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serpens
Just in case anyone missed it, Emily provided an update on Curiosity's investigations including the intriguing Rock Hall drill initial results. http://www.planetary.org/blogs/emily-lakda...-2257-2312.html with a link to the LSPC abstract. https://www.hou.usra.edu/meetings/lpsc2019/pdf/1127.pdf
Sheer conjecture, but the decreasing phyllosilicates and increasing amorphous with elevation at VRR combined with the identification of akaganeite would seem to strengthen the case for volcanic outgassing providing precipitation, acid snow perhaps including dissolved HCl. Subsequent melting and interaction with groundwater would provide ferrous and chloride ions in acidic conditions.
HSchirmer
Curious if a new theory about the Pathfinder site might be relevant for Curiosity...

The Pathfinder landing site may have been shaped by water overflowing from Mar's northern ocean into a depression.

    The 1997 Mars Pathfinder Spacecraft Landing Site: Spillover Deposits from an Early Mars Inland Sea
    J. A. P. Rodriguez, V. R. Baker, T. Liu, M. Zarroca, B. Travis, T. Hui, G. Komatsu, D. C. Berman, R. Linares, M. V. Sykes, M. E. Banks & J. S. Kargel

    Scientific Reportsvolume 9, Article number: 4045 (2019)


    “Our paper shows a basin, with roughly the surface area of California, that separates most of the gigantic Martian channels from the Pathfinder landing site. Debris or lava flows would have filled the basin before reaching the Pathfinder landing site. The very existence of the basin requires cataclysmic floods as the channels’ primary formational mechanism” said Rodriguez.


Given that Gale may have been close to the shoreline



and a Martian ocean would have waves capable of sediment transport,

    https://gsa.confex.com/gsa/2017AM/webprogra...aper303500.html
    WIND, WAVES, AND SHORELINE DEVELOPMENT ON MARS
    Our results indicate that winds ranging from 5-35 m/s blowing across fetch distances from 10 – 100 km would have generated breaking wave velocities ranging from about 1 – 4 m/s. These velocities, in turn, would have been capable of transporting basalt boulders up to about 50 cm.


Could Gale basin have occasionally been filled from the ocean side?

    CuriousMars: Box Shaped Martian Features and Deep Water Lake Deposits Offer New Rover Destinations
    By Craig Covault



I'm curious, has anybody modeled whether an asteroid or comet impact into an early Mars ocean would generate a Tsunami?

We see many references to sudden "mega floods" carving channels along the Martian coastlines, which are often attributed to impacts melting ices and releasing melt waters. What sort of water movement would an ocean impact generate?
HSchirmer
QUOTE (serpens @ Dec 2 2012, 01:27 AM) *
nprev. I'm with you in that Mount Sharp probably has a central uplift core, but the bulk of the mountain is sedimentary. Have a look at a couple of the complex Lunar craters such as Maunder to get an idea of the relative size of a pretty much pristine central uplift.

The puzzle (and I deliberately avoid the word mystery) is why the sediment ended up as a central mound. I have difficulty accepting the explanation that the crater was overfilled to the height of (or greater than) Mt Sharp and then excavated, despite the credentials and credibility of the proposers. That hypothesis requires that the sediment that must have covered the rest of the crater and the surrounding area was totally removed while that on Mount Sharp was significantly more resistant. I'm backing a shallow crater lake for the phyllosilicates and a vortexing effect for the remainder. I don't have the smarts to model something so complex so take the last as being accompanied by wild guestures from the depths of an armchair.


Yep, quoting from quite a while back, but I thought that given recent papers about a possible Mars- groundwater-level, and about possible "slush-tsunami" it was appropriate to go back to early questions about Gale Crater.


Gale, crater combines two (perhaps three) interesting elements: a deep depression AND equatorial location AND (maybe) proximity to the Northern ocean (shoreline within reach of Tsunami waves expected from asteroid and comet strikes.)

- Gale's equatorial location is roughly analagous to an East African rift valley lake on Earth, Lake Turkana, that generates it's own wind due to the thermal inertia of the water versus the land.
- Gale seems to be deep enough to tie into any local, regional and planetary groundwater level, and it's depth and warnth would allow liquids over a long, long time.
- Gale's location near a possible shoreline might tie-in with a Northern ocean Tsunami theory.


