Help - Search - Members - Calendar
Full Version: Geomorphology of Gale Crater
Unmanned Spaceflight.com > Mars & Missions > MSL
Pages: 1, 2, 3, 4, 5, 6
Don1
@Gerald: I recently came across another very interesting possible explanation for the faint young sun paradox. In his "Lectures on physics", Feynman discussed the possibility that the gravitational constant G had changed over time. It turns out that the luminosity of the Sun is strongly affected by changes in G, with the luminosity proportional to G to the sixth power. Feynman points out that this would have made the ancient earth far too warm. However Feynman wrote that in 1962, which was a few years before the faint young sun paradox was identified. It turns out that a warmer earth is just what we need.

I did some digging around on the internet and it appears the current observational constraints on G can't rule out the possibility of G changing by enough to solve the faint young Sun paradox. So the idea that G has always been constant is really an assumption.
Don1
From the GSA meeting abstracts:

"LONG-LIVED DEEP LAKES IN EARLY MARS: SEDIMENTOLOGICAL EVIDENCE FROM THE CURIOSITY ROVER AT GALE CRATER"

"... the Striated and the Murray formations represent a subaqueous fan in a large lake, estimated to be 1 - 3 km deep. Fining-upward layers of the Striated formation are coarse-grained turbidites deposited on the proximal part of the fan by sediments delivered by floods through the northern rim of the crater. The Murray formation formed on the distal part of the fan and extended into the center of the lake in waters so deep that bottom sediments were unaffected by wave actions, lake-level fluctuations, and storm activities....."

"The rhythmic nature of layering indicates a regulated flow of flood waters into the lake, possibly controlled by changes in climate. The most likely forcing mechanism was variations in obliquity. Floods occurred during hothouse periods when the Martian climate was warmer than Present. The lake became saline at least to gypsum saturation during subsequent cold and/or dry climate of icehouse intervals and precipitated sulfate-rich nodules in the Murray formation. "

My comment: This was a deep lake. Other abstracts indicate that it likely lasted for millions of years.

"TESTING A MECHANICAL MODEL OF FRACTURE FORMATION BY COMPACTION-RELATED BURIAL IN GALE CRATER, MARS; IMPLICATIONS FOR THE ORIGIN OF AEOLIS MONS"
"These results imply that formation of these fractures [in the Murray and Stimson rocks] requires at least one significant burial event in the evolution of Mt. Sharp, providing key insight into the geologic history of Gale crater. "

My comment: After the lake dried up, sand dunes formed which later became the Stimson formation. Then the crater filled in and the pressure fractured the rocks.

"DIAGENESIS ALONG FRACTURES IN AN EOLIAN SANDSTONE, GALE CRATER, MARS"
" The mineralogy and geochemistry of the altered sandstone suggest a complicated history with several (many?) episodes of aqueous alteration under a variety of environmental conditions (e.g., acidic, alkaline). "

My comment: More water flowed through the fractures and altered the rocks.

"MINERALOGY OF MUDSTONE AT GALE CRATER, MARS: EVIDENCE FOR DYNAMIC LACUSTRINE ENVIRONMENTS"

" At the time of writing, CheMin has analyzed 14 samples, seven of which were drilled from lacustrine deposits. The mineralogy from CheMin, combined with in-situ geochemical measurements and sedimentological observations, suggest an evolution in the lake waters through time, including changes in pH and salinity and transitions between oxic and anoxic conditions. "

My comment: The mention of "oxic conditions" is interesting. Anoxic conditions are not surprising on a planet with a CO2 atmosphere. However, what produced the oxic conditions? Where did the oxygen come from?
serpens
Re your comment on "TESTING A MECHANICAL MODEL.....". The Stimson Murray interface is an erosional unconformity covered by an fragile aeolian dune deposit that does not seem to demonstrate any significant compaction or lithification. Rather than being an early construct buried by crater infill the Stimson deposit was potentially laid down following the erosion of the crater infill with a large contribution from landslips from a degrading Mount Sharp. In other words the Murray formation is an erosional endstate for the mudrock (mudstone/siltstone because it is hard to tell the difference) lacustrine Murray formation and the easily eroded sandstone of the Stimpson is a late feature (in Mount Sharp erosional terms) .
Gerald
QUOTE (Don1 @ Aug 27 2016, 10:07 AM) *
In his "Lectures on physics", Feynman discussed the possibility that the gravitational constant G had changed over time.... So the idea that G has always been constant is really an assumption.

Although G isn't known very accurately, varying G over (space)time would challenge present cosmological models, including the Einstein field equations. Missions like EUKLID might eventually narrow down according constraints.
Feynman hadn't access to astronomical and astrometrical data as we have today. I don't think, that with contemporary knowledge Feynman would have suggested to assume G as variable within our observable universe (might be except very close to the Big Bang).

I'm sure, that the faint young sun paradox will turn out to be soluble within established standard physics.

