Few fossil groups can provide the biostratigraphic zonal resolution achieved with calcareous nannoplankton - 200,000 years to about 2 mya for Paleogene to Neogene, 1 - 2 my for the Cretaceous and somehat longer for the Jurassic- with the advantage of the minute size , which permits age determinations, often from a few minutes study, from very small samples such as from welll cuttings (1 - 2 gm), cores and sidewall cores (a few mm³). Due to their planktic mode of life, calcareous nannofossils are not clear palaeodepth indicators, but palaeoenvironmental interpretations can be made with respect to temeperature, deposition in restricted marine conditions, open shell sea and oceanic conditions.