Lake Turkana- https://en.wikipedia.org/wiki/Lake_Turkana
"On-shore and off-shore winds can be extremely strong, as the lake warms and cools more slowly than the land. Sudden, violent storms are frequent."


Mount Sharp-
We known that equatorial lakes in deserts can create their own microclimate and strong local wind patterns- during the day winds blow from the lake onto the shore, at night the wind reverses and blows from the shore onto the lake


Lake Turkana Wind Power Station- https://en.wikipedia.org/wiki/Lake_Turkana_...d_Power_Station
The Lake Turkana Wind Farm Project - M. Burlando, F. Durante; DEWI GmbH, Branch in Italy, Genoa, ItalyL. Claveri; DEWI GmbH, Oldenburg
https://www.dewi.de/dewi_res/fileadmin/pdf/...gazin_37/02.pdf
"A semi­permanent low pressure cell centered over Lake Victoria forces the main air­streams of both the monsoons, which are roughly parallel to the coastline over eastern Kenya, to flow zonally westward over north­western Kenya. This thermally­induced synoptic­scale deflection interacts with the orography of Eastern Africa to generate some con­vergence zones over the Ethiopian and Kenyan highlands. Just in between the Ethiopian and Kenyan highlands, the Turkana­Marsabit Corridor occurs, which is one of the windiest among these convergence zones. "


I wonder if crater lake microclimates might help explain Mount Sharp and other "tall mound" craters.
Theory is, during the day, the rocks around the lake warm up, that warm air rises and that draws cool dry air down onto the crater lake and peak. This creates a cool microclimate at the central peak, and a cool moist microclimate around the crater lake. The moist climate around the lake shore should accellerate weathering.
During the night, relatively warm moist air rises from the lake, that rising air kicks up wind that carries dust from the surrounding area onto the central peak. Dust should stick to any snow or moist soil on the central peak. Any extra dust or very fine dust is carried by rising moist air, the dust nucleates snow, snow falls on the central peak. When the snow eventually melts, it leaves behind the dust.
Repeat for aeons, and you should get a net transfer of dust from the surrounding shoreline onto a snow capped central peak.





Depth is important for two reasons - first it appears that the crater would be deep enough to tap into local and regional groundwater networks. It's ALSO deep enough and warm enough that it would have been one of the last places where liquid water was stable as the Martian atmosphere thinned out. If Mars had an atmospheric cycle of freeze-deflate and thaw-inflate then Gale would conversely be one of the first areas to "thaw out".

Equatorial location is important becase this means Gale crater one of the best places on Mars for insolation, heat, and therefore evaporation of liquid water.

Coastline is interesting because this puts Gale within possible reach of Tsunami or slushie-Tsunami effects.

    Tsunami waves extensively resurfaced the shorelines of an early Martian ocean
    J. Alexis P. Rodriguez, Alberto G. Fairén, Kenneth L. Tanaka, Mario Zarroca, Rogelio Linares, Thomas Platz, Goro Komatsu, Hideaki Miyamoto, Jeffrey S. Kargel, Jianguo Yan, Virginia Gulick, Kana Higuchi, Victor R. Baker & Natalie Glines
    Scientific Reports volume 6, Article number: 25106 (2016)
    https://www.nature.com/articles/srep25106
    "The simulations also show that bolide impacts causing craters ~30 km in diameter would have generated tsunami waves with typical onshore heights of ~50 m and local variations from ~10 m to as much as ~120 m..."


Interesting twist - if an impact occurs during a warm to mild conditiions, a 150-360 foot tall Tsunami hits the shore, waves of water flow in, then flow out. If Mars is cold to cryogenic, you get an "ice surge" https://www.youtube.com/watch?v=OgMBQFf64JM which his basically a one-time long-run-out glacier. In between temperatures, and you might get a Tsunami where liquid water flows inland and then freezes in place.


So, perhaps we have a good Earth analog for Gale?


https://www.spectator.co.uk/2018/03/to-thos...place-on-earth/]To those with a taste for desolation, Lake Turkana may be the most beautiful place on Earth
A postcard from Kenya
Matthew Parris[/url]
serpens
HSchirmer, could I perhaps suggest that you may like to post images as thumbnails, it would make your posts easier to read.

