I think geologists are often very interested in getting accurate dates. One reads often a statement about high precision dating methods being used to refine the dating of events.
For instance careful work has been done to refine the order of the eruption of the Deccan Traps compared to the Chicxulub meteorite and the End-Cretaceous extinction. Also similarly to see the exact relation between the Siberian Traps eruptions and the End-Permian extinction.
A great amount was known about the order of fossils before RMD was available. Now they have been dated, knowing the fossil can give you the date without needing a RMD test.
An example of index fossils is the use of a succession of about 40 different ammonites to delineate time zones for about 40,000,000 years of the first half of the Cretaceous.