A buried non-depositional or erosion rock surface that separates a couple of rock strata which were formed during different time frames is called an unconformity. Usually the deposition that takes place to form an unconformity is not continuous because as the process takes place old rocks go through erosion activity in intervals prior to when young rocks are deposited. Basically the term is used in the description of a situation when rocks underneath are relatively older compared to the rocks above. It represents a break in sedimentary and geologic record and also represents a time interval when there is no preservation of sediments in a certain region
Nonconformity-Metamorphic rock or maybe igneous rock may be uplifted to the surface of the Earth after numerous crustal movements. When the rock becomes highly exposed there becomes several erosions which take place hence allowing for sediments to be deposited on the surface that had undergone through erosion. The boundary that forms between the metamorphic or igneous rock and the newly formed sedimentary rock represents an indefinite time period and is what is known as non-conformity.
Disconformities- There are cases when sedimentary rock layers are lifted towards the earth surface with no tilting or any form of folding. These layers go through erosion which leads to the eventual deposition as the area subsides. Meanwhile either sides of the rock boundary become nearly horizontal on the layers. By this stage rock layers seem to have been deposited overtime causing the formation of a relatively large gap to be formed between the lower and the upper gaps which is called disconformities.
Angular Unconformity- As the formation of angular unconformity takes place, a rock is usually deposited in stratified horizontal layers which are then tilted and folded before an erosion takes place. A horizontal layer emerges by deposition just above the tilted rock layer as soon as the erosion activity stops. Therefore an angular unconformity is formed when bedding planes of old rock deposits are not placed parallel to those of the overlying young and recently formed rocks.
Paraconformity – has a very close appearance and looks like any other disconformities. It is also referred to as a diastem and is formed when there is little or no erosive activity taking place. There is no sedimentary record when erosion levels drops to zero or becomes little during the formation of paraconformity forming a gap over a long period of time. A paraconformity is differentiated from a disconformity using fossils that will always show the presence of a diastem at a given period of time. This implies that rocks were deposited sequentially in a horizontal manner and sedimentation halted in relation to the change in various conditions that took place at the bottom of a basin. After some time sedimentation began yet there was no cases of deposition.
Buttress unconformity – This is a situation when rocks that are overlying are cut because of prolonged contact. The young sediments are however deposited on the old rocks.