[MOD: Agreed, and a reminder to all to review rule 1.9 as well as to stay on topic.]
Don1
@serpens....Yes, I was wondering about that when I wrote the post. I thought Stimson was supposed to be young, but the abstract didn't read that way. I went back this morning and took another look at it, and the authors do seem to be arguing that the cracking in Stimson was produced by burial in the same way that the cracking in Murray was produced. It seems to me that that would only be possible if Stimson is old.

The authors by the way are Watkins, Grotzinger and Avouac at Caltech.

"TESTING A MECHANICAL MODEL OF FRACTURE FORMATION BY COMPACTION-RELATED BURIAL IN GALE CRATER, MARS; IMPLICATIONS FOR THE ORIGIN OF AEOLIS MONS"
" Large fractures which exhibit complex banding structures with distinct chemical trends (e.g. halos) are primarily found in the Stimson formation, but do extend into the Murray formation in one location. Smaller, sulfate-filled fractures are most prevalent in the Murray but are also associated with haloed fractures in the Stimson."
serpens
The Watkins, Grotzinger and Avouac paper in no way precludes the probability that the Stimpson was laid down subsequent to a significant burial and then exhumation of the crater. The extension of minor fractures into the Stimpson with limited examples of larger fractures can be readily explained through reactivation.
A possible scenario would be that the initial fractures in the Murray formation occurred as a kilometres thick overburden was removed through erosion and pore water was released. Subsequent deposition of the Stimpson material would have provided a compression force on the Murray formation, albeit at a comparatively minor level. The catastrophic channel outflow events, combined with a surge in volcanic activity would have provided sufficient acidic water through groundwater recharge and limited precipitation to replenish pore water to a degree, as well as (poorly) lithify the Stimpson. Subsequent erosion of the Stimpson would have caused a change in pore pressure in the underlying Murray sequence which could cause the pre-existing fractures to propagate up into the overlying Stimpson rock. This propagation could be assisted by pore water at the fracture tip causing chemical weakening of the overlying rock. Fracture propagation would have been restricted by the limited availability of acidic pore water due to the minor compression unloading.
MarkG
In reading this, please keep in mind the profound ancient-ness of these landforms.
tty
"The mention of "oxic conditions" is interesting. Anoxic conditions are not surprising on a planet with a CO2 atmosphere. However, what produced the oxic conditions? Where did the oxygen come from?"


There is actually an abiotic mechanism for producing appreciable amounts of oxygen photochemically in a cold glacial/interglacial environment. UV light will produce small quantities of hydrogen peroxide which will be stable enough at low temperatures to be stored in ice. When an interglacial arrives and the ice melts the hydrogen peroxide decomposes into water and oxygen.
serpens
Probably photodissociation of CO2 and H2O. This recent release by JPL provides some substantiation.
http://www.jpl.nasa.gov/news/news.php?feature=6544
tty
Yes. The process has actually been rather extensively discussed in the literature in connection with Archaean/Proterozoic glaciations ("Snowball Earth") since there is evidence for oxic conditions immediately after the glaciations. And hydrogen peroxide is actually found in measurable amounts in snow in Antarctica. Incidentally the quantity deposited increases in early summer when ozone is low.

http://rstb.royalsocietypublishing.org/content/363/1504/2755

http://www.pnas.org/content/103/50/18896

https://www.academia.edu/15042568/Productio..._photosynthesis

http://web.gps.caltech.edu/~jkirschvink/pd...iewAndModel.pdf
Greg Malone
QUOTE (serpens @ Dec 20 2016, 11:02 PM) *
Nice little berry to the right of Paul's image. I make it around 8mm diameter and it wouldn't be (visually) out of place in Opportunity's domain.


Looks good enough to have on my breakfast cereal. More seriously, it looks somewhat out of place, but it's a small frame so can't see context. Will find the source image and see what's up.

LATER:
That individual berry-looking object is pretty unique in that immediate area, though there appear to be fragments of similar material nearby in same frame.

While scanning for similar objects in the immediate area on 1553, I did spot this little gem:

Sol 1553 13:12 Site 59/3004 1553ML0079770020604748E01_DXXX
serpens
QUOTE (Greg Malone @ Dec 22 2016, 01:24 AM) *
...While scanning for similar objects in the immediate area on 1553, I did spot this little gem:.....

The thing is that if these items are extremely resistant to erosion as seems the case then they could have been emplaced at any level of the kilometres of material that overlaid the current surface.
Gladstoner
QUOTE (Greg Malone @ Dec 21 2016, 06:24 PM) *
While scanning for similar objects in the immediate area on 1553, I did spot this little gem:


Stony-iron meteorite?
HSchirmer
QUOTE (PaulH51 @ Dec 22 2016, 12:04 PM) *
Swaying towards mud-cracks, yesterday I was convinced these were fractures smile.gif
Click to view attachment


Yep, looks like mudcracks, but what's really interesting is the variation in polygon size,
there are small .5 cm polygons and medium 2-3 cm polygons and what seem to be 10 cm polygons.

