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Geomorphology of Gale Crater, Rock on!
HSchirmer
post Jun 16 2019, 11:18 PM
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QUOTE (serpens @ Jun 14 2019, 01:33 AM) *
(snip)
There is clear evidence that the sedimentary formations investigated by Curiosity since landing predominantly reflect fluvial lacustrine environments and the accessible 300 metre odd thickness of the Murray formation was laid down over some considerable time in a reasonably deep, neutral pH lake.
(snip)


There is a caveat there, layers of sediment on the bottom of a lake sample the conditions at the bottom of the lake.
If there's a neutral pH salt spring in an otherwise acidic or basic lake, the sediments record the neutral pH, because the neutral salt spring water is denser and accumulates in the depths of the lake.

Same problem with seasonal temperature and lake turnover.
Lake sediments in freeze-thaw climates are deposited at only two temperatures:
EITHER 4 Celcius wich is where water is densest, during winter, spring and summer, OR when the lake "turns over" in fall when the water is average ambient temperature.


Let's imagine a Mars where there is fine hydrophobic dust and fine hydrophilic dust.
You'll have a buoyancy gradient between those chemical particles, a constant wind might give you "tiger-stripes"
so that different chemicals from dust concentrate along the lake surface and only some reach the lake bottom.

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serpens
post Jun 18 2019, 01:30 AM
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I don't think that a pseudo Langmuir circulation effect has any relevance to the Murray formation or indeed to the sum of data and analysis covering Curiosity's traverse.

[Edit] Apologies if that comment seems terse but concepts must at least bear some relation to the features. Stack, Grotzinger, Gupta, Edgar et al. "Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation" assessed Pahrump hills to be deposits from hyperpycnal flow (turbidity currents) attributed to rivers from the rim plunging into the lake. Hyperpycnal plumes can travel significant distances before dropping entrained sediment loads so this does not constrain the size of the lake, but it does mean that it lasted a very long time
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HSchirmer
post Jun 18 2019, 04:33 PM
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QUOTE (serpens @ Jun 18 2019, 02:30 AM) *
I don't think that a pseudo Langmuir circulation effect has any relevance to the Murray formation or indeed to the sum of data and analysis covering Curiosity's traverse.

[Edit] Apologies if that comment seems terse but concepts must at least bear some relation to the features. Stack, Grotzinger, Gupta, Edgar et al. "Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation" assessed Pahrump hills to be deposits from hyperpycnal flow (turbidity currents) attributed to rivers from the rim plunging into the lake. Hyperpycnal plumes can travel significant distances before dropping entrained sediment loads so this does not constrain the size of the lake, but it does mean that it lasted a very long time


No problem, terse is accurate; but sometimes "not relevant" means nobody thought to look?

A bit more reading shows that it's likely languir circulation would be more important for mixing material, rather than separating material. The important point is that hydrothermal flow should keep an early warm lake mixed, while wind-driven circulation could have kept a later lake mixed for much longer.

We see evidence of steady winds in the yardangs, and the sheer amount of material at the central mound at Gale crater;
those steady winds should have kept an open water lake stirred up as well. This should have kept clay and silt in suspension, but also 'mixed' the lake vertically. This suggests that pulses of fine sediment or water that are basic, salty, or acidic would have time to achieve chemical equilibrium with the bulk properties of the lake because the silt and clay sediment stay suspended in the lake long enough to reach chemical equilibrium with the previously laid down lake sediments.

Another point is that a freezing and thawing lake would experience 2 annual sedimentation events; spring and fall.
Dirt, sand, and dust accumulate on the frozen lake, when the ice thaws, the heavier material settles to form a new coherent layer across the lake bottom. However, the fine clays should stay in suspension thanks to wind-driven water circulation.
At the onset of winter, as the lake freezes over, wind-driven circulation stops, and the fine clays precipitate out (IIRC clays stay suspended for 1-3 weeks under earth gravity, not sure about Mars).


    Langmuir circulation driving sediment entrainment into newly formed ice: Tank experiment results with application to nature (Lake Hattie, United States; Kara Sea, Siberia)
    "Uzaki and Matsunaga [2000] suggested that Lc plays a role in near coastal sediment transport processes, and Gargett et al. [2004] showed that Langmuir cells penetrating a shallow water column down to the seabed are an important mechanism for major sediment resuspension (redistribution of bottom sediment throughout the water column) and sediment transport events on midlatitude continental shelves."
    https://agupubs.onlinelibrary.wiley.com/doi...29/2005JC003259


    Langmuir Supercells: A Mechanism for Sediment Resuspension and Transport in Shallow Seas
    "Recent measurements at a cabled sea-floor node in 15 meters of water off the coast of New Jersey suggest that Langmuir supercells, Langmuir circulations that achieve vertical scales equal to the water depth under extended storms, are an important mechanism for major sediment resuspension events on the extensive shallow shelves off the eastern U.S. coast. "
    https://science.sciencemag.org/content/306/5703/1925




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HSchirmer
post Jun 18 2019, 07:45 PM
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Let me take a step back-

