Wednesday, April 28, 2010

The Jackson Creek lava delta and the 'two' Bogus lavas

The upper photo is a slightly less common shot (for our group at least) of the Jackson Creek lava delta. We usually see this from the river and look mainly at the south-facing exposure. This is the north-facing exposure. Since I took this picture a while back, I have actually walked out on that outcrop to get a gigapan image of Jackson Hole. In so doing, I found that the two conspicuous lava flows are separated by the lacustrine silt package indicated in the previous post. No surprise given that the outcrop is right across the trib canyon from the much better exposure shown in that post. The difference in quality of exposure of the lacustrine silts is controlled by the presence of a thick lag of Bogus Rim lava mantling the surface.

The photo below is the 'classic' view of this outcrop (taken almost exactly two(!) years ago). The lava delta is associated with the lower Bogus lava unit. You can't see the intervening lacustrine silt package, but the Bogus Rim lava at the top is obvious.

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