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South from the landing site, sols 72-xxx, Starting the science traverse
Bill Harris
post Sep 18 2021, 09:17 PM
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The study of induration and lithification of sediments on Mars seems to me to be in a state of flux. We have many on-the-ground observations, currently from Curiosity as she scales Mt Sharp in Gale crater. And if course the current work of Perseverance in Jezero.
My general take is that without deep burial, compaction is going to be mild, and induration will be limited to low-temperature hydrothermal processes involving sulfates.
This should prove to be an interesting trek.

--Bill


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HSchirmer
post Sep 18 2021, 09:53 PM
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QUOTE (Bill Harris @ Sep 18 2021, 07:59 PM) *
Although my 'inner voice' says a basalt, I keep finding ways to stray. The initial Abrasion on Sol 206 (shown above) is clearly sedimentary, poorly sorted, angular and poured in. The start of the abrasion was on that top 'weathering crust. The mineralogy of this section will be interesting.
--Bill

Actually, this kinda-sorta reminds me of the layering you see in 'pegmatite' in the Atlantic rift basin.

Basically, in the same way that a drying sea, deposits different layers of less and less soluble salts, but because as magma cools, you get a similar effect because magma and that doesn't flash freeze into glass, has time to let mineral crystals "snow out" as the flow cools.
The very bottom of the magma chamber has crystals of the first minerals to freeze, while the top of the magma chamber concentrates those minerals and elements that are the last to freeze- which is why diabase or dolerite anticlines are associated with gold, copper, silver deposits

Basically, "applejack" the same way that people have made hard cider, and then freeze out the water into slush, and keep the fractionated / enriched liquid as a liquor.
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Julius
post Sep 18 2021, 09:58 PM
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What looks like light green colour coatings?
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nprev
post Sep 18 2021, 10:29 PM
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ADMIN: 9 posts moved to new topic for discussion of image hosting/size/etc.


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serpens
post Sep 19 2021, 12:11 AM
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QUOTE (tdemko @ Sep 18 2021, 05:33 PM) *
.......My interpretation right now is that these are subaqueous sediment gravity flow deposits of altered or lightly weathered volcaniclastic sediment, essentially delta front turbidites........


The reason I suggested floodplain was the resemblance of Ingenuity images to ridge / swale configurations.
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Nah˙m
post Sep 19 2021, 09:12 AM
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This SuperCam shot (Sol 206) makes me feel quite confused about the origin of this rock. It seems like a layer that has been altered from botton to top (attending to the higher degree of cementation in the lower part and the more massive appearance of the top). Even there are some translucent grains.


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tau
post Sep 19 2021, 10:15 AM
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Sol 205 SuperCam Remote Micro Imager with sol 205 Mastcam-Z context and sol 206 Navcam context.
Judging from the Navcam image, the SuperCam looked at a rock slab from the same layer that was abraded next day/sol.
Two sol 205 Mastcam-Z images (the overexposed ones) taken at the same time allow the distance and size of the SuperCam image to be calculated.
If there is no systematic error in my calculations, the imaged circle has a diameter of about 44 mm and is about 2.4 m away from the Mastcam-Z.
The average diameter of the grains (crystals?) is about 1.4 mm, corresponding to very coarse sand.
However, the grains are angular and not rounded, and I cannot see any cement, matrix, or pores between the grains.
The brighter material on some upper grain boundaries is external dust.
Although it most likely belongs to the same layer, the interior of the abraded rock on sol 206 looks quite different.

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tau
post Sep 19 2021, 01:40 PM
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QUOTE (Nah˙m @ Sep 19 2021, 11:12 AM) *
This SuperCam shot (Sol 206) makes me feel quite confused about the origin of this rock. It seems like a layer that has been altered from botton to top (attending to the higher degree of cementation in the lower part and the more massive appearance of the top). Even there are some translucent grains.
Attached Image

An interesting rock, indeed.
Here is my processing of the same SuperCam RMI raw image with slightly enhanced colors, sol 205 Mastcam-Z context and sol 206 Navcam context.
As for the cement: maybe that's not cement, but the start of weathering at the grain boundaries and/or very fine dust?
The translucent grains seem to have a more olive cast compared to the opaque grains.

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Bill Harris
post Sep 20 2021, 01:20 AM
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Looking at these Super Cam images, I keep returning to a fractionated basalt. On the wind-abraded fracture surface I see olivine as the green-tinted transparent clasts and pyroxenes as the blue-tinted clasts (or phenocrysts) near the top. This could be considered an ambiguous specimen in need of coring.
Here is a terrestrial example of a differentiated igneous rock:

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serpens
post Sep 20 2021, 02:51 AM
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For my part these images reflect somewhat poorly sorted clastic rock encompassing the range of angular and spherical shapes. The potential cement does not match the colour of the dust coating the upper surface of the rock and protruding parts of the fractured surface. The Jezero catchment is mafic and olivine rich so olivine particles could be anticipated in immature sedimentary rock.
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Bill Harris
post Sep 20 2021, 08:15 AM
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I'm a mess.
I vacillate between these two views.

--Bill


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Guest_Actionman_*
post Sep 20 2021, 05:10 PM
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The texture seems to be about that of 20-grit sandpaper.
The crystals are very interesting!
They seem to be the softness of salt as they easily grind into a white powder.
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Saturns Moon Tit...
post Sep 20 2021, 07:07 PM
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Haha I feel the same way. Just about every week I flip flop between 'basalt' or 'sandstone'. That supercam image though... to me that really looks like the angular grains of a well sorted sandstone, which has a basaltic mineralogy (unsurpising given this is Mars we're talking about), though I understand how others see crystals where I see grains. I know scientists will be very eager to get their hands on this core. The layering and rock textures here are fascinating - perhaps the most interesting site Perseverance has reached yet smile.gif
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Phil Stooke
post Sep 21 2021, 12:33 AM
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Don't forget the possibility that the rocks originated as ash deposits rather than lava flows. Ash onto land, ash onto water, lava flows, basaltic material redistributed by fluvial action - there are lots of options, all with potentially similar compositions.

Phil


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Bill Harris
post Sep 21 2021, 10:50 AM
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And pyroclastics are another possibility.

--Bill
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