On the Road Again - volume 5 - Page 13

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Author Message
Barsoomer


Posts: 344

Reply: 241



PostPosted: February 21, 2010 2:10 AM 

I agree with Winston. The berries are a mystery that have not yet been fully understood. I remember a time when the "rock guys" disputed that any berries had stems. At this site, for the first time, we have encountered several rocks that have rows upon rows of berries on stalks. The rock Horton called Porcupine is an amazing seemingly regular lattice-work of berries. To say that "the berries are uninteresting, let's move on and talk about the dust instead" seems like an incredibly shortsighted dismissal. If the geology folks are so certain that the stems are just wind tails, then why not take MIs of the rows upon rows of them that we see here, so that we can confirm and document that supposition. Observation trumps theory.

LWS


Posts: 3062

Reply: 242



PostPosted: February 21, 2010 8:08 AM 

Serpens; Thanks for the info on Laura Kirkland. I had found her web site but I had not thought of emailing her directly.

Barsoomer; Thanks for your input at #241. I was beginning to feel quite lonely in this discourse. I couldn't understand, with the wealth of berries around why they could not take some MI's specifically looking at the berries on stalks in the air. Now I think know. Everything has been explained in good earthcentric geology terms and there is no need to look further.

Winston

Bill Harris


Posts: 72

Reply: 243



PostPosted: February 21, 2010 8:09 AM 

> OK ; Now lets talk about all the dust piled around the ejecta

> Any thoughts on why ?

The impact created a mass of highly fragmanted rock which is now exposed and weathering. The wind just hasn't had time to sort things out, as it were. I'd also speculate that at these intermediate stages of weathering the particles are larger than at later stages and are less mobile.

Nice textures on these rocks; the aeolian sandblasting is doing a good job of selective etching. I note that some rocks are weathering at a much higher rate than the (former} surface rock. Do these evaporites work harden as they weather? Have we bee travelling along a particularly resistant unit of the Burns Fm for a while? (only semi-serious uber-speculation)

At any rate, I'd suggest that things are going to get more interesting as we drop in elevation.

--Bill

LWS


Posts: 3062

Reply: 244



PostPosted: February 21, 2010 10:25 AM 

Bill; Now we're getting somewhere. I agree with you.

It is a young site, a geological instant after the impact, erosion has not started to make an impact, chemical weathering around the rocks is still evident.

Where does that leave the conclusion that the impact is an old one?

this site is a most important one if we really want to have some idea of what happens after an impact. We still see lots of small pieces of berry bearing rock in the process of disintegrating. How does this and the other signs of the pieces of "crust" still adhering to the rocks add to data points for assessing the age of the impact?

I have an outlandish suggestion. The crust is neither impact melt nor fracture fill. It is a bio-mediated tissue that quickly grew on the rocks soon after impact when conditions might have modified the local water cycle environment. Since that period, as conditions returned to the norm, the crust tissue has deteriorated rapidly with wind action and some chemical weathering. We are therefore very fortunate to have come here at a time to observe the crust in situ. a few more years and the rocks would look just like all the other craters we have examined so far.

Has anyone looked closely at the berries on the rocks. Most of them appear distorted. I think that is not happenstance. Concepcion has not yet reached the stage of unaffected berries inside the rocks becoming subject to aeolian erosion and so most of the berries we are likely to see on rocks will show signs of melt or other distortions.

I also think that the observations at Concepcion have the potential to offer significant challenges to the desert pavement theory for retention of berries at the surface. I think other agents are at play there.

Winston

Ben


Posts: 2270

Reply: 245



PostPosted: February 21, 2010 1:15 PM 

Thanks Bill; You confirm my impression that the crater is younger than the others we have passed by.
However,I don't believe the geologists on this forum think the crater is billions of years old but certainly more than a thousand .
The rock does appear softer and has more berries than normal which could also account for some of the apparent differences
in erosion at this location.

I have been pondering the concept that we will be going down-section as we progress toward Endurance which would be true if the slope represents an unconformity that cuts deeper in the beds.
But is it possible that the Meridiani beds slope into the deep Endurance depression at a greater rate than the surface slope therefore we are rising in the section?

I say this because the (younger) beds we see here may be softer due to shallower burial .

The increase in berries could also represent a change in depositional environment.

I also recall that the deeper layers in VC were x-bedded (aeolian)and somewhat more indurated.

