Epsl (november 30, 2005) Options

[Guest_AlexBlackwell_*]

The November 30, 2005, issue of the journal Earth and Planetary Science Letters, Volume 240, Issue 1, pp. 1-190, has just been published online. It is a special issue entitled "Sedimentary Geology at Meridiani Planum, Mars," edited by Steven W. Squyres and Andrew H. Knoll.

[Guest_AlexBlackwell_*]

Doug, the topic line got truncated. Could you chage it to something like "EPSL (November 30, 2005)"? Thanks.

[djellison]

Done - these are the papers that Steve mentions in the Q'n'A - pity about the subscription requirement - I would love to read the whole damn lot of them

Doug

[paxdan]

Done - these are the papers that Steve mentions in the Q'n'A - pity about the subscription requirement - I would love to read the whole damn lot of them

Doug

<cough>BugMeNot</cough>

[djellison]

Sadly is a fiscal subscription, not just a normal subscription - and although bugmenot had many suggestions (i gave up after 30) , none actually worked Hey ho - I have all the JGR-Planets inprints to read in Spain

Doug

[Guest_AlexBlackwell_*]

Sadly is a fiscal subscription, not just a normal subscription - and although bugmenot had many suggestions (i gave up after 30) , none actually worked   Hey ho - I have all the JGR-Planets inprints to read in Spain

Doug

Doug, give me a good email address in the "other group" and I think I might be able to add to your reading pile for Spain :-)

[djellison]

Thanks

At this rate, Douglas Adams Triology of Four wont even leave the suitcase

Doug

[Stephen]

In summary, we interpret the Burns formation to be sedimentary rocks formed in a wind-swept, arid surface environment with a fluctuating water table. Water rose occasionally to the surface, forming pools in which evaporation led to production of sulfate-rich sand grains that were reworked by the wind to form dunes and sand sheets. The rocks observed by Opportunity to date record a transition from dunes to dune-marginal sand sheets to transient pools of surface water. Multiple introductions of ground water governed diagenesis, including the formation of the ubiquitous hematite-rich “blueberries.”

(from "Sedimentary rocks at Meridiani Planum: Origin, diagenesis, and implications for life on Mars", by Squyres and Knoll).

I note they refer only to "transient pools of surface water".

Have the MER team moved away altogether from the idea of the Meridani site being at the edge of a one-time lake or sea or is that still a possibility?

======
Stephen

[Bill Harris]

Current thought is a desert-playa environment. Still, the fluctuating water table represents a large volume of water plus a mechanism to introduce the water. And remember, "transient", in geological time, can be a long time in human terms.

--Bill

[dvandorn]

Also, that description is of the area of Burns Cliff that Oppy was able to reach -- isn't that the area of the sequence *below* the main evaporite beds?

In other words, that description applies to the Meridiani area prior to its periodic inundation by a shallow sea. The desert playa formations predate the deposition of tens of meters of evaporite.

At least, that's how I read it.

-the other Doug

[Guest_AlexBlackwell_*]

I don't know if it's been mentioned here previously or not; however, for those who don't have access to EPSL and the Grotzinger et al. paper, the lecture materials for John's Grotzinger's October 13, 2005, presentation "The 2004 Mars Exploration Rover Mission: Evidence for Water and Prospects for Life," are now online. See the left side under "Lecture Archives."

[Guest_AlexBlackwell_*]

Have the MER team moved away altogether from the idea of the Meridani site being at the edge of a one-time lake or sea or is that still a possibility?

I think this particular interpretation became widely accepted when Opportunity saw the vertical stratigraphic sequence at Endurance Crater and after the first geochemical and geomorphological data were analyzed. In fact, even before that many in the Mars science community were skeptical of a "Meridiani Planum sea" to explain the hematite and pointed out that the regional topography really doesn't support the idea of an enclosed basin/paleosea.

[CosmicRocker]

I've been looking over Grotzinger's October 13th lecture Power Point presentation, on and off, since it was released some weeks ago. It's a good read. I've tried to view the archived webcast of the lecture, but have not been able to get it to replay beyond the first few introductory words. If anyone else has been successful and has any suggestions, I'd appreciate hearing them.

Regarding interpretations of the depositional and post-depositional environments that created these rocks, it appears the team developed a composite stratigraphic section based on visual observations of rock texture along the Endurance ingress route, at Burns Cliff, and probably sites in between. Thanks to some concurrent spectral measurements, they were also able to create a chemostratigraphic section that was correlated to the textural one. Together, those two sections provide a really nice basis for an initial environmental interpretation.

In the limited section observed in Endurance, several transitions were observed, but I think the most notable was the unconformity observed at Burns Cliff. I didn't know it had been named, but it's called the Wellington Contact in Grotzinger's presentation. That contact suggests an environment that changed from wind-blown dunes to wet sediments deposited in shallow water. The chemostratigrapy also supports an arid environment that led to the deposition of quite a lot of evaporite salts within the sediments.

I've "borrowed" a couple of the images from Dr. Grotzinger's Power Point file, that I think are relevant to this discussion. But I would recommend that anyone seriously interested in this stuff check out his entire presentation. It's very good and contains images of earthly analogues. Ignore the second copy of the column. I don't know where it comes from, but it is a duplicate, and I can't delete it. Other important notes about the stratigraphic column were not attached to that image. See the original PPT file to view it as the author intended.

By the way, as I recall, they did a super-res set of images of the Wellington contact when they realized they weren't going to chance going all the way across Burns cliff to get to the contact. The "borrowed" image of that contact is the best one I have seen of it. Could it be the result of the super-res stack?

Attached thumbnail(s)

 

[Guest_AlexBlackwell_*]

In the limited section observed in Endurance, several transitions were observed, but I think the most notable was the unconformity observed at Burns Cliff.  I didn't know it had been named, but it's called the Wellington Contact in Grotzinger's presentation.  That contact suggests an environment that changed from wind-blown dunes to wet sediments deposited in shallow water.

Yes, this is the so-called "White Plains" model with playas, etc. that many on the Opportunity science team favor, though one of the $64,000 (or $850 million) questions is from whence the water was derived. Precipitation from the atmosphere, transient groundwater release, melting of retreating ice sheets, etc.?

EDIT (11/23/05): Oops. Change "White Plains" to "White Sands." What was I thinking?

This post has been edited by AlexBlackwell: Nov 23 2005, 09:04 PM

[CosmicRocker]

Ahh, yes. If someone only had the details about the history of water on Mars. These intriguing glimpses provided by the two rovers in two very different geologic terrains really only give us a pair of limited windows into Martian geological history. While it is tempting to grab these new and high-resolution ground-truth samples, and then attempt to extrapolate martian history, the fact is that we do not have the boots-on-the-ground observations we need to paint a sufficiently long section of Martian geological history.

It seems that the window we are looking through might be showing the late stages of the water history and an arid environment, but the sedimentological clues of things like the festoon crossbedding indicate flowing water. You can throw in complications, like aeolian erosion down to the capillary fringe, and other intricacies, but the fact of the matter remains. We do not have enough of the fine geological observations needed to determine where Meridiani's sediments lie in the the history of water on Mars. Is this only the late stages of a previously wet, primordial planet, are we seeing only a stage in a cyclical process, or is it a transient or episodic event?

I think you hit the nail on the head. As far as we really know, it could have been any of those processes. Am I sounding evasive? I think so. Damn, you've got to love these Rovers, though.