Angular Unconformity

An angular unconformity is evident between the eroded limb of the syncline and the overlying horizontal younger layers.

An unconformity occurs when deposition of sediment is "not conform" to an ideal continuous sequence of materials that would record time uninterruptedly (given that rocks are our only evidence of past events). Unconformities can be of different kinds, but they all imply that an interval of time is not present in our rock record.

This unconformity is called "angular" because there is an angle between the layers of the lower unit (the limb of the Miocene Barstow syncline) and those, more recent, of the upper unit.

After the layers that now form the syncline were deposited, the area was subject to compression and the layers folded. After the folding, the area was exposed to the atmosphere and eroded. Then new sedimentation started (the upper unit). The time interval not represented in this image is that between the beginning of the folding and the beginning of the new cycle of deposition.

 

Note the Joshua Trees on top of the mountain for scale.

 

Barstow, California

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