That suggests a very interesting interplay between the available water, the available sediment, and depth.

image is from Columbia University's earth sciences page about basin filling
https://www.ldeo.columbia.edu/~polsen/nbcp/breakupintro.html


The thick deposits of mudstone made of thin sheets of sun dried mud is paradoxical when you think about it...
Shouldn't a crater fill up with deep lake sediments, then shallow lake, then mud, then sand?

It does raise a neat question, involving faults and geology...
On earth, you get thick deposits of shallow water sediments in extensional basins;
when a half-graben opens up, the land drops slowly, so it starts shallow and stays shallow,
in contrast a crater, should start deep, then gets shallower as it fills in.

http://www.lpi.usra.edu/meetings/lpsc2013/pdf/3106.pdf
serpens
QUOTE (HSchirmer @ Dec 22 2016, 03:16 PM) *
The thick deposits of mudstone made of thin sheets of sun dried mud is paradoxical when you think about it...
Shouldn't a crater fill up with deep lake sediments, then shallow lake, then mud, then sand?
http://www.lpi.usra.edu/meetings/lpsc2013/pdf/3106.pdf


It would be reasonable to expect that the water availability in the Gale lake would vary as would the amount of available sediment, particularly airfall. But this very thin sheet of cracked material does seem to be an anomaly and difficult to reconcile to dessication. Chemcam should reveal something about the makeup of the sheet as it could be possible that these cracks formed sub aqueous in a thin, possibly localised layer of clay rich sediment. Subsequent settling of underlying sediment causing the cracking would explain the variation in shape and size.
HSchirmer
QUOTE (serpens @ Dec 22 2016, 10:54 PM) *
It would be reasonable to expect that the water availability in the Gale lake would vary as would the amount of available sediment, particularly airfall.


I really find the juxtapositions interesting.
Surface precipitation might weather clays, but IS need to move sediment, as in peace vallis.
Ground water might weather clays, but IS probably needed for later mineral veins.

https://www.youtube.com/watch?v=xq65TVKDZXs...utu.be&t=11
Gives a really excellent over view of the issues.

Well, if you've got a valley network, availability of water, and sediment are a bit easier to estimate...

Mineralogy and fluvial history of the watersheds of Gale, Knobel, and Sharp craters:
A regional context for the Mars Science Laboratory Curiosity's exploration
Bethany L. Ehlmann, Jennifer Buz
wildespace
QUOTE (Fran Ontanaya @ Dec 25 2016, 11:05 AM) *

Any idea what is this spherical object?
PDP8E
Hematite? (aka Squyers' blueberries)
Steve5304
QUOTE (PDP8E @ Dec 25 2016, 06:19 PM) *
Hematite? (aka Squyers' blueberries)



To big...process may be similiar but material is probably different.... Don't think we have all the pieces to the puzzle I hope curl does some sciene on that. We passed two others that looked identical on sol 937, 1185, in different sorts of terrain. Pretty strange formation it would be about the size of a marble.
HSchirmer
QUOTE (Steve5304 @ Dec 28 2016, 05:00 AM) *
To big...process may be similiar but material is probably different.
...
Pretty strange formation it would be about the size of a marble.


Well, it looks very similar in size to the low grade copper concretions that occur along the US east coast.
Triassic mudstones + igneous intrusions = marble sized ore concretions, usually copper, silver, gold, arsenic.
In my experience, they're usually within about 1 km of the igneous contact.
When the contact is is folded, (scallop shell) instead of flat (clam shell)
they mudstone ores seem to occur more in the peaks (anticlines).

You can see concretions in situ and some spherical voids where others weathered out.

US penny for scale.
Steve5304
QUOTE (HSchirmer @ Dec 28 2016, 07:29 PM) *
Well, it looks very similar in size to the low grade copper concretions that occur along the US east coast.
Triassic mudstones + igneous intrusions = marble sized ore concretions, usually copper, silver, gold, arsenic.
In my experience, they're usually within about 1 km of the igneous contact.
When the contact is is folded, (scallop shell) instead of flat (clam shell)
they mudstone ores seem to occur more in the peaks (anticlines).

You can see concretions in situ and some spherical voids where others weathered out.

US penny for scale.




Thank you for that.


Not to sound like a jerk but i think we should run this thing over and take the chemcam see what it really is.Somebody from nasa is reading i hope!
serpens
After the exhaustive work to identify the provenance of Opportunity's berries there is a tendency to consider small spherical objects seen on Mars as concretions. This particular example is isolated so if it is a concretion then transport was involved. However we cannot rule out other causes such as an impact artefact, molten material with a reasonably high ferric component that assumed a spherical shape and cooled in flight, possibly quenched by fall into water. Note Greg Malone's post #810, page 54 on 22 December.
Steve5304
QUOTE (serpens @ Dec 28 2016, 10:47 PM) *
After the exhaustive work to identify the provenance of Opportunity's berries there is a tendency to consider small spherical objects seen on Mars as concretions. This particular example is isolated so if it is a concretion then transport was involved. However we cannot rule out other causes such as an impact artefact, molten material with a reasonably high ferric component that assumed a spherical shape and cooled in flight, possibly quenched by fall into water. Note Greg Malone's post #810, page 54 on 22 December.



