Final answer:
Stratigraphy is the study of rock layers and layering in sedimentary rocks, focusing on determining depositional environment and geologic time. It includes subfields such as lithostratigraphy and biostratigraphy.
Step-by-step explanation:
Stratigraphy is the study of rock layers and layering in sedimentary rocks. It is a branch of geology that focuses on determining the depositional environment and geologic time of sedimentary rocks. Stratigraphy includes subfields such as lithostratigraphy, which focuses on the type of rock and depositional environment, and biostratigraphy, which uses fossils to determine the relative age and correlate successions of sedimentary rocks.