Radiometrically dating adjacent rocks
== == == Erosion and weathering of igneous, metamorphic, and sedimentary rocks eventually leads to formation of more sedimentary rock.
Additionally, huge areas of continents have been covered by inland seas at one time or another in geologic time creating vast amounts of sedimentary rock.
Sedimentary rock is composed of the weathered remains of a variety of rocks of all ages.
In a sense they do, but not in the geologic sense that a metamorphic rock does.
Most sedimentary rocks are formed from particles of other rocks which could be a mixture of all three types (sedimentary, igneous, metamorphic). Most sedimentary rock, and the fossils contained therein cannot be dated directly with radiometric techniques, but can be dated indirectly.
Rather, the sediments have been weathered from rocks of diverse ages.