On the Road Again - volume 5

1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 ... 29 Next
Author Message
hortonheardawho







PostPosted: February 7, 2010 1:23 PM 

It's time for a new volume of this topic. Posts are taking longer and longer and more and more errors are occurring when referencing the topic.

Volume 4 is here.

sol 2147 ( Feb 7, 2010 ) L0R0 detail of "Chocolate Hills":

s-1N318788745EFFABCRP1972L0R0v-x2c1

Notice how the "rind" or "fracture fill" or whatever-the-stuff-is on the top appears to wrap around the curving side on the left.

The "whatever-the-stuff-is" looks more like a coating draped over the rock after is was blasted into its current position.

I look forward to more detailed pancam views of the left side of this rock.

LWS


Posts: 3062

Reply: 1



PostPosted: February 7, 2010 1:56 PM 

Hort;

Beautiful observation!!!

But also, It seems to me that the "coating" not only seems to be an unnatural veneer on the rock running against the natural layers and conforming with the curved rock surface but also appears to be DEVELOPING a new and different orientation of the layers of berries on the rock as compared with the main rock layers. Are we seeing the results of birth of some new berry layers here on top of the old layers that were blown out of the crater and perhaps recent aeolian plus other erosion?

Winston

LWS


Posts: 3062

Reply: 2



PostPosted: February 7, 2010 2:11 PM 

Hi Hort, re my last comment in Volume 4 of this discussion I had intended to make a suggestion that Oppy should to try to overturn some small pavement rocks and look for flat surfaces, evidence of below surface erosion, etc. to get some sort of statistical picture of how far those rocks in general are anchored in the soil and if there is erosion below ground.

Winston

Bill Harris


Posts: 72

Reply: 3



PostPosted: February 7, 2010 2:39 PM 

Even though the simplest, most reasonable explanation is "fracture fill", that explanation is getting mightily frayed about the edges, especially since it appears to be draped over the rock. And in at least two layers.

Maybe we'll get some Pancams this evening.

--Bill

Ben


Posts: 2270

Reply: 4



PostPosted: February 7, 2010 4:19 PM 

Bill; On the other hand, one can't say these aren't old buried cracks (dessication ?)
that were enlarged in the subsurface by the action of ground water .

The same fluid movement could have also deposited the ensuing, dark fill material.

serpens


Posts: 169

Reply: 5



PostPosted: February 7, 2010 5:05 PM 

Ben. I am with you on this one. I can see areas of (for want of a better name) fracture fill in patches on the top of the rock. The top of the rock seems very smooth,and could well be the original smooth dessication crack surface. The sides of the rock are more eroded and there appears to be parts of the rock adhering to the fracture fill and overlaying it. A result of the impact fracturing pattern?

False colour would help to identify differences in material but Hortonheardawho's saturatd color image at post 271 seems to provide clear differentiation between the fracture fill and other parts of the rock. The fracture fill does not drape.

Bill describes of the rock as dirty sand poorly cemented by salts (where kieserite dominates the final precipitation sequence). Dessication cracking would be an expected feature (the Dead Sea is a good analogy) and a groundwater recharge sequenceFe would set the scene for fracture fill and berry formation.

Barsoomer


Posts: 344

Reply: 6



PostPosted: February 7, 2010 5:54 PM 

In the past, "fracture fill" has been presented as something more resistant to erosion than the underlying rock. However, the coating in Horton's #0 post appears to be eroding more rapidly than the rock it covers, at least to my eye.

To the left and below the main rock, there is a small rock that looks as if it might possibly be a fragment of the main rock, or coating that has fallen off the main rock. This small rock has a curious appearance, looking something like a bunch of grapes.

Barsoomer


Posts: 344

Reply: 7



PostPosted: February 7, 2010 6:25 PM 

Top left rock does not have a regular grain; instead it seems to have fibrous features on its surface.

LWS


Posts: 3062

Reply: 8



PostPosted: February 7, 2010 8:16 PM 

Hi Barsoomer; Here's an RGB image of your reply 7.