Barsoomer


Posts: 344

Reply: 246



PostPosted: February 21, 2010 2:53 PM 

Winston, I like your "outlandish suggestion" very much. When I see that crust, I can't help thinking about something like mildew or mold, or some uniquely Martian atmospheric weathering process.

Your points that we likely see this here only because this is a young crater, and that is is a golden opportunity are very appealing.

One additional data point that would be useful is to determine whether the crust is preferentially on sky-facing surfaces. Other statistics about whether it favors one type of rock or another might be suggestive. Has there been any panorama of the whole crater area with false color that emphasises the crust? That might be useful to help in compiling such statistics.

Bill Harris


Posts: 72

Reply: 247



PostPosted: February 21, 2010 3:10 PM 

Ben pondered:

"I have been pondering the concept that we will be going down-section as we progress toward Endurance which would be true if the slope represents an unconformity that cuts deeper in the beds.
But is it possible that the Meridiani beds slope into the deep Endurance depression at a greater rate than the surface slope therefore we are rising in the section?"

No marker beds, minimal stratigraphic control, we don't know the orientation of the beds with certainty. But given the origin of these rocks and weak tectonics in the region, we can safely assume "essentially flat-lying" until we get better data. We'll see what we see as we descend.

On the slope we don't see the stairstep patterns characteristic of regions with flat-lying strata but there may be no resistant units in the section to form bluffs. Or the beds may be a mantling deposit, draped over the base topography. This may be wishful thinking on my part, but I'm assuming that we will start down-section as we go downhill. If not, well, opinions can be changed.

Concepcion is another data point on the section with "mini-Endurance" as the next major "roadcut".

--Bill

hortonheardawho


Posts: 3465

Reply: 248



PostPosted: February 21, 2010 3:11 PM 

Barsoomer et al, I am planning on a super-saturated false color panorama of the crater - as soon as the last strips of the pan are down. ( Maybe today? )

No "aha" moments yet, eh?

I rely on the rock guys to explain away as much as they possibly can, since whatever is left over is not geology.

I really thought I had you guys stumped with the berry and stem firmly embedded in the fracture fill. Now exactly when did the berry and wind tail have time to form, wind erode and then "fall" into the crack before the fracture fill, er, filled the fracture???

Again I think the best way to proceed is develop a parameterized geological model ( your job rock guys ) and demonstrate that some observations fall outside the boundaries of the model.

LWS


Posts: 3062

Reply: 249



PostPosted: February 21, 2010 3:15 PM 

Barsoomer; Thanks

Here's a crop of a rock that we have been seeing portions of in several pancam images since last week but its only now we are seeing the full rock. Could it be another porcupine rock?

Ben; any other thoughts on the dust around the rocks?

Winston

hortonheardawho


Posts: 3465

Reply: 250



PostPosted: February 21, 2010 7:58 PM 

sol 2161 ( Feb 21, 2010 ) L0 5x1 ( 180 deg ) at new location:

with a link to a false color panorama.

Lots more "fracture fill" - including one rock that appears to have fill on at least three sides.

Ben


Posts: 2270

Reply: 251



PostPosted: February 21, 2010 9:03 PM 

Hort; From my perspective, all of the observations presentd by various persons on this forum have been explained with a simplistic geologic model which follows.

Deposition of sediments consisting of alternating Meridiani bed layers with the concurrent formation of small berries(in the more resistant layers)which are composed of the same material as the host rock,

Compaction ,followed by a shift in environmental conditions that allowed the formation of near vertical dessication cracks .

Continued erosion of the surface and the cracks causing widening and berries being exposed on the crack walls as well as released on the surface.

Erosional exposure of the berries located on the more resistant bedding planes left some with stems pointing generally outward from the hard layers.

Stems could not form upward on berries located on the eroded surface of the bedding planes because the intervening soft layers could not support a stem.

Fluid ( from below) enters the fractures openings and begins the process of filling by the accretion of secondary minerals
in layers starting on the fracture walls.

These secondary mineralization ,layers enveloped loose material in the cracks plus berries in the cracks including some on stems that had survived because their stems were part of the hard layer to which they were attached.

Continued erosion placed the fracture fills at a depth shallow enough that a small impact ejected angular blocks encrusted with the fill onto the surface.

