Name three kinds of unconformities. How does each type form?

There are three primary types of unconformities: angular unconformities, nonconformities, and disconformities.

An angular unconformity occurs when younger sedimentary layers are deposited above older, tilted or folded sedimentary layers. This type of unconformity forms by: 1. The deposition of sedimentary layers, followed by the tilting or folding of these layers due to tectonic forces. 2. The erosion of the tilted or folded layers, creating an irregular surface. 3. The accumulation of new sedimentary layers on top of the eroded tilted or folded layers, sometimes at a different angle.

A nonconformity is a type of unconformity where sedimentary layers are deposited above a non-sedimentary rock, such as igneous or metamorphic rocks. Nonconformities form by: 1. The exposure of igneous or metamorphic rocks at the Earth's surface, typically due to tectonic uplift or the erosion of overlying sedimentary layers. 2. The erosion of the exposed non-sedimentary rocks, creating a weathered surface. 3. The deposition of sedimentary layers over the weathered surface of the igneous or metamorphic rocks, creating a distinct boundary between the two different rock types.

A disconformity is an unconformity where two sedimentary layers are separated by a gap in time, although the layers are parallel to one another. Disconformities form by: 1. The deposition of sedimentary layers, followed by a cessation of sedimentation, often due to a change in environmental conditions or tectonic activity. 2. The erosion of the uppermost sedimentary layers during the time of no deposition, creating a gap (sometimes referred to as a hiatus) in the rock record. 3. The resumption of sediment deposition, creating a new layer of sedimentary rock on top of the eroded surface, which is parallel to the underlying layers. In summary, the three major types of unconformities are angular unconformities, nonconformities, and disconformities. Each type forms by a different sequence of geological events, leading to distinct characteristics within the rock record.