Unconformity contact, also named angular unconformity（Figure 4-49）, it refers to the spatial relationship of the mutual contact between strata. The adjacent old strata occurrence is inconsistent with new strata, there is an erosion surface seperated them, the occurrence of the erosion surface is consistent with the overlying strata while inconsistant with the underlying strata. Unconformity contact indicates that after the strata has been formed, which becomes fold uplifting and has been erosion because of strong tectonic movements, forming erosion surface, then the crust becomes decreased, which accepting deposition on the erosion surface to form new bottom layer.

Figure 4-49 Angle Unconformable Contact and the process of its formation

 (1) the different times strata forming continuously; (2) the tectonic movement leads to the fold of strata; (3) the fold strata uplifting out of the water and has been erosion to form the erosion surface; (4) the crust decreased and forming new strata on the erosion surface