworth_II]

<font color="yellow">"What is the evidence for icebergs?"</font><br />He probably means ice floes. I remember some evidence for glacier activity being presented. I suppose the past existence of martian iceburgs would depend on whether a glacier ran down to a large body of water or not. No evidence for that yet, I suspect.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[JonClarke]

Thanks for the clarification. They are interesting questions<br /><br />The problem is we don't know the timing of those shorelines with what we see at Meridiani - i.e. are the related or different events? To be honest, I am not sure of the elevation of the supposed shorelines (which are still debated) and the Meridiani deposits, again whether they could be related or not.<br /><br />Icebergs? Certainly possible. Icebergs typically leave characteristic features called drop stones, as they melt, these are pebbles to boulders of different rock types which drop out onto the sea or lake floor. We haven't seen any of these yet at Meridiani so either (1) they weren't present or (2) the water was too shallow to allow much ice rafting. There is sediment succession not far from here, deposited in a shallow shelf during the Permian ice age. The deeper water deposits are full of evidence of ice rafting - boulders the size of a piano - the evidence in the interbedded shallow water deposits is scanty, only a few small pebbles.<br /><br />Jon<br /><br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[arkady]

At the time when the first rover images was released, I was struck by how much it resembled Icelandic landscapes created by volcanic activity below glaciers. My knowledge on geology is rather limited at best, but as I said the similarities was striking. Does this have any merit ?<br /><br />The 1996 eruption at Grimsvötn comes to mind.<br /> <div class="Discussion_UserSignature"> "<font color="#0000ff"><em>The choice is the Universe, or nothing</em> ... </font>" - H.G Wells </div>

 

[paulanderson]

I received an interesting e-mail this morning from Tom McCollom at Colorado University, one of the authors of one of the new research papers in question. Quote:<br /><br />"First, we considered in our our article all of the chemical compositional data that have been published to date. The chemical compositions on which the more recent interpretations mentioned by Steve Squyres are based have not been published, and the MER team refused us access to these data when we requested. However, based on what we have seen in recent publications and information presented at conferences, there is nothing in these new data that would be inconsistent with our volcanic scenario, contrary to the claims that Squyres has made in the mass media. We intend to demonstrate this as soon as the data are made available to the broader scientific community."<br /><br />This will be a long debate...<br /><br />More articles also:<br /><br /><b>ASU geologists suggest Mars feature linked to meteorites, not evaporated lakes</b><br />http://www.asu.edu/news/stories/200512/20051222_mars_meteorites.htm<br /><br /><b>Mars Not so Wet After All?</b><br />http://www.nature.com/news/2005/051219/full/051219-10.html<br /><br />And a new phyllosilicates abstract:<br /><br /><b>Phyllosilicates on Mars and implications for early martian climate</b><br />http://www.nature.com/nature/journal/v438/n7068/abs/nature04274.html