I've been thinking about some great ideas from earlier parts of this discussion-

    Phil Stooke

    At some point if the debris breaks down into sufficiently small particles it can be removed from the vicinity, even lifted out of Gale crater completely. So it might not remain in this area to choke off further erosion.


    ngunn

    An internal heat source beneath Gale can do more than locally hardening the sediments once formed. It could be the reason they formed in the first place. Imagine a largely frozen Mars with plenty of water in the form of ice or ice-capped seas. Now in Gale Crater picture a geothermally heated lake that is at least sometimes ice-free. The liquid surface acts as an effective dust trap 'quickly' filling the whole thing with horizontal sediments. This avoids the need to bury and exhume a similar pile of sediments on a planet-wide scale.



    elakdawalla

    One thing I would want to check is the direction of the tilt and how that relates to the long-term changes in Mars' shape due to, say, the construction of the Tharsis volcanic complex. The MESSENGER team has shown how lava-filled craters near Mercury's pole now have tilted floors that must once have been horizontal, due to tectonic activity. My own work on Venus dealt with the same thing, measuring current topography of lava surfaces that you assume started out as flat in order to get at ancient tectonics. I'm sure the same could happen on Mars. We certainly know Mars' shape has changed in the past, and it's been suggested that the entire crust has reoriented (true polar wander). I'd love to see if the tilting observed here is consistent with geophysical work on Mars' tectonics -- or inconsistent, which would be just as interesting.


They're all interesting because they've all recently gotten some support,

A- A regional Martian groundwater level, which could supply sufficient water to a crater hydrothermal system to dissolve basalt breccia into sufficiently small particles to blow away, or perhaps flow way as muddy ground water.

B- If Gale crater had 1,800 cubic KM of impact melt in a magma chamber, we'd expect it to stay warm and wet for a long time, such that the lake, any peak ring, and the central mound, would all initially have fumaroles and brines and hydrated minerals to trap dust to create Mount Sharp. As the site cooled and a crater lake formed, expect more dust to accumulate.

C- Earlier modeling of boxwork features around -3600 elevation might make more sense if we consider a possible -3707 level for a Northern "Arabian Ocean" once the Olympus Mons bulge is removed. Alternate idea, work backwards to figure out the the volume of water moving through the 500 km long watershed, into Farah Vallis and into Gale.
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serpens
post Jun 23 2019, 03:08 AM
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Immediately following the Gale impact there would have been a lava pool on the crater floor and intense hydrothermal activity. But the final crater floor is well below the current floor and a consideration is how long it took for at least a kilometre of sediment to build up. Certainly by the time the Pahrump Hills sediment was deposited hydrothermal influences do not seem to have been significant. All indications are that this deposition was traction controlled in deep, neutral pH water.

During the 7 years since the inception of this thread Curiosity has revealed important information, not the least of which is the evidence of a fluvial / lacustrine mudstone dominated environment across the transit. Kimberly revealed a delta that would have defined the edge of a lake at that point in time. This is some 60 metres below Pahrump hills and 350 metres below the top of the ridge. By the time the sediments were deposited at the level of the ridge the lake must have covered most of the crater. Impact heat and associated hydrothermal activity may have lasted a couple of hundred thousand years. The Crater Lake would have had to have lasted closer to a million. Though an apples and watermelon comparison, Lake Malawi sediment cores dating back a million years were taken at a depth of around 300 metres.
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HSchirmer
post Jun 23 2019, 09:13 AM
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QUOTE (serpens @ Jun 23 2019, 04:08 AM) *
(snip)
the evidence of a fluvial / lacustrine mudstone dominated environment across the transit.
Kimberly revealed a delta that would have defined the edge of a lake at that point in time. This is some 60 metres below Pahrump hills and 350 metres below the top of the ridge.
...
The Crater Lake would have had to have lasted closer to a million.
(snip)


Probably MUCH longer, filling Gale crater with the material for 350 meters of rock in only 1 million years would require sedimentation rates 2.5x faster than what has been measured for rift basins on Earth at Newark basin.

    The NSF funded Newark Basin Coring Project (NBCP) (Fig. 3.2.2.1) resulted in the recovery of about 6.8 km of continuous core from 7 coring sites making up a combined 4.7 km stratigraphic section spanning nearly all of the Late Triassic age strata of the Newark rift basin (Olsen et al., 1996a). Additional core from the Army Corps of Engineers, completed the Jurassic age part of the Newark basin section (Olsen et al., 1996b). This core spans roughly 32 million years
    https://www.ldeo.columbia.edu/~polsen/nbcp/cyclcicity.html


So, 32 million years of erosion into a similar sized dead-end basion on Earth creates 4.7 km of sediment, 350 meters of sediments under Earth conditions would take ~2.4 million years. However, those "Earth conditions" erosion numbers are from the Triassic/Jurassic period during the opening of the Atlantic ocean allowed seasonal monsoons to begin eroding the former northern central desert of Gondwanaland-

That level of rain and erosion is something that is unlikely to have occurred at Gale crater.

