Biostratigraphy allows us to accurately divide rocks according to their ages, relying exclusively on quantifiable data obtained by examining the vertical and horizontal distribution of floral and faunal successions.
It is the ireversible process of evolution that validates biostratigraphy. As such, a good understanding of the processes and results of selective forces and geographic isolation on organisms is important. The understanding of these theories introduces the diachronous nature of fossils. Without understanding the diachronous nature of fossils and the inherent causes, one could have a difficult time in defending their conclusions. Biostratigraphic correlations are often compared to data appropriated from geochemical and geophysical studies to further assist in the validation of one's conclusions.
The first task of the biostratigrapher is to accurately determine the taxa present in the sample. Because of their resistance to drilling procedures and their abundance, microfossils are those best suited for these types of study. Morphological changes, speciation, radiation, extinctions and hiatuses are marked to determine which ranges of which fossil assemblages are those most desirable to establish horizons with . These marker beds are correlated between wells, and as such, biostratigraphy is one of the best tools available to geologists for subsurface mapping and relative age determinations.
The applications of data gathered from correlations are varied and quite valuable. From the exploration geologist seeking oil to the paleontologist recreating ancient marine environments, biostratigraphy fills an important niche in the scientific milieu.