[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

[MarsIsImportant]

I agree with CosmicRocker.

Although I can see how evidence of Impact surge could be common on Mars, I hardly see it as the only one. IMHO the impact model doesn't fit well with Meridiani--particularly in isolation. There are simply too many signs of both wind and water type erosion and deposition on the these plains. The lack of course material and sulfides cannot be discribed as minor problems. The fact that high rates of oxidation would be required for the surge process to explain what has been observed suggests massive changes in the Marsian environment every bit as complex and messy as anything that the MER team has proposed.

Let's face it. The Marsian environment has changed dramatically. The question is how. IMHO, the fact that massive amounts of water ice have been discovered in the subsurface and polar regions of Mars requires that when the KISS principle is used water in some form or another must have actively participated in the geology of part of the Marsian surface at sometime when the atmosphere was likely much thicker. IMHO, denying the impact of water based processes on early Mars would be a stretch of the imaginiation. There is simply too much of it.

With so many visible impact craters, it is also hard to deny the likely impact of surge processes over large parts of the surface. I just don't think one model alone can explain all the observations...when the evidence to supposrt any one model is marginal at best. All this combined highly suggests that complexity is closer to the truth. So in this case, the KISS principle when properly applied is not nearly as simple as we might want it to be.