One of the recent papers about regional hydrology at Gale raised the possibility that the crater wall was breached by Fara Vallis only AFTER Mount sharp was in place, based on on the morphology of the "pancake delta" and other landforms along the southwestern crater rim, which are light blue below


Sequence and relative timing of large lakes in Gale crater (Mars) after the formation of Mount Sharp - 2016
https://agupubs.onlinelibrary.wiley.com/doi...02/2015JE004905

If that is the case, then you wouldn't have sediment transport into Gale via river valley networks until much later when the crater was mostly filled.

So, I do agree that comparing Gale Crater to the Newark Basis is an "apples to watermelons" comparison, but it's the best data-point I know of for a "piano tuner problem" where you don't have the data on Martian climate or erosion.
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serpens
post Jun 24 2019, 11:50 PM
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The introduction of the paper you link indicates that the authors believed that the lower section of Mount Sharp (the Murray formation) was Aeolian, formed from erosion of sediments identified during Curiosity’s transit and evidence of surface inflow to Gale occurred following the formation of Mount Sharp. However we now have empirical evidence that deposition at least to the level of Vera Rubin Ridge was lacustrine.

Over a few billion years erosion has removed much evidence but my wet fingered guess would be that evidence of inflow dates to the Murray formation lake and any later inflow following the formation of Mount Sharp involved reactivation. The fan dates from this period and we are going to get a good look at it. Any concept or hypothesis should reflect current data.

To put the depth of sediment and the size of the lake in context, unless Mr Steno got it wrong the sediment would have been deposited across this view to at least the same level at the crater rim. Water level would have been higher.
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ngunn
post Jun 25 2019, 08:24 AM
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Maybe it's worth noting that we see absolutely no sign of any former shoreline on the rim mountain range. Of course being steeply sloping we would expect plenty of erosion there in the meantime, but viewing now on a level with it one might think that some features could have lined up.
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serpens
post Jun 25 2019, 01:52 PM
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In their supplementary materials for their paper "deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars", Grotzinger, Gupta, Malin et al provided the results of topographic analysis of Gale and the power law relations for the calculated “fresh” final crater conditions. They estimate the rim horizontal back stepping distance through erosion to be 4.8 km. That is a heck of a lot of material. How much of this occurred before the lake filled and how much after it dried is unknown but given the amount transferred to form Mount Sharp, erosive conditions after the lake dried must have been pretty severe, removing evidence that might have been visible from a distance.
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stevesliva
post Jun 25 2019, 03:05 PM
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QUOTE (ngunn @ Jun 25 2019, 04:24 AM) *
Maybe it's worth noting that we see absolutely no sign of any former shoreline on the rim mountain range. Of course being steeply sloping we would expect plenty of erosion there in the meantime, but viewing now on a level with it one might think that some features could have lined up.


The hillside shorelines you see in the Great Basin are mere thousands of years old....
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serpens
post Jul 4 2019, 11:41 PM
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Some interesting and thought provoking abstracts from the Ninth International Conference on Mars.

https://www.hou.usra.edu/meetings/ninthmars...019_program.htm

I found the abstracts from sessions on Tuesday covering Geology and Geochemistry of Gale and the Glaciers, Oceans, Rivers, Lakes of particular interest with respect to this thread. Reading these abstracts and also back through the thread which covers 7 years I am struck by the extent to which Curiosity's ground truth has altered and refined the perceptions of Gale crater's history. With the MER and MSL, NASA/JPL have established a baseline for value for money.
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HSchirmer
post Jul 8 2019, 01:47 AM
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QUOTE (serpens @ Jul 5 2019, 12:41 AM) *
Some interesting and thought provoking abstracts from the Ninth International Conference on Mars.

https://www.hou.usra.edu/meetings/ninthmars...019_program.htm

I found the abstracts from sessions on Tuesday covering Geology and Geochemistry of Gale and the Glaciers, Oceans, Rivers, Lakes of particular interest with respect to this thread. Reading these abstracts and also back through the thread which covers 7 years I am struck by the extent to which Curiosity's ground truth has altered and refined the perceptions of Gale crater's history. With the MER and MSL, NASA/JPL have established a baseline for value for money.


Um, that seems like a rather long lead in for a post, which then omits any discussion about what the papesr actually found.

I read through most of the papers, and my take-away was that basically everyone is saying, there's a possibility of IMPORTANT science, but at this stage nothing is definitive, we need more research (i.e. funding).
Which is perfectly fine as graduate papers go, but, eh, less than stirring as far as actually stating findings.
But, I could be wrong.

Are there any important findings or definitive conclusions about Mars in these papers? Something that I might have missed?
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jccwrt
post Jul 8 2019, 03:01 AM
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I'd expect most of the new science results were shown at LPSC back in March. The Mars conference is more about reviewing the last several years of science and getting a community sense of the directions that Mars research is going. It's more of a "here's the big picture and problems we need to address" conference rather than a "here's what we found this year" conference.
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serpens
post Jul 8 2019, 04:03 AM
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Exactly.
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