It is now clear that Vera Rubin Ridge was laid down as part of the Murray formation and the erosion resistance is a product of post deposition diagenetic/alteration episodes. The comparative hematite, phyllosilicate, amorphous and opal CT proportions with elevation combined with the identification of akaganeite is indicative of low pH fluids infiltrating from above. The likely formation candidates from the options proposed to date are a springline during the Mount Sharpe erosion process or a much earlier, low energy stream after the lake dried.

It is pretty clear that clay rich Glen Torridon is not associated with the Murray formation, is possibly cemented with clay and does not seem to have undergone significant compaction. I retain the belief that this formed following the erosion of the Murray formation on both sides of the resistant ridge, and is potentially a function of the formation of the fan. Basalt buffered water and sediment originating in upper Mount Sharp pooling in the hollow between ridge and mount. In the absence of tidal influences the rhythmic laminations or “bundling” could well reflect a shallow lake with annual ice cover. During winter dust collects on the ice and on thawing settles to form the thin laminations. During summer ice on the mount melts and a thicker layer of sediment is deposited.

Or it could be something completely different which the experts, having actual data to work with will advise in due course.
HSchirmer
Already received that admonition from a Mod.

Curious,


QUOTE (serpens)
The comparative hematite, phyllosilicate, amorphous and opal CT proportions with elevation combined with the identification of akaganeite is indicative of low pH fluids infiltrating from above.


Why a preference for low pH from ABOVE, rather than BELOW?
serpens
QUOTE (HSchirmer @ Jun 9 2019, 11:14 PM) *
[quote name='serpens'}
Why a preference for low pH from ABOVE, rather than BELOW?


Taking a very broad brush approach from the depths of an armchair, smectites are sensitive to acid leaching and the result of this decomposition is amorphous silica. As can be seen from the Chemin results the phyllosilicates decrease with elevation while the amorphous silica proportion increases which is indicative of top down infiltration of low pH water

https://www.hou.usra.edu/meetings/lpsc2019/pdf/1127.pdf

I used the term indicative because is obvious that while the Murray formation which includes the ridge has been subject to complex diagenetic/alteration processes the alteration of the ridge was anomalous. The only thing we can be sure of while the professionals unravel the data is that during the early modification of Gale crater there was quite literally water, water everywhere.
jccwrt
In addition, acidic waters rapidly neutralize in basaltic systems due to weathering reactions. Groundwater flowing up from below would need to interact with a far greater volume of rock than water coming from above, so it is less likely to contain strongly acidic fluids. There would have been a very clear acidic alteration signature in the underlying stratigraphy associated with the level of alteration seen at VRR if it were groundwater.
HSchirmer
QUOTE (jccwrt @ Jun 10 2019, 05:38 PM) *
In addition, acidic waters rapidly neutralize in basaltic systems due to weathering reactions. Groundwater flowing up from below would need to interact with a far greater volume of rock than water coming from above, so it is less likely to contain strongly acidic fluids. There would have been a very clear acidic alteration signature in the underlying stratigraphy associated with the level of alteration seen at VRR if it were groundwater.


Good point, but wouldn't acidic groundwater working through a deep fissure weather the basalt to silicate and "skin over" the reactive surface? Rather like aluminum is so reactive that it doesn't rust?


Given Gale's proximity to a possible highstand ocean shoreline, does the possibility that the crater
had significant interaction with a Martian northern ocean/saltwater change the chemistry a bit?
I'm specifically thinking about how slumping effects and saltwater lenses might be tied to groundwater chemistry.

"Chesapeake Bay impact structure:Morphology, crater fill, and relevance for impact structures on Mars" from 2006.

serpens
There is no indication that the northern ocean interacted directly with Gale crater and in any case it would be highly unlikely to be salty at its maximum extent. But jccwrt's point is germane regarding acidic alteration signatures in the underlying sedimentary Murray formation. All data indicates top down infiltration.

