Biostratigraphy deals with the documentation, analysis and interpretation of the ordered succession of fossils, their relationships to evolving earth and life history, and their application to the elucidation thereof (Emery and Myers, 1996; Jones, 1996; Doyle and Bennett, 1998; Backman, in Briggs and Crowther, 2001; Bowring and Martin, in Briggs and Crowther, 2001; Marshall, in Briggs and Crowther, 2001; Rawson, in Briggs and Crowther, 2001; Coe, 2003; Harries, 2003; Gradstein et al., in Gradstein et al., 2005; McGowran, in press). Together with sequence stratigraphy, it is one of the principal bases for chronostratigraphic subdivision and correlation of lithological units, thus providing a spatiotemporal context for their interpretation, and is a fundamental building-block of earth science. This chapter deals with applications of biostratigraphy and sequence stratigraphy in the interpretation of earth – and life – history.

Biostratigraphy

The stratigraphic distributions of the principal fossil groups discussed in Chapter 3 are summarised in Fig. 6.1. The ranges over which they are stratigraphically useful are shown by broad bands. It is evident that most are only useful over certain time intervals, and then only in the appropriate facies. Note also that the potential biostratigraphic usefulness of fossils can be impaired by natural factors, such as post-mortem transportation and diagenetic effects (see Section 2.2), and reworking. The biostratigraphic usefulness of fossils can also be impaired by artificial factors, such as sample acquisition and processing, and subjectivity in specific identification.

Some of the more stratigraphically useful fossil groups are the dinoflagellates, diatoms, calcareous nannoplankton, acritarchs, Bolboforma, foraminiferans, radiolarians, calpionellids, plants, archaeocyathans, ammonoids, belemnites, tentaculitids, trilobites, graptolites, chitinozoans, conodonts and mammals (see appropriate sections in Chapter 3; see also Sub-section 6.1.1). Other groups are only locally important.

Significantly, the more stratigraphically useful fossil groups share two common characteristics: firstly, relatively rapid rates of evolutionary turnover, and hence restricted stratigraphic distributions, and/or essentially isochronous first and last appearances; and secondly, essentially unrestricted ecological distributions (for example, throughout the marine realm, and across a range of biogeographic provinces, in the case of many planktonic or nektonic forms). The most useful groups for practical purposes are also, typically, abundant, well preserved, and easy to identify. These are referred to as ‘marker fossils’ or ‘index fossils’. Conversely, the less stratigraphically useful groups characteristically exhibit relatively slow rates of evolutionary turnover, and/or diachronous or time-transgressive first and last appearances.