Winston

LWS


Posts: 3062

Reply: 9



PostPosted: February 7, 2010 8:55 PM 

Ben; Re. your reply #4 it looks like we are getting somewhere. I am pleased to see that you posit "one can't say these aren't old buried cracks (dessication ?) that were enlarged in the subsurface by the action of ground water. The same fluid movement could have also deposited the ensuing, dark fill material."

Can I take that to mean that you see a possibility that ground water could have been involved in the development of the "fill"?

Since the crater is a relatively small one and reasonably shallow, the ejecta probably came from fairly close to the surface and not from the putative layers in which the original berries were presumably formed in that shallow lake a few billion years ago. Also, if it is accepted that the crater itself is reasonably young geologically speaking, Do you think that the ground water action might have taken place relatively recently (again geologically speaking)?

Do these new observations fit snugly into the rationale for the current accepted hypotheses about berry development and meridiani?

Barsoomer; What excites me about these observations on the "fill" on the evaporite ejecta is that the fill appears to be substantially composed of berries at this stage (further pancam work may negate this observation). This suggests to me that these berries were either formed in the fill material below the surface before the impact or above the surface after the impact and are now eroding. The fill material looks less strongly binded than the rock surface on which they rest which might also mean that it is different chemically to the evaporite rock. Indeed, some of the colour images suggests that the fill might indeed be composed of 2 different materials, one resulting in a smooth textured wavy surface and one a somewhat roughened darker surface with what looks like embedded atypical berries.

I look forward to the close up pancams and the MI's of the rock surfaces.

Winston

Bill Harris


Posts: 72

Reply: 10



PostPosted: February 7, 2010 9:55 PM 

Let's look at fracture fills.

Rocks fracture and groundwater flows through the fractures. Groundwater in contact with rock dissolves minerals and the anion-cation suite reflects the composition of the rock types that the groundwater has contacted. By various mechanisms, these ions can be precipitated out of the groundwater or crystalized on the walls of the fracture, thereby filling the crack with crystals. In limestones, a typical fracture fill is calcite, which is a constituent of the limestone. In metamorphic (heat-altered) rocks, a typical fracture fill is quartz, derived from silica leched out of rocks by hydrothermal fluids (fancy work for hot water).

I'm not a geochemist, so this is presented in general terms.

There are a lot of general references to "fracture fills", but I've not come across a good intro. Here is the Google search if you want to dig:

http://www.google.com/search?hl=en&q=fracture+fills&start=0&sa=N

--Bill

serpens


Posts: 169

Reply: 11



PostPosted: February 7, 2010 10:11 PM 

LWS. Your comment that ground water was involved in the fill seems most sensible. As I understand it the fracture fill is primarily mechanically introduced material (sand, fragments and the occasional berry) cemented by Fe dominated groundwater activity. In many instances the desiccation cracks seem to have widened considerably since the event which explains the facture fill adhering to one side of a wide crack.

I also think your idea of water films holds for formation of the rinds or veneers that have been seen, but I cannot see that for the berries. I think that these, like the fracture fill would need a groundwater environment. The fact that we have berries in the cemented Meridiani rock indicates that there is a deflationary process going on and erosion has dropped the surface to (below) the old water level in this area (as opposed to say the Victoria annulus where ejecta erosion has produced the multitude of berries, and the way that berries disappeared as we climbed above the old water table in the transit to Victoria.).

But we see rinds on rock that has been eroded down to the lag level so these may have formed under dunes or at least a sand covering as the sedimentary deposit finally dried out. But again these seem to be eroded remnants so I’m not sure that the process is still ongoing. Maybe brushing a sand deposit off a rock would be a more productive look-see than trying to overturn a piece of bedrock. I’m surprised that a rock hasn’t been dislodged and exposed by accident over the years.