We know that Vera Rubin Ridge is part of the Murray formation and it would be safe to assume that the lake and hence the Murray formation extended to the central uplift, at a height pretty much commensurate with the top of VRR. So the problem is when and how did acidic water interact with a discrete , long and thin section of the formation. One critical data point we do not have and unfortunately cannot get is the length of the altered section because quite limited cover would hide the signature from orbit. Increased length would imply a stream because even the length of the visible portion would be unusual for a springline.
HSchirmer
QUOTE (serpens @ Jun 11 2019, 01:55 AM) *
(snip)
So the problem is when and how did acidic water interact with a discrete , long and thin section of the formation.


Well, since AFAIK, Mars lack creeks or rivers that happen to run in a straight line for ~6.5 km, the most likely explanation would seem to be a fault in the area.

TECTONIC FORMATION OF MOUNT SHARP, GALE CRATER, MARS.
http://www.lpi.usra.edu/meetings/lpsc2013/pdf/3106.pdf




Recent Mars grounwater level research https://agupubs.onlinelibrary.wiley.com/doi...29/2018JE005802
notes that early Mars had a groundwater network.

Recent work on the Chesapeake bay impact crater

https://pubs.usgs.gov/circ/2003/circ1262/#f...caption45212960

raises the interesting point that there would have been a "breccia aquifer" UNDER mount sharp. So, impact-heated breccia, interacting with a regional groundwater system, should give you plenty of hot, wet, altered rock under Mount sharp, as well as brines enriched in minerals, salts or perhaps acids.
serpens
The proportional change in phyllosilicate and amorphous content is just one indicator of what influenced VRR. Once again taking a generalist approach, based on the evidence the groundwater within the Murray formation would have had a reasonably neutral pH (6-7) and low Eh voltage. This would provide for a stable, high level ferrous solution. Now if this groundwater mixed with precipitation from volcanic activity, say acid snow melt the following would take place.
4Fe++ + O2 + 4H+ ------> 4Fe+++ + 2H2O
There is then a pathway to hematite through Ferric Oxide Trihydrate to Goethite or even direct to hematite if the pH of the mixed solution, mitigated by the phyllosilicate consumption of acidity, is around 5.

Top down infiltration really is the only process that fits.
jccwrt
I'm not sure we can entirely discount a contribution from acidic groundwater traveling along a fault - especially since Gale Crater seems to host some diverse evidence of igneous activity (float rocks from an igneous suite on the northwest rim, K-rich sedimentary layers apparently derived from a different source region, a possible(?) exposed intrusion at Ireson Hill [my memory is fuzzy on this one, I remember an LPSC talk in 2018 talking about finding a new kind of igneous float rock there] and tridymite detections). In addition we do see extensive alteration haloes in places in the Murray which are also suggestive of acidic groundwater.

That said, I'm not sure that points to a bottom-up process - a regional/global groundwater system should be at or neutral pH given the sheer volume of rock it needs to travel through, so it would need to be something local to Gale Crater. I'd wager that for the most part even the local groundwater was neutral. There's a hydrofractured interval in the Murray that suggests considerable groundwater content at some point in the crater's history, and these don't appear to be associated with much alteration.

So I think it comes down to the existence of an acidic brine reservoir, the existence of which is difficult to prove. Offhand I could think of a couple of tests: 1) check for highly altered rocks in Ellipse Edge Crater and Slagnos Crater ejecta, 2) do a geochemical balance to see how much acid you need to reach equilibrium with the surrounding rocks and still remain acidic (or failing that, how long an acidic solution would last before neutralizing).

And even if you have a pathway, you also need a mechanism to get a dense brine moving towards the surface - a brine pool has persisted in Chesapeake Bay so long precisely because it is dense and hard to dislodge.

I think on the balance, a top-down alteration pattern is a more convenient explanation. We're not stratigraphically far below a sequence of rocks containing abundant evidence for a more acidic environment, and we also saw evidence for surface conditions starting to slide towards more water-limited and oxidizing conditions on the approach to VRR. Something weird happening along a redox interface within the lake or some sort of alteration process that managed to proceed deeper along a fault-line seems more likely to me.
HSchirmer
QUOTE (jccwrt @ Jun 12 2019, 06:13 AM) *
And even if you have a pathway, you also need a mechanism to get a dense brine moving towards the surface - a brine pool has persisted in Chesapeake Bay so long precisely because it is dense and hard to dislodge.


