Final answer:
Radiometric dating of a mineral in a sedimentary rock clast reveals the age of the source rock, not the sedimentary rock itself. Geological history and sediment provenance are derived from these ages, while the formation age of the actual sedimentary rock requires different dating methods.
Step-by-step explanation:
Radiometrically dating a mineral in the clast of a sedimentary rock would not yield the age of formation of the sedimentary rock because the date would give the age of the older source rock from which the sediment was derived. When we age-date minerals in sedimentary rocks, we are actually getting information on the time when the mineral grain crystallized in its original source rock, not the time when the sedimentary rock itself was formed. This is because the sediment that forms sedimentary rocks is composed of debris from pre-existing rocks which are often igneous or metamorphic, and the age of these minerals reflects the history of that original rock, not the subsequent history of the sedimentary rock.
To accurately determine the age of a sedimentary rock, geologists rely on relative dating techniques combined with radiometric dating of cross-cutting igneous or metamorphic events, as well as the presence of fossils with known age ranges. Radiometric dating is also used to gather information about the provenance of sediments, which can provide valuable insights into geological processes and the history of a region.