Smile

LWS


Posts: 3062

Reply: 12



PostPosted: February 7, 2010 10:22 PM 

Serpens; Thanks! I appreciate the comments from you, Ben and Bill Harris. I know very little of Geology beyond what I have picked up from this forum and so I appreciate what little feedback I get from my perhaps wild-eyed and uninformed speculations. Bill's references are very helpful in that regard also.

Re. dislodgement of rocks. There are a few that I've seen but Oppy did not go the extra mile to try to move the loosened rocks further. What I was suggesting was an experiment to deliberately try to move some pavement stones.

I'll look for some of the dislodged stones and post the images if I find them.

Winston

Ben


Posts: 2270

Reply: 13



PostPosted: February 7, 2010 11:33 PM 

Barsroomer; The rock you refer to in your #7 reply looks like it contains festoon bedding viewed from an oblique angle.

Winston; In addition to Serpens comments, here is how I envision the Meridiani beds at this locality.

1. They were deposited as mud in a shallow -water, playa environment marked by interspersed periods of dessication.

2. Early in their history, these soft sediments were compacted and indurated so that small impacts created horizontal fractures and probably expanded the dessication cracks.

3.Further cyclic deposition added to the thickness of the beds and shallow ground water moving thru them deposited fracture coatings and contemporaneous coatings on the spherules.

4. As the shallow lakes finally dried up
fluvial action of the departing water caused local erosion and deposition of lag gravels.

5. The area then became a desert , the water table dropped and wind erosion and destruction of the horizontal beds became dominant.The finer fraction of the eroded material was carried away in dust storms and deposited far away leaving only the larger grains. Many spherules were released and a few fracture fills were exposed.( remember the long one in Duck Bay)

6. Increased wind velocity moved the larger grains and formed the sand ripples which eventually became stabilized by some unknown process.

7.Late cratering "Concepcion" has exposed some of the subsurface beds described above
and weaker winds continue to erode and wear down the ejecta, gently exposing spherules on stems, and slowly dislodging many.
These winds tend to seperate the Fe rich material and form dust piles of it.

LWS


Posts: 3062

Reply: 14



PostPosted: February 7, 2010 11:43 PM 

Ben; Re. your #13 Thanks! Looks reasonable but I still have this bee in my bonnet that there has been recent water activity rather than billions of years ago.

Thanks again

Winston

hortonheardawho


Posts: 3465

Reply: 15



PostPosted: February 8, 2010 12:26 AM 

sol 2145 ( Feb 5, 2010 ) 3D closeup rubble pile below mass of blueberry stems on Chocolate Hills rock on the rim of Concepcion crater:

I got really excited when I was processing the "shadows" version of the Chocoloate Hills image and noticed something!

Where did the rubble pile between the two rocks come from?

If the pile fell from the right side of the rock where the long blueberry stems are located "recently" then it is very likely that the blueberry stems were exposed at the same time as the berries - thus "proving" that they are intrinsic to the berries!

Notice that the rock surface with the berries and stems is "rough" - as are the surfaces of the rocks in the rubble pile. Also notice there is none of the darker dust covering any of the rubble pile - supporting the idea that it is a recent "fall".

Whoo hoo!

Boy would I like a detailed closeup of both the berry rock face and the rubble pile to see if they fit together.

Any counter-arguments?

RJS


Posts: 125

Reply: 16



PostPosted: February 8, 2010 8:53 AM 


Great photo Hort; thanks for all your hard work... Question; is the yellow/orange coloring in the rubble real or a picture processing issue. Thx.

RJS

LWS


Posts: 3062

Reply: 17



PostPosted: February 8, 2010 9:07 AM 

HiHort; re. your #15. Great logic as usual. One counter argument might be eddy wind current downdrafts that could dislodge the softer matrix and leave the berries and their stems still attached to the rock.

However, I fully agree with the thrust of your argument that the "dust" fall is probably very recent since the blue exudate that normally exudes from the bottom of these rocks is below the dust and has not yet stained or reacted with it.

