Disconformity

Part of speech: noun

Definitions

1. A surface of erosion between rock layers that are not parallel, indicating a significant break in the geological record where tilted or folded strata are overlaid by younger horizontal layers
2. A geological surface where younger horizontal rock layers rest upon older tilted or folded strata with erosion between them, marking a major gap in the depositional record
3. An unconformity featuring erosion between non-parallel rock strata where inclined or deformed lower layers are covered by overlying sedimentary beds that lack the same inclination

Etymology: The word is built from the prefix "dis-", meaning "apart" or "reversing", and "conformity," which comes from the Latin "conformitas," from "conformis," "similar in form." Put together, "disconformity" describes a lack of agreement in form, and in geology it names a boundary between two layers of rock where the upper layer is younger than the lower one, yet the two are not parallel. That mismatch records a gap in time, when older rock was tilted, eroded, or left uncovered before new sediment settled on top. The geological sense gives the word its specific role. Where the layers on either side of such a boundary lie parallel, geologists call the break a "paraconformity," and an unbroken, undisturbed sequence has no visible boundary at all. The prefix does the work here: the layers are not in agreement, so the surface between them reveals a missing chapter in the rock record.

Synonyms: inconformity