Duck Bay Adventure - Page 17

Hi Kye. Personally I think most of the regolith (rather than soil because soil by definition includes organic remains - although admittedly the term has been used in many MER research papers) came from weathering of basaltic rock before the onset of stasis. At Meridiani, it also includes hematite spherule fragments. [link] AGU is an excellent data source and has reasonably cheap access to papers for non members.

The etched terrain with bedrock visible between armoured dunes that have been inactive for Gyrs is compelling evidence that there is no dust deposition in this area and that current erosion levels are at the lower end of Golombek's scale. The regolith, protected by the duricrust would seem to have been in place for a long time.

The Victoria promentories show that there was extensive aeolian deposition at Meridiani. Mayhap there are some thin impact surge layers in there but the primary process seems to be dune formations and sandsheets. Erosion of the crater and ejecta blanket sandstone would have contributed some material to the local regolith and dune fields. The Victoria impactor hit before the atmosphere loss, but how long Victoria weathered before statis set in the we can never know.

Thanks for the pointer Arizona St. The paper outcomes were reported in Scienceworld but it is unfortunate though understandable that so many interesting papers are limited to 'members only' circulations. Abstracts provide tantalising hints but without the analytical meat in the papers they can sometimes be interpreted to reflect our pet theories and are potentially misleading.

I thought that the jury was still out on whether the trace carbonates detected in the dust were the result of current interaction with the atmosphere or not. Ralf Gellert, the lead scientist and co-developer of the APXS recently stated that 'no mineralogy instrument has yet detected significant amounts of carbonate on Mars'. Not sure what significant means as a metric but there seems to be a dearth of papers addressing carbonat4s (or lack thereof) since the MER landed. Do you have any feeling on just what volume of carbon dioxide the carbonate traces would account for?

brian, This article points out strong similarities in chemistry and mineralogy between the dust and the soil at both MER sites:

[link]

I happen to have the full text on paper. It makes the case for the dust having contributed a large component to the soil (and likely the soil to the dust).

I have to be away from the Net for a couple of days. Thanks for the exchange. I hope we can take it up again.

Thanks Kye. Have a good break (which I trust is recreational).

sol 1355-1382 L0 ( Nov 16 - Dec 14, 2007 ) animation:

Oppy has moved about 3 meters north.

Several meters of traversable, inviting, partially exposed bedrock down there.

where is the impact surge ejecta or melted fragments from the impact here brian?

G'day Mann.
I gather you are cross referencing my HP discussion with Ben on another thread. I have posted this link before but it is an outstanding reference for crater formation. http://www.lpi.usra.edu/publications/books/CB-954/chapter3.pdf
Figure 3.7 indicates where allochthonous breccia would be primarily found (ie under the current crater bottom).

I'm not sure what your ejecta comment relates to? We have been driving over impact ejecta since we reached the annulus. Given the visibility of the old surface in the etched terrain and the wind energy required to form the armoured dunes, any fine surge particles would have blown away. I don't think the genisis of the cobbles has been explained yet and these could well be ejecta related.

We saw one 'conchlike' rock during the drive from Erebus to Victoria (which I cannot now locate) that looked remarkably like a fusiform bomb (melted impact ejecta can respond in the same way as volcanic ejecta).

John>>>

Is this it?

[link]

yt
dx

Sorry...

I meant 'brian'

yt
dx

Thanks dx. No this was the one I meant from sol 882.

But now I have found it I believe that while it is ejecta, the resemblance to a fusiform bomb is purely co-incidental.

thanks for the response brian, and i shall read through your link.

This is an odd chunk, i think i'll use the new raws from mer to make abetter image.

I keep trying to imagine what the impacts would look like and create, here at Meridiani. If it was dry when it hit, then lots of dust and rock. If dry, then why are the fracure fills atributed to the strike?

