Tuesday, July 17, 2012

rock unit behavior

A few weeks ago I spent some quality time "under the Wingate" my all time favorite Canyonlands rock unit. In fact, the Wingate sandstone has its own facebook page. The Wingate sandstone was formed in the early Jurassic as a large sand sea or erg in the western US. It is quite easy to find cross bedding indicative of sand dunes. The sand grains are all very uniform in size and shape which creates some great erosional formations. In these images you can see how the Wingate has eroded to make some impressive towers. This is a classic formation found once the over-laying Kayenta formation erodes away. The Kayenta formation, is a combination of siltstone, sandstones and even some conglomerates and it acts as a cap rock for the easier-to-erode Wingate sandstone. 

With the protective layers above gone, the uniformed grained Wingate starts to fall apart with equally spaced cracks running vertically down the cliff face. As time proceeds and geology happens the crack widen until there are separate Wingate towers and eventually even they will erode down to nothing. 

This area along the Green River in Labyrinth Canyon shows the whole sequence of events from a large cliff face to totally missing.

The Wingate Towers
 The Wingate Towers head on
 The whole sequence: The left side shows an intact cliff face with an intact cap rock. The towers are found in the center while the right side shows the Wingate missing from the stratigraphic sequence. 

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