Graphic Correlation
Keith Olin Mann, Helen R. Lane · SEPM (Society for Sedimentary Geology) eBooks · 1995
Abstract While working as a civil engineer in England, William Smith played a key role in establishing the science of biostratigraphy when he noted that different species of invertebrate fossils characterized the successive Secondary formations in England (Rudwick, 1976). From this, Smith formulated what geologists now recognize as the principle of faunal succession about sixty years before Darwin (1859) published the Origin of Species. Darwin’s theory of evolution, through variation and natural selection, explained why the geologic succession of organisms occurs. Augmenting the principle of superposition with the principle of faunal succession not only allowed geologists to develop a better relative geologic time scale, but it also enabled them to extend their correlations geographically. Although biostratigraphy, paleobiogeography, and paleoecology address temporal and spatial distributions of fossils in rocks, biostratigraphers place primary emphasis on the vertical sequence of fossils and use this sequence to place strata in temporal order and to correlate rocks separated in space. Since conceptualization of the fossil zone in the 19lh Century, biostratigraphers have traditionaliy used zonal schemes to establish the relative time scale. Idealiy, biostratigraphic zones are temporaliy confined, spatialiy widespread, and possess approximately synchronous boundaries. Biostratigraphic zones carry time significance and are recognized in rocks where the fossils are present (Johnson, 1992). Despite a number of factors that limit the distribution and preservation of organisms in rocks (e.g., facies control, ecologic barriers, migration, dispersai barriers, local extermination, taphonomic effects, misidentification, erosion, and metamorphism), geologists have been able to define zones and erect a