Biostratigraphy involves the use of fossils in establishing the ordering of containing rocks in time and in relation to evolving Earth history (McGowran, 2005; Jones, 2006). It is one of the principal bases for chronostratigraphic subdivision and correlation of lithological units, thus providing a spatio-temporal context for their interpretation, and is a fundamental building block of Earth science.

I make no formal distinction between biostratigraphy (which essentially records relative age, or time) and lithostratigraphy (which records rock), in the characterisation of sequences, that is, intervals of time represented by rock, such as the Devonian Old Red Sandstone. I do so only in the characterisation of non-sequences, that is, intervals of time unrepresented by rock, such as that between the Late/Upper Devonian Old Red Sandstone and underlying Silurian greywacke observed at ‘Hutton's Unconformity’ at Siccar Point in East Lothian in Scotland. Note in this context that the absolute age, or extent in time, of the intervals of time either represented or unrepresented by rock can only be determined by absolute chronostratigraphy or geochronology, which actually measures time rather than simply recording or representing it (or by biostratigraphy calibrated against the absolute chronostratigraphic or geochronological time-scale).