The mechanism would be freeze distillation of an impact created acidic mineral brine.

Ten minutes after impact, you've got hot-basin filled with breccia.
That breccia basin has a huge surface area, a huge pore area, and a huge amount of latent heat.
As Martian groundwater percolates back in, it would initially boil off, creating fumaroles, geysers and
chemically enriched geyser deposits.
As the groundwater level rebounds, perhaps hot springs and black-smokers along any faults at the bottom of the crater lake.

Summary, as the impact site cools, you get, eh, a few million years of steam and geysers, then circulating hot water, then still warm water, then still cold water, and finally a frozen aquifer.

That progression seems likely to create deposits of enriched minerals, then mineral enriched or acid enriched brines.
Eventually, as the aquifer freezes, hydrostatic pressure forces brines to the surface, rather like the Occator salt deposits on Ceres.
ngunn
In such well informed company I have nothing to add except to say how much I am appreciating the quality of this discussion, not only for the insights shared but for the the clarity and accessible language of the posts. Anyone following could not fail to have their imagination stirred about past and present geological processes on Mars. It's a perfect example of the best that happens on this forum, alongside the image work.
HSchirmer
QUOTE (ngunn @ Jun 13 2019, 09:41 AM) *
(snip)
to say how much I am appreciating the quality of this discussion, not only for the insights shared but for the the clarity and accessible language of the posts. Anyone following could not fail to have their imagination stirred about past and present geological processes on Mars. It's a perfect example of the best that happens on this forum, alongside the image work.


Good post, the images are breathtaking, but the conversations have lagged a bit of late.

Here is some interesting modeling of the aquifers under Martian impact craters.
A study modeled 100km and 180km craters, for reference, Gale crater is ~154km.
The length of time an impact site stays warm and the potential volume of warm-wet-rock is quite interesting.

QUOTE
IMPACT-INDUCED HYDROTHERMAL ACTIVITY ON EARLY MARS
"that the most extensive hydrothermal alteration would have occurred in the central peak (for smaller craters) or the peak ring (for larger craters), and the modification zone where fluid flow is facilitated by faults."

System lifetimes ... were ...290,000 years for the 100-km crater, and 380,000 for the 180-km crater.
(snip)
These lifetimes provide ample time for ... impact-induced hydrothermal systems ... volume reaches a maximum of 6,000 km 38,500 years after the impact in the 180-km crater model.

https://www.lpi.usra.edu/science/abramov/pa..._kring_2005.pdf


The most interesting point for this discussion is probably at pages 10-11. During the time when the crater is cooling, "dry model" has no crater lake only groundwater, "wet model" has a crater lake.
QUOTE
in the 100-km and 180-km crater models, a similar trend can be observed. While the ‘‘dry’’ model is on the whole hotter, there are regions in the ‘‘wet’’ model, such as the peak ring, where long-lived hot water upwellings have significantly increased the temperature. Conversely, there are numerous downwellings of cold water that led to a localized temperature decrease.


That certainly raises a neat question- what if Vera Rubin Ridge is an arc of sediment deposited over top of an earlier peak ring of hydrothermally altered rock? Wet sand and mud at VRR would leach minerals and acidic compounds from the groundwater directly beneath them.

Second interesting point.

QUOTE
{Without a crater lake} Unlike the previous model, there is no flow through the central peak and by 20,000 years most of the activity is concentrated in the center of the crater, which eventually develops into a single vigorous upwelling in the center of the crater by 200,000 years. This long-lived upwelling, coupled with the overall lower fluxes seen in this run, results in a longer system lifetime (700,000versus 430,000 years) for this simulation compared to a case with the crater lake present.


So, without a crater lake, we might expect a long-term upwelling of warm groundwater under the center of the crater. "
Well, that seems like a perfect mechanism for a humid micro-climate inside Gale crater, trapping dust to form Mt. Sharp.
HSchirmer
Perhaps Gale crater was, for perhaps half-a-million-years, like the Dallol hydrothermal field?
Hot basalt mixing with marine sediments can generate some REALLY nasty water.

