[X] My Assistant

[CosmicRocker]

Bill: I don't know if I am way out in left field on this, but I think the Halfpipe formation really is the coarse and dark, mostly massive layer below the lighter colored and layered ripples. We have often seen it on the surface, but there are many fewer observations of it and it's contacts in cross section. After looking at almost all of the panoramas between Endurance and the current location, it seems to me that this stuff is present below the finer ripples almost everywhere.

In the few places I have seen it in section it is mostly massive, with the occasional hint of a layer. I don't know what depositional environment to ascribe to it. I have been looking for a wheel trench that cuts through it, but I don't think there was one. Without much other evidence, one must wonder about an earlier residual layer weathered out of the Meridiani section that has been removed...as you previously suggested. Then, we found that big chunk of dark stuff sitting on the surface in the same area as the cross-sectional view I previously posted. My pile of puzzle pieces has been growing lately, too.

...and then we climb up onto the Victoria apron and find the same stuff being revealed below the diminishing drifts... Maybe I am missing something, but I would think that a wheel trench is long overdue.

[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