Weathering and minor wind erosion caused the break-down of smaller ejecta into friable(rotten rocks). The same process has resulted in local removal of the fracture fill and the accumulation of dust around the ( not yet rounded) angular ejecta.

*My personal opinion is that the Meridiani beds here may be younger than those traversed todate which might explain the abundance of berries and less compacted rock.

Barsoomer


Posts: 344

Reply: 252



PostPosted: February 21, 2010 9:36 PM 

The rock shown here with the "figure 8" shaped crusty material may be an example of the crust on 3 sides that Horton alludes to. The crust on the top face appears to drape onto the figure 8 face and also a third face that is out of view. This seems like a tough case for the fracture fill model to explain.

serpens


Posts: 169

Reply: 253



PostPosted: February 21, 2010 10:14 PM 

Just as a matter of interest, here is what a brand new crater of reasonably similar size looks like.

Concepcion has been pretty well filled in and there is clear evidence of significant erosion of the ejecta. I wonder how long it would take to fill this crater?

Barsoomer


Posts: 344

Reply: 254



PostPosted: February 21, 2010 10:14 PM 

Stu on the blue blog has posted an excellent colored closeup of the "figure 8" rock.

link

LWS


Posts: 3062

Reply: 255



PostPosted: February 21, 2010 11:12 PM 

Serpens; Re. your #253, Very Good idea to present a comparison picture.

What is the white stuff coating many of the rocks? Was that crater from a meteor impact in South America a few years ago? I think I remember seeing that picture in connection with such an impact.

Winston

LWS


Posts: 3062

Reply: 256



PostPosted: February 21, 2010 11:29 PM 

Barsoomer; re. your 254

Here are 4 images from today's Exploratorium pancam releases that seem to indicate that the "crust" can be found on all the visible sides of the concepcion rocks including the top. It includes a false colour composite of the same image that stu has up at UMSF.

Seems to be a stretch to consider that the crust could be fracture fill under those circumstances.





Winston


LWS


Posts: 3062

Reply: 257



PostPosted: February 21, 2010 11:48 PM 

Ben and Others. Aha! Hort's colour composite panorama below shows a rock that has some of the coating on it that must have developed after the impact. The rock is one near the bottom with a curved fracture over which the fill extends. It seem reasonable to assume that the fracture occured with the impact, yet the crust extends over the edge of the broken surface.

The crust is not fracture fill. It developed after the rock was fractured in the impact. QED

sizes/o/


Winston

hortonheardawho


Posts: 3465

Reply: 258



PostPosted: February 22, 2010 12:18 AM 

Here is a 2X saturated false color of the rocks of reply 252 and here is a peek into the shadows of the same rocks.

Ben, just some general questions about your model:

what overburdon material could provide the almost uniform compaction of loose soil that became the almost uniform bedrock over hundreds of km2?

Where did the compacting overburden "go"?

When did it go?

Did the dessication cracks go as deep as the mineralization liquids?

How deep?

What I am looking for is a numerical parameterized model ( mass and height of overburdon, height and width of cracks, diameter and number of berries, length of stems assuming wind erosion of host rock... )

The parameters can have the same generality as, for example, the Drake equation to establish a observation volume accurate to perhaps an order of magnitude in each parameter. THEN any observations that fall outside the parameter space would signal that the model is wrong.

Maybe I am asking too much - but isn't geology "just" a subset of physics and therefore quantifiable?

Remember, science can only disprove models - not prove them.

Ben


Posts: 2270

Reply: 259



PostPosted: February 22, 2010 12:33 AM 

Winston; It would not be unusual for fluid moving on the four sides of a cube to have deposited fracture fill on all of them.

I have examined the images in your 256 and only in the last one is there a suggestion fracture fill is on a bedding plane surface and I can't be sure of that.

But even so ,if you peruse horizontal dessication cracks you will find instances where they occur.
Also look at many photos of modern mud-cracks and you will find void space beneath concave upward plates that could become buried leaving room for fracture fill.

I will now turn the table and ask you to present logical,evidence that it isn't fracture fill. Sad

Barsoomer


Posts: 344

Reply: 260



PostPosted: February 22, 2010 1:02 AM 

Ben, what sort of observational evidence would persuade you that the crust is not fracture fill? For a scientific theory to be testable, it should make predictions that are falsifiable. What predictions does your model make that are potentially falsifiable? (Beyond what we have observed already.)

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