If that was formed by water it would not be on the surface..it would be below I would think. That had to have broken off or out in the last 100,000 years. Again...I would think but
HSchirmer
QUOTE (Steve5304 @ Dec 29 2016, 12:27 AM) *
If that was formed by water it would not be on the surface..it would be below I would think. That had to have broken off or out in the last 100,000 years. Again...I would think but


Eh, remember that there would be a cycle that repeats thousands or millions of times:
dry lake bed, playa, shallow lake, deep lake, shallow lake, playa - dry lake
The dry to wet cycle is nicknamed a van-houten cycle, in the best studied mudstone basins on earth, one cycle is ~20k years, and about 1 meter thick.
Expect you'd have something similar on mars - gale probably went from lake to dry lake and back many times,
based on orbit and eccentricity. there could be "wet" areas both above and below
[what appear to be] the current mud flats.

Yes, there is a tendency to consider small spherical things on mars as concretions,
however, we're looking at fractured mudstones, and experience on earth shows that
fluids moving through cracked mudstones are good at making concretions.
They're common in earth mudstones, so it's acceptable to expect they're common on mars as well...
serpens
We have to climb around another hundred metres of Murray formation mudstone and sixty metres or more above that to the hematite ridge. Nicolas Steno's principle of lateral continuity holds that this strata would have originally covered Curiosity's current position, requiring significant water influence over a long period of time. As an aside, the more I look at the hematite ridge the more I wonder whether it could be an inverted bed of what was a reasonably well oxidised stream.
Julius
Simply brilliant stuff!
Greg Malone
To add to the mix of ideas about dessicated mudcracks is the notion of syneresis, believed to have possibly been active at some sites investigated in Gale -- where differential salinity in interstitial water causes lower salinity water (I believe) to migrate out of the muds being replaced by denser higher salinity water, creating cracks that are somewhat similar to dessication cracks... all the while the entire environment being saturated with subsurface water... i.e. not a 'drying out' or dessication.

Greg Malone
QUOTE (Gladstoner @ Dec 21 2016, 11:38 PM) *
Stony-iron meteorite?


I've since noticed a couple of other features that, to the eye, appear possibly similar to the mentioned 'meteorite', in the same general location. Clearly not enough info to really know what we're seeing here, but still fun to muse on.


HSchirmer
QUOTE
We have to climb around another hundred metres of Murray formation mudstone
and sixty metres or more above that to the hematite ridge.


Good point. There are still hundreds of meters of strata to climb.
My point was that it takes a long time, (eh 3-30 million years?) and a huge amount of water
to transport the sediment that is eventually compressed to become those 100 meters of mudtone and 60 meters of hematite.

So, we should see orbital and processional effects (roughly 100k and 1.25 million years) in the lake levels,
as the lake in Gale goes from overflowing to a "dead sea", and goes from a salt lake to playa.

Yes, I guessed about 3-30 million years for 160 km of rock strata. So, gale crater is sedimentary basin.
The gale basin (90-100 miles) is close to the size of the well studied Newark basin (90-100 miles) on Earth.
We can calculate that the Newark rift basins filled in with about one meter of rock per 20k years under
Triassic Earth conditions (dry and hot, not too far from Mar's dry but cool..)
So, rough estimate, the optimal wet Martian climate at gale would be, at best, comparable to Earth's dry Triassic climate and take 3 million to fill 160 meters, but leave a 10x range, erosion during a wet period on Mars would still take ten times longer than erosion during a dry age on Earth, which gives 30 My.

What we see on Earth is that celestial mechanics creates 20ky patterns and 404ky patterns, and other effects create patterns within the patterns of climate that create wet / dry swings.
Same for Mars, but it seems that Mars has 100 thousand year and 1.25 million year patterns

QUOTE
Nicolas Steno\'s principle of lateral continuity holds that this strata would have originally covered Curiosity\'s current position,
requiring significant water influence over a long period of time.


The lake in Gale crater may have been there for 10 thousand years, or 10 million years.
On Mars, is that a long time, or is that a short time?

Mars seems to have a 1.25 Million year climate cycle, built out of smaller ~100k year cycles.
http://www2.physics.ox.ac.uk/sites/default...3_pdf_93344.pdf

You'd expect wet to dry climate to be a direct progression, like a piano scale exercise. Down the scale.
That is not what happens.
Climate happens in the moment; it is patterns within patterns, within patterns, within patterns-
Mars rotates each day, Mars revolves each year, Mars' poles shift each age,
and Mars' orbit bends to the will of the other planets sailing and circumnavigate the celestial ocean.
Mars' climate is not playing scales, it is playing Bach, patterns within patterns within patterns.

