What is "unconformity"

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

1. Want of conformity; incongruity; inconsistency.
   --South.

2. (Geol.) Want of parallelism between strata in contact.

   Note: 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.

c.1600, from un- (1) "not" + conformity. Geological sense is from 1829.

n. 1 (context nonstandard English) a lack of conformity 2 (context geology English) a gap in time in rock strata, where erosion occurs while deposition slows or stops

An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe any break in the sedimentary geologic record. The significance of angular unconformity (see below) was shown by James Hutton, who found examples of Hutton's Unconformity at Jedburgh in 1787 and at Siccar Point in 1788.

The rocks above an unconformity are younger than the rocks beneath (unless the sequence has been overturned). An unconformity represents time during which no sediments were preserved in a region. The local record for that time interval is missing and geologists must use other clues to discover that part of the geologic history of that area. The interval of geologic time not represented is called a hiatus.