Sunday, December 1, 2013

Geo 365: Dec. 1, Day 335: Shear: Sheer Puzzlement

Sometime after I got home last night, it occurred to me, despite my comment yesterday, "I see no other supporting evidence for this supposed fault..." that Dana and I had spent a few minutes at another portion of the outcrop, to the east (inland/down section), looking at shearing in a mud/siltstone bed. The clues I'm looking at here are the pervasive joints in the finer bed terminating in the lower left corner of the photo, which in this tilted sequence are vertical. But with respect to the original horizontal bedding, they'd be to the right on the upward side, and left downward. If I'm interpreting this correctly, that would mean the upper bed (Quick reminder: I have no idea which direction is stratigraphically "up," but that doesn't really matter in this situation.) was shearing to the right, and the lower one to the left. "Aha!" thought I, "A possible solution!"

Sadly, it was not to be. That darned recumbent fold in yesterday's photo seems to indicate horizontal shear in precisely the opposite sense: upper to the left, lower to the right. Curses! Foiled again.

I don't like this outcrop anymore. It's being mean to me.

Photo unmodified. May 7, 2013. FlashEarth location.

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