On the Road Again - volume 8 - Page 19

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Ben


Posts: 5

Reply: 361



PostPosted: June 5, 2011 12:38 PM 

Young blocky does not appear to have much larger chunks of ejecta which could be signifigant for any of several reasons.

Ben


Posts: 5

Reply: 362



PostPosted: June 5, 2011 1:01 PM 

Barsoomer; No one knows the age of these meteorites except they are younger than the sulphate beds and older than the ensuing ripples.
This probably represents a considerable time span so any view of their history is (as Serpens says) SWAG.
Personally, I think we attach to much credence to many of these workers opinions. Wink

Ben


Posts: 5

Reply: 363



PostPosted: June 5, 2011 1:16 PM 

Kye & Serpens; I have had a second thought on the ridges under the ripples and consider it possible that it is just post ripple erosion that is deepening the intervening areas and leaving uneroded high areas (ridges) beneath the dunes . Surprised

Serpens


Posts: xxx

Reply: 364



PostPosted: June 5, 2011 11:45 PM 

test

Serpens


Posts: xxx

Reply: 365



PostPosted: June 5, 2011 11:53 PM 

Hortonheardawho. Sorry to use this thread for admin but when trying to post to the geology section I got a 'fail' with the comment The precondition on the request for the URL /cgi-bin/mt/reply.fcgi evaluated to false.

'Test' posted ok here. Any ideas? Sad

hortonheardawho


Posts: 3465

Reply: 366



PostPosted: June 6, 2011 8:53 AM 

Serpens, the Precondition Failed error in a post means you typed something that offended the movable type server.

Profanity will trigger the response.

You rock guys talk dirt about vugs all the time and that upsets normal folk. What's a vug anyway?

Seriously, the triggers in Movable Type are brain dead. Try posting the reply one sentence at a time until you find the offending phrase. I will clean up afterwards.

Serpens


Posts: xxx

Reply: 367



PostPosted: June 6, 2011 11:22 AM 

Thamk you Hortonheardawho. Your assistance is much appreciated.

Barsoomer


Posts: 344

Reply: 368



PostPosted: June 6, 2011 4:51 PM 

It seems to be a "slow news day," so I will ask a question on a general topic. If meters of the sulfate outcrop have eroded away at Meridiani, why does not the sand have a high sulfate component? AFAIK, it is mostly basalt. And where did the basaltic sand come from?

Serpens


Posts: xxx

Reply: 369



PostPosted: June 6, 2011 7:04 PM 

Hi Barsoomer. Good question. The term sulphate rock is a possibly careless collective term. The ‘bedrock’ matrix that Opportunity has been driving over is actually made up of reworked siliclastic debris and a chemical stew dominated by evaporate minerals such as jarosite, hematite and sulphates. Mars is a basaltic environment and so the siliclastics have a basaltic provenance. The sulphates dominate and are the glue that cements the grains. It’s a pretty weak cement and as has been seen it erodes (albeit extremely slowly in the current environment) unless protected by lag or frozen dunes. As the rock erodes tiny particles of the sulphate cement are freed and these are so small they can be suspended despite the low atmospheric pressure and blow away, possibly ending up at the bottom of the gravitational gradient in the Northern depression. But the basaltic grains are heavier and drop to the ground where in the past they probably contributed to the ripples and dunes. But of late any that do drop tend to remain near the parent rock. You have probably noticed in Hortonheardawho’s false colour images that there are bluish debris at the base of many rocks?
Originally I think the massive amount of material that makes up the Meridiani sediments had to have come from the highlands to the south. That’s a heck of a lot of erosion and Mars in its youth would have been a really energetic, nasty place.

Barsoomer


Posts: 344

Reply: 370



PostPosted: June 6, 2011 7:54 PM 

Serpens, thanks. That's very interesting.

Ben


Posts: 5

Reply: 371



PostPosted: June 6, 2011 10:02 PM 

Good reply Serpens, right on the money .

Kye Goodwin


Posts: 1166

Reply: 372



PostPosted: June 7, 2011 12:31 AM 

Serpens, re your 369, How much unaltered basaltic material does the bright rock contain? How much unaltered basaltic material does the dark sand contain? I don't think that the bright rock is a plausible source for the dark sand because the "siliciclastic" component of the bright rock appears to be very highly water altered. Here are a couple of papers:

http://authors.library.caltech.edu/13483/

http://aram.ess.sunysb.edu/tglotch/TDG12.pdf

The only basaltic component in the bright rock is 15% plagioclase. Olivine and pyroxene are not detected. The dark sand is thought to be 10 to 15% olivine with twice as much pyroxene.