Goethe once said "Architecture is solidified music”
I think it's safe to say that geology is solidified climate...

Consider the diagram below, each section is an octave on a piano....
serpens
Basically a closed system I expect. One needs to pull back a bit to see the big picture. Aeolis Serpens to the NE of Gale is an inverted river complex over 500 kilometres long that spans a period somewhere between 1 to 20 million years with evidence of varying water and sediment supply and occasional desiccation. It would have terminated at the northern ocean and this would imply a shoreline to the north of Gale. Groundwater at Gale could reasonable be expected to reflect the level of the Northern ocean, creating a lake, while impact tsunami could also have overflowed the northern crater wall.
The problem is that empirical data from the rovers and orbiters prove an early warm wet Mars with a complex hydrological cycle spanning millions of years. No model of plausible environments can explain this. But Curiosity has a long way to climb and hopefully more clues will be found to help complete the jigsaw.
dburt
QUOTE (serpens @ Dec 30 2016, 07:06 PM) *
... empirical data from the rovers and orbiters prove an early warm wet Mars with a complex hydrological cycle spanning millions of years ...

Umm. The conflict with plausible environments may be more apparent than real. I remind you here that it is important not to confuse actual data with interpretations based on that data. Furthermore, much of the martian "data" (e.g., the detection of clay minerals) is itself based on interpretations of analytical or spectroscopic data. And the mere detection of clays gives no indication of how or when the clay minerals formed. Another example would be the imaging of channels or fans interpreted to have been formed exclusively by flowing water. Such interpretations, in some cases, prove nothing other than the bias of the observer. In science, multiple working hypotheses should dominate, although in practice they rarely do. A new year's resolution for Mars, perhaps.
DBurt
HSchirmer
QUOTE (serpens @ Dec 31 2016, 02:06 AM) *
Basically a closed system I expect.
...
Groundwater at Gale could reasonable be expected to reflect the level of the Northern ocean, creating a lake, while impact tsunami could also have overflowed the northern crater wall.
...
The problem is that empirical data from the rovers and orbiters prove an early warm wet Mars with a complex hydrological cycle spanning millions of years.


Good summary,
I've cleaned up my prior post a bit, but basically-
Laying down 90 miles of mudstone outcrop takes millions of years' worth of water.
Celestial mechanics suggests that Mars dries up every 1.25 million years,
when there is no water, erosion just halts and waits for a wet epoch to return.

Hmm, interesting point about tsunami, I hadn't thought of the possibility before...
The central mound in gale crater might be tidal wave debris.


HSchirmer
QUOTE (fredk @ Dec 31 2016, 03:00 AM) *
Wind action while we sat from 1526-52:
Click to view attachment
I like the advancing mini ripples.


Neat, was that a drill dump?

Thinking of drills, we've seen that rocks react strangely to vibration...

And there's actually a paper about erosion by vibration....

Seismicity and the strange rubbing boulders of the Atacama Desert, northern Chile
http://geology.gsapubs.org/content/40/9/851.abstract
HSchirmer
QUOTE (serpens @ Dec 31 2016, 03:06 AM) *
Basically a closed system I expect. One needs to pull back a bit to see the big picture. Aeolis Serpens to the NE of Gale is an inverted river complex over 500 kilometres long that spans a period somewhere between 1 to 20 million years with evidence of varying water and sediment supply and occasional desiccation. It would have terminated at the northern ocean and this would imply a shoreline to the north of Gale. Groundwater at Gale could reasonable be expected to reflect the level of the Northern ocean, creating a lake, while impact tsunami could also have overflowed the northern crater wall.
The problem is that empirical data from the rovers and orbiters prove an early warm wet Mars with a complex hydrological cycle spanning millions of years. No model of plausible environments can explain this. But Curiosity has a long way to climb and hopefully more clues will be found to help complete the jigsaw.


Since the discussion has been clipped out -



A new paper about the morphology of gale, compared to other high peaked craters....

GALE CRATER MORPHOLOGY COMPARED TO OTHER HIGH CENTAL PEAK CRATERS ON
MARS.
http://www.hou.usra.edu/meetings/lpsc2016/pdf/2822.pdf


Should also note that the central mound at Gale appears to be within the elevation (global -4087m to -3191) which has been suggested to be within the reach of norther ocean tidal waves.
http://www.nature.com/articles/srep25106

Interesting to think of a martian sea, not stirred by tides, but stirred by impact events.
http://www.lpl.arizona.edu/~shane/publicat...icarus_2013.pdf

HSchirmer
QUOTE (Greg Malone @ Dec 29 2016, 06:34 PM) *
To add to the mix of ideas about dessicated mudcracks
... i.e. not a 'drying out' or dessication.


