Burns cliff

The "painted-on" strips could be along especially narrow cracks. In these, water could remain in place as it slowly passed through and altered the surrounding rock. Wider cracks could have been unable to hold water as effectively. It would simply flow through too quickly to do any alteration.

Perhaps they may be able to figure out some characteristics of the (former) subsurface hydrology if there is any correlation between crack size and alteration.

The dunes are merely the top of sand that is slowly filling all of the craters in the vicinity. Endurance is relatively fresh. The oldest craters, as seen on MGS images, are no more than light, faint rings. They are completely filled in, and the raised bedrock rims are eroded down to nearly the level of the surrounding plain.

The image at:

_tiled/R14/R1400021.jpg

(left half) shows Endurance (bottom) and a larger crater above it that is nearly filled in and stripped down. The presence of dunes in the center indicate that it is still filling in. The other half of the image, featuring Victoria, seems to show a few of these filled-in "ghost" craters in the light mottled terrain.

Ok, I'll try to make it easier.

Just remove the double underline "__" between "jp" and "g" in the middle after copying and pasting.

Heck with it. Just go to

[link]

and click the left image. Sheesh!

Hi rpage

There is no way that can be ice.

First of all the morphology is exactly what you would expect from sand (not silt, silt does not form dunes onless it has been aggregated into sand-sized particles). there are two interfering sets of first order dunes, and interferring set of second order dunes and third order ripples on those.

Second, if this was ice it would have been immediately obvious in the first min-TES scan of the crater. Water has a huge IR absorbtion band that sticks out like a dog's hind leg. There is no way this could be missed. Finding ice would be the most exciting thing either rover would have found to date and there is no way we would have not heard about it almost as soon as the readings came in. Even a few percent water is extremely obvious in IR spectroscopy.

Third ice is going to sublime at the equator unless it is protected by a thick layer of dust. Subliming ice deposits are quite rough - we have examples on earth in Antarctica, Greenland, and Bolivia. This stuff is smooth.

Cheers

Jon

Jon,

You may have misunderstood me. Pure water ice would not last for long on Mars at the Endurance location.

My discussion in the previous post concerns a briney ice-like material that has very little or no H2O.

Jon,

To further clarify, it is possible that the dune field in endurance is an evaporite-like material with little or no H2O. If that were the case or if it was a briney ice with little or no H2O I would suspect it to be composed of sulferous and halogenated compounds.

Also silt can and does form dunes:
http://www.wetlands.org/RDB/Ramsar_Dir/Jordan/Jo001D02.htm

Cheers,
Robert

Hi robert

Certainly dunes have form from evaporite materials. On earth gypsum dunes are very common. On water is neccessary. In fact, given the composition of the local rock, I would be surprised if these dunes did not contain some sulphate minerals.

The "silt" dunes at Azraq Oasis are classic lunettes. These form downwind of ephermal lakes. Lunnetes are so-called because of the shape of many is like a crescent moon. They are indeed composed of silt and clay but the dunes develop from deposition of sand-sized electrostatically bound aggregates deflated from the episodic desiccation of the lake floor. On earth these aggregates often break up with rainfall, making the "silt" or "clay" dune a homogeneous mass resistant to erosion.

The distinction between sand and silt is very important in sediments. Silt is transported by suspension, sand by saltation (bouncing) and sliding. Hence silt forms topography mantling deposits of loess and parna as it settles out of suspension, whereas sand forms dunes or sheets, often topographically controlled.

Cheers

Jon

Jon,

I was merely pointing out that there are dunes or dune-like structures that are composed of silt sized particles in reply to your assertion that silt cannot form dunes.

Does anyone have a handle on how one can prove that the "dunefield" at the bottom of Endurance is either an ablated material or dunes composed of individual particles.

regards,
Robert

Interesting images. Some craters fill with dust but parts of Endurance appears to have been cleaned or even excavated by the winds. One earlier image showed different rocks in a mosaic "weathered" down to same level. Only at the base of the crater does dust acumulate and form the amazing dune patterns. (I for one is pleased NASA did not vandalize the natural feature by drilling holes into it- how would we feel if an alien race turned up and zapped the Mona Lisa for analysis? )
Back to dust - the winds over the surface must be high enough to generate a swirling vortex in the crater, removing anything loose around the Burns Cliff area and forming the pattern at the base of the crater as a sort of standing wave. NASA was lucky to have such a crater near the Opportunity landing site giving us the Burns Cliff exposure.

