Biyostratigrafi

Biyostratigrafi, also known as biostratigraphy, is a subfield of stratigraphy that uses the distribution of fossils within sedimentary rocks to establish relative ages and to correlate rock units across regions. It relies on the first and last appearances of fossil taxa (FADs and LADs) and on the stratigraphic ranges of taxa to define biozones and interpret temporal relationships in the rock record.

Fossil groups commonly used include microfossils such as foraminifera and conodonts, as well as macrofossils like ammonites, trilobites, and vertebrates. Biostratigraphic zoning creates different types of zones: assemblage zones (based on a characteristic fossil assemblage), interval zones (bounded by co-occurring FADs/LADs of two taxa), and named biozones (based on a single taxon). The construction of biozones enables correlation of rock sections that may be geographically separated but share similar fossil successions.

Biostratigraphy supports relative dating and correlation, helps construct chronostratigraphic frameworks, and is widely used in petroleum geology for locating potential reservoir, source, and seal horizons. It complements absolute dating methods when datable materials are scarce by providing a pragmatic means to interpret the temporal sequence of sedimentary rocks.

Limitations include diachronous ranges (the same taxa may appear at different times in different regions), reworking of fossils, facies and sampling biases, and environmental factors that affect fossil preservation. Robust biostratigraphic interpretation often requires integration with lithostratigraphy and sequence stratigraphy, as well as other dating methods, to build a coherent timeline of the rock record.