Erebus may be up section, but OTOH, it may be down section. Or we may be "across section", looking at a facies change. We're trying to figure out a complex geology on what is essentially an initial walk-though of the site. But those guys in the left seat have prioritized getting to Mogollon and this feature is not a big enough blip to warrant several Sols of IDD work. I think that the "roadcut" at Mogollon will answer a lot of these questions.

Darned if they do, darned if they don't. When they stop and do a scratch-and-sniff at every interesting rock, we clamor go, go, go to Erebus; when they get going, we say stop, stop, look at that.

The Blueberries are a mystery wrapped in an enigma. My first thought at Eagle crater was "tektites or lapilli". Then it looked like they were a lag weathered out of hematite concretions in an erodable evaporite. But there are so many questions about their genesis and distribution that we'll have to wait for more pieces of this puzzle. The organic source noted by Bruce has great merit.

--Bill

I agree 100%.

Thank you for posting that information BruceMoomaw.
"It sounds too good to be true"
It certainly are one amazing find - if confirmed - but its organic chemistry and not the 'L' word so I wont run around waving my arms in the air just yet.

Hmmm... spherical concretions occur in lots of places here on Earth, too. I guess the first set of questions to ask includes the following:

1) Are there any terrestrial concretions that display similar chemistry, i.e., hematitic?

2) If the answer to the above is Yes, is there an accepted theory that organics played a role in their formation?

I know, I know, the Apollo 16 lesson is learned well, here -- that assuming terrestrial-like processes to explain observed phenomenah on other worlds can lead you down the wrong path. But if we're talking about organics here, we need to at least compare the situation at Meridiani to anything and everything even remotely similar in our terrestrial experience.

-the other Doug

Here is an article that explains how organics can reduce hematite (as in the first possible reaction set for formation of the Blueberries posted by Bruce) :

"Surface stabilization of organics on hematite by conversion from terminal to bridging adsorption structures"
Geochimica et Cosmochimica Acta, Volume 67, Issue 5, March 2003, Pages 1055-1063
by Michael A. Henderson.

The reaction studied in the above article is : CH3OH(g)+Fe3+-O2−-Fe3+→H2CO(g)+H2O(g)+2 Fe2+
Hematite is reduced by an alcohol (methanol) (Fe3+ --> Fe2+)

Here is some relevant literature on hematite formation :

Hydrocarbon related bleaching of strata and hematite deposition in red beds at Moab, Utah: a possible analogous process that formed bright layers and hematite deposits on Mars
J. Ormö and G. Komatsu, Proc. Lunar Planet. Sci. Conf. 34th (2003) Abstract #1356.

Meridiani Planum hematite deposit and the search for evidence of life on Mars—iron mineralization of microorganisms in rock varnish
Icarus, Volume 171, Issue 1, September 2004, Pages 20-30
Carlton C. Allen, Luke W. Probst, Beverly E. Flood, Teresa G. Longazo, Rachel T. Schelble and Frances Westall

Laboratory simulations of Mars aqueous geochemistry
Icarus, Volume 170, Issue 2, August 2004, Pages 404-423
Mark A. Bullock, Jeffrey M. Moore and Michael T. Mellon

Geological features indicative of processes related to the hematite formation in Meridiani Planum and Aram Chaos, Mars: a comparison with diagenetic hematite deposits in southern Utah, USA
ICARUS 171 (2): 295-316 OCT 2004
Ormo J, Komatsu G, Chan MA, et al.


Diagenetic hematite and manganese oxides and fault-related fluid flow in Jurassic sandstones, southeastern Utah
AAPG BULL 84 (9): 1281-1310 SEP 2000
Chan MA, Parry WT, Bowman JR

Edited to add a couple more references.

This post has been edited by TheChemist: Oct 26 2005, 09:04 PM

Organic matter certainly could create locally reducing conditions that would mobilize iron ions. But I'm not certain that organic matter would be necessary to create hematite concretions. I don't know what the oxidation state of the Meridiani sediments was at the time they formed, nor when the concretions formed, and that is critical to what happens later. Iron ions are relatively soluble in water when they are in the chemically reduced Fe+2 state, and pretty much insoluble when in the oxidized Fe+3 state.

Oxidation-reduction (redox) reactions are responsible for much of the secondary, iron mineral redistribution on earth. I've seen many examples of hematite concretions that formed around crystals of iron sulfide or other reduced iron minerals. They are often rounded but irregular in shape; but there are examples of very round and regular ones also. In these cases I think the concretions are formed by the diffusion of oxygen into the reduced environment around the sulfides, eventually converting them to iron oxides.