QUOTE
The hydrothermal springs of Dallol discharge anoxic, hyper-acidic (pH <0), hyper-saline (almost 10 times more saline than seawater), high temperature (> 108 °C (226 °F)) brines that contain more than 26 g/L of iron. The main gas phases emitted from the springs and fumaroles are CO2, H2S, N2, SO2 and traces of H2, Ar, and O2 [8]

https://en.wikipedia.org/wiki/Dallol_(hydrothermal_system)

Cite is Kotopoulou, Electra; et al. (2018-12-06). "A poly-extreme hydrothermal system controlled by iron: the case of Dallol at the Afar Triangle". ACS Earth and Space Chemistry. 3: 90–99. doi:10.1021/acsearthsacechem.8b00141.
https://pubs.acs.org/doi/10.1021/acsearthspacechem.8b00141

It does create a stunning landscape.


With some rocks and minerals that we've heard of at Gale crater-
QUOTE
The main mineral phases encountered at Dallol are halite (NaCl), jarosite (KFe3+3(SO4)2(OH)6), hematite (Fe2O3), akaganeite (β-FeOΟΗ) and other Fe-oxyhydroxides, gypsum (CaSO4•2H2O), anhydrite (CaSO4), sylvite (KCl) and carnallite (KMgCl3•6H2O).[12]


Here's the cited paper

Geochemistry and mineralogy of the hyper-acidic hydrothermal system of Dallol, Ethiopia
Conference Paper (PDF Available) · January 201
https://www.researchgate.net/publication/31...Dallol_Ethiopia
serpens
Given the height of the Gale crater central peak the development of a peak ring is unlikely since this is predicated on the collapse of the central peak.

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. We do not know just how deep the Murray formation extends; or indeed if it is actually the basal layer of Mount Sharp or whether beneath it is a sedimentary formation reflecting the environment you describe. Certainly the veins and halos indicate that there have been extensive hydraulic fracturing and deposition incidents, primarily alkaline but in the lower levels acidic on occasion.

The clear transition from the phyllosilicate bearing Murray formation to the sulphate bearing layers represents a change in the local environment from water dominated to arid, acidic conditions. But there is clear evidence of significant water, both surface features and groundwater well into the Mount Sharp erosion period. For example hydraulic fractures extend across the contact between the Murray formation and the much later, aeolian Stimson.

The thing I think we all struggle with is the timescale represented by the sedimentary layers of Mount Sharp and the subsequent erosional end state of Gale crater. On Earth we have only fragments of the Eoarchean crust which date to the time of the Gale impact. The evidence of long standing surface water on Mars presents a real challenge to the traditional view of the early solar system.
HSchirmer
Hypothesis - Vera Rubin Ridge's odd chemistry is the result of the ridge's location above the inner ring of Gale crater; hydrothermal activity concentrates at crater peaks and rings, so the ring is associated with mineral deposits. Water flowing down through sediments leached minerals into the overlying strata which alter the overburden to create the erosion-resistant Vera Rubin Ridge.

QUOTE (serpens @ Jun 14 2019, 12:33 AM) *
Given the height of the Gale crater central peak the development of a peak ring is unlikely since this is predicated on the collapse of the central peak.


Not necessarily, the peak ring can also be an uplift effect.

QUOTE
A MASSIVE CENTRAL PEAK AND A LOW PEAK RING IN GALE CRATER – IMPORTANT INFLUENCES ON THE FORMATION OF MT. SHARP.

Gale’s central peak and peak ring were emplaced immediately after the impact, and influenced the subsequent history of deposition and erosion that formed Mt. Sharp
(snip)
Spray et al { Spray J. et al (2013) LPS XLIV, Abs. #2959.} suggested that a peak ring in Gale crater could have influenced the location Mt. Sharp’s lower segment by localizing the deposition of sediments. This effect could account for the fact that the northern, eastern, and western boundaries of Mt. Sharp correspond to a ~ 80 km diameter circle (Fig. 4).

https://ntrs.nasa.gov/archive/nasa/casi.ntr...20150001905.pdf


Also important - Gale crater's rim and floor tilt down towards the North. Assuming this is not due to post-impact subsidence, that suggests the breccia reservoir is also tiled, and the Northern edge of the reservoir is deeper than the southern edge.

