A boundary between rock strata where there is a discontinuity in the time sequence where the rocks were created. "Unconformity" also refers to the time gap between the two strata.

Unconformities can be created by faulting, but they most often appear where a landscape was exposed to the surface, eroded for awhile, then much later, buried with sediment or lava.

A major unconformity appears over much of North America, at the boundary between the Precambrian and later periods, sometimes with a gap of as much as 300 million years. This unconformity is dramatically revealed at the Grand Canyon, where John Wesley Powell spotted it and named it The Great Unconformity during an 1876 expedition.

Un`con*form"i*ty, n.


Want of conformity; incongruity; inconsistency.


2. Geol.

Want of parallelism between strata in contact.

⇒ With some authors unconformity is equivalent to unconformability; but it is often used more broadly, for example, to include the case when the parallelism of strata once conformable has been disturbed by faulting and the like.


© Webster 1913.

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