Good call on the syneresis folds and cracks.
Just noticed, we have what appear to be iron concretions in Mars Gale crater images...
Looks fairly similar to copper concretions in Earth Newark basin...
Julius
Sulphates on Earth require oxygen to form either by volcanic eruptions or the action of sulphate reducing bacteria. Deposits of iron pyrite have been attributed to rising levels of atmospheric oxygen. Varying sulphur isotopes have been regarded as biosignitures.

What do findings of sulphates, gypsum, manganese oxide and haematite on Mars tell us about climatic condition's with regard to atmospheric and water oxygen levels? Is Curiosity rover equipped to measure isotope ratios?
serpens
SAM has the capability to conduct isotopic analysis of the lighter elements. You have a few misconceptions in that sulphate reducing bacteria uses sulphates as an energy source, producing sulphides. Iron pyrite forms in a reducing, not a oxidising environment and on Mars probably formed through melt separation during magma crystallisation.
With respect to your question on what rover and orbital findings indicate about previous environments, these have been the subject of a huge number of erudite papers and articles by acknowledged experts in their fields and address the dramatically different environments encountered by the landers and rovers. A good search engine and some careful culling to separate the grain from the chaff will provide you with your answers and attempting to paraphrase these would take up immense space and justifiably draw the wrath of the overworked moderators.
dburt
Julius, I agree with what Serpens said, but to try to save you a bit of trouble, let me summarize (with some trepidation) what you are likely to find in an exhaustive literature search. In short, sulfates don't tell you a great deal about environments. Yes, they are oxygen-bearing, but so are virtually all the other minerals that make up planetary crusts, such as silicates and carbonates. Sulfates require a tad more oxygen than most, to avoid forming sulfides instead, but not much more. There are igneous and hydrothermal sulfates as well as sulfides, so sulfates are not unique to a particular environment (at least on Earth). Some elements (e.g., calcium) form sulfates more easily than others (e.g., iron), but you didn't ask about that.

Manganese oxides and hematite on the surface of Mars probably don't tell you a great deal either, because the surface of Mars is believed to be locally far more oxidizing than the inside, owing to the influence of solar ultraviolet light, not from an oxygen-rich atmosphere (as on Earth). It doesn't take a great deal of oxygen to form either type of oxide. Finding manganese or iron oxides inside a rock can tell you that it or its ingredients were formerly exposed to sunlight at the paleo-surface, and presumably to some moisture (to assist their growth), but nothing more.

I won't address sulfur isotopes, because there is no data and they are not my area of expertise.
Julius
The consensus up to now seems to have been that sulphate minerals tend to rest on top of more ancient clay minerals and has been interpreted as reflecting a climatic change on Mars from neutral water environment to a time when the planets water turned acidic indicating a drier environment. The finding of jarosite at Pahrump hills and lack of clay minerals sandwiched if you like between abundant clay containing Yellowknife bay rocks and abundant clays found in Murray buttes would seem to contradict this . Any thoughts about this?
Gerald
My first thought about the silica enrichment has been a process connected to the hematite enrichment at Vera Rubin ridge, kind of leaching and precipitation cycle. But there are lots of gaps, of course, and those two layers could have formed independently. I don't see an immediate connection to the overlying sulfate layer thus far.
One may also conclude, that we are going to learn more about the details of Martian history, but our understanding of the long-term geological structure doesn't need to be challenged.
serpens
Julius, I think that Curiosity will need to get up close and personal with the clay bearing trough before they can assess how and when it was formed. In their brilliant Geological mapping and characterisation of Gale as a potential landing site, Anderson and Bell depicted the clay as a thin bedding plane with a segment exposed by the trough and that characterisation has carried forward. As I understand it the clay signature seems to indicate smectites. The overlying hydrated sulphates would likely have formed in an acidic environment and smectites are pretty good at consuming acidity with the end product being amorphous silica. So if the smectites had been exposed to the acidic waters during sulphate deposition, wouldn't hydrated silica and kaolinite have been detected, unless the clay had been covered by an impervious layer? An alternative is that the clay was formed following deposition of the sulphates as a function of erosion of the sulphate and formation of the fan. Could this clay be a localised deposit formed from pooled water that had leached Mg from the higher sulphate deposits? Both the hematite ridge and the clay trough are going to tell interesting stories.
serpens
QUOTE (HSchirmer @ Nov 8 2018, 05:06 PM
...Given the elevation of Gale crater, and recent northern-ocean papers, is there any way to differentiate whether Gale was lacrustine or perhaps an interior estuary?

All evidence to date implies lacustrine. Dichotomy elevation differences aside, the northern crater rim is heavily degraded compared to the northern rim and the area directly north of Gale is somewhat atypical compared to adjoining topography. it is possible that it was overtopped by lake water or by catastrophic events such as impact driven tsunami although there is no evidence of such. The rim is above the elevation assessed for proposed shorelines for the northern ocean(s).

