Biofacies analysis (in Poldervaart, A., ed., Crust of the earth--a symposium)
Special Paper - Geological Society of America (July 1955): 449-463
Many lines of geological and biological investigation depend upon inferences drawn from a study of biofacies (the total biological characteristics of a sedimentary deposit). Three steps can be recognized in the process of drawing such inferences: analysis, synthesis, and interpretation. Of these, analysis must be considered as fundamental because it involves the primary observations on which synthesis and interpretation depend. The scope and accuracy of our interpretations, therefore, are basically limited by the potentialities of the original observational data. If new dimensions of evolutionary, ecological, and geochronological understanding are to be attained, our observational techniques must be sharpened to extract a maximum of information. At least seven basically different methods of biofacies analysis can be employed: (1) taxonomic analysis, based on enumeration of the kinds of organisms represented in a sample; (2) morphologic analysis, in which observations on organic size and form, not explicit in formal taxonomy, are recorded; (3) frequency-distribution analysis, involving observations on the shape of frequency distributions of biological variates; (4) abundance analysis, in which estimates of absolute or relative individual abundances are obtained; (5) incomplete-specimen analysis, in which consideration is given to broken or disarticulated specimens; (6) compositional analysis, in which information on the mineralogical, chemical, or isotopic composition of skeletal material is utilized; (7) textural analysis, in which field and laboratory observations are made on the arrangement of organisms in a deposit. Some of these techniques (especially those dealing with taxonomic and morphologic analyses) have been widely used, but most of them have not been systematically exploited. Synthesis of this primary information is usually accomplished by bringing together data on available collections and considering the biofacies pattern thus formed in relation to the known ecologic or stratigraphic framework. A variety of synthetic techniques are in widespread use. It is judged that future work will emphasize more strongly (1) comparisons of modern and fossil data, and (2) simultaneous study of lithofacies and biofacies.