If wet, then i would expect more splatt bombs, that might look like the odd chunk you have posted.
the result created from such a hit must of created some sort of heated, hardened material, that should withstand the test of time, it seems lacking.

The cobbles have not been seen within any sort of matrix as of yet, why do i find this odd?, or are the cobbles the result, the final remnents of the hardened slag?

I have this confusion if i picture the impactor as iron nickel, but, things fit together a bit clearer, if the impactor was ice.

is this melt from Fram brian? or fracture fill?

How can a dry strike create fracture fills?

I read through the link, but what i would like is a picture of, (in words), of the strike here at victoria, and endurance.

Also, very Large berries at fram, from such a shallow hole.

I keep thinking the strikes themselves are responsible for the berries in some way.

Hi Mann. I can't seem to match your thumbnail to a Fram shot. Could you advise the camera and sol please?

Fracture fill results from mineral-laden water percolating through cracks (which may or may not be caused by an impact) leaving deposits behind, forming veins, (the "fracture fill"). The 'rock hedges' seen in both Endurance and Victoria are an erosional structuer. The mineral deposits being harder than the surrounding material, as the rock eroded away it left a harder residual ridge behind. To me the significant fact is that the cracks must have formed a long time after the original sediments were laid down, since the original unconsolidated sediment layers had to have time to compact into stone (lithification) hard enough to form clearly defined sharp cracks. Apart from the possibility of the cracks being impact induced, the fracture fill is not attributed to the impact.

The fracture fill, like the concretions, are a function of groundwater. Since the concretions are found in the ejecta the impact occurred after the water event(s) that formed them and this is probably (though not certain) the same for the fracture fill.

Not a terribly good explanation I'm afraid. Ben or Arizona St can do much better and correct any errors.

Brian; A very good explanation . The only thing I would add is that subsequent erosion has enlarged VC so the original impact surface has been removed.

I wonder how far Oppy will go? will she reach the cliff?

Brian/Ben - The mineralogy of the fracture fills actually show little or no Na or Cl enrichment which likely means that the fills are not primarily precipitated. The close similarity of fracture fill and country rock lithology suggests that fractures were filled by material derived from adjacent outcrop. Also the origin of some of the fractures may be related to volume reduction upon dehydration of hydrated minerals (as demonstrated by the presence of polygonal fractures)......my two cents

AZ St.;They don't look like the sand filled crevasses seen on earth.
It looks like we are headed toward one of the really long ones . Maybe it will shed more light.

Hi Arizona St.
I was basing conceptions on JPL reports. ie for Roosevelt quote "Roosevelt lines a fracture in the local pavement and scientists hypothesize that it is a fracture fill, formed by water that percolated through the fracture.....The image shows fine laminations (layers about 1 millimeter or .04 inch thick) that run parallel to the axis of the fin. Some of the textures visible in the image likely indicate that minerals precipitated from the outcrop rocks, but sediment grains are also apparent".

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1938.pdf drew a possible association between iron rich laminations and fracture fill material (although not a definite attributing). From your comment a misconception. What is the mineralogy of the fracture fill if not iron rich?

I assume that your comments relate to Endurance 'rock hedges'. What's your feeling on the rather long, apparent hedges at Victoria?

It would certainly seem like water had something to do with the fracture fills but more so as a means of slow cementation of grains falling into the crack rather then the source of a secondary fracture fill made exclusively of precipitated minerals (i.e., hydrothermal deposit). The flip side are the reaction rims that are preserved on some of the harder rocks of basaltic composition where Na and Cl are major ions of the alteration, a good indicator of water. No problem with an iron rich fracture fill but the iron probably comes from the surrounding rock, not carried and precipitated into the fracture by a circulating hydrothermal fluid. Obviously every fill has not been examined but the ones looked at show similarities. I have not seen or heard much about fracture fills lately including Victoria hedges, but with limited resources remaining for each rover, science targets are based on greatest return and IMO most are satisfied that the hedges are fairly well understood.