It seems that rain or surface water could flow into the central ring, so water in the sloped 80km diameter inner ring would have collected into a crescent-shaped lake along the Northern edge of the inner ring. That water would have percolated through the warm outer ring breccia, experience hydrothermal alterations, and then exited at roughly the location of the current Vera Rubin Ridge.

Surface water from a large area enters Gale from the southwest and flows clockwise across the area between the inner and outer ring. This would seem to suggest that 2 different types of water 1-hydrothermal springs associated with the northern arc of the inner ring, and 2- surface water flowing across the crater floor from the west, would have mixed in roughly the location where we now find Vera Rubin Ridge.

The early hydrothermal system could have created acidic mineral deposits along faults and along the inner crater ring.
Those minerals could leech out and cement later lake sediments.

Another interesting article on impact crater hydrothermal systems, this one specific to Gale Crater
Gale Crater: Formation and post-impact hydrous environments
https://www.sciencedirect.com/science/artic...1274?via%3Dihub
HSchirmer
Here's a thought- Ahuna Mons on Ceres seems to the result of mud burping up from an underground chamber.


Immediately after the impact, Gale crater would have had an underground chamber of hot-to-partially melted breccia.
As water percolated into the chamber (groundwater, surface water, or perhaps an "Arabian sea" at ~-3707 meters)
the result is hot basalt mixing with water, which creates an underground chamber of hot silicate mud.
That should trigger more subsidence as the mud is forced to the surface as the breccia chamber collapses on itself.

Perhaps Mount Sharp is like Ahuna Mons, the end result of mud being forced out of an underground chamber onto the surface as an underground chamber slowly collapsed?

serpens
On Earth it would be a reasonably simple matter to confirm or deny your hypothesis of Vera Rubin Ridge being an artefact of a peak ring. However while the visual and analytical data from Curiosity is frankly stunning, it is also extremely limited with respect to the footprint investigated and the fact that such investigation is skin (or at least drill) deep. Regardless any hypothesis, by definition, should reflect the available empirical data. This data reflects a transition to a more acidic influence with elevation. If the ridge were the result of covering a peak ring then the influence would be evident across the entire ridge slope. As far as Mount Sharp being a mud volcano is concerned, this was a hypothesis put forward very early on but was dismissed based on the evidence.

Jccwrt’s 12 June comment regarding tridymite detection jogged my memory with respect to the detection of not insignificant amounts of opal CT in the Highfield drill sample. Presumably caused by diagenesis under burial of amorphous silica Opal A to the micro-crystalline SiO2 polymorphs cristobalite and tridymite. I wonder if estimation of the transition depth for Opal A to Opal CT under Mars gravity could give a wet finger estimate of the overburden.
HSchirmer
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.

serpens
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
HSchirmer
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




HSchirmer
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.
serpens
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.
HSchirmer
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.
serpens
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.
ngunn
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.
serpens
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.
stevesliva
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....
serpens
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.
HSchirmer
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?
jccwrt
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.
serpens
Exactly.
PaulH51
This open source paper appears to address some of the early questions in this thread, well at least for the Vera Rubin Ridge...

"Regional Structural Orientation of the Mount Sharp Group Revealed by In Situ Dip Measurements and Stratigraphic Correlations on the Vera Rubin Ridge"

link
serpens
Thanks for that link. The conclusion that "the possibility that VRR members are distinguished primarily by diagenetic processes that did not follow strata boundaries" seems to be supported by Chemin results (link below). The difference between Grey Jura and Red Jura with significant akaganeite in Rock Hall would seem to indicate a localised concentration of chloride rich acidic fluid within the Jura member.

https://www.hou.usra.edu/meetings/lpsc2020/pdf/1601.pdf
PaulH51
Curiosity Rover Finds Clues to Chilly Ancient Mars Buried in Rocks (NASA Goddard News Release) Link
Associated paper (pay-walled) Link
serpens
I don't feel there is any contradiction with the Gale crater sediment requiring millions to tens of millions of years to form in warm, humid conditions and some of the carbonates within that sediment possibly being formed in icy conditions. For the last 3 million years or so Earth has experience cyclical glaciation with shorter, warm and humid interglacials, initially on a 41 kyr cycle and then, for currently unknown reasons, switching to a 100kyr period. Even during interglacials there are significant temperature variations. It would probably be more surprising if there were no indications of temperature variability.
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