GL102 Lecture Notes - Lecture 4: Wind Wave, Erosion Surface, Hypocenter
Document Summary
Unconformities: unconformities are an important type of contact, each type of contact has a very different implication about what took place in the geologic past. A graben is a valley or rift created by the dropping of a block bounded by normal faults. A horst is a block that has been uplifted along normal faults. Because it often appears to be just another sedimentary contact (or bedding plane) in a sequence of sedimentary rock, a disconformity is the hardest type of unconformity to detect in the field. Rarely, a telltale weathered zone is preserved immediately below a disconformity. Usually, the disconformity can be detected only by studying fossils from the beds in a sequence of sedimentary rocks. If certain fossil beds are absent, indicating that a portion of geologic time is missing from the sedimentary record, it can be inferred that a disconformity is present in the sequence.
