BIOZONES 305 data, it is never correct to regard local biozones as being equivalent to chronozones Even when the physical data necessary for absolute dating are available, it is no simple matter to accurately interpolate the ages of biozone boundaries from radioisotopically dated horizons Fortunately, several methods exist whereby stratigraphers can compare sets of biostratigraphical observations in different successions or cores and, through use of a few simple rules, create a summary of the chronostratigraphically relevant data contained in all such sections/cores Graphic correlation (Figure 10A) and ranking and scaling (Figure 10B) are two of the more common quantitative methods used for bridging the gap between observational biostratigraphies and the ideal of a ‘biochronostratigraphy’ The ongoing incorporation of raw biostratigraphical data into internally consistent and synthetic composite successions based on the application of these methods, along with improvements in consistent identifying fossil morphologies (e.g., via automated object recognition) promise to take the science of biostratigraphy, and its foundation concept – the biozone – into the twenty-first century There it will, once again, serve as the single most useful contrivance in the practical stratigrapher’s toolkit Glossary Constrained optimization A mathematical technique involving the search for the optimal condition or structure of a system of observations given one or more consistently applied external rules Depositional hiatus A horizon within a body of sedimentary rock that represents a gap in time due to the nondeposition of sediment, active erosion, or structural complications Diachrony The condition of taking place at different times Facies A stratigraphic body distinguished from other such bodies by a difference in appearance or composition Homotaxis The condition of occupying the same position in a sequence Isochrony The condition of being created at the same time Microfossil Fossil shells or other hard parts of tiny organisms or parts of organisms studied with the aid of a microscope Phylogenetic systematics A method of determining evolutionary relations between taxa based on the nested patterns of shared characteristics derived from the same pre-existing condition Stratum (strata) A tabular section of a rock body that consists of the same type of rock material Taxon (taxa) Generalized term for any level within the Linnean hierarchy of biological classification (e.g., order, family, genus) See Also Analytical Methods: Geochronological Techniques Mesozoic: Triassic; Jurassic; Cretaceous; End Cretaceous Extinctions Palaeozoic: Cambrian; Ordovician; Silurian; Devonian; Carboniferous; Permian; End Permian Extinctions Precambrian: Vendian and Ediacaran Sequence Stratigraphy Stratigraphical Principles Tertiary To Present: Paleocene; Eocene; Oligocene; Miocene; Pliocene; Pleistocene and The Ice Age Time Scale Further Reading Cubitt JM and Reyment RA (1982) Quantitative strati graphic correlation Chichester: Wiley Gradstein FM, Agterberg FP, Brower JC, et al (1985) Quantitative stratigraphy Dordrecht: D Reidel Hedberg HD (1971) Preliminary report on biostratigraphic units Montreal, Canada: International Subcommission on Stratigraphic Classification Hedberg HD (1976) International stratigraphic guide: a guide to stratigraphic classification, terminology, and procedure New York: John Wiley & Sons Kauffman EG and Hazel JE (1977) Concepts and methods in biostratigraphy Stroudsburg, Pennsylvania: Dowden, Hutchinson & Ross, Inc Mann K, Lane HR, and Stein J (1995) Graphic correlation Tulsa: Society of Economic Paleontologists and Mineral ogists, Special Publication 53 Miall AD (1984) Principles of sedimentary basin analysis New York: Springer Verlag Rawson PF, Allen PM, Brenchley PJ, et al (2002) Strati graphical procedure London: The Geological Society Reyment RA (1980) Morphometric methods in biostrati graphy London: Academic Press Shaw A (1964) Time in stratigraphy New York: McGraw Hill