Burns cliff

Jon,

There may or may not be ice at the bottom of Endurance Crater. The "dune field" in Endurance is believed by most people to be a simple sand (or silt) dune deposit. It is possible that it is nothing more than a dune deposit, perhaps it was deposited during one of the global dust storms that envelope Mars from time to time. It may have been deposited relativly recently or more likely sometime long ago (millions of years).

Maybe it was deposited at a time when Mars was going through a warmer period and water vapor or other cohesive vapors mixed with the dust in a storm, these dunes formed, and then become more solidified when the temperatures dropped. For example: If it snows on Earth and the temperature is between say 30 and 20 degrees F and then the winds blows the snow around we typically see snow drifts form. If the temperature drops to say 10 to 0 degrees F the drifts usually become more solid or cemented and remain stable during subsequest snow storms as long as the temperature remains below freezing. Perhaps the dunes at the bottom of Endurance are "fossilized sand or silt dunes that formed in conjunction with a cohesive material or vapor.

The "ice" refers to what myself and some other people believed they were seeing. The Endurance dune field appears similar to ablated ice or ablated ice-like/evaporite material. If the rover had performed a simple RAT sample on the "dune material" we would likely understand much more about this material. If it is an ablated briney ice and not simple sand/silt dunes (fossilized or otherwise), then the implications of this material could be instrumental in explaining the spherule formation.

L2/L5 Burns Cliff:

Warning: 1.9 MB link.

Color by horticolor.

(R,G,B)=(L2,0.70(L5),2G-R) -- plus final tweak of color.

OK, Rock guys, go crazy.

> OK, Rock guys, go crazy

Whew, insane. Thanks!

Orient my thinking: those gray streaks left of center, are they running down dip? Why would they not follow the joints in many instances? The streaks look painted on!

I presume that the bedding dip is caused by the upturned rim created by the impact. The stata ought to be essentially flat-lying.

Waiting for a close up examination!

--Bill

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.