Hmm, reminds me of the Newark Basin paradox- a 2-mile deep deposit of shallow water mudstone interbedded with fanglomerates and sandstones. (It is a paradox because with a 2-mile deep basin [~about the average depth of the Atlantic or Pacific] you'd expect to start with deep water sediments which get shallower as you fill in the basin over time. Instead, the Newark basin was shallow during the entire time that 2 miles of sediment were deposited.)

I thought the Newark basin was the result of a slow graben process? As the land sank the rate was matched by shallow lake deposition.
HSchirmer
QUOTE (serpens @ Nov 9 2018, 01:14 AM) *
The rim is above the elevation assessed for proposed shorelines for the northern ocean(s).


Curious about that, a recent paper suggested that early shorelines make sense, IF you remove the Tharsis bulge, and the corresponding antipodal bulge near Gale.



That puts the Arabia shorline (purple line) right around the elevation of Gale


QUOTE (serpens @ Nov 9 2018, 01:14 AM) *
I thought the Newark basin was the result of a slow graben process? As the land sank the rate was matched by shallow lake deposition.


Yep. Newark is a hanging wall/graben.
Which is interesting with the possible faulting/slumping of Gale's north crater wall.
But the twist for Newark - clays interbedded with fanglomerates and sand, might illuminate what happened at Gale.
If you have sediment from 2 sources, young rivers cutting into the hanging wall side, providing mineral rich fanglomerates; while flat rivers from the Martian interior providing weathered clay sediments.

Earlier papers discuss the hypothesis of an Elysium lake overtopping the north rim,
https://vdocuments.mx/hydrogeologic-evoluti...biological.html
but either way, the notch in the north crater rim would let north draining rivers flow into Elysium lake/Arabia sea during wet periods,
but would/should also result in shallow areas to the north draining fine clays back INTO Gale-

I'm thinking of the paradox that ~250 million years ago, US east coast rivers- Potomac, Susquehenna, Schuylkill and Delaware, initially drained NORTHWEST.
When the Atlantic ocean opened up, the rivers reversed course and began cutting back from the new ocean, causing the same valleys to drain SOUTHEAST.

I wonder if something similar applies to Peace Vallis, where the notch in the northern rim allowed drainage from the southern highlands into Elysium lake or Arabia sea,
but when those streams dried up, the notch allowed the lake and sea to drain back into Gale.

http://spaceref.com/mars/curiousmars-box-s...stinations.html
serpens
I suspect that this would represent the maximum fill with your suggested high ocean level, with the northern rim less degraded and above water level. Occasional tsunami drain back cutting the few possible channel like features but who knows. Certainly the mount would not exist at this time and the central uplift would be the sole feature within the lake. There is some evidence from tsunami features that the proposed first ocean was not iced over although the second, shallower ocean was.
HSchirmer
Theory - Gale Crater was a bay when the Arabia Ocean filled the northern lowlands of Mars.


QUOTE
Certainly the mount would not exist at this time and the central uplift would be the sole feature within the lake.


Perhaps but if Gale was a beach environment, why wouldn\'t there be sand, and perhaps dunes?
If there was an ocean, then there had to be an atmosphere, and had to be wind, and had to be waves,
and had to be sand, and sand plus wind means dunes.

If there was a northerly wind, why wouldn\'t the central peak of Gale trap a static barchan style dune?
Is there a name for the barchan-dune looking half-crater north of the Gale notch?


QUOTE
I suspect that this would represent the maximum fill with your suggested high ocean level, with the northern rim less degraded and above water level.


A bit of digging finds that early plaotting of the "Arabia Sea" aka "Contact 1" goes right through Gale crater.

QUOTE (PALEOSHORELINES AND THE EVOLUTION OF THE LITHOSPHERE OF MARS)
https://eprints.ucm.es/33193/1/3-Marte%20SL.pdf]
Parker et al. (1989, 1993) also proposed an older, higher-standing Contact 1, later on
renamed Arabia shoreline (Clifford and Parker, 2001). This shoreline, which would be of
Noachian age (see Clifford and Parker, 2001), is roughly coincident with the Martian
dichotomy separating the lowlands from the highlands,


figure #2 from the paper is enlarged as the first image below

At the Arabia shoreline, Gale crater would have been a bay.
HSchirmer
QUOTE
I suspect that this would represent the maximum fill with your suggested high ocean level, with the northern rim less degraded and above water level.


Actually, "just overtopping" is the Arabia Ocean level, Meridiani would be higher, making Gale the entrance to an estuary.

QUOTE (Topographic evidence for lakes in Gale Crater)
https://www.lpi.usra.edu/meetings/lpsc2013/pdf/1844.pdf
Figure 1: Three lake levels at Gale:at - 2277 m spilling over the northern rim


The shorelines suggest 3 oceans, Deuteronilus, Arabia, and Meridiani.

