Compactional microfaulting in shale below Worland Limestone
The hammer head (nearly hidden by a covering of sticky
clay) lies just
below the reddish iron oxide layer that marks the top of the varicolored
claystone. The dark colored shale above that is broken by compactional
microfaulting. Microfaults are heavily slickensided, and are marked by
narrow diagonal zones of yellow-tinted clay. The color comes from iron
oxides brought in by water that readily infiltrates along the fractures.
Microfaulting here resulted from shearing in relatively soft shale below
an abrupt thickness change in the overlying Worland Limestone. The
shale microfault blocks were apparently squeezed laterally from beneath
the thicker limestone toward a less compacted region of incompetent
shale a few feet into the exposure. These effects die out in a "detachment"
zone just above the iron oxide layer, so neither the iron oxide layer nor
the varicolored claystone are affected. The green color at the upper right
is from algae coating an overhang at the base of the Worland Limestone.
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