Geologic age and depositional environment can be interpreted from both modern- and paleo-marine sediments using calcareous nannofossils (nannos) and foraminifera (forams). All nannos and forams are widely distributed in the world’s oceans and typically occur in large quantities, which means that statistically significant counts can be quickly generated for interpretation. The nanno and planktic foram fossil records both start in the Jurassic, and the nature of their rapid evolution makes for an excellent high-resolution chronostratigraphic tool through to the present day. Finally, given the non-ubiquitous nature of microfossils, if one group is absent, you need to be able to use another.