A zoom in from the Paeloshorelines paper shows the various shorelines in black in the images attached below-

QUOTE
Figure 6. The Deuteronilus (yellow), Arabia (green) ... shorelines after Clifford and Parker (2001), represented on the Martian topography (scale in km). Also represented (black) are the contour of the a) -1.5 km, cool.gif -2.09 km, and c) -3.792 km elevation levels.


Three images below (which of course are out of order...) To judge the ocean height, look at Elysium.
Working left to right- Gale crater is due north of the left most yellow dot at the bottom center of the images.

At the Arabia shorline, (left image) Elysium is an island with wide flanks, and Gale is a circular bay.

At the lowest shoreline Deuteronilus, (middle image) Elisum is still attached to the continent, and Gale is a notch at the fall-line.

At hightest shoreline, Meridiani, (right image) Elysium is a small island, and Gale is the entrace to a large estuary including the lowlands to the east.
HSchirmer
Reaching way back to discussions about the thickness of sediment deposits in Gale-

QUOTE (serpens @ Dec 22 2016, 10:54 PM) *
It would be reasonable to expect that the water availability in the Gale lake would vary as would the amount of available sediment, particularly airfall.
But this very thin sheet of cracked material does seem to be an anomaly and difficult to reconcile to dessication. Chemcam should reveal something about the makeup of the sheet as it could be possible that these cracks formed sub aqueous in a thin, possibly localised layer of clay rich sediment.
Subsequent settling of underlying sediment causing the cracking would explain the variation in shape and size.


Well, now it looks like the Gale crater was NOT filled to the brim with sediment-
Thanks to some creative re-purposing of accelerometers and gyroscope to go gravity/density measurements-
'Mars Buggy' Curiosity Measures a Mountain's Gravity
The rocks aren't compressed in the way that would be expected if they were deeply buried-and-then-excavated.
A surface gravity traverse on Mars indicates low bedrock density at Gale crater

So, what process raised Mount Sharp? Nice summary of depositional models at
https://marsoweb.nas.nasa.gov/landingsites/...er_Gale_opt.pdf


Initial expectations mentioned possible contact with non-sedimentary basement-basalt.

I may have missed it, but was there any outcrop or exposure that looked like basement-rock basalt?
http://marsjournal.org/contents/2010/0004/...s_2010_0004.pdf

Anybody have a link to the most recent stratigraphic mapping?
serpens
The basal/basalt misinterpretation was explained, in fact done to death in pages 7 to 9 of this thread. Let's not resurrect it.

The accelerometer analysis by Lewis et al is innovative although I am not certain that their conclusion on the extent of overburden considers all the variables. I do not question their methodology or measurement results. However I do note that during the ascent of Mount Sharp the Murray formation has consisted primarily of mudstone with some sandstone lenses. Depositional muds have high porosity (up to 65- 70%) due to the nature of the particles and electrostatically bound water and compaction of such in Mars' low gravity takes significant overburden. Given the thickness of the mudstone significant pore fluids may have been retained, retarding compaction and retaining density indicative of shallower depth than was the case.
atomoid
As referenced in an article on sciencenews.org accelerometer-based gravity readings suggest:

"...the rock beneath Curiosity's wheels is less dense than its mineral composition led them to expect. It's "more like the density of soil than a fully cemented rock," Lewis says. That means the crater must never have completely filled with rock — the upper layers would have crushed the lower ones — and supports the windblown sands theory for how Mount Sharp formed...
...suggests there were two different periods of mountain-building in Gale Crater, one that laid down lake sediments and a drier one that built Mount Sharp's peak. Curiosity might find the transition point as it keeps climbing...
...measurements suggest that the rocks beneath Curiosity are riddled with holes. “But the rover doesn’t see any holes,” Kite says. Either the pores are too small for Curiosity to see, less than 10 micrometers wide, “or there’s something unusual about the rocks right at the surface where Curiosity is driving.”..."


Assuming an accelerometer measurement wouldn't be able to discriminate between holes/pores at surface vs subsurface... so seems simpler that the subsurface pore fluids desiccating could lead to mineral solidification of their environs preventing the sedimentary compaction due to pore collapse could help explain away some of the missing mass?
serpens
The hardness of the Jura and upper Pettegrove Point members combined with CRISM results indicate that they are well cemented with iron oxide, primarily hematite. This localised and comparatively shallow phenomena most likely occurred post lithification and the erosion resistant upper surface of the ridge is indeed different to the underlying Murray formation. Mudstone is a bit of an anomaly where compaction is concerned because the platy particles compact at surfaces rather than points, significantly reducing porosity. But this reduction means that the remaining pore water is retained despite increases in load, so bulk density is not necessarily an accurate yardstick to measure load (overburden).
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.
Invision Power Board © 2001-2020 Invision Power Services, Inc.