I'm also looking forward to closeups and MI's. Hope I won't be disappointed as I have been so many times before

Winston

hortonheardawho


Posts: 3465

Reply: 18



PostPosted: February 8, 2010 10:31 AM 

RJS, the yellow-orange is a shadow artifact caused by the rock shadow moving during the 3 filter exposures.

Before you ask, the right pancam is a "tinted" R1 filter only, so the dark grey sand appears the same color as the rock - but it's not.

As an aside, I think the reason so few right pancam images are being taken now ( or any activity for that matter ) is that power levels have dropped to low-low levels. The only planned activity for today is a tau measurment.

The Feb 3 power reading was 270 watt-hours. I remember several years ago that 250 watt-hours was stated as a critically low level ( in order for the vehicle to continue functioning ) -- but Oppy survived 125 watt-hours for a few weeks. I doubt it would survive 6 months at that level.

Perhaps the decision will be made for Oppy to "winter over" at Concepcion. If I were driving I would park Oppy on a rock on the south side of the crater and spend the winter studying a neighboring rock or two.

Better the port you're in than the open sea during a winter gale.

Bill Harris


Posts: 72

Reply: 19



PostPosted: February 8, 2010 10:44 AM 

Good summary of the history of this site, Ben.

Good catch, Hort. The buff-colored rubble is clearly from the evaporite boulders and post-dates the blue hematite sand. This is a part of the weathering process here, but the question is, which boulder face did it come from-- the one on the left with the b'berry nubbins or the one on the right with the cracks? This may tie in to my observation in Reply# 280 of Volume4 about the evident friable nature of the weathering rock fragments.

Lets look at the weathering/erosional processes here. This is an arid, cold desert environment, so wind (aeolian) erosion is the dominant process. Eons of the relentless wind moving sand-sized particles by saltation and, IMO, more importantly, silt- and possibly clay-sized silica and evaporite particles in actual suspension in the wind. Notice the fine dust accululation at the top of the antenna on Oppy. With little available liquid water to aggregate and consolidate eroded rock particles, the dust can become become exceedingly fine, finer than can be possible in the terrestrial environment. Look at this as sandblasting, or the more delicate procedure, soda blasting. As we see, over eons, it can plane the soft evaporite down to a flat surface.

Another process is thermal fracturing. With the temperature extremes here, rocks can break from thermal expansion.

Water can be a great force in weathering, but currently on Mars, there is probably little moisture available to do much at the surface. This is limited to transient water films and frost, which, over time, can react with and alter minerals in the rocks.

I think that one factor that is uniquely Martian is "radiation weathering". Weak magnetic field, thin atmosphere and cosmic rays are incessantly hitting the surface. Look at a Rover image with a long exposure (like an L7 or R1 of a dark scene). Dozens of pixel-sized spots, "cosmic ray hits". Over millenia, this can degrade and weaken the crystal structure of the component minerals.

Any other factors I've not thought of?

--Bill


The preceding was brought to you by the Letter "W"... Wink

Ben


Posts: 2270

Reply: 20



PostPosted: February 8, 2010 12:42 PM 

Excellent summary of weathering processes Bill'
IMO what we are seeing here is called exfoliation along bedding planes, caused by the heating and cooling of the ,thermally variable , alternating ,thin layers of the Meridiani beds.

Because these thin planar layers vary in hardness is what allows the formation of the berry stems, parallel along the hard layers . Sort of like wind-tails.

Stems don't form in the vertical plane because the intervening softer layers won't support them

Millions of years of weathering and erosion has provided what must be billions of tons of dust from the soft material and yet there is no evidence of it on the current surface.

IMO it has been picked up by global dust storms and dispersed over the planet winding up in deeper craters.

What we have left are the coarser material ripples the lag gravels and the occasional chunk of ejecta or meteorite material.

1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 ... 29 Next


Join the conversation:















Very Happy Smile Sad Surprised
Shocked Confused Cool Laughing
Mad Razz Embarassed Crying or Very Sad
Evil or Very Mad Twisted Evil Rolling Eyes Wink
Powered by MTSmileys