As I understand it, the early atmosphere on earth was chemically reducing, and the very early oceans were loaded with soluble, reduced, iron ions (Fe+2). Even after life and photosynthesis began, it took a long time before oxygen accumulated in the atmosphere, because initially most of the photosynthetic oxygen produced was consumed in the oceans, oxidizing the Fe+2 ions and precipitating vast quantities of Fe+3 as Fe2O3 (hematite), thus forming the amazing banded iron formations of the Precambrian period. I'm sure the actual reaction mechanisms might have been a bit more complicated, perhaps with a goethite or other precursor mineral. The main point is that the young earth had a lot of soluble, reduced iron available. So may have Mars, and that may have resulted in the precipitation of reduced iron species in the sediments, especially if the conditions were arid, or there was a lot of sulfur around.

If the early conditions on Mars were reducing, as they were on the early earth, there may have already been reduced iron minerals in the young Meridani sediments. They could have been oxidized later as the Martian atmosphere slowly became more oxidizing. It seems that such a scenario would eliminate the need for local concentrations of organic matter to reduce insoluble Fe+3 in order to mobilize the iron for diffusion. It seems that we only need a relatively homogenous distribution of small, iron mineral crystals in the sediments under reducing contions as a starting point. Then slowly and uniformly change those conditions to a moderately oxidizing state to create those lovely and uniform concretions known affectionately as blueberries.

Sorry about the rant folks, but Bruce started it. The diverse manifestations of redox geochemistry have fascinated me for much of my life. I worked on iron formations as a grad student, and my first real job was exploring for roll-front uranium deposits. Later, I studied huge redox interfaces that draped oil and gas deposits. It's a fascinating subject, and it gets more fascinating when you throw in the unknown or poorly known conditions during the early history of a planet. This stuff is really fun!

A panoramic view of bedrock and Blueberries around Erebus.

Taken on Sol 616 with the R6 pancam.

jvandriel

CR, I agree that organics do not appear to be necessary, a reducing spot is all that is needed to start either of the
two working scenaria for blueberry formation put forthin Bruce's post.
Maybe organics are implicated because people would prefer to find a scenario that
explains both the formation of hematite concretions AND the lack of organics on the surface ?
That would be simpler and more elegant


Rubbish. Given your background you should apologize when NOT expressing an opinion on such matters

TheChemist and CR: Your comments are very interesting and I enjoyed reading it.

About the picture's post by Jvandriel: The many small stones alike on the bedrocks aren't blueberries? These are the rest of broken stones due to the age (aeolian and water erosion).

Rodolfo

CR makes a good point and it is a plausible explanation for the origin of the Blueberries. My own "day job" involves the prevention of acid mine drainage and bacteria can accelerate the breakdown of iron sulfides into soluble iron and sulfates. There are bacteria that metabolize the Fe+2 iron and leave the Fe+3 iron and others that feed on sulfates. There are types of terrestrial bacteria that utilize iron and sulfur so it is quite possible that this class of critters may have been on Mars.

Did we ever hear more about the composition of the "cobbles" (the dark angular chunks of my sometimes rant) that Oppy MI'd and MB'd on the Erebus Highway? I recall SS saying something about "new and interesting", then nothing. They may be basalt ejecta, but my little intuition voice says "massive hematite". And now that we have been seeing larger pieces of this material on the easy-going bedrock paths, I wish we'd stopped to take a closer look...


--Bill

I don't know, Bill. It really is curious that we haven't learned more about the interesting, dark cobbles. I think SS mentioned in a previous update that they weren't meteorites, but that was it. I really would have expected there to be more investigation of them, especially some of the larger ones Opportunity has passed by.

All I can guess is that they figured out what they are in the initial investigation a while back, and they decided to only tell us what they are not. If they are from that apparently darker layer, we should learn more when Opportunity gets to the rim. If the dust storm doesn't interfere, that could be within the week.

I don't think that this is A Great Conspiracy or an ESA datahoard. They have initial ideas on the strat/lith of this area and the cobbles are the key, so they are likely waiting for more data at Mogollon. Heck, they're paying for this ride, so I'll go along.

I've been looking at bedrock pics from Sol-One and the conclusion I've reached is .

--Bill

I wasn't implying any kind of conspiracy, Bill. Sorry if it sounded that way. I only meant they haven't told us what they think it is yet. That's pretty standard. They usually don't divulge everything they are thinking, and with good reason.

CosmicRocker said:

"All I can guess is that they figured out what they are in the initial investigation a while back, and they decided to only tell us what they are not."

I think it's much more likely that they have NOT figured out what they are. The cobbles are clearly different, but the team doesn't understand them yet. They need more data, which might be found at Payson. There has been no shortage of discussion of different rock types at Gusev in recent months.

Phil

I wasn't seriously thinking anything conspiratorial; I was being light. They aren't publically going into wild speculation, although a lot of ideas have probably been tossed about over coffee. Or whatever they drink in Pasadena...

--Bill