Journey to Mt Sharp - Part 5A: Pahrump Hills, Sites 42-45, Sol 753-923, Sep 18, 2014-March 12, 2015 Options

[algorithm]

Yeah, I noticed that also, didn't spot any tumble or bounce marks though.

Suppose it could have been broken off and catapulted straight into place !

[algorithm]

MR pan of the current area Sol 901

[elakdawalla]

Holy cow those are fine laminations in the rock.

[algorithm]

This image is a cut from my above post,





It's something I have seen many times before but have often wondered, whether the stone caused the trench or if the stone just happened to roll/drop into the trench.


So, which came first, the stone or the trench?

[algorithm]

Holy cow those are fine laminations in the rock.

Looks like it was a really small farmer doing some ploughing!


Joking aside, short lived wet = fine lamination, long lived wet=deeper laminations?

[dburt]

Yes, fine laminations, as also seen elsewhere, but why is low-angle cross-bedding so evident in these layers and elsewhere? This widespread feature would seem to indicate repeated active scouring, as by moving currents, and what kind of a shallow little lake has those?

[serpens]

Actually I was about to suggest that such fine laminations would fit suspension settling in a low energy (minimal current) environment. Rather than erratics perhaps the blocky (mudstone/clay) rocks are remnants from final suspension fallout in a no energy, alkaline environment. If so then the water would have been a little deeper than a couple of feet.

[dburt]

Umm. If "minimal current," then why the apparent scouring (as revealed by the cross beds)? Slow settling of sediment through quiet water wouldn't seem to imply active erosion, unless I am missing something important.

[Blue Sky]

It looks to me like the fine lines running lower left to upper
right happened before the larger scale cracks and shattering.
I wonder what that second event was. Maybe just settling?
Or something more dramatic?

[serpens]

Umm. If "minimal current," then why the apparent scouring (as revealed by the cross beds)? .....

To my ageing eyes this seems to be very fine scale cross lamination which would more likely reflect a very low velocity bottom current impacting the suspension settling. This would reflect declining input to a water body. A quite gentle deposition synonymous to the penultimate stage (D) of a Bouma Sequence. But this is Mars and potentially nothing is exactly what it seems.

[Eutectic]

Holy cow those are fine laminations in the rock.

What strikes me is their regularity -- they reflect some recurring event. Time to send out the undergrad with a Brunton compass. Because the appearance of the layers is a function the intersection of their geometry with the geometry of the exposed surface I think it's difficult to interpret them with much confidence before working out their true internal geometry. Not that that ever stops anyone.

[elakdawalla]

Getting a second look from another angle helps you pin down bed orientations, which is why there was that funny first leg in the sol 862 drive where they drove away from the outcrop, came at it again from the east, and then drove back downhill!

Yes, you're right that the regularity implies a recurring event, usually a seasonal one....wonder if each one of those layers represents a Martian year...

[Gerald]

Could be a varve from annual melts at the rim with sedimentation in a sufficiently deep lake.

[Guest_Actionman_*]

Do the layers have layers?

Attached thumbnail(s)

 

[serpens]

Anyone got any idea of the surface slope in this area to get the apparent dip in context?