kinks, bends, fractures, fillings.. oh my.. (by Ale*)
Many of the iron-rich layers in this outcrop show extremely fine lamination. In this example there are four couples of pink and brown bands at the base, followed by a few whitish bands and then an overall lighter pattern before ending up in the black cherts. If one looks to the right, it is possible to see a discontinuity, a microfault, that breaks the bands. Across the fault, the bands have different thicknesses, but they are consistent in number and order. It looks like that when the bands were folded, they expanded towards the outside the bend. The cracks have been filled likely with calcite, but they stop at the edge of the iron layer: you can not follow the cracks into the chert, indicating that the iron was already a solid rock when the chert, above and below, was plastic enough to flow following the deformation.
Banded Iron Formations
Fuente: Flickr / greenriver