What characterizes a nonconformity in geology?

A nonconformity in geology is specifically characterized by the presence of a boundary between igneous (or sometimes metamorphic) rocks and overlying sedimentary layers. This indicates a significant geological event where older, usually crystalline, rocks are exposed at the surface and then overlain by younger sedimentary deposits. The relationship suggests that there was a period of erosion or non-deposition during the time between the formation of the igneous rocks and the deposition of the sedimentary layers.

The key aspect of nonconformities is that they highlight a break in the geological history, showing that the igneous rock was formed first, followed by later sediment deposition. This is distinct from other types of geological unconformities, such as disconformities and angular unconformities, which involve sedimentary layers in various arrangements and conditions. The presence of such a boundary is fundamental in interpreting the geological history of an area and understanding the processes that have shaped its landscape over time.