Strict creationists often claim that "polystrate fossils"--ones which cut through several or more sedimentary layers--prove that geologic strata were deposited very quickly, and that this evidence supports a young earth and Flood Geology. However, this argument is based on faulty reasoning (and in some cases flawed observations), as shown in the resources linked below.
Alleged polystrate fossils by Andrew MacRae and Darby South