Welcome Professor "brine splat" Burt, "a chance to ask questions... or raise objections" Options

[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

[dburt]

Thanks for all the thoughtful replies about water flowing over a horizontal surface, in relation to "festoons". I agree such flow is theoretically possible, just not highly plausible (e.g., why don't you see "festoons" everywhere, across the entire area, if there was sheet flow, with no channels?). I'm reminded of the one about the procrastinating student who tells me he wants to take a make-up test because his grandmother died on the date of the first test and I say fine. Then he tells me the same thing again for the second test, and I think, well, okay, but that's kind of a coincidence. This kid is sure hard on grandmas, and he's all out. Then he comes up to me well after the third test and asks for a third make-up, "because my grandmother died". I say, hey wait a minute, you only had two, and he tells me something like, "well, my grandfather had a sex change operation" or "my father's mom was adopted, so she actually had two different mothers" or "my mom's mom was married to another woman, and my mom was fathered by an anonymous sperm donor" or "my father's family got divorced and remarried an awful lot, so I currently have 10 grandmothers". I think, well that's all theoretically possible, so I have to give him the makeup exam, but is it at all plausible? That's how we came to feel about the coincidences involved in the highly convoluted Meridiani story. Plus it doesn't explain how to form nearly identical-appearing, cross-bedded, sandy, salty, spherule-bearing rocks at Home Plate or anywhere else on Mars.

Making rare little "festoons" or trough-shaped current ripple cross-beds by the odd little eddy or vortex in a turbulent impact surge cloud seems far simpler conceptually. Such small trough shapes do occur in volcanic surge deposits - see figure and discussion in Knauth's 2007 LPSC abstract here:

http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1757.pdf

Actually, to a field geologist who habitually visualizes things in 3-D, most of the alleged Meridiani "festoons" appear to represent a topographic misinterpretation of a low-angle cross-bedded rock as viewed from above - see figure and discussion here:

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1869.pdf

Geologists sometimes call this effect "V-ing upstream". (When viewed from above, the horizontal bedding planes appear to bend up each crack and wrap around each ridge, like contour lines on a topographic map. Think of a person wearing horizontally striped pants, with you looking down at their rump from 5-feet up. The horizontal stripes will look like little troughs: UU.) The 5-foot high rover cameras can't bend down the way a real geologist could, to view the flat-lying beds from the side. Perhaps some of the 3-D image-processing gurus here at UMSF would like to take a stab at the rover "festoon" images to see if we're right or wrong about what look like troughs, but perhaps really aren't. (In other words, I'm asking for your help in discovering and visualizing the truth.)

Whatever the results of that important test, there would still be an awful lot of dead grandmothers at Meridiani, if you ask me.

BTW, the processes involved in forming impact surge deposits will probably never be as well studied or understood as those for deposition by wind and water. You can't confine a nuclear bomb to a wind tunnel, or to a tilted flume channel. If you want to observe surge deposition up close, you're dead, just like all those alleged grandmas. In the case of terrestrial impacts, fine-grained deposits begin to erode as soon as they're formed, and they're quickly gone. The extremely slow rate of wind erosion on Mars means that fine-grained impact deposits have a much better chance of being buried (and thus preserved) by later geological processes, such as more impacts. That preservation perhaps occurred at Meridiani and Home Plate, if we are correct.

--Don

[ElkGroveDan]

why don't you see "festoons" everywhere, across the entire area, if there was sheet flow, with no channels?)

Come on Don, now you're an educated guy. That's a bit like asking why paleontologists don't see fossils all over the Earth considering the widespread history of life here. After billions of years of who-knows-what, of impacts, wind erosion, ices, and even fluids, the region has changed. That we have to look carefully for something as small and fragile as fossilized festoons is not surprising. Their present day abundance is not necessarily indicative of historical conditions.