Geo-pic of the week: Folded Rock In 3 Dimensions

 

folded rock together cross sectionfolded rock cross section close up

                                                         

Above are several images of the same rock sample: a highly deformed quartzose siltstone collected from the Womble Formation, Ouachita Mountains, Arkansas.  The uppermost image shows a cut and polished surface.  The green line that’s been added to the picture defines a fracture that split the sample after it was cut.  Ordinarily, that would be a bitter turn of events but, in this case, it was a fortunate accident.  The fracture provides a rare, multi-dimensional view inside a tightly folded rock (lower photo).  Luckily, the fracture propagated across the bedding rather than breaking along a bed, which makes the beds of the fold appear to fan out like a deck of cards showing a lot of the detail of the structure. 

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