biostratigraphy

This term is a specialized technical noun used almost exclusively within the fields of geology and paleontology. It describes a methodology of dating rock strata based on the presence of specific fossil assemblages, distinguishing it from chronostratigraphy, which focuses on absolute time.

As a field of study or a scientific discipline, the word is uncountable. It refers to the abstract body of knowledge and the application of the method rather than a discrete object that can be counted.