Getting closer to the mysterious strips:

Robert

Silt sized particles do not make dunes. If they are aggregated to form sand sized particles then they can. But then they are no longer silt from a sedimentological perspective.

By the same token granite and basalt cannot make dunes. If they are disaggregated to sand the fragments can form dunes, but then they are no longer the rocks granite or basalt, but granitic and basaltic sand.

These are subtle but important differences.

Cheers

Jon

Additional note:

As I have already pointed out, the morphology of this feature shows that it is a dune field and not ablated material.

Jon

Er, Burns Cliff, guys?

Warning: 2.1 MB link.

I think the streaks are very fine dust from the basalts that cap Burns Cliff.

What intrigues me is the fact that the beds seem defined by the density of blueberries. IE, the factors that controlled the blueberry formation controlled the bedding.

Hmm. What else do I know that behaves that way?

Forgot to mention the usual color by horticolor warning.

These are (R,G,B)=(L2,0.78(L5),2G-R) with a final color and contrast tweak.

I balanced the streaks to gray -- so they may be some other color entirely ( but not likely ).

Are the new MI images (November 4) from before or after the rover rolled on top of the cliffs?

New pancam/navcam/hazcam images indicate the rover is sitting on the formation - but the new MI images really don't seem to look like what I would expect at the formation...

No, they're from October 16 -- Wopmay.

> Certainly dunes have form from evaporite materials.

And many examples of this on Mars from the MOC images. In the "meridiani" region where there are exposures of the "whiterock" formation you will frequently see light-colored dunes.

>The distinction between sand and silt is very important in sediments.

and

>Back to dust - the winds over the surface must be high enough to generate a swirling vortex in the crater, removing anything loose around the Burns Cliff area and forming the pattern at the base of the crater as a sort of standing wave.

The aeolian conditions on Mars are quite different than those we a accustomed to. A very thin atmosphere moving at high veolocites (200-300+ mph) would likely have unusal material transport characteristics. Have there been studies done on aeolian erosion-transport-deposition of the Martian atmosphere?

The winds travelling over the flatish Merdiani Plains at high speed and encountering Endurance crater would no doubt do unusual things. Endurance crater is plenty ood, and Victoria more so. I'm trying to figure out the "scallops" around it's rim.

Hort, I figured that the "grey" streaks were not really grey. The important thing is that they are a different color. From the first close-ish up pics (sol 278 navcam) they almost look fine silty-material deposited from water seeping from bedding planes.

--Bill

Well, I agree with Horton that the dark vertical stripes appear to be sand, it is the same dark material we have been seeing all over the place, even in the forground of Horton's image in post 34.

But, why is it forming sharply defined vertical bands? IT seesm to be flowing from the cracks in the material above the cliff, that seems obvious, but why doesn't the wind blow it around or even blow it away? It seems to be sticking to the cliff somehow, I don't have any guess for what is going on there.

Well, one possibility is that the sand flow is very active, that is there is significant replacement flow daily. The dark material spills and flows just like a stream or spring does, But, that would be very active indead. The wind keeps cleaning the material away and then new material spills down and forms these dramatic vertical bands.

I also agree that the spherules density follows the bedding planes., I think they were depositied IN the beds orginally, which would explain that nicely, but then how they formed is a complete mystery, unless they are biogenic.

Horton, what do you mean by "What else do I know that behaves that way?" What else DOES behave that way? Are you sugesting they are biogenic or is there something else you are hinting at?

Hmmk, about winds and endurance. High speed wind flowing accross the plains would create a beroulif force vaccum when it flows over endurance. If we are talking about VERY high speeds, this might create substantial updrafts. Combined with possible thermal updrafts we might generatye exaoitc air flow patterns.