[X] My Assistant

[aldo12xu]

A brief discussion on this began on the Route thread after Pando posted an interesting route map. Pando's image is attached to a lower resolution version below that extends the coverage up to Erebus Crater. What caught the eye of a few people were the areas labeled as the "Halfpipe Formation", coloured yellow below. This unit would seem to represent a new statigraphic horizon that overlies the Burns Formation.


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I went back to images of the Payson outcrop from sol 748-50, where the name Halfpipe first appeared. There was mention of a Mogollon Contact. I wonder if the contact could correspond to the rough textured, darker zone running diagonally in the central part of this photo. It seems similar to the Whatanga Contact between the Middle and Upper units of the Burns Formation. The Whatanga contact is interpreted to be a zone of recrystallization created above the water table.

And I don't know if this was mentioned before, but there seems to be a lot of evidence for cross-bedding (festoon geometry?) and possible soft-sediment deformation at Payson lying below the possible contact. Could this be the equivalent of the Burns Upper Unit?

The other location where the Halfpipe Formation was observed was on sol 818 at our "Sinkhole Crater".

http://marsrovers.jpl.nasa.gov/gallery/all...VMP2410L5M1.JPG

But what about the other Halfpipe location on Pando's image, off the route map to the east? On what basis would NASA have those outcrops to be similar to those at Sinkhole and Payson?

[Bill Harris]

I think you've got it. Whereas the current "soil" is a basalt sand-blueberry composition, the Halfpipe Fm is a paleosoil composed of subangular basaltic cobbles and other components. It is widespread and in that earlier era was the equivalent to the drifts we see on Meridiani today. Perhaps not a 'soil', strictly, but a surface unit more weathered than a regolith. It is different from the current soil because the environmental conditions were different in that earlier time. Nothing astounding: in the terrestrial Sahara desert we can find evidence of earlier, wetter, more temperate conditions under all the sand dunes currently present.

The "Stump", that disintegrating boulder we looked at from Overgaard, is likely connected with Halfpipe, and should have been examined while Oppy was there. Along with several other areas along the way to Victoria. This is not so much 20/20 hindsight as there were folks here saying "Stop. Look!". I'm not finger-pointing, but simply relaying observations.

Hopefully, we'll make a stop at the "Epsilon" crater ahead and look at the ejecta unit and the underlying units before heading on to Victoria. And perhaps we'll be able to see the same sequence once we get to Victoria, if there is not too much disruption.

Exciting times, no?

--Bill