Disconformity when contrasted with angular unconformities disconformities are more common, but usually conspicuous because the strata on either side are essentially parallel. For example, look at the disconformities in the cross section of the Grand Canyon in Figure 11 Many disconformities are difficult to identify because the rocks above and below are similar a there
is little evidence of erosion. Such a break often resembles an ordinary the ancient erosion surface is cut deeply into the older rocks below.
Nonconformity The third basic type of unconformity is a nonconformity. Here the break separates older metamorphic or intrusive igneous rocks from younger sedimentary strata(Figures 11.6 and 11.7). Just as angular unconformities and disconformities imply crustal movements, so too do nonconformities. Intrusive igneous masses and metamorphic rocks originate far below the surface. Thus, for a nonconformity to develop, there must be a period of uplift and the erosion of overlying rocks. Once exposed at the surface, the igneous or metamorphic rocks are subjected to weathering and erosion prior to subsidence and the renewal of sedimentation.