[X] My Assistant

[dburt]

Relevant to Emily's boulder observation, the "Gullies and layers" HiRISE image was not the first to show layers with abundant boulders, indicating poor sediment sorting in layered slopes. Previous images included, e.g., PSP_001691_1320 "Gullied trough in Noachis Terra, released on 28 Feb., and PSP_001942_2310 "Signs of fluids and ice in Acidalia Planitia" released on 9 May. That these bouldery layers might represent ancient ballistic impact ejecta seems a reasonable suggestion, because much of the present martian surface is littered with boulders presumed to be ballistic impact ejecta. Other possibilities for boulder deposits might include, e.g., ancient talus or landslide deposits at the foot of slopes, stream boulders in channels, volcanic ejecta near vents, glacial moraines, or iceberg dropstones.

As an aside, the related suggestion that at least some of the fine-grained layers above or below any boulder deposits (or elsewhere on Mars) could likewise represent ancient impact deposits (non-ballistic fine-grained sand and dust distributed over vast areas by fast-moving, turbulent, erosive gaseous density currents - a.k.a. impact surge clouds - or by the winds as later fallout) already seems to have aroused considerable controversy on this forum, but again that's peripheral to Emily's boulder comment.

--Don

[MOD EDIT: "Brine Splat Burt" discussion moved here -> http://www.unmannedspaceflight.com/index.p...ic=4308&hl= -EGD]

[centsworth_II]

As an aside, the related suggestion that at least some of the fine-grained layers above or below any boulder
deposits (or elsewhere on Mars) could likewise represent ancient impact deposits (non-ballistic fine-grained
sand and dust distributed over vast areas by fast-moving, turbulent, erosive gaseous density currents - a.k.a.
impact surge clouds - or by the winds as later fallout) already seems to have aroused considerable controversy
on this forum, but again that's peripheral to Emily's boulder comment.

So you're the dburt of Basal Surge fame?

"ASU geologists L. Paul Knauth and Donald Burt, who along with Kenneth Wohletz of Los Alamos National
Laboratory, say that base surges resulting from massive explosions caused by meteorite strikes offer a simpler
and more consistent explanation for the rock formations and sediment layers found at the Opportunity site."
http://www.asu.edu/news/stories/200512/200..._meteorites.htm

I haven't followed the situation closely enough to ask any good questions, but I wonder if anyone else here
would like to ask about your current views.

for reference, the basal surge thread is here:
http://www.unmannedspaceflight.com/index.p...surge&st=30

[silylene]

Don,

Thanks for taking the time for a detailed reply.

I was thinking that deposition of suspended dust clouds from impacts could give uniform thin layers, as we saw in Meridiani. However, I do not have a good mechanism for glueing these settling dusts down into a layer unless the substrate had a moisture content.

Or perhaps, the impact dusts settled down onto a very shallow lake, and left layers underwater as they settled below? And the festoons are ripples from wind driven flow? Sorry, I don't know enough geology to differentiate if one possibility is more likely than another.

However, I don't see how surges could have produces all the thin fine bedded layers of similar thickness we have observed at Meridani. If it were surges, I would have expected some layers to be very thick, some thinner, and some containing jumbles of debris of various size. We haven't seen this.

On your criticism of the Fe/Ni ratios on the spherules, you do bring up some good points. However, I don't see how a surge mechanism would create spherules of this composition either.

Same goes for the Br/Cl ratios - the high Br levels always struck me as 'odd'. I wondered if Cl salts are more friable and thus more likely to be blown away, or something like that. Preferential erosion of Cl slats would ultimately cause the Br salts to enrich. All that said, I don't understand how a surge mechanism would account for the Br/Cl ratios either.