Conodonts--Models of Pragmatic Paleontology: ABSTRACT

Abstract

The composition, size, diversity, and distribution of conodonts make them unique and invaluable geologic tools. These marine apatitic microfossils that evolved and spread rapidly throughout the Paleozoic and Triassic undergo visible color changes from 50 to 500°C as a End_Page 718------------------------------ result of organo-mineral metamorphism. Consequently, they are useful thermal indices, especially for carbonate rocks and cherts in which other organic and mineral indices are virtually absent. Because of their mineral composition, conodonts can be concentrated from a variety of sedimentary rocks (particularly limestone, dolomite, shale, and chert) and persist into low-grade metamorphic rocks (marble and metacarbonate interbedded with chlorite-, biotite-, and garnet-bearing pelitic rocks). Relatively new applications for conodonts include: (1) dating of siliceous facies; (2) dating of low to medium-grade metamorphic rocks; (3) timing of thermal events; (4) assessment of hydrocarbon and mineral-resource potential; and (5) tectonic interpretation. New techniques for thermal assessment and age determination, such as autofluorescence and stable-isotope analysis, are being actively investigated by several workers. Conodonts are versatile tools that provide chronologic and thermal clues for interpretation of the geologic history and evaluation of the resource potential of Paleozoic and Triassic sedimentary and metasedimentary terranes throughout the world. End_of_Article - Last_Page 719------------