Serpens


Posts: xxx

Reply: 373



PostPosted: June 7, 2011 3:02 AM 

Kye Goodwin. Cool question. Yep I agree that the bulk of the basaltic sand came from elsewhere - weathered rims like Endeavour or from the Southern Highlands. I also agree with you that while the siliclastic debris have a basaltic provenance, there is probably no unaltered basalt in the matrix.
You have made a good observation in your last post. The basaltic sand has a significant olivine content while the matrix has trace olivine at best. The implication is quite clear. The matrix has been subject to significant alteration via groundwater. The dark sand has not. So during the time that the basaltic sand was eroded out, transported to the Meridiani plains and frozen in dunes it has not been exposed to water. That plus kieserite is pretty compelling for very long term total dessication isn’t it?
The Tim Glotch paper does nominate Nontronite as a possible component of the matrix. Notronite is an acid resistant clay. But deconvolving spectral signatures from remote measurements of ‘contaminated’ samples is perhaps not as precise as one could wish and the presence of Nontronite remains just a possibility as Opportunity continues her headlong rush towards the Cape York deposits.

Serpens


Posts: xxx

Reply: 374



PostPosted: June 7, 2011 3:05 AM 

Kye Goodwin. Just realized that I did say basaltic grians instead of reworked grains in reply 369. My compliments on a great pickup. Cool

hortonheardawho


Posts: 3465

Reply: 375



PostPosted: June 7, 2011 8:38 AM 

sol 2619 ( Jun 7, 2011 ) color detail of "Gemini5" crater:

Well. That was weird.

Not only did Oppy not move closer to "Young Blocky" aka Gemini5 - the new images taken of the crater were L5 L7 filters only - which required a registration with previous L2 images to create color images.

WHY?! An L2 image whould have "cost" about 100 Kbytes of the bandwidth budget - about 3 frames of the 27 frame L1 panorama done on the previous sol.

As I have said many times the greatest Martian mystery is the thought processes of the MER team.

MERhaps there is a crater ahead with the name Apollo11?

hortonheardawho


Posts: 3465

Reply: 376



PostPosted: June 7, 2011 9:52 AM 

sol 2619 ( Jun 7, 2011 ) in the next drive direction:

Looks like the next drive ( sol 2620 - early tomorrow morning? ) will be to the north of Gemini 5 - perhaps to examine the largest ray closer?

hortonheardawho


Posts: 3465

Reply: 377



PostPosted: June 7, 2011 5:50 PM 

Well.

It's a little after sunrise for Oppy and the sol 2620 plan is now posted to the MER Pancam Data Tracking Web Interface.

A drive is planned this sol -- but the end of drive next drive direction azimuth is 144 ( towards Cape York - not towards the west or northwest heading I would expect for a stop to examine Gemini5).

There appears to be a mid-drive 3x1 Navcam panorama planned - so my guess is that the team decided "nothing to see here folks - move along, move along" and will do another long ( 140+ meters ) drive with only a brief pause for imaging this crater.

Barsoomer


Posts: 344

Reply: 378



PostPosted: June 7, 2011 6:05 PM 

These ripples seem to be armoured with berries, and the berries seem to be associated with the ripple encroachment onto slabs.

Interesting interplay of berry-covered areas, smooth areas, ripples and slabs.

Serpens


Posts: xxx

Reply: 379



PostPosted: June 7, 2011 9:21 PM 

Barsoomer. I actually don’t see any ripples in that image. A bit hummocky at the back there possibly but that seems connected to a tilted rock (see the surrounding outline?). To me it looks as though accumulated berries on low rocks have trapped dust providing a good cover and protection for the bedrock. The pancam image below is the same day/position but different pointing. In this image the lag is evident. Ripples have overrun the lag but are themselves clear of berries. The ripples encountered after we left the mound are very low (the pancam/navcam give an illusion of height whereas the hazcams, having the wheels as a yardstick put it into perspective).

The ripples actually tell a story of just how benign the Martian environment is. As Mars lost atmosphere the wind energy declined. Not only was there insufficient force to saltate sand up stoss slopes but the basalt highlands no longer experienced meaningful erosion and the sand supply in this area was lost. The surface armouring would have evolved over millennia.

hortonheardawho


Posts: 3465

Reply: 380



PostPosted: June 8, 2011 8:01 AM 

Today's drive plan ( sol 2620 ) didn't make it to Oppy because of DSN problems in Australia. ( According to a tweet from Scott Maxwell, MarsRoverDriver.)

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