Faulted layer of radiolarian chert

The upper surface of this specimen is a lt stripped structural surface lts made clean and bare because of weathering and erosion of whatever soft layer (probably mudstone) at one time ‘sandwiched’ the resistant chert layer. A set of high-angle faults (relative to layering) systematically down-drop the surface from one end of the layer to the other. At first glance, the tiny closely spaced fractures appear to be joints, but looking more closely we see that they are tiny little faults, each of which is bound by a scarp. These are all normal faults, but the surface expression of the system resembles the diamond pattern that we expect of strike-slip faulting. This conceivably could be a hand-specimen-example of faulting within a three dimensional strain field.

This is from the Chert Series Beds exposed on Mt. Lykaion near Megalopolis in the Peloponnesos. I collected it during the summer of 2009.  The fact that the specimen holds together even though it is full of faults is one of its remarkable features, …making it a ‘collectable.’

Age & Formation
Faults cutting and displacing radiolarian chert layer, Peloponnesos, Greece. Jurassic is age of original layer. Faulting took place during late Cretaceous and early Tertiary.