18 October 2013

Friday fold: Sliced BIF from Joburg

Posted by Callan Bentley

Remember the Contorted Bed outcrop from downtown Johannesburg, South Africa, right across the street from the University of Witwatersrand? I brought home two small “pocket folds” from that site, both found as cobbles of float adjacent to the dirty Johannesburg sidewalk. One I gave to Aaron Barth, my former structural geology student and protégé. The other I promised to cut in half and then share half with Alan Pitts, Aaron’s good buddy and a second Appalachian geology mentee of mine. I finally got around to cutting it on Monday of this past week. As it turned out, I felt confident enough in its integrity to cut it into three pieces. Since then, I’ve ground each cut-face down with grit (60-90 at first, then 120-220) and will polish it further in the future. But I needed a fold for today, so here’s an image of all three slices, arranged non-geologically but with a pleasant tripartite symmetry. I’ll eventually submit these lovely samples to GIGAmacro treatment, so the world will be able to explore their details in a macro GigaPan. But not yet. For now, this photo will have to be sufficient.