A break in the sequence of sedimentary rocks that exposes an eroded surface is called an "unconformity." An unconformity represents a period of time where there was either a lack of sediment deposition or erosion occurred, resulting in a missing portion of the geologic record.
Unconformities are significant in understanding the geological history of an area as they indicate gaps in the rock record and provide evidence of past tectonic, erosional, or depositional events. They can be classified into different types based on the relationship between the underlying and overlying rock layers.
The three main types of unconformities are:
Angular Unconformity: It occurs when the underlying layers are tilted or folded, and subsequent layers are deposited horizontally on top of them. The tilted or folded layers are then eroded, resulting in an angular relationship between the two sets of rocks.
Disconformity: It occurs when there is a break in deposition between parallel sedimentary layers. In a disconformity, the upper sedimentary layers are deposited on top of an eroded surface of the lower layers, representing a period of erosion or non-deposition.
Nonconformity: It occurs when sedimentary rocks are deposited directly on top of older igneous or metamorphic rocks. The underlying rocks have undergone significant geological processes such as uplift, erosion, and metamorphism before being covered by sedimentary rocks.
Unconformities